WO1994001974A1 - A method of performing mobile assisted hand-off in a communication system - Google Patents

A method of performing mobile assisted hand-off in a communication system Download PDF

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Publication number
WO1994001974A1
WO1994001974A1 PCT/US1993/005621 US9305621W WO9401974A1 WO 1994001974 A1 WO1994001974 A1 WO 1994001974A1 US 9305621 W US9305621 W US 9305621W WO 9401974 A1 WO9401974 A1 WO 9401974A1
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Prior art keywords
signals
steps
hand
receiver
power levels
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Application number
PCT/US1993/005621
Other languages
French (fr)
Inventor
Kamyar Rohani
Walter J. Rozanski, Jr.
Original Assignee
Motorola Inc.
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Filing date
Publication date
Application filed by Motorola Inc. filed Critical Motorola Inc.
Priority to DE4393250T priority Critical patent/DE4393250T1/en
Priority to JP6503310A priority patent/JPH06510654A/en
Publication of WO1994001974A1 publication Critical patent/WO1994001974A1/en

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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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0055—Transmission or use of information for re-establishing the radio link
    • H04W36/0058—Transmission of hand-off measurement information, e.g. measurement reports
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/34—Reselection control
    • H04W36/36—Reselection control by user or terminal equipment
    • H04W36/362—Conditional handover

Definitions

  • the present invention relates, in general, to communication systems and, more particularly, to a method of performing Mobile Assisted Hand-Off (MAHO) in a communication system.
  • MAHO Mobile Assisted Hand-Off
  • the objective of MAHO is to have a subscriber communication unit (e.g. portable, mobile, etc.) measure the power of adjacent cells in a cellular communication system and make hand-off decisions based upon those power measurements. These decisions may be made either by the subscriber unit or the base site. If the base site is to make the decisions, the power measurements are still taken by the subscriber unit and transmitted back to the base site.
  • a subscriber communication unit e.g. portable, mobile, etc.
  • the current methods of performing MAHO require that several measurements be made over multiple time periods in order to obtain information on all of the potential hand- off candidates. Multiple measurements are required because the control signal for each cell is set up to transmit on different frequencies, making it impractical for the receiver to shift between as many as 24 different frequencies (depending upon the reuse pattern) within one time period. This creates a further problem in that by the time the last measurements are made, the first measurements are rendered inaccurate because the subscriber has changed locations. Change of location causes a change in lognormal (sometimes referred to as shadowing caused by buildings) . These changes occur on the order of seconds. Thus, it is desirable to have a measuring scheme which performs averaging over short periods (not more than several seconds) .
  • the present invention consists of a method for performing MAHO in a communication system having a plurality of base sites, each base site having an identifying signal.
  • a ID signal from each base site is transmitted during a synchronized MAHO time frame.
  • the power of each ID signal is measured and the results are used to make a hand-off decision.
  • FIG. 1 is a graphical representation of a portion of a cellular communication system
  • FIG. 2 is a time line of a data stream illustrating a method of performing MAHO
  • FIG. 3 is a time line of a data stream illustrating a method of performing MAHO in accordance with the present invention
  • FIG. 4 is a block diagram of a portion of a receiving circuit for measuring power to be used in making a MAHO decision in accordance with the present invention.
  • FIGS. 5 and 6 are process flow diagrams of a method embodying the present invention.
  • FIG. 1 a graphical representation of a portion of a cellular communication system, generally designated 10, is illustrated.
  • System 10 shows a source cell 11 which is currently servicing a subscriber; and three target cells (T 1 -T 3 ) 12-14 which will be measured to determine hand-off.
  • T 1 -T 3 target cells
  • the number of target cells has been limited to three for discussion purposes. In actual practice, there could be many more cells. In general, depending upon the reuse pattern and any sectors of the cells, the subscriber may be required to measure as many as 24 or more sectors/cells.
  • a time line of a data stream, generally designated 20, illustrating a method of performing MAHO is provided.
  • This data stream is used to describe a MAHO process for a standard Frequency Division Multiple Access (FDMA) system.
  • the receiver in this case a subscriber, will receive standard speech signals in frames 21, 23, and 25. Interspersed within the data stream are MAHO frames 22 and 24.
  • each cell site would broadcast a signal to be used for MAHO purposes on a frequency assigned to each cell according to the frequency reuse pattern.
  • the receiver would adjust its frequency to pick-up and measure as many of the different signals as possible. It should be noted here that there is no requirement that the entire frame be dedicated to MAHO and that other functions, such as signalling, can be implemented in the same frame.
  • FIG. 3 a time line of a data stream, generally designated 30.
  • each cell site is assigned a code.
  • all of the cell sites transmit their respective codes on the same frequency.
  • Data stream 30 illustrates this in a frequency hopping system, although hopping is not required for this invention to function.
  • data stream 30 consists of speech frames 31, 33, and 34. Between each frame, the frequency of the channel (Fi ... F n - ⁇ , F n ) is varied to provide a frequency hopping system.
  • the receiver will go to a MAHO frequency, F x , and receive a signal that contains a mixture of the codes from the various cells. Since the codes are received within one time frame, 32, the hand-off decision can be made from data taken over one frame rather than several. Since all base sites are measured simultaneously, the total number of measurements necessary for making hand-off decisions is reduced. This is important in that it improves cell edge reliability which becomes increasingly important as cells get smaller and mobiles are capable of crossing through a cell in a matter of minutes.
  • Circuit 40 consists of a plurality of cross correlators 41-44 and power measurement means, such as peak magnitude detectors, 46-49; all of which could be implemented in a single digital signal processor (DSP) .
  • DSP digital signal processor
  • each cell transmits its code (e.g. C s for source cell 11, Ci for target cell i, etc.) in a code signal S, Ti, T 2 , etc.
  • code e.g. C s for source cell 11, Ci for target cell i, etc.
  • Each of these code signals are then processed in peak magnitude detectors 45- 49 to determine the power (P s , Pi, etc.) of the code signals. Once the power is determined, it may be used by the subscriber to make a hand-off decision; or, all of the power information can be relayed back to the source base site where the base site will make the decision.
  • the advantage of having the subscriber perform the hand-off decision is in the time and overhead saved.
  • the advantage of having the decision made at the base site is that the decision making process can be redefined by only changing the base site software and not having to adjust each subscriber.
  • FIGS. 5 and 6 flow diagrams of a process, generally designated 50, embodying the present invention are illustrated.
  • the MAHO process begins, for the base site transceiver, at step 51.
  • the transceiver is directed to go to MAHO frequency F x at a MAHO time, T x , step 52.
  • the transceiver then transmits a signal containing the ID
  • the base site After the code is transmitted, the base site then returns to its normal operation, step 54.
  • the subscriber side of process 50 begins at step 56.
  • the process then directs the transceiver of the subscriber to receive on frequency F x at time T x , step 5 .
  • Signal R is received, step 58, which contains all of the code signals which were transmitted by the base sites within the subscribers range. This signal is then cross correlated with their component code signals using cross correlators 41-44 or the like. The resulting signals are then measured to determine their corresponding powers, step 60.
  • the power levels of the code signals measured in step 60 are then used to make a hand-off decision, step 61.
  • This hand-off decision is executed, step 62, before process 50 returns, step 63.
  • the hand-off decision may be to do nothing (i.e. not make a hand-off) because the current source transmitter is the preferred transmitter.
  • a "make-before- break" hand-off system may be employed in which the subscriber will be served by the source and target cells simultaneously as a transition from the source cell to the target cell.
  • the codes should be long - on the order of 16 to 32 bits - having low cross correlation.
  • an orthogonal code set can be tailored for the system. There are two requirements for the short orthogonal code design to work. First, the cells need to be synchronized. Since this is already a requirement of most new systems, this condition is met.
  • the second condition is that the symbol time be much greater than the propagation delay.
  • the propagation delay is approximately 10 ⁇ sec for the case where the propagation path length is two radii. Therefore, a symbol duration much greater than 10 ⁇ sec. (e.g. 10 times the propagation delay) . should be used. This is to keep the symbol times aligned nearly simultaneously in the correlators in the subscriber. If the symbol durations were the same duration as the propagation delays, then codes would be offset and lose the benefit of being orthogonal.
  • each row of the matrix is a code (or pilot sequence) assigned to a particular transmitter.
  • a 32x32 matrix is recommended to allow the subscriber to check the power of all neighboring cells simultaneously.
  • orthogonal pilots by using sine waves of differing frequencies where each cell would be assigned a different frequency.
  • the C s , Ci, C2, C3 inputs to cross correlators 41-44, respectively would be the various frequencies for the sine waves of the cells being measured.
  • the resulting signals would then be processed through peak magnitude devices 46-49, respectively, to determine the power of the received signals. This information would then be used in the same manner as set forth above.
  • the sine wave method would work in substantially the same manner. The only difference being that in step 52, the frequencies to which the base sites transfer would be different for each base site.
  • the ID signal transmitted in step 53 would then be the sine wave transmitted at that frequency.
  • the present method may also be utilized for power control of the subscriber unit. Referring back to FIG. 4, the power P s of the source cell is one of the signals measured during the MAHO process. This power reading can be compared with a standard value to determine the amount of power adjustment needed.

Abstract

During a MAHO time period, each base site broadcasts an identifying signal (53). The subscriber receives a signal containing all of the ID signals within its range (58). The power of each ID signal is then measured (60) and the results are used to make a hand-off decision (61).

Description

A METHOD. OF PERFORMING MOBILE ASSISTED HAND-OFF IN A COMMUNICATION SYSTEM
Field of the Invention
The present invention relates, in general, to communication systems and, more particularly, to a method of performing Mobile Assisted Hand-Off (MAHO) in a communication system.
Background of the Invention
The objective of MAHO is to have a subscriber communication unit (e.g. portable, mobile, etc.) measure the power of adjacent cells in a cellular communication system and make hand-off decisions based upon those power measurements. These decisions may be made either by the subscriber unit or the base site. If the base site is to make the decisions, the power measurements are still taken by the subscriber unit and transmitted back to the base site.
The current methods of performing MAHO require that several measurements be made over multiple time periods in order to obtain information on all of the potential hand- off candidates. Multiple measurements are required because the control signal for each cell is set up to transmit on different frequencies, making it impractical for the receiver to shift between as many as 24 different frequencies (depending upon the reuse pattern) within one time period. This creates a further problem in that by the time the last measurements are made, the first measurements are rendered inaccurate because the subscriber has changed locations. Change of location causes a change in lognormal (sometimes referred to as shadowing caused by buildings) . These changes occur on the order of seconds. Thus, it is desirable to have a measuring scheme which performs averaging over short periods (not more than several seconds) .
Therefore, in order to perform a MAHO function in an efficient manner, there is a need for a method of measuring the received power from a plurality of cell sites in as short a time as possible.
Summary of the Invention
The present invention consists of a method for performing MAHO in a communication system having a plurality of base sites, each base site having an identifying signal. A ID signal from each base site is transmitted during a synchronized MAHO time frame. The power of each ID signal is measured and the results are used to make a hand-off decision.
Brief Description of the Drawings
FIG. 1 is a graphical representation of a portion of a cellular communication system; FIG. 2 is a time line of a data stream illustrating a method of performing MAHO;
FIG. 3 is a time line of a data stream illustrating a method of performing MAHO in accordance with the present invention; FIG. 4 is a block diagram of a portion of a receiving circuit for measuring power to be used in making a MAHO decision in accordance with the present invention; and
FIGS. 5 and 6 are process flow diagrams of a method embodying the present invention.
Detailed Description of the Drawings Referring initially to FIG. 1, a graphical representation of a portion of a cellular communication system, generally designated 10, is illustrated. System 10 shows a source cell 11 which is currently servicing a subscriber; and three target cells (T1-T3) 12-14 which will be measured to determine hand-off. It should be noted here that the number of target cells has been limited to three for discussion purposes. In actual practice, there could be many more cells. In general, depending upon the reuse pattern and any sectors of the cells, the subscriber may be required to measure as many as 24 or more sectors/cells. In FIG. 2, a time line of a data stream, generally designated 20, illustrating a method of performing MAHO is provided. This data stream is used to describe a MAHO process for a standard Frequency Division Multiple Access (FDMA) system. The receiver, in this case a subscriber, will receive standard speech signals in frames 21, 23, and 25. Interspersed within the data stream are MAHO frames 22 and 24. In operation, each cell site would broadcast a signal to be used for MAHO purposes on a frequency assigned to each cell according to the frequency reuse pattern. During MAHO frame 22, the receiver would adjust its frequency to pick-up and measure as many of the different signals as possible. It should be noted here that there is no requirement that the entire frame be dedicated to MAHO and that other functions, such as signalling, can be implemented in the same frame. This would resemble the operation of a Time Division Multiple Access (TDMA) system, except that all of the slots within the frame are received by the same subscriber. Because of the time required to change frequencies and make the measurements, only four to eight measurements (F1-F4 in this example) may be taken during any one frame. Therefore, in the next MAHO frame, 24, the next set of cells/frequencies (F5-F8) would be read. This process would continue until all of the measurements had been made. However, because of the movement of the subscriber and the time needed to make all of the measurements, the reliability of the first data taken becomes more suspect by the time the last data is taken. This can result in inaccurate hand-offs and inefficient use of the system.
Therefore, a system has been developed in which the measurements may be made within one MAHO frame thereby providing accurate and timely data to the hand-off decision maker. This present method is illustrated in FIG. 3 with a time line of a data stream, generally designated 30. In this embodiment, each cell site is assigned a code. At a synchronized time, all of the cell sites transmit their respective codes on the same frequency.
Data stream 30 illustrates this in a frequency hopping system, although hopping is not required for this invention to function. Here, data stream 30 consists of speech frames 31, 33, and 34. Between each frame, the frequency of the channel (Fi ... Fn-ι, Fn) is varied to provide a frequency hopping system. At predetermined times, the receiver will go to a MAHO frequency, Fx, and receive a signal that contains a mixture of the codes from the various cells. Since the codes are received within one time frame, 32, the hand-off decision can be made from data taken over one frame rather than several. Since all base sites are measured simultaneously, the total number of measurements necessary for making hand-off decisions is reduced. This is important in that it improves cell edge reliability which becomes increasingly important as cells get smaller and mobiles are capable of crossing through a cell in a matter of minutes.
Referring now to FIG. 4, a block diagram of a portion of a receive circuit, generally designated 40, for measuring power in accordance with the present invention is illustrated. Circuit 40 consists of a plurality of cross correlators 41-44 and power measurement means, such as peak magnitude detectors, 46-49; all of which could be implemented in a single digital signal processor (DSP) . For the MAHO process, each cell transmits its code (e.g. Cs for source cell 11, Ci for target cell i, etc.) in a code signal S, Ti, T2, etc. When a signal, R, consisting of all of the code signals, is received, it is mixed in cross correlators 41-44 with the codes (Cs, Ci, etc.) to recover the code signals. Each of these code signals are then processed in peak magnitude detectors 45- 49 to determine the power (Ps, Pi, etc.) of the code signals. Once the power is determined, it may be used by the subscriber to make a hand-off decision; or, all of the power information can be relayed back to the source base site where the base site will make the decision. The advantage of having the subscriber perform the hand-off decision is in the time and overhead saved. The advantage of having the decision made at the base site, is that the decision making process can be redefined by only changing the base site software and not having to adjust each subscriber. It should be noted that while a hand-off decision can be made from the information obtained during one MAHO frame; the average of several measurements is typically required in order to remove the effects of changes due to Rayleigh fading. In FIGS. 5 and 6, flow diagrams of a process, generally designated 50, embodying the present invention are illustrated. The MAHO process begins, for the base site transceiver, at step 51. The transceiver is directed to go to MAHO frequency Fx at a MAHO time, Tx, step 52. The transceiver then transmits a signal containing the ID
(e.g. frequency, color code, or pilot pattern) of the cell.
After the code is transmitted, the base site then returns to its normal operation, step 54.
In FIG. 6, the subscriber side of process 50 begins at step 56. The process then directs the transceiver of the subscriber to receive on frequency Fx at time Tx, step 5 .
Signal R is received, step 58, which contains all of the code signals which were transmitted by the base sites within the subscribers range. This signal is then cross correlated with their component code signals using cross correlators 41-44 or the like. The resulting signals are then measured to determine their corresponding powers, step 60.
The power levels of the code signals measured in step 60 are then used to make a hand-off decision, step 61. This hand-off decision is executed, step 62, before process 50 returns, step 63. It should be noted that quite often the hand-off decision may be to do nothing (i.e. not make a hand-off) because the current source transmitter is the preferred transmitter. Alternatively, a "make-before- break" hand-off system may be employed in which the subscriber will be served by the source and target cells simultaneously as a transition from the source cell to the target cell.
To achieve the best results with the above process, the codes should be long - on the order of 16 to 32 bits - having low cross correlation. However, it may not be possible for a system to provide a code of this length during the MAHO time frame. In these situations, an orthogonal code set can be tailored for the system. There are two requirements for the short orthogonal code design to work. First, the cells need to be synchronized. Since this is already a requirement of most new systems, this condition is met.
The second condition is that the symbol time be much greater than the propagation delay. In a system having a cell radius of one mile, the propagation delay is approximately 10 μsec for the case where the propagation path length is two radii. Therefore, a symbol duration much greater than 10 μsec. (e.g. 10 times the propagation delay) . should be used. This is to keep the symbol times aligned nearly simultaneously in the correlators in the subscriber. If the symbol durations were the same duration as the propagation delays, then codes would be offset and lose the benefit of being orthogonal.
A set of orthogonal codes can then be defined for QPSK modulation by equation (1) :
Figure imgf000009_0001
This would provide a two symbol code for two cells. If more are needed, the code and cells can be increased by substituting equation (1) into recursive equation (2) :
Figure imgf000009_0002
where each row of the matrix is a code (or pilot sequence) assigned to a particular transmitter. For MAHO use, a 32x32 matrix is recommended to allow the subscriber to check the power of all neighboring cells simultaneously. Alternatively, it is possible to achieve orthogonal pilots by using sine waves of differing frequencies where each cell would be assigned a different frequency. As set out in FIG. 4, the Cs, Ci, C2, C3 inputs to cross correlators 41-44, respectively, would be the various frequencies for the sine waves of the cells being measured. The resulting signals would then be processed through peak magnitude devices 46-49, respectively, to determine the power of the received signals. This information would then be used in the same manner as set forth above.
With regard to FIGS. 5 and 6, the sine wave method would work in substantially the same manner. The only difference being that in step 52, the frequencies to which the base sites transfer would be different for each base site. The ID signal transmitted in step 53 would then be the sine wave transmitted at that frequency. The present method may also be utilized for power control of the subscriber unit. Referring back to FIG. 4, the power Ps of the source cell is one of the signals measured during the MAHO process. This power reading can be compared with a standard value to determine the amount of power adjustment needed.
Thus, it will be apparent to one skilled in the art that there has been provided in accordance with the invention, a method for performing mobile assisted hand-off that fully satisfies the objects, aims, and advantages set forth above.
While the invention has been described in conjunction with specific embodiments thereof, it is evident, that many alterations, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alterations, modifications, and variations in the appended claims.

Claims

Claims
1. A method of performing MAHO in a communication system comprising the steps of: A) transmitting an ID signal from each of a plurality of transmitters during a time frame;
B) receiving a signal having said plurality of ID signals at a receiver during said time frame;
C) measuring a power level of each of said plurality of ID signals; and
D) using said power levels to make a hand-off decision.
2. The method of claim 1 further comprising the steps of: repeating said steps A-C; and averaging said power level measurements for each of said plurality of ID signals taken in step D.
3. The method of claim 1 wherein said step of using said power levels to make said hand-off decision comprises the steps of: selecting a target transmitter based upon said power levels of said plurality of ID signals; and directing a source transmitter to hand-off said receiver to said target transmitter.
4. The method of claim 1 wherein said step of using said power levels to make said hand-off decision comprises the steps of: transmitting said power levels of each of said plurality of ID signals to a source transmitter; selecting a target transmitter to which said receiver is to be handed-off; and handing-off said receiver from said source transmitter to said target transmitter. 5. A method of performing MAHO in a communication system comprising the steps of:
A) transmitting an ID signal from each of a plurality of base sites during a time frame; B) receiving a signal having said plurality of ID signals at a subscriber during said time frame;
C) measuring a power level of each of said plurality of ID signals;
E) selecting a target transmitter based upon said power levels of said plurality of ID signals; and
F) directing a source transmitter to hand-off said receiver to said target transmitter.
6. The method of claim 5 further comprising the steps of: repeating said steps A-C; and averaging said power level measurements for each of said plurality of ID signals taken in step C.
7. A method of performing MAHO in a time division multiple access (TDMA) communication system comprising the steps of:
A) transmitting an ID signal from each of a plurality of transmitters during a time frame; B) receiving a signal having said plurality of ID signals at a receiver during said time frame;
C) measuring a power level of each of said plurality of ID signals; and
D) using said power levels to make a hand-off decision.
8. The method of claim 7 further comprising the steps of: repeating said steps A-C; and averaging said power level measurements for each of said plurality of ID signals taken in step C. 9. The method of claim 7 wherein said step of using said power levels to make said hand-off decision comprises the steps of: selecting a target transmitter based upon said power levels of said plurality of ID signals; and directing a source transmitter to hand-off said receiver to said target transmitter.
10. The method of claim 7 wherein said step of using said power levels to make said hand-off decision comprises the steps of: transmitting said power levels of each of said plurality of ID signals to a source transmitter; selecting a target transmitter to which said receiver is to be handed-off; and handing-off said receiver from said source transmitter to said target transmitter.
AMENDED CLAIMS
[received by the International Bureau on 8 November 1993 (8.11.93); original claims 1, 2, 10 and 16 amended; remaining claims unchanged (3 pages)]
1. A method of performing MAHO in a communication system comprising the steps of: A) transmitting an ID signal from each of a plurality of transmitters during a time frame;
B) receiving a signal having said plurality of ID signals at a receiver during said time frame;
C) measuring a power level of each of said plurality of ID signals; and
D) using said power levels to make a hand-off decision.
2. The method of claim 1 further comprising the steps of: repeating said steps A-C; and averaging said power level measurements for each of said plurality of ID signals taken in step D.
3. The method of claim 1 wherein said step of using said power levels to make said hand-off decision comprises the steps of: selecting a target transmitter based upon said power levels of said plurality of ID signals; and directing a source transmitter to hand-off said receiver to said target transmitter.
4. The method of claim 1 wherein said step of using said power levels to make said hand-off decision comprises the steps of: transmitting said power levels of each of said plurality of ID signals to a source transmitter; selecting a target transmitter to which said receiver is to be handed-off; and handing-off said receiver from said source transmitter to said target transmitter.
5. A method of performing MAHO in a communication system comprising the steps of:
A) transmitting an ID signal from each of a plurality of base sites during a time frame; B) receiving a signal having said plurality of ID signals at a subscriber during said time frame;
C) measuring a power level of each of said plurality of ID signals;
E) selecting a target transmitter based upon said power levels of said plurality of ID signals; and
F) directing a source transmitter to hand-off said receiver to said target transmitter.
6. The method of claim 5 further comprising the steps of: repeating said steps A-C; and averaging said power level measurements for each of said plurality of ID signals taken in step C.
7. A method of performing MAHO in a time division multiple access (TDMA) communication system comprising the steps of:
A) transmitting an ID signal from each of a plurality of transmitters during a time frame; B) receiving a signal having said plurality of ID signals at a receiver during said time frame;
C) measuring a power level of each of said plurality of ID signals; and
D) using said power levels to make a hand-off decision.
8. The method of claim 7 further comprising the steps of: repeating said steps A-C; and averaging said power level measurements for each of said plurality of ID signals taken in step C.
9. The method of claim 7 wherein said step of using said power levels to make said hand-off decision comprises the steps of: selecting a target transmitter based upon said power levels of said plurality of ID signals; and directing a source transmitter to hand-off said receiver to said target transmitter.
10. The method of claim 7 wherein said step of using said power levels to make said hand-off decision comprises the steps of: transmitting said power levels of each of said plurality of ID signals to a source transmitter; selecting a target transmitter to which said receiver is to be handed-off; and handing-off said receiver from said source transmitter to said target transmitter.
PC17US93/05621 94/01974
15
STATEMENT UNDER ARTICLE 19
In the search report, claims 1, 10, and 16 were indicated as lacking novelty because of Gilhousen (US 5,101,501). The Gilhousen reference describes the process set forth in the background of the present invention. In Gilhousen, a scan receiver is utilized to search out the individual pilot carrier signal codes (column 4, lines 16-26). This is distinguishable from the present invention which, in one time period, will analize the received signal for a plurality of ID signals received in the received signal. Specifically, claims 1, 10, and 16, as amended, each contain the step, inter alia, of
"measuring a power level of each of said plurality of ID signals in said signal received during said time frame". This step is not shown or taught by the Gilhousen reference. Therefore, Applicants contend that claims 1, 10, and 16, and their associated dependent claims, are allowable over the Gilhousen reference.
Many of the remaining claims were indicated as lacking an inventive step based upon Gilhousen and Schmidt (US 4,765,753) and areas of common knowledge in the art. Applicants contend that, based upon the previous argument and the dependency of these claims from dependent claims 1, 10, and 16, that these claims are also allowable over the references .
PCT/US1993/005621 1992-07-01 1993-06-14 A method of performing mobile assisted hand-off in a communication system WO1994001974A1 (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
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US5634192A (en) * 1995-02-23 1997-05-27 Northern Telecom Limited Mobile-assisted handoff technique
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US5634192A (en) * 1995-02-23 1997-05-27 Northern Telecom Limited Mobile-assisted handoff technique
WO1997025827A1 (en) * 1996-01-04 1997-07-17 Siemens Aktiengesellschaft Process and device for data transmission in a cellular radio system
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SE9400667D0 (en) 1994-02-28
FR2693330A1 (en) 1994-01-07
JPH06510654A (en) 1994-11-24
DE4393250T1 (en) 1994-10-20

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