JP2007521678A - Frame synchronization method in a general-purpose mobile telephone system receiver - Google Patents

Abstract

  A UMTS (Universal Mobile Telephone System) receiver performs slot synchronization using the received primary synchronization subchannel (PSCH) (305). Following slot synchronization, the UMTS receiver performs frame synchronization using the received secondary synchronization subchannel (SSCH) (320), and the UMTS receiver uses the received PSCH to A change in state is detected (325, 330, 335, 350, 355, 360).

Description

  The present invention relates generally to wireless receivers, and more particularly to user equipment (UE) in a spread spectrum based wireless system such as the Universal Mobile Telephone System (UMTS).

  The basic time unit of a UTMS radio signal is a 10 millisecond (ms) radio frame, which is divided into 15 slots of 2560 chips each. A UMTS radio signal from a cell (base station, base station) to a UMTS receiver is called a “downlink signal”, and a radio signal in the opposite direction is called an “uplink signal”. When the UMTS receiver is powered on, the UMTS receiver performs a “cell search” to search / search for a cell to communicate with. The UMTS receiver first looks for a downlink synchronization channel (SCH) transmitted from the cell, synchronizes to it at the slot / frame level, and locates a specific scramble code group for the cell. decide. Voice / data communication is started only after the cell search is successful.

  For cell search, the SCH is a sparse downlink channel that operates only during the first 256 chips of each slot. The SCH consists of two subchannels: PSCH (Primary SCH: primary synchronization subchannel) and SSCH (Secondary SCH: secondary synchronization subchannel). The PSCH 256 chip sequence (or PSCH code) is the same in all slots of the SCH for all cells. In contrast, the 256 chip sequence (SSCH code) of the SSCH is different in each of the 15 slots of the radio frame and is used to identify one of the 64 scramble code groups. That is, each radio frame on the SCH repeats a sequence of scramble code groups associated with each transmission cell. Each SSCH code is taken from the alphabet of 16 SSCH codes.

  As part of the cell search, the UMTS receiver first achieves slot synchronization using the PSCH. The UMTS receiver correlates the received PSCH samples against a 256-chip sequence of known PSCH (which is the same for all slots), and based on the position of the correlation peak, the slot reference time To decide. Once the slot reference time is determined, the slots of the UMTS receiver are synchronized and the UMTS receiver can determine when each slot starts in the received radio frame.

  After slot synchronization, the UMTS receiver stops processing the PSCH and starts processing the SSCH. The UMTS receiver correlates the 15 SSCH codes in the received radio frame to a known sequence, achieves frame synchronization, and determines the scramble code group for the cell. By identifying the scramble code group, the UMTS receiver descrambles all other downlink channels (eg, Common Pilot Channel (CPICH)) for the cell for voice / data communication. Starts.

  There are several drawbacks to the cell search described above. One is time. Since the SSCH processing involves the identification of a series (one sequence) of 15 SSCH codes, the SSCH code processing is performed over a plurality (10-20) of received radio frames, and the cell search is completed. 100-200 ms is required. Another disadvantage is that the UMTS receiver can achieve frequency synchronization only after the CPICH is descrambled. This occurs after cell search is complete, as described above. Since the UMTS receiver is mobile, the channel state changes during the SSCH process, and the UMTS receiver loses slot synchronization (eg, correlation peaks move or disappear). When this happens, the SSCH process fails. This failure is not detected by the UMTS receiver until the SSCH process is completed. Therefore, the entire “cell search” must start over (restart). That is, the time that the user has to wait until voice / data communication can be started becomes longer.

(Summary of Invention)
In accordance with the principles of the present invention, the wireless receiver uses the received first synchronization channel to perform slot synchronization and uses the received second synchronization channel following completion of slot synchronization. The received first synchronization channel is used at the wireless receiver to detect channel state changes.

  In an embodiment of the present invention, the wireless receiver is part of a UMTS user equipment (UE), the first synchronization channel is a subchannel (PSCH), and the second synchronization channel is a subchannel (SSCH). It is. During the SSCH processing, the wireless receiver continues to process the PSCH and monitors the channel status. When the correlation peak associated with the PSCH subchannel falls below a predetermined threshold, the SSCH processing is stopped. If the SSCH process is stopped within a predetermined time, the SSCH process is newly started. If the SSCH processing is stopped after a predetermined time, the SSCH processing attempts to estimate the scramble code group based on the currently stored data. That is, the PSCH channel acts as an “early warning” system to detect sudden channel changes early to save processing time and to enable users to start voice / data communication after the UE is powered on. The waiting time can be shortened.

  A cell search method according to another embodiment of the present invention uses PSCH processing as an early warning of changing channel conditions and notifies the SSCH processing of channel state changes. In this way, in a situation where the SSCH process is continued and the channel state is significantly changed to produce an erroneous result, the SSCH process is not continued.

  Apart from the inventive concept, the elements shown in the drawings are well known and will not be described in detail. Wireless communication systems based on UMTS are also well known and will not be described in detail. Besides the inventive concept, spread spectrum transmission / reception, cell (base station, base station), user equipment (UE), downlink channel, uplink channel and RAKE receiver are well known I will not explain it here. Also, conventional programming techniques are used to implement the inventive concept and will not be described. Finally, like numbers in the figures represent like elements.

  FIG. 1 illustrates a portion of a UMTS wireless communication system 10 in accordance with the principles of the present invention. The cell (base station, base station) 15 broadcasts a downlink SCH (synchronization channel) signal including the above-described PSCH and SSCH subchannels. As described above, the SCH signal 16 is used in the UMTS user equipment (UE) for synchronization as a precondition for voice / data communication. The UE processes the SCH signal during “cell search”. In this example, the UE (for example, a mobile phone) 20 starts a cell search when the power is turned on. The purpose of the cell search is (a) to synchronize the cell transmission at the slot / frame level of the UMTS radio frame, (b) to determine the scramble code group of the cell (eg cell 15), Etc. In accordance with the principles of the present invention, UE 20 processes the SSCH subchannel while using the PSCH subchannel to monitor channel state changes to achieve frame synchronization with cell 15. The following example illustrates the inventive concept for this initial cell search (ie when the UE is powered on), but the inventive concept is not limited to this, and other cell search The case also applies (eg when the UE is in “idle mode”).

  FIG. 2 illustrates a block diagram of a portion of UE 20 in accordance with the principles of the present invention. UE 20 includes a front end 105, an analog / digital (A / D) converter 110, a cell search element 115, a searcher element 120, a RAKE receiver 125, a host interface block 130, and a processor 135. In addition to the inventive concept, additional elements known in the art are also included in the block shown in FIG. 2, but are not described here for the sake of brevity. For example, the A / D converter includes a digital filter, a buffer, and the like.

  The front end 105 receives a radio frequency (RF) signal 101 transmitted from the cell 15 (FIG. 1) via an antenna (not shown) and generates a baseband analog signal 106 representing the PSCH / SSCH subchannel. Supply. Baseband analog signal 106 is sampled by A / D converter 110, which provides a stream 111 of received samples. The received sample 111 is used by three components (cell search element 115, searcher element 120, RAKE receiver 125). Cell search element 115 processes the PSCH and SSCH subchannels. If the cell search is successful, the searcher element 120 evaluates the received samples and assigns a multipath to each finger of the RAKE receiver 125. The RAKE 125 receiver combines data from multiple paths, provides symbols, and then decodes with a decoder (not shown) for voice / data communication. Since only the cell search element 115 is relevant to the inventive concept, the searcher element 120 and the RAKE receiver 125 will not be discussed further. Host interface block 130 couples data between the aforementioned components and processor 135, and processor 135 receives the results from cell search element 115 via signal 134. The processor 135 is an accumulation program control processor (for example, a microprocessor), and includes a memory (not shown) that stores programs and data.

  FIG. 3 illustrates a block diagram of the cell search element 115. The cell search element 115 comprises a PSCH element 205 and an SSCH element 210. FIG. 4 shows a flowchart in accordance with the principles of the present invention for processing downlink subchannels (PSCH and SSCH) in cell search element 115. In step 305, the processor 135 of the UE 20 initiates a cell search and attempts to process the downlink PSCH subchannel to achieve slot synchronization. The processor 135 activates the PSCH element 205 in response to the signal 206 to process the received sample 111. For example, because the downlink PSCH subchannel is a known PSCH 256 chip sequence (or PSCH code) and occurs periodically (repeated for each slot of the downlink SCH signal), the PSCH element 205 may receive the received sample 111. Correlate to the PSCH code and provide an associated peak correlation value. The PSCH element 205 consists of a matched filter and a buffer (both not shown) and stores the output signal of the matched filter. The PSCH element 205 provides the peak value to the processor 135 by means of the signal 206. This peak value is averaged over several slots (4-20 slots) of the received radio frame, reducing the possibility of false locks. If the peak value is not greater than the predetermined threshold, the processor 135 controls the PSCH element 205 and continues to process the received signal to continue searching for cells. If the peak value is greater than the predetermined threshold, UE 20 completes slot synchronization and processor 135 continues the cell search for frame synchronization and determines the scramble code group for the associated cell. Another method considers that slot synchronization is complete when the peak correlation value exceeds the next maximum correlation value by a predetermined addition or multiplication factor.

  In step 310 (FIG. 4), processor 135 enables (enables) SSCH element 210 and PSCH element 205 in accordance with inventive principles. The SSCH element 210 processes the received sample 111 and uses it to attempt to synchronize the frame and identify the scramble code group for the cell 15. The PSCH element 205 processes the sub-channel PSCH, acts as an early warning / detector, monitors the channel state and detects channel state changes during the SSCH process.

  FIG. 5 shows step 310 of FIG. 4 in more detail. Step 310 includes step 320 (related to SSCH processing) and steps 325, 330, 335 (related to channel status monitoring). Step 320 corresponds to SSCH processing and is performed by SSCH element 210 (FIG. 3) and processor 135 (FIG. 2). SSCH element 210 is coupled to processor 135 by signal 211. The SSCH 256 chip sequence (SSCH code) is different for each of the 15 slots of the radio frame for a particular cell. Each radio frame repeats a unique 15 SSCH code associated with a particular cell. The SSCH element 210, when activated by the processor 135, correlates a specific sequence of 15 SSCH codes in the received radio frame to a known sequence and is used to achieve frame synchronization. And the scramble code group of the cell (scramble code group associated with cell 15) is determined. In order to obtain a robust estimate for a sequence of 15 received SSCH codes, the UE 20 averages the correlation over a plurality of consecutive data frames, so that, as described above, the processing of the SSCH involves multiple received (10 ~ 20) radio frames need to be processed. Therefore, the time required for the SSCH process is 100 to 200 ms. During this time frame, the UE loses slot synchronization. In accordance with aspects of the present invention, processor 135 uses PSCH element 205 as a detector to provide early warning of channel state changes during SSCH processing. At the start of the SSCH process, the processor 135 also allows a timer (not shown) to track the processing time for step 320 (described below). As is known in the art, the timer can be implemented in software and / or hardware.

  At step 325, the PSCH element 205 correlates the received sample 111 to a known PSCH code during each slot and provides the corresponding correlation peak magnitude to the processor 135 via signal 206. At step 330, the processor 135 compares the received correlation peak with a predetermined threshold. It does not matter if a larger peak appears there (eg from a different cell). What is important is that the original peak (i.e. the peak from which the processing of the SSCH is currently tuned, i.e. the signal from the cell 15) is still there (even if it is currently weak). If the received correlation peak is greater than a predetermined threshold (eg, 50% of the original peak value), the channel state is not likely to change and processor 135 executes step 335. In step 335, it is determined whether the SSCH processing has been completed. If the SSCH process has been completed, the cell search is completed. If the SCH processing is not complete, the processor 135 returns to step 325 and continues to use the sub-channel PSCH as a detector to alert early on channel state changes.

  If, at step 330, the received correlation peak is less than or equal to a predetermined threshold, it is inferred that the channel condition has changed and the processing of the continued SSCH is degraded, and processor 135 causes step 320 to Is stopped (represented by a stop signal 216 in FIG. 3). The processor 135 then proceeds to steps 350, 355, 360 (FIG. 6). In step 350, the processor 135 evaluates the value of the above-described timer (measuring the time elapsed for SSCH processing). If the elapsed time is less than or equal to the predetermined value (ie, the elapsed time is “early” in the processing of the SSCH), at step 305 (FIG. 4), the processor 135 restarts the cell search. To do. In this case, the SSCH process does not yet have enough data to make a reliable decision regarding the frame synchronization and the 15 scrambling code groups of the cell, and it is better to restart the cell search. is assumed. “Early” is defined as, for example, 50% or less, or 75% or less until the processing of the SSCH is completed. If SSCH processing is pre-defined to process at least 10 radio frames (each frame is 10 ms), the exemplary time value used in step 350 would be 75 ms.

  If the elapsed time is greater than a predetermined value (SSCH processing is “delayed”), it is assumed that if the SSCH processing is continued, the accumulated data is contaminated with unreliable data. At step 355, processor 135 checks whether the scramble code group of cell 15 can be estimated based on the currently stored data. In step 355, the processor 135, in conjunction with the SSCH element 210, consists of 15 received SSCH code sequences currently estimated by the signal 211 and 15 SSCH codes representing a scramble code group. It is determined whether there is a match (match) with one of the 64 sequences. If there is a match, at step 360 it is assumed that the received sequence has correctly identified the received sequence and frame synchronization and scramble code groups are determined. This match is an exact match for all 15 SSCH codes, or a match with at least N of the 15 SSCH codes if a unique scramble code group can be identified. N is defined in advance (for example, N = 13). If there is no match, at step 305 (FIG. 4), processor 135 restarts the cell search.

  In step 320 / step 360, if the SSCH is successfully processed, the scramble code group of cell 15 is identified, and UE 20 uses the other downlink channel (Common Pilot Channel ( (Including CPICH) can be descrambled, and from the identified scramble code group, the actual scramble code can be determined for the cell, and voice / data communication is started.

  As described above, according to the principles of the present invention, the PSCH subchannel monitors the state of the channel during processing of the SSCH subchannel. This method improves the performance of SSCH processing. Although described with respect to the initial cell search, the concept of the present invention is that any part of wireless operation can be used if a downlink channel, such as an SSCH subchannel, is processed when the channel state is changing. Applied.

  Although the foregoing is merely illustrative of the principles of the present invention and is not explicitly described herein, those skilled in the art will devise numerous alternative configurations that embody the principles of the present invention and are within its spirit and scope. It will be understood that it can be done. For example, although illustrated herein as separate functional elements, these functional elements may include one or more integrated circuits (ICs) and one or more storage program control processors (e.g., a microprocessor or digital Embodied in a signal processor DSP). Similarly, although illustrated as a UMTS based system, the inventive concept applies to any communication system that processes signals in the presence of changing channel conditions. Accordingly, it should be understood that numerous modifications can be made to the disclosed embodiments and that other configurations can be devised without departing from the spirit and scope of the invention as set forth in the appended claims.

1 illustrates a portion of a wireless communication system in accordance with the principles of the present invention. 3 illustrates an embodiment of a wireless receiver in accordance with the principles of the present invention. 3 illustrates an embodiment of a wireless receiver in accordance with the principles of the present invention. 1 illustrates a flowchart according to the principles of the present invention. 1 illustrates a flowchart according to the principles of the present invention. 1 illustrates a flowchart according to the principles of the present invention.

Claims (11)

(A) processing a first synchronization channel of the received wireless signal to obtain slot synchronization (305);
(B) processing a second synchronization channel of the received wireless signal to obtain frame synchronization and using the first synchronization channel to detect a change in channel state (310); How to use for wireless receivers.   The first synchronization channel is a primary synchronization subchannel (PSCH), and the second synchronization channel is a secondary synchronization subchannel (SSCH) of a universal mobile telephone system (UMTS). The method according to 1. The step (b)
Processing a second synchronization channel to obtain frame synchronization;
Processing a first synchronization channel and providing correlation data associated therewith; and
If the correlation data is smaller than a predetermined value,
Stopping processing of the second synchronization channel to obtain frame synchronization;
Before stopping, if the time elapsed in processing of the second synchronization channel is less than a predetermined time value, restarting in step (a);
2. Estimating a scramble code group conveyed in the second synchronization channel based on already accumulated data if the elapsed time is greater than a predetermined value. Method. Processing a first synchronization channel of the received wireless signal to obtain frame synchronization;
A method for use with a wireless receiver comprising: processing a second synchronization channel to detect a change in channel state during processing of the first synchronization channel.   5. The method of claim 4, wherein the second synchronization channel is a primary synchronization subchannel (PSCH) and the first synchronization channel is a universal mobile telephone system (UMTS) secondary synchronization subchannel (SSCH). In processing the second synchronization channel,
Processing a second synchronization channel and providing correlation data associated therewith;
If the correlation data is less than a predetermined value, stopping the processing of the first synchronization channel;
Before stopping, if the time elapsed in processing of the first synchronization channel is greater than a predetermined value, the scramble code transmitted on the first synchronization channel based on the already accumulated data The method of claim 4, comprising: estimating a group; otherwise, starting a new processing of the first synchronization channel. A front end (105) that receives the wireless signal and provides a stream of received samples;
Primary synchronization that operates on the received samples, acquires slot synchronization to the primary synchronization signal of the received wireless signal, and further processes the primary synchronization signal following slot synchronization to provide data representative of the channel state Element (205);
A secondary synchronization element (210) that operates on the received samples and obtains frame synchronization to the secondary synchronization signal of the received wireless signal;
A wireless device comprising: a processor (135) responsive to further processing of the primary synchronization signal by the primary synchronization element and stopping the secondary synchronization element in response to data representative of the channel status   8. The wireless device of claim 7, wherein, following the synchronization of the slot, the primary synchronization element continues to process the primary synchronization signal of the received wireless signal simultaneously with processing of the received wireless signal by the secondary synchronization element.   8. The data representing the channel state represents a correlation between a known primary synchronization code and a received primary synchronization signal, and if the correlation is less than a predetermined value, the processor stops the secondary synchronization element. The wireless device as described.   8. When stopped, the secondary synchronization element provides an estimate of the scramble code group to the processor if the time elapsed in acquiring frame synchronization before stopping is greater than a predetermined value. The wireless device as described.   8. The wireless device of claim 7, wherein when stopped, the processor restarts the secondary synchronization element if the time taken to acquire frame synchronization before stopping is less than a predetermined value.

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