HK1076548B - Method and apparatus for power level adjustment in a wireless communication system - Google Patents

Description

Method and apparatus for power level adjustment in a wireless communication system

Technical Field

The present invention relates to wireless voice and data communications, and more particularly, to a novel and improved method and apparatus for call recovery in a wireless communication system.

Background

A wireless communication network typically includes a plurality of Base Stations (BSs), each associated with a cell and/or sector, that communicate with a number of Mobile Stations (MSs). The base stations are controlled by a Base Station Controller (BSC). As the mobile station moves within the system, the quality of the received signal from the base station is not stable. When a communication link between a base station and a given mobile station deteriorates, communication loss can be prevented by establishing a link with at least one other base station. The handoff process provides for the initiation of such an alternate communication link. In the case of a handover, the infrastructure negotiates with each base station and mobile station. However, the signal typically degrades too quickly to be negotiated.

Therefore, there is a need for a method and apparatus for resuming a call in various situations. Further, there is a need for a reliable method of restoring a call in a wireless communication system.

Disclosure of Invention

The disclosed embodiments provide a novel and improved method of recovering a damaged call in a wireless communication system. According to one aspect, in a wireless communication system having a plurality of base stations, each of the plurality of base stations having a neighborhood group including neighboring base stations, each of the neighboring base stations having a default channel, a method includes transmitting default channel information to a mobile station; detecting an occurrence of a call recovery trigger; all base stations within the neighborhood group are instructed to transmit on the corresponding default channel.

In one aspect, a wireless device comprises: an antenna; a processor coupled to the antenna; transmit circuitry coupled to the antenna and the processor; receiver circuitry coupled to the antenna and the processor; a first set of computer readable instructions executable by a processor to receive a neighborhood list of base stations, the list including a default channel allocation for each neighborhood; a second set of computer readable instructions executable by the processor to identify a call recovery trigger and disable the transmit circuitry in response thereto; and a third set of computer readable instructions executable by the processor to establish a handoff with the at least one neighbor.

In another aspect, a wireless device includes: a transmitter circuit; a restoration adjustment unit following the call restoration operation to generate a predetermined power control command; and a power adjustment unit coupled to the recovery adjustment unit and the transmitter circuit, the power adjustment unit for adjusting the transmitter circuit in response to the power control command.

In yet another aspect, a computer program comprising computer-executable instructions embodied on a computer-readable medium, wherein the program comprises: a first set of instructions for identifying a particular event; a second set of instructions for disabling call recovery during a particular event; and a third set of instructions for notifying the wireless communication system of the particular event.

According to another aspect, in a wireless communication system, a method of call recovery includes: transmitting a pilot strength measurement message at a first transmit power level, waiting for a predetermined time period; and transmitting a pilot strength measurement message at a second transmit power level, wherein the second transmit power level is greater than the first transmit power level.

A wireless device includes: an antenna; a processor coupled to the antenna; transmit circuitry coupled to the antenna and the processor; and a first set of computer readable instructions executable by the processor to increase the transmit power of the pilot strength measurement message during call recovery.

Drawings

Fig. 1 illustrates, in block diagram form, a wireless communication system in accordance with one embodiment.

Fig. 2 illustrates, in block diagram form, portions of the wireless communication system of fig. 1 in accordance with one embodiment.

Fig. 3 illustrates, in timing diagram form, signal quality for two base stations in the wireless system of fig. 2 in accordance with one embodiment.

Fig. 4 illustrates, in block diagram form, a portion of the wireless communication system of fig. 1 during recovery in accordance with one embodiment.

Fig. 5 illustrates, in timing diagram form, signal quality for two base stations in a wireless system in accordance with one embodiment.

Fig. 6A and 6B illustrate, in flow diagram form, a method of resuming a call at a base station in accordance with one embodiment.

Fig. 7A and 7B illustrate, in flow diagram form, a method of resuming a call at a mobile station in accordance with one embodiment.

FIG. 8 illustrates, in block diagram form, a hierarchy of the system of FIG. 1 in accordance with one embodiment.

Fig. 9 illustrates, in a timing diagram, call recovery operations of the system of fig. 1 in accordance with one embodiment.

Fig. 10 illustrates, in timing diagram form, the initiation of a transmit power level at a mobile station after call resumption in accordance with one embodiment of the present invention.

Fig. 11 illustrates, in block diagram form, a mobile station in a wireless communication system in accordance with one embodiment.

Fig. 12A and 12B illustrate in timing diagram form a restart of the transmit power of a mobile station during recovery in accordance with one embodiment.

Fig. 13 illustrates, in flow diagram form, a restart of the transmit power of a mobile station during recovery in accordance with one embodiment.

Detailed Description

A method of call recovery in a wireless system according to one embodiment provides information about neighboring cells and/or sectors that are available and capable of call recovery for mobile stations that may lose a communication link. Each base station with call recovery function recovers the channel by a default forward call identified by a predetermined code. In another embodiment, each neighborhood is assigned to more than one default forward call recovery channel and the mobile station uses a hash function with IMSI (international mobile station identity), TIMSI (temporary international mobile station identity), ESN (electronic serial number), system time, or a combination thereof to deterministically determine which channels to use to receive transmissions from each recovery-capable base station. The mobile station may then receive the signal from the recovery base station using the channel. The mobile station may then be instructed to combine the power control subchannels from the multiple neighboring recovery base stations with an overhead message when the mobile station accesses the base station. This may also occur when the mobile station enters the coverage area of the base station in an idle state, i.e., when there is no continuous communication link, through traffic channel messages at call initiation or when the active set of the mobile station changes.

Fig. 1 illustrates a communication system 10 with a plurality of cells 12, 14, 16, 18, 20, 22, 24. The cells 12, 14, 16, 18, 20, 22, 24 communicate with the BSC over a radio broadcast interface. Each cell 12, 14, 16, 18, 20, 22, 24 has a corresponding neighborhood group consisting of cells within geographic and/or transmission proximity. For example, the neighborhood group of cells 18 includes cells 12, 14, 16, 20, 22, 24. In Spread Spectrum transmission Systems, such as Code Division Multiple Access (CDMA) Systems as defined by the standards "TIA/EIA/IS-95 Mobile Station-Base Station compatibility Standard for Dual-Mode Wideband Spread Spectrum cellular System", hereinafter referred to as "the IS-95 Standard", or "TIA/EIA/IS-2000 Standard for CDMA2000 Spread Spectrum Systems", hereinafter referred to as "the CDMA2000 Standard", Spread Spectrum signals occupy the same channel bandwidth, each having its own distinct Pseudorandom Noise (PN) sequence. The operation of a CDMA SYSTEM is described IN U.S. Pat. No. 4901307 entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS" and U.S. Pat. No. 5103459 entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMACELLULAR TELEPHONE SYSTEM", both of which are assigned to the assignee of the present invention and are incorporated herein by reference. In this way, multiple users can transmit messages simultaneously on the same channel bandwidth.

Fig. 2 illustrates a portion of the system 10 of fig. 1 including a base station 32, labeled BS1, in communication with an MS 38. BS132 is within cell 18 of fig. 1. Two other base stations 34, 36, labeled BS2 and BS3, respectively, are located within the cells 16, 24. The radio broadcast interface provides a medium for a Forward Link (FL) for communications from BS132 to MS38 and a Reverse Link (RL) for communications from MS38 to BS 132. Notably, the MS38 may move within the system 10 such that the signal quality to and from the BS132 deteriorates. To initiate a call, the MS38 sends a transmission on the access channel. BS132, BS 234, and BS 336 transmit channel assignment messages on the paging channel. The channel assignment identifies the Walsh code index of each base station.

Signal quality is typically measured as the signal-to-noise ratio (SNR) and can be expressed as the energy of the pilot signal per chip over the total received power density (E)_c/I₀). Fig. 3 illustrates a pilot at MS38 for the signal quality measured by BS132 and BS 234. The signal quality of BS 234 increases from time T0 and continues to increase beyond the threshold level labeled T ADD at time T1. The threshold level T _ ADD provides a reference signal quality that, when exceeded, instructs the MS38 to inform the base station to assume the base station is in its Active Set (AS). The AS consists of a base station in active communication with the MS38, both transmitting and receiving communications. The AS is typically selected from the base stations in the Candidate Set (CS). The CS includes base stations that are candidates for active communication with the MS 38. The CS is typically selected from base stations in a neighbor set of domains (NS).

Continuing with fig. 3, the signal quality of BS 234 is improving, while the signal quality of BS132 is deteriorating. Since the signal quality for a given base station is the ratio of the signal energy from that base station to other existing signals, an increase in the energy level of the signal received from BS 234 exacerbates the degradation of the signal from BS 132. At time T1, the MS38 measures the signal energy of the BS 234 above T _ ADD. This indicates to the MS38 the appropriate action required, i.e., the trigger for the handoff. At time t2, MS38 transmits a Pilot Strength Measurement Message (PSMM) to BS132 and BSC 26 that includes measurement information for BS132 and BS 234. At time t3, the BSC 26 sets up the link for the MS38 from the BSC 26 to the BS 234. The BSC 26 contains a selector. BSC 26 establishes a communication link with MS38 forming a "backhaul" communication network between BS132, BS 234, and BSC 26. At t4, BS132 transmits a Handoff Direction Message (HDM) that includes an associated code index that identifies BS132 and BS 234 and their Forward Link (FL) channels from BS132 and BS 234. This information allows MS38 to receive and demodulate signals from BS132 and BS 234. At time t5 MS38 receives the HDM from BS132 and begins demodulating signals from BS 234 in addition to signals from BS 132. It is noted that in this example, the handover involves only one new base station. However, such a handoff situation may involve any number of base stations, where those base stations in communication with the MS38 form an AS. When the MS38 receives signals, including symbols for example, from multiple base stations within the AS, the MS may combine the signals to produce a stronger signal. The combining process is referred to as "soft combining" of the FL and is usually done at an optimal ratio, i.e. weighting based on signal quality. At time t6, MS38 sends an acknowledgement or a Handoff Completion Message (HCM) indicating successful completion of the handoff to the HDM received from BS 132.

Referring again to fig. 3, a situation may arise when the signal quality of the BS 234 increases too quickly. In this case, the signal strength of BS 234 deteriorates relative to the signal quality of BS132 that will be BS132 together. The MS38 is prevented from communicating with the infrastructure prior to receiving the information necessary for handoff, such as the pseudo-random noise (PN) offset necessary to identify the BS 234 or the channel used by the BS 234 for the MS 38.

In a typical CDMA handoff process, the handoff prevents the loss of a communication link when a mobile station moves from the coverage area of one base station into the coverage area of another base station. In one type of handoff, a mobile station maintains a connection with two or more base stations at the same time in the case of a soft handoff. The current location of the mobile station may be considered the source cell and the next cell to which the mobile station moves may be referred to as the target cell. The mobile station uses a rake type receiver to demodulate multiple signals received on the FLs of multiple base stations. The two signals are combined to produce a composite signal of improved quality. When each of the plurality of base stations involved in the soft handoff demodulates the received signal separately, each transmits the demodulated and decoded information to the BSC. The BSC includes a selector that selects a best frame from the plurality of received frames. Other types of handoffs may be used for various conditions and system requirements.

In Mobile Assisted Handoff (MAHO), a mobile station measures signal quality for FL pilot signals from multiple base stations. This information is reported to the source base station. The signal quality is compared to various thresholds to make a decision to add the base station to the AS. If the signal quality of a given pilot is greater than the pilot detection threshold T _ ADD, the pilot is added to the AS. In an alternative embodiment, the pilot may be added to the CS first and then to the AS. In effect, the thresholds allow for the transition of the base station state from one group to another.

In the case where handoff negotiation is not possible, call recovery provides information to the mobile station in advance. Call recovery is initiated in various circumstances. In normal operation, the mobile station and the base station use triggers to determine their proper operation. For example, different thresholds are used by mobile stations within system 10 to make decisions regarding which information to report back to the base station. The aforementioned threshold T _ ADD represents the signal quality level at which the base station is added to the AS. When the mobile station receives a signal measuring the above-mentioned T _ ADD, the mobile station moves the base station into the CS, searches for the base station more frequently, and reports the situation to the system through its existing AS. Another threshold T DROP provides a signal quality level below which the base station is discarded by the AS. When the mobile station receives a signal below the measurement T _ DROP that lasts longer than T _ TDROP, the mobile station reports this to the system through the existing AS. In each case, the base stations within the AS relay this information to the base station controller.

For call recovery, the base station within the AS looks for any of a variety of possible triggers. The first type of call recovery trigger occurs when the FL signal quality falls below a threshold level for a duration longer than another threshold. The class of triggers includes when the base station receives a continuous Power Control (PC) request from the mobile station to increase the base station's transmit level. Typically the base station has already transmitted to the mobile station at the highest upper power level. For example, FL traffic transmission is maintained at a high level for a predetermined period of time. The mobile station may send many requests to increase power, i.e., UP commands. Alternatively, the mobile station may report a large number of erasures. Erasure occurs when more than one bit threshold level is received without reaching a predetermined confidence value. In other cases, the mobile station transmits a message indicating to the base station that its outer loop setpoint is high or at its maximum allowed level, or at those levels for an extended time.

The second type of trigger occurs when a certain response from the mobile station is expected, but no response, or a different response is received. This type of trigger includes the lack of an acknowledgement from the mobile station to the message sent by the base station requiring an acknowledgement. The message may be retransmitted a predetermined number of times before the triggering condition is met. The predetermined number of times may be fixed or variable and variable in air. Also, the base station may receive a repeated RL message from a mobile station requiring an acknowledgement, where the message is received after the base station sends the acknowledgement.

The third type of trigger involves poor quality of the reverse link, e.g., when the Frame Error Rate (FER) of the RL is above a certain threshold level. Alternatively, the RL may be maintained at a high level for a predetermined period of time. Another case may have a high RL setpoint. The base station to be added to the AS also has a call recovery trigger that initiates recovery action. The most important trigger is a notification from the BSC indicating that there is a potential problem with a given mobile station. When this occurs, the base station begins searching for signals from the mobile station.

The mobile station may also use different call recovery triggers to enter call recovery. The first type of trigger occurs when there is an abnormal number of errors in the received signal. For example, FL deletion over a moving window may exceed a predetermined threshold level. In one embodiment, the threshold level is 12 consecutive frames that are subject to deletion. In this case, the mobile station will turn off the transmitter portion of the mobile station and may turn the transmitter back on if at least two consecutive FL frames are not erased.

The second type of recovery trigger for a mobile station occurs when the mobile station receives a PC command from a base station indicating a power increase. The base station may have difficulty in receiving the RL signal due to a large path loss from the mobile station.

A third type of recovery trigger occurs when one or more RL messages requesting acknowledgement from the base station are not acknowledged. This is called a retransmission retry trigger. Also, there may be an improper or no response between messages from the base station to the mobile station. A similar type of trigger occurs when a duplicate FL message is received requiring an acknowledgement, after the mobile station actually sends out the acknowledgement.

A fourth type of recovery trigger occurs when the mobile station transmits at a high level for a predetermined period of time. In this case, it is assumed that the RL does not have enough energy to pass to the base station.

In one embodiment, the threshold for the flexibility is implemented for one or several different call recovery triggers. The call recovery trigger may be based on several transmission attempts within the system 10. These attempts are often made between the signaling and physical link layers. The link layer is referred to as layer 2 and will be discussed below in fig. 8. In a system with recovery functionality, such as system 10 of fig. 1, MS38 performs a recovery procedure to maintain a call when a communication link, such as the FL, deteriorates. Triggers often initiate recovery operations, where a trigger indicates when a parameter or metric exceeds a threshold. These thresholds may be dynamically adapted to the conditions of the system 10 and the environment. Also, the threshold may be adjusted based on historical or statistical records of system 10 operation.

In one embodiment, the number of relayed transmissions on the RL, or the time between successive erasures, or the MS transmitter disabling may be in response to instructions transmitted from the system 10 infrastructure, such as BS132 and/or BSC 26. In another embodiment, a fixed parameter is defined for a particular action, such as a particular maximum number of allowable retransmissions. In another embodiment, the movement condition and/or location provides a trigger. The proximity of the MS38 current transmit level to a predetermined maximum value may trigger call recovery. Other triggers include FL quality measured in the current AS transmission erasures, insufficient inner loop power control, where the desired SNR for the MS38 is different from that provided by the inner loop, and so on. Still other embodiments may combine specific parameters and movement conditions into a trigger.

The system 10 infrastructure may provide information on the type of operation that the MS38 is to facilitate in determining the call recovery trigger threshold and may utilize this information to select the fixed parameters provided to the MS38 to use as the trigger threshold. In one embodiment, there is a general number of retries for a call that is problematic or has been dropped. An alternative embodiment uses a load RL to set and adjust the threshold. Still alternative embodiments may use the location of the MS38 within the system, such as a sector of a given cell. Still other embodiments contemplate days of the week or times of the day coordinated with known mobile traffic patterns. Any combination of these mechanisms may be implemented as applicable or desired.

In the system 10 of fig. 1 and 2, each base station 32, 34, 36 transmits header information to the mobile stations with which it is in communication. The header information for each BS 32, 34, 36 includes its corresponding neighbor list. The neighborhood list identifies pseudo-random noise (PN) code offsets for corresponding neighborhoods.

Referring to fig. 4, BSC 26 responds to any of the different triggers by placing a roundtrip connection with BS132 and BS 234. According to one embodiment, the method 100 of call recovery is initiated as illustrated in FIG. 6. An example specific signal quality graph is illustrated in fig. 5. In this example, there is a time when a potential problem with the MS38 is identified.

In one embodiment of call recovery method 100 illustrated in fig. 6A and 6B, BS132 sends a default channel assignment for the set of neighbor base stations to MS38 at step 102. The base stations within the neighborhood group are units with recovery functions, with the necessary software and/or hardware to implement call recovery and with overlapping coverage with the base station transmitting the neighborhood group. The default channel assignment identifies the default channel code index used by base stations within the neighborhood group, including the code of BS 234. Each recovery-capable base station in the neighborhood group has a default spreading code that is used to identify the mobile station when call recovery is required. The spreading code of one embodiment is a special Walsh code. The BS 234 sends a retransmission retry trigger to the MS38 at step 104. The retry re-try trigger specifies the number of retries allowable by the MS38 before initiating the call recovery operation. BS132 then determines whether a recovery trigger has occurred at decision diamond 106. If a recovery trigger has not occurred, processing waits for a trigger to occur. When the trigger occurs, processing continues to step 108 to instruct all base stations within the NS of BS132 to transmit on their respective default channels to print MS 38. Notably, some base stations within the NS may be unable to establish a communication link due to the weak FL or RL, however, each base station within the NS begins transmitting to the MS 38. Several transmissions provide a stronger FL signal at the MS38 and a more reliable RL to the BSC 26.

It is noted that, according to this embodiment, the number of retries of the RL message, or the amount of time allowed for the successive erasures, is determined by the BSC 26 and provided to the MS38 via radio link-specific messages and broadcasts. Alternate embodiments use fixed parameters that differ from other parameters. One embodiment includes a function of the movement condition. The mobility condition may take into account how close the actual transmission level of the MS38 is compared to the maximum transmit level. Also, another mobility condition considers the quality of the FL, such AS deletion of the current AS. In addition the movement conditions take into account internal circulation deficiencies. The inner loop deficiency is the difference between the target SNR and the SNR given by the inner loop PC. Another embodiment combines the movement conditions and the transmission type.

The number of allowable retries may be adjusted based on statistics related to dropped or problematic calls. For example, there may be an average number of retries beyond which most problematic calls cannot be recovered. Other considerations include RL loading, MS38 location, and/or time of day or date. In the latter case, some mobile traffic types affect the number of mobile phones that require fast call recovery.

Continuing with fig. 6A, the BSC 26 determines the current AS of the MS at step 110. The BSC 26 then starts an HDM timer at step 112 and transmits the HDM at step 114. At this point, system 10 desires to remove the communication link from the default channel. The default channel may be used by any mobile station within system 10 and thus usage is optimized. When the MS38 uses a given default channel, that channel is not available to other mobile stations. The base station within the NS is instructed to start transmission on a new channel that is either alternative or parallel to the transmission on the default channel. This is the initiation of a handoff condition.

If the BSC 26 has received a message from the MS38 indicating that the handoff is complete at decision diamond 118, processing continues to step 120 to interrupt the communication link between the MS38 and the NS member on the default channel. Processing then continues to step 124. Conversely, if a handoff completion message is not received, the BSC 26 checks whether the HDM timer has expired at decision diamond 122. If the HDM timer expires, the appropriate default channel terminates transmission to the MS38, call resumption is cancelled at step 124, and the default channel and the new channel are terminated at step 125. Normal operation continues at step 126. If the timer has not expired at decision diamond 122, processing returns to decision diamond 118 to await a handoff complete message from the MS 38.

Fig. 6B details a portion of method 100, wherein step 110 illustrates starting a timer at step 130. The BSC 26 checks the PSMM from the MS38 at decision diamond 132. If a PSMM has been received, processing proceeds to step 134 to set the AS to include the neighborhood within the PSMM. If a PSMM has not been received, processing continues to decision diamond 138 to determine whether a timer (initiated at step 130) has expired. If the timer has expired, processing continues at decision diamond 144. If the timer has not expired, processing returns to decision diamond 132.

After the AS is set at step 134, if the RL is enhanced at decision diamond 136, the BSC 26 determines whether there is a neighbor that has acquired the MS38 signal but is not included in the PSMM at decision diamond 140. These neighborhoods are called the auditory field (HL) and are added to the AS at step 142. Processing then returns to step 112 of fig. 6A.

If the timer expires without receiving a PSMM, the BSC 26 determines at decision diamond 144 whether there is a neighbor acquiring RL MS38 signal, i.e., HN. In this case, AS is set to include these HNs at step 146. If no HN is found at decision diamond 114, the call is resumed is terminated at step 148 and the call is terminated.

At decision diamond 110, the method determines whether the transmitter of the MS38 is off. If the transmitter is off, the BSC 26 instructs the MS38 to turn the transmitter on at step 110.

A call recovery method 200 for a mobile station of an embodiment is illustrated in fig. 7. At step 202, the MS38 communicates with a base station within the AS (0). It identifies the current AS. If a call trigger has occurred at decision diamond 204, processing continues to decision diamond 208. The recovery trigger may be one of those discussed above, or another indicating that the MS38 requires a rescue type operation, i.e., the MS38 may lose the FL communication link. If no trigger has occurred, normal operation continues at step 206. Decision diamond 208 determines whether the transmitter of the MS38 is available. If the transmitter is enabled, processing continues to step 214, and if not, the MS38 checks for a trigger condition at decision diamond 210. If a trigger condition exists indicating that the MS38 disables the transmitter, appropriate action processing continues to step 214 at step 212. If no trigger indicates that the transmitter is disabled, processing continues to step 214. In step 214, a wait timer is set. The wait timer is checked at decision diamond 216 and upon expiration the resume timer begins at step 218. If the wait timer has not expired, processing continues to determine if the MS38 returns to the normal mode of operation at decision diamond 222. Normal operation continues from step 206, otherwise processing returns to waiting for the expiration of the timer.

Continuing with FIG. 7, from step 218, if the transmitter of the MS38 is disabled, the transmitter is enabled at step 220. The MS38 transmits a predetermined preamble for time period Y. The header provides information about the MS38 transmission but no actual data or symbols. The MS38 transmits a PSMM message at step 228. At decision diamond 228, if an HDM is received or if some acknowledgment acknowledging the PSMM is received, then the MS38 process proceeds to wait a predetermined time period X after which the AS is updated. If no HDM or PSMM acknowledgements are received at decision diamond 230, processing continues to decision diamond 232 to check that the transmission of PSMM has not exceeded the maximum allowed secondary value. If the PSMM can be retransmitted, i.e., the maximum value has not been reached, processing returns to step 228 and the PSMM is transmitted. However, if the maximum value has been reached, processing continues to step 236 and call recovery is terminated.

According to another method of call recovery, the BSC 26 informs the BS132 of all recovery-enabled neighbors of potential problems. The BSC instructs the MS38 to turn on the transmitter portion of the MS38 and instructs the base stations in the neighborhood group to listen to the MS 38. The base stations within each neighborhood group transmit reports upon detection or acquisition of a signal from the MS 38. The report is received from a subset of base stations, where the subset may include all or a portion of the base stations within the neighborhood group. The BSC 26 informs the MS38 of the default channel for each base station in the subset. The base stations within the subset then use the appropriate default channel to initiate communication with the MS 38.

In yet another approach, a subset of the neighborhood group is determined based on the most recently transmitted PSMMs. There may be a problem because the most recently transmitted PSMM may not have been received correctly, in which case the PSMM used to identify the subset is incorrect. As an example, call recovery is blocked when the most recently received PSMM identifies BS132 and BS 336, but MS38 then transmits an unreceived PSMM identifying BS132 and BS 234. BSC 26 and BS 336 set up the backhaul network and BS 336 begins transmitting to MS38 on the default channel. Unfortunately, the MS38 assumes that communication with the BS 234 will be established for call recovery and is ready to be excluded on a different default channel. More than the transmission from BS 336 is wasted and actually results in more noise within system 10.

When call recovery is initiated by the MS38, a timer may be used to delay the initiation following the call recovery trigger. The time period of the timer may be set by the BSC 26. Upon expiration of the timer, the MS38 transmits a preamble on the RL pilot channel. The header includes a call recovery message. In one embodiment, the header is a predetermined constant that may be set by the BSC 26. In another embodiment, the header is a variable length determined by the system operator. Following the preamble transmission, the MS38 sends a message regarding the FL change. The message may be a PSMM. The message may be sent multiple times to ensure receipt by the BS 234.

The combination of the above approaches provides the benefits of different call resumption. In one embodiment, the call recovery method is based on the radio frequency transmission environment of the base station of the source cell. When the number of neighbors with recovery function is small, e.g., 2, the BSC 26 will instruct all neighbors to transmit on the corresponding default channel. The AS is updated and the MS38 transmitter is enabled without delay. More neighbors with recovery functions, the BSC 26 instructs the neighbors to listen for signals from the MS 38. These auditory neighborhoods are instructed to use the default channel after waiting for a delay for the neighborhood to report whether they have received a signal from MS 38. Similarly, if the PSMM is received from the MS38 within a predetermined time period, these base stations identified by the PSMM are instructed to use the default channel. It is worth noting that PC commands sent over the PC subchannel are considered valid when FL operation is appropriate, as defined by a fixed number of consecutive good frames.

Fig. 8 illustrates the structure of the wireless communication system 10 of fig. 1 in a layer structure format. Structure 700 includes three layers: a signaling layer 702; a link layer 704; and a physical layer 706. The signaling layer 702 provides higher layer signaling 708, data services 710, and voice services 712. The signaling layer 702 provides voice, packet data, simple circuit data, and synchronous voice and packet data services. The protocols and services are provided at this layer to the two lower layers accordingly. The link layer 704 is divided into a Link Access Control (LAC) sublayer 714 and a Medium Access Control (MAC) sublayer 716. The application and signaling layer 712 protocols utilize services provided by the LAC sublayer 714. The link layer 704 acts as an interface between upper layer protocol and signaling layer 702 applications and the physical layer 706. The MAC sublayer 716 also includes a multiplexing and quality of service (QoS) delivery module 722. The link layer 704 and the signal layer 702 are coupled to a physical layer 706. The physical layer 706 consists of the physical channels 724 that are transmitted.

Fig. 9 provides a system 10 operation synchronization scheme according to one embodiment. See the methods of fig. 6A, 6B and 7. The horizontal axis represents time and the vertical axis represents different channels for transmission. The source cell base station, BS132, is in the middle where information is transmitted to MS38 over a traffic channel. Two channels are illustrated for the MS 38: a transmission channel Tx, and a receiver channel Rx. Two schemes are illustrated for the receiver channel: rx₁And Rx₂. Also illustrated in the neighbor base station is the target base station BS 234. Both the default channel and the new channel are illustrated. The new channel is a channel for communicating with the MS38 after the handoff. Processing receives from the MS38 a second message identified AS AS (0)Transmission from an AS begins. The MS38 simultaneously transmits on the traffic channel of the source cell BS 132. At time t1, a call recovery trigger occurs. The MS38 and BS132 recognize the trigger. Notably, the trigger may be a generic event, such as a PS request from the MS38 to the BS132 that is continuous to increase the transmit power of the FL, or may be a separate event. Also, the MS38 and BS132 may not be able to recognize the trigger simultaneously. The MS38 may often recognize the trigger before the BS 132.

When a trigger is identified at time t1, BS132 initiates transmission of a default channel from neighbor BS 234. This initiation may be through the BSC 26. At time t2, the BS 234 begins transmitting on the default channel. The transmission is in parallel with the same transmission from BS 132. When the trigger occurs, the MS38 disables the transmitter for a predetermined waiting period. The waiting period ends at time t3 and the MS38 transmits a preamble for period Y. At the same time, the AS of the MS38 changes from AS (0) to AS (1). The base stations identified within AS (1) are all the base stations mentioned within the most recent PSMM. In an alternative embodiment, AS (1) may also be all neighborhoods of BS 132.

At the expiration of the header at time t4, MS 28 begins transmitting the current PSMM. In response to receiving the PSMM at time t5, BS132 and BS 234 transmit HDMs at time t 6. The HDM signals this change in AS (2) AS at time t 8. Notably, the next PSMM is transmitted at time t7, where the PSMM is transmitted periodically to identify the signal received at the MS 38.

At time t8, the BS 234 begins MS38 transmission on the new channel. The MS38 transmits the HCM, which triggers the termination of the transmission of the MS38 on the default channel at time t 9. In the scenario illustrated in FIG. 9, call resumption begins at time t2 and terminates at time t 9. At time t9 the handoff is complete and BS 234 is the MS38 current source cell base station.

Another scenario is illustrated for receiver channel Rx 2. Here AS (0) remains active until time t 5. Following time t5, MS38 continues to receive from AS (0) for a predetermined period of time X, after which AS (1) is changed. In this case, AS (1) includes only those base stations that can receive signals from MS 38. At time t8, there is a sequential change in the HDM response from AS (1) to AS (2). This case corresponds to a method in which only the neighbourhood from which a signal can be obtained from the MS38 is indicated for transmission over the respective default channel.

Once call recovery is complete and handoff is complete, MS 28 must determine the initial transmission power level. According to one embodiment, the system 10 of fig. 1 uses closed loop power control to adjust the transmission power level. Alternative embodiments may use an open loop approach to power control. Open loop refers to transmitter (or mobile or base station) controlled operation in which the receiver is not directly involved. For example, a particular directional link open loop power control requires the mobile to adjust the directional link transmit power based on the power level of the signal received from the base station over the forward link. Closed loop power control extends open loop operation whereby the receiver is actively involved in power adjustment decisions. For example, an RL closed loop power control base station compares the received signal power level from a given mobile to a threshold. The base station then instructs the mobile to increase or decrease the reverse link transmit power based on the comparison. Instead, the mobile monitors the received signal power level on the FL and provides FL quality feedback to the base station. Closed loop operation is used to compensate for power fluctuations associated with fading, such as rayleigh (Raleigh) fading, of a given link.

Immediately after the handoff and prior to the establishment of power control, the MS38 begins transmitting at the initial power level. The RL transmit power level may be restored before disabling the transmitter of MS 38. The power level may remain at this initial level until closed loop power control continues to be performed.

In an alternative embodiment, the power level is initiated at the last level before disabling the transmitter and gradually increased at a predetermined rate until power control continues to be performed. The rate of increase is generally set by BS132 and/or BS 234 and may be a fixed or variable. The increase continues before RL closed loop power control resumes.

Another embodiment begins recovery with open loop control based on the total power received by the band. This process is similar to the access process. It may be corrected for several forward link base stations visible to the MS 38. Open loop control continues until closed loop power control continues to be performed. Fig. 10 illustrates power regulation according to an embodiment. The horizontal axis represents time and the vertical axis represents transmission power level. After the first period of time, at time t2, the transmit power is increased by a predetermined increase value. The incremental value may be a fixed or variable value that increases or decreases over time. In one embodiment, the increment value accommodates and is responsive to conditions of system 10, wherein the increment value may increase or decrease from one time period to the next. Eventually, a predetermined maximum transmit power level may be reached after a predetermined number of time periods. The transmit power waits at this maximum limit for the closed loop power control to continue to be performed.

In another embodiment, the initial transmit power is based on the received pilot signal quality. The signal quality is represented by a pilot E_o/I₀Or pilot frequency E_cIs the planned AS measurement. In open loop power control, the transmit power typically has a given relationship Tx (-Rx) + k, where k is the cumulative correction constant and Tx is the RL transmit energy and Rx is the FL receive energy. For closed loop power control methods, the transmit power is typically given by the relationship Tx (-Rx) + k + y (t), y (t) with an additional cumulative correction variable. The term (k + y (t)) is referred to as β. In other forms, the following relationship guarantees Tx + Rx ═ k + y (t).

The determination of the initial transmit power applies the beta of the previous transmission to the new transmission. The new transmit power level is calculated via Tx (t) — (Rx (t) + Tx (0) + Rx (0), where Tx (0) is the transmit energy before call recovery and Rx (0) is the receive energy before call recovery.

Fig. 11 illustrates a wireless device MS38, such as a cellular telephone or Personal Digital Assistant (PDA), operating within the system 10 of fig. 1. The MS38 includes an antenna 300 for transmission and reception. The antenna 300 is coupled to a duplexer 302 to isolate the receiver path from the transmitter path. The duplexer is coupled to receiver circuitry 308 that constitutes a receiver path and is also coupled to amplifier 304 and transmit circuitry 306 that constitutes a transmitter path. The amplifier 304 is also coupled to a power conditioning unit 310 that provides control of the amplifier 304. Amplifier 304 receives the transmit signal from transmit circuitry 306.

The signal received by the antenna 300 is provided to a power control unit 314 which implements a closed loop power control scheme. The power control unit 314 is coupled to a communication bus 318. Communication bus 318 provides a common connection between modules within MS 38. The communication bus 318 is also coupled to a memory 322 and a recovery adjustment unit 316. The memory 322 stores computer readable instructions for applying various operations and functions to the MS 38. Processor 320 implements instructions stored in memory 322. For normal operating conditions, the power control unit generates a PC signal to power adjust 310 through multiplexer 312. Power adjustment 310 then transfers the PC signal as an amplification level to amplifier 304.

The MS38 may disable the transmitter when call resumption occurs. When the transmitter is re-enabled, a handoff completion signal is provided to the call recovery unit 316. The handoff completion signal instructs the call recovery unit 316 to generate a predetermined PC signal. The PC signal so produced may implement any of the aforementioned schemes for initial RL transmit power generation, and may implement another approach. The handoff completion signal is also used to control the multiplexer 312. Following call recovery, the PC signal generated by the recovery adjustment unit 316 is forwarded to the power adjustment unit 310. In parallel, closed loop power control begins. Once closed loop power control is completely resumed, the handoff complete signal is inverted and the multiplexer 312 selects the PC signal generated by the power control unit 314 to provide to the power regulator 310. The operation of the recovery proxy unit 316 may be implemented by the microprocessor 320 in software instructions or in efficient and reliable hardware.

In one embodiment, the specific operation of the MS38 or BS132 is considered a special event. Special events include a number of conditions and processes that may cause false triggers. In other words, a special event may cause a call recovery trigger to occur, but the trigger is not important. A special event is a rover search. The MS38 is instructed to search for a Global Positioning System (GPS) on another frequency. The GPS message provides the location of the MS 38. The mobile location is scheduled to be periodically searched. Typically, the MS38 has a deductive message regarding the synchronization of such searches. Alternate embodiments may implement any of the special events in which the trigger is ignored.

Other events may include actions taken by the MS38 when the trigger is ignored. Among these types of events, the MS38 notifies the source cell BS132 of a special event. In one embodiment, the special event is a candidate frequency search in which the MS38 tunes to a different frequency to find a signal from a neighboring base station on that frequency. This may allow for a better transition in coverage of different frequencies, such as exchanges between Personal Communication System (PCS) frequencies and cellular frequencies. Upon the occurrence of a special event of this type of mobile station initiation, the MS38 notifies the source cell BS132 to ignore the trigger on the MS38 for a specified period of time or until a later re-notification.

In order to avoid such false triggering during special events, according to one embodiment, the source cell base station, such as BS132, informs the MS38 of search synchronization including at least when to start searching and the length of time allocated for searching. During a special event, the MS38 disables the call recovery trigger from the initial call recovery.

In another embodiment, the MS38 notifies the BS132 of an upcoming special event. In response to the notification BS132 may acknowledge the special event, negate the event or reschedule the event. Again, this provides the MS38 with sufficient information to disable call recovery triggers during special events.

Thus described herein is a novel and improved method of maintaining communications in a wireless communication system. When there is a problem with the communication link between the mobile station and the corresponding source cell base station, the mobile station and the infrastructure prearrange potential rescue base stations. The source cell base station contacts all recovery-capable neighbors as potential rescuers. The recovery-enabled neighborhood has a predefined default channel that is compatible with the soft handoff of the mobile station. The default channel is only temporarily used during the initial part of the handover. Each rescue base station is instructed to use the default channel for rescue transmissions. Rescue transmissions are considered call recovery operations. The mobile station establishes a soft handoff with the rescue base station, wherein the FL uses a default channel. The rescue base station then initiates transmission on the additional channel. The rescue base station discontinues default channel use for transmissions to the mobile station once the handoff is complete. In one embodiment, the source cell base station provides the mobile station with a recovery-enabled neighbor list as overhead in transmission and before there is a communication link problem. In this way, the mobile station has sufficient information to handle the handoff in the event that the FL is lost before receiving the handoff information.

In another embodiment, more than one default channel is allocated to the domain BS 234. The use of several default and rescue channels increases the recovery capabilities of the system 10. Each domain can give the call resumption to more than one mobile station, such as MS 38. In operation, source cell BS132 provides MS38 with identifiers corresponding to several channels associated with BS 234 prior to call resumption. The MS38 and the BS 234 each store a deterministic function, such as a hash function, to map the identifier to a particular channel. The use of a hash function is in particular a pseudo-random process. In addition, an electronic serial number is also assigned to the MS 38. The electronic serial number may be stored within the MS38 or may be provided to the MS38 upon call resumption. Upon call resumption, source cell BS132 provides the electronic serial number of MS38 to BS 234. Both the BS 234 and the MS38 apply a predetermined function to calculate the appropriate default channel.

The hash function of the data structure allows exactly one probe to be used within the data structure to identify a key in a set of words, the hash function mapping its parameters to a predetermined type of result. The hash function is deterministic and stateless. That is, the values depend only on the parameters, and the same parameters yield the same results. It is important for the hash function to avoid collisions, where a collision is defined as two different parameters hashing to the same value. It is also important that the distribution of hash values is unique, i.e., the probability of any particular value of a predetermined type of hash function range should be roughly equal to the probability that it returns any other value. In alternative embodiments, other forms of encryption functions may be implemented for several default channel identifications at call recovery.

The mobile station transmit power level is not controlled by the base station when the call is resumed. When the base station enables or reinitiates the transmitter, a decision is made to select the transmit power. In one embodiment, the initial power level of transmission of the preamble and the PSMM are predetermined prior to call recovery. The initial level may be a fixed level or may be dynamically adjusted based on system configuration, environmental considerations, geographic considerations, usage history, or any of a variety of factors that have an impact on communications.

With respect to the system of fig. 1, the MS38 determines the transmit power level for the transmit header and PSMM information. Different schemes are possible to implement to adjust the transmit power, two of which are illustrated in fig. 12. In one embodiment illustrated in fig. 12A, the header and PSMM are designated at a predetermined designation k₁Is transmitted. The transmission power level is predetermined to be a fixed value, P_fixed. The fixed value may be the last transmit power before the incoming call is resumed. The fixed transmit power level is the final transmit power level adjusted by a different, increase or decrease. Additionally, the transmit power level may be calculated as a function of a previous transmit power level, such as by increasing by an increase value Δ. In one embodiment, the transmit power level is a constant level that was previously transmitted by the base station to the mobile station. In another embodiment, the constant level is determined via the mobile station's limitations, e.g., related to transmitter capacity.

As illustrated, the first header is transmitted at time t1 and the PSMM is transmitted at time t 2. The header and PSMM are transmitted until time t 3. Notably, in the exemplary embodiment, the preamble is a reverse pilot that is active in PSMM transmissions. At time t3 interval k₁Beginning and continuing until time t 4. The next header is transmitted at time t 4. The process continues until MS38 receives an acknowledgement from BS132 that the PSMM has been received. The acknowledgement may be an HDM message or may be a PSMM layer 2 acknowledgement. If the MS38 fails to receive the HDM or an acknowledgement within a predetermined period of time, MS38 terminates transmitting the header and PSMM information and cancels call recovery. The transmit power level resumes power control when the MS38 determines that the forward link guarantees transmission quality. In one embodiment, the quality criterion is guaranteed by the correct frames received in succession by the forward link. According to one embodiment, when the forward link quality is guaranteed to transmit and reverse power control resumes, the mobile station also resumes normal traffic transmission on the reverse link while it continues with k-out without a header₁Spaced PSMM transmissions. Whether a link can meet transmission quality criteria is generally determined by system configuration and parameters, however, any of a number of criteria may be used. In addition, the criteria may be dynamically adjusted to accommodate system operation.

Fig. 12B illustrates another embodiment in which the transmit power level is adjusted in increments during start-up of the transmitter. The first preamble and PSMM are transmitted at a first power level P1. The ratio of the total transmit power of the PSMM and preamble to the transmit power of the preamble and then pilot channel is maintained at a predetermined ratio, described herein as y. As shown in FIG. 12A, the header and PSMM are at k₁The intervals are relayed, however, the total transmit power increases with successive occurrences. The increase may be an incremental increase, where the increment is predetermined and specific to the system. In addition, the increments may be provided by the base station to the mobile user. Note that alternative embodiments may be this different time interval. In addition, the number of transmissions of the header and PSMM information may be different each time. The transmission power level increases to a maximum value P_MAX. The transmit power level also continues to increase but remains at a maximum value in subsequent transmissions. In one embodiment, level P_MAXDetermined by BS132 and transmitted to MS 38. Alternative embodiments may fix P_MAXOf (c) is detected. Upon receiving the layer 2 acknowledgement of the HDM or PSMM, the mobile station resumes normal traffic and reverse power control from the base station. According to another embodiment, when the forward link reception quality reaches a predetermined value, the transmission of the header and PSMM continues until a layer 2 acknowledgement of the HDM or PSMM is received and reverse power control of the base station resumes.

FIG. 13 illustrates an embodimentA method 400 of restarting a transmitter at a mobile station upon call recovery is shown. Transmission Power P of preamble and PSMM at step 402_TxAs the last transmitted power level P of the mobile station prior to the recovery process_TxOLDThe function of (2) is initiated. In one embodiment, P_TxSet equal to the total power P received by the mobile station prior to the recovery procedure_RXOLDAnd total power P received by the mobile station after call recovery initiation_RxNEWRegulated P_TxOLD. This equation is given at step 402 of fig. 13. The enabled transmit power level is the last transmit power level adjusted by the difference, increase, and decrease in the total power received at the MS38 since it last disabled its transmitter. The preamble and the PSMM are transmitted according to the power level. Further embodiments may apply a predetermined power level for the initial transmit power. The mobile station waits to receive an acknowledgement from the base station that the PSMM passed. In the illustrated embodiment, the mobile station checks for receipt of an HDM at decision diamond 404. Another embodiment checks the layer 2 acknowledgement of the PSMM. Yet another embodiment checks for layer 2 acknowledgements or HDMs of PSMMs. Mobile station at k₁The interval transmits a header and PSMM information. The mobile station continues to check for HDM while transmitting, or between transmissions. When HDM is at k₁The inter-cell is received and the mobile station returns to normal traffic processing in step 406 where reverse power control continues to receive power control commands from the base station. If at k₁The HDM is not received within the interval and the mobile station is ready to transmit the next header and PSMM. At decision diamond 408, the mobile station compares the current transmit power P_TxAnd maximum power level P_MAX. It is noted that in one embodiment, the process checks the received transmission quality after step 406. In one example, the process checks for two good frames received in succession. If two consecutive good frames have not been received, processing continues to decision diamond 408. However, if two consecutive good frames are received, processing transmits the preamble and PSMM at the controlled power level and processing transfers to decision diamond 416.

Also, note that when the mobile station checks for receipt of an HDM at step 404, and other PSMM acknowledgements, reverse power control is reactivated after two consecutive good frames are received. The result of two consecutive good frames being received is a jump out process that increases the transmit power for the preamble and PSMM.

When P is present_TXLess than P_MAXThen processing proceeds to step 412 to increase P_TX. The increase may be based on some fixed increment value, and may be a variable increment. Further embodiments may transmit several times at each transmit power level before each increase. The mobile station transmits the preamble and PSMM at the adjusted power level in step 414. Processing then proceeds to decision diamond 416 to determine whether the time period for the transmitter to restart has expired. If P is_TXIs equal to or greater than P_MAXIf so, processing continues to step 410 at P_MAXAnd carrying out transmission. Continuing from decision diamond 408, if the time period has expired, processing returns to decision diamond 404. If the time period has expired, the mobile station terminates the call recovery in step 418.

In one embodiment, to avoid unnecessarily triggering call recovery at the base station, the mobile subscriber reports "off time" when searching for hard handoff candidate frequencies. In this search, the mobile user may move away from the current frequency for a period of time sufficient to trigger call recovery. Call recovery is thus avoided by providing the base station with information that is not actually a call recovery condition.

Concurrently with the transmitter restart, the mobile station waits for the forward link to recover, where recovery is typically defined by the successive reception of two good frames at the mobile station. Upon recovery, reverse power control is initiated.

There has thus been described a novel and improved method and apparatus for power level adjustment in a wireless communication system. The different examples, embodiments, aspects and figures are provided for the understanding that they do not exclude other embodiments within the spirit and scope of the invention. Those of skill in the art would understand that the data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description are advantageously represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. Similarly, when describing different embodiments in terms of different polarity diagrams, the format and symbols are relative terms and are not strictly limited to high and low logic levels.

Those of skill would further appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, firmware, and/or combinations of both. Various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, software, or firmware depends upon the particular application and design constraints imposed on the overall system. The skilled person will recognize the interactivity of the hardware and software in these cases and how best to implement the described functionality for each particular application. Additionally, with regard to the flow diagrams, there are functional steps that may interact while maintaining the spirit and scope of the invention.

The various illustrative logical blocks, modules, and algorithm steps may be implemented or performed in connection with: a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components. A processor executing a set of firmware instructions, any conventional programmable software module, and any combination of devices designed to perform the functions described herein may be used. The processor is preferably a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary processor is preferably coupled to the storage device for enabling reading of information from, and writing of information to, the storage medium. The processor and the storage medium may reside in an application specific integrated circuit, ASIC. The ASIC may reside in a telephone or other terminal. In addition, the processor and the storage medium may reside in a telephone or other terminal. A processor may be implemented as a combination of a DSP and a microprocessor, or as two microprocessors in conjunction with a DSP core, etc.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. 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. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A method for adjusting a transmit power level during call recovery in a wireless communication system, comprising:

transmitting a pilot strength measurement message at a first transmit power level;

waiting for a predetermined period of time; and

the pilot strength measurement message is transmitted at a second transmit power level, wherein the second transmit power level is greater than the first transmit power level.

2. The method for adjusting transmit power level during call recovery in a wireless communication system as recited in claim 1, wherein the second transmit power level is a maximum transmit power level.

3. An apparatus for adjusting a transmit power level during call recovery in a wireless communication system, comprising:

means for transmitting a pilot strength measurement message at a first transmit power level;

means for waiting a predetermined period of time; and

means for transmitting a pilot strength measurement message at a second transmit power level, wherein the second transmit power level is greater than the first transmit power level.

4. A method for adjusting a transmit power level during call recovery in a wireless communication system, comprising:

starting call recovery; and

the transmit power level of the pilot strength measurement message is increased prior to receiving the handoff direction message.

5. The method for adjusting transmit power level during call recovery in a wireless communication system as set forth in claim 4, further comprising:

a pilot strength measurement message is transmitted at each transmit power level.

6. The method for adjusting transmit power level during call recovery in a wireless communication system as claimed in claim 4, wherein the pilot strength measurement message is transmitted at predetermined time intervals.

7. The method for adjusting transmit power level during call recovery in a wireless communication system as recited in claim 4, wherein the pilot strength measurement message comprises a header message.

8. A wireless device, comprising:

an antenna;

a processor coupled to the antenna for increasing a transmit power of the pilot strength measurement message during call recovery; and

transmit circuitry coupled to the antenna and the processor.

9. The wireless apparatus of claim 8, wherein the processor is further configured to maintain the transmit power below a maximum power level.