KR20010012229A - Subscriber handoff between multiple access communications system - Google Patents

Abstract

In the cellular communication system method for performing subscriber 28 handoff 216 from a first multiple access communication system to a second multiple access communication system, the subscriber terminal in communication with the first multiple access communication system, The signal characteristic of the signal from the second multiple access communication system is measured 206 to generate a signal characteristic value. In response to this signal characteristic value, the subscriber station is set to communicate with the second multiple access communication system. A subscriber handoff 216 is then performed from the first multiple access communication system to the second multiple access communication system. The signal characteristic value may be signal strength, and the signal characteristic may be measured by the receiver 92 for the first multiple access communication system.

Description

Subscriber handoff between multiple access communication systems {SUBSCRIBER HANDOFF BETWEEN MULTIPLE ACCESS COMMUNICATIONS SYSTEM}

In order to maximize the use and reuse of radio frequencies, wireless communication systems employ various structures that allow multiple users to access communication resources simultaneously or nearly simultaneously. For example, in a cellular telephony system, several cellular subscribers can access to wired communication resources (ie, public switched telephone network (PSTN)) through various air interfaces that enable multiple subscriber connections.

The multiple access structure may be defined as a set of rules for sharing communication resources such as radio frequency spectrum by allocating a combination of transmit / receive time, channel frequency, channel band width, channel code, transmit / receive position, and the like. Well known multiple access structures include AMPS, NAMPS, TACS, GSM, TDMA and CDMA. These multiple access structures are well organized with industry standards proposed by the Cellular Communications Industry Association (CTIA), the Communications Industry Association (TIA), and other standards bodies. One example is the standard IS-95 for code division multiple access cellular communication systems.

When a new multiple access structure is developed, the service area of this new multiple access system is generally not larger than that of the conventional communication system. Therefore, in order to provide a wider communication service area to a subscriber using this new multiple access structure, when the subscriber is provided with a service from the new multiple access system and leaves the service area of the new multiple access system, the subscriber terminal is previously or Dual mode subscriber stations have been developed that enable communication with alternate multiple access systems.

1 illustrates a typical relationship between a service area of a communication system having a first multiple access structure and a service area of a communication system using a second multiple access structure. More specifically, the cellular service area 20 of FIG. 1 is, for convenience of description, a code division multiple access (CDMA) structure shown as a hexagonal cell 22 and an alternative multiple access shown as a circular cell 24. The communication system using the (MA) structure is shown. The boundary between the area covered by the CDMA cell 22 and the area covered by an alternate MA having another MA cell 24 is indicated by the border line 26, shown in bold solid lines.

When the subscriber 28 moves between CDMA cells 22, the CDMA base station controller 30 monitors and manages handoffs between the CDMA cells 22, and the subscriber 28 likewise replaces the alternate MA cell ( When moving between 24), the alternate base station controller 32 monitors and manages handoffs between the alternate MA cells 24. Handoff is a process in which a traffic channel is switched from communication with one cell to communication with another cell in a cellular communication system.

TECHNICAL FIELD The present invention relates to a wireless communication system, and more particularly to an improved method and system for performing handoff between cellular communication systems having different multiple access structures.

1 is a sample service area according to the prior art in two communication systems using two different multiple access schemes, wherein the handoff between the two systems is made using pilot beacons.

2 is a top schematic diagram of an apparatus for performing handoff between different multiple access communication systems, in accordance with the method and system of the present invention.

3 illustrates another embodiment of an apparatus for performing handoff between different multiple access communication systems, in accordance with the method and system of the present invention.

4 is a top schematic diagram of a code division multiple access system for performing handoff with an alternate MA communication system, in accordance with the method and system of the present invention;

5 is a 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.

Figure 6 is a detailed block diagram of a second embodiment of a signal characteristic measurement circuit that can be used to implement the method and system of the present invention.

7 is a high level logic flow diagram illustrating a method for performing handoff with an alternate MA communication system in accordance with the present invention.

8 is a detailed flowchart illustrating a subscriber station initialization process according to the present invention.

9 is a detailed flowchart illustrating a signal characteristic measurement process in an alternative MA communication system according to the present invention.

10 is a detailed flowchart illustrating a receiver setting process for measuring signal characteristics in an alternative MA communication system according to the present invention.

The problem to be solved in the present invention occurs when a communication system using a first MA tries to hand off a subscriber to a communication system using a second MA. This problem occurs in FIG. 1 when the subscriber 28 moves from the CDMA cell 22 across the boundary 26 to the replacement MA cell 24. This problem occurs even when the subscriber 28 does not cross the boundary 26, for example, the subscriber to an alternate MA cell 24 having a service area within the area covered by the first MA communication system. This problem can also occur if one wishes to handoff a.

In the prior art, for example, when the first MA is CDMA, the pilot beacon to inform the CDMA base station controller 30 that the subscriber 28 is nearing the end of the CDMA service area (i.e., borderline 26). 34 is used. As described below, the pilot beacon 34 is a transmission signal defined within the first MA, i.e., the MA that is the source of the handoff, or generally received by an element in the first MA. For example, if the CDMA is the source MA, the pilot beacon 34 is a pilot channel beacon that makes the alternate MA cell 24 proximate the boundary 26 appear to 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, thereby providing an alternate MA base station controller (through the MA base station control period communication link 36). It means making it possible to arrange handoff with 32). See US Pat. No. 5,594,718 to Weaver, Jr. et al., Published January 14, 1997, for more details.

Placing the pilot beacon 34 in a cell adjacent to the perimeter of the boundary 26 presents a number of problems. First, it costs too much. Each pilot beacon 34 requires a transmitter that is connected to an antenna installed on a suitable structure.

Secondly, increase the complexity of the communication system. The CDMA pilot beacons must be synchronized with other elements of the system, must be identified with a specific timing offset, and the power level must be set to an appropriate level.

Third, additional antenna sites must be rented or purchased. Some of these site contracts may require negotiations with cellular system competitors for space on competitor towers.

Fourth, the pilot beacon may add noise floor of the system operating in the same radio frequency band by different licensees.

Fifth, the pilot beacon measured by the first or source MA communication system may not be a good indicator of the communication quality of the radio frequency link using the second MA communication system. That is, the signal quality of the CDMA pilot beacon transmitted from the combined AMPS cell and specified at the subscriber location may not exactly correspond to the AMPS signal quality at the same subscriber location. This is because AMPS signals undergo fading, while CDMA pilot beacons do not. This can be caused by the difference in propagation between the CDMA pilot signal on one frequency and the AMPS signal on the other frequency.

An alternative to using pilot beacons for handoffs between different MA systems is blind handoff. This refers to handoff performed without knowledge of traffic channel conditions within the second MA communication system. However, this alternative can more easily result in dropped calls. In addition, when the second communication MA system manipulates traffic channels in one or more cells, there is no preferred method of selecting which better hand-hop candidates.

For the reasons mentioned above, there is a need for an improved method and apparatus for performing handoff between communication systems having different multiple access structures.

2 is a high schematic diagram of an apparatus for performing handoff between different multiple access communication systems, in accordance with the method and system of the present invention. As shown, subscriber station 50 generally includes a first multiple access transceiver 52 and a second multiple access transceiver 54, both transceivers being coupled to an antenna 56. As shown in FIG. The first MA transceiver 52 is coordinated to communicate with cells in a first communication system using the first multiple access structure, and similarly the second MA transceiver 54 uses a second communication using the second multiple access structure. It is arranged to communicate with the cells in the system. A suitable duplexer (not shown) can be used to separate the transmitted and received signals. 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 oscillators 58 and 60 may be set to a frequency selected by a command or signal from control circuit 62.

In the embodiment of FIG. 2, a second MA measurement circuit 64 is also shown having an input connected to the antenna 56 and a measurement output connected to the control circuit 62. In addition, the second MA measurement circuit 64 receives a control signal through a control line from the control circuit 62.

Looking back at the first MA transceiver 52, downlink traffic 66 is output from the first MA transceiver 52, which is coupled to the control circuit 62 and the clock 68. Downlink traffic 66 may include control information, clock or synchronization information, and other data processed by voice data or other circuitry in the subscriber terminal, not shown.

The uplink traffic 70 becomes the input signal of the first MA transceiver 52, which may include voice or other subscriber data and control information from the control circuit 62.

The second MA transceiver 54 may include an output for downlink traffic 72 and an input for uplink traffic 74 in a similar manner. Both downlink traffic 66 and 72 and uplink traffic 70 and 74 are processed through methods known in the cellular subscriber station technology in the portion of subscriber terminal 50, not shown, to provide voice or computer data communication services. Will be provided.

In operation, subscriber terminal 50 communicates with a cell in a first multiple access communication system via transceiver 52. Subscriber terminal 50 is instructed to tune first MA transceiver 52 to a specific frequency set or derived from local oscillator 58. Periodically, control circuit 62 may receive a command to initiate a switch or handoff process to a traffic channel in a second multiple access communication system. After such a command is received, control circuit 62 causes second MA measurement circuit 64 to measure the characteristics of the signal from the second communication system. Typically, this signal characteristic is signal strength. The second MA signal characteristic is measured to determine if a handoff between the first MA communication system and the second MA communication system has occurred successfully. The measurement of the second MA signal is generally made at a predetermined time according to the clock 68, preferably at a time that avoids interference of the downlink traffic 66 or the uplink traffic 70. The second MA measurement circuit reports the measured signal characteristic to the control circuit 62. The control circuit 62 then reports the measured second MA signal characteristic through the uplink traffic 70 and the first MA transceiver 52 to the first MA base station controller and in what manner. Determine.

The measurement frequency of the second MA measurement circuit 64 is controlled by the frequency of the local oscillator 60 set by the control circuit 62.

Once the report of the second MA signal measurement is received by the base station controller in the first MA communication system, the base station controller determines whether a handoff to the second MA communication system is appropriate and successful. Alternatively, this handoff decision may be made by the subscriber terminal, in which case the subscriber requests the first MA base station controller to plan the handoff.

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 same time, the control circuit 62 switches the down and uplink traffic in the subscriber station 50 from the first MA transceiver 52 to the second MA transceiver 54, thereby from the first MA communication system to the second MA. Complete the handoff to the communication system.

Referring now to FIG. 3, there is shown another embodiment of an apparatus for performing handoff between different multiple access communication systems, in accordance with the method and system of the present invention. In this embodiment, the measurement of the signal from the second multiple access communication system is performed by the second MA transceiver 80. Such measurements are implemented by RSSI (receive signal strength indicator) as included in many AMPS transceivers. To accurately measure the second MA signal characteristic, the control circuit 62 may send control information to the second MA transceiver 80. Such control information includes gain setting, frequency, frequency range, type of multiple access signal being measured, time slot information and timing of the second MA signal measurement.

The embodiment of FIG. 3 also includes one local oscillator 82. Thus, the two transceivers 52 and 80 for the first and second MA communication systems share the same local oscillator under control of the control circuit 62. The local oscillator 82 should be able to quickly switch between the two frequencies so that it can measure the second MA signal characteristic without undue interference with the downlink traffic 66 or the uplink traffic 70 and settle in a short period of time. You should be able to.

4 is a high schematic diagram of a code division multiple access (CDMA) system for performing handoff with an alternate communication system, in accordance with the method and system of the present invention. As shown, subscriber station 90 includes an antenna 56 for transmitting and receiving signals from cells in two systems, CDMA and alternate MA communication systems. In this embodiment, the alternate MA communication system is a communication system using a multiple access structure different from CDMA. CDMA receiver 92 includes downconverter 94, gain controller 96, filter 98, analog-to-D converter 100, spreader 102, and CDMA demodulator. A CDMA downlink traffic path consisting of 104. CDMA downlink traffic 106 is output by CDMA demodulator 104.

The down converter 94 frequency converts the radio frequency signal at the antenna 56 to a lower intermediate frequency and sends it to the gain controller 96. Local oscillator 108 provides an input reference frequency for downconverter 94.

The gain controller 96 may be implemented as a variable gain amplifier that operates under control of the signal from the control circuit 110.

A-to-D converter 100 converts the analog signal into a digital word sampled at discrete time.

This digital word is input to the despreader 102, which is multiplied by the despread code from the despread code source 112 during normal CDMA operation.

According to one important aspect of the invention, the spreader signal 114 is selected by the spreader signal selector 116 under the control of the control circuit 110. When the despread code source 112 is selected to provide a despreader signal 114, the output of the despreader 102 provides a CDMA providing a CDMA downlink traffic signal 106 for operation in a normal CDMA demodulation mode. Direct to demodulator 104. In the measurement mode, the spreader signal selector 116 selects the spreader signal 114 from the alternate signal source 118. Thus, when a signal from the alternate signal source 118 is input to the spreader 102, the output of the spreader 102 is directed directly to the signal characteristic measurement circuit 120. Subsequently, 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 in connection with FIGS. 5 and 6.

In addition, the reference level 124, control signal 126, and clock 128 are provided as inputs to the control circuit 110, and the measurement signal 130 from the replacement MA transceiver 132 is optionally also controlled by the control circuit 110. Is provided as input.

CDMA transmitter 134 is coupled to antenna 56 to transmit CDMA uplink traffic 136. The CDMA transmitter 134 also operates under the control of the signal from the control circuit 110.

Alternate MA transceiver 132 is coupled to antenna 56 for reception of downlink traffic 138 and transmission of uplink traffic 140 in accordance with the rules of the alternate MA structure. The replacement MA transceiver 132 operates under control of the signal from the control circuit 110. These control signals are the frequency of the alternate MA transceiver 132, the type of MA used by the alternate MA transceiver 132, the downlink traffic 138 and the uplink traffic 140 transmitted and received through the alternate MA transceiver 132 rules. Accurate timing, and similar controls for switching to.

In operation, control circuit 110 receives a command to initiate a handoff procedure to an alternate MA communication system via CDMA downlink traffic 106. However, before the handoff is made, signal measurements from the MA communication system are performed and reported to the CDMA base station controller. In the embodiment of Figure 4, the CDMA receiver 92 operates in two modes. That is, normal CDMA demodulation mode and alternative MA signal measurement mode.

In the normal CDMA demodulation mode, the spreader signal selector 116 selects a signal from the spread code source 112 for the spreader signal 114 input to the spreader 102. In this mode, regular CDMA downlink traffic 106 is output by CDMA demodulator 104. The CDMA downlink traffic 106 includes control signals 126 and timing signals or queues that are input to the control circuit 110 and the clock 128, respectively.

In the alternate MA signal measurement mode, the spreader signal selector 116 selects a signal from the alternate signal source 118 for the spreader signal 114 input to the spreader 102. The output of the despreader 102 is then used by the signal characteristic measurement circuit 120 to measure the signal characteristics of the signal from the alternative MA system. The signal characteristic value 122 that is the result of this measurement is input to the control circuit 110 and compared with the reference level called from or calculated by the reference level 124. According to the reporting criteria, the control circuit 110 reports this comparison result to the CDMA base station controller 30 (see FIG. 1) via the CDMA transmitter 134. When data related to the handoff decision has been collected, this handoff decision may be made by the subscriber station, base station controller or some other location. The specific place or functional unit making this decision is up to the system designer.

When instructed to perform a handoff between communication systems, subscriber terminal 90 receives alternate MA downlink traffic 138 and alternates from using CDMA downlink traffic 106 and CDMA uplink traffic 136. Will switch to using MA uplink traffic 140.

5 is a 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. As shown, the signal characteristic measurement circuit 120 includes a narrowband filter 150, a power measurement function 152, and an integrator 154. Thus, the output of the signal characteristic measurement circuit 120 is an estimated power level integrated over a time period. This power level value is compared with the reference signal in the control circuit 110. If the signal characteristic measurement circuit 120 is measuring a signal from one AMPS communication system channel, the narrowband filter 150 is tuned to 30 kHz, which is the bandwidth of the AMPS channel.

Figure 6 shows a detailed block diagram of 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, the second embodiment of this signal characteristic measurement circuit 120 includes a wideband filter 156 and a frequency analysis circuit 158. In operation, wideband filter 156 may be configured to receive a frequency range covering, for example, several AMPS channels. The frequency analysis circuit 158 is used to Fourier transform the filtered signal. This Fourier transform causes several AMPS frequencies to appear from several AMPS base stations, one of which may be selected as the destination base station of the handoff from the CDMA system to the AMPS system.

Before the measurement by the signal characteristic measurement circuit 120 shown in FIG. 5 or FIG. 6, it is necessary to appropriately set the gain in the gain control circuit 96 (see FIG. 4). Depending on the measurement circuit used and on which multiple connection system is measured, the control circuit 110 sets the gain control circuit 96 in an appropriate manner so that valid measurements can be made.

7 is a high level logic flow diagram illustrating a method for performing handoff with an alternate MA communication system in accordance with the present invention. As shown, the process begins at block 200 and proceeds to block 202, which initializes the subscriber station. This initialization process includes the process of parameter transmission and protocol negotiation between the base station controller and the subscriber station. This initialization process will be described in more detail below with reference to FIG. 8.

The subscriber station then measures the signal characteristics of the signal from the alternate multiple access communication system, as described at block 204. This measurement may be performed by an alternative MA transceiver in the subscriber terminal as shown in FIG. 3 or by an alternative MA measurement circuit in the subscriber terminal as shown in the example of FIG. 2. Another way to measure the replacement MA signal is to use a current MA receiver, as shown in FIG. Here, the CDMA receiver can be reconfigured to measure a signal in an alternate MA, such as AMPS.

After measuring the replacement MA signal, the subscriber station optionally measures the signal characteristics of the signal from the current MA communication system, as described at block 206. In some communication systems, this step may be optional because the signal characteristics of the signal from the current MA system may be independent of the handoff decision. However, some systems can be designed to compare the signal characteristics of the signal from the alternate MA with the signal characteristics of the signal from the current MA.

As shown in block 208, after properly measuring the signal characteristics, the subscriber station reports these signal characteristic measurements to the base station controller. Criteria for reporting signal characteristic measurements may be negotiated during the initialization process of block 202. Some measurements may only be reported if they exceed a predetermined threshold, and if no signal characteristic is reported, then values below this threshold may be interpreted as being measured.

It should be noted that if the system is designed to allow the subscriber station to determine when and where to hand off, the step of block 208 may not be necessary. That is, in this case, the subscriber station does not report signal characteristic measurements, but asks whether it will be handled off.

After all signal characteristic measurements are reported to the current MA base station controller, it is then determined whether a handoff should be attempted to the alternate MA communication system, as described in block 210. If no handoff attempt should be made for any reason, the process returns to block 204 to measure signal characteristics again. If the system determines that a handoff should be performed from the current MA communications system to the alternate MA communications system, then the next step is to determine whether the alternate MA system can accept subscriber traffic, as described in block 212. To judge.

If the alternate system cannot accept the subscriber traffic, return to block 204 to update the measurements. If the alternative MA communication system can accommodate the subscriber terminal, then the process then assigns a handoff with the alternative MA communication system as described in block 214. This process is implemented by communication between the current MA base station controller and the alternate MA base station controller via the MA base station controller communication link 36 (see FIG. 1). The assignment of the handoff may include parameters such as the destination frequency of the channel in the alternate MA communication system, the specific handoff occurrence time, and the like.

After the handoff assignment is completed, the next step is to perform subscriber handoff from the current MA communication system to the alternate MA communication system as described at block 216. Like handoffs between cells in any cellular communication system, handoffs between communication systems with different MAs must also be made quickly so that the subscriber traffic channel is not terminated improperly.

Through the above processes, the handoff process from the first MA communication system to the second MA communication system ends at block 218.

8 is a detailed flowchart illustrating a subscriber station initialization process according to the present invention. As shown, the initialization process begins at block 300 and proceeds to the next block 302, where it transmits an alternate MA communication system type to the subscriber. If the subscriber station is designed to be handed off to one other alternative communication system type, this process can be considered concealed. The alternative communication system type may, for example, specify an AMPS system, a TDMA system, a GSM system, or some other standardized multiple access system.

After receiving the alternate MA communication system type, the next process sends a frequency list or frequency range used by the alternate MA communication system as described in block 304. The frequency list includes, for example, a list of frequencies of the control channel used at various base stations in the AMPS system. Alternatively, a frequency range can be specified, where the signal strength or other signal characteristic of some frequencies within that range can be reported back to the base station controller.

Next, as described in block 306, the subscriber terminal receives reporting criteria for reporting signal measurements from the alternate MA communication system. Such reporting criteria may include instructions not to report signal characteristics from alternative MAs below the threshold. Thus, if there is no response to the report request, the base station may interpret it as a value below the threshold. The reason for using such a reporting criterion is that the reporting traffic between the subscriber station and the base station controller can be reduced.

Next, as shown in block 308, the timing of the replacement MA signal measurement is negotiated with the current MA communication system. As a result of this negotiation, the measurements are taken at predetermined time intervals or only when there is a demand.

The initialization process then ends at block 310.

9 is a detailed flowchart illustrating a signal characteristic measurement process in an alternative MA communication system according to the present invention. As shown, the process begins at block 400 and then proceeds to block 402, where it is determined whether or not it is time to measure the signal characteristics of the signal from the alternate MA communication system. If it is not time to measure, the process repeats the loop until the time to measure is reached. The time to be measured may be set at predetermined intervals, or only if requested by the base station controller of the current MA communication system. The alternative MA communication system measurement time may be negotiated during the initialization process of FIG.

If it is time to measure the signal characteristics of the signal from the alternate communication system, then set up the subscriber station for the alternate MA signal measurement, as described in block 404 in the following procedure. In some embodiments of this invention, this setup process prepares the signal characteristic circuit 120 for measurement and also sets various filters and gain adjustments so that the measurement circuit can provide effective measurements. This subscriber setup process will be described in more detail below with reference to FIG. 10.

Next, as described in block 406, the signal characteristics of the signal from the alternate MA communication system are measured. In this embodiment, signal strength is used as such signal characteristic. According to the architecture of the subscriber station, signal measurements are made by the configuration of a particular current MA demodulator or by an assigned receiver that receives an alternate MA signal, or by the receiver portion of an alternate MA transceiver. These various subscriber architectures are described with reference to FIGS. 2-4.

After measuring the signal characteristics, the next procedure is to reset the subscriber station for normal operation of the current MA communication system as described in block 408. If the circuit used to measure signal characteristics is not completely independent of the current MA transceiver, the time period between block 404 and block 408 should be minimized to ensure that subscriber traffic is not unreasonably interrupted.

After resetting the subscriber station for normal demodulation in the current MA communication system, it then determines whether the replacement MA signal measurement was valid as described at block 410. If the measurement is valid, the process ends as shown in block 412. If the measurement is not valid, the next step is to adjust measurement configuration parameters such as filter and gain settings as shown in block 414. Thereafter, the process returns to block 402 to wait for another measurement time. Obviously, the subscriber station will return to normal operation while waiting for the next measurement opportunity.

10 is a detailed flowchart illustrating a receiver setting process for measuring signal characteristics in an alternative MA communication system according to the present invention. As shown, the process begins at block 500 and then proceeds to block 502, where code division multiple access handset, or stop demodulation. It should be noted here that the process described in connection with FIG. 10 is particularly relevant to CDMA receivers used to measure signal characteristics of signals from alternative MA communication systems, such as the CDMA receivers shown in FIG.

In the next process, as shown in block 504, the local oscillation frequency is set to receive the alternate MA communication system frequency. This process can be done by setting the local oscillator 108 using the control signal from the control circuit 110 in the subscriber terminal 90 shown in FIG.

After setting up the local oscillator, the next procedure is to set up a filter and signal gain for receiving signals from the alternate MA communication system, as described in block 506. Similarly, control circuit 110 sends signals to gain control circuit 90 and filter 98 to prepare for signal measurements from an alternate MA communication system.

The process of steps 504 and 506 may be referred to as setting a tuner to receive a signal from an alternate MA system. This tuner is shown by reference numeral 142 in FIG. 4. Next, as shown in block 508, select an alternate spread signal for use in the CDMA spreader. With reference to FIG. 4, this process may be performed by switching the spreader signal selector 116 to an alternate signal source position such that the spreader signal 114 is input from the alternate signal source 118. Alternate signal source 118 may be a series of zeros or ones and produces a constant value signal that stops the despreading operation in spreader 102.

After selecting the alternate spread signal, the next process enables the alternate MA signal characteristic measurement circuit, as described at block 510. This process may be accomplished by clearing the register or by resetting the signal characteristic measurement circuit 120. Thereafter, the setup process ends at block 512.

In order to set up a subscriber station having an architecture as shown in FIG. 3, the setting process performs blocks 502, 504, 506, and then blocks to enable the measurement circuitry in the second MA transceiver 80. FIG. Jump to 510. For a subscriber station with the architecture shown in FIG. 2, the measurement setup process jumps to step 510 to perform a measurement with the second MA measurement circuit 64 after performing step 506. Since this measuring circuit uses an independent local oscillator 60, the step of setting up the local oscillator is not necessary.

In summary, the present invention described above provides a handoff from a first multiple access communication system to a second multiple access communication system, where the dual mode subscriber station measures at the subscriber terminal a signal from the second multiple access communication system, This handoff is supported. Accordingly, a plurality of pilot beacons for transmitting signals in the MA structure of the first multiple access communication system are not required, thereby enabling inter-system handoff at low system structure cost.

While the specific embodiments described above relate to handing off a subscriber station from a CDMA system to an AMPS system, the principles and basic architecture of the present invention also provide for performing handoff from any MA communication system to any other MA communication system. Can be used.

Various means for measuring alternative MA signal characteristics have been described. That is, using a subscriber system using independent measurement circuits, a subscriber station sharing one local oscillating circuit between transceivers of different MAs, and a CDMA receiver reconfigured to measure signal characteristics of signals from alternative MA communication systems. The subscriber station and the like. Such a CDMA receiver can be set to stop the despreading operation, and the replacement signal passing through the spreader can be analyzed by integrating power over the narrowband or by analyzing the wideband frequency spectrum.

In some embodiments of the invention, the alternate signal source 118 may be a special signal that enhances the measurement of the alternate MA signal, or a signal having unknown characteristics. For example, this signal can include a plurality of discrete frequencies that can be used to detect the power of several alternative MA signals.

The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and should not be construed as limiting the scope of the invention in its precise form. Various modifications or variations can be made based on the above disclosure. The described embodiments can best explain the principles of the invention, those skilled in the art can use the invention in various embodiments, and various modifications can be made to suit the particular intended use. It was chosen to be. All such modifications and variations are intended to fall within the scope of the invention as defined by these claims, provided that they are duly duly legally patented and interpreted in accordance with the granted breadth.

Claims (16)

A method for performing subscriber handoff from a first multiple access communication system to a second multiple access communication system in a cellular telephone communication system, the method comprising: Measuring a signal characteristic of a signal from the second multiple access communication system from a subscriber station communicating with the first multiple access communication system, and generating a signal characteristic value; In response to the signal characteristic value, setting the subscriber station to communicate with the second multiple access communication system; And Performing subscriber handoff from the first multiple access communication system to the second multiple access communication system; Method for performing subscriber handoff comprising a. 2. The method of claim 1 wherein the signal characteristic is signal strength. The system of claim 1, wherein the first multiple access communication system is a code division multiple access system, and the subscriber station includes a spreader using a spreading signal, and the signal characteristic is measured. The steps to Selecting an alternate despreading signal for use in the spreader; Passing the signal from the second multiple access communication system through the spreader; And And measuring a signal characteristic of the signal from the second multiple access communication system to generate a signal characteristic value. 4. The method of claim 3, wherein the alternate spreading signal comprises a constant value of spreading signal. 4. The method of claim 3, wherein the alternate despreading signal comprises a signal having several preselected discrete frequencies for measuring the power of several signals in the second multiple access communication system having different frequencies. A method for performing subscriber handoff. 4. The method of claim 3, wherein measuring signal characteristics of a signal from the second multiple access communication system to generate signal characteristic values comprises: generating the signal power values over a frequency range to generate the second signal. And performing a frequency analysis of the signal from the subscriber. The method of claim 1, wherein the step of setting the subscriber station to communicate with the second multiple access communication system in response to the signal characteristic value comprises: the second in response to the signal characteristic value exceeding a predetermined threshold value; Setting up the subscriber station to communicate with a multiple access communication system. The method of claim 1, Generating a first system signal characteristic value from the subscriber station by measuring signal characteristics of a signal from the first multiple access communication system; Comparing the signal characteristic value with the first system signal characteristic value; And Setting the subscriber station to communicate with the second multiple access communication system in response to the signal characteristic value exceeding the first system signal characteristic value; Subscriber handoff method further comprises. 2. The method of claim 1, wherein setting the subscriber station to communicate with the second multiple access communication system in response to the signal characteristic value comprises: communicating with the second multiple access communication system in response to the signal characteristic value. And switching the subscriber downlink and uplink traffic from the first multiple access transceiver to the second multiple access transceiver. A method for measuring signal characteristics of a signal from an alternative multiple access communication system at a code division multiple access subscriber terminal, the method comprising: Setting a tuner to receive the signal from the alternate multiple access communication system; Selecting an alternate spreading signal for use in a spreader in the code division multiple access subscriber terminal; Passing the signal from the alternate multiple access communication system through the spreader; And Measuring the signal characteristic of the signal from the alternate multiple access communication system Method at code division multiple access subscriber terminal comprising a. 11. The method of claim 10, wherein setting a tuner to receive the signal from the alternate multiple access communication system comprises: adjusting a frequency, gain, and filter to receive the signal from the alternate multiple access communication system. The method further comprises the step of setting a code division multiple access subscriber terminal. 12. The method of claim 10, wherein the alternate spreading signal is a constant value signal. 11. The method of claim 10, wherein measuring the signal characteristic of the signal from the alternate multiple access communication system further comprises performing a frequency analysis of the signal from the alternate multiple access communication system. A method in a code division multiple access subscriber terminal. An apparatus for receiving a code division multiple access signal and measuring signal characteristics of a signal from an alternative multiple access communication system, A spreader having a signal input, a spreading input, and a spreader output; A despreading code signal source; An alternate despreading signal source; A despreader signal selector having inputs coupled to the despreading code signal source and the alternate despreading signal source and an output coupled to the despreading input; A tuner having an output coupled to the signal input; A signal characteristic measurement circuit coupled to the spreader output; And A control circuit coupled to the tuner and the spreader signal selector for setting the apparatus for receiving the code division multiple access signal or for measuring signal characteristics of a signal from an alternate multiple access communication system Apparatus for measuring signal characteristics of signals from code division multiple access signal reception and replacement multiple access communication systems comprising a. 15. The apparatus of claim 14, wherein the alternate despreading signal source is a constant value signal source. 15. The apparatus of claim 14, wherein the alternate despreading signal source generates a signal having several preselected discrete frequencies. .