WO2007081595A2

WO2007081595A2 - Systems and methods for providing modulation on demand in a narrowband communication system

Info

Publication number: WO2007081595A2
Application number: PCT/US2006/049704
Authority: WO
Inventors: Alvin Dale Kluesing; Sai C. Manapragada
Original assignee: Photron Technologies Ltd.
Priority date: 2005-12-30
Filing date: 2006-12-29
Publication date: 2007-07-19
Also published as: WO2007081595A3; TW200742362A

Abstract

Systems and methods for providing modulation on demand in a narrowband communication system are provided. Modulation on demand is accomplished by a novel modulation scheme that achieves high bandwidth efficiency for various channel conditions and modulation parameters. Such modulation parameters may include the carrier frequency, the number of RF cycles per bit, and the number of samples per RF cycle, among others. A communication system employing the modulation on demand scheme transmits a message signal via one or more look-up tables storing samples representing the modulated message signal.

Description

SYSTEMS AND METHODS FOR PROVIDING MODULATION ON DEMAND IN A NARROWBAND COMMUNICATION SYSTEM

RELATED APPLICATIONS [0001] This patent application claims the benefit of and priority to United States

Provisional Patent Application serial number 60/755,353 filed on December 30, 2005 entitled "Systems and Methods for Providing Modulation on Demand in a Narrowband Communication System," the entire disclosure of which is hereby incorporated by reference. [0002] This patent application is related to pending United States. Patent Application Serial No. 11/171,177, filed on June 29, 2005 entitled "Systems and Methods for High-

Efficiency Transmission of Information through Narrowband Channels;" United States Patent Application Serial No. 11/171,592, filed on June 29, 2005 entitled "Systems and Methods for Designing a High-Precision Narrowband Digital Filter for Use in a Communications System with High Spectral Efficiency;" and United States Patent Application Serial No. 11/430,366 filed on May 8, 2006 entitled "Multiresolution-Based

Communication Systems and Methods for the High Efficiency Transmission of Information through Narrowband Channels," the entire disclosures of all of which are hereby incorporated by reference.

FIELD OF THE INVENTION

[0003] The present invention relates generally to the transmission of information through communication systems. In particular, the systems and methods of the present invention provide a user-configurable modulation scheme that may be modified on demand to achieve a given data rate for a given channel bandwidth for the transmission of information through narrowband communications channels.

BACKGROUND INFORMATION

[0004] Advances in communications technologies, combined with the widespread adoption of personal communication appliances, have revolutionized the way information is disseminated and shared. Information can now be delivered directly to computer desktops, laptops, personal digital assistants, cellular telephones, digital music players, and other portable devices over wired or wireless connections, providing a virtually unlimited connection experience for all users. In particular, the rapid expansion of wireless technologies has fueled the demand for faster and more efficient wireless transmission of voice, data, and video on a global basis.

[0005] Information is transmitted over a wireless channel from an information source to a destination by means of a wireless communication system, such as the conventional system shown in FIG. 1. At its simplest form, wireless communication system 100 includes: (1) modulator 105; (2) transmitter 110; (3) wireless channel 115; (4) receiver 120; and (5) demodulator 125. Modulator 105 processes the information into a form suitable for transmission over wireless channel 115. The information maybe in the form of voice, data, audio, imagery, video, or any other type of content conveyed in an information signal, also referred to as a message signal. Modulator 105 essentially translates the message signal into a modulated signal suitable for transmission over wireless channel 115 by modifying one or more characteristics of a carrier signal.

[0006] The modulated signal is passed on to wireless channel 115 by transmitter 110, which usually filters and amplifies the modulated signal prior to its transmission. The function of wireless channel 115 is to provide a wireless link or connection between the information source and destination. Once transmitted through wireless channel 115, the modulated signal is detected and amplified by receiver 120 to take into account any signal attenuations introduced during transmission by wireless channel 115. Finally, the transmitted signal is demodulated by demodulator 125 so as to produce a close estimate of the original message signal.

[0007] The performance of a wireless communications system such as wireless communication system 100 is, in part, dictated by the performance of its modulator, e.g., modulator 105. For it is the modulator that is responsible for converting the message signal into a signal suitable for transmission so as to maximize the use of the overall system resources. For example, a high performance modulator should generate a modulated signal having a frequency spectrum that, when filtered and transmitted by a transmitter such as transmitter 110, would utilize only a small fraction of the total channel bandwidth, thereby enabling many users to share the channel bandwidth simultaneously. A high performance modulator should also work in conjunction with a high performance filter in the transmitter to ensure optimal preservation of the frequency spectrum of the modulated signal.

[0008] Current wireless communication systems use many different modulation techniques, including, but not limited to, amplitude shift keying ("ASK"), frequency shift keying ("FSK"), binary phase shift keying ("BPSK"), quadrature phase shift keying ("QPSK") and its variations, minimum shift keying ("MSK"), Gaussian minimum shift keying ("GMSK"), and quadrature amplitude modulation ("QAM"), among others. These modulation techniques are digital techniques in which the message signal is represented by a sequence of binary symbols. Each symbol may have one or more bits, depending on the modulation technique used.

[0009] Typically, these modulation techniques switch or key the amplitude, frequency, and/or phase of a carrier signal according to the binary symbols in the message signal, e.g., according to binary symbols "0" and "1." For example, different amplitudes are used to represent both binary symbols in ASK, different frequencies are used to represent both binary symbols in FSK, and different phases are used to represent both binary symbols in BPSK. QPSK is a variation of BPSK in which two bits or more are used per symbol. The phase of the carrier takes on one of four equally spaced values, such as 0, p/2, p, and 3p/2, with each value corresponding to a unique symbol, e.g., 00, 10, 11, and 01. QAM changes the amplitude of two carrier waves that are out of phase. MSK and GMSK are variations of FSK in which the change in carrier frequency from one binary symbol to another is half the bit rate of the message signal.

[0010] The selection of a digital modulation technique for use in a wireless communication system depends on several factors. A desirable digital modulation technique provides low bit error rates at low signal-to-noise ratios, occupies a minimum bandwidth, performs well in the presence of multipath and fading conditions, and is cost-effective to implement. Depending on the physical characteristics of the channel, required levels of performance and target hardware trade-offs, some modulation techniques may prove to be a better fit than others. Consideration must be given to the required data rate, acceptable level of latency, available bandwidth, and target hardware cost, size, and power consumption. For example, in personal communication systems that serve a large subscriber community, the cost and complexity of the receivers must be minimized. In this case, a modulation technique that is simple to detect is most attractive. In cellular systems where intersymbol interference is a major issue, the performance of the modulation technique in an interference environment is extremely important. [0011] The performance of a modulation technique is often measured in terms of its power efficiency and bandwidth efficiency. Power efficiency describes the ability of a modulation technique to preserve the fidelity, i.e., an acceptable bit error probability, of the message signal at low power levels. In digital communication systems, higher fidelity requires higher signal power. The amount by which the signal power should be increased to obtain a certain level of fidelity depends on the type of modulation employed. The power efficiency of a digital modulation technique is a measure of how favorably this tradeoff between fidelity and signal power is made, and is often expressed as the ratio of the signal energy per bit to noise power spectral density required at the receiver input for a certain probability of error.

[0012] Bandwidth efficiency describes the ability of a modulation technique to accommodate data within a limited bandwidth. In general, increasing the data rate implies decreasing the pulse- width of a digital symbol, which increases the bandwidth of the signal. Bandwidth efficiency reflects how efficiently the allocated bandwidth is utilized. Bandwidth efficiency is defined as the ratio of the throughput data rate per Hertz in a given bandwidth. The system capacity of a digital modulation technique is directly related to the bandwidth efficiency of the modulation technique, since a modulation technique having a greater bandwidth efficiency will transmit more data in a given spectrum allocation. [0013] In general, modulation techniques trade bandwidth efficiency for power efficiency. For example, FSK is power efficient but not as bandwidth efficient and QPSK and GMSK are bandwidth efficient but not as power efficient. Since most wireless systems are bandwidth limited due to frequency spectrum allocations, modulation techniques that concentrate their performance on bandwidth efficiency are generally preferable. In fact, most wireless communication standards available today use more bandwidth- efficient modulation techniques such as QPSK and its variations, in use by the PHS and PDC Japanese standards, and IS-54 and IS-95 American standards, and GMSK, in use by the GSM global standard. [0014] The bandwidth efficiencies achieved by the digital modulation techniques currently adopted by the wireless standards are, however, only in the order of 1-10 bps/Hz. Such bandwidth efficiencies are not able to satisfy the rapidly rising demand for faster and more efficient wireless services that are capable of serving a large number of users simultaneously.

[0015] To address these concerns, two new sets of modulation techniques have been developed: (1) spread spectrum modulation techniques; and (2) narrowband modulation techniques. Spread spectrum modulation is a technique in which the modulated signal bandwidth is significantly wider than the minimum required signal bandwidth. Bandwidth expansion is achieved by using a function that is independent of the message and known to the receiver. The function is a pseudo-noise ("PN") sequence or PN code, which is a binary sequence that appears random but can be reproduced in a deterministic manner by the receiver. Demodulation at the receiver is accomplished by cross-correlation of the received signal with a synchronously-generated replica of the wide-band PN carrier. [0016] Spread spectrum modulation has many features that make it particularly attractive for use in wireless systems. First and foremost, spread spectrum modulation enables many users to simultaneously use the same bandwidth without significantly interfering with one another. The use of PN codes allows the receiver to separate each user easily even though all users occupy the same spectrum. As a result, spread spectrum systems are very resistant to interference, which tends to affect only a small portion of the spectrum and can be easily removed through filtering without much loss of information. Additionally, spread spectrum systems perform well in the presence of multipath fading and Doppler spread.

[0017] The main disadvantage of spread spectrum systems is that they are very bandwidth inefficient for a single user or a single wireless cell, since the bandwidth utilized is much more than that necessary for transmission. In fact, bandwidth efficiency for a single user is so low that most spread spectrum systems report bandwidth efficiency for the whole channel, to emphasize their ability to simultaneously serve many users with the available channel bandwidth. In addition, spread spectrum systems are also much more complex than systems employing traditional modulation techniques, thereby increasing overall system design, deployment, and maintenance costs.

[0018] Narrowband modulation techniques, such as those described in U.S. Patent

No. 5,930,303, U.S. Patent No. 6,748,022, and U.S. Patent No. 6,445,737, provide an entirely different approach. Instead of spreading the signal over a wide bandwidth range to optimize the number of users sharing the channel bandwidth simultaneously, narrowband modulation techniques attempt to squeeze the frequency spectrum into a as narrow of a band as possible in order to maximize both the bandwidth efficiency for an individual user and the overall channel utilization for a large number of users. In the narrowband modulation techniques described therein, phase reversals occurring before, in the middle, at the end, or after a bit period are used to generate a modulated signal having most of its energy concentrated in a very narrow peak centered at a carrier frequency. As most of the signal energy is concentrated in the narrow peak, transmission of the modulated signal may be accomplished by transmission of the narrow peak, thereby significantly improving the bandwidth efficiency for an individual user. [0019] While achieving higher bandwidth efficiencies than spread spectrum techniques, these narrowband modulation techniques are not very practical because they require the use of a specialized analog crystal filter with a resonant frequency tuned by a shunt capacitor. Such a filter is very difficult to implement in practice due to tuning imperfections of the shunt capacitor, irregularities of the crystal material employed, and other challenges associated with designing high-precision analog crystal filters. Furthermore, these narrowband modulation techniques are very susceptible to intersymbol interference, may not perform well under high bit error rates, and require higher transmission power than traditional modulation techniques such as FSK and BPSK. [0020] Because currently-available modulation techniques have not been able to achieve high bandwidth and power efficiencies while performing well under various channel conditions, broadband wireless services that reach a large number of users simultaneously have not yet been fully deployed. Such services should be able to serve users with voice, data, audio, imagery, and video at high data rates and low infrastructure costs to service providers and consumers alike. Such services should also be able to optimize the number of users served by better utilization of the allocated frequency spectrum. [0021] To address these concerns, a novel narrowband modulation scheme that achieves very high bandwidth efficiency under various channel conditions has been developed. The narrowband modulation scheme, referred to as Ultra Spectral Modulation ("USM") and described in commonly-owned, currently pending U.S. Patent Application No.

11/171,177, the entire disclosure of which is incorporated herein by reference, comprises a return-to-zero modulation scheme that uses abrupt phase changes to represent incoming binary symbols in a modulated signal that has a double-sideband suppressed carrier ("DSSC") frequency spectrum with two wide spectrum sidebands and no carrier. [0022] Because the USM technique represents all the information in the message signal with abrupt phase shifts in the modulated signal, narrowband transmission of information maybe accomplished by transmitting only a narrow band of frequencies required for identifying the phase shifts, i.e., by transmitting only a portion of one or both sidebands in the modulated signal within a narrow band of frequencies. The modulated signal may be transmitted by filtering it a with high-Q, low-tolerance sophisticated digital filter that is able to preserve the positions of the phase shifts in a very narrow band of frequencies, as described in commonly-owned, currently pending U.S. Patent Application No. 11/171,592, the entire disclosure of which is incorporated herein by reference. [0023] The modulated signal may also be transmitted using a fractal-based table lookup approach in which the modulated signal is transmitted through use of a simple look-up table storing samples extracted from the fractal modeling of the frequency spectrum of a filtered modulated signal. Transmission of a binary symbol may be accomplished by simply encoding the symbol into its corresponding samples stored in the look-up table.

[0024] The USM scheme may achieve data rates exceeding 5 Mbps to be delivered through frequency channels as narrow as 50 KHz under a variety of channel conditions. In addition, use of USM in a communication system can enable wireless service providers to provide broadband wireless services to a large number of users simultaneously by accessing a fully-utilized frequency spectrum that may be divided into various channels of very narrow bandwidths.

[0025] As described in the commonly-owned, currently-pending U.S. Patent

Application Nos. 11/171,177 and 11/171,592, the USM scheme achieves a given data rate by having pre-determined modulation parameters, such as a pre-determined carrier frequency and a pre-determined number of RF cycles per bit. In one example given, a data rate of 5

Mbps may be achieved in a 50 kHz channel using a carrier frequency of 20 MHz and four RF cycles per bit. If a total channel bandwidth of, for example, 100 MHz is provided, a total of 2000 modulated signals may be transmitted in channels of 50 kHz each, with each channel operating at a carrier frequency that is 50 kHz apart from its adjacent channels. In this case, as each channel is operating at a different carrier frequency, a different data rate will be achieved in each channel.

[0026] Achieving a variable data rate for each channel may be desired in several applications, including streaming media applications, video-on-demand applications, Internet traffic, and satellite applications, among others. However, conventional, spread spectrum and narrowband modulation schemes are currently not capable of achieving variable data rates for different channels having different carrier frequencies without significant modifications to the modulation scheme parameters, channel bandwidth, signal-to-noise ratio ("SNR"), or the communication system itself. [0027] For example, changing the data rate for a streaming media application on a communication system employing QAM may require a change in the modulation constellation, from, say, 16-QAM to 32-QAM, to be able to accommodate the higher data rate with a higher bandwidth efficiency and higher signal-to-noise ratio. And in a system employing CDMA, changing the data rate may imply a change in the spreading ratio and coding gain.

[0028] It is also desirable to change modulation parameters on the fly without degrading the SNR of each channel or requiring modifications in the channel bandwidth or in the communication system itself. Adapting the modulation scheme to various channel and system conditions enables designers of wireless communication systems to have flexible systems that may be tuned to a large assortment of carrier frequency, channel bandwidth, and data rate combinations without necessarily degrading the SNR in the channel. [0029] For example, if the communication system is not reliable with a given set of system parameters, then the bandwidth could be increased to improve the channel's reliability without further degrading the SNR in the channel. Similarly, if the communication system is more reliable than desired, then the bandwidth could be reduced to achieve the desired reliability. The modulation system should also be able to easily accommodate variable and constant data rates on different channels for a desired reliability and other system constraints. [0030] Thus, there is a need to provide a modulation-on-demand scheme that achieves high bandwidth efficiency for various modulation parameters and channel conditions.

[0031] There is also a need to provide communication systems and methods that implement a modulation-on-demand scheme for achieving a constant bandwidth efficiency with different modulation parameters in different channels without significant degradation of the signal-to-noise ratio in each channel. [0032] There is yet a further need to provide communication systems and methods that optimize bandwidth utilization when providing wireless services to a large number of users simultaneously under various channel conditions and modulation parameters. Thus, further developments are needed.

SUMMARY OF THE INVENTION

[0033] In view of the foregoing, a general object of the present invention is to provide a modulation-on-demand scheme that achieves high bandwidth efficiency for various channel conditions and modulation parameters.

[0034] In one aspect, embodiments of the present invention provides communication systems and methods that implement a modulation-on-demand scheme for achieving a constant bandwidth efficiency with different modulation parameters in different channels without significant degradation of the signal-to-noise ratio in each channel. [0035] In another aspect, embodiments of the present invention provides communication systems and methods that promote improved bandwidth utilization when providing wireless services to a large number of users simultaneously under various channel conditions and modulation parameters.

[0036] Embodiments of the present invention provide a novel modulation-on-demand scheme that achieves high bandwidth efficiency for various channel conditions and modulation parameters, hi one embodiment a modulator for modulating a carrier signal with a message signal to generate a modulated signal is provided, characterized in that: the modulated signal is modified responsive to user-selective modulation parameters, hi other embodiments, the modulation-on-demand scheme comprises a return-to-zero Ultra Spectral Modulation technique, hereinafter referred to as the Ultra Spectral Modulation-On-Demand ("USMoD") technique, that uses abrupt phase changes to represent incoming binary symbols in a modulated signal. The USMoD technique also comprises a number of modulation parameters that may be changed on demand, or in real-time, (also referred to as on the fly) in a communication system while maintaining a constant bandwidth efficiency without significant degradation of the signal-to-noise ratio ("SNR") in the channel. Such modulation parameters may include one or more of the carrier frequency, the number of RF cycles per bit, the number of samples per RF cycle, among others.

[0037] In another aspect, the present invention provides narrowband communication systems and methods that implement the USMoD scheme for achieving broadband-like services within a narrow frequency spectrum. The communication system may be implemented with a look-up table approach, in which modulated signals are transmitted through use of a simple look-up table storing samples representing a modulated carrier for a given binary symbol, e.g., a "0" or a "1". [0038] In one exemplary embodiment, the samples may be taken directly from a modulated signal, such as a sinusoid modulated with the return-to-zero, abrupt-phase USM technique described in more detail in commonly-owned, currently pending U.S. Patent Application Nos. 11/171,177 and 11/171,592, the entire disclosures of which are incorporated by reference herein. In another exemplary embodiment, the look-up table samples may be extracted from the fractal modeling of the frequency spectrum of a modulated signal, as described in the above-identified, commonly-owned and currently-pending U.S. Patent

Application Nos. 11/171,177 and 11/171,592. In both embodiments, transmission of a binary symbol may be accomplished by simply encoding the symbol into its corresponding samples stored in the look-up table. [0039] In another exemplary embodiment, two look-up tables may be used, one for each binary symbol. In this exemplary embodiment, the look-up tables may be addressed with the use of a simple Finite State Machine ("FSM") that loads the look-up tables with the modulation parameters and the input data samples to be transmitted. A FIFO buffer may also be used to maintain a uniform data rate — and a constant bandwidth efficiency — in a narrowband communications channel.

[0040] For example, in some embodiments a system for transmitting information through a narrowband communications channel is provided, comprising: a modulator for modulating a carrier signal with a message signal to generate a modulated signal with modulation parameters selected on demand; and one or more look-up tables for storing samples of the modulated signal and selecting a portion of the samples for transmission through the communications channel according to the modulation parameters. [0041] In some embodiments, modulation parameters are selected from any one or more of: number of RF cycles used for a binary symbol; number of samples per RF cycle; carrier frequency; fractal bifurcation index; and number of words used to represent each sample in the one or more look-up tables.

[0042] . Additionally, in some embodiments the modulator is comprised of an encoder for encoding a first binary symbol into a first portion of a carrier signal, the first portion of the carrier signal having an integer number n of cycles and at a first phase, followed by a second portion of the carrier signal, the second portion of the carrier signal having an integer number n of cycles and at a second phase, wherein the second phase is at a phase shift away from the first phase. The encoder may further comprise encoding a second binary symbol into a third portion of the carrier signal, the third portion of the carrier signal having an integer number n of cycles and at the second phase, followed by a fourth portion of the carrier signal, the fourth portion of the carrier signal having an integer number n of cycles and at the first phase.

[0043] In another aspect, embodiments of the present invention provide a modulator for modulating a carrier signal with a message signal to generate a modulated signal. In one example, the modulator comprises one or more look-up tables for storing samples representing the modulated signal; a finite state machine for loading a set of modulation parameters into the one or more look-up tables, the modulation parameters selected on demand; and a multiplexer for selecting a portion of the samples for transmission across a communications channel. In an illustrative example, the one or more look-up tables comprises a first look-up table for storing a first set of samples corresponding to a first binary symbol in the message signal and a second look-up table for storing a second set of samples corresponding to a second binary symbol in the message signal. [0044] In yet another aspect, methods for transmitting information through a narrowband communications channel are provided. In an exemplary embodiment methods comprise the steps of: modulating a carrier signal with a message signal to generate a modulated signal with modulation parameters selected on demand; storing samples of the modulated signal into one or more look-up tables; selecting a portion of the samples for transmission through the communications channel according to the modulation parameters; and transmitting the portion of the samples though the communications channel

[0045] Advantageously, the systems and methods of the present invention enable designers of a communication system to achieve very high and constant bandwidth efficiency across different channels with different modulation parameters for each channel. Further, the systems and methods of the present invention provide a modulation-on-demand scheme that may be integrated in a narrowband communication system to provide broadband-like services in a very narrow band of frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The foregoing and other objects of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

[0047] FIG. 1 shows a general schematic diagram of a conventional wireless communication system; [0048] FIG. 2 shows a diagram of an exemplary message signal and a modulated signal according to the principles and embodiments of the present invention;

[0049] FIG. 3 shows a schematic diagram of an exemplary communication system for transmitting a message signal modulated according to the principles and embodiments of the present invention; [0050] FIG. 4 shows a diagram of an exemplary embodiment of a modulator designed according to the principles and embodiments of the present invention;

[0051] FIG. 5 shows an exemplary state diagram of a finite state machine for use in a modulator designed according to the principles and embodiments of the present invention; [0052] FIG. 6 shows a diagram of another exemplary embodiment of a modulator designed according to the principles and embodiments of the present invention; [0053] FIG. 7 illustrates exemplary modulation parameters and data rates for an exemplary modulator designed according to FIG. 6. [0054] FIG. 8 illustrates other exemplary modulation parameters and data rates for an exemplary modulator designed according to FIG. 6;

[0055] FIG. 9 illustrates yet other exemplary modulation parameters and data rates for an exemplary modulator designed according to FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0056] Generally, in accordance with exemplary embodiments of the present invention, systems and methods are provided for transmitting information through narrowband communications channels by using a modulation-on-demand scheme that achieves high and substantially constant bandwidth efficiencies across different channels with different modulation parameters for each channel. Information, as used herein, may be in the form of voice, data, audio, imagery, video, or any other type of content conveyed in an information signal, also referred to as a message signal. The message signal represents information by means of binary symbols, with each symbol having one or more bits. [0057] In one embodiment a modulator for modulating a carrier signal with a message signal to generate a modulated signal is provided, characterized in that: the modulated signal is modified responsive to user-selective modulation parameters.

[0058] Message signals according to the present invention are modulated prior to transmission through a communications channel. A channel, as used herein, may be any communications channel, including a wired channel, e.g., cable, or a wireless channel. In general, modulation refers to the process by which information conveyed in the message signal is encoded in a carrier signal to generate a modulated signal. Typically, the encoding involves modifying one or more characteristics of the carrier signal according to the binary symbols in the message signal. A carrier signal may be any analog signal of a given frequency, for example, a sinusoidal wave at 100 MHz. A modulated signal, as used herein, refers to the carrier signal that has been modified according to the message signal.

[0059] The modulated signal has a frequency spectrum representation comprising its frequency components. Modulated signals according to the USMoD technique of the present invention have frequency spectrums comprising no carrier and two bands or "sidebands" of frequencies, one above (the "upper sideband" or "USB") and one below (the "lower sideband" or "LSB") the carrier frequency. Transmission of one of the sidebands is referred to as single-sideband suppressed-carrier ("SSSC") transmission and transmission of both sidebands is referred to as double-sideband suppressed carrier ("DSSC") transmission. [0060] Transmission of the modulated signal through a communications channel may be accomplished by using one or more look-up tables that store samples representing a binary symbol, e.g., a "0" or a "1". In one exemplary embodiment, the samples may be taken directly from a modulated signal. In another exemplary embodiment, the samples may be extracted from the fractal modeling of the frequency spectrum of a modulated signal, as described in the above-identified, commonly-owned and currently-pending U.S. Patent

Application Nos. 11/171,177 and 11/171,592, the entire disclosures of which are incorporated by reference herein. In both embodiments, transmission of a binary symbol may be accomplished by simply encoding the symbol into its corresponding samples stored in the one or more look-up tables. [0061] Aspects of the invention further provide for the one or more look-up tables to be loaded with USMoD parameters that may be changed on the fly. Such modulation parameters may include, but are not limited to, the carrier frequency, the number of RF cycles per bit, the number of samples per RF cycle, among others. The modulation parameters are loaded into the look-up tables via a Finite State Machine ("FSM"), which, as used herein, generally refers to a behavioral model composed of states, transitions, and actions.

[0062] It is appreciated that the USMoD technique of the present invention may be used to transmit information through a narrowband communications channel at very high data rates for various different configurations of modulation parameters. For example, data rates of 5-10 Mbits/sec (and even higher) may be achieved on 50 kHz channels with carrier frequencies that are 50 kHz apart and with different number of RF cycles per binary symbol or bit. For example, a data rate of 5 Mbits/sec may be achieved on a 50 kHz channel with a 20 MHz carrier having 4 RF cycles per bit and the same data rate may be achieved on a 50 kHz channel with a 70 MHz carrier having 15 RF cycles per bit. In general, the width of a narrowband channel will vary depending upon the application. Without limitation, in one example a channel having a bandwidth of about 200 KHz and below may be generally characterized as a narrowband channel, and more typically a bandwidth of about 100 KHz and below. It should be appreciated that while embodiments of the present invention describe application of the invention in a narrowband communications channel and system, the system and methods of the present invention may be employed in other communication systems as well.

[0063] As used herein, a channel bandwidth generally refers to the band of frequencies allocated for transmission of one or more modulated signals. For example, a channel having a bandwidth of 100 MHz may support the transmission of one or more modulated signals within a frequency spectrum of 100 MHz. If, for example, each modulated signal occupies a bandwidth of 10 kHz, then the channel is able to support the transmission of 10,000 such signals. The amount of data that can be transferred in a channel having a given bandwidth may be generally referred to herein as the channel's data rate (expressed in bits per second). The maximum data rate supported by a channel for a given bandwidth, noise level, and other channel assumptions may be generally referred to as the channel capacity. [0064] The Ultra Spectral Modulation ("USM") technique, described in commonly- owned, currently-pending U.S. Patent Application Nos. 11/171,177 and 11/171,592, the entire disclosures of which are incorporated by reference herein, comprises a return-to-zero modulation technique that uses abrupt phase changes in a carrier signal to represent incoming binary symbols. The abrupt phase changes occur mid-pulse, i.e., in the middle of a bit period, after an integer number of cycles of the carrier signal, or at a bit boundary. In an exemplary embodiment, a binary symbol, e.g., "0" or "1", is represented with an integer number of cycles, e.g., n cycles, of a carrier signal, of which n/2 cycles are used at a given phase and the other n/2 cycles are used at a phase shift, with the abrupt phase shift occurring mid-pulse. The modulated carrier signal is referred to herein as the "modulated signal." [0065] Referring to FIG. 2, an exemplary schematic diagram of a message signal and a modulated signal according to the principles and embodiments of the present invention is described. Message signal 200 is a signal represented by the following binary sequence:

"010010." Message signal 200 is modulated using the USM technique into a sinusoidal carrier having a given carrier frequency, which in this case is four cycles per binary symbol or bit. For example, if the carrier frequency is set at 20 MHz and the number of RF cycles per bit is set at 4, a data rate of 5 Mbps may be achieved with the USM technique. [0066] Using USM to modulate message signal 200 with a sinusoidal carrier having a carrier frequency at least twice the data rate produces modulated signal 205. Modulated signal 205 is a sinusoidal wave having abrupt phase shifts every mid-pulse. Each bit is represented with two sinusoidal patterns, a "data bit" pattern lasting for the first half of the pulse-width, e.g., for the first two cycles of the carrier frequency, and a "datum bit" pattern lasting for the second half of the pulse- width, e.g., for the last two cycles of the carrier frequency.

[0067] A data bit pattern for a given binary digit, e.g., "0" or "1," has a phase that is 180° degrees away from the phase of the datum bit pattern. Additionally, a data bit pattern for a given binary digit has a phase that is 180° degrees away from the phase of the data bit pattern of the other binary digit. For example, as illustrated, a data bit pattern for a "0" bit has a phase of q while the datum bit pattern for the "0" bit has a phase of q - p. Conversely, a data bit pattern for a "1" bit has a phase of q - p while the datum bit pattern for the "1" bit has a phase of q. As shown, each data bit pattern and datum bit pattern have two RF cycles, resulting in four RF cycles being used to represent each binary symbol. [0068] The main characteristic of the USM technique lies in the abrupt phase shifts occurring mid-pulse. The abrupt phase shifts may be viewed as another layer of phase reversals occurring on top of traditional BPSK modulation techniques, in which phase shifts occur only at the bit transitions, i.e., at the edge of each pulse. Having the datum bit pattern inserted in each pulse ensures a return-to-zero modulation technique with a DSSC frequency spectrum.

[0069] According to the principles and embodiments of the present invention, the

USM technique may have parameters specified on demand. For example, the USM technique may have various values of carrier frequency, number of RF cycles per bit, and number of samples per RF cycle, all selected on demand as desired. A USM technique having modulation parameters that are selected on demand is hereinafter referred to as a Ultra Spectral Modulation-on-Demand technique, or "USMoD" for short. [0070] Sample USMoD parameters are shown below in Table I. The illustrated parameters are provided for illustration only and are not intended to limit the invention in any way. Other parameters may be selected according to the teaching of the present invention. Modulation parameters that may be selected and modified on the fly include the number of RF cycles used for each binary symbol, the number of samples per RF cycles, the carrier frequency, and the number of 12-bit words used to represent each sample in the look-up tables. It is appreciated that the values shown below in Table I are exemplary values only and other values may be selected without deviating from the principles and embodiments of the present invention. It will also be appreciated that other modulation parameters may be selected on demand, including, for example, the type of carrier signal used, e.g., a sinusoid, a square wave, etc.

Table I — Exemplary USMoD Parameters

[0071] Referring now to FIG. 3, a schematic diagram of an exemplary communication system for transmitting a message signal modulated according to the principles and embodiments of the present invention is described. Communication system 300 includes USMoD modulator 305 for modulating a message signal according to user- configurable modulation parameters that may be selected on demand. USMoD modulator may modulate the message signal according to the USM technique as described above with the modulation parameters selected by the user. [0072] Communication system 100 also includes one or more look-up tables

("LUTs") 310 for storing samples of a modulated signal generated by USMoD modulator 305. LUTs 310 may have these samples already stored therein, and depending on the modulation parameters that are selected by the user, a portion of these samples may be selected for transmission across the communications channel. Alternatively, LUTs 310 may have its samples loaded in real-time or on the fly. The samples may be extracted from the modulated signal itself, or from a multiresolution-based decomposition of the signal using signal primitives, such as fractal bifurcations or wavelets, as described in more detail in currently-pending U.S. Patent Application Nos. 11/171,177 , 11/171,592, and 11/430,366, the entire disclosures of all of which are incorporated by reference herein. [0073] For example, signal primitives, such as fractals, may be bifurcated a number of times to generate smaller, self similar primitives at different scales or levels of detail. The number of bifurcations is given by a bifurcation index. When fractals are used as the signal primitive, the fractals may be generated for example by a fractal pattern generator capable of generating fractals, such as various fractal pattern generators implemented as software routines. For example, a Moire or Mandelbrot fractal pattern generator as implemented in the art with Java® or Matlab® may be used to generate fractal primitives. Other programs are available to be used to generate wavelet primitives.

[0074] As described in more detail herein below, a simple finite state machine may be used to control the loading of the modulation parameters into LUTs 310. A data buffer may also be used to guarantee a given bandwidth efficiency for the modulation parameters selected by the user.

USMoD MODULATOR

[0075] Referring now to FIG. 4, an exemplary diagram of an exemplary embodiment of a modulator designed according to the principles and embodiments of the present invention is described. USMoD modulator 400 includes input line 405 to load modulation parameters into look-up tables 420-425. Input line 405 may load the parameters serially, i.e., one bit at a time. Modulation parameters that may be loaded into look-up tables 420-425 may include the parameters shown above in Table I. The modulation parameters that are loaded via input line 405 are loaded into look-up tables 420-425 via finite state machine ("FSM") 415. FSM 415 controls the loading sequence of the modulation parameters into look-up tables 420-425.

[0076] As illustrated in the state diagram shown in FIG. 5, FSM 415 may be implemented with two states, "wait" state 500 and "load" state 505. In "wait" state 500, FSM 415 waits to receive a load signal that indicates that modulation parameters are to be loaded into look-up tables 420-425. Upon receiving the load signal, FSM 415 determines the number of samples that are to be loaded for each binary symbol based on the USMoD modulation parameters, i.e., by multiplying the number of RF cycles to be used to represent a binary symbol by the number of samples per RF cycle. FSM 415 then enters "load" state 505 and starts loading look-up tables 420-425 with samples corresponding to the modulated representation of the given binary symbol.

[0077] In one exemplary embodiment, the samples may be taken directly from a modulated signal, such as modulated signal 205 shown in FIG. 2, based on the modulation parameters selected by the user, including the number of RF cycles per binary symbol and the number of samples that need to be extracted per RF cycle. Li another exemplary embodiment, the samples may be extracted from the fractal modeling of the frequency spectrum of a modulated signal, as described in the above-identified, commonly-owned and currently-pending U.S. Patent Application Nos. 11/171,177 and 11/171,592. In both embodiments, transmission of a binary symbol may be accomplished by simply encoding the symbol into its corresponding samples stored in look-up tables 420-425. [0078] It is appreciated that in the fractal-based embodiment, the samples stored in look-up tables 420-425 are independent of the message signal, that is, the same samples are stored therein regardless of the modulation parameters selected by the user. In this case, the modulation parameters may be used to control the number of samples to be extracted for each RF cycle and which samples out of look-up tables 420-425 to be transmitted across the communications channel. [0079] Referring back to FIG. 4, USMoD modulator 400 may be implemented with two look-up tables, i.e., look-up tables 420-425, with each table storing samples for a given binary symbol. For example, look-up table 420 may be used to store samples for a "0" and look-up table 425 may be used to store samples for a "1."

[0080] Samples from each table are selected by the message signal to be modulated, which is input into multiplexer 430 via input line 410. Multiplexer 430 uses each binary symbol in the message signal as a selector for the modulated signal samples stored in look-up tables 420-425. For example, if the message signal has the sequence "010," multiplexer 430 outputs samples from look-up table 320, then samples from look-up table 425 and again from look-up table 420. The samples from look-up tables 420-425 are the modulated samples that are eventually transmitted in a communications channel; they are output by multiplexer 430 in output line 435.

[0081] It is appreciated that USMoD modulator 400 shown in FIG. 4 outputs samples as they come into the system without any data rate control to provide a constant data rate or constant bandwidth efficiency. To ensure a uniform data rate coming out of multiplexer 430, data synchronization approaches may be necessary. Such approaches may be used to synchronize a clock with the input data and minimize the amount of null data that may be needed to guarantee a given data rate.

[0082] Referring now to FIG. 6, an exemplary diagram of another exemplary embodiment of a modulator designed according to the principles and embodiments of the present invention is described. USMoD modulator 600 has FIFO data buffer 605 to ensure that the input data is synchronized with a clock to provide a constant bandwidth efficiency across a communications channel. FIFO data buffer 605 takes the message signal as input and outputs the message signal at the clock rate provided by clock 610. Null data is provided in the output to guarantee a given data rate. [0083] It is appreciated that data coming into the buffer could be either synchronized or non-synchronized with clock 610. It is also appreciated that the data rate of message signals being input into FIFO data buffer 605 could also be greater than, equal to, or less than the output data rate generated by USMoD modulator 600. [0084] The message signal may be synchronized with the clock signal provided by clock 610 in input data sync 615. The buffer will synchronize the input data to the output, by either storing data or sending null data. Input data sync 615 takes the data output by FIFO buffer 605 and outputs the data at a desired clock rate, computed from the USMoD parameters loaded into FSM 620. The desired clock rate may be given by the clock signal from clock 610 divided by the total number of samples for a given binary symbol in the message signal, that is, divided by the number of RF cycles per binary symbol and the number of samples in each RF cycle.

[0085] The synchronized data may then be used to select the samples stored in lookup tables 630-635 via multiplexer 640. It is appreciated that doing so ensures that the message signal is modulated to guarantee a given data rate across a communications channel of fixed bandwidth, thereby guaranteeing a constant bandwidth efficiency. [0086] It is appreciated that the modulation parameters of USMoD modulator 400 may be easily modified on demand. For example, if the input data traffic is bursty or has increased, such that FIFO buffer 605 may be filled up, then the number of RF cycles per binary symbol may be reduced to increase the channel bandwidth. If the new bandwidth is increased to a level above what is tolerated by communication system 100, then the required bandwidth may be reduced by increasing the fractal bifurcation index, as described in the above-identified, commonly-owned and currently-pending U.S. Patent Application Nos. 11/171,177 and 11/171,592. Conversely, if the input data is low and FIFO buffer 605 is sending out null data, then the number of RF cycles per symbol could be increased to reduce the amount of null data sent.

[0087] In another example, if the logical communication channel is moved from, say, physical channel Fl to a different physical channel F2, the data rate and the required bandwidth may change if the number of RF cycles per binary symbol remains the same. The number of RF cycles per binary symbol or the fractal bifurcation index may then be changed to keep the message signal within the preset limits of the new channel, i.e., F2. USMoD PERFORMANCE

[0088] Referring now to FIG. 7, the performance of an exemplary modulator designed according to the principles and embodiments of the present invention is described. Table 700 shows data rates that may be achieved with different USMoD parameters in three adjacent channels. Each channel may have a bandwidth of 50 kHz, with a carrier frequency at the center frequency. The carrier frequencies may then be 50 kHz apart, ranging from 149,950 kHz to 150 MHz and 150,050 kHz. Table 700 shows that a data rate of at least 10 Mbits/sec may be achieved with a carrier frequency of 150 MHz by using 15 RF cycles to represent each binary symbol and a total of 8 samples per RF cycle. [0089] As illustrated in Table 700, using USMoD as the modulation scheme on each channel therefore guarantees that a given data rate for an integer set of modulation parameters may be achieved on a constant bandwidth channel. It is appreciated that a data rate of 10 Mbits/sec may be achieved for a carrier frequency of 150 MHz (710) with a given set of modulation parameters. The same modulation parameters may result in slightly lower (705) and slightly higher (715) data rates for adjacent channels for lower and higher carrier frequencies, respectively. A simple change in the modulation parameters may be performed on a channel of lower carrier frequency to achieve a data rate of at least 10 MHz . For example, lowering the number of RF cycles from 15 to 14 in the channel having a carrier frequency of 149,950 kHz results in a data rate slightly higher than 10 Mbits/sec (720). [0090] Similar performance results may be achieved for a different set of carrier frequencies, as shown in FIG. 8 for carrier frequencies ranging from 69,950 kHz to 70,050 kHz and as shown in FIG. 9 for carrier frequencies ranging from 19,950 kHz to 20,050 kHz. These sets of carrier frequencies may be used to achieve data rates of up to 5 Mbits/sec in narrowband communications channels of only 50 kHz of bandwidth. [0091] It is appreciated that designers of communication systems may use USMoD to achieve very high - and constant — bandwidth efficiencies in communications channels of very narrow bandwidths by simply tuning modulation parameters. The modulation parameters may be changed on the fly without leading to significant SNR degradation in the system. [0092] The foregoing descriptions of specific embodiments and best mode of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Specific features of the invention are shown in some drawings and not in others, for purposes of convenience only, and any feature may be combined with other features in accordance with the invention. Steps of the described processes may be reordered or combined, and other steps may be included. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. Further variations of the invention will be apparent to one skilled in the art in light of this disclosure and such variations are intended to fall within the scope of the appended claims and their equivalents. The publications referenced above are incorporated herein by reference in their entireties.

Claims

WHAT IS CLAIMED IS:

1. A system for transmitting information through a narrowband communications channel, the system comprising: a modulator for modulating a carrier signal with a message signal to generate a modulated signal with modulation parameters selected on demand; and one or more look-up tables for storing samples of the modulated signal and selecting a portion of the samples for transmission through the communications channel according to the modulation parameters.

2. The system of claim 1, wherein the modulation parameters are selected from any one or more of: number of RF cycles used for a binary symbol; number of samples per RF cycle; carrier frequency; fractal bifurcation index; or number of words used to represent each sample in the one or more look-up tables.

3. The system of claim 1 , wherein the modulator comprises: an encoder for encoding a first binary symbol into a first portion of a carrier signal, the first portion of the carrier signal having an integer number n of cycles and at a first phase, followed by a second portion of the carrier signal, the second portion of the carrier signal having an integer number n of cycles and at a second phase, wherein the second phase is at a phase shift away from the fvrst phase.

4. The system of claim 3, wherein the encoder further comprises encoding a second binary symbol into a third portion of the carrier signal, the third portion of the carrier signal having an integer number n of cycles and at the second phase, followed by a fourth portion of the carrier signal, the fourth portion of the carrier signal having an integer number n of cycles and at the first phase.

5. The system of claim 1, further comprising a finite state machine for loading the samples into the one or more look-up tables.

6. The system of claim 1, further comprising a multiplexer for selecting a first set of samples from the one or more look-up tables for representing a first binary symbol in the message signal and a second set of samples from the one or more look-up tables for representing a second binary symbol in the message signal.

7. The system of claim 6, wherein the look-up tables comprise a first look-up table for storing the first set of samples and a second look-up table for storing the second set of samples.

8. The system of claim 6, further comprising a clock connected to the multiplexer for generating a clock signal.

9. The system of claim 8, further comprising a buffer and a synchronizer for synchronizing the message signal with the clock signal.

10. A method for transmitting information through a narrowband communications channel, the method comprising: modulating a carrier signal with a message signal to generate a modulated signal with modulation parameters selected on demand; storing samples of the modulated signal into one or more look-up tables; selecting a portion of the samples for transmission through the communications channel according to the modulation parameters; and transmitting the portion of the samples though the communications channel.

11. The method of claim 10, wherein modulating a carrier signal to generate a modulated signal with modulation parameters selected on demand comprises selecting the modulation parameters from any one or more of: number of RP cycles used for a binary symbol; number of samples per RF cycle; carrier frequency; or number of words used to represent each sample in the one or more look-up tables.

12. The method of claim 10, wherein modulating a carrier signal to generate a modulated signal comprises encoding a first binary symbol into a first, portion of a carrier signal, the first portion of the carrier signal having an integer number n of cycles and at a first phase, followed by a second portion of the carrier signal, the second portion of the carrier signal having an integer number n of cycles and at a second phase, wherein the second phase is at a phase shift away from the first phase.

13. The method of claim 12, further comprising encoding a second binary symbol into a third portion of the carrier signal, the third portion of the carrier signal having an integer number n of cycles and at the second phase, followed by a fourth portion of the carrier signal, the fourth portion of the carrier signal having an integer number n of cycles and at the first phase.

14. The method of claim 10, further comprising loading the samples into the one or more look-up tables.

15. The method of claim 10, further selecting a first set of samples from the one or more look-up tables for representing a first binary symbol in the message signal and a second set of samples from the one or more look-up tables for representing a second binary symbol in the message signal.

16. The method of claim 15, further comprising selecting a first look-up table for storing the first set of samples and a second look-up table for storing the second set of samples.

17. The method of claim 10, further comprising buffering the message signal according to a clock signal.

18. The method of claim 17, further comprising synchronizing the message signal with the clock signal.

19. A modulator for modulating a carrier signal with a message signal to generate a modulated signal, the modulator comprising: one or more look-up tables for storing samples representing the modulated signal; a finite state machine for loading a set of modulation parameters into the one or more look-up tables, the modulation parameters selected on demand; and a multiplexer for selecting a portion of the samples for transmission across a communications channel.

20. The modulator of claim 19, wherein the one or more look-up tables comprise a first look-up table for storing a first set of samples corresponding to a first binary symbol in the message signal and a second look-up table for storing a second set of samples corresponding to a second binary symbol in the message signal.

21. The modulator of claim 19, wherein the modulation parameters comprise modulation parameters selected from any one or more of: number of RP cycles used for a binary symbol; number of samples per RF cycle; carrier frequency; or number of words used to represent each sample in the one or more look-up tables.

22. The modulator of claim 20, wherein the multiplexer comprises a selector input serially connected to the message signal for selecting the first set of samples when the message signal comprises the first binary symbol and the second set of samples when the message signal comprises the second binary symbol.

23. The modulator of claim 19, wherein the samples representing the modulated signal comprise samples of the modulated signal.

24. The modulator of claim 19, wherein the samples representing the modulated signal comprise samples of a modulated signal modeled based on fractal bifurcations.

25. A modulator for modulating a carrier signal with a message signal to generate a modulated signal, characterized in that: the modulated signal is modified responsive to user- selective modulation parameters.