CA2426314A1 - Method and apparatus for space division multiple access receiver - Google Patents
Method and apparatus for space division multiple access receiver Download PDFInfo
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- CA2426314A1 CA2426314A1 CA002426314A CA2426314A CA2426314A1 CA 2426314 A1 CA2426314 A1 CA 2426314A1 CA 002426314 A CA002426314 A CA 002426314A CA 2426314 A CA2426314 A CA 2426314A CA 2426314 A1 CA2426314 A1 CA 2426314A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
- H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
- H04L1/0618—Space-time coding
- H04L1/0631—Receiver arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
- H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
- H04B7/0842—Weighted combining
- H04B7/0848—Joint weighting
- H04B7/0854—Joint weighting using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
Abstract
Methods and systems consistent with this invention receive a plurality of transmitted in a receiver having a plurality of receive elements, wherein ea ch transmitted signal has a different spatial location. Such methods and system s receive the plurality of transmitted signals at the plurality of receive elements to form a plurality of receive element signals, form a combined signal derived from the plurality of receive element signals, and detect eac h of the plurality of transmitted signals from the combined signal by its different spatial location. To achieve this, methods and systems consistent with this invention generate a plurality of arbitrary phase modulation signals, and phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals. Such methods and systems then combine the plurality of phase modulated signals into a combined signals, generate expected signal s, and cross-correlate the combined signal with the expected signals to form correlation signals. Such methods and systems then store the correlation signals in a correlation signal memory and analyze the correlation signals t o extract information from the transmitted signals.
Description
1~~IETHOD AND APPARATUS rOR
RL:CEIVER
rield of the Invention The present invention relates to wireless communication networks, and morn paI-ticularly to space-division multiple access (SUMA) in wireless communication networks.
Background of the Invention Vfireless communication services are an increasingly common form of conununication, and demand fur wireless services continuos to grow. Examples of wireless services include cellular mobile telephones, wireless Internet service, wireless local area computer networks, satellite communication networks, satellite television, and multi-user paging systems. Unfortunately, these communication systems are conEned to a limited frequency spectrum either by practical considerations or, as is often the case, by government regulation. As the maximum number of users, or "capacity," of these systems is reached, user demand for more service may be met by either ( 1) allocating more frequency spectrum to the wireless service, or (2) using the allocated frequency spectrum more efficiently.
Because the frequency spectrum is limited and cannot keep pace with user demand, there is a ~0 critical need for new technology that uses the allocated frequency spectrum more efficiently.
~t'ireless communication systems are generally composed of one ur more base stations through which wireless users, such as mobile telephone users, gain access to a communications network, such as a telephone network. A base station ~5 serves a number of wireless users, fixed ur nlubile, in a local area. To increase the capacity of the systems, service providers may install more base stations, reducing the area and the number of users handled by each base station. This approach increases system capacity without allocating Inure spectrum frequency bands, but is quite costly because: it requires signiCcantly more hardware.
~U Alll7thCr appl'OaCh t0 L1S111~ the f1'ttluCllCy SpL'CtI-Lllll InOI'e C;
fllClt'ntly IS 1?f improving "multiple access" icchnidues. Multiple access tcchnidues allwv multiple _?_ users to share the allocated frequency spectrum so that they do not interfere with each other. The most common multiple access schemes are Frequency-Division Multiple Access (FUMA), Time-Division Multiple Access ('TDMA), C.~ode-Division Multiple Access (CDMA), and more recently Space-Division Multiple Access (SDMA).
FDMA slices the allocated frequency band into multiple frccluency channels.
Each user transmits and receives signals on a different frequency channel to avoid interfering with the other users. When one user no longer requires the frequency channel assigned to it, the frequency channel is reassigned to another user.
With 'fDMA, users may share a common frequency channel, but each user uses the common frequency channel at a different time. In other words, each user is allocated a time slot in which the user may transmit and receive. Thus, TDMA
interleaves multiple users in the available time slots.
CDMA allolvs multiple users to share a common frequency channel by using coded modulation schemes. CDMA assigns distinct codes to each of the multiple users. The user modulates its digital signal by a v=ideband coded pulse train based on its district code, and transmits the modulated coded signal. 'I°he base station detects the user's transmission by recognizing the modulated code.
In SDMA, a system may separate a desired user's signal from other signals ~0 by its direction of arrival, ar spatial characteristics. 'this is sometimes referred to as "spatial filtering." Thus, even though two users may be transmitting an the same frequency at the same time, the base station may distinguish them because the transmitted signals from the users are arriving from different directions. It is possible to use SDMA in combination with FDMA, TDMA, or CDMA.
~5 A conventional SDMA receiver requires an array of multiple recc.?ive elements. Further, a conventional SDMA receiver uses a bank of 1)hase shifters that cooperates with the receive element array to farm a'"beam" that "looks" in a particular direction. It is generally hare desirable to farm multiple beams, each directed toward a different direction, 1.e., toward different users. The mare beams, 3U the IIloI'e S1111L11taIleoLlS llSerS the SDMA Sy5teT11 Ina1' hallllle optl'atlng an the Sallle ll'ClllICIICy at thP. 5allle t1111t;. Thl', IIloI'P. bei1111S, hoV'ever, the'.
nloI'e CaI11p11Cated th('.
SDMA receiver, For instance, each beam may require a separate bank of phase shifters and circuits that perform signal tracking. Additionally, each beans may require a separate "signal combincr," which combines the signals received from each receive element to form a "combined signal." FuI-tller still, each combined signal may require a separate signal detector, which detects the transmitted signal from the user. This hardware complexity greatly increases the cost of an SDMA receiver.
Using well known algorithms, hardware complexity may be reduced by performing phase shifting, signal tracking, signal combining and signal detecting in signal processing software. Current signal processing techniques, however, have difficulty identifying and tracking large numbers of simultaneously transmitted signals on the same frequency, paI-ticularly in a "multipathing" ~:nvironment.
A
multipathing environment is ogle where transmitted signals may reach the receiver over multiple paths. For instance, a transmitted signal may reach tile receiver (1) directly, and (2) indirectly after reflecting off objects. Multipath signals may also further complicate the complexity of the conventional SDMA receiver in the same manner as described above.
Thus, there is a need to provide an improved SDMA receiver that can simultaneously receive from multiple directions and operate in a multipath environment without likewise increasing hardware or software complexity of the ~0 receiver.
Summary of the Invention The summary and the following detailed description should not restrict the scope of the claimed invention. F3oth provide examples and explanations to enable others to practice the invention.
~5 Methods and systems consistent with this invention may incorporate a multi-element receive signal array that may achieve polarization independent isotropic reception, with power gain that may be greater than isotropic. Such methods and systems may receive multiple signals having the same or different carrier frequencies, distinguish the signals, and establish their dirc~cticlns of arrival.
30 Methods and systems consistent with this invention receive a plurality of tl'anSlllltted SlgnalS III a rf:CP.lver havlllg tl p1111'allty of I'ecClve c'ltIlll;llt5, V'hcrl.'l11 each _:~_ transmitted signal has a different spatial location. Such methods and systems receive the plurality of transmitted signals in the plurality of receive elements to form a plurality of receive element signals, form a combined signal derived from the plurality of receive element signals, and detect the plurality of transmitted signals from the combined signal by its different spatial location.
To achieve this, methods and systems consistent with this invention generate a plurality of phase modulation signals that may be arbitrary or uncorrelated, and phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals.
Such methods and systems then combine the plurality of phase modulated signals into a combined signal, generate expected signals, and correlate the combined signal with the expected signals to form correlation signals. Such methods and systems then store the con-elation signals in a correlation signal memory and analyze the correlation signals to extract information from the detected transmitted signals.
Brief Description of the Drawings The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings, ~U FIG. 1 is a block diagram, consistent with this inv ention, of a receiver;
FIG. 2 is a diagram of an environment, consistent with this invention, in which the receiver of FIG. 1 may operate;
FIG. 3A is a diagram of phase modulation signals, consistent with this invention generated by a modulation signal generator as shown in FIG. I;
FIG. 3B is a diagram of phase modulated signals generated by a signal modulator as shown in FIG. l, and a combined signal, all consistent with this invention; and FIG. ~ is a flow chart of a process 4UU for space-division multiple access receiving consistent with this iwention.
3U Detailed Description of the Invention Overview _5_ The following description of embodiments of the present invention refers to the accompanying drawings. Where appropriate, the same reference numbers in different drawings refer to the same or similar elements.
Methods and systems consistent with this invention overcome the hardware and software complexity of the conventional SDMA receiver in a wireless system.
Such methods and systems comprise a receive element array with a plurality of receive elements. Users of the wireless system transmit a plurality of signals, each signal having a different direction or spatial location relative to the receive element array. 'The users may be, for instance, mobile telephone users.
The receive element array receives the plurality of transmitted signals in the plurality of receive elements to form a plurality of receive element signals.
Such methods and systems form a single combined signal derived from the plurality of receive element signals, and nlay detect each of the plurality of transmitted signals from the single combined signal based upon its different spatial location.
Thus, such methods and systems do not need multiple banks of phase shifters, multiple signal combiners, ur multiple signal detectors. Instead, such methods and systems may detect signals from multiple users based on their different spatial location fi°om a single combined signal, as opposed to forming a different combined signal for each signal from each user and detecting a signal from each combined signal.
?0 To achieve this, methods and systems consistent with this invention generate a plurality of phase modulation signals that nlay be arbitrary or uncorrelated phase modulation signals, and phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals. Such methods and systems then combine the plurality of ~5 phase modulated signals into the combined signal, generate expected signals, and correlate the combined signal with the expected signals to form correlation signals.
The expected signals are the combined signals expected from the directions of the users, and may be a function of the phase modulation signals and the direction of the users. Such methods and systems then store the correlation signals in a correlation U Slgn~ll IIlelIlUry Gild allalyLe tlll,' ClarI'elatlull S1g17a1S tU eXt1'tlct tllt', tl'a17S1711tt1;d information in the signals from the users.
-G-Implementation Details Methods and systems consistent with this invention receive a transmitted signal in a receiver having a plurality of receive dements. FIG. 1 is a block diagram of a receiver 1 OU consistent with this invention. Receiver 100 comprises an array 1 having a plurality of receive elements, a modulation signal generator 8, a signal modulator ), a signal combiner 10, a receiver configuration memory G, a receiver calculator 7, a signal memory 12, a signal correlator 1 l, a signal muter 14, a plurality of signal memories 15, and a signal processor 120. Receiver 100 may include other components not specifically described above such as alters, mixers, amplifiers, and power supplies. The location of these components may vary depending upon the preference of designers skilled in the an.
FIG. 2 is a diagram of an environment 200, consistent with this invention, in which receiver 100 may operate. In environment 20D, remote transmitter A and remote transmitter B may transmit signals 2 and 3, respectively from remote transmitter space ''U?. Remote transmitters A and B may be mobile telephones, for example.
Transmitted signals 2 and 3 impinge un array I, and the plurality of elements receive signals ? and 3 to form a plurality of receive element signals. The plurality of receive element signals are conveyed (via lines 102) to a signal modulator J, ?0 which is described in detail below.
Methods and systems consistent with this invention generate a plurality of phase modulation signals. Modulation signal generator $ generates phase modulation signals fur the receive elements of array I . These phase modulation signals may be arbitrary or uncurrelated (correlation less than one). The ~5 uncorrelated phase modulation signals may be substantially un correlated or only slightly uncorrelated. For instance, the uncurrelated random please signals may have a correlation less than 1, but greater than 0.75; less than ur equal to 0.75, but greater than 0.50; less than ur equal to 0.50, but greater than D.25; less than ur equal to D.~~.
but greater than ur equal to zero. On the other hand, some ur all of these signals 3D may be well correlated ur even be identical. 'I'lm phase modulation signals may be arbitrary in that they may nut be correlated with, ur otherwise ~i~~pendent on, the geometry of the elements of array 1. The phase modulation signals may be independent of the direction of the transmitted signal.
FIG. 3A is a diagram of exemplary phase modulation signals for several elements of array 1. As shown in FIG. 3A, modulation signal generator 8 generates a phase ~" for a duration of Tc for a first please modulation signal 302 for a first receive element. Modulation signal generator $ then generates a phase c~, ~
fur a duration of Tc fur first phase modulation signal 302. 'I°his continues, but is shown for N periods of Tc, where Tc is the period of a "chip." The allowed values of phase shift cp for each element of array 1 may be continuously variable fi-um U to 2n radians or may be limited to a finite number of values, such as Q and n radians. If a finite number of values for phase shift ~p is used, each element may be assigned differing allowed values.
The same process occurs for a second phase modulation signal 304 fur a second receive element. As shown in FIG. 3A, modulation signal generator 8 generates phases ~p,, and ~p~,, each for a duration of Tc, fur the second phase modulation signal 304. This process likewise repeats for a third receive element with third phase modulation signal 306 through a Jth receive element with Jth phase modulation signal 308, where J is the total number of receive elements in array 1.
The phase modulation signals are output to signal modulator 9. Modulation signal 2U generator 8 also outputs the phase modulation signals to receiver calculator 7, which is described in detail below. Although the phases may be random, they are known to receiver 100.
Methods and systems consistent with this invention phase modulate each of the plurality of receive element signals with one of the please modulation signals to form a plurality of phase modulated signals. Thus, signal modulator 9 phase modulates, ur "chips," each element signal ~~~ith one of the phase modulation signals generated by modulation signal generator 8. FIG. 3B is a diagram of phase modulated signals consistent urith this invention. As shown in FIG. 3B, a first chip of first receive element phase modulated signal 310 is edual to the first receive element signal, but phase shifted by c~", the lust phase of phase modulation signal 302. Likewise, a second chip of phase modulated signal 310 is equal to the first _g_ receive element signal, but phase shifted by ~p,~, the second phase of phase modulation signal 302. Likewise, the second through the Jth receive element signals are phase modulated to form second 312 through Jth 316 phase modulated signals.
Phase modulated signals 310-316 output from signal modulator 9 to signal combiner 10 (via lines 104). Methods and systems consistent with this invention combine the plurality of phase modulated signals into a combined signal 318.
Thus, signal combines 10 combines the phase modulated signals into combined signal 318.
In one embodiment, signal combines 10 sums, chip by chip, the plurality of phase modulated signals to form combined signal 318. Far example, all of the first chips from first phase modulated signal 310 through Jth phase modulated signal 316 are added to form a combined signal first chip 320, all of the second chips from phase modulated signal 310 through Jth phase madulated signal 31 G are added to form a combined second chip 322, and so forth. Each chip of combined signal 318 may have a vector magnitude that conforms to a Rayleigh density function and may have a random phase angle. Combined signal 318 is output from signal combines 10 to a signal correlates 11 (via line 106).
Methods and systems consistent with this invention generate an expected signal. The expected signal is the signal that the combined signal 318 is expected to be if an unmodulated carrier were transmitted from a particular direction relative to array 1. Receiver calculator 7 calculates the expected signal. For example, refen-ing to FIG. 2, receive calculator 7 may generate an expected signal fur a cau-ier from the direction of transmitter A. Receiver calculator 7 inputs information from modulation signal generator 8 and receiver configuration memory 6 in order to calculate the expected signal. Receiver configuration memory ~ may provide information that affects the amplitude, phase, and polarization of receive element signals and phase modulated signals before being combined in signal combines 10.
'This information may include the carrier frequency of transmitted signals 2 and 3, their estimated direction, flue conFiguration of the receive elements within array 1, and the transmission lint: lengths of the elements. Modulation signal generator 8 may provide information giving the relative phase of each chip w°ithin the phase modulation Signals 3D2-308. Receiver calculator 7 calculates and outputs the expected signal to the signal memory 12 for temporary storage. The expected signal is output from the signal memory 1? and input to signal currelatur 1 1.
Because the polarization of the transmitted signal may influence the phase and magnitude of the combined signal, receiver calculator 7 may calculate the expected signal based upon an assumed polarization of the transmitted signal.
Methods and systems consistent with this invention cross-correlate combined signal 318 with the expected signal to form a correlation signal. Signal correlator I 1 inputs combined signal 318 and the expected signal and correlates the two signals.
In one embodiment, signal correlator I 1 may cross-correlate the corresponding N
ID consecutive chips of combined signal 318 and the expected signal. In this embodiment, the value N may be 50. Signal correlator 1 1 may perform a new cross-correlation between combined signal 318 and the expected signal each time N
new chips (or time period N x Tc) of combined signal 318 enters correlator I 1.
Each time a new correlation is performed, receiver calculator 7 may update the expected signal to include the next N chips and may delete the previous chips so that the value of N may remain 50, for example. Signal correlator 1 I produces an output that is a measure of the cross-correlation of combined signal 318 and the expected signal. In the example of FIG. 2, signal correlator I 1 produces an output that is the correlation signal for receiver l OD "looking" in the direction of remate transmitter A
~D provided that the expected signal being cross-correlated with combined signal 3 I 8 is that from the direction of transmitter A. The correlation signal is output to signal muter I d.
Methods and systems consistent with this invention may generate a plurality of expected signals from a plurality of directions and may correlate combined signal 'S 3 I 8 vfith the plurality of expected signals to form a plurality of correlation signals.
For example, referring to FIG. ?, receive calculator may generate an expected signal for a carrier from the direction of transmitter A and an expected signal for a carrier of the same or different frequency from the direction of transmitter B.
'I"hus, receiver 1 DO may simultaneously "look" in multiple (M) directions at one time, and 30 receiver calculator 7 may generate M expected Signals and signal currclatur 1 1 may cross-correlate M expected signals vrith combined signal 318 to form M
correlation signals. Each correlation signal is the detection signal for receiver 100 "looking" in that one particular direction. The M correlation signals are output to signal router l~
(via line 10~).
Methods and systems consistent with this invention store the M correlation signals in correlation signal memory 15 and analyze the correlation signals.
Using signal processor 120, infornlation such as voice or other data is extracted fi-onl the correlation signals. Signal muter 14 passes each of the M correlation signals to one of the several signal memory units 1 to M, respectively. Signal memory units I
to M store successive correlation signals from an assigned direction 1 to M, respectively.
If the processing is at sufficiently high speeds, receiver 100 can simultaneously process and detect signals from many directions. Alternatively, signal memories 1 to M stole correlation signals for different individual transmitters, such as transmitter A or B. This is useful if a translllitter is mobile, and thus I S constantly changing direction with respect to receiver 100. In this case, the direction used by receiver calculator 7 to establish the expected signal for a mobile transmitter is continuously updated to correspond to the cul-I-ent transmitter location.
Array I may not have directianal characteristics, but rather it may be isotropic (omnidirectional). The arbitrary relationship of the phase modulation signals may give a combined signal block of I\T chips, regardless of the transmitted signal's direction of arrival, the same average energy within the receiver.
Array 1 and receiver 1 p0 also may be designed such that it is isotropic with respect to transmitted signals within a more limited transmitter space.
FIG. d is a flow chart of a process 100 for space-division multiple access receiving consistent with this invention. First, methods and systems consistent with this invention receive a transmitted signal ill the plurality of receive elements to farm a plurality of receive element signals (step d02). Such systems then generate a plurality of phase modulation signals (step clod) and phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a 1)lurality of phase modulated signals (Step d06). Such methods and Sy5teI11S tllell CUlllbllle the plLl1'alltf Of 1)ll~tSC IIlOdLllatP_d S1g11t115 IIltO a COmbIIled signal (step 408). Such methods and systems then generate an expected signal (step ~ 10) and cross-correlate combined signal 318 with the expected signal to forth a correlation signal (step 412). Such methods and systems then store the correlation signal in a correlation signal memory and analyze the correlation signal (step d 14).
Expected Signal Polarization The polarization of the transmitted signal, in general, may affect the expected signal. If the polarization of the transmitted signal is known in advance, then receiver calculator 7 may use this value in calculating the expected signal. If the value of the polarization is not known in advance, receiver calculator 7 has several options. One option is to assume a value for the polarization and calculate the expected signal based upon this assumed value. In this option, the component of the polarization of the transmitted signal that coincides with the assumed polarization is detected.
Another option is for receiver calculator 7 to calculate two expected signals.
The first expected signal is calculated based upon an assumed polarization as before, and the second expected signal is calculated based upon a polarization normal (orthogonal) to the first polarization. The transmitted signal is detected by separately correlating the combined signal with the first and second expected signals, forming two correlation signals. These two correlation signals may be processed individually or may be combined by signal processor 120 in order to extract the information from the transmitted signal.
Yet another option is to calculate two expected signals as before, the first expected signal based upon an assumed polarization and the second exported signal based upon a normal (ot~thogunal) polarization. In this option, the two expected ~5 signals are summed ur otherwise combined to funn a third expected signal.
The transmitted signal is detected by correlating the combined signal with the third expected signal. Regardless of the polarization of the transmitted signal, in this option there is good correlation with the third expected signal.
These techni~Iues, along v ith others, devised by those skilled in the art tray be used to detect and extract information from transmitted signals with any type of polarization characteristics, such as linear, circular, ur elliptical.
Processing Gain Methods and systems consistent with this invention may generate a plurality of phase modulation signals, wherein the phase modulation signals have a chipping rate and the chipping rate exceeds a modulation rate of the transmitted signal. In one embodiment, signal modulator 9 may chip the received element signals continuously at a rate that is at least one-hundred times the period of the highest modulation frequency of the transmitted signal. This chipping rate may allow signal correlator 1 l, which in one embodiment processes a block of fifty clips at one time, to contain no more than one half cycle or one half wave of the modulation signal impressed upon any carrier, thus meeting the minimum Nyquist sampling rate.
Thus, in one embodiment, the correlation length of fifty chips at a chipping rate of at least one-hundred times the highest modulation rate corresponds to the maximum Nyquist sampling interval. This may permit complete recovery of the modulation information from any cannier. Values of M other than 50 are possible, and satisfying the minimum Nyquist rate may result in different chipping rates.
'The amplitude and phase of each chip within combined signal 318 (Fig. 3B) on line 1U6 (Fig. I) may depend upon the angle of arrival of a transmitted signal at the receive elements of array 1. Receiver calculator 7, in order to differentiate between signals arriving from different directions, anticipates and calculates for each direction the expected chip amplitude and phase patterns that may be present within combined signal 318. lion each direction, signal eorrelator 1 I cross-correlates the expected chip patterns i.e., the expected signal, with combined signal 318. In signal memory 12, there are K o~:pected chip patterns from K different directions. In one embodiment, K is equal to M, as discussed above.
?5 Signal currelator 1 1 may Dave a processing gain of ~~, where i~' is the number of chips, within the combined signal 318, processed together at the same time. The: N chips form a block of duration T. 'fhe cross-correlation described is between combined signal 318 and the plurality of K expected signals.
In one embodiment the value fur processing gain is established as follows.
A combined signal block containing I\' chips (spanning the time interval from a start time fl of first chip to an end time tl+T of the Nth chip) has a correlation energy expression of t l ,-n ->
Rlylz(K,e)= vn~(t) ~ v (t)e dt, fl where yr;(t) is combined signal 31$ comprising N chips and v~,h.(t) is the corresponding Kth expected signal also comprising N chips. Each chip of v~~(t) and vL.~(t) has a mean-square value of an and a~,~. respectively and a rout-mean-square (rms) value of aR and ally respectively. They may be substantially random vectors that confortrt to Rayleigh density functions with random phase and expected magnitude values of ~ aR and ~ aC~ respectively. These substantially random 1 U vectors may each be composed of the sum of random phase chips within the phase modulated signals input to signal combiner 1U. The phase shift term e~~° may be applied equally to all chips of a combined signal block where the parameter 8 may be chosen to maximize the correlation output for each processed combined signal block. In wireless systems where the transmitted signal is phase modulated, as with QPSK, the parameter 8 is part of the correlation signal and may be used to derive the carrier phase information. In systems where the transmitted signal is amplitude modulated, the magnitude of the cross-correlation is part of the correlation signal and may be used to derive the carrier amplitude information.
The magnitude of the correlation energy of N chips that are well correlated is T
2U Na~a~.x ~ N ) , where T is the combined signal block duration and where ~
~T ) is the time interval of a single chip, or Tc.
If, on the other hand, the combined signal block of chips is random with respect to the corresponding expected signal block of chips, i.e., they are nut correlated, the magnitude of the correlation energy of the h chips is ~~a a .
.~ T ) .
rr H ~ N
~'S In this case, the N combined signal vectors (chips) have random phases with respect to the corresponding N expected signal vectors (chips). The sum of N random vectors (with r.m.s. value of art) is two-dimensional Gaussian (with r.m.s.
value of ~~af~). This two-dimensional Gaussian density function may also be described as a Rayleigh density function.
1~ -The value for processing gain is found by forming the ratic.~ of the correlator output for a well core°elated signal Na~~al.h ~ T ~ and an uncorrelated signal N
T
~anae,~ ~ ~) .
N
Une skilled in the art appreciates that numerous variations to this system exist, For example, methods and systems consistent with this invention also may function with acoustic signals, not only electromagnetic signals. For instance, the transmitted signals may be acoustic signals conveyed through water, and the receive element signals, the combined signal, and the expected signals may all represent acoustic signals in a receiver and processor. Such a system may provide for an ID undersea data link or any type of sonic signal detection, In such a system, the receive elements of array 1 are acoustic sensors, Also, it is generally easier for signal processors to generate pseudo-random numbers rather than purely random numbers, and thus the teen "random" includes "pseudo-random." Therefore, modulation signal generator 8 may generate pseudo-random phase modulation signals arid signal modulator 9 may generate pseudo-random phase modulated signals. This applies for phase modulation signals ~
that are either continuously variable or limited to a finite number of values.
Further, the technique used for comparing the combined signal with the expected signals, herein described as correlation, may draw upon any suitable signal 2D comparison techniques well known in signal processing for recovering the magnitude and phase information from the transmitted signal.
Further still, array I may take an many different shapes. For example, array 1 may be flat, spherical, or cylindrical. It may also conform to a surface, such as the outside of an airplane or an automobile.
~5 Lastly, all or some of the functions performed by signal modulator 9, signal combiner 1 D, modulation signal generator 8, signal memory I ~, signal correlator 1 1, signal renter 1~, receiver calculator 7, receiver configuration memory 6, and signal processor 1<D may be implemented in software, not necessarily hardware.
Although methods and systems consistent with the present invention have 30 been described with referee ce to an embodiment thereof, those skilled in the art know various changes in form and detail that may be made without departing from the spirit and scope of the present invention as defined in the appended claims and their full scope of equivalents.
RL:CEIVER
rield of the Invention The present invention relates to wireless communication networks, and morn paI-ticularly to space-division multiple access (SUMA) in wireless communication networks.
Background of the Invention Vfireless communication services are an increasingly common form of conununication, and demand fur wireless services continuos to grow. Examples of wireless services include cellular mobile telephones, wireless Internet service, wireless local area computer networks, satellite communication networks, satellite television, and multi-user paging systems. Unfortunately, these communication systems are conEned to a limited frequency spectrum either by practical considerations or, as is often the case, by government regulation. As the maximum number of users, or "capacity," of these systems is reached, user demand for more service may be met by either ( 1) allocating more frequency spectrum to the wireless service, or (2) using the allocated frequency spectrum more efficiently.
Because the frequency spectrum is limited and cannot keep pace with user demand, there is a ~0 critical need for new technology that uses the allocated frequency spectrum more efficiently.
~t'ireless communication systems are generally composed of one ur more base stations through which wireless users, such as mobile telephone users, gain access to a communications network, such as a telephone network. A base station ~5 serves a number of wireless users, fixed ur nlubile, in a local area. To increase the capacity of the systems, service providers may install more base stations, reducing the area and the number of users handled by each base station. This approach increases system capacity without allocating Inure spectrum frequency bands, but is quite costly because: it requires signiCcantly more hardware.
~U Alll7thCr appl'OaCh t0 L1S111~ the f1'ttluCllCy SpL'CtI-Lllll InOI'e C;
fllClt'ntly IS 1?f improving "multiple access" icchnidues. Multiple access tcchnidues allwv multiple _?_ users to share the allocated frequency spectrum so that they do not interfere with each other. The most common multiple access schemes are Frequency-Division Multiple Access (FUMA), Time-Division Multiple Access ('TDMA), C.~ode-Division Multiple Access (CDMA), and more recently Space-Division Multiple Access (SDMA).
FDMA slices the allocated frequency band into multiple frccluency channels.
Each user transmits and receives signals on a different frequency channel to avoid interfering with the other users. When one user no longer requires the frequency channel assigned to it, the frequency channel is reassigned to another user.
With 'fDMA, users may share a common frequency channel, but each user uses the common frequency channel at a different time. In other words, each user is allocated a time slot in which the user may transmit and receive. Thus, TDMA
interleaves multiple users in the available time slots.
CDMA allolvs multiple users to share a common frequency channel by using coded modulation schemes. CDMA assigns distinct codes to each of the multiple users. The user modulates its digital signal by a v=ideband coded pulse train based on its district code, and transmits the modulated coded signal. 'I°he base station detects the user's transmission by recognizing the modulated code.
In SDMA, a system may separate a desired user's signal from other signals ~0 by its direction of arrival, ar spatial characteristics. 'this is sometimes referred to as "spatial filtering." Thus, even though two users may be transmitting an the same frequency at the same time, the base station may distinguish them because the transmitted signals from the users are arriving from different directions. It is possible to use SDMA in combination with FDMA, TDMA, or CDMA.
~5 A conventional SDMA receiver requires an array of multiple recc.?ive elements. Further, a conventional SDMA receiver uses a bank of 1)hase shifters that cooperates with the receive element array to farm a'"beam" that "looks" in a particular direction. It is generally hare desirable to farm multiple beams, each directed toward a different direction, 1.e., toward different users. The mare beams, 3U the IIloI'e S1111L11taIleoLlS llSerS the SDMA Sy5teT11 Ina1' hallllle optl'atlng an the Sallle ll'ClllICIICy at thP. 5allle t1111t;. Thl', IIloI'P. bei1111S, hoV'ever, the'.
nloI'e CaI11p11Cated th('.
SDMA receiver, For instance, each beam may require a separate bank of phase shifters and circuits that perform signal tracking. Additionally, each beans may require a separate "signal combincr," which combines the signals received from each receive element to form a "combined signal." FuI-tller still, each combined signal may require a separate signal detector, which detects the transmitted signal from the user. This hardware complexity greatly increases the cost of an SDMA receiver.
Using well known algorithms, hardware complexity may be reduced by performing phase shifting, signal tracking, signal combining and signal detecting in signal processing software. Current signal processing techniques, however, have difficulty identifying and tracking large numbers of simultaneously transmitted signals on the same frequency, paI-ticularly in a "multipathing" ~:nvironment.
A
multipathing environment is ogle where transmitted signals may reach the receiver over multiple paths. For instance, a transmitted signal may reach tile receiver (1) directly, and (2) indirectly after reflecting off objects. Multipath signals may also further complicate the complexity of the conventional SDMA receiver in the same manner as described above.
Thus, there is a need to provide an improved SDMA receiver that can simultaneously receive from multiple directions and operate in a multipath environment without likewise increasing hardware or software complexity of the ~0 receiver.
Summary of the Invention The summary and the following detailed description should not restrict the scope of the claimed invention. F3oth provide examples and explanations to enable others to practice the invention.
~5 Methods and systems consistent with this invention may incorporate a multi-element receive signal array that may achieve polarization independent isotropic reception, with power gain that may be greater than isotropic. Such methods and systems may receive multiple signals having the same or different carrier frequencies, distinguish the signals, and establish their dirc~cticlns of arrival.
30 Methods and systems consistent with this invention receive a plurality of tl'anSlllltted SlgnalS III a rf:CP.lver havlllg tl p1111'allty of I'ecClve c'ltIlll;llt5, V'hcrl.'l11 each _:~_ transmitted signal has a different spatial location. Such methods and systems receive the plurality of transmitted signals in the plurality of receive elements to form a plurality of receive element signals, form a combined signal derived from the plurality of receive element signals, and detect the plurality of transmitted signals from the combined signal by its different spatial location.
To achieve this, methods and systems consistent with this invention generate a plurality of phase modulation signals that may be arbitrary or uncorrelated, and phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals.
Such methods and systems then combine the plurality of phase modulated signals into a combined signal, generate expected signals, and correlate the combined signal with the expected signals to form correlation signals. Such methods and systems then store the con-elation signals in a correlation signal memory and analyze the correlation signals to extract information from the detected transmitted signals.
Brief Description of the Drawings The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings, ~U FIG. 1 is a block diagram, consistent with this inv ention, of a receiver;
FIG. 2 is a diagram of an environment, consistent with this invention, in which the receiver of FIG. 1 may operate;
FIG. 3A is a diagram of phase modulation signals, consistent with this invention generated by a modulation signal generator as shown in FIG. I;
FIG. 3B is a diagram of phase modulated signals generated by a signal modulator as shown in FIG. l, and a combined signal, all consistent with this invention; and FIG. ~ is a flow chart of a process 4UU for space-division multiple access receiving consistent with this iwention.
3U Detailed Description of the Invention Overview _5_ The following description of embodiments of the present invention refers to the accompanying drawings. Where appropriate, the same reference numbers in different drawings refer to the same or similar elements.
Methods and systems consistent with this invention overcome the hardware and software complexity of the conventional SDMA receiver in a wireless system.
Such methods and systems comprise a receive element array with a plurality of receive elements. Users of the wireless system transmit a plurality of signals, each signal having a different direction or spatial location relative to the receive element array. 'The users may be, for instance, mobile telephone users.
The receive element array receives the plurality of transmitted signals in the plurality of receive elements to form a plurality of receive element signals.
Such methods and systems form a single combined signal derived from the plurality of receive element signals, and nlay detect each of the plurality of transmitted signals from the single combined signal based upon its different spatial location.
Thus, such methods and systems do not need multiple banks of phase shifters, multiple signal combiners, ur multiple signal detectors. Instead, such methods and systems may detect signals from multiple users based on their different spatial location fi°om a single combined signal, as opposed to forming a different combined signal for each signal from each user and detecting a signal from each combined signal.
?0 To achieve this, methods and systems consistent with this invention generate a plurality of phase modulation signals that nlay be arbitrary or uncorrelated phase modulation signals, and phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals. Such methods and systems then combine the plurality of ~5 phase modulated signals into the combined signal, generate expected signals, and correlate the combined signal with the expected signals to form correlation signals.
The expected signals are the combined signals expected from the directions of the users, and may be a function of the phase modulation signals and the direction of the users. Such methods and systems then store the correlation signals in a correlation U Slgn~ll IIlelIlUry Gild allalyLe tlll,' ClarI'elatlull S1g17a1S tU eXt1'tlct tllt', tl'a17S1711tt1;d information in the signals from the users.
-G-Implementation Details Methods and systems consistent with this invention receive a transmitted signal in a receiver having a plurality of receive dements. FIG. 1 is a block diagram of a receiver 1 OU consistent with this invention. Receiver 100 comprises an array 1 having a plurality of receive elements, a modulation signal generator 8, a signal modulator ), a signal combiner 10, a receiver configuration memory G, a receiver calculator 7, a signal memory 12, a signal correlator 1 l, a signal muter 14, a plurality of signal memories 15, and a signal processor 120. Receiver 100 may include other components not specifically described above such as alters, mixers, amplifiers, and power supplies. The location of these components may vary depending upon the preference of designers skilled in the an.
FIG. 2 is a diagram of an environment 200, consistent with this invention, in which receiver 100 may operate. In environment 20D, remote transmitter A and remote transmitter B may transmit signals 2 and 3, respectively from remote transmitter space ''U?. Remote transmitters A and B may be mobile telephones, for example.
Transmitted signals 2 and 3 impinge un array I, and the plurality of elements receive signals ? and 3 to form a plurality of receive element signals. The plurality of receive element signals are conveyed (via lines 102) to a signal modulator J, ?0 which is described in detail below.
Methods and systems consistent with this invention generate a plurality of phase modulation signals. Modulation signal generator $ generates phase modulation signals fur the receive elements of array I . These phase modulation signals may be arbitrary or uncurrelated (correlation less than one). The ~5 uncorrelated phase modulation signals may be substantially un correlated or only slightly uncorrelated. For instance, the uncurrelated random please signals may have a correlation less than 1, but greater than 0.75; less than ur equal to 0.75, but greater than 0.50; less than ur equal to 0.50, but greater than D.25; less than ur equal to D.~~.
but greater than ur equal to zero. On the other hand, some ur all of these signals 3D may be well correlated ur even be identical. 'I'lm phase modulation signals may be arbitrary in that they may nut be correlated with, ur otherwise ~i~~pendent on, the geometry of the elements of array 1. The phase modulation signals may be independent of the direction of the transmitted signal.
FIG. 3A is a diagram of exemplary phase modulation signals for several elements of array 1. As shown in FIG. 3A, modulation signal generator 8 generates a phase ~" for a duration of Tc for a first please modulation signal 302 for a first receive element. Modulation signal generator $ then generates a phase c~, ~
fur a duration of Tc fur first phase modulation signal 302. 'I°his continues, but is shown for N periods of Tc, where Tc is the period of a "chip." The allowed values of phase shift cp for each element of array 1 may be continuously variable fi-um U to 2n radians or may be limited to a finite number of values, such as Q and n radians. If a finite number of values for phase shift ~p is used, each element may be assigned differing allowed values.
The same process occurs for a second phase modulation signal 304 fur a second receive element. As shown in FIG. 3A, modulation signal generator 8 generates phases ~p,, and ~p~,, each for a duration of Tc, fur the second phase modulation signal 304. This process likewise repeats for a third receive element with third phase modulation signal 306 through a Jth receive element with Jth phase modulation signal 308, where J is the total number of receive elements in array 1.
The phase modulation signals are output to signal modulator 9. Modulation signal 2U generator 8 also outputs the phase modulation signals to receiver calculator 7, which is described in detail below. Although the phases may be random, they are known to receiver 100.
Methods and systems consistent with this invention phase modulate each of the plurality of receive element signals with one of the please modulation signals to form a plurality of phase modulated signals. Thus, signal modulator 9 phase modulates, ur "chips," each element signal ~~~ith one of the phase modulation signals generated by modulation signal generator 8. FIG. 3B is a diagram of phase modulated signals consistent urith this invention. As shown in FIG. 3B, a first chip of first receive element phase modulated signal 310 is edual to the first receive element signal, but phase shifted by c~", the lust phase of phase modulation signal 302. Likewise, a second chip of phase modulated signal 310 is equal to the first _g_ receive element signal, but phase shifted by ~p,~, the second phase of phase modulation signal 302. Likewise, the second through the Jth receive element signals are phase modulated to form second 312 through Jth 316 phase modulated signals.
Phase modulated signals 310-316 output from signal modulator 9 to signal combiner 10 (via lines 104). Methods and systems consistent with this invention combine the plurality of phase modulated signals into a combined signal 318.
Thus, signal combines 10 combines the phase modulated signals into combined signal 318.
In one embodiment, signal combines 10 sums, chip by chip, the plurality of phase modulated signals to form combined signal 318. Far example, all of the first chips from first phase modulated signal 310 through Jth phase modulated signal 316 are added to form a combined signal first chip 320, all of the second chips from phase modulated signal 310 through Jth phase madulated signal 31 G are added to form a combined second chip 322, and so forth. Each chip of combined signal 318 may have a vector magnitude that conforms to a Rayleigh density function and may have a random phase angle. Combined signal 318 is output from signal combines 10 to a signal correlates 11 (via line 106).
Methods and systems consistent with this invention generate an expected signal. The expected signal is the signal that the combined signal 318 is expected to be if an unmodulated carrier were transmitted from a particular direction relative to array 1. Receiver calculator 7 calculates the expected signal. For example, refen-ing to FIG. 2, receive calculator 7 may generate an expected signal fur a cau-ier from the direction of transmitter A. Receiver calculator 7 inputs information from modulation signal generator 8 and receiver configuration memory 6 in order to calculate the expected signal. Receiver configuration memory ~ may provide information that affects the amplitude, phase, and polarization of receive element signals and phase modulated signals before being combined in signal combines 10.
'This information may include the carrier frequency of transmitted signals 2 and 3, their estimated direction, flue conFiguration of the receive elements within array 1, and the transmission lint: lengths of the elements. Modulation signal generator 8 may provide information giving the relative phase of each chip w°ithin the phase modulation Signals 3D2-308. Receiver calculator 7 calculates and outputs the expected signal to the signal memory 12 for temporary storage. The expected signal is output from the signal memory 1? and input to signal currelatur 1 1.
Because the polarization of the transmitted signal may influence the phase and magnitude of the combined signal, receiver calculator 7 may calculate the expected signal based upon an assumed polarization of the transmitted signal.
Methods and systems consistent with this invention cross-correlate combined signal 318 with the expected signal to form a correlation signal. Signal correlator I 1 inputs combined signal 318 and the expected signal and correlates the two signals.
In one embodiment, signal correlator I 1 may cross-correlate the corresponding N
ID consecutive chips of combined signal 318 and the expected signal. In this embodiment, the value N may be 50. Signal correlator 1 1 may perform a new cross-correlation between combined signal 318 and the expected signal each time N
new chips (or time period N x Tc) of combined signal 318 enters correlator I 1.
Each time a new correlation is performed, receiver calculator 7 may update the expected signal to include the next N chips and may delete the previous chips so that the value of N may remain 50, for example. Signal correlator 1 I produces an output that is a measure of the cross-correlation of combined signal 318 and the expected signal. In the example of FIG. 2, signal correlator I 1 produces an output that is the correlation signal for receiver l OD "looking" in the direction of remate transmitter A
~D provided that the expected signal being cross-correlated with combined signal 3 I 8 is that from the direction of transmitter A. The correlation signal is output to signal muter I d.
Methods and systems consistent with this invention may generate a plurality of expected signals from a plurality of directions and may correlate combined signal 'S 3 I 8 vfith the plurality of expected signals to form a plurality of correlation signals.
For example, referring to FIG. ?, receive calculator may generate an expected signal for a carrier from the direction of transmitter A and an expected signal for a carrier of the same or different frequency from the direction of transmitter B.
'I"hus, receiver 1 DO may simultaneously "look" in multiple (M) directions at one time, and 30 receiver calculator 7 may generate M expected Signals and signal currclatur 1 1 may cross-correlate M expected signals vrith combined signal 318 to form M
correlation signals. Each correlation signal is the detection signal for receiver 100 "looking" in that one particular direction. The M correlation signals are output to signal router l~
(via line 10~).
Methods and systems consistent with this invention store the M correlation signals in correlation signal memory 15 and analyze the correlation signals.
Using signal processor 120, infornlation such as voice or other data is extracted fi-onl the correlation signals. Signal muter 14 passes each of the M correlation signals to one of the several signal memory units 1 to M, respectively. Signal memory units I
to M store successive correlation signals from an assigned direction 1 to M, respectively.
If the processing is at sufficiently high speeds, receiver 100 can simultaneously process and detect signals from many directions. Alternatively, signal memories 1 to M stole correlation signals for different individual transmitters, such as transmitter A or B. This is useful if a translllitter is mobile, and thus I S constantly changing direction with respect to receiver 100. In this case, the direction used by receiver calculator 7 to establish the expected signal for a mobile transmitter is continuously updated to correspond to the cul-I-ent transmitter location.
Array I may not have directianal characteristics, but rather it may be isotropic (omnidirectional). The arbitrary relationship of the phase modulation signals may give a combined signal block of I\T chips, regardless of the transmitted signal's direction of arrival, the same average energy within the receiver.
Array 1 and receiver 1 p0 also may be designed such that it is isotropic with respect to transmitted signals within a more limited transmitter space.
FIG. d is a flow chart of a process 100 for space-division multiple access receiving consistent with this invention. First, methods and systems consistent with this invention receive a transmitted signal ill the plurality of receive elements to farm a plurality of receive element signals (step d02). Such systems then generate a plurality of phase modulation signals (step clod) and phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a 1)lurality of phase modulated signals (Step d06). Such methods and Sy5teI11S tllell CUlllbllle the plLl1'alltf Of 1)ll~tSC IIlOdLllatP_d S1g11t115 IIltO a COmbIIled signal (step 408). Such methods and systems then generate an expected signal (step ~ 10) and cross-correlate combined signal 318 with the expected signal to forth a correlation signal (step 412). Such methods and systems then store the correlation signal in a correlation signal memory and analyze the correlation signal (step d 14).
Expected Signal Polarization The polarization of the transmitted signal, in general, may affect the expected signal. If the polarization of the transmitted signal is known in advance, then receiver calculator 7 may use this value in calculating the expected signal. If the value of the polarization is not known in advance, receiver calculator 7 has several options. One option is to assume a value for the polarization and calculate the expected signal based upon this assumed value. In this option, the component of the polarization of the transmitted signal that coincides with the assumed polarization is detected.
Another option is for receiver calculator 7 to calculate two expected signals.
The first expected signal is calculated based upon an assumed polarization as before, and the second expected signal is calculated based upon a polarization normal (orthogonal) to the first polarization. The transmitted signal is detected by separately correlating the combined signal with the first and second expected signals, forming two correlation signals. These two correlation signals may be processed individually or may be combined by signal processor 120 in order to extract the information from the transmitted signal.
Yet another option is to calculate two expected signals as before, the first expected signal based upon an assumed polarization and the second exported signal based upon a normal (ot~thogunal) polarization. In this option, the two expected ~5 signals are summed ur otherwise combined to funn a third expected signal.
The transmitted signal is detected by correlating the combined signal with the third expected signal. Regardless of the polarization of the transmitted signal, in this option there is good correlation with the third expected signal.
These techni~Iues, along v ith others, devised by those skilled in the art tray be used to detect and extract information from transmitted signals with any type of polarization characteristics, such as linear, circular, ur elliptical.
Processing Gain Methods and systems consistent with this invention may generate a plurality of phase modulation signals, wherein the phase modulation signals have a chipping rate and the chipping rate exceeds a modulation rate of the transmitted signal. In one embodiment, signal modulator 9 may chip the received element signals continuously at a rate that is at least one-hundred times the period of the highest modulation frequency of the transmitted signal. This chipping rate may allow signal correlator 1 l, which in one embodiment processes a block of fifty clips at one time, to contain no more than one half cycle or one half wave of the modulation signal impressed upon any carrier, thus meeting the minimum Nyquist sampling rate.
Thus, in one embodiment, the correlation length of fifty chips at a chipping rate of at least one-hundred times the highest modulation rate corresponds to the maximum Nyquist sampling interval. This may permit complete recovery of the modulation information from any cannier. Values of M other than 50 are possible, and satisfying the minimum Nyquist rate may result in different chipping rates.
'The amplitude and phase of each chip within combined signal 318 (Fig. 3B) on line 1U6 (Fig. I) may depend upon the angle of arrival of a transmitted signal at the receive elements of array 1. Receiver calculator 7, in order to differentiate between signals arriving from different directions, anticipates and calculates for each direction the expected chip amplitude and phase patterns that may be present within combined signal 318. lion each direction, signal eorrelator 1 I cross-correlates the expected chip patterns i.e., the expected signal, with combined signal 318. In signal memory 12, there are K o~:pected chip patterns from K different directions. In one embodiment, K is equal to M, as discussed above.
?5 Signal currelator 1 1 may Dave a processing gain of ~~, where i~' is the number of chips, within the combined signal 318, processed together at the same time. The: N chips form a block of duration T. 'fhe cross-correlation described is between combined signal 318 and the plurality of K expected signals.
In one embodiment the value fur processing gain is established as follows.
A combined signal block containing I\' chips (spanning the time interval from a start time fl of first chip to an end time tl+T of the Nth chip) has a correlation energy expression of t l ,-n ->
Rlylz(K,e)= vn~(t) ~ v (t)e dt, fl where yr;(t) is combined signal 31$ comprising N chips and v~,h.(t) is the corresponding Kth expected signal also comprising N chips. Each chip of v~~(t) and vL.~(t) has a mean-square value of an and a~,~. respectively and a rout-mean-square (rms) value of aR and ally respectively. They may be substantially random vectors that confortrt to Rayleigh density functions with random phase and expected magnitude values of ~ aR and ~ aC~ respectively. These substantially random 1 U vectors may each be composed of the sum of random phase chips within the phase modulated signals input to signal combiner 1U. The phase shift term e~~° may be applied equally to all chips of a combined signal block where the parameter 8 may be chosen to maximize the correlation output for each processed combined signal block. In wireless systems where the transmitted signal is phase modulated, as with QPSK, the parameter 8 is part of the correlation signal and may be used to derive the carrier phase information. In systems where the transmitted signal is amplitude modulated, the magnitude of the cross-correlation is part of the correlation signal and may be used to derive the carrier amplitude information.
The magnitude of the correlation energy of N chips that are well correlated is T
2U Na~a~.x ~ N ) , where T is the combined signal block duration and where ~
~T ) is the time interval of a single chip, or Tc.
If, on the other hand, the combined signal block of chips is random with respect to the corresponding expected signal block of chips, i.e., they are nut correlated, the magnitude of the correlation energy of the h chips is ~~a a .
.~ T ) .
rr H ~ N
~'S In this case, the N combined signal vectors (chips) have random phases with respect to the corresponding N expected signal vectors (chips). The sum of N random vectors (with r.m.s. value of art) is two-dimensional Gaussian (with r.m.s.
value of ~~af~). This two-dimensional Gaussian density function may also be described as a Rayleigh density function.
1~ -The value for processing gain is found by forming the ratic.~ of the correlator output for a well core°elated signal Na~~al.h ~ T ~ and an uncorrelated signal N
T
~anae,~ ~ ~) .
N
Une skilled in the art appreciates that numerous variations to this system exist, For example, methods and systems consistent with this invention also may function with acoustic signals, not only electromagnetic signals. For instance, the transmitted signals may be acoustic signals conveyed through water, and the receive element signals, the combined signal, and the expected signals may all represent acoustic signals in a receiver and processor. Such a system may provide for an ID undersea data link or any type of sonic signal detection, In such a system, the receive elements of array 1 are acoustic sensors, Also, it is generally easier for signal processors to generate pseudo-random numbers rather than purely random numbers, and thus the teen "random" includes "pseudo-random." Therefore, modulation signal generator 8 may generate pseudo-random phase modulation signals arid signal modulator 9 may generate pseudo-random phase modulated signals. This applies for phase modulation signals ~
that are either continuously variable or limited to a finite number of values.
Further, the technique used for comparing the combined signal with the expected signals, herein described as correlation, may draw upon any suitable signal 2D comparison techniques well known in signal processing for recovering the magnitude and phase information from the transmitted signal.
Further still, array I may take an many different shapes. For example, array 1 may be flat, spherical, or cylindrical. It may also conform to a surface, such as the outside of an airplane or an automobile.
~5 Lastly, all or some of the functions performed by signal modulator 9, signal combiner 1 D, modulation signal generator 8, signal memory I ~, signal correlator 1 1, signal renter 1~, receiver calculator 7, receiver configuration memory 6, and signal processor 1<D may be implemented in software, not necessarily hardware.
Although methods and systems consistent with the present invention have 30 been described with referee ce to an embodiment thereof, those skilled in the art know various changes in form and detail that may be made without departing from the spirit and scope of the present invention as defined in the appended claims and their full scope of equivalents.
Claims (80)
1. A method for receiving signals in a receiver having a plurality of receive elements, the method comprising the steps of:
receiving a transmitted signal in the plurality of receive elements to form a plurality of receive element signals;
generating a plurality of arbitrary phase modulation signals; and phase modulating each the plurality of receive element signals with a different one of the plurality of arbitrary phase modulation signals to form a plurality of phase modulated signals.
receiving a transmitted signal in the plurality of receive elements to form a plurality of receive element signals;
generating a plurality of arbitrary phase modulation signals; and phase modulating each the plurality of receive element signals with a different one of the plurality of arbitrary phase modulation signals to form a plurality of phase modulated signals.
2. The method of claim 1, wherein the arbitrary phase modulation signals are uncorrelated random phase signals.
3. The method of claim 1, further including the step of combining the plurality of phase modulated signals into a combined signal.
4. The method of claim 3, wherein the step of combining includes the step of summing the plurality of phase modulated signals into the combined signal.
5. The method of claim 3, including the step of detecting the transmitted signals from the combined signal.
6. The method of claim 5, including the step of extracting information from the detected transmitted signal.
7. The method of claim 3, further including the steps of generating an expected signal; and correlating the combined signal with the expected signal to form a correlation signal.
8. The method of claim 7, wherein generating an expected signal includes the step of generating the expected Signal as a function of the plurality of please modulation signals.
9. The method of claim 7, wherein generating the expected signal includes the step of generating the expected signal froth a particular direction.
10. The method of claim J, wherein the step of generating the expected signal includes the step of generating a plurality of expected signals from a plurality of directions; and wherein the step of correlating the combined signal includes correlating the combined signal with each of the plurality of expected signals from a plurality of directions to form a plurality of correlation signals.
11. The method of claim 7, wherein the step of correlating the combined signal with the expected signal includes cross-correlating the combined signal with the expected signal to form a cross-correlation signal.
12. The method of claim 7, wherein the step of correlating the combined signal with the expected signal includes the step of repeating correlating the combined signal with the expected signal over a first period of time every second period of time, wherein the second period of time is shorter than the first period of time.
13. The method of claim 7, further including the steps of:
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
14. A receiver comprising:
a plurality of receive elements, each receiving a transmitted signal to form a plurality of receive element signals;
a modulation signal generator to generate a plurality of arbitrary phase modulation signals; and a signal modulator to phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals.
a plurality of receive elements, each receiving a transmitted signal to form a plurality of receive element signals;
a modulation signal generator to generate a plurality of arbitrary phase modulation signals; and a signal modulator to phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals.
15. The receiver of claim 14, wherein the phase modulation signals are uncorrelated random phase signals.
16. The receiver of claim 14, further including a signal combines to combine the plurality of phase modulated signals into a combined signal.
17. The receiver of claim 16, wherein the signal combines sums the plurality of phase modulated signals into the combined signal.
18. The receiver of claim 16, including a detector to detect the transmitted signals from the combined signal.
19. The receiver of claim 18, including a signal processor for extracting information from the detected transmitted signal.
20. The receiver of claim 16, further including a receiver calculator to generate an expected signal; and a signal correlator to correlate the combined signal with the expected signal to form a correlation signal.
21. The receiver of claim 20, wherein the receiver calculator generates the expected signal as a function of the plurality of phase modulation signals.
22. The receiver of claim 20, wherein the receiver calculator generates the expected signal from a particular direction.
23. The receiver of claim 18, wherein the receiver calculator generates a plurality of expected signals front a plurality of directions; and wherein the signal correlator separately correlates the combined signal with each of the plurality of expected signals from a plurality of directions to form a plurality of correlation signals.
24. The receiver of claim 20, wherein the correlator includes a cross-correlator to correlate the combined signal with the expected signal to form a cross-correlation signal.
25. The receiver of claim 20, wherein the correlator repeatedly correlates the combined signal with the expected signal over a first period of time every second period of time, wherein the second period of time is shorter than the first period of time.
26. The receiver of claim 20, further including:
a correlation signal memory to store the correlation signal; and a signal processor to analyze the correlation signal.
a correlation signal memory to store the correlation signal; and a signal processor to analyze the correlation signal.
27. A method for simultaneously receiving a plurality of transmitted signals in a receiver having a plurality of receive elements, wherein each transmitted signal has a different spatial location, the method comprising the steps of:
receiving the plurality of transmitted signals in the plurality of receive elements to form a plurality of active element signals;
forming a combined signal derived from the plurality of receive element signals; and detecting each of the plurality of transmitted signals from the combined signal by its different spatial location.
receiving the plurality of transmitted signals in the plurality of receive elements to form a plurality of active element signals;
forming a combined signal derived from the plurality of receive element signals; and detecting each of the plurality of transmitted signals from the combined signal by its different spatial location.
28. The method of claim 27, further comprising generating a plurality of phase modulation signals; and phase modulating each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals.
29. The method of claim 22, wherein the phase modulation signals are uncorrelated random phase modulation signals.
30. The method of claim 28, wherein forming the combined signal includes the step of combining the plurality of phase modulated signals into a combined signal.
31. The method of claim 30, wherein the step of combining includes the step of summing the plurality of phase modulated signals into the combined signal.
32. The method of claim 27, including the step of extracting information from the detected transmitted signal.
33. The method of claim 27, wherein the step of detecting includes the steps of generating an expected signal; and correlating the combined signal with the expected signal to form a correlation signal.
34. The method of claim 33, wherein generating an expected signal includes the step of generating the expected signal as a function of the plurality of phase modulation signals.
35. The method of claim 33, wherein generating the expected signal includes the step of generating the expected signal from a particular direction.
36. The method of claim 35, wherein the step of generating the expected signal includes the step of generating a plurality of expected signals from a plurality of directions; and wherein the step of correlating the combined signal includes correlating the combined signal with each of the plurality of expected signals from a plurality of directions to form a plurality of correlation signals.
37. The method of claim 33, wherein tile step of correlating the combined signal with the expected signal includes cross-correlating the combined signal with the expected signal to form a cross-correlation signal.
38. The method of claim 33, wherein the step of correlating the combined signal with the expected signal includes the step of repeating correlating the combined signal with the expected signal over a first period of time every second period of time, wherein the second period of time is shorter than the first period of time.
39. The method of claim 33, further including the steps of:
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
40. A receiver for simultaneously receiving a plurality of transmitted signals, wherein each transmitted signal has a different spatial location, the receiver comprising:
a plurality of receive elements to receive the plurality of transmitted signals to form a plurality of receive element signals;
a signal combiner to form a combined signal derived from the plurality of receive element signals; and a detector to detect each of the plurality of transmitted signals from the combined signal by its different spatial location.
a plurality of receive elements to receive the plurality of transmitted signals to form a plurality of receive element signals;
a signal combiner to form a combined signal derived from the plurality of receive element signals; and a detector to detect each of the plurality of transmitted signals from the combined signal by its different spatial location.
41. The receiver of claim 40, further comprising a modulation signal generator to generate a plurality of arbitrary phase modulation signals; and a signal modulator to phase modulate each of the plurality of receive element signals with a different one of the phase modulation signals to form a plurality of phase modulated signals.
42. The receiver of 41, wherein the plurality of arbitrary phase modulation signals are uncorrelated random phase signals.
43. The receiver of claim 41, wherein the signal combiner combines the plurality of phase modulated signals into a combined signal.
44. The receiver of claim 43, wherein the signal combiner sums the plurality of phase modulated signals into the combined signal.
45. The receiver of claim 40, including a signal processor for extracting information from the detected transmitted signal.
46. The receiver of claim 40, further including:
a receiver calculator to generate an expected signal; and a signal correlator to correlate the combined signal with the expected signal to forth a correlation signal.
a receiver calculator to generate an expected signal; and a signal correlator to correlate the combined signal with the expected signal to forth a correlation signal.
47. The receiver of claim 46, wherein the receiver calculator generates the expected signal as a function of the plurality of phase modulation signals.
48. The receiver of claim 46, wherein the receiver calculator generates the expected signal from a particular direction.
49. The receiver of claim 48, wherein the receiver calculator generates a plurality of expected signals from a plurality of directions; and wherein the signal correlator correlates the combined signal with each of the plurality of expected signals from a plurality of directions to form a plurality of correlation signals.
50. The receiver of claim 46, wherein the signal correlator cross-correlates the combined signal with the expected signal to form a cross-correlation signal.
51. The receiver of claim 46, wherein the signal correlator repeatedly correlates the combined signal with the expected signal over a first period of time every second period of time, wherein the second period of time is shorter than the first period of time.
52. The receiver of claim 46, further including:
a memory to store the correlation signal in a correlation signal memory; and a signal processor to analyze the correlation signal.
a memory to store the correlation signal in a correlation signal memory; and a signal processor to analyze the correlation signal.
53. A method for receiving signals in a receiver having a plurality of receive elements, the method comprising the steps of:
receiving a transmitted signal in the plurality of receive elements to form a plurality of receive element signals, wherein the transmitted signal has a modulation rate;
generating a plurality of phase modulation signals, wherein the phase modulation signals have a chipping rate and the chipping rate exceeds the modulation rate; and phase modulating each of the plurality of receive element signals with a different one of the phase modulation signals from a plurality of phase modulated signals.
receiving a transmitted signal in the plurality of receive elements to form a plurality of receive element signals, wherein the transmitted signal has a modulation rate;
generating a plurality of phase modulation signals, wherein the phase modulation signals have a chipping rate and the chipping rate exceeds the modulation rate; and phase modulating each of the plurality of receive element signals with a different one of the phase modulation signals from a plurality of phase modulated signals.
54. The method of claim 53, wherein the phase modulation signals are arbitrary phase modulation signals.
55. The method of claim 54, wherein the arbitrary phase modulation signals are uncorrelated random phase signals.
56. The method of claim 53, further including the step of combining the plurality of phase modulated signals into a combined signal.
57. The method of claim 56, wherein the step of combining includes the step of summing the plurality of phase modulated signals into the combined signal.
58. The method of claim 56, including the step of detecting the transmitted signals from the combined signal.
59. The method of claim 58, including the step of extracting information from the detected transmitted signal.
60. The method of claim 56, further including the steps of generating an expected signal; and correlating the combined signal with the expected signal to form a correlation signal.
61. The method of claim 60, wherein generating an expected signal includes the step of generating the expected signal as a function of the plurality of phase modulation signals.
62. The method of claim 60, wherein generating the expected signal includes the step of generating the expected signal from a particular direction.
63. The method of claim 62, wherein the step of generating the expected signal includes the step of generating a plurality of expected signals from a plurality of directions; and wherein the step of correlating the combined signal includes correlating the combined signal with each of the plurality of expected signals from a plurality of directions to form a plurality of correlation signals.
64. The method of claim 60, wherein the step of correlating the combined signal with the expected signal includes cross-correlating the combined signal with the expected signal to form a cross-correlation signal.
65. The method of claim 60, wherein the step of correlating the combined signal with the expected signal includes the step of repeating correlating the combined signal with the expected signal over a first period of time every second period of time, wherein the second period of time is shorter than the first period of time.
66. The method of claim 60, further including the steps of:
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
67. A method for receiving signals in a receiver having a plurality of receive elements, the method comprising the steps of:
receiving a transmitted signal in the plurality of receive elements to form a plurality of receive element signals;
generating a plurality of phase modulation signals independent of the direction of the direction of the transmitted signal; and phase modulating each the plurality of receive element signals with a different one of the plurality of arbitrary phase modulation signals to form a plurality of phase modulated signals.
receiving a transmitted signal in the plurality of receive elements to form a plurality of receive element signals;
generating a plurality of phase modulation signals independent of the direction of the direction of the transmitted signal; and phase modulating each the plurality of receive element signals with a different one of the plurality of arbitrary phase modulation signals to form a plurality of phase modulated signals.
68. The method of claim 67, wherein the phase modulation signals are arbitrary phase modulation signals.
69. The method of claim 68, wherein the arbitrary phase modulation signals are uncorrelated random phase signals.
70. The method of claim 67, further including the step of combining the plurality of phase modulated signals into a combined signal.
71. The method of claim 70, wherein the step of combining includes the step of summing the plurality of phase modulated signals into the combined signal.
72. The method of claim 70, including the step of detecting the transmitted signals from the combined signal.
73. The method of claim 72, including the step of extracting information from the detected transmitted signal.
74. The method of claim 70, further including the steps of generating an expected signal; and correlating the combined signal with the expected signal to form a correlation signal.
75. The method of claim 74, wherein generating an expected signal includes the step of generating the expected signal as a function of the plurality of phase modulation signals.
76. The method of claim 74, wherein generating the expected signal includes the step of generating the expected signal from a particular direction.
77. The method of claim 76, wherein the step of generating the expected signal includes the step of generating a plurality of expected signals from a plurality of directions; and wherein the step of correlating the combined signal includes correlating the combined signal with each of the plurality of expected signals from a plurality of directions to form a plurality of correlation signals.
78. The method of claim 74, wherein the step of correlating the combined signal with the expected signal includes cross-correlating the combined signal with the expected signal to form a cross-correlation signal.
79. The method of claim 74, wherein the step of correlating the combined signal with the expected signal includes the step of repeating correlating the combined signal with the expected signal over a first period of time every second period of time, wherein the second period of time is shorter than the first period of time.
80. The method of claim 74, further including the steps of:
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
storing the correlation signal in a correlation signal memory; and analyzing the correlation signal.
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| US09/697,187 US6823021B1 (en) | 2000-10-27 | 2000-10-27 | Method and apparatus for space division multiple access receiver |
| US09/697,187 | 2000-10-27 | ||
| PCT/US2001/042815 WO2002035729A2 (en) | 2000-10-27 | 2001-10-26 | Method and apparatus for space division multiple access receiver |
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2000
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- 2001-10-26 MX MXPA03003622A patent/MXPA03003622A/en unknown
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- 2001-10-26 JP JP2002538586A patent/JP2004533729A/en not_active Withdrawn
- 2001-10-26 CN CNA018181783A patent/CN1473404A/en active Pending
- 2001-10-26 CA CA002426314A patent/CA2426314A1/en not_active Abandoned
- 2001-10-26 AU AU2002213509A patent/AU2002213509A1/en not_active Abandoned
- 2001-10-26 EP EP01981897A patent/EP1329038A2/en not_active Withdrawn
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2014
- 2014-07-01 US US14/321,297 patent/US10778373B2/en not_active Expired - Lifetime
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| AU2002213509A1 (en) | 2002-05-06 |
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| US8767796B2 (en) | 2014-07-01 |
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