JP3930055B2 - Method and apparatus for performing handoff between communication systems having different multiple access schemes - Google Patents

Method and apparatus for performing handoff between communication systems having different multiple access schemes Download PDF

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JP3930055B2
JP3930055B2 JP54805498A JP54805498A JP3930055B2 JP 3930055 B2 JP3930055 B2 JP 3930055B2 JP 54805498 A JP54805498 A JP 54805498A JP 54805498 A JP54805498 A JP 54805498A JP 3930055 B2 JP3930055 B2 JP 3930055B2
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signal
multiple access
communication system
access communication
ma
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JP2001524289A (en
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ロッシュ,ジェイソン・ヘインズ
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モトローラ・インコーポレイテッド
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Priority to US08/841,879 priority
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Priority to PCT/US1998/005047 priority patent/WO1998050909A1/en
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/24Reselection being triggered by specific parameters used to improve the performance of a single terminal
    • H04W36/30Reselection being triggered by specific parameters used to improve the performance of a single terminal by measured or perceived connection quality data
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/14Reselecting a network or an air interface

Description

Field of Invention
The present invention relates generally to wireless communication systems, and more particularly to improved methods and systems for performing handoffs between cellular communication systems having different multiple access schemes.
Background of the Invention
In order to maximize utilization and reuse of the radio frequency spectrum, wireless communication systems employ various schemes that allow multiple users to access communication resources simultaneously or nearly simultaneously. For example, in a cellular telephone system, many cellular subscribers use a wireline communication resource (ie, a public switched telephone network (PSTN)) via various air interfaces that allow multiple subscriber connections. ) Is permitted.
Multiple access schemes are used to provide communication resources such as radio frequency spectrum by assigning combinations of transmission or reception time, channel frequency, channel bandwidth, channel code, transmission or reception position, etc. It can be defined as a series of rules. Examples of well-known multiple access schemes include AMPS (Advanced Mobile Phone System), NAMPS (Narrowband AMPS), TACS (Total Access Communication System), GSM (Global System for Mobile Communications), TDMA (Time Division Multiple Access: Time Division). Multiple Access) and CDMA (Code Division Multiple Access). Many of these multiple access schemes are well documented in industry standards distributed by Cellular Telecommunications Industry Association (CTIA), TIA (Telecommunication Industry Association) and other standards bodies. One example is the standard IS-95 for code division multiple access cellular communication systems.
As newer multiple access schemes are employed, the coverage areas of new multiple access systems are not as prevalent as traditional established communication systems that utilize different multiple access schemes. Therefore, to provide a wider communication service area for subscribers using the new multiple access method, subscribers can receive services from the new multiple access system and move out of the coverage of the new multiple access system. Then, dual mode subscriber units have been developed so that the subscriber units can communicate with legacy or other multiple access systems.
With reference to FIG. 1, a typical relationship between the coverage of a communication system employing a first multiple access scheme and the coverage of a communication system employing a second multiple access scheme is shown. Specifically, the cellular cover area 20 of FIG. 1 includes a code division multiple access (CDMA) scheme indicated by a hexagonal cell 22 and a separate cell indicated by a circular cell 24 for clarity. 1 shows a cellular system utilizing multiple access (MA) scheme. The boundary between the area covered by the CDMA cell 22 and the area covered by another MA is indicated by a border line 26 represented by a thick line.
As subscriber 28 moves between CDMA cells 22, CDMA base station controller 30 monitors or manages handoffs between CDMA cells 22. Similarly, when the subscriber 28 moves between different MA cells 24, the different MA base station controller 32 monitors or manages handoffs between the different MA cells 24. Handoff is a process in a cellular communication system for switching traffic channels from communication in one cell to communication in another cell.
The problem solved by the present invention arises when a communication system utilizing a first MA desires to handoff a subscriber to a communication system utilizing a second MA. This problem occurs when the subscriber 28 moves from the CDMA cell 22 over the boundary line 26 to another MA cell 24 in FIG. Also, for example, when the first MA communication system wishes to hand off the subscriber 28 to another MA cell 24 that has coverage in the area covered by the first MA communication system, the subscriber 28 crosses the boundary 26. Problems arise even if not.
In the prior art, for example, if the first MA is CDMA, a pilot beacon is used to alert the CDMA base station controller 30 that the subscriber 28 is approaching the end of CDMA coverage (ie, the boundary 26). (Pilot beacon) 34 is used. As used herein, the pilot beacon 34 refers to a transmission signal that is defined in the first MA, ie, the MA that is the source of handoff, or that is generally received by components in this first MA. . For example, if the CDMA is the original MA, the pilot beacon 34 is a pilot channel beacon so that another MA cell 24 outside and adjacent to the boundary 26 appears to be another CDMA cell 22. This is because the subscriber 28 reports the presence and strength of the pilot beacon 34 to the CDMA base station controller 30 in accordance with the rules of CDMA IS-95, so that the inter-MA base station controller communication link. ) 36 can negotiate a handoff with another MA base station controller 32. For a more detailed description, see U.S. Pat. No. 5,594,718 issued Jan. 14, 1997.
There are a number of problems with placing pilot beacons 34 in cells adjacent to and outside border 26. First, it is expensive. Each pilot beacon 34 requires a transmitter coupled to an antenna mounted on a suitable structure.
Second, it increases the complexity of the communication system. The CDMA pilot beacon must be synchronized with the rest of the system and identified with a unique timing offset. Also, the power level must be set appropriately.
Third, extra antenna sites must be rented or purchased. These site arrangements may require negotiations with cellular system competitors over the space of the competitor's tower.
Fourth, pilot beacons may be added to the noise floor of a system operated on the same radio frequency band by another licensee.
Fifth, the pilot beacon measured by the first MA communication system or the original MA communication system may not be a good indicator of the communication quality of the radio frequency link utilizing the second MA communication system. That is, the signal quality of a CDMA pilot beacon transmitted from an AMPS at the same location and measured at the subscriber location may not accurately correspond to the AMPS signal quality at the same subscriber location. That is, the AMPS signal may be fading, but the CDMA pilot beacon is not fading. This may be caused by propagation differences between a CDMA pilot signal on one frequency and an AMPS signal on another frequency.
An alternative to pilot beacons for handoff between different MA systems is blind handoff, ie handoff in which the traffic channel conditions in the second MA communication system are not known in advance. This alternative method is prone to dropped calls. Also, in more than one cell, when the second MA communication system handles a traffic channel, there is no intelligent choice as to which is a good handoff candidate.
For the above reasons, there is a need for an improved method and apparatus for performing handoffs between communication systems having different multiple access schemes.
[Brief description of the drawings]
The novel features believed characteristic of the invention are set forth in the appended claims. However, the invention itself, its preferred form of use, further objects and advantages will best be understood by referring to the following detailed description of an example embodiment, taken in conjunction with the accompanying drawings. .
FIG. 1 shows a sample coverage area provided by two communication systems utilizing two different multiple access schemes where the handoff between two systems utilizes a pilot beacon according to the prior art.
FIG. 2 is a high level block diagram of an apparatus for performing handoffs between different multiple access communication systems in accordance with the method and system of the present invention.
FIG. 3 illustrates another embodiment of an apparatus for performing handoffs between different multiple access communication systems in accordance with the method and system of the present invention.
FIG. 4 shows a high level block diagram of a code division multiple access system for performing handoff with another MA communication system by the method and system of the present invention.
FIG. 5 is a more detailed block diagram of a first embodiment of a signal characteristic measurement circuit that can be used to implement the method and system of the present invention.
FIG. 6 shows a second embodiment of a signal characteristic measurement circuit that can be used to implement the method and system of the present invention.
FIG. 7 is a high level logic flow diagram illustrating a method for performing a handoff with another MA communication system in accordance with the present invention.
FIG. 8 is a more detailed flowchart illustrating the process of subscriber unit initialization according to the present invention.
FIG. 9 is a more detailed flowchart illustrating a process for measuring signal characteristics in another MA communication system according to the present invention.
FIG. 10 is a more detailed flowchart illustrating a process for constructing a receiver to measure signal characteristics in another MA communication system according to the present invention.
Detailed Description of the Invention
Referring now to the drawings, and in particular to FIG. 2, a high level block diagram of an apparatus for performing handoffs between different multiple access communication systems according to the method and system of the present invention is shown. As shown, the subscriber unit 50 is generally configured by a first multiple access transceiver 52 and a second multiple access transceiver 54, both of which are coupled to an antenna 56. The first MA transceiver 52 is adapted to communicate with cells in the first communication system utilizing a first multiple access scheme. Similarly, the second MA transceiver 54 is adapted to communicate with cells in the second communication system utilizing a second multiple access scheme. An appropriate duplexer (not shown) may be utilized to distinguish the transmitted signal from the received signal. The frequency of the first MA transceiver 52 is controlled by the local oscillator 58, and the frequency of the second MA transceiver 54 is controlled by the local oscillator 60. Both local oscillators 58 and 60 can be set to a selected frequency by a command or signal from the control circuit 62.
In the embodiment of FIG. 2, a second MA measurement circuit 64 is shown. The second MA measurement circuit 64 has an input coupled to the antenna 56 and a measurement output coupled to the control circuit 62. Have. The second MA measurement circuit 64 receives a control signal from the control circuit 62 via the control line.
Referring back to first MA transceiver 52, downlink traffic 66 may be output from first MA transceiver 52 and coupled to control circuit 62 and clock 68. Downlink traffic 66 may include control information, clock or synchronization information and voice data or other data for processing by circuitry within the subscriber unit (not shown).
Uplink traffic 70 is an input signal of the first MA transceiver 52. Uplink traffic 70 may include voice or other subscriber data as well as control information from control circuit 62.
Second MA transceiver 54 may similarly include an output for downlink traffic 72 and an input for uplink traffic 74. Both downlink traffic 66, 72 and uplink traffic 70, 74 are processed in the portion of subscriber unit 50 (not shown) in a manner well known in the cellular subscriber unit arts to provide voice or computer data communication services. To provide either.
In operation, subscriber unit 50 communicates with cells in the first multiple access communication system via transceiver 52. Subscriber unit 50 is instructed to tune first MA transceiver 52 to a specific frequency set or derived from local oscillator 58. Periodically, the control circuit 62 can receive an instruction to initiate a process for switching to or handing off a traffic channel in the second multiple access communication system. When such a command is received, the control circuit 62 causes the second MA measurement circuit 64 to measure the signal characteristics of the signal from the second MA communication system. Such signal characteristics are generally signal strength. The second MA signal characteristic is measured to determine whether a handoff can be successful between the first MA communication system and the second MA communication system. The measurement of the second MA signal is generally performed at a predetermined time by the clock 64, and preferably at a time to avoid interruption of the downlink traffic 66 or the uplink traffic 70. The second MA measurement circuit reports a characteristic measurement signal to the control circuit 62. The control circuit 62 then determines whether and how to report the second MA signal characteristic measurement to the first MA base station controller via the uplink traffic 70 and the first MA transceiver 52.
The number of measurements of the second MA measurement circuit 64 is controlled by the frequency of the local oscillator 60, and this frequency can be set by the control circuit 62.
When the second MA signal measurement report is received by the base station controller in the first MA communication system, the base station controller can determine that the handoff to the second MA communication system is appropriate and successful. Alternatively, this handoff determination can be made by the subscriber unit, in which case the subscriber requests the first MA base station controller to schedule a handoff.
A subscriber handoff to the second MA communication system is initiated by a command received via the antenna 56 and the first MA transceiver 52. At the agreed time, the control path 62 switches downlink traffic and uplink traffic at the subscriber unit 50 from the first MA transceiver 52 to the second MA transceiver 54, thereby from the first MA communication system to the second MA communication system. Complete the handoff.
Referring now to FIG. 3, another embodiment of an apparatus for performing handoffs between different multiple access communication systems according to the method and system of the present invention is shown. In the present embodiment, measurement of signals from the second multiple access communication system is performed by the second MA transceiver 80. Such a measurement is performed by RSSI (Receive Signal Strength Indicator) as incorporated in many AMPS transceivers. In order to correctly perform the second MA signal characteristic measurement, the control circuit 62 can pass control information to the second MA transceiver 80. Such control information includes gain setting, frequency, frequency range, type of multiple access signal to be measured, time slot information, and timing of second MA signal measurement.
The embodiment of FIG. 3 also includes a single local oscillator 82. Accordingly, the transceivers 52, 80 of both the first and second MA communication systems share the same local oscillator 82, which is under the control of the control circuit 62. The local oscillator 82 must be able to switch quickly between two frequencies and settle in a short time so that the second MA signal characteristics can be measured without significant disruption of downlink traffic 66 or uplink traffic 70. Don't be.
Referring now to FIG. 4, a high level block diagram of a code division multiple access (CDMA) system for performing handoff with another communication system according to the method and system of the present invention is shown. As shown, subscriber unit 90 includes an antenna for transmitting and receiving signals from cells in both CDMA and other MA communication systems. In this example, the separate MA communication system is a communication system using a multiple access method different from CDMA. The CDMA receiver 92 includes a downconverter 94, a gain control 96, a filter 98, an analog / digital (A / D) converter 100, a despreader 102 and a CDMA demodulator 104 through a CDMA downlink traffic path. Including.
The down converter 94 performs frequency conversion from the radio frequency signal at the antenna 56 to a lower intermediate frequency that is sent to the gain control 96. Local oscillator 108 provides an input reference frequency for downconverter 44.
The gain control 96 can be constructed with a variable gain amplifier that operates under the control of a signal from the control circuit 110.
The A / D converter 100 converts the analog signal into a digital word sampled at discrete times.
Such a digital word is input to a despreader 102 where the digital word is multiplied by a despread code from a despreading code source 112 during normal CDMA operation.
In accordance with an important aspect of the present invention, despreader signal 114 is selected by despreader signal selector 116 under the control of control circuit 110. When despread code source 112 is selected to provide a despreader signal, the output of despreader 102 is sent to CDMA demodulator 104, which operates in the normal CDMA demodulation mode for CDMA. A downlink traffic signal 106 is provided. In the measurement mode, the despreader signal selector 116 selects the despreader signal 114 from another signal source 118. Therefore, when a signal from another signal source 118 is input to the despreader 102, the output of the despreader 102 is sent to the signal characteristic measurement circuit 120. The signal characteristic value 122 generated by the signal characteristic measurement circuit 120 is input to the control circuit 110. Two embodiments of the signal characteristic measurement circuit 120 will be described below with reference to FIGS.
Also provided to the control circuit 110 are a reference level 124, a control signal 126, a clock 128, and optionally a measurement signal 130 from another MA transceiver 132.
CDMA transmitter 134 is coupled to antenna 56 for transmitting CDMA uplink traffic 136. The CDMA transmitter 134 operates under the control of the signal from the control circuit 110.
The separate MA transceiver 132 is coupled to the antenna 56 for receiving downlink traffic 138 and transmitting uplink traffic 140 according to the rules of another MA scheme. The separate MA transceiver 132 operates under the control of a signal from the control circuit 110. Such control signals may include the frequency of the separate MA transceiver 132, the type of MA utilized by the separate MA transceiver 132, and switching to downlink traffic 138 and uplink traffic 140 transmitted and received via the separate MA transceiver 132. Exact timing as well as other similar controls.
In operation, control circuit 110 receives a command via CDMA downlink traffic 106 to initiate a handoff procedure to another MA communication system. However, before the handoff is performed, the signal from the MA communication system is measured and reported to the CDMA base station controller. In the embodiment shown in FIG. 4, the CDMA receiver 92 operates in two modes: a normal CDMA demodulation mode and another MA signal measurement mode.
In the normal CDMA demodulation mode, the despreader signal selector 116 selects a signal from the despread code source 112 for the despreader signal 114 that is input to the despreader 102. In this mode, normal CDMA downlink traffic 106 is output by CDMA demodulator 104. Such CDMA downlink traffic 106 may include control signals 126 and timing signals or queues that are input to control circuit 110 and clock 128, respectively.
In the separate MA signal measurement mode, the despreader signal selector 116 selects a signal from the separate signal source 118 for the despreader signal 114 input to the despreader 102. The output of the despreader 102 is used by the signal characteristic measurement circuit 120 to measure the signal characteristic of a signal from another MA system. The signal characteristic value 122, that is, the result of the measurement, is input to the control circuit 110 and can be compared with a reference level that is called from the reference level 124 or calculated by the reference level 124. Based on the agreed reporting conditions, the control circuit 110 reports such a comparison to the CDMA base station controller 30 (see FIG. 1) via the CDMA transmitter 134. Once the data associated with the handoff decision is collected, a decision for handoff is made at either the subscriber unit, base station controller or other location, and the particular location or functional unit making this decision is the system It is up to the designer.
When instructed to perform a handoff between communication systems, the subscriber unit 90 utilizes the CDMA downlink traffic 106 and the CDMA uplink traffic 136, and thus another MA downlink traffic 138 and another MA. Switch to using uplink traffic 140.
Referring now to FIG. 5, a more detailed block diagram of a first embodiment of a signal characteristic measurement circuit that can be utilized in implementing the method and system of the present invention is shown. As shown, the signal characteristic measurement circuit 120 includes a narrowband filter 150, a power measurement function 152, and an integrator 154. Therefore, the output of the signal characteristic measuring circuit 120 becomes an estimated power level integrated over a certain time period. Such a power level value can be compared with a reference level in the control circuit 110. If signal characteristic measurement circuit 120 measures a signal from a single AMPS communication system channel, narrowband filter 150 can be tuned to the AMPS channel bandwidth, which is 30 kHz.
Referring now to FIG. 6, there is shown a second embodiment of a signal characteristic measurement circuit that can be used to implement the method and system of the present invention. As shown, this second embodiment of the signal characteristic measurement circuit 120 includes a wideband filter 156 and a frequency analysis circuit 158. In operation, the wideband filter 156 can be configured to receive a frequency range covering, for example, several AMPS channels. A frequency analysis circuit 158 can be used to perform a Fourier transform on the filtered signal. Such a Fourier transform can indicate multiple AMPS frequencies from multiple AMPS base stations, any one of which can be selected as the destination base station for handoff from the CDMA system to the AMPS system. .
Prior to measurement by the signal characteristic measurement circuit 120 shown in FIG. 5 or FIG. 6, it may be necessary to set an appropriate gain in the gain control 96 (see FIG. 4). Depending on which measurement circuit is used and which multiple access system is being measured, the control circuit 110 can set the gain control 96 in an appropriate manner so that a valid measurement can be made.
Referring now to FIG. 7, there is shown a high level logic flowchart illustrating a method for performing a handoff with another communication system according to the present invention. As shown, the process begins at block 200 and then proceeds to block 202 where the process initializes the subscriber unit. This initialization process transfers parameters and negotiates protocols between the base station controller and the subscriber unit. Such an initialization process is described in more detail below with reference to FIG.
The subscriber unit then measures the signal characteristics of the signal from another multiple access communication system, as shown in block 204. Such a measurement can be performed by a separate MA transceiver in the subscriber unit, as shown in FIG. 3, or by a separate MA measurement circuit in the subscriber unit, as shown in FIG. Yet another method of measuring another MA signal utilizes a current MA receiver, as shown in FIG. 4, where the CDMA receiver can be reconfigured to measure the signal at another MA, such as AMPS.
After measuring another MA signal, the subscriber unit optionally measures the signal characteristics of the signal from the current MA communication system, as shown in block 206. In some communication systems, this step may be omitted because the signal characteristics of the signal from the current MA system are irrelevant to the handoff decision. However, some systems may be designed to compare the signal characteristics of a signal from another MA with the signal characteristics of a signal from the current MA.
After making the appropriate signal measurements, the subscriber unit reports these signal characteristic measurements to the base station controller as shown in block 208. Conditions for reporting signal characteristic measurements may be negotiated during the initialization procedure at block 202. If a certain threshold is exceeded, only some measurements may be reported, where the absence of a signal characteristic report is interpreted as a measurement of a value below the threshold.
Note that the step of block 208 may not be necessary if the system is designed to let the subscriber determine when and where to handoff, in which case the subscriber instead of reporting signal measurements, Request to hand off.
After all signal characteristic measurements have been reported to the current MA base station controller, the process determines whether a handoff to another MA communication system should be attempted, as shown in block 210. If for any reason a handoff attempt should not be made, the process iteratively returns to block 204 to update the signal measurement. If the system determines that a handoff from the current MA communication system to another MA communication system is to be performed, the process determines whether another MA system can accept the subscriber traffic, as shown at block 212.
If another system cannot accept the subscriber traffic, the process recursively returns to block 204 where the measurement is updated. If another MA communication system can accept the subscriber traffic, the process coordinates the handoff with another MA communication system, as shown at block 214. This step can be performed by communication between the current MA base station controller and another MA base station controller via the MA base station controller-to-controller communication link 36 (see FIG. 1). The handoff adjustment may include parameters such as a channel destination frequency and a specific time for handoff in another MA communication system.
After adjusting the handoff, the process performs a subscriber handoff from the current MA communication system to another MA communication system, as shown at block 216. Similar to handoffs between cells in any cellular communication system, handoffs between communication systems with different MAs should be done quickly so that the subscriber traffic channel is not severely interrupted.
The process of performing a handoff from the communication system having the first MA to the communication system having the second MA ends at block 218.
Referring now to FIG. 8, a more detailed flow chart illustrating the process of initializing a subscriber unit according to the present invention is shown. As shown, the initialization procedure begins at block 300 and then proceeds to block 302 where the process sends another MA communication system type to the subscriber. This step is implicit if the subscriber unit is designed to handoff only to another communication system type. Another communication system type may specify, for example, an AMPS system, a TDMA system, a GSM system, or any other standardized multiple access system.
After receiving another MA communication system type, the process transmits a frequency list or frequency range used by another MA communication system, as shown in block 304. The frequency list may include, for example, a list of control channel frequencies used in each base station in the AMPS system. Alternatively, a frequency range may be specified, where the signal strength or other signal characteristics of some frequencies within this range can be reported to the base station controller.
The subscriber unit then receives reporting conditions for reporting signal measurements from another MA communication system, as shown in block 306. Such a report condition may include an instruction not to report a signal characteristic from another MA that falls below a threshold. Thus, the absence of a response to a report request can be interpreted by the base station controller as a measurement of a value below the agreed threshold. The reason for such reporting conditions is to reduce reporting traffic between the subscriber unit and the base station controller.
Thereafter, the process negotiates the timing of another MA signal measurement with the current MA communication system, as shown in block 308. As a result of such negotiation, the measurement can be performed at predetermined time intervals, or can be performed only when requested.
The initialization process then ends as indicated at block 310.
Referring now to FIG. 9, there is shown a more detailed flowchart illustrating the process of measuring signal characteristics or signals in another MA communication system according to the method of the present invention. As shown, the process begins at block 400 and then proceeds to block 402 where the process determines whether it is time to measure the signal characteristics of a signal from another MA communication system. If it is not time to make a measurement, the process repeats iteratively until it is time to make a measurement. The measurement time may be set at a predetermined interval or may be set only in response to a request from a base station in the current MA communication system. The time for performing another MA communication system measurement may be negotiated during the initialization procedure as described with reference to FIG.
If it is time to make signal characteristic measurements of signals from another communication system, the process builds a subscriber unit for another MA signal measurement, as shown in block 404. In some embodiments of the present invention, this construction process may prepare the signal characteristic circuit 120 to perform measurements and set each filter and gain adjustment so that the measurement circuit performs valid measurements. This subscriber building process will be described in more detail with reference to FIG. 10 below.
Next, the process measures the signal characteristics of the signal from another MA communication system, as shown in block 406. In the preferred embodiment, this signal characteristic is signal strength. Depending on the architecture of the subscriber unit, signal measurements can be made with a special construction of the current MA demodulator, with a dedicated receiver that receives another MA signal, or with the receiver of another MA transceiver. Also good. These various subscriber architectures have been described with reference to FIGS.
After making the signal characteristic measurements, the process reconstructs the subscriber unit for normal operation in the current MA communication system, as shown at block 408. If the circuitry used to measure the signal characteristics is not completely independent of the current MA transceiver, the time period between block 404 and block 408 should be minimized so that subscriber traffic is not significantly interrupted. It is.
After rebuilding the subscriber unit for normal demodulation in the current MA communication system, the process determines whether another MA signal measurement was valid, as shown at block 410. If the measurement is valid, the process ends as shown in “Return” block 412. Alternatively, if the measurement was not good, the process adjusts the measurement construction parameters, such as the filter and gain settings, as shown in block 414. The process then returns iteratively to block 402 to wait for another measurement time. For obvious reasons, the subscriber unit is returned to normal operation while waiting for the next opportunity to make a measurement.
Referring now to FIG. 10, a more detailed flow chart illustrating a process for constructing a receiver to measure signal characteristics in another MA communication system according to the method of the present invention is shown. As shown, the process begins at block 500 and then proceeds to block 502 where the process interrupts code division multiple access speech and listening, ie, modulation and demodulation. Note that the process described with respect to FIG. 10 is particularly relevant for CDMA receivers used to perform signal characteristic measurements of signals from another MA communication system, such as the CDMA receiver shown in FIG. I want to be.
Next, the process sets a local oscillator frequency to receive another MA communication system frequency, as shown in block 504. This step can be used to set the local oscillator 108 by a control signal from the control circuit 110 in the subscriber unit 90 shown in FIG.
After setting the local oscillator, the process sets the signal gain and filter to receive signals from another MA communication system, as shown in block 506. Similarly, control circuit 110 may send a signal to gain control 96 and filter 98 in preparation for measuring a signal from another MA communication system.
Note that steps 504 and 506 may be to build a tuner to receive signals from another MA system. Such a tuner is indicated by reference numeral 142 in FIG. The process then selects another despread signal for use with the CDMA despreader, as shown in block 508. Referring to FIG. 4, this step can be accomplished by switching the despreader signal selector 116 to a different signal source position so that the despreader signal 114 comes from another signal source 118. The separate signal source 118 may be a series of “0” or “1”, which is a constant value signal that interrupts the despreading operation in the despreader 102.
After selecting another despread signal, the process enables another MA signal characteristic measurement circuit, as shown in block 510. This step is accomplished by clearing the register or resetting the signal characteristic measurement circuit 120. Thereafter, the construction process ends as indicated at block 512.
When building a subscriber unit having an architecture such as that shown in FIG. 3, the build process can execute blocks 502, 504, 506 and then proceed to block 510 to enable the measurement circuitry in the second MA transceiver 80. . In the subscriber unit having the architecture shown in FIG. 2, the measurement construction process can execute step 506 and then jump to step 510 to perform measurement with the second MA measurement circuit 64. Setting the local oscillator is not necessary because the measurement circuit uses an independent local oscillator 60.
In summary, the above invention allows a handoff from a first multiple access communication system to a second multiple access communication system, where a dual mode subscriber unit receives signals from the second multiple access system at the subscriber unit. Assist handoff by measuring. There is no need for multiple pilot beacons to transmit signals in the MA scheme of the first multiple access communication system, thus reducing the infrastructure cost required to enable intersystem handoff.
Although some of the specific examples above relate to handing off a subscriber unit from a CDMA system to an AMPS system, the principles and basic architecture of the present invention is from any MA communication system to any other MA communication. Can be used to perform a handoff to the system.
For various means of measuring different MA signal characteristics, a subscriber system utilizing independent measurement circuits, a subscriber unit sharing a local oscillator circuit between transceivers for different MAs, and signals of signals from different MA communication systems A description has been given, including a subscriber unit that utilizes a reconstructed CDMA receiver to measure characteristics. In such a CDMA receiver, the despreading operation is interrupted, and another signal passing through the despreader can be analyzed by integrating power in a narrow band or analyzing a wideband frequency spectrum. Can be set.
In some embodiments of the present invention, the separate signal source 118 may be a special signal that improves the measurement of the separate MA signal, or a signal having a known characteristic. For example, such a signal may include a plurality of discrete frequencies that can be used to detect the power of a plurality of separate MA signals.
The foregoing description of the preferred embodiment of the present invention has been presented for purposes of illustration. This is inclusive and is not intended to limit the invention to the precise form. Modifications or variations are possible in light of the above teaching. The embodiments can best utilize the principles of the invention and its practical application, and can be used by those skilled in the art in various embodiments and with various modifications suitable for the particular application envisaged. Was chosen and explained. Any such modifications and variations are within the scope of the invention as determined by the claims when interpreted in accordance with the fair, legal and legitimate scope.

Claims (9)

  1. A method in a cellular communication system for performing a subscriber handoff from a first multiple access communication system to a second multiple access communication system comprising:
    Measuring a signal characteristic of a signal from the second multiple access communication system and generating a signal characteristic value from a subscriber unit communicating with the first multiple access communication system, the first multiple access communication system; And the subscriber unit communicates according to a first multiple access scheme, and the signal from the second multiple access communication system for generating the signal characteristic value is a second multiple access different from the first multiple access scheme. Communicating to the subscriber unit according to a scheme;
    Configuring the subscriber unit to communicate with the second multiple access communication system in response to the signal characteristic value; and
    Performing a subscriber handoff from the first multiple access communication system to the second multiple access communication system when the subscriber unit is configured to communicate with the second multiple access communication system;
    A method comprising the steps of:
  2. The method for performing a subscriber handoff according to claim 1, wherein the signal characteristic is signal strength.
  3. The first multiple access communication system is a code division multiple access system, wherein the subscriber unit includes a despreader that utilizes a despread signal, and the steps of measuring signal characteristics include:
    Selecting another despread signal different from the despread signal for use in the despreader;
    Passing a signal from the second multiple-access communication system through the despreader; and measuring the signal characteristic of the signal from the second multiple-access communication system to generate the signal characteristic value ;
    The method for performing a subscriber handoff according to claim 1, further comprising:
  4. 4. A method for performing a subscriber handoff according to claim 3, wherein the other despread signal comprises a constant value despread signal.
  5. The another despread signal includes a signal having a plurality of preselected discrete frequencies for measuring the power of the plurality of signals in the second multiple access communication system having different frequencies. A method for performing a subscriber handoff according to claim 3.
  6. The step of measuring a signal characteristic of a signal from the second multiple access communication system and generating a signal characteristic value performs a frequency analysis of the signal from the second multiple access communication system, and a signal power in a frequency range The method for performing a subscriber handoff according to claim 3, further comprising generating a value.
  7. In response to the signal characteristic value, the step of configuring the subscriber unit to communicate with the second multiple access communication system is responsive to the signal characteristic value exceeding a predetermined threshold, The method for performing a subscriber handoff according to claim 1, further comprising configuring the subscriber unit to communicate with a two-multiple access communication system.
  8. Measuring a signal characteristic of a signal from the first multiple access communication system from the subscriber unit to generate a first system signal characteristic value;
    Comparing the signal characteristic value with the first system signal characteristic value; and in communication with the second multiple access communication system in response to the signal characteristic value exceeding the first system signal characteristic value. Building the subscriber unit;
    The method for performing a subscriber handoff according to claim 1, further comprising:
  9. In response to the signal characteristic value, the step of constructing the subscriber unit to communicate with the second multiple access communication system communicates with the second multiple access communication system in response to the signal characteristic value. The subscriber handoff of claim 1, further comprising: switching subscriber uplink and downlink traffic from the first multiple access transceiver to the second multiple access transceiver. Way for.
JP54805498A 1997-05-05 1998-03-13 Method and apparatus for performing handoff between communication systems having different multiple access schemes Expired - Lifetime JP3930055B2 (en)

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US84187997A true 1997-05-05 1997-05-05
US08/841,879 1997-05-05
PCT/US1998/005047 WO1998050909A1 (en) 1997-05-05 1998-03-13 Subscriber handoff between multiple access communications system

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WO1998050909A1 (en) 1998-11-12
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IL132358D0 (en) 2001-03-19
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GB2339999B (en) 2002-02-13
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DE19819423A1 (en) 1998-11-12
GB2339999A (en) 2000-02-09
BR9808711A (en) 2000-07-11
FR2763195B1 (en) 2003-09-26
BR9808711B1 (en) 2011-05-31
CN1255225A (en) 2000-05-31
TW392397B (en) 2000-06-01
SE517614C2 (en) 2002-06-25
FI117420B1 (en)
CA2288713A1 (en) 1998-11-12

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