HK1070490B - Verification methods and apparatus for improving acquisition searches of asynchronous cells - Google Patents

Description

Verification method and apparatus for improving acquisition search of asynchronous cells

Background

FIELD

The present invention relates generally to communications, and more particularly to a system for verifying search failures for asynchronous cell addresses.

Background

The field of wireless communications has many applications including, for example, cordless telephones, paging, wireless local loops, Personal Digital Assistants (PDAs), internet telephony, and satellite communication systems. One particularly important application is cellular telephone systems for mobile subscribers. The term "cellular" system is used herein to encompass both cellular and Personal Communications Service (PCS) frequencies. Various air interfaces have been developed for such cellular telephone systems including, for example: frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). In connection therewith, various national and international standards have been established including, for example: advanced Mobile Phone Service (AMPS), global system for mobile communications (GSM), and interim standard 95 (IS-95). IS-95 and its derivative standards IS-95A, IS-95B, ANSI J-STD-008 (commonly referred to as IS-95) and proposed high data rate systems are promulgated by the Telecommunications Industry Association (TIA) and other well known standard entities.

Cellular telephone systems configured pursuant to the use of the IS-95 standard employ CDMA signal processing techniques to provide efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. patent nos. 5,103,459 and 4,901,307, both assigned to the assignee of the present invention and incorporated herein by reference. An exemplary system using CDMA techniques is CDMA2000 ITU-R Radio Transmission Technology (RTT), telecommunications published by the TIA (referred to herein as CDMA 2000). The standard for cdma2000 IS given in a draft version of IS-2000 and has been approved by the TIA. Another CDMA standard is the W-CDMA standard, which is described inThird generation partnership project “3GPP”Document numbers 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3GTS 25.214.

Transmissions between two constituent parties of a WCDMA system may be transmitted in time division duplex mode (TDD) or frequency division duplex mode (FDD) according to the frequency band available to the service provider. Due to the complexity of allowing operation in either mode, the system transmits information in terms of logical and physical channels. (logical channels are also referred to as transport channels in the WCDMA standard.) data is encoded and interleaved according to the logical channel to which the data is assigned, and then the logical channels are mapped to physical channels. The number and type of logical channels and physical channels vary according to the direction of signal transmission. Transmissions from the mobile station to the base station are referred to as "uplink" and transmissions from the base station to the mobile station are referred to as "downlink".

On the uplink, the physical channels are a Physical Random Access Channel (PRACH), a Dedicated Physical Control Channel (DPCCH), and a Physical Common Packet Channel (PCPCH). On the downlink, the physical channels are a Synchronization Channel (SCH), a common pilot channel (CPICH), a primary common control physical channel (P-CCPCH), a secondary common control physical channel (S-CCPCH), a Paging Indicator Channel (PICH), an Acquisition Indicator Channel (AICH), a Dedicated Physical Channel (DPCH), a physical downlink co-channel (PDSCH), a Common Packet Channel (CPCH), and a CPCH Status Indicator Channel (CSICH).

Signals or data transmitted on the physical channel are communicated within a message entity, which is constructed using radio frames. Each radio frame includes 15 slots, each slot corresponding to 2560 chips. A "chip" refers to a bit within a sequence formed after an original information signal has been spread with a spreading code. Thus, each radio frame comprises 38400 chips. However, since each message entity may include a variable number of radio frames, the length of the message entity may be variable. In the current WCDMA standard, the duration of a radio frame is specified as 10ms, and the message entity may be distributed or transmitted in 1, 2, 4 or 8 radio frames.

WCDMA service providers may set up base stations in asynchronous mode so that each base station has an independent timing reference. To operate within range of such asynchronous base stations, the mobile station must be able to acquire the frame timing of each base station with which the mobile station wishes to communicate. In order to correctly receive and decode the variable length message entity from the base station, the mobile station must first acquire the frame timing of the base station by performing an acquisition search on the signal carrying the base station frame timing information. Therefore, if there are multiple base stations, the mobile station must perform multiple acquisition searches for the timing of each base station.

The computational complexity and amount of time required to perform such acquisition searches can be extremely problematic for mobile stations that are traveling within the range of multiple base stations. In particular, if a mobile station moves from the range of one base station to the range of another base station, delays in determining frame timing signal acquisition for the new base station can result in call drops. The process of maintaining a call as a mobile station travels from the communication range of one base station to the communication range of another is referred to as "hand-off". Handoffs may occur between multiple sectors of one base station, between multiple base stations of a single service provider, between multiple base stations of different service providers, and between base stations operating at different frequencies. Thus, a propagating mobile station is likely to need to acquire frame timing information from multiple base stations.

Unfortunately, transmissions between a mobile station and a base station are subject to dynamic and random radio environments, where a phenomenon known as "fading" causes the quality of the received transmission to fluctuate. Fading occurs when multiple copies of the same signal arrive at the receiver with different phases, which can cause destructive interference. To produce smooth fading of the entire frequency bandwidth, substantial multipath interference occurs, both with very small delay spread.

Therefore, the mobile station must be able to synchronize with the frame timing of the base station in the face of rapidly changing channel conditions that cause the mobile station to temporarily lose the signal from the base station. Currently in the art, if a mobile station loses signal during a frame timing acquisition procedure, the mobile station restarts the frame timing acquisition procedure from the beginning. Restarting the frame timing acquisition process consumes time, wastes processing resources, and consumes battery life. There is a need in the art for a mechanism to cope with acquisition failures caused by unstable transmission environments without having to restart the acquisition process. The embodiments described herein address the above stated needs by implementing a verification search mechanism to improve the probability of a successful acquisition search.

SUMMARY

Methods and apparatus are presented herein to address the above-mentioned needs. In one aspect, a method is presented for increasing the likelihood of successful acquisition of base station timing by a mobile station, the method comprising: performing a frame timing acquisition search based on a transmission from a base station, wherein the frame timing acquisition search comprises a plurality of phases and the transmission comprises a plurality of radio frames; and if it is determined that a failure occurred in at least one of the plurality of stages, performing a verification search after the at least one of the plurality of stages.

In another aspect, an apparatus is presented for improving the likelihood of successful acquisition of base station timing by a mobile station, the apparatus comprising: a memory element; and a processor for executing a set of instructions stored within the memory element, the set of instructions for: performing an acquisition search based on a transmission from a base station, wherein the acquisition search comprises a plurality of phases and the transmission comprises a plurality of radio frames; and if it is determined that a failure occurred in at least one of the plurality of stages, performing a verification search after the at least one of the plurality of stages.

Brief Description of Drawings

Fig. 1 is a diagram of a wireless communication network.

Fig. 2 is a timing diagram illustrating an acquisition search.

FIG. 3 is a flow diagram illustrating a validation mechanism for increasing the likelihood of a successful acquisition search.

Detailed Description

As shown in fig. 1, a wireless communication network 10 generally includes a plurality of mobile stations (also referred to as subscriber units or user equipment) 12a-12d, a plurality of base stations (also referred to as Base Transceiver Stations (BTSs) or node bs) 14a-14c, a Base Station Controller (BSC) (also referred to as a radio network controller or packet control function) 16, a Mobile Switching Center (MSC) or switch 18, a Packet Data Serving Node (PDSN) or interworking function (IWF)20, a Public Switched Telephone Network (PSTN)22 (typically a telephone company), and an Internet Protocol (IP) network 24 (typically the internet). For simplicity, four mobile stations 12a-12d, three base stations 14a-14c, one BSC 16, one MSC18, and one PSDN 20 are shown. Those skilled in the art will appreciate that there may be any number of mobile stations 12, base stations 14, BSCs 16, MSCs 18, and PDSNs 20.

In one embodiment, the wireless communication network 10 is a packet data service network. The mobile stations 12a-12d may be any of a number of different types of wireless communication devices such as a portable telephone, a cellular telephone that is connected to a portable computer that runs an IP-based Web browser application, a cellular telephone with an associated hands-free car kit, a Personal Data Assistant (PDA) that runs an IP-based Web browser application, a wireless communication module incorporated into a portable computer, or a fixed location communication module as may be found in a wireless local loop or meter reading system. In the most general embodiment, the mobile station may be any type of communication unit.

The mobile stations 12a-12d are preferably configured to execute one or more wireless packet data protocols, such as those described in the EIA/TIA/IS-707 standard. In particular embodiments, mobile stations 12a-12d generate IP packets that are directed to IP network 24 and encapsulate the IP packets within frames using a point-to-point protocol (PPP).

In one embodiment, the IP network 24 is coupled to a PDSN 20, the PDSN 20 is coupled to a MSC18, the MSC18 is coupled to a BSC 16 and a PSTN 22, and the BSC 16 is coupled to the base stations 14a-14c by wireline configured for voice and/or data packet transmission in accordance with any of several known protocols, including, for example: e1, T1, Asynchronous Transfer Mode (ATM), IP, PPP, frame relay, HDSL, ADSL, or xDSL. In another embodiment, the BSC 16 is coupled directly to the PDSN 20, while the MSC18 is not coupled to the PDSN 20.

During typical operation of the wireless communication network 10, the base stations 14a-14c receive and demodulate sets of uplink signals from various mobile stations 12a-12d involved in a telephone call, Web browsing, or other data communication. The respective uplink signals received by a given base station 14a-14c are processed within that base station 14a-14 c. Each base station 14a-14c may communicate with a plurality of mobile stations 12a-12d by modulating and transmitting sets of downlink signals to the mobile stations 12a-12 d. For example, as shown in fig. 1, the base station 14a communicates with first and second mobile stations 12a, 12b simultaneously, and the base station 14c communicates with third and fourth mobile stations 12c, 12d simultaneously. The resulting packets are forwarded to the BSC 16, and the BSC 16 provides call resource allocation and mobility management functions, including orchestrating soft handoffs of calls for a particular mobile station 12a-12d from one base station 14a-14c to another base station 14a-14 c. For example, the mobile station 12c communicates with two base stations 14b, 14c simultaneously. Eventually, when the mobile station 12c is far enough away from one base station 14c, the call will be handed off to another base station 14 b.

If the transmission is a conventional telephone call, the BSC 16 will route the received data to the MSC18, which 18 provides additional routing services for interaction with the PSTN 22. If the transmission is a packet-based transmission, such as a data call directed to the IP network 24, the MSC18 will route the data packet to the PDSN 20, and the PDSN 20 will send the packet to the IP network 24. Alternatively, the BSC 16 may route the packets directly to the PDSN 20, and the PDSN 20 sends the packets to the IP network 24.

As described above, a WCDMA communication system may be set up with asynchronous base stations, such that adjacent base stations have timing references that are independent of each other. In the case of a handoff between a first asynchronous base station and a second asynchronous base station, the mobile station may drop a call if the mobile station is not properly synchronized with the second asynchronous base station. In order to synchronize with the second asynchronous base station, the mobile station must process the frame timing information of the second asynchronous base station. In some implementations of WCDMA systems, the first asynchronous base station may have processed the timing information of the second asynchronous base station and communicated this timing information to the mobile station. However, if the first asynchronous base station does not process the timing information of the second asynchronous base station, the mobile station is faced with the task of having determined the frame timing information itself.

According to the WCDMA standard, the acquisition of base station timing information is achieved in a complex three-step process. In a first step, the mobile station acquires slot synchronization of the base station by searching for a Primary Synchronization Code (PSC), which is transmitted by the base station within the first 256 chips of each slot. The PSC is constructed using a generalized hierarchical Golay sequence and is always found at the beginning of the slot period. Thus, to determine the beginning of a 2560 chip slot cycle, the mobile station attempts to find the correlation peaks of all possible chip position-correlated PSCs.

After determining the slot timing, the mobile station must determine where the start of the radio frame is. In a second step, the mobile station acquires frame synchronization of the base station by searching for a sequence of Secondary Synchronization Codes (SSCs) transmitted by the base station with the PSCs in the first 256 chips of each slot. In the WCDMA standard, 64 sequences are constructed from 16 orthogonal SSCs, dividing 512 different primary scrambling codes into 64 scrambling code groups. The search is performed by: correlating the received signal with a sequence formed from possible SSCs; the maximum correlation value is then identified. Since the SSC sequences are structured such that the cyclic shift of one sequence is not equivalent to the cyclic shift of any other sequence, the determination of the SSC sequence can be used to identify the primary scrambling code group associated with the SSC sequence.

In a third step, the mobile station determines the identity of the base station by correlating the pilot symbols with all possible primary scrambling codes in the code group identified by the search of the second step above. The "pilot" signal does not carry any information bits. The pilot signal is typically constructed of known symbols and can be used as a reference for time, phase, and signal strength. The known symbols are the result of using a particular spreading or scrambling code.

Each base station may be identified by a unique primary scrambling code, which repeats every 10ms of the beginning of the radio frame. The scrambling codes are divided into 512 groups, where each group comprises one primary scrambling code and 15 secondary scrambling codes. The primary scrambling codes are also divided into 64 scrambling code groups, each group comprising 8 primary scrambling codes. The code set searched in the third step is identified by the SSC sequence found in the second step. Thus, once a code group is identified in step 2, the search for 512 primary scrambling codes is reduced to 8 primary scrambling codes.

Fig. 2 illustrates the three-step frame capture search described above. Reference counter 200 represents a 10ms radio frame comprising 15 slots, each slot having a duration of 0.667 ms. The first step 210 is to search for a correlation peak located at the beginning of a slot when a particular PSC is used. A second step 220 searches for the start of a radio frame by correlating the slot with a sequence formed from the SSCs. Once the start point of the radio frame is identified, a third step 230 searches for primary scrambling codes located within the first 256 chips at the start of the radio frame. The identity of the primary scrambling code at the beginning of the radio frame is used to identify the base station broadcasting the radio frame.

Acquisition of slot timing, frame timing, and base station identification is pre-requisite for the mobile station to successfully receive and decode the message from the base station. However, due to the variable nature of the transmission medium, the process of acquiring frame timing information from an unknown base station is complex. As discussed above, fading can cause the transmission energy level of a signal to fluctuate. If the mobile station is unable to compensate for rapid changes in the radio environment, an interruption in the three-step frame timing acquisition process can occur. Because no compensation mechanism is embedded in the above process, the mobile station is forced to start the three-step frame timing acquisition process again. . Embodiments herein describe methods and apparatus for implementing a frame timing acquisition procedure that is resilient to rapid changes in the transmission medium.

Fig. 3 is a flow diagram illustrating an embodiment of a frame timing acquisition process with a verification mechanism that optimizes the likelihood of successful results. The acquisition process may be implemented by additional processing elements and memory elements within the mobile station or may be incorporated into processing elements and memory elements already present within the mobile station. In step 300, the mobile station begins the acquisition process by locking a demodulation element within the mobile station to the first frequency F1. In step 302, a processor within the mobile station controls a search for slot timing information by using a primary synchronization code (PCS). The search for slot timing information is performed in accordance with the first step search described above of the three-step frame timing acquisition search. In step 304, the processor determines whether a slot peak has been found. If a slot peak is found, program flow proceeds to step 306. If no slot peak is found, program flow proceeds to step 330.

The verification process begins at step 330 where the processor verifies whether further searching of the current frequency is required. If further authentication is required, program flow proceeds to step 332 where the processor performs an authentication search. In an embodiment, the validation search can include a slot timing search using PSCs. If no further verification search is required, then an acquisition failure is declared and program flow proceeds to step 336, which is the end of the acquisition process for the first frequency F1.

If a validation search is implemented in step 332, then step 334 continues in which the results of the validation search are analyzed. If the result confirms that the frame timing acquisition process does not need to be restarted, program flow proceeds to step 306. If the results of the validation search indicate that the frame timing acquisition process may need to be restarted, program flow continues back to step 330. In embodiments where the validation search is a slot timing search, a slot peak is found indicating that the frame timing acquisition process needs to be restarted. If no slot peak is found, there is no need to restart any further frame timing acquisition process.

In step 306, the processor searches for frame timing information by correlating the sequence of the Secondary Synchronization Code (SSC) during demodulation of the received signal. The search for frame timing information is performed in accordance with the second step search of the three-step frame timing acquisition search described above. In step 308, the processor determines whether a frame peak has been found. If a frame peak is found, program flow proceeds to step 310. If a frame peak is not found, program flow proceeds to step 330.

In step 310, the processor searches for a base station identification, which is subject to a current search that correlates pilot symbols with scrambling codes. The identification is performed in accordance with the third step of the three-step frame timing acquisition search described above. In step 312, the processor determines whether a base station can be identified. If a base station is identified, program flow proceeds to step 314. If the base station cannot be identified, program flow proceeds to step 330.

Since the slot timing, frame timing, and transmit base station identification are known after successful completion of step 312, a processor within the mobile station may assign demodulation elements to the transport channels of the base station. In step 314, the processor determines a frequency correction value for the local oscillator using the pilot signal energy of the base station.

In step 316, the processor determines whether the local oscillator can be corrected using a frequency tracking mechanism. The frequency tracking mechanism may be included within the demodulation element of the mobile station or may be separate from the demodulation element. Frequency tracking mechanisms are well known in the art and will not be discussed further below. If the frequency correction value cannot be achieved, program flow proceeds to step 330. If the frequency correction value can be achieved, program flow advances to step 318.

In step 318, the processor attempts to synchronize the demodulation element with the timing of the broadcast channel. In step 320, the processor determines whether a successful broadcast channel timing synchronization has occurred. If the mobile station is not able to synchronize with the broadcast channel, program flow proceeds to step 330. If the mobile station can synchronize with the broadcast channel, program flow proceeds to step 336 where acquisition is declared successful and the process ends.

The above-described embodiments ensure that if a failure occurs in any step of the acquisition process, the mobile station can perform an additional authentication search rather than declaring the acquisition process to fail directly. Thus, the additional verification search delays the failure of the acquisition process so that rapid time fluctuations in the radio environment do not cause premature failure of the acquisition process.

The number of verification searches performed by an embodiment depends on the stage at which failure may occur. In step 330, where the processor determines whether more verification searches are needed, the processor may use a predetermined quantitative value corresponding to the stage at which the verification search was invoked. For example, if a failure occurs in step 304, i.e., no slot peak is found, then in step 330 the processor may refer to a lookup table that stores a low value, e.g., 1 or 2, for the total number of validation searches to be performed. However, if a failure occurs in step 320, i.e., the mobile station is unable to synchronize with the broadcast channel timing, then in step 330 the processor may refer to a lookup table that stores a higher value, e.g., 2 or 3, for the total number of authentication searches to be performed. The actual number ranges in the lookup table do not affect the scope of the embodiments herein.

The difference in the number of verification searches allowed is based on logical reasoning: failures that occur at a later stage are more likely to be caused by momentary fading or environmental conditions than by the radio frequency range, and are also based on reasoning: the presence of the pilot signal on the current radio frequency F1 is acknowledged by the successful completion of the previous search phase.

It should be noted that the step of synchronizing the broadcast channel timing of the mobile station with the base station and the step of synchronizing the frame timing of the mobile station with the base station are different timing issues. As discussed above, broadcasts from WCDMA base stations are sent on different physical channels, including variable sized message entities. The message entity unit is called a Transmission Time Interval (TTI). Data transmitted within a TTI is convolutionally encoded (or encoded with a turbo code), undergoes symbol repetition, and is interleaved. In the WCDMA standard, timing synchronization of the broadcast channel is performed in two phases. Phase 1 is primary common physical channel synchronization, which is achieved by the three-step search described above. Phase 2 is TTI synchronization, achieved by successfully decoding the broadcast channel message.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

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, or combinations of both. To clearly illustrate this interchangeability of hardware and software, 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 or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The implementation or execution of the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments described herein may be implemented or performed with: a general purpose processor, 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, or any combination designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. 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 storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a subscriber terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

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 (15)

1. A method for increasing the likelihood of successful acquisition of base station timing by a mobile station, comprising:

performing a frame timing acquisition search based on a transmission from a base station, wherein the frame timing acquisition search comprises, in order, a first phase for searching for slot timing synchronization to identify a plurality of slot peaks, a second phase for searching for frame timing synchronization to identify a plurality of radio frames, and a third phase for searching for a WCDMA cell identification to determine an identification of the base station, the transmission comprising the plurality of radio frames; and

performing a validation search upon failure of at least one of the plurality of stages, wherein the validation search is a search for identifying a plurality of slot peaks, returning to a second stage to search again for frame timing synchronization if a slot peak is found during the validation search; if the validation search fails, then more validation searches are performed.

2. The method of claim 1, wherein the step of performing a verification search after at least one of the plurality of stages is performed a variable number of times, wherein the variable number of times is based on a stage type.

3. The method of claim 1, further comprising:

determining a frequency correction value for a local oscillator within the mobile station;

correcting the local oscillator according to the frequency correction value; and

the mobile station is timing synchronized with the broadcast channel of the base station.

4. The method of claim 3, further comprising:

if the mobile station is unable to correct the local oscillator or is timing synchronized with the broadcast channel, an authentication search is performed.

5. The method of claim 4, wherein the validation search is repeated if the mobile station is unable to correct a local oscillator or is timing synchronized with a broadcast channel.

6. An apparatus for increasing the likelihood of successful acquisition of base station timing by a mobile station, comprising:

a memory element; and

a processor configured to execute a set of instructions stored within a memory element, the set of instructions to:

performing a frame timing acquisition search based on a transmission from a base station, wherein the frame timing acquisition search comprises, in order, a first phase for searching for slot timing synchronization to identify a plurality of slot peaks, a second phase for searching for frame timing synchronization to identify a plurality of radio frames, and a third phase for searching for a WCDMA cell identification to determine an identification of the base station, the transmission comprising the plurality of radio frames; and

performing a validation search upon failure of at least one of the plurality of stages, wherein the validation search is a search for identifying a plurality of slot peaks, returning to a second stage to search again for frame timing synchronization if a slot peak is found during the validation search; if the validation search fails, then more validation searches are performed.

7. The apparatus of claim 6, wherein the set of instructions is further for performing a verification search after at least one of the plurality of stages a variable number of times, wherein the variable number of times is based on a stage type.

8. The apparatus of claim 6, wherein the set of instructions is further for:

determining a frequency correction value for a local oscillator within the mobile station;

correcting the local oscillator according to the frequency correction value; and

the mobile station is timing synchronized with the broadcast channel of the base station.

9. The apparatus of claim 8, wherein the set of instructions is further for: if the mobile station is unable to correct the local oscillator or is timing synchronized with the broadcast channel, an authentication search is performed.

10. The apparatus of claim 9, wherein the set of instructions is further for: the verification search is repeated if the mobile station is unable to correct the local oscillator or is timing synchronized with the broadcast channel.

11. At a mobile station, an apparatus for optimizing the likelihood of successful acquisition of base station frame timing information, comprising:

for performing an acquisition search based on a transmission, wherein the acquisition search order includes a first phase for searching slot timing synchronization to identify a plurality of slot peaks, a second phase for searching frame timing synchronization to identify a plurality of radio frames, and a third phase for searching WCDMA cell identification to determine an identification of a base station, the transmission including a plurality of radio frames;

means for performing a validation search upon failure of at least one of the plurality of stages, wherein the validation search is a search for identifying a plurality of slot peaks, and if a slot peak is found during the validation search, returning to a second stage to search again for frame timing synchronization; performing more validation searches if the validation search fails; and

means for implementing a frequency correction value based on the local oscillator.

12. A method for improving tolerance of a frame acquisition process to fluctuations in a dynamic radio environment, comprising:

sequentially segmenting a frame timing acquisition search into a first stage for searching slot timing synchronization to identify a plurality of slot peaks, a second stage for searching frame timing synchronization to identify a plurality of radio frames, and a third stage for searching WCDMA cell identification to determine an identification of a base station;

performing a validation search upon failure of at least one of the plurality of stages, wherein the validation search is a search for identifying a plurality of slot peaks, returning to a second stage to search again for frame timing synchronization if a slot peak is found during the validation search; if the validation search fails, then more validation searches are performed.

13. The method of claim 12, wherein the performing of the verification phase is repeated a predetermined number of times, wherein the predetermined number of times varies according to each of the first, second, and third phases.

14. An apparatus for improving tolerance of a frame acquisition process to fluctuations in a dynamic radio environment, comprising:

means for sequentially segmenting a frame timing acquisition search into a first stage for searching slot timing synchronization to identify a plurality of slot peaks, a second stage for searching frame timing synchronization to identify a plurality of radio frames, and a third stage for searching WCDMA cell identification to determine an identification of a base station;

means for performing a validation search upon failure of at least one of the plurality of stages, wherein the validation search is a search for identifying a plurality of slot peaks, returning to a second stage to search again for frame timing synchronization if a slot peak is found during the validation search; if the validation search fails, then more validation searches are performed.

15. The apparatus of claim 14, wherein the means for performing the verification phase is further for repeating the performing of the verification phase a predetermined number of times, wherein the predetermined number of times varies according to each of the first, second, and third phases.