CA2094951A1 - Sequential power estimation for cellular system handoff - Google Patents
Sequential power estimation for cellular system handoffInfo
- Publication number
- CA2094951A1 CA2094951A1 CA002094951A CA2094951A CA2094951A1 CA 2094951 A1 CA2094951 A1 CA 2094951A1 CA 002094951 A CA002094951 A CA 002094951A CA 2094951 A CA2094951 A CA 2094951A CA 2094951 A1 CA2094951 A1 CA 2094951A1
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- Prior art keywords
- mobile
- sampling
- measurement
- recited
- handoff
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- 230000001413 cellular effect Effects 0.000 title claims abstract description 19
- 238000005259 measurement Methods 0.000 claims abstract description 71
- 238000000034 method Methods 0.000 claims description 27
- 238000005070 sampling Methods 0.000 claims description 19
- 238000005562 fading Methods 0.000 description 25
- 230000008569 process Effects 0.000 description 15
- 238000012545 processing Methods 0.000 description 8
- 238000012935 Averaging Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 238000009825 accumulation Methods 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- AYFVYJQAPQTCCC-GBXIJSLDSA-N L-threonine Chemical compound C[C@@H](O)[C@H](N)C(O)=O AYFVYJQAPQTCCC-GBXIJSLDSA-N 0.000 description 1
- 125000000205 L-threonino group Chemical group [H]OC(=O)[C@@]([H])(N([H])[*])[C@](C([H])([H])[H])([H])O[H] 0.000 description 1
- 240000004543 Vicia ervilia Species 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000005311 autocorrelation function Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000013507 mapping Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/24—Reselection being triggered by specific parameters
- H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
- H04W36/302—Reselection being triggered by specific parameters by measured or perceived connection quality data due to low signal strength
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/24—Reselection being triggered by specific parameters
- H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
Abstract
Abstract SEQUENTIAL POWER ESTIMATION FOR CELLULAR SYSTEM HANDOFF
Cellular handoff is improved by tailing or adapting the measurement tine based on the characteristics of the received signal intensity or power. More particularly, base stations typically measure mobile signal power in order to determine the necessity for handoff and the identity of a new cell. The measurement time must be of a duration which is sufficient to characterize the environment of the mobile. In accordance with the invention, the duration of the measurement time is determined from the received signal itself. Once the duration of the measurement time is determined, that data may be passed to a target cell along with other handoff data.
Cellular handoff is improved by tailing or adapting the measurement tine based on the characteristics of the received signal intensity or power. More particularly, base stations typically measure mobile signal power in order to determine the necessity for handoff and the identity of a new cell. The measurement time must be of a duration which is sufficient to characterize the environment of the mobile. In accordance with the invention, the duration of the measurement time is determined from the received signal itself. Once the duration of the measurement time is determined, that data may be passed to a target cell along with other handoff data.
Description
PD-N91014 1 X~
SEQUENTIAL POWER ESTIMATION FOR CELLULAR SYSTEM HANDOFF
DESCRIPTION
Teehnieal Field The present invention relate~ to i~provement~ in cellular S telephone technology and ~ore partieularly improveuents in the handoff proeess.
Background Art Cellular telephone teehnology has now been in uae for more than ten year~. The cellular telephone concept ~ubdivides a geographic region into a plurallty of cells. Each cell eontains either a ba~e station to control the call or plural base ~tations to control different sector- of the eall. Mobile unit~ eommunieate by radio to the base sta~ions which in turn are conneeted via land line6 to a switching offiee. Cells or eell ~eetors are a~signed their own carrier frequancy bando 80 that inter~erence froD ad~aeent eells or seetor~ i~ limited. Typieally, the earrier fregueneies employed in a eell or eell seetor o~ a elucter of eells are unigu , but those earrier ~requeneies ean be reused in ad~aeent eell clusters. One example of thi~ arehitecture is the Advanced Mobile Phone Serviee (AMPS). Sinee the introduetion of AHPS, the eapaeity provided by that architeeture has, at least in ~ome loealities, been exhausted 80 that further eapacity i~provements have been found neeessary. The Teleeommunications Industry A~soeiation has more recently promulgated a new standard IS-54 whieh allow~ the AMPS
arehiteeture to co-exist along with an arehitecture based on time division ~ultiplexing. Nevertheless, even the new - . .
.
time division multiplexing arch~tecture requires a sinilar cell architecture.
Conventional cellular telephony u~e~ one of two dlffQrent geometries for the area controlled by a base station. One of these geonetrie~ i~ generally a closed hexagonal region. For finer control, the alternative geometry ha~
the hexagonal region ~ubdivided into aectors, i.-. three or six sector~ per hexagon. Typically, the hexagonal region i~ served by a single base station optimally located at the center of the hexagon. In the alternative architecture, the base station~ are located at the vertices of the hexagons with directional antenna~, each directed to a particular sector of the hexagon. Because thi~ invention works with either geometry, ter~inology i~
lS si~plified by ignoring the distinction between the~e geometries. Consequently, throughout the re~aining portion of this application, the ter~ ~cell~ is u~ed to de~ignate either the generally hexagonal region or the segment or sector of such a hexagonal region.
A~ a consequence of a geographic mapping of operating carrier frequencies, it is essential for a nobile station to be handed off from one cell to another a~ it changes location. It has been recognized that this handoff i~ one of the mo~t critical aspects of operation of a cellular telephone ~ystem.
Handoff processe~ are described in Patents 4,829,554;
~,912,756; 5,042,082; 5,081,671 and Tekinay, ~Handover and Channel Assignment in Mobile Cellular Network~, IEE~
Communication~ Maaazine, November 1991, pp. 42 et ~eq.
~ . .
PD-N91014 3 æa9 ~9 ~ 1 It ls also known that mobile radio propagation i~ sub~ect to short-tern fluctuations in power generally characterized a~ Rayleigh or multipath fading. The signal pOWQr c~n fluctuate as much as 30 dB over half a wavelength of the RF carrier. Reliable handoff between cells i8 es~ential for high quality cellular operation.
An important part of the hando~f proce~ is the ability to measurQ the average power in the physical location of the mobile station. Short term fluctuation~ aust be ~moothed or averaged in order to obtain a good measure of the average power received from the location~. This averaging should be done over several cycles of the small ~cale fluctuations. Since the duration of these several cycle depends on the wavelength, the averaging time depends on the time needed for the mobile to traver~e ~everal wavelengths. This in turn is related to vehicle speed.
The ~lower the ~peed of the vehicle, the longer the averaging time i8 required for an accurate measurement.
In ~he absence of a priori ~nowledge of the vehicle speed, the system must allocate a time duration to the ~easurement process which sati~fie~ wor~t case conditions, i.e. is adequate for a ~low moving vehicle. m e alternative, assuming something les~ than worst case conditions, will nece~sarily result in sub-par performance fox those 510w moving vehicles. Howeverj allocating a ~easurement time ~ufficient to provide an accurate measurement for the slow moving vehicles penalizes the handoff operation with respect to high ~peed vehicles.
Because of the vehicle's high speed, its measurement proces6 could be accompli6hed in a significantly shorter time. Moreover, unnecessarily delaying the handoff proces6 for a high speed vehicle could result in ~ub-par handoff perfornance or even los$ng the call.
PD-N9101~ ~ 2 ~ 9 ~ 9 3 1 Summary of the Invention The inventlon overcomes the problem o~ devoting ~ufflcient time to mea~uring mobile power without unnecessarlly penalizlng a fast moving vehlcle. Thi~ advantage is obtained by recogniz$ng that t~e system can obtaln an estimato of that tlme necessary for accurate measurement of mobile power by monitorlng the statiotical variatlons in the mobilo power samples whlc~ are detected. More particularly, mobile power is measured for a first predeter~ined duration such as 160 ms or four 40 m8 frames. In ter~ of the presently-implemented standards, a full rate coded mobile will transmit two 6.67 m8 packets per frame, or eight packets per 160 ms. after measuring th~ mobile signal power at a rate of 1.82 KHz, well within conventional technology, a determination iB made as to whether or not there iB a significant variation in signal intensity in each of the eight packets. If there is such a significant variation in each of the eight packet~, then the measurements already concluded are an accurate measurement of the mobile power.
On the other hand, if there i~ not a ~ignifican~ variation in amplitude over each of the eight packets, then a fu~ther measurement is taken for a further predeteroined duration, for example two additional frames or four more packets. With this further information, rather than examining the intensity variation per packet, the examination iB to see if there is an intensity ~ariation from packet to packet. If a significant variation i5 determined, then the numbex of samples already collected are adequate for measurement puxpose~. on the other hand, still further sampling of additional packets can be , ~ , ~: , PD-N91014 5 2 ~ 9 !~ 9 ~1 lmplemented in the event that there i~ not a ~ignificant variation in intensity from packet to packet.
Whlle the method ~u~t de~cribed rQfere to the measurement for a predeter~ined duration and the optional ~easurement for a further predeter-ined duration and etill a further measurement time in the event certain condition~ ~re not met, it ~hould be apparent that the nunber of different measuring durations beyond the first two (the predetermined duration and the further predeter~ined duration) are optional and depend on a tradeoff between measurement complexity and time saving.
Typically, the handoff process involves a channel unit in the serving cell, the cell with which the mobile is in communication. The channel unit will be receiving and demodulating the RF carrier from the nobil-. AB the mobile moves through the coverage area for the cell, the channel unit continues to receive its signal. Over thi~
time period the channel unit ob~erves the fading characteristics of the transmission and estimatee the amount of time needed to make an accurate power measurement. Typically, the channel unit relay~ the power measurement information to a handoff controller which determines whether power measurements should be ~ade by locating receivers in other cells (target cells) to support the handoff process. The handoff controller can reguest neighboring cells to perform the handoff measurement. This request, from the handoff controller, contains a recommended duration of the locating receiver measuremente. The recommended duration nay be obtained from the serving cell.
PD-N91014 6 2~949~i The duration lnformation comes from the channel unit or locating receiver which demodulates the ~ignal received from the mobile. This ~ignal contain~ implicit infor~ation about the mobile'~ local propagation environment. Thi~ infor~ation take~ the fora of power and phaso fluctuation~ which can be mea~ured in the channol unit. The channel unit sample~ the power level of the ~ignal and determine~ its auto-correlation. Other implementations can use other properties of the received signal. The width of the main lobe of the auto-correlation function determines the amount of averaging needed.
When the modulation i~ digital, the channel units extracts information about the phase fluctuations on the channel.
The speed at which the phase varies is related to the vehicle speed and serves as an additional input into the power measurement algorithms.
This clas~ of ~tatistical processing is called seguential estimation where the duration of the test varies with the nature of the samples.
Some Qnvironments may not produce short ter~ fluctuations which are referred to above. These are almost always locations with direct line of sight between the mobile and the base station. In these circumstances, however, a hand-off operation is rarely required.
Generally, and following the invention, the handoff process measurement time constants can be adapted to the local environment of the mobile in order to accelerate the handoff proces~. Applying the present invention add~ a new parameter to the locating receiver request. The ~'~ ` ' '.
. :
SEQUENTIAL POWER ESTIMATION FOR CELLULAR SYSTEM HANDOFF
DESCRIPTION
Teehnieal Field The present invention relate~ to i~provement~ in cellular S telephone technology and ~ore partieularly improveuents in the handoff proeess.
Background Art Cellular telephone teehnology has now been in uae for more than ten year~. The cellular telephone concept ~ubdivides a geographic region into a plurallty of cells. Each cell eontains either a ba~e station to control the call or plural base ~tations to control different sector- of the eall. Mobile unit~ eommunieate by radio to the base sta~ions which in turn are conneeted via land line6 to a switching offiee. Cells or eell ~eetors are a~signed their own carrier frequancy bando 80 that inter~erence froD ad~aeent eells or seetor~ i~ limited. Typieally, the earrier fregueneies employed in a eell or eell seetor o~ a elucter of eells are unigu , but those earrier ~requeneies ean be reused in ad~aeent eell clusters. One example of thi~ arehitecture is the Advanced Mobile Phone Serviee (AMPS). Sinee the introduetion of AHPS, the eapaeity provided by that architeeture has, at least in ~ome loealities, been exhausted 80 that further eapacity i~provements have been found neeessary. The Teleeommunications Industry A~soeiation has more recently promulgated a new standard IS-54 whieh allow~ the AMPS
arehiteeture to co-exist along with an arehitecture based on time division ~ultiplexing. Nevertheless, even the new - . .
.
time division multiplexing arch~tecture requires a sinilar cell architecture.
Conventional cellular telephony u~e~ one of two dlffQrent geometries for the area controlled by a base station. One of these geonetrie~ i~ generally a closed hexagonal region. For finer control, the alternative geometry ha~
the hexagonal region ~ubdivided into aectors, i.-. three or six sector~ per hexagon. Typically, the hexagonal region i~ served by a single base station optimally located at the center of the hexagon. In the alternative architecture, the base station~ are located at the vertices of the hexagons with directional antenna~, each directed to a particular sector of the hexagon. Because thi~ invention works with either geometry, ter~inology i~
lS si~plified by ignoring the distinction between the~e geometries. Consequently, throughout the re~aining portion of this application, the ter~ ~cell~ is u~ed to de~ignate either the generally hexagonal region or the segment or sector of such a hexagonal region.
A~ a consequence of a geographic mapping of operating carrier frequencies, it is essential for a nobile station to be handed off from one cell to another a~ it changes location. It has been recognized that this handoff i~ one of the mo~t critical aspects of operation of a cellular telephone ~ystem.
Handoff processe~ are described in Patents 4,829,554;
~,912,756; 5,042,082; 5,081,671 and Tekinay, ~Handover and Channel Assignment in Mobile Cellular Network~, IEE~
Communication~ Maaazine, November 1991, pp. 42 et ~eq.
~ . .
PD-N91014 3 æa9 ~9 ~ 1 It ls also known that mobile radio propagation i~ sub~ect to short-tern fluctuations in power generally characterized a~ Rayleigh or multipath fading. The signal pOWQr c~n fluctuate as much as 30 dB over half a wavelength of the RF carrier. Reliable handoff between cells i8 es~ential for high quality cellular operation.
An important part of the hando~f proce~ is the ability to measurQ the average power in the physical location of the mobile station. Short term fluctuation~ aust be ~moothed or averaged in order to obtain a good measure of the average power received from the location~. This averaging should be done over several cycles of the small ~cale fluctuations. Since the duration of these several cycle depends on the wavelength, the averaging time depends on the time needed for the mobile to traver~e ~everal wavelengths. This in turn is related to vehicle speed.
The ~lower the ~peed of the vehicle, the longer the averaging time i8 required for an accurate measurement.
In ~he absence of a priori ~nowledge of the vehicle speed, the system must allocate a time duration to the ~easurement process which sati~fie~ wor~t case conditions, i.e. is adequate for a ~low moving vehicle. m e alternative, assuming something les~ than worst case conditions, will nece~sarily result in sub-par performance fox those 510w moving vehicles. Howeverj allocating a ~easurement time ~ufficient to provide an accurate measurement for the slow moving vehicles penalizes the handoff operation with respect to high ~peed vehicles.
Because of the vehicle's high speed, its measurement proces6 could be accompli6hed in a significantly shorter time. Moreover, unnecessarily delaying the handoff proces6 for a high speed vehicle could result in ~ub-par handoff perfornance or even los$ng the call.
PD-N9101~ ~ 2 ~ 9 ~ 9 3 1 Summary of the Invention The inventlon overcomes the problem o~ devoting ~ufflcient time to mea~uring mobile power without unnecessarlly penalizlng a fast moving vehlcle. Thi~ advantage is obtained by recogniz$ng that t~e system can obtaln an estimato of that tlme necessary for accurate measurement of mobile power by monitorlng the statiotical variatlons in the mobilo power samples whlc~ are detected. More particularly, mobile power is measured for a first predeter~ined duration such as 160 ms or four 40 m8 frames. In ter~ of the presently-implemented standards, a full rate coded mobile will transmit two 6.67 m8 packets per frame, or eight packets per 160 ms. after measuring th~ mobile signal power at a rate of 1.82 KHz, well within conventional technology, a determination iB made as to whether or not there iB a significant variation in signal intensity in each of the eight packets. If there is such a significant variation in each of the eight packet~, then the measurements already concluded are an accurate measurement of the mobile power.
On the other hand, if there i~ not a ~ignifican~ variation in amplitude over each of the eight packets, then a fu~ther measurement is taken for a further predeteroined duration, for example two additional frames or four more packets. With this further information, rather than examining the intensity variation per packet, the examination iB to see if there is an intensity ~ariation from packet to packet. If a significant variation i5 determined, then the numbex of samples already collected are adequate for measurement puxpose~. on the other hand, still further sampling of additional packets can be , ~ , ~: , PD-N91014 5 2 ~ 9 !~ 9 ~1 lmplemented in the event that there i~ not a ~ignificant variation in intensity from packet to packet.
Whlle the method ~u~t de~cribed rQfere to the measurement for a predeter~ined duration and the optional ~easurement for a further predeter-ined duration and etill a further measurement time in the event certain condition~ ~re not met, it ~hould be apparent that the nunber of different measuring durations beyond the first two (the predetermined duration and the further predeter~ined duration) are optional and depend on a tradeoff between measurement complexity and time saving.
Typically, the handoff process involves a channel unit in the serving cell, the cell with which the mobile is in communication. The channel unit will be receiving and demodulating the RF carrier from the nobil-. AB the mobile moves through the coverage area for the cell, the channel unit continues to receive its signal. Over thi~
time period the channel unit ob~erves the fading characteristics of the transmission and estimatee the amount of time needed to make an accurate power measurement. Typically, the channel unit relay~ the power measurement information to a handoff controller which determines whether power measurements should be ~ade by locating receivers in other cells (target cells) to support the handoff process. The handoff controller can reguest neighboring cells to perform the handoff measurement. This request, from the handoff controller, contains a recommended duration of the locating receiver measuremente. The recommended duration nay be obtained from the serving cell.
PD-N91014 6 2~949~i The duration lnformation comes from the channel unit or locating receiver which demodulates the ~ignal received from the mobile. This ~ignal contain~ implicit infor~ation about the mobile'~ local propagation environment. Thi~ infor~ation take~ the fora of power and phaso fluctuation~ which can be mea~ured in the channol unit. The channel unit sample~ the power level of the ~ignal and determine~ its auto-correlation. Other implementations can use other properties of the received signal. The width of the main lobe of the auto-correlation function determines the amount of averaging needed.
When the modulation i~ digital, the channel units extracts information about the phase fluctuations on the channel.
The speed at which the phase varies is related to the vehicle speed and serves as an additional input into the power measurement algorithms.
This clas~ of ~tatistical processing is called seguential estimation where the duration of the test varies with the nature of the samples.
Some Qnvironments may not produce short ter~ fluctuations which are referred to above. These are almost always locations with direct line of sight between the mobile and the base station. In these circumstances, however, a hand-off operation is rarely required.
Generally, and following the invention, the handoff process measurement time constants can be adapted to the local environment of the mobile in order to accelerate the handoff proces~. Applying the present invention add~ a new parameter to the locating receiver request. The ~'~ ` ' '.
. :
2~9~9~1 channel unit which i8 in contact with the mobile in it~
serving cell estimates the required measurement period froa data that has been collecting over the duratlon of the call.
The seguential type measurement can be generalized as follows: the serving or target cell can sample and average the received signal power over Nl frames. Ba~ed on this 6ampling, the statistics of the received ~ignal are calculated which descr$be whether the fading rate is higher or lower than ~ threshold rate R1. If the fading rate is higher than the threshold rate ~ then tho mea~urement is concluded and the current average power i~
accepted as the eligible measurement. Alternatively, if the calculated fading rate is less than the thre~hold Rl, then the base station continues sampling the received ~ignal and averages the received signal power over N2 frames ~where N2 is greater than N1). Based on the sampling over N2 frames, the base station calculates statistics describing whether the fading rate i8 higher or lower than a second threshold R2. If the calculation indicates that the fading rate is higher than R2, then the measurement i8 ter~inated and the current average power measurement is accepted as the desired power measurement.
Clearly, the fading rate R~ is less than the fading rate R1. Also, the 6teps of continuing the sampling proce~s, averaging the received power and calculating the fading rate over the entire 6ampling period can be continued and the threshold fading rate again6~ which the calculated fading rate is compared is continually reduced. Thi~
continued iteration i8 terminated when the calculated fading rate i8 larger than some preselected threshold and/or a predetermined time out duration for the entire measurement i8 exceeded.
, ~
. .
.
2~9-3'1 ~rief Description of the Drawings The present invention will now be described in the following portions of thi~ speci~ication ~o a~ to enablo those skilled in the art to make and use the ~ame, S wherein:
Fig. 1 i8 a block diagram showing the apparatus employed with the present invention:
Fig. 2 illustrates the variation of signal power with respect to distance;
Fig. 3 shows a sequence of packets and several frames, Fig. 4 i8 a flow diagram showing processing in accordance with the one embodiment of the pre~ent invention;
Fig. 5 is a flow diagram showing processing in accordance with another generalized embodiment of the present invention; and Fig. 6 is a further detail of the fixed eguipment of Fig.
1.
Detailed Description of Preferred Embodiments Fig. 1 illustrates the ma~or components of a typical cellular telephone system involved in a handoff process.
More particularly, the mobile station V is shown ~oving with respect to a base ~tation 1 and a base station 2.
The signal received at the MS from any base station depends on the totality of the propagation environment.
Due to reflections and interaction with tationary and other moveable ob~ect~, the propagation environment can be - : ~
.:
PD-N91014 9 2 0 9 ~ 9 ~ 1 con~idered to set up a standing wave pattern ~uch a~ i~
illustrated in Fig. 2. Fig. 2 plot~ received signal intensity vs. distance. Fig. 2 can be considered to illustrate a constant or mean oignal power with fluctuations superimposed on that nean power. The power variation over the distance labelled F1 is the power intensity varlation that would be ~een by a vehicle moving at a given speed during one frame time, i.e. 40 ~.
However, for a vehicle moving at a significantly slower speed, the variation of the standing wave illustrated in Fig. 2 that would be seen within one frame t~me may be as small as that 6hown by F2. Clearly, the measurement over Fl produces a more accurate measurement of the propagation environment than does the measurement over the distance F2.
Unfortunately for cellular telephony, the speed at which a mobile station is moving is unknown. Because power measurements are an important part of the handoff process, and because handoff6 mu~t be handled guickly to avoid degrading the voice quality of the telephone connection, conventional cellular telephony systems are hampered by the need to fix the measurement duration. The operator of a cellular telephony ~ystem ust nakQ some estimate of the distribution o~ speQd of mobile ~tations and provide enough measurement time to accurately measure the propagation ~nvironment for the large ma~ority of mobile stations. Because some of these mobile stations are ~oving faster than the averaqe, it follows that unnecessary measurement time is expended in taking measurements on fast moving mobile6.
There are two conseguences which flow from unneces6arily extending the measurement duration, and both are adverse to optimum operation of a cellular telephone 6y~te~. In the fir6t place, devoting excessive measurement time to a PD-N91014 10 2 0 9 4 9 ~1 mobil~ ~eans that there is le~o measurement time available for other u~er~. In addition, it i8 the fast moving mobile that requires a quick~r handoff operation in order to maintain call guality, but it ie ~ust thio mobilo that is discriminated against by unnecessarily delaying the measurement process.
Fig. 3 represents the frame fornat of the IS-54 standard showing the location of typical channel A for three sequential frames. More particularly, as shown in Fig. 3, each channel occupies two time olots in a frame which has a capacity of six time slots. ~ecause there are two bursts per frame, in four frameo there will be eight bursts in a oingle channel.
When a handoff process is initiated, the serving ~tation 1 communicates with the handoff controller, typically at a Ba~e Switching Center or a MST0. The handoff controller, as part of the handoff process, may direct a target cell such as station 2 to perfor~ power measurement~ on the ~obile otation V. In addition, the handoff proces~ it~elf will be initiated by ~tation 1 based on its power measurements of the signal from the mobile station V. The present invention i~ useful in detercining the time that should be allocated to the mea~urement process, ~ither at the serving cell station 1 or at the target cell ~tation 2.
Fig. 4 shows the proces~ing which will be engaged in by the channel unit at a serving station to monitor the signal from a MS. When a meacurement is necessary, the receiver tunes to the particular channel (this includes tuning to the appropriate carrier frequency as well as monitoring the particular time slot or slot~ in the frame ~ -.
. ~-. . ~; .
, ~ ~
PD-N9101~ ll 20~9~1 allocated to the channel being measured). Sample~ o~ the received ~ignal are accumulated from a fir~t given nu~k~r of packets in the channel. For exa~ple, ~tep Fl can b~
u~ed to accumulate sample~ from four fra~e~ or eight S packet~. At t~e conclusion o~ ~tep Fl, ~tep F2 exa~ine~
the statistics of the samples, particularly, the statistics of the samples within a pacXet. The next function i~ a decision point which branches dQpending on whether there i~ a significant variation within the sample~ in each of the packet~. If there iB a ~ignificant variation, then the measurement proces~ for thi~
partlcular mobile has been completed and the mea~urement time for this mobile is the fir~t number of packet~, for example four frames. The measure~ent time parameter can be usQd by other stations performing a measurement on this mobile.
On the other hand, if the deci~ion point F3 does not branch to step F4 because there is not a ~ignificant variation among ~amples within a packet, then function F5 is performed to continue the accumulation of sample~ fro~
a second number of packet~, i.e. two additional fra-e~ or a total of ~lx frames. Function F6 then examine~ the stati~tics of all of the ~amples accumulated throughout the eight frame~. Function F6 exa~ines whether or not there is a significant variation from packet to packet.
Function F7 branches on the result. If there i~ a 6ignificant variation, then function F8 is perfon ed to set the measurenent time for thi6 mobile at the second number of packets, i.e. twelve packets (six frame~).
Otherwise, the process can continue with examination of the ~tatistics accumulated over the previou~ samples a~
well as the succeeding 6amples. The processing ~ay be terminated after another measurement if the total time for - , . ~ .
:' . .; . :
~094~ ~
sample accumulation l~ appropriate for the typical worst case mobile. Otherwise, proce~ing can continue in thi~
fashion (accu~ulation of further samples and branch on the rQsult) until some predetermined ti~eout i8 eXCeQdQd.
Such a timeout would be selected in accordance with the result~ of a worst ca6e analysi~ a~ the time nece~sary to accuoulate an appropriate measurement for a slow moving mobile.
Fig. 5 illustrates generalized proce~sing that can bQ
employed in taking power measurements on the signal from a mobile. The time scale at the left (time increases downward) represents the time required to accumulate the necessary sample~ for the different processing steps.
Since each frame is 40 ms in duration, N1 frame~ is 0.04N
lS seconds in duration, etc. As shown in Fig. 5, the first function, FlO, accumulates samples from the mobile over N
frames ~for example four frame~). Once sa~ples from Nl frames have been accumulated, then the statistics of those samples are calculated to determine the relationship between the calculated fading rate and a fir~t threshold fading rate R1. Function Fll branche6 on the result. If the calculated fading rate in function FlO is greater than the threshold ~, then function Fl2 i~ performed to terminate the measurement and accept the current average power as the appropriate measurement~
Alternatively, if the comparison at function Fll indicates that the calculated fading rate is not higher than R~, then function Fl3 is performed to average the received signal power over N2 frames (for example eight frames). Once the desired number of samples has been accumulated, ~unction Fl3 calculates the statistic~ and particularly the fading rate. Function Fl4 branches on the comparison between the ' :; '~
PD-N91014 13 2 0 9 ~ 9 ~1 calculated fading rate and the second threshold fading rate F~. If the fading rate calculated by function F13 i~
greater than F~, then the measurement i8 terminated at function F15 and the calculated average power mea~urement i8 accepted. On the other hand, if the deci~ion point at function F14 indicates that the calculated fading rate i~
les~ than the second thres~old F~, processing can continue to take sample~ over a longer duration, calculate fading rates and compare those fading rate~ to other fading rate thresholds. Generally, the process can be concluded when:
(1) The calculated fsding rate i8 greater than the appropriate threshold (wherein the threshold continually decreases with longer and longer measurement times), or (2) The measurement time extends beyond some predetermined time out duration.
Fig. 6 is a further detail showing the equipment implementing the foregoing functions. More particularly, station 1, the serving cell i~ illustrated at the botto~
of Fig. 6 with the designation BTSs, station 2, the target cell, is represented in Fig. 6 at the top with the designation BTST. A handoff controller is illustrat0d as including the Base Switching Centor as~ociated with the serving cell BTS~ and designated BSC~, and a si~ilar Base Switching Center a~sociated with the target cell, designed BSC~ and a mobi~e switching center MSC. Those skilled in the art will understand that Fig. 6 then represents not only a handoff from one serving cell to another but where tho~e cells are associated with different base switching centers. While thi~ is only one example of application of the invention, it is also within the scope of the invention that a handoff from a serving cell to a target , ~
PD-N91014 14 2 ~ 9 ~
cell can be accomplished whereln both cells are served by the same base switching center. In addition, whlle Fig. 6 illustrates a handoff, the eystem proposed by the assignee of thle application, which is more completely described in S co-pending application S.N. 07/622,232 filed Dece~ber 6, 1990, the principles of the present invention can be used with cellular telephone systems having different architectures.
As seen in Fig. 6, each BTS includes a radio freguency stage coupled to a Modulator Downconverter Module (HDM), which operates at an inter~ediate frequency. MDM in turn is coupled to a Demodulator Module (DEM) which actually performs the measurement processes shown in Figs. 4 and 5.
The DEM in turn is coupled to a Control Processor (CP).
The CP interprets commands received from the associated BSC and controls the elements of the cell, DEM, MDM and RF
accordingly. Measurement information, in turn, is passed on by the CP to the associated BSC.
As i~ illu~trated in Fig. 6, measurement requests (MReq) and measurement re~ults (MRe~) are exchanged between the serving base switching center (BSCs) and the targ~t base ~witching center (BSCT)~ In addition, when handoff is appropriate, the BSC~ sends a handoff request message (HOReq) to the MSC. The NSC responds with a handoff message (HOM) to a potential target cell via the associated BSC~.
Accordingly, this application has described a new technique in association with mobile handoff; a technique which adapts the measurement time to the received signal.
Application of the invention provides a new parameter in the handoff process, spezifically, the measurement time.
,~
209i~9al This mes~urement time parameter can be provided, ~rom the handoff controller to a target cell, to allow the target cell to tailor the measurement time to the particular moblle under inve~tigation. Those skilled in tb art will understand that the invention i~ not restricted to th~ two processing examples de~cribed therein, but that other processing variations come within the spirit and scope of tbe invention which is to be construed fro~ the claims attached hereto.
serving cell estimates the required measurement period froa data that has been collecting over the duratlon of the call.
The seguential type measurement can be generalized as follows: the serving or target cell can sample and average the received signal power over Nl frames. Ba~ed on this 6ampling, the statistics of the received ~ignal are calculated which descr$be whether the fading rate is higher or lower than ~ threshold rate R1. If the fading rate is higher than the threshold rate ~ then tho mea~urement is concluded and the current average power i~
accepted as the eligible measurement. Alternatively, if the calculated fading rate is less than the thre~hold Rl, then the base station continues sampling the received ~ignal and averages the received signal power over N2 frames ~where N2 is greater than N1). Based on the sampling over N2 frames, the base station calculates statistics describing whether the fading rate i8 higher or lower than a second threshold R2. If the calculation indicates that the fading rate is higher than R2, then the measurement i8 ter~inated and the current average power measurement is accepted as the desired power measurement.
Clearly, the fading rate R~ is less than the fading rate R1. Also, the 6teps of continuing the sampling proce~s, averaging the received power and calculating the fading rate over the entire 6ampling period can be continued and the threshold fading rate again6~ which the calculated fading rate is compared is continually reduced. Thi~
continued iteration i8 terminated when the calculated fading rate i8 larger than some preselected threshold and/or a predetermined time out duration for the entire measurement i8 exceeded.
, ~
. .
.
2~9-3'1 ~rief Description of the Drawings The present invention will now be described in the following portions of thi~ speci~ication ~o a~ to enablo those skilled in the art to make and use the ~ame, S wherein:
Fig. 1 i8 a block diagram showing the apparatus employed with the present invention:
Fig. 2 illustrates the variation of signal power with respect to distance;
Fig. 3 shows a sequence of packets and several frames, Fig. 4 i8 a flow diagram showing processing in accordance with the one embodiment of the pre~ent invention;
Fig. 5 is a flow diagram showing processing in accordance with another generalized embodiment of the present invention; and Fig. 6 is a further detail of the fixed eguipment of Fig.
1.
Detailed Description of Preferred Embodiments Fig. 1 illustrates the ma~or components of a typical cellular telephone system involved in a handoff process.
More particularly, the mobile station V is shown ~oving with respect to a base ~tation 1 and a base station 2.
The signal received at the MS from any base station depends on the totality of the propagation environment.
Due to reflections and interaction with tationary and other moveable ob~ect~, the propagation environment can be - : ~
.:
PD-N91014 9 2 0 9 ~ 9 ~ 1 con~idered to set up a standing wave pattern ~uch a~ i~
illustrated in Fig. 2. Fig. 2 plot~ received signal intensity vs. distance. Fig. 2 can be considered to illustrate a constant or mean oignal power with fluctuations superimposed on that nean power. The power variation over the distance labelled F1 is the power intensity varlation that would be ~een by a vehicle moving at a given speed during one frame time, i.e. 40 ~.
However, for a vehicle moving at a significantly slower speed, the variation of the standing wave illustrated in Fig. 2 that would be seen within one frame t~me may be as small as that 6hown by F2. Clearly, the measurement over Fl produces a more accurate measurement of the propagation environment than does the measurement over the distance F2.
Unfortunately for cellular telephony, the speed at which a mobile station is moving is unknown. Because power measurements are an important part of the handoff process, and because handoff6 mu~t be handled guickly to avoid degrading the voice quality of the telephone connection, conventional cellular telephony systems are hampered by the need to fix the measurement duration. The operator of a cellular telephony ~ystem ust nakQ some estimate of the distribution o~ speQd of mobile ~tations and provide enough measurement time to accurately measure the propagation ~nvironment for the large ma~ority of mobile stations. Because some of these mobile stations are ~oving faster than the averaqe, it follows that unnecessary measurement time is expended in taking measurements on fast moving mobile6.
There are two conseguences which flow from unneces6arily extending the measurement duration, and both are adverse to optimum operation of a cellular telephone 6y~te~. In the fir6t place, devoting excessive measurement time to a PD-N91014 10 2 0 9 4 9 ~1 mobil~ ~eans that there is le~o measurement time available for other u~er~. In addition, it i8 the fast moving mobile that requires a quick~r handoff operation in order to maintain call guality, but it ie ~ust thio mobilo that is discriminated against by unnecessarily delaying the measurement process.
Fig. 3 represents the frame fornat of the IS-54 standard showing the location of typical channel A for three sequential frames. More particularly, as shown in Fig. 3, each channel occupies two time olots in a frame which has a capacity of six time slots. ~ecause there are two bursts per frame, in four frameo there will be eight bursts in a oingle channel.
When a handoff process is initiated, the serving ~tation 1 communicates with the handoff controller, typically at a Ba~e Switching Center or a MST0. The handoff controller, as part of the handoff process, may direct a target cell such as station 2 to perfor~ power measurement~ on the ~obile otation V. In addition, the handoff proces~ it~elf will be initiated by ~tation 1 based on its power measurements of the signal from the mobile station V. The present invention i~ useful in detercining the time that should be allocated to the mea~urement process, ~ither at the serving cell station 1 or at the target cell ~tation 2.
Fig. 4 shows the proces~ing which will be engaged in by the channel unit at a serving station to monitor the signal from a MS. When a meacurement is necessary, the receiver tunes to the particular channel (this includes tuning to the appropriate carrier frequency as well as monitoring the particular time slot or slot~ in the frame ~ -.
. ~-. . ~; .
, ~ ~
PD-N9101~ ll 20~9~1 allocated to the channel being measured). Sample~ o~ the received ~ignal are accumulated from a fir~t given nu~k~r of packets in the channel. For exa~ple, ~tep Fl can b~
u~ed to accumulate sample~ from four fra~e~ or eight S packet~. At t~e conclusion o~ ~tep Fl, ~tep F2 exa~ine~
the statistics of the samples, particularly, the statistics of the samples within a pacXet. The next function i~ a decision point which branches dQpending on whether there i~ a significant variation within the sample~ in each of the packet~. If there iB a ~ignificant variation, then the measurement proces~ for thi~
partlcular mobile has been completed and the mea~urement time for this mobile is the fir~t number of packet~, for example four frames. The measure~ent time parameter can be usQd by other stations performing a measurement on this mobile.
On the other hand, if the deci~ion point F3 does not branch to step F4 because there is not a ~ignificant variation among ~amples within a packet, then function F5 is performed to continue the accumulation of sample~ fro~
a second number of packet~, i.e. two additional fra-e~ or a total of ~lx frames. Function F6 then examine~ the stati~tics of all of the ~amples accumulated throughout the eight frame~. Function F6 exa~ines whether or not there is a significant variation from packet to packet.
Function F7 branches on the result. If there i~ a 6ignificant variation, then function F8 is perfon ed to set the measurenent time for thi6 mobile at the second number of packets, i.e. twelve packets (six frame~).
Otherwise, the process can continue with examination of the ~tatistics accumulated over the previou~ samples a~
well as the succeeding 6amples. The processing ~ay be terminated after another measurement if the total time for - , . ~ .
:' . .; . :
~094~ ~
sample accumulation l~ appropriate for the typical worst case mobile. Otherwise, proce~ing can continue in thi~
fashion (accu~ulation of further samples and branch on the rQsult) until some predetermined ti~eout i8 eXCeQdQd.
Such a timeout would be selected in accordance with the result~ of a worst ca6e analysi~ a~ the time nece~sary to accuoulate an appropriate measurement for a slow moving mobile.
Fig. 5 illustrates generalized proce~sing that can bQ
employed in taking power measurements on the signal from a mobile. The time scale at the left (time increases downward) represents the time required to accumulate the necessary sample~ for the different processing steps.
Since each frame is 40 ms in duration, N1 frame~ is 0.04N
lS seconds in duration, etc. As shown in Fig. 5, the first function, FlO, accumulates samples from the mobile over N
frames ~for example four frame~). Once sa~ples from Nl frames have been accumulated, then the statistics of those samples are calculated to determine the relationship between the calculated fading rate and a fir~t threshold fading rate R1. Function Fll branche6 on the result. If the calculated fading rate in function FlO is greater than the threshold ~, then function Fl2 i~ performed to terminate the measurement and accept the current average power as the appropriate measurement~
Alternatively, if the comparison at function Fll indicates that the calculated fading rate is not higher than R~, then function Fl3 is performed to average the received signal power over N2 frames (for example eight frames). Once the desired number of samples has been accumulated, ~unction Fl3 calculates the statistic~ and particularly the fading rate. Function Fl4 branches on the comparison between the ' :; '~
PD-N91014 13 2 0 9 ~ 9 ~1 calculated fading rate and the second threshold fading rate F~. If the fading rate calculated by function F13 i~
greater than F~, then the measurement i8 terminated at function F15 and the calculated average power mea~urement i8 accepted. On the other hand, if the deci~ion point at function F14 indicates that the calculated fading rate i~
les~ than the second thres~old F~, processing can continue to take sample~ over a longer duration, calculate fading rates and compare those fading rate~ to other fading rate thresholds. Generally, the process can be concluded when:
(1) The calculated fsding rate i8 greater than the appropriate threshold (wherein the threshold continually decreases with longer and longer measurement times), or (2) The measurement time extends beyond some predetermined time out duration.
Fig. 6 is a further detail showing the equipment implementing the foregoing functions. More particularly, station 1, the serving cell i~ illustrated at the botto~
of Fig. 6 with the designation BTSs, station 2, the target cell, is represented in Fig. 6 at the top with the designation BTST. A handoff controller is illustrat0d as including the Base Switching Centor as~ociated with the serving cell BTS~ and designated BSC~, and a si~ilar Base Switching Center a~sociated with the target cell, designed BSC~ and a mobi~e switching center MSC. Those skilled in the art will understand that Fig. 6 then represents not only a handoff from one serving cell to another but where tho~e cells are associated with different base switching centers. While thi~ is only one example of application of the invention, it is also within the scope of the invention that a handoff from a serving cell to a target , ~
PD-N91014 14 2 ~ 9 ~
cell can be accomplished whereln both cells are served by the same base switching center. In addition, whlle Fig. 6 illustrates a handoff, the eystem proposed by the assignee of thle application, which is more completely described in S co-pending application S.N. 07/622,232 filed Dece~ber 6, 1990, the principles of the present invention can be used with cellular telephone systems having different architectures.
As seen in Fig. 6, each BTS includes a radio freguency stage coupled to a Modulator Downconverter Module (HDM), which operates at an inter~ediate frequency. MDM in turn is coupled to a Demodulator Module (DEM) which actually performs the measurement processes shown in Figs. 4 and 5.
The DEM in turn is coupled to a Control Processor (CP).
The CP interprets commands received from the associated BSC and controls the elements of the cell, DEM, MDM and RF
accordingly. Measurement information, in turn, is passed on by the CP to the associated BSC.
As i~ illu~trated in Fig. 6, measurement requests (MReq) and measurement re~ults (MRe~) are exchanged between the serving base switching center (BSCs) and the targ~t base ~witching center (BSCT)~ In addition, when handoff is appropriate, the BSC~ sends a handoff request message (HOReq) to the MSC. The NSC responds with a handoff message (HOM) to a potential target cell via the associated BSC~.
Accordingly, this application has described a new technique in association with mobile handoff; a technique which adapts the measurement time to the received signal.
Application of the invention provides a new parameter in the handoff process, spezifically, the measurement time.
,~
209i~9al This mes~urement time parameter can be provided, ~rom the handoff controller to a target cell, to allow the target cell to tailor the measurement time to the particular moblle under inve~tigation. Those skilled in tb art will understand that the invention i~ not restricted to th~ two processing examples de~cribed therein, but that other processing variations come within the spirit and scope of tbe invention which is to be construed fro~ the claims attached hereto.
Claims (13)
1. A method of handing off a mobile station from one cell to another in a cellular telephone system comprising the steps of:
a) sampling received signal intensity from the mobile for a predetermined duration, and b) determining from samples collected in step a) whether further sampling is or is not required for an accurate measurement.
a) sampling received signal intensity from the mobile for a predetermined duration, and b) determining from samples collected in step a) whether further sampling is or is not required for an accurate measurement.
2. A method as recited in claim 1 comprising the further steps, in the event that further sampling is determined to be required, of:
c) sampling the received signal from the mobile for a further predetermined duration, and d) determining from the samples collected in steps a) and c) if further sampling is or is not required for an accurate measurement.
c) sampling the received signal from the mobile for a further predetermined duration, and d) determining from the samples collected in steps a) and c) if further sampling is or is not required for an accurate measurement.
3. A method as recited in claim 2 wherein the measurement is carried out at the serving cell.
4. A method as recited in claim 3 comprising the further steps of:
e) determining from the samples collected from the mobile station whether or not an accurate measurement can be obtained from the mobile in the predetermined time, and f) in the event an accurate measurement can be obtained in the predetermined time, transmitting an indication of that determination to a target cell.
e) determining from the samples collected from the mobile station whether or not an accurate measurement can be obtained from the mobile in the predetermined time, and f) in the event an accurate measurement can be obtained in the predetermined time, transmitting an indication of that determination to a target cell.
5. A method as recited in claim 4 comprising, in the event an accurate measurement cannot be obtained in the predetermined time, the step of transmitting an indication to a target cell that sampling to obtain an accurate measurement from the mobile requires more than the predetermined time.
6. A method as recited in claim 2 wherein the measurement is carried out at the target cell.
7. A method as recited in claim 6 comprising the further step of receiving, at a target cell, an indication from the serving cell of the required sampling duration required for an accurate measurement of the mobile signal.
8. A method as recited in claim 1 wherein said sampling step includes:
(a1) calculating from the samples collected in step (a) a calculated fade rate R, and wherein said determining step (b) includes:
(b1) comparing the calculated fade rate R to a threshold fade rate R1, and (b2) concluding that further sampling is not required if said calculated fade rate R exceeds said threshold fade rate R.
(a1) calculating from the samples collected in step (a) a calculated fade rate R, and wherein said determining step (b) includes:
(b1) comparing the calculated fade rate R to a threshold fade rate R1, and (b2) concluding that further sampling is not required if said calculated fade rate R exceeds said threshold fade rate R.
9. A method as recited in claim 8 wherein said determining step (b) further includes:
(b3) concluding that further sampling is required if said calculated fade rate R does not exceed said threshold fade rate R.
(b3) concluding that further sampling is required if said calculated fade rate R does not exceed said threshold fade rate R.
10. Apparatus for handing off a mobile station from one cell to another in a cellular telephone system comprising:
a) means for sampling received signal intensity from the mobile, b) a controller including first means to control said sampling means to sample said received signal for a predetermined duration, and c) means for determining, from samples collected by the means for sampling, whether further sampling i8 or is not required for an accurate measurement.
a) means for sampling received signal intensity from the mobile, b) a controller including first means to control said sampling means to sample said received signal for a predetermined duration, and c) means for determining, from samples collected by the means for sampling, whether further sampling i8 or is not required for an accurate measurement.
11. Apparatus as recited in claim 10 further comprising second means in said controller to control said sampling means to sample the received signal from the mobile for a further predetermined duration.
12. Apparatus as recited in claim 10 and further comprising means responsive to the means for determining for transmitting an indication of an appropriate measurement time for the mobile to a target cell.
13. Apparatus as recited in claim 11 and further comprising means responsive to to means for determining for transmitting an indication of an appropriate measurement time for the mobile to a target cell.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US881,271 | 1992-05-11 | ||
| US07/881,271 US5367559A (en) | 1992-05-11 | 1992-05-11 | Sequential power estimation for cellular system handoff |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2094951A1 true CA2094951A1 (en) | 1993-11-12 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002094951A Abandoned CA2094951A1 (en) | 1992-05-11 | 1993-04-27 | Sequential power estimation for cellular system handoff |
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| US (1) | US5367559A (en) |
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| US5590177A (en) * | 1994-09-30 | 1996-12-31 | Motorola, Inc. | Method for preventing a dropped call during a handoff in a radiotelephone system |
| US5649293A (en) * | 1995-05-25 | 1997-07-15 | Motorola, Inc. | Method for assigning subscribers between narrowbeam sectors |
| US5787348A (en) * | 1995-12-06 | 1998-07-28 | Motorola, Inc. | Method of measuring speed of a mobile unit and a receiver for use in a wireless communication system |
| US6047189A (en) * | 1996-10-11 | 2000-04-04 | Arraycomm, Inc. | Adaptive method for channel assignment in a cellular communication system |
| US7035661B1 (en) | 1996-10-11 | 2006-04-25 | Arraycomm, Llc. | Power control with signal quality estimation for smart antenna communication systems |
| US6275543B1 (en) | 1996-10-11 | 2001-08-14 | Arraycomm, Inc. | Method for reference signal generation in the presence of frequency offsets in a communications station with spatial processing |
| US6463295B1 (en) | 1996-10-11 | 2002-10-08 | Arraycomm, Inc. | Power control with signal quality estimation for smart antenna communication systems |
| US6040800A (en) * | 1997-04-22 | 2000-03-21 | Ericsson Inc. | Systems and methods for locating remote terminals in radiocommunication systems |
| US6754497B1 (en) * | 1997-10-09 | 2004-06-22 | Interdigital Technology Corporation | Seamless handoff system and method |
| US5960347A (en) * | 1997-10-09 | 1999-09-28 | Interdigital Technology Corporation | Seamless handoff system and method |
| US7299071B1 (en) | 1997-12-10 | 2007-11-20 | Arraycomm, Llc | Downlink broadcasting by sequential transmissions from a communication station having an antenna array |
| JP3805520B2 (en) * | 1998-01-28 | 2006-08-02 | 富士通株式会社 | Speed estimation apparatus and method in mobile communication |
| US6615024B1 (en) | 1998-05-01 | 2003-09-02 | Arraycomm, Inc. | Method and apparatus for determining signatures for calibrating a communication station having an antenna array |
| US6542482B1 (en) * | 1998-10-05 | 2003-04-01 | Telefonaktiebolaget Lm Ericsson (Publ) | Load sharing for MCPA-equipped base station |
| KR100326326B1 (en) * | 1998-11-19 | 2002-06-26 | 윤종용 | Apparatus for measuring received signal strength indicator in radio communication system |
| US6600914B2 (en) | 1999-05-24 | 2003-07-29 | Arraycomm, Inc. | System and method for emergency call channel allocation |
| US6141567A (en) | 1999-06-07 | 2000-10-31 | Arraycomm, Inc. | Apparatus and method for beamforming in a changing-interference environment |
| US7139592B2 (en) | 1999-06-21 | 2006-11-21 | Arraycomm Llc | Null deepening for an adaptive antenna based communication station |
| JP3383618B2 (en) * | 1999-08-18 | 2003-03-04 | 松下電器産業株式会社 | Mobile communication terminal apparatus and reception strength detection method |
| US6985466B1 (en) | 1999-11-09 | 2006-01-10 | Arraycomm, Inc. | Downlink signal processing in CDMA systems utilizing arrays of antennae |
| EP1156609A1 (en) * | 2000-05-15 | 2001-11-21 | TELEFONAKTIEBOLAGET LM ERICSSON (publ) | Transmission quality measurement in a communication network |
| JP4453168B2 (en) * | 2000-06-23 | 2010-04-21 | 日本電気株式会社 | Mobile communication control method, cellular system, mobile station, base station, and base station controller |
| US7062294B1 (en) | 2000-09-29 | 2006-06-13 | Arraycomm, Llc. | Downlink transmission in a wireless data communication system having a base station with a smart antenna system |
| US6982968B1 (en) | 2000-09-29 | 2006-01-03 | Arraycomm, Inc. | Non-directional transmitting from a wireless data base station having a smart antenna system |
| US6795409B1 (en) | 2000-09-29 | 2004-09-21 | Arraycomm, Inc. | Cooperative polling in a wireless data communication system having smart antenna processing |
| US9246698B2 (en) * | 2004-05-07 | 2016-01-26 | Nokia Technologies Oy | Apparatus, and associated method, for facilitating a radio resource measurement in a radio communication system |
| GB2447887B (en) * | 2007-03-14 | 2011-08-10 | Vodafone Plc | Radio measurements in cellular telecommunications systems |
| US20110026430A1 (en) * | 2009-07-30 | 2011-02-03 | Qualcomm Incorporated | Method and apparatus for detecting a channel condition for a wireless communication device |
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| US4549311A (en) * | 1982-08-03 | 1985-10-22 | Motorola, Inc. | Method and apparatus for measuring the strength of a radio signal frequency |
| US4829554A (en) * | 1985-01-31 | 1989-05-09 | Harris Corporation | Cellular mobile telephone system and method |
| US4718081A (en) * | 1986-11-13 | 1988-01-05 | General Electric Company | Method and apparatus for reducing handoff errors in a cellular radio telephone communications system |
| SE460941B (en) * | 1988-04-26 | 1989-12-04 | Ericsson Telefon Ab L M | PROCEDURE IN A CELL-DIVIDED MOBILE PHONE SYSTEM TO REDUCE SUSPENSION BY TRANSFER OF CALLS |
| US4972456A (en) * | 1989-02-10 | 1990-11-20 | Gte Mobilnet Incorporated | Rural radiotelephone system |
| US4912756A (en) * | 1989-04-07 | 1990-03-27 | Unilink Corporation | Method and apparatus for error-free digital data transmission during cellular telephone handoff, etc. |
| US5042082A (en) * | 1989-06-26 | 1991-08-20 | Telefonaktiebolaget L. M. Ericsson | Mobile assisted handoff |
| US5239667A (en) * | 1990-01-31 | 1993-08-24 | Nec Corporation | Method of controlling handoff in cellular mobile radio communications system |
| US5203010A (en) * | 1990-11-13 | 1993-04-13 | Motorola, Inc. | Radio telephone system incorporating multiple time periods for communication transfer |
| US5187808A (en) * | 1990-11-05 | 1993-02-16 | Motorola, Inc. | Repeater site failure detector in communication system |
| US5170485A (en) * | 1990-11-07 | 1992-12-08 | Motorola, Inc. | Hand-off algorithm for elongated radiotelephone cells |
| US5175867A (en) * | 1991-03-15 | 1992-12-29 | Telefonaktiebolaget L M Ericsson | Neighbor-assisted handoff in a cellular communications system |
-
1992
- 1992-05-11 US US07/881,271 patent/US5367559A/en not_active Expired - Lifetime
-
1993
- 1993-04-27 CA CA002094951A patent/CA2094951A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| US5367559A (en) | 1994-11-22 |
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