GB2362297A - Location based consideration for cellular telephone handoff - Google Patents

Location based consideration for cellular telephone handoff Download PDF

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Publication number
GB2362297A
GB2362297A GB0031101A GB0031101A GB2362297A GB 2362297 A GB2362297 A GB 2362297A GB 0031101 A GB0031101 A GB 0031101A GB 0031101 A GB0031101 A GB 0031101A GB 2362297 A GB2362297 A GB 2362297A
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Prior art keywords
mobile station
station
base station
base
geographic position
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GB0031101A
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GB0031101D0 (en
GB2362297B (en
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Scott T Droste
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Motorola Solutions Inc
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Motorola Solutions Inc
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Classifications

    • 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
    • H04W36/32Reselection being triggered by specific parameters used to improve the performance of a single terminal by location or mobility data, e.g. speed data
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/08Reselecting an access point

Abstract

A degradation in the signal quality of a communication link between a mobile station (4) and a first base station 10 of a cellular communication network(2) is detected, and the network (2) determines whether it has information relating to a geographic position of the mobile station (4). If not, the geographic position is acquired. A decision is made as to whether further handoff processing should be performed based upon the geographic position of the mobile station (4), the further handoff processing to enable the mobile station (4) or the cellular communication network (2) to determine whether the mobile station (4) is a handoff candidate for a second base station (12) of the cellular communication network (2).

Description

2362297 METHOD OF AND APPARATUS FOR LOCATION BASED CONSIDERATION FOR

CELLULAR TELEPHONE HANDOFF

FIELD OF THE INVENTION

This invention generally relates to wireless telecommunications. More specifically, this invention relates to performing a handoff between cell sites in cellular telephone systems.

BACKGROUND OF THE INVENTION

In a cellular telephone system, the mobile station is configured for radio communication with one or more remote base stations. A particular cellular communication system is defined by an air interface standard. The standard defines aspects such as the uplink and downlink frequency bands and the type of modulation to be used.

For example, one type of cellular communication system that has been adopted by the Telecommunications Industry Association (TIA) is the IS-95 interface standard. This is a code division multiple access standard. There are other CDMA standards, such as TIA-EIA-95B and IS-2000, as well as third generation CDMA standards still in development.

In operation, a cellular mobile station establishes a communication link with a base station. As the mobile station travels within the cellular communication system, it can move out of the range of the base station that it is linked to, and so the mobile station must establish a link with another base station. This can occur in either a soft handoff or hard handoff fashion.

A soft handoff occurs when the mobile station establishes a communication link with a second base station before the communication link with the first base station is terminated. A hard handoff occurs when the communication link with the first base station is terminated before the link with the new base station is established.

-I- DOCKET NO.: CS10303 As a mobile station travels, it is possible that it moves into a different cellular system. This new system can be characterized as operating with a different modulation scheme, different uplink and downlink frequency bands, or a combination of both. It may thus become necessary for a mobile to perform a hard handoff from one set of frequency bands of operation to another set of frequency bands.

Standards exist that describe procedures that allow a serving network to direct a mobile station to make signal quality measurements of specified target frequency band signals to enable the network to determine the likelihood of success of a hard handoff.

The signal quality measurements also enable the network to determine the target frequency band that a new base station should use to communicate with the mobile station. The signaling and procedures associated with this process are called mobile assisted hard handoff (MAHHO).

Although the signaling and procedures for executing a MAHHO are defined within at least some of the standards given above, the conditions, or triggering event, for initiating the MAHHO is not defined or described. The conditions are thus left to the network manufacturer and/or operator to define. Typical techniques include assessing the quality of the reverse link (e.g. mobile to base station). An example of an indication of the quality of the reverse link is frame error rate. Another possibility of assessing the quality of the link involves analysis of the strength of the pilot signal via a pilot strength measurement message that is sent by the mobile station to the base station.

The above quality assessing techniques, however, can fail under certain conditions. For example, the strength of the pilot signal may not be an accurate indication of handoff success because blocking or multipath fading may be present. Thus, base stations may direct mobile stations that are not true candidates for a MAHHO to make time consuming and power consuming measurements associated with a MAHHO procedure. For example, the mobile station might have to move from the current frequency band of operation to make a signal quality measurement on a target frequency band of operation. This false triggering can result in the particular mobile station experiencing degraded voice quality or reduced data throughput. False triggering also detrimentally consumes network resources.

U.S. Pat. No. 5,669,061, issued to Schipper, discloses the use of GPS to make a decision as to whether a mobile station should be handed off from one base station to another base station. However, the decision is based solely upon the location of the DOCKET NO.: CS10303 mobile station, and this could lead to erroneous results due to, for example, blocking conditions which may limit a mobile station's ability to communicate with a second base station. Using position information alone also does not take into account the deleterious effects of multipath propagation. Further, the cellzone map disclosed is stored in the mobile station, and excessive memory requirements on the mobile station, and the necessity to update the mobile stations map as a result of changing network coverage.

Still further, the position determination is made at the mobile station, and this requires that a GPS receiver must be included in the handset, thereby limiting design choices.

Brief Description of the Drawings

FIG. 1 is a block diagram of a cellular communication network; FIG. 2 is a block diagram of a mobile station operable in the cellular communication network of FIG. 1; FIG. 3 depicts coverage areas for two base stations operating in the cellular communication network of FIG. 1; and FIG. 4 is a flow chart illustrating a method for deterrnining whether the mobile station of FIGs. I and 2 is a candidate for further handoff processing and evaluation.

Detailed Description of Preferred Embodiments

FIG. I is a system diagram of a cellular communication network 2. The cellular communication network 2 includes a first plurality of base stations, including a first base station 10, that operates via a first set of frequencies and a second plurality of base stations, including second base station 12, that operates via a second set of frequencies.

A base station controller 14 is coupled to both the first base station 10 and the second base station 12 generally for controlling operation of the cellular communication network 2 as is known in the art.

Mobile station 4 initially establishes a communication link with the first base station 10, and the first base station 10 has a first geographic coverage area. In the illustrated embodiment, the first plurality of base stations, including the first base station 10, employs a first type of code division multiple access (CDMA) technology air interface DOCKET NO.: CS10303 standard that is outlined in TLAJEIA Interim Standard IS-95 entitled "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System." The second plurality of base stations, including the second base station 12, employs either the same type of CDMA air interface technology operating on a different frequency or frequency band, or a second type of CDMA air interface standard different from the first type and operating on the same or different frequency or frequency band. In addition, the second plurality of base stations can use a different pilot structure, chip rate, channelization, and other system characteristics, such as those currently proposed for third generation wideband CDMA systems. Still further, the cellular communication network 2 alternatively may operate via some other type of air interface standard that utilizes time division multiple access technology.

As just described, some of the base stations in the cellular communication network 2 employ a different set of uplink and downlink frequencies than the other spread spectrum base stations in the cellular communication network 2. For example, the first base station 10,operates via a first downlink frequency and a first uplink frequency to communicate with the mobile station 4. The second base station operates via at least a second downlink frequency that is different than the first downlink frequency, and the second base station 12 operates via at least a second uplink frequency that is different than the first uplink frequency. In addition, the mobile station 4 can employ antenna and transceiver technology known in the art to enable the mobile station 4 to communicate using different frequency bands for different base stations.

The hardware configuration of the mobile station 4 depends upon the type of location identification system employed in the cellular communication network 2. For example, the mobile station 4 can employ a global positioning system (GPS) receiver for communication with GPS satellites, here shown as GPS satellite 16. In that instance, the mobile station 4 may employ a first antenna 6 for communication with the cellular communication network 2 and a second antenna 8 for communication with the GPS satellite 16. For an autonomous GPS position location implementation, the mobile station 4 acquires and measures the GPS satellite signal without the aid of cellular communication network 2 intervention. The mobile station can then use the satellite signal to calculate its location. However, to allow for the mobile station 4 to not have to store a geographic map, the mobile station 4 can format the timing information of the DOCKET NO.: CS10303 received satellite signal and sent the formatted information to the cellular communication network 2 for a calculation of the mobile station 4 location.

Moreover, the cellular communication network 2 can employ network assisted GPS, wherein the cellular communication network 2 provides information to the mobile station 4 to aid in acquiring the GPS satellite signal as is known in the art. The mobile station 4 can then either calculate its position or send the timing information to the cellular communication network 2 as described above.

In addition, or alternatively, the mobile station 4 can be equipped to receive and process downlink signals of the cellular communication network 2 to aid in location determination of the mobile station 4; this is known as forward link triangulation. In forward link triangulation the mobile station 4 processes multiple downlink signals and determines times of arrival as part of the position determination as is known in the art.

The mobile station 4 can then determine the mobile station 4 location if it has information relating to the base station locations that have sent the multiple pilot signals.

Alternatively, the mobile station can send the time of arrival information to the cellular communication network 2 for location calculation, and the mobile station 4 then would not have to have base station location information or would not have to have to store a geographic map.

Still further, the cellular network 2 can include circuitry to allow the reception and processing at multiple base stations of the uplink signal transmitted by the mobile station 4 to determine the geographic location of the mobile station 4. This is referred to reverse link triangulation as is known in the art.

As shown, the mobile station 4 is in communication with the first base station 10, but the mobile station 4 is also in the vicinity of the coverage areas of second base station 12. The geographic position of the mobile station 4 can contribute to a determination as to whether a mobile station 4 should switch from communicating via at least one of the first plurality of base stations (e.g. first base station 10) to communicating via at least one of the second plurality of base stations (e.g. second base station 12).

FIG. 2 shows a block diagram of an exemplary embodiment of the mobile station 4. The mobile station 4 is configured to receive and transmit spread spectrum signals to communicate with a plurality of base stations. In the illustrated embodiment, the first base station 10 (FIG. 1) transmits various spread spectrum signals, such as an information signal on a traffic channel, to the mobile station 4. The symbols comprising the DOCKET NO.: CS10303 information signal are coded using a Walsh code in a process known as Walsh covering.

Each mobile station such as mobile station 4 is assigned a unique Walsh code so that the traffic channel transmission to each mobile station is orthogonal to traffic channel transmissions to every other mobile station.

In addition to traffic channels, the first base station 10 broadcasts other signals such as a spread spectrum pilot signal over a pilot channel, a synchronization signal over a synchronization channel, and a paging signal over a paging channel. The pilot channel is commonly received by all mobile stations within range and is used by the mobile station 4 for identifying the presence of a CDMA system, initial system acquisition, idle mode hand-off, identification of initial and delayed rays of communicating and interfering base stations, and for coherent demodulation of the synchronization, paging, and traffic channels. The synchronization channel is used for synchronizing mobile station timing to base station timing. The paging channel is used for sending paging information from the first base station 10 to mobile stations including mobile station 4.

In alternate embodiments, the pilot signals comprise multiple pilot signals transmitted over a plurality of channels. Some of the pilot signals can be used, for example, for initial acquisition and signal strength determination. Other of the pilot signals can be used for storing group information, such as a group of base station identities.

In addition to the Walsh covering, all channels transmitted by the base station are spread using a pseudorandom noise (PN) sequence. In the illustrated embodiment, the first base station 10 and other spread spectrum base stations in the cellular communication network 2 are uniquely identified by using a unique starting phase, also referred to as a starting time or phase shift, for the pilot channel PN sequence. The PN sequence is of a length 2'5 chips that are produced at a chip rate of 1. 2288 Mega-chips per second, and the PN sequence repeats at approximately every 26.66 milliseconds (msec).

The minimum permitted time separation is 64 chips, allowing a total of 512 different PN code phase assignments. The spread pilot channel modulates a radio frequency (RF) carrier and is transmitted to all mobile stations including mobile station 4 in a geographic area served by the first base station 10. The PN sequence can be complex in nature, comprising both in-phase (I) and quadrature (Q) components.

In an alternate embodiment, the base stations are asynchronous to one another, meaning that there is no common timing reference synchronizing all of the base stations DOCKET NO.: CS10303 together. The pilot signals transmitted from one base station are thus not synchronous to pilot signals transmitted by another base station. The mobile station 4 comprises a first antenna 6, an analog front end 20, microprocessor, logic, and control circuitry 22, a receive path, and a trarisrnit path. The receive path includes an analog to digital converter (ADC) 24 and a receiver modem 26, while the transmit path includes a digital to analog converter 28 and a transmission path circuit 30. The receiver modem 26 includes a RAKE receiver 32, a searcher receiver 34, and various timing circuitry not shown so as not to unduly complicate the drawing figure.

The antenna 6 receives RF signals from the first base station 10 and from other base stations in the vicinity. Some of the received RF signals are direct line of sight rays transmitted by the base station. Other received RF signals are reflected or multi-path rays and are therefore delayed in time relative to the line of sight rays.

Received RF signals are converted to electrical signals by the antenna 6 and provided to the analog front end 20. The analog front end 20 performs functions such as filtering, automatic gain control, and conversion of signals to baseband signals. The analog baseband signals are provided to the ADC 24 for conversion to streams of digital data for further processing.

The RAKE receiver 32 includes a plurality of demodulation branches, including first demodulation branch 36, second demodulation branch 38, third demodulation branch 40, and fourth demodulation branch 42. In the illustrated embodiment, the RAKE receiver 32 includes four demodulation branches. However, other numbers of demodulation branches can be used. In fact, a demodulation branch may also perform the searcher receiver function, though that will not result in optimum performance for cellular telephone applications.

The microprocessor, logic, and control circuitry 22 includes a microprocessor 44 and a clock 46. The clock 46 controls timing of the mobile station 4. The microprocessor, logic, and control circuitry 22 is coupled to other elements of the mobile station 4 (e.g. the microphone, speaker, digital signal processor), but such interconnections are not shown in FIG. 2 so as to not unduly complicate the drawing figure.

Generally, the searcher receiver 34 within the receiver modem 26 detects pilot signals received by the mobile station 4 from a plurality of base stations, including the first base station 10 (FIG. 1). The searcher receiver 34 despreads the pilot signals using a DOCKET NO.: CS10303 correlator with PN codes generated in the mobile station 4. After this despreading, the signal values for each chip period are accumulated over a pre-selected interval of time.

This provides a coherent sum of chip values. This sum is compared against a threshold level. Sums exceeding the threshold level generally indicate a suitable pilot signal ray that can be used for pilot signal timing synchronization.

Once a suitable ray is identified and timing synchronization is accomplished, a demodulation branch in the RAKE receiver 32 is assigned to that signal path. The mobile station 4 can then demodulate information signals as is known in the art.

If the mobile station 4 utilizes GPS for location determination, the mobile station 4 also employs a GPS receiver 48. The second antenna 8 then receives location information signals from the GPS satellite 16 (FIG. 1), and the GPS signals are processed by the GPS receiver 48 and forwarded to the microprocessor, logic, and control circuit 22.

The mobile station 4 can use the transmitter of the transmit path to transmit the mobile station 4 geographic position I to the at least one of the first plurality of base stations. The GPS receiver 48 and the receive path of the mobile station 4 may optionally share at least some circuitry to reduce the size and cost of the mobile station 4. The use of a separate GPS receiver 48 provides the mobile station with what may be referred to as autonomous GPS, wherein the mobile station interacts principally with the GPS system for location determination.

Altematively, the base stations of the cellular communication network 2 may participate in the mobile station identification using GPS as is known in the art, and this can be referred to as network assisted GPS. Still further, forward link triangulation may be employed to determine the latitude and longitude information of the mobile station as is known in the art. Some of these position location techniques are being proposed in air interface standards, such as standard TLAJEIA/IS-801. In the future, many of the new mobile stations and/or cellular networks will provide for mobile station location determination.

FIG. 3 depicts a first coverage area 50 corresponding to the first base station 10 (FIG, 1) and a second coverage area 52 corresponding to the second base station 12 (FIG.

1). Since each base station has a finite, maximum transmit power, each base station will cover a certain geographic area. Generally, when a mobile is in that coverage area, the mobile station can reliably communicate with the corresponding base station.

DOCKET NO.: CS10303 FIG. 3 also shows that the first base station 10 and the second base station 12 have what may be referred to as a mutual coverage area 54. This area corresponds to locations where both the first base station 10 and the second base station 12 can transmit power strong enough to reach a mobile station.

As the mobile station 4 (FIGs. 1 and 2) communicates with the first base station 10, the mobile station may move to the outer area of the first coverage area 50. The communication link can show signs of degradation, and a handoff to another base station may soon become necessary. The cellular communication network 2 typically performs signal quality measurements to determine if a handoff is necessary. This may involve a signal strength measurement, such as the signal strength of the uplink signal transmitted by the mobile station 4. This may also involve a measure of a frame error rate as is known in the art. The mobile station 4 might even send a pilot strength measurement message to the first base station 10.

Since the geographic location of the mobile station 4 is known, the location information can be used as an additional screening for handoff determination. Moreover, knowledge of the mobile station location, velocity, and direction of travel can be used as means (or additional) means of screening mobile stations to determine handoff candidates.

In the illustrated embodiment, first base station 10 (FIG. 3) provides radio coverage via at least a first uplink and a first downlink frequency. The second base station 12 provides radio coverage on via at least a second uplink and a second downlink frequency, wherein the first and second uplink frequencies are different, and the first and second downlink frequencies are different as was described previously. The mutual coverage area 54 is the CDMA hard handoff area in which handoffs between the first frequency of the first base station 10 and the second frequency of the second base station 12 are appropriate and have a likelihood of success.

For the purposes of illustration, three examples are presented, and these examples correspond to first location 56, second location 58, and third location 60 (FIG. 3). For the first example, corresponding to first location 56, the cellular communication network 2 has experienced degraded signal quality in communicating with the mobile station 4 via first base station 10. The first base station 10 determine the mobile station's present location and velocity to analyze whether the mobile station 4 is a handoff candidate for further CDMA hard handoff processing.

DOCKET NO.: CS10303 To determine the mobile station's present location and velocity, the first base station and the cellular communication network 2 can access short-term position and velocity information stored within a cellular communication network database.

Alternatively, the first base station 10 can query the mobile station 4 for current location by means such as described in TIA/EIA/IS-801 CDMA Location Services Standard. Still further, the cellular communication network 2 can utilize autonomous network location capabilities to determine the mobile station's location and travel velocity.

Considering the first example, the mobile station 4 is in the mutual coverage area 54. This determination is made based on the position information of the mobile station 4 coupled with prior knowledge of the first base station 10 coverage area (also referred to as network radio coverage area). Thus, information relating to the geographic coverage area of the first base station 10 is stored in memory circuitry either in the first base station 10 or elsewhere in the cellular communication network 2, such as in memory coupled to the base station controller 14 (FIG. 1).

In addition, based upon the information on the velocity of the mobile station 4 coupled with prior knowledge of the radio coverage area, the cellular communication network 2 would determine that the mobile station 4 is a candidate for further MMA hard handoff processing. This determination can be made by either the first base station or by other hardware associated with the cellular communication network 2 (e.g. a base station controller that is not shown). The mobile station 4 can then search via the second frequency of the second base station 12 for a suitable pilot signal; a determination can be made, either by the mobile station 4 or the cellular communication network 2, as to whether a hard handoff should be initiated.

Since the mutual coverage area 54 is the area in which a mobile station can be a candidate for a hard handoff, mutual coverage area 54 may also be referred to as a hard handoff area or hard handoff zone. Several different criteria can be established for the initial determination as to whether the mobile station 4 is a candidate for further CDMA hard handoff processing. A determination may be made, for example, when a degradation in signal quality is detected and then it is determined that the mobile station 4 is in the mutual area of coverage 54. Alternatively, the determination may be made based upon knowledge that the mobile station is in the mutual area of coverage 54 and the mobile station 4 is moving away from the first base station 10.

DOCKET NO.: CS10303 Next, the second example, corresponding to the mobile station 4 being in the second location 58 (FIG. 3), is explained. As previously explained, the location and velocity of the mobile station 4 is determined. The mobile station 4 is not within the mutual area of coverage 54, but it is near that hard handoff zone. As a result, the cellular communication network determines that the mobile station is not an immediate candidate for further CDMA hard handoff processing. However, since the cellular communication network 2 determines that the mobile station 4 is traveling towards the mutual area of coverage 54, the network may determine that further location updates in the immediate future would be beneficial to determine when to invoke additional CDMA hard handoff processing.

The third example corresponds to the mobile station 4 being in the third location (FIG. 3). In this instance, the cellular communication network 2 determines that the mobile station is not within or near the mutual area of coverage 54 (e.g. hard handoff zone). If the mobile station 4 represents a pedestrian rather than a mobile station traveling at automobile velocities, the cellular communication network also notes that.

As a result, the cellular communication network 2 determines that the mobile station 4 is not a candidate for further CDMA hard handoff processing.

FIG. 4 is a flow chart illustrating a method for determining whether a mobile station is a candidate for further handoff processing and evaluation. The method begins at block 70, and at block 72 a degraded signal quality is detected. This can be a detection made at the mobile station 4 (FIGs. 1, 2, and 3) or alternatively at the cellular communication network 2 (FIG. 1).

At decision block 74, it is determined whether the cellular communication network 2 (FIG. 1) has timely, substantially current information about the mobile station 4. This timely or current information can include the geographic position/location of the mobile station 4, the velocity of the mobile station 4, and even the direction of travel of the mobile station 4. If the cellular communication network 2 does not have timely information, then at block 76 the cellular communication network 2 queries the mobile station 4 for the necessary information. The mobile station 4, for example, can employ GPS for location determination. The mobile station 4 then transmits a signal indicative of its geographic position to the cellular communication network 2 (FIG. 1). Alternatively, if a different type of location determination is employed, such as network assisted GPS or DOCKET NO.: CS10303 forward link triangulation, the method continues at block 78 wherein the network derives the timely information of the mobile station 4.

Next, at decision block 80 after the cellular communication network 2 has timely information, the cellular communication network 2 determines whether the mobile station 4 is in a mutual area of coverage. If the mobile station is in a mutual area of coverage between at least two basestations, the method continues at decision block 82, where it is determined whether the mobile station 4 is moving away from the base station that it is currently communicating. If yes, the method continues at block 84 where it is decided that the mobile station 4 is a candidate for further handoff processing.

The mobile station 4 can then perform further handoff processing, such as searching for a pilot signal on the frequency of the second base station covering the mutual coverage area. A determination is made as to the quality of the communication link between the mobile station 4 and the second base station 12 to determine whether a handoff to the second base station should be initiated. A communication link between the mobile station 4 and the second base station 12 can be established responsive to the quality of the received pilot signal being within a predetermined quality level (e.g. of a certain signal strength and/or yielding an acceptable, predetermined frame error rate, etc.).

Thus, for the embodiment where the mobile station 4 transmits its geographic position to the cellular communication network 2, the cellular communication network 2 uses the signal in conjunction with signal quality information to determine whether a handoff should be initiated.

In an alternate embodiment, it is not considered as to whether the mobile station 4 is moving away from the base station that it is currently communicating, and the method proceeds directly from decision block 80 to block 84. After block 84, the method ends at block 86.

In an altemate embodiment, additional information can be determined at decision block 82. For example, it can be determined whether the mobile station is moving toward a second base station of a mutual area of coverage, and that information may serve as an additional screening criteria.

If at decision block 80 it is found that the mobile station 4 is not in a mutual coverage area, then at block 88 it is determined whether the mobile station is moving toward a mutual coverage area. If the mobile station 4 is not, then it is determined at block 90 that the mobile station 4 is not curTently a candidate for further handoff DOCKET NO.: CS10303 processing, and the method ends at block 86. If the mobile station 4 is moving toward a mutual coverage area, then the method continues at block 72 (or alternatively at decision block 74. In addition, if at decision block 82 it is determined that the mobile station 4 is not moving away from the current base station, then the method continues either at block 72 or decision block 74.

The previous description of the preferred embodiments are provided to enable any person skilled in the art to use the method of or make the apparatus for activating a spread-spectrum radiotelephone receiver. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. For example, the location determination can be utilized to determine whether a mobile station is a candidate for further soft handoff processing rather than hard handoff processing. In addition, the mutual area of coverage can be between two base stations operating via different air interface standards, such as CDMA and time division multiple access (TDMA) technology. Still further, the handoff analysis between a first base station and a second base station can involve

Claims (1)

  1. I claim:
    DOCKET NO.: CS10303 CLAIMS 1 1. In a cellular communication network, an apparatus for contributing to a 2 determination as to whether a mobile station in communication with a first base station is 3 a handoff candidate to a second base station, the apparatus comprising a location 4 identification system coupled to the mobile station to determine a geographic position of the mobile station and to couple a signal indicative of the geographic position to at least 6 one of the first base station and the second base station, at least one of the first base 7 station and the second base station to use the signal to decide if the mobile station should 8 make signal quality measurements of a transmission signal transmitted by the second base 9 station to determine if the mobile station should be handed off the second base station.
    1 2. The apparatus as in claim 1 further comprising memory circuitry coupled to at 2 least one of the first base station and the second base station to store information 3 indicative of a network radio coverage area related to at least one of the first base station 4 and the second base station.
    1 3. The apparatus as in claim I wherein:
    2 the first base station utilizes a first downlink frequency and a first uplink 3 frequency to communicate with the mobile station; and 4 the second base station utilizes a second downlink frequency and a second uplink frequency to communicate with the mobile station, 6 the first downlink frequency different than the second downlink frequency, the 7 first uplink frequency different than the second uplink frequency.
    1 4. The apparatus as in claim 1 wherein the first base station operates via a 2 different air interface standard than the second base station.
    1 5. The apparatus as in claim I wherein the geographic position comprises latitude 2 and longitude information of the mobile station.
    DOCKET NO.: CS10303 1 6. The apparatus as in claim 1 wherein the transmission signal comprises a spread 2 spectrum pilot signal.
    1 7. The apparatus as in claim 6 wherein the handoff comprises a hard handoff 2 between the first base station and the second base station.
    1 8. The apparatus as in claim 1 wherein the geographic position comprises latitude 2 and longitude information of the mobile station and a velocity of the mobile station.
    1 9. The apparatus as in claim 1 wherein the location identification system 2 comprises a global positioning system (GPS) receiver coupled to the mobile station.
    1 10. The apparatus as in claim 9 wherein the location identification system 2 comprises network assisted GPS.
    1 11. The apparatus as in claim 1 wherein the location identification system 2 comprises a forward link triangulation.
    1 12. The apparatus as in claim 1 wherein the cellular communication network 2 operates via code division multiple access (CDMA).
    3 DOCKET NO.: CS10303 3 1 13. In cellular communication network having a first plurality of base stations 2 operating on a first set of uplink and downlink frequencies and a second plurality of base 3 stations operating on a second set of uplink and downlink frequencies, the first set of 4 uplink and downlink frequencies different than the second set of uplink and downlink frequencies, an apparatus for contributing to a determination as to whether a mobile 6 station should switch from communicating via at least one of the first plurality of base 7 stations to communicating via at least one of the second plurality of base stations, the 8 apparatus comprising:
    9 a global positioning system (GPS) receiver coupled to the mobile station to determine a geographic position of the mobile station; I I a transmitter coupled to the mobile station to transmit the geographic position of 12 the mobile station to the at least one of the first plurality of base stations; and 13 a controller coupled to the at least one of the first plurality of base stations to use 14 the geographic position to determine if the mobile station is within a coverage area of at least one of the second plurality of base stations to decide if the mobile station should 16 make a signal quality measurement of a transmission signal transmitted by the at least one 17 of the second plurality of base stations to determine if the mobile station should be 18 handed off to the at least one of the second plurality of base stations.
    1 14. The apparatus as in claim 13 wherein when the mobile station is within a 2 coverage area of at least one of the second plurality of base stations, the controller 3 determines that the mobile station is a handoff candidate to the at least one of the second 4 plurality of base stations and directs the mobile station to make the signal quality measurement of the transmission signal transmitted by the at least one of the second 6 plurality of base stations to determine if the mobile station should be handed off to the at 7 least one of the second plurality of base stations.
    1 15. The apparatus as in claim 13 further comprising memory coupled to any of 2 the first plurality of base stations and the second plurality of base stations to store 3 information indicative of a geographic coverage area of at least one base station.
    DOCKET NO.: CS10303 16. The apparatus as in claim 15 wherein the controller initiates a handoff 2 between the mobile station and the at least one of the first plurality of base stations to the 3 at least one of the second plurality of base stations when the mobile station is within a 4 coverage area of the at least one of the second plurality of base stations and when the mobile station determines that the signal quality measurement indicates a predetermined 6 communication link quality.
    1 17. The apparatus as in claim 13 wherein any of the first plurality of base stations 2 and the second plurality of base stations utilize a spread spectrum modulation.
    1 18. The apparatus as in claim 17 wherein the spread spectrum modulation 2 comprises code division multiple access (CDMA).
    1 19. The apparatus as in claim 13 wherein the geographic position comprises 2 latitude and longitude information of the mobile station.
    1 20. The apparatus as in claim 19 wherein the geographic position comprises 2 latitude and longitude information of the mobile station and a velocity of the mobile 3 station.
    4 17- DOCKET NO.: CS10303 4 1 21. In cellular communication network including a first plurality of base stations 2 operating via a first set of frequencies and a second plurality of base stations operating via 3 a second set of frequencies, an apparatus for determining whether a mobile station is a 4 handoff candidate from one of the first plurality of base stations to one of the second plurality of base stations, the apparatus comprising:
    6 means for determining a geographic position of the mobile station; 7 memory coupled to the cellular communication network to store a coverage area 8 of the one of the first plurality of base stations and a coverage area of the one of the 9 second plurality of base stations; and means for determining whether the geographic position of the mobile station is 11 within the coverage area of the one of the second plurality of base stations, wherein the 12 mobile station performs further handoff processing when the mobile station is within the 13 coverage area of the one of the second plurality of base stations, the further handoff 14 processing to enable any of the mobile station and the cellular communication network to is determine whether the mobile station is a handoff candidate.
    1 22. The apparatus as in claim 21 wherein the geographic position of the mobile 2 station comprises latitude and longitude information of the mobile station.
    1 23. The apparatus as in claim 22 wherein the further handoff processing comprises 2 the mobile station determining a quality of a communication link with the one of the 3 second plurality of base stations.
    1 -18 DOCKET NO.: CS10303 1 24. In cellular communication network including a plurality of base stations, an 2 apparatus for determining whether a mobile station is a handoff candidate from a first 3 base station to a second base station, the apparatus comprising:
    4 means for determining a geographic position of the mobile station; means for storing at the cellular communication network a coverage area of the 6 first base station and a coverage area of the second base station; and 7 means for determining whether the geographic position of the mobile station is 8 within the coverage area of the second base station, wherein the mobile station performs 9 further handoff processing when the mobile station is within the coverage area of the second base station, the further handoff processing to enable any of the mobile station and 11 the cellular communication network to determine whether the mobile station is a handoff 12 candidate.
    1 25. The apparatus as in claim 24 further comprising means for establishing a 2 communication link between the mobile station and the second base station responsive to 3 determining that the geographic position is within the coverage area of the second base 4 station and responsive to the mobile station determining via the further handoff processing that a communication link can be established with the second base station to 6 yield a predetern-fined quality of communication.
    7 DOCKET NO.: CS10303 7 1 26. In cellular communication network including a plurality of base stations, an 2 apparatus for determining whether a mobile station, in communication with a first base 3 station, is in a position to consider a second base station as a handoff candidate, the 4 apparatus comprising:
    means for determining a geographic position of the mobile station; 6 memory coupled to the cellular communication network to store a coverage area 7 of the first base station and a coverage area of the second base station; and 8 means for determining whether the geographic position of the mobile station is 9 within a coverage area of the second base station, wherein when the geographic position is within the coverage area of the second base station, the mobile station performs further 11 handoff processing when the mobile station is within the coverage area of the second base 12 station, the further handoff processing to enable any of the mobile station and the cellular 13 communication network to determine whether the mobile station is a handoff candidate.
    1 27. The apparatus as in claim 26 wherein when the mobile station considers the 2 second base station as the handoff candidate, the mobile station measures a quality of a 3 communication link with the second base station for a determination as to whether a 4 handoff should be initiated.
    1 28. The apparatus as in claim 27 wherein the cellular communication network 2 operates via a code division multiple access (CDMA).
    1 29. The apparatus as in claim 28 wherein the first base station and the second 2 base station operate via uplink frequency bands that are different from each other and 3 operate via downlink frequency bands that are different from each other.
    1 30. The apparatus as in claim 26 wherein the geographic position of the mobile 2 station comprises latitude and longitude information of the mobile station and a velocity 3 of the mobile station.
    1 DOCKET NO.: CS10303 1 3 1. In a cellular communication network including a plurality of base stations, a 2 method of determining whether a mobile station in communication with a first base 3 station should consider a second base station as a handoff candidate, the method 4 comprising:
    determining a geographic position of the mobile station; 6 coupling the geographic position of the mobile station to at least one of the first 7 base station and the second base station; 8 deciding whether the geographic position is within a coverage area of the second 9 base station; and directing the mobile station to perform a quality measurement of a transmission 11 signal transmitted by the second base station, the quality measurement to enable any of 12 the mobile station and the cellular communication network to determine whether the 13 mobile station is a handoff candidate.
    1 32. The method as in claim 31 further comprising:
    2 transmitting a signal from the second base station; 3 receiving the signal at the mobile station responsive to deciding the geographic 4 position is within the coverage area of the second base station; and measuring a quality of the signal at the mobile station responsive to receiving the 6 signal at the mobile station.
    1 33. The method as in claim 32 wherein the signal is a spread spectrum pilot 2 signal.
    1 34. The method as in claim 32 wherein the geographic position of the mobile 2 station comprises latitude and longitude information of the mobile station and a velocity 3 of the mobile station.
    1 35. The method as in claim 32 wherein the first base station and the second base 2 station operate via uplink frequency bands that are different from each other and operate 3 via downlink frequency bands that are different from each other.
    DOCKET NO.: CS10303 1 36. The method as in claim 32 further comprising establishing a communication 2 link with the second base station responsive to the quality of the signal being within a 3 predetermined quality level.
    1 37. The method as in claim 32 further comprising initiating a handoff to the 2 second base station responsive to the quality of the signal being within a predetermined 3 quality level.
    1 DOCKET NO.: CS10303 1 38. In a code division multiple access cellular communication network including 2 a plurality of base stations, a method of determining whether a mobile station in 3 communication with a first base station is a handoff candidate for a second base station, 4 the method comprising:
    determining a geographic position of the mobile station; 6 coupling the geographic position of the mobile station to at least one of the first 7 base station and the second base station; 8 deciding whether the geographic position of the mobile station is in a coverage 9 area of the second base station; and directing the mobile station to perform a quality measurement of a transmission 11 signal transmitted by the second base station, the quality measurement to enable any of 12 the mobile station and the cellular communication network to determine whether the 13 mobile station is a handoff candidate.
    1 39. The method as in claim 38 further comprising detecting a degraded signal 2 quality, wherein the step of determining is performed responsive to detecting the 3 degraded signal quality.
    1 40. The method as in claim 38 further comprising establishing whether the 2 cellular communication network has information relating to the geographic position of the 3 mobile station.
    1 41. The method as in claim 40 wherein the step of determining the geographic 2 position of the mobile station is responsive to establishing that the cellular 3 communication network does not have the information relating to the geographic position 4 of the mobile station.
    1 42. The method as in claim 41 further comprising querying the mobile station for 2 the geographic position of the mobile station responsive to establishing that the cellular 3 communication network does not have the information relating to the geographic position 4 of the mobile station.
    1 DOCKET NO.: CS10303 43. The method as in claim 38 further comprising:
    2 transmitting a signal from the second base station; 3 measuring at the mobile station a quality of the signal; and 4 establishing a communication link with the second base station when the quality is within a predetermined level.
    1 44. The method as in claim 38farther comprising analyzing whether the mobile 2 station is moving away from the first base station, wherein the mobile station is the 3 handoff candidate when the mobile station is in the coverage area of the second base 4 station and the mobile station is moving away from the first base station.
    DOCKET NO.: CS10303 1 45. In a cellular communication network including a plurality of base stations, a 2 method of determining whether a mobile station in communication with a first base 3 station is a handoff candidate for a second base station, the method comprising:
    4 establishing whether the cellular communication network has information relating to a substantially current geographic position of the mobile station; 6 acquiring the substantially current geographic position of the mobile station if the 7 cellular communication network does not have the information; 8 deciding whether the substantially current geographic position of the mobile 9 station is in a zone of mutual coverage of the first base station and the second base station; 11 analyzing whether the mobile station is moving away from the first base station 12 responsive to deciding that the substantially current geographic position of the mobile 13 station is in the zone of mutual coverage of the first base station and the second base 14 station; and searching for a signal transmitted by the second base station responsive to 16 analyzing that the mobile station is moving away from the first base station; 17 measuring a quality of the signal transmitted by the second base station; 18 deciding whether the mobile station is the handoff candidate responsive to 19 measuring the quality of the signal transmitted by the second base station.
    1 46. The method as in claim 45 wherein the signal comprises a spread spectrum 2 signal.
    1 47. The method as in claim 46 wherein the wherein the spread spectrum signal 2 comprises a pilot signal.
    I 1 48. The method as in claim 47 further comprising establishing a communication 2 link between the mobile station and the second base station if the step of deciding 3 indicates the mobile station is the handoff candidate.
    DOCKET NO.: CS10303 1 49. The method as in claim 48 further comprising breaking a communication link 2 between the mobile station and the first base station before establishing the 3 communication link between the mobile station and the second base station.
    1 -26 DOCKET NO.: CS10303 1 50. In a spread spectrum cellular communication network, a method of 2 determining whether a mobile station in communication with a first base station is a 3 handoff candidate for a second base station, the method comprising:
    4 establishing whether the spread spectrum cellular communication network has information relating to a geographic position of the mobile station; 6 acquiring the geographic position of the mobile station if the spread spectrum 7 cellular communication network does not have the infon-nation relating to the geographic 8 position of the mobile station; 9 deciding whether the geographic position of the mobile station is in a zone of mutual coverage of the first base station and the second base station; 11 analyzing whether the mobile station is moving away from the first base station 12 responsive to deciding that the geographic position of the mobile station is in the zone of 13 mutual coverage of the first base station and the second base station; 14 transmitting a spread spectrum pilot signal from the second base station; and searching at the mobile station for the spread spectrum pilot signal if the step of 16 analyzing indicates that the mobile station is moving away from the first base station.
    1 5 1. The method as in claim 50 further comprising:
    2 measuring at the mobile station a quality of the spread spectrum pilot signal; and 3 establishing a communication link between the mobile station and the second base 4 station when the step of measuring indicates the quality of the spread spectrum pilot signal is at a predetermined level.
    1 52. The method as in claim 51 wherein the information relating to the geographic 2 position of the mobile station comprises a substantially current geographic position of the 3 mobile station and a travel velocity of the mobile station.
    1 53. The method as in claim 52 wherein the information further comprises a 2 direction of travel of the mobile station.
    3 1 54. In a cellular communication network, a method for detem-lining whether a 2 mobile station in communication with a first base station is in a position to consider a 3 second base station as a handoff candidate, the method comprising:
    4 detecting a degradation in a communication link between the mobile station and the first base station; 6 determining whether information relating to a geographic position of the mobile 7 station is available at the cellular communication network; 8 acquiring the information relating to the geographic position of the mobile station 9 responsive to determining the information relating to the geographic position of the mobile station is not available; and 11 deciding whether further handoff processing should be performed based upon the 12 information relating to the geographic position of the mobile station., the further handoff 13 processing to enable any of the mobile station and the cellular communication network to 14 determine whether the mobile station is a handoff candidate for the second base station.
GB0031101A 2000-01-07 2000-12-20 Method and apparatus for location based consideration for cellular telephone handoff Expired - Fee Related GB2362297B (en)

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