KR20060065669A - Frame synchronization in a universal mobile telephone system receiver - Google Patents

Abstract

A Universal Mobile Telephone System (UMTS) receiver performs slot synchronization using a received primary synchronization channel (PSCH) (305). Subsequent to completion of slot synchronization, the UMTS receiver performs frame synchronization using a received secondary synchronization channel (SSCH) (320) in such a way that the UMTS receiver uses the received primary synchronization channel (PSCH) to detect a change in channel conditions (325, 330, 335, 350, 355, 360).

Description

FRAME SYNCHRONIZATION IN A UNIVERSAL MOBILE TELEPHONE SYSTEM RECEIVER}

TECHNICAL FIELD The present invention generally relates to wireless receiving devices, and more particularly to user equipment (UE) in spread spectrum based wireless systems such as Universal Mobile Telephone System (UMTS).

The basic time unit in a UMTS radio signal is a 10 ms radio frame, which is divided into 15 slots of 2560 chips each. The UMTS radio signal from the cell (or base station) to the UMTS receiver is a "downlink signal" while the radio signal in the reverse direction is called an "uplink signal". When the UMTS receiver is turned on for the first time, the UMTS receiver performs a "cell search" for searching for a cell to communicate with. In particular, as described below, the UMTS receiver initially searches for a downlink synchronization channel (SCH) transmitted from the cell, synchronizes to the channel at the slot and frame level, and performs a special scrambling code group of the cell. Is determined. Only after successful cell search can voice / data communication be started.

In terms of cell search, the SCH is a sparse downlink channel that is active only for the first 256 chips of each slot. The SCH consists of two subchannels, namely, a primary SCH (PSCH) and a secondary SCH (SSCH). The PSCH 256 chip sequence or PSCH code is the same in every slot of the SCH for every cell. In contrast, an SSCH 256 chip sequence or SSCH code may be different in each of the 15 slots of a radio frame and is used to identify one of the 64 possible scrambling code groups. That is, each radio frame of the SCH repeats a scrambling code group sequence associated with each transmission cell. Each SSCH code is obtained from the alphabet of 16 possible SSCH codes.

As part of cell search, a UMTS receiver first uses a PSCH to obtain slot synchronization. In this regard, the UMTS receiver correlates the received sample of the received PSCH against a known PSCH 256 chip sequence (which is the same for all slots) and based on the location of the correlation peak. The slot reference time is determined. When the slot reference time is determined, the UMTS receiver can slot synchronize and 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. In particular, the UMTS receiver correlates a particular sequence of 15 SSCH codes in a received radio frame against a known sequence to obtain frame synchronization and determine a group of scrambling codes of the cell. Next, due to the identification of the scrambling code group, the UMTS receiver will descramble all other downlink channels (e.g., Common Pilot Channel (CPICH)) in the cell to begin voice / data communication. Can be.

Unfortunately, the cell search process described above has some disadvantages. One of them is time. Since SSCH processing identifies a sequence of 15 special SSCH codes, typically SSCH code processing occurs for a number of received radio frames, for example 10-20. Therefore, it may take 100 to 200 ms to complete the cell search. Another disadvantage is that the UMTS receiver does not acquire frequency synchronization until the CPICH is descrambled, which frequency synchronization occurs after successful completion of the cell search described above. As such, and because the UMTS receiver may be mobile, channel conditions may change during SSCH processing such that the UMTS receiver cannot maintain slot synchronization (e.g., a correlation peak moves). Or disappear). In this case, SSCH processing may fail. This failure is also not detected by the UMTS receiver until SSCH processing is complete. So the whole cell search process has to be restarted, and the user has to wait longer to start voice / data communication.

Therefore, according to the principles of the present invention, the wireless receiver performs slot synchronization using the received first synchronization channel, and when slot synchronization is completed, performs frame synchronization using the received second synchronization channel, One synchronization channel is used by the wireless receiver to detect channel state changes.

In an embodiment of the invention, the wireless receiver is part of a UMTS user equipment (UE), the first synchronization channel is a PSCH subchannel, and the second synchronization channel is an SSCH subchannel. The wireless receiver continues to process the PSCH during SSCH processing to monitor the channel condition. In particular, when the correlation peak associated with the PSCH subchannel falls below a predetermined threshold, SSCH processing stops. If the SSCH processing stops within a predetermined initial time period, the SSCH processing begins again. However, if SSCH processing stops after a predetermined initial time period, SSCH processing attempts to estimate the scrambling code group based on the data accumulated so far. That is, the PSCH channel acts as an "early-warning" system that detects sudden channel changes early, thus saving processing time and allowing the user to initiate voice / data communication after the UE is turned on. Reduce your overall time to wait.

According to another embodiment of the present invention, the cell search method uses PSCH processing as an early warning indicator of channel state change, and notifies the SSCH processing of the channel state change. Thus, SSCH processing cannot continue in a situation where the channel state is seriously changed. In this situation, if the SSCH processing continues, there may be an incorrect result.

1 illustrates part of an exemplary wireless communication system in accordance with the principles of the invention;

2 and 3 illustrate an exemplary embodiment of a wireless receiver in accordance with the principles of the invention.

4, 5 and 6 illustrate exemplary flowcharts in accordance with the principles of the present invention.

Of the elements shown in the drawings are not related to the concept according to the invention is known and will not be described in detail. In addition, it is assumed that the UMTS-based wireless communication system is familiar and will not be described in detail herein. For example, spread spectrum transmission and reception, a cell (base station), a user equipment (UE), a downlink channel, an uplink channel and a RAKE receiver, which are not related to the concept according to the present invention, are known and described herein. I never do that. In addition, the concepts according to the invention may be implemented using conventional programming techniques, which will not be described herein. Finally, like numerals in the drawings indicate like elements.

An exemplary portion of a UMTS wireless communication system 10 in accordance with the principles of the present invention is shown in FIG. The cell (or base station) 15 broadcasts a downlink synchronization channel (SCH) signal 16 including the above-described PSCH and SSCH subchannels. As noted above, the SCH signal 16 is used as a pre-condition to voice / data communication by a UMTS user equipment (UE) for synchronization purposes. For example, the UE processes the SCH signal during a "cell search" operation. In this example, the UE 20, for example a mobile phone, initiates cell search, for example when the UE 20 is turned on or powered up. The purpose of the cell search operation includes (a) synchronization for cell transmission at the slot and frame level of the UMTS radio frame, and (b) determination of the scrambling code group of the cell (eg, cell 15). As described below, in accordance with the principles of the present invention, the UE 20 processes the SSCH subchannel to obtain frame synchronization with the cell 15, while monitoring the change in channel state using the PSCH subchannel. The following example illustrates the concept according to the present invention in this initial cell search, i.e., when the UE 20 is turned on, but the concept according to the present invention is not limited thereto, and is another example of cell search. For example, it should be noted that the UE is also applicable when in "idle mode".

Referring now to FIG. 2, shown is an exemplary block diagram of a portion of a UE 20 in accordance with the principles of the present invention. The UE 20 includes a front end 105, an analog to digital (A / D) converter 110, a cell search element 115, a searcher element 120, a RAKE receiver 125, a host interface block. 130 and processor 135. Additional elements known in the art, which are not related to the concept according to the present invention, may be included in the block shown in FIG. 2, but it should also be noted that for simplicity of description they are not described herein. For example, the A / D converter 110 may include a digital filter, a buffer, and the like.

The front end 105 receives a radio frequency (RF) signal 101 transmitted from the cell 15 (see FIG. 1) through an antenna (not shown) and represents a base representing PSCH and SSCH subchannels. Provides a base band analog signal 106. Baseband analog signal 106 is sampled by A / D converter 110, which provides a stream 111 of received samples. The received sample 111 is available to three components: cell search element 115, searcher element 120, and RAKE receiver 125. The cell search element 115 processes the PSCH and SSCH subchannels in accordance with the principles of the present invention described below. After successful cell search, searcher element 120 evaluates the received sample for multipath assignment to each of the fingers of RAKE receiver 125, and the RAKE receiver is, for example, a decoder (not shown). Providing a symbol for subsequent decoding by means of combining data from multiple paths may provide voice / data communication. Since only cell search element 115 relates to the concept according to the invention, search component 120 and RAKE receiver 125 are no longer described herein. The host interface block 130 combines the data between the three aforementioned components and the processor 135, in which the processor receives the results from the cell search component 115 via signaling 134. do. The processor 135 is illustratively a program stored controller processor, for example a microprocessor, and includes a memory (not shown) for storing programs and data.

Referring now to FIG. 3, an exemplary block diagram of cell search element 115 is shown. The cell search element 115 includes a PSCH element 205 and an SSCH element 210. Reference should also be made to FIG. 4, which illustrates an exemplary flowchart in accordance with the principles of the present invention for processing downlink PSCH and SSCH subchannels in the cell search element 115 of FIG. 3. The processor 135 of the UE 20 initiates cell search by processing the downlink PSCH subchannel in step 305, at step 305, attempting to obtain slot synchronization. In particular, the processor 135 activates the PSCH element 205 via signaling 206 to process the received sample 111 as is known in the art. For example, since the downlink PSCH subchannel is a known PSCH 256 chip sequence or PSCH code that occurs periodically (i.e., repeats every slot of the downlink SCH signal), the PSCH element 205 is a received sample 111. ) Is correlated to the PSCH code and provides an associated peak correlation value. In this regard, the PSCH element 205 includes a matched filter and a buffer that stores the output signal of the matched filter (both not shown). The PSCH element 205 provides the peak value to the processor 135 via signaling 206. This peak value is averaged over a plurality of slots, e.g., 4-20 slots, of the received radio frame, reducing the probability of "false lock." If the peak value is less than the predetermined threshold, processor 135 controls PSCH element 205 to continue processing any received signal to continue searching for the cell. However, if the peak value is greater than the preset threshold, UE 20 completes slot synchronization, processor 135 continues the cell search process for frame synchronization, and determines a special scrambling code group for the relevant cell. . An alternative method considers slot synchronization to be complete if the peak correlation value exceeds the next highest correlation value by a predetermined addition or multiplication factor.

In particular, according to step 310 of FIG. 4 and the principles of the present invention, the processor 135 enables both the SSCH element 210 and the PSCH element 205. The SSCH element processes the received sample 111 as known in the art, attempts frame synchronization, and identifies a group of scrambling codes of cell 15. The PSCH element processes the PSCH subchannels, acting as an early warning detector for monitoring or detecting changes in channel conditions during SSCH processing.

Referring now to FIG. 5, step 310 of FIG. 4 is shown in detail. As shown, step 310 includes step 320 associated with SSCH processing and steps 325, 330, and 335 associated with monitoring channel status. Step 320 corresponds to SSCH processing known in the art and is performed by each of the SSCH elements 210 and processor 135 of FIGS. 2 and 3 as shown. The SSCH element 210 connects with the processor 135 via signaling 211. As mentioned above, the SSCH 256 chip sequence or SSCH code is different in each of the 15 slots of a radio frame for a particular cell. As such, each radio frame repeats a particular 15 SSCH code associated with a particular cell. When active by the processor 135, the SSCH element 210 uses a particular sequence of 15 SSCH codes in a received radio frame to obtain frame synchronization and uses a group of scrambling code groups (here, cell 15). Correlated to a known sequence for use in determining the scrambling code group associated with < RTI ID = 0.0 > As mentioned above, SSCH processing may require processing of numerous, for example, 10-20 received radio frames, in which the UE 20 averages the correlation over successive frames of data, This is because a rough estimate of the 15 SSCH code sequences is obtained. As a result, the time period for SSCH processing may be on the order of 100-200 ms. Unfortunately, during this time frame, the UE 20 may not be able to maintain slot synchronization. Therefore, in accordance with an aspect of the present invention, processor 135 uses PSCH element 205 as an early warning detector of channel state changes during SSCH processing. In this regard, in the course of the SSCH processing, the processor 135 allows a timer (not shown) to track the processing time (described below) for step 320. As is known in the art, the timer may be executed in software and / or hardware.

In particular, at step 325, the PSCH element 205 correlates the received sample 111 for the known PSCH code during each slot, and signals the magnitude of the corresponding correlation peak via the processor 206 via signaling 206. To provide. In step 330, the processor 135 compares the received correlation peak with a preset threshold. It does not matter if there is a taller peak (eg from a different cell), and it is important that the original peak (i.e. the peak at which SSCH processing currently tunes to the signal from cell 15) still exists (if weak). It should be noted that In this regard, it is assumed that if the magnitude of the received correlation peak is greater than a predetermined threshold (eg 50% of the original peak value), the channel condition has not changed, and the processor 135 executes step 335. Step 335 determines whether SSCH processing is terminated. When the SSCH processing ends, the cell search ends. However, if the SSCH processing is not complete, the processor 135 returns to step 325 to continue using the PSCH subchannel as an early warning detector of channel state changes.

However, in step 330, if the received correlation peak is less than or equal to the predetermined threshold, the channel state is assumed to have changed, and the ongoing SSCH processing stops. As such, the processor 135 stops the SSCH processing of step 320, as illustrated by the halt signal 216 of FIG. Processor 135 then proceeds to exemplary steps 350, 355, and 360 of FIG. In step 350, the processor 135 evaluates the value of the timer described above, which measures the elapsed time to date for SSCH processing. If the elapsed time is less than or equal to a predetermined value, ie "early" in the SSCH processing, the processor 135 restarts the cell search in step 305 of FIG. In this case, it is assumed that SSCH processing does not yet have enough data to make frame synchronization and a reliable decision for the scrambling code group of cell 15, so it is preferable to restart the cell search. The definition of “early” is that, for example, the completion of SSCH processing is less than 50%, or less than 75%. For example, if the SSCH processing presets as processing at least 10 radio frames, where each frame is 10 ms, an exemplary time value for use at step 350 may be 75 ms.

On the other hand, if the elapsed time is greater than a predetermined value, i.e. " late " in the SSCH processing, the ongoing SSCH processing makes the accumulated data up to now unreliable with unreliable data. As such, the processor 135 checks at step 355 whether the scrambling code group for the cell 15 can be estimated based on the data accumulated so far. In particular, at step 355, the processor 135, in conjunction with the SSCH element 210 via signaling 211, receives 64 possible 15 sequences of 15 SSCH codes representing the received 15 SSCH code sequences estimated to date and a group of scrambling codes. Determines if a match between sequences exists. If there is a match, assume that the SSCH element 210 correctly identifies the received sequence, and frame synchronization and scrambling code group determination is completed at step 360. This match can match exactly over at least N SSCH codes of the 15 SSCH codes if all 15 SSCH codes or a particular group of scrambling codes are identifiable. N is, for example, preset as N = 13. However, if no match exists, processor 135 restarts the cell search in step 305 of FIG.

If the SSCH processing is successfully completed in step 320 or step 360, the scrambling code group of cell 15 is identified, which causes UE 20 to use all other downlink channels of the cell (eg, for frequency synchronization). And descramble a CPICH (Common Pilot Channel) that determines the actual scrambling code for the cell from the identified scrambling code group, and voice / data communication can begin.

As noted above, in accordance with the principles of the present invention, a PSCH subchannel is used to monitor channel status during processing of an SSCH subchannel. As such, this approach may improve the performance of SSCH processing. Although described in the context of an initial cell search process, the concept according to the present invention is applicable to any part of wireless operation in which a downlink channel, such as an SSCH subchannel, is processed under a change of channel state.

Since the foregoing is merely illustrative of the principles of the present invention, those skilled in the art, although not explicitly described herein, embody the principles of the present invention and provide numerous alternative devices that exist within the spirit and scope of the present invention. It will be appreciated that arrangements can be devised. For example, while described in the context of separate functional elements, such functional elements may be implemented on one or more integrated circuits (ICs) and / or on one or more stored program controlled processors (eg, microprocessors or digital signal processors (DSPs)). It can also be implemented. Similarly, although described in a UMTS-based system environment, the concept according to the invention is applicable to any communication system that processes a signal in the presence of a frequency offset. Therefore, it will be understood that numerous modifications may be made to the exemplary embodiments, and that other arrangements may be devised without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (11)

As a method for use in a wireless receiver, (a) processing a first synchronization channel of the received wireless signal to obtain slot synchronization (305), and (b) processing a second synchronization channel of the received wireless signal to obtain frame synchronization, wherein the first synchronization channel is used to detect a change in channel state (310). How to include. The method of claim 1, Wherein 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 of claim 1, In step (b), Processing the second synchronization channel to obtain frame synchronization; Processing the first synchronization channel to provide relevant correlation data; and If the correlation data is less than a preset value, Stopping processing of the second synchronization channel to obtain frame synchronization; Restarting step (a) if the elapsed time for processing of the second synchronization channel is less than a predetermined time value before being stopped, and If the elapsed time is greater than a predetermined value, executing a step of estimating a group of scrambling codes carried in the SSCH based on already accumulated data How to include. As a method for use in a wireless receiver, Processing the first synchronization channel of the received wireless signal to obtain frame synchronization, and During processing of the first synchronization channel, processing a second synchronization channel to detect a change in channel state How to include more. The method of claim 4, wherein Wherein the second synchronization channel is a primary synchronization subchannel (PSCH) and the first synchronization channel is a secondary synchronization subchannel (SSCH) of a universal mobile telephone system (UMTS). The method of claim 4, wherein The processing of the second synchronization channel may include Processing the second synchronization channel to provide relevant correlation data; and If the correlation data is less than a preset value, Stopping processing of the first synchronization channel, and If the elapsed time for processing of the first synchronization channel before stopping is greater than a predetermined time value, the scrambling code group transmitted in the first synchronization channel is estimated based on already accumulated data, and the elapsed time If less than this predetermined time value, executing the step of restarting processing of the first synchronization channel. How to include. As a wireless device, A front end 105 for receiving a wireless signal and providing a stream of received samples, Operating on the received sample to obtain slot synchronization for the primary synchronization signal of the received wireless signal, and upon obtaining slot synchronization, subsequent processing of the primary synchronization signal to provide data indicative of channel conditions. Primary synchronization element (205), A secondary synchronization element 210 for operating on the received sample to obtain frame synchronization for a secondary synchronization signal of the received wireless signal, and A processor 135 for stopping the secondary synchronization element as a function of data indicative of the channel state in response to subsequent processing of the primary synchronization signal by the primary synchronization element Wireless equipment comprising a. The method of claim 7, wherein Subsequent to slot synchronization, the primary synchronization element continues to process the primary synchronization signal of the received radio signal concurrently with the processing of the received radio signal by the secondary synchronization element. The method of claim 7, wherein The data indicative of the channel state represents a correlation between a known primary synchronization code and the received primary synchronization signal, and the processor is configured to determine the secondary synchronization element if the correlation is less than a predetermined value. Stationary wireless equipment. The method of claim 7, wherein If stopped, the secondary synchronization element provides an estimate for the scrambling code group to the processor if the elapsed time for obtaining frame synchronization before stopping is greater than a predetermined value. The method of claim 7, wherein If stopped, the processor restarts the secondary synchronization processor if the elapsed time to obtain frame synchronization before stopping is less than a predetermined value.

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