JP3706038B2 - Spread spectrum receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spread spectrum receiver in a third generation mobile communication system employing a CDMA (Code Division Multiple Access) system, and more particularly to a searcher generally used for synchronization acquisition (path search) in a CDMA communication system. The present invention relates to a spread spectrum receiving apparatus that can be used for determination of synchronization loss of a DLL that is a synchronization tracking circuit.
[0002]
[Prior art]
In recent years, a multiple access method called a CDMA method using a spread spectrum communication technology has become widespread as a wireless communication method that is a basic technology of the third generation mobile communication system, and technical proposals and technical developments are actively performed in this regard. ing.
In the CDMA system, a radio signal having a sufficiently wider band than the original signal is transmitted by performing a spreading process of multiplying a target signal by a spreading code on the transmission side. With this process, signals from other base stations / terminals can be regarded as equivalent to noise as long as codes that are orthogonal to each other are used. The target signal can be received separately.
[0003]
The despreading process is a process of extracting the original primary modulation signal by multiplying the reception side by the same spreading code as that of the transmission side. At this time, it is necessary to capture and follow the reception timing in units of chips, which is the bit rate unit of the spread code.
On the other hand, as an essential feature of wireless communication, there is a case where a phenomenon called multipath in which a plurality of propagation paths are generated due to reflection of a signal wave by a building or terrain may occur. Therefore, signals transmitted at the same timing are received with a time difference.
[0004]
In the CDMA system, it is possible to perform despreading processing in accordance with a plurality of path timings on the receiving side and synthesize demodulated signals having a time difference. However, because of the mobile communication, this multipath varies with time.
Due to such characteristics, a phenomenon called fading occurs in which the signal strength of the received signal varies with time. Under such a multipath fading environment, it is indispensable for the CDMA reception technique to select an optimal reception path, accurately adjust reception timing in units of chips, and follow the received signal synchronously.
[0005]
In a CDMA receiver, a DLL (Delayed Locked Loop) is generally employed as a circuit that plays a role of synchronization tracking. That is, as shown in FIG. 3, each received signal is multiplied by a code by a correlator at a certain timing earlier and later than the synchronized timing, and the loop control of the loop filter is performed with the difference between the correlation outputs of the two. The synchronization tracking is realized by determining the advance / delay of the code generation phase.
In general, ± 0.5 chips are used for this fixed amount. In the prior art, the result of actual demodulation from the DLL output is evaluated by the control unit to determine whether or not the DLL has lost synchronization.
[0006]
In FIG. 3, 301 is a received signal, 302, 303 and 304 are correlation circuits, 305 is a differential output circuit, 306 is a loop filter, 307 is a spread code generator, 308 and 309 are delay circuits, 310 is demodulated data, Reference numeral 311 denotes a timing signal generator, 312 denotes an operation start signal, and 313 denotes a DLL synchronization signal.
[0007]
Furthermore, according to the technique described in Japanese Patent Laid-Open No. 2000-92026, the reception synchronization characteristics are improved by utilizing the information of the synchronization acquisition unit for the DLL synchronization loss determination.
That is, in the technique described in Japanese Patent Application Laid-Open No. 2000-92026, as shown in FIG. 4, as a component of the CDMA receiver, an allocation control unit in addition to the synchronization acquisition unit 411 and the synchronization tracking units 413, 414, and 415 412 is added.
[0008]
The synchronization acquisition unit 411 outputs the timing at which the power value of the correlation output is large to the allocation control unit 412 as the acquisition synchronization position S411A. The allocation control unit 412 selects a plurality of acquisition synchronization positions S411A that have a phase difference equal to or greater than a threshold value, and outputs them as allocation synchronization positions S412A, S412B, and S412C.
The synchronization tracking units 413, 414, and 415 receive the allocated synchronization positions S412A, S412B, and S412C, perform a synchronization tracking operation, and output the tracking synchronization positions S413A, S414A, and S415A and tracking correlation power values S413B, S414B, and S415B. As the synchronization followers 413, 414, and 415, DLLs that are common in this technical field are usually used.
[0009]
The allocation control unit 412 compares the acquisition synchronization position S411A and the tracking synchronization positions S413A, S414A, and S415A, excludes the tracking synchronization position whose phase difference is equal to or less than a predetermined threshold, and avoids following the same synchronization position. ing. When each of the tracking correlation power values S413B, S414B, and S415B of the synchronization tracking units 413, 414, and 415 is equal to or less than a predetermined threshold value, another capture synchronization position is selected and the synchronization tracking unit is assigned.
[0010]
By adopting such a method, even when the received wave power is reduced due to fading or the path itself is lost, new synchronization positions can be continuously assigned without interrupting the demodulation operation. For this reason, compared with the prior art which relies only on the correlation output of DLL, it has become a receiving system and a circuit excellent in the synchronization tracking characteristic.
[0011]
[Problems to be solved by the invention]
However, among the above-described conventional techniques, in the synchronous circuit in which the DLL output itself in the former is a synchronization loss determination, in consideration of an actual environment such as multipath fading, the normal operation period of the DLL ( If the means for determining the result is used for each frame (10 ms), the amplitude may change greatly due to fading during the operation period, and as a result, the synchronization tracking determination may be erroneous.
[0012]
Further, since the DLL itself performs synchronous tracking with a width of typically ± 0.5 chip, the tracking capability is limited. Furthermore, the circuit scale increases, and the accompanying increase in power consumption is inevitable.
[0013]
In the technique described in Japanese Patent Laid-Open No. 2000-92026, it is possible to reinforce the limit of the synchronization tracking capability of the DLL by utilizing the synchronization acquisition unit, and to increase the accuracy of the synchronization loss determination. It is said that the circuit scale is suppressed because the existing configuration remains unchanged.
However, in the synchronization loss determination method, a timing at which the correlation power of the synchronization follower is large is adopted as a method of determining the acquisition synchronization position of the basic synchronization acquisition unit. In this respect, as in the former prior art, the determination based on the power value of the DLL is vulnerable to fading, and there is a possibility that the determination may be erroneous.
[0014]
Further, in the third generation mobile communication system, a system has been proposed in which a received channel demodulation of a communication channel is performed using a common pilot on a common pilot channel in which a known symbol is transmitted in propagation path estimation.
In addition, a system using an individual pilot on a communication channel for channel estimation has been proposed. In this case, channel estimation is performed using the individual pilot. For example, in order to improve reception characteristics, STTD or FeedBack type transmission diversity, closed-loop high-speed transmission as shown in IEICE Technical Report RCS99-12 “Effect of Downlink Transmission Diversity in W-CDMA” A scheme has been proposed in which power control is applied to a communication channel having dedicated pilots.
[0015]
In the technique described in the above-mentioned Japanese Patent Laid-Open No. 2000-92026, with a specific communication system in mind, for example, for a specific channel having a common pilot or an individual pilot, such as a third generation mobile communication system. This does not propose a method of performing a sliding correlation process by a searcher and determining a DLL synchronization loss.
[0016]
The present invention has been made in view of the above-described circumstances. In particular, it is intended to be applied to a third-generation mobile communication system, and accurately and appropriately without interrupting synchronization tracking monitoring that is essential in a CDMA receiver. An object of the present invention is to provide a spread spectrum receiver capable of executing and reducing power consumption and circuit scale.
[0017]
[Means for Solving the Problems]
In order to achieve the above-described object, the spread spectrum receiver of the present invention has the following features.
[0018]
That is, the spread spectrum receiver of the present invention is a correlation spread position obtained from a correlation profile obtained by correlating with a spread spectrum reception signal while changing the phase of the spread code in the spread spectrum receiver employing the CDMA system. A searcher for searching for and outputting the timing information, a control unit for controlling the operation of the timing controller in response to the timing information from the searcher, and a timing for providing an operation timing signal for the subsequent DLL A controller and a DLL for performing despreading on a received signal that has been subjected to spectrum spreading by receiving the operation timing signal using a code sequence, and performing synchronization tracking and demodulation. The timing controller receives the DLL synchronization tracking signal and outputs it to the control unit as a synchronization tracking timing signal. Force , Also The operation start pulse is output to the searcher, and the control unit compares the synchronization timing expected from the timing information of the searcher with the timing signal from the DLL that is actually following the synchronization, and the timing difference is a constant value. When it is determined that the DLL is operating, it is determined that the DLL operating at that timing is a synchronization loss, and the operation of the DLL is stopped, or the restart of the DLL is started from another peak timing detected by the searcher. It is characterized by giving timing.
[0019]
The spread spectrum receiving apparatus may be configured to determine a target signal to be path-searched by the searcher as a common pilot channel used for propagation path estimation, and to perform synchronization loss determination of the DLL.
[0020]
In the spread spectrum receiver, the target signal to be path-searched by the searcher is determined as a communication channel of a system that performs channel estimation using individual pilots of the communication channel, and the synchronization loss determination of the DLL is performed. Is possible.
[0021]
In the spread spectrum receiver of the present invention, the following operation is performed.
That is, a synchronization acquisition unit called a searcher obtains a partial correlation output and acquisition synchronization timing information for each phase of a spread code of a certain length while shifting the phase. The timing controller outputs an operation start timing signal of a DLL that is a synchronization tracking unit based on an instruction from the control unit, and also receives a tracking synchronization timing signal from the DLL and passes it to the control unit as timing information.
[0022]
The DLL actually correlates the spreading code that has been advanced by 0.5 chips and the delayed code that has been delayed by 0.5 chip from the phase synchronization timing, and the spreading code of the spreading code through the difference. It consists of three correlation calculation circuit units of two sets of correlation calculation circuit units (early and late) that perform phase control, and outputs a despread demodulation output and a synchronization tracking timing signal. The control unit compares the basic operation control of each unit and especially the search timing information of the searcher with the DLL synchronization tracking timing signal from the timing controller, and assigns the DLL, determines the synchronization loss, stops the operation, restarts, etc. Direct through.
[0023]
Then, it performs accurate synchronization loss determination, stops the operation of the DLL that has lost synchronization, further determines the DLL operation timing from the searcher output result, and resumes the reception operation at an appropriate timing. By doing so, the influence of fading can be reduced and good reception characteristics can be obtained.
[0024]
By the way, with respect to the synchronization loss determination, the method using the DLL demodulated output is greatly affected by fading, and there is a possibility that the synchronization loss is erroneously determined. On the other hand, in the spread spectrum receiving apparatus of the present invention, the influence of fading can be minimized as much as possible by using the result of the synchronization acquisition operation of the searcher whose operation cycle is shorter than that of the DLL.
[0025]
In addition, since the searcher and DLL timing information is used for synchronization loss determination, it is less susceptible to fading compared to the conventional technology using amplitude information, and without interrupting the synchronization tracking operation. It is possible to operate by appropriately assigning a DLL in accordance with the synchronization tracking timing that varies with time. For this reason, power consumption can be reduced.
[0026]
In addition, since the DLL is composed of at least three correlation operation circuits, if the number of DLLs is increased in order to improve the reliability, the circuit scale increases and power consumption inevitably increases. On the other hand, according to the spread spectrum receiver of the present invention, there is no need to newly provide a circuit for performing correlation calculation for the purpose of determining synchronization loss, and it has been used for the initial synchronization acquisition operation (path search) conventionally. Because it uses the output of the existing searcher, the timing controller for determining the operation of the DLL, and the output of the DLL and the searcher, just make a small change to the control unit to determine the synchronization loss A circuit can be configured. For this reason, since an increase in circuit scale can be suppressed, power consumption can be reduced also from this point.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a spread spectrum receiving apparatus of the present invention will be described based on specific examples shown in the drawings. The spread spectrum receiving apparatus of the present invention is particularly intended for use in a third generation mobile communication system employing a CDMA system.
[0028]
<Spread spectrum receiver>
FIG. 1 is a block diagram showing a configuration of a spread spectrum receiving apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the spread spectrum receiver according to the embodiment of the present invention includes DLLs 101, 102, and 103 that are synchronization tracking circuits, and a RAKE combining circuit 104 that combines outputs from these DLLs 101, 102, and 103. The searcher 105, DLL 101, 102 for obtaining the received signal correlation output while changing the phase of the spreading code of a certain length, and outputting the timing information obtained the correlation output greater than a certain threshold value from the internal timing counter value , 103 and the searcher 105 are provided with an operation start timing, and similarly to the searcher 105, a timing controller 106 having a timing counter for determining timing information therein, setting of operation conditions of each part and DLLs 101, 102 in particular , 103 regarding synchronization loss judgment It is configured to include a control unit 107 for performing constant.
[0029]
In FIG. 1, S100 is a received signal from an antenna, S108 is a synchronization acquisition timing signal that has a correlation value of a certain level or more obtained from an output signal from a searcher 105, and S109 is an output from a plurality of DLLs 101, 102, and 103. The demodulated data as a result of the RAKE synthesis, Sll0 is a DLL operation instruction output from the control unit 107 to the timing controller 106, and S111 is the DLL 101, 102, 103 output from the timing controller 106 to the control unit 107. Synchronous tracking timing signals S112, S113, and S114 indicate synchronous tracking signals output from the DLLs 101, 102, and 103 to the timing controller 106, respectively.
[0030]
In the embodiment shown in FIG. 1, the configuration includes three DLLs 101, 102, and 103, but the configuration includes more DLLs depending on conditions such as system requirements and circuit scale restrictions. It is also possible. Even in this case, the essential operation and the intention of the present invention are the same, and a sufficient effect can be obtained.
[0031]
The spread spectrum receiver performs a synchronization acquisition operation in the searcher 105 and performs a synchronization tracking operation in the DLLs 101, 102, and 103.
The operation timing of the DLLs 101, 102, and 103 is given from the timing controller 106 in response to an instruction from the control unit 107 upon receiving an output from the searcher 105. When the received signal S100 is input, the searcher 105 performs a path search, and the DLLs 101, 102, and 103 perform synchronous tracking at an appropriate timing in response to the result, and the received signal is demodulated. After that, the RAKE combining circuit 104 combines a plurality of signals at different timings resulting from the multipath.
Further, although not explicitly shown, the control unit 107 not only controls the timing controller 106 but also controls the DLLs 101, 102, 103, the RAKE combining circuit 104, and the searcher 105, such as a power threshold for basic operation. The parameter setting is performed by the control unit 107.
[0032]
The searcher 105 receives the operation start pulse from the timing controller 106, multiplies the spread code of a certain length with respect to the received signal S100 while shifting the phase, and at the timing when the correlation more than a certain threshold is obtained. Is started, that is, the output of the synchronization acquisition timing signal S108 is started.
[0033]
The timing controller 106 receives this synchronization acquisition timing signal S108 and outputs operation start timing signals of the DLLs 101, 102, and 103. Here, when there are a plurality of peak positions, the control unit 107 assigns to the plurality of DLLs 101, 102, and 103, and instructs the timing controller 106 to output an operation start timing signal to each.
[0034]
Upon receiving the operation start timing signal, the DLLs 101, 102, and 103 perform a synchronous tracking operation independently at each timing. Outputs from the DLLs 101, 102, and 103 are combined by the RAKE combining circuit 104 to become demodulated data S109.
[0035]
Further, the searcher 105 is operated during the following operation of the DLLs 101, 102, and 103, and the synchronization acquisition timing signal S 108 is input to the control unit 107. On the other hand, the DLLs 101, 102, and 103 receive the synchronous follow-up signals S 112, S 113, and S 114 reflecting the follow-up operation of the DLLs 101, 102, and 103 with respect to the timing controller 106 using the operation start timing signal as a starting point in addition to data demodulation. Output.
[0036]
The timing controller 106 receives the synchronization tracking signals S112, S113, and S114, and outputs a corresponding internal timing counter value to the control unit 107 as the synchronization tracking timing signal S111. The searcher 105 operates in response to an operation start pulse of the timing controller 106, and can synchronize both internal timing counters.
[0037]
Therefore, the control unit 107 can simply compare the synchronization acquisition timing signal S108 and the synchronization follow-up timing signal S111, and if the positional relationship has changed beyond a predetermined threshold, or the disappearance of timing has been confirmed. If it is determined that the corresponding DLL (any one of 101, 102, 103) has already lost synchronization, the corresponding DLL (any one of 101, 102, 103) is determined. An instruction to stop the operation is issued. Further, in some cases, an instruction is issued to the timing controller 106 to restart the operation at a new timing.
[0038]
By adopting such a circuit configuration, due to the influence of fading, the synchronization follow-up timing of the DLLs 101, 102, 103 greatly moves, or the path itself disappears, and any of the DLLs 101, 102, 103 is synchronized. Even in the case of losing, it is possible to quickly determine the synchronization losing and stop the operation or to restart the operation at another new timing.
[0039]
In addition, since the operation timing information is used for the synchronization loss determination, the possibility of erroneous determination due to amplitude fluctuation due to fading is reduced compared to the case of using amplitude, and accurate determination can be performed. .
Therefore, by accurately continuing the synchronization tracking operation of the DLLs 101, 102, and 103 without interruption, it is possible to improve the reception characteristics and to obtain the effect of reducing power consumption by efficient operation. Further, from the viewpoint of circuit design, since the searcher 105 is already used in the correlation peak position detection for determining the operation start timing of the DLLs 101, 102, and 103 as a conventional technique, the control unit 107 performs synchronization acquisition timing. By comparing the signal S108 with the synchronization tracking timing signal S111 of the DLLs 101, 102, and 103 obtained from the timing controller 1 06, it is sufficient to make a synchronization determination and change the control so that each unit is controlled. Changes can be kept relatively small.
[0040]
<Transmission signal format>
Next, a specific example of a transmission signal format in the spread spectrum receiving apparatus according to the embodiment of the present invention will be described.
2A and 2B are explanatory diagrams of a transmission signal format in the spread spectrum receiving apparatus according to the embodiment of the present invention. FIG. 2A shows Example 1 of the transmission signal format, and FIG. 2B shows Example 2 of the transmission signal format. .
[0041]
<Transmission signal format: Example 1>
As shown in FIG. 2A, in the third generation mobile communication system, a common pilot channel is transmitted with a constant power, and pilot symbols on the channel are known. Therefore, it is a general method to obtain a demodulated output by operating a searcher for this pilot channel and estimating a transmission path from the pilot symbol. The common pilot symbol is a slot unit, and at least a stable synchronization tracking characteristic is required during this period.
Therefore, when the spread spectrum receiver of the present invention is applied to this communication system, it is possible to operate the searcher for the pilot channel and realize stable synchronization loss determination by the synchronization circuit.
[0042]
<Transmission signal format: Example 2>
As shown in FIG. 2 (b), in the third generation mobile communication system, it has been proposed to use a communication channel as a channel for channel estimation, and the dedicated pilot symbol has a shorter period. In addition, since power control is performed on a slot basis, the amplitude fluctuation of the received signal is further increased. However, in this case as well, as in the case of the common pilot channel, it is possible to monitor synchronization loss with high accuracy by operating the searcher on the communication channel.
[0043]
<Application to 3rd generation mobile communication systems>
The spread spectrum reception apparatus of the present invention has a configuration in which a searcher that is originally used for path search for finding the synchronization tracking timing of DLL is used for DLL synchronization monitoring.
Therefore, it is not necessary to consider a significant increase in circuit scale as compared with the conventional spread spectrum receiving apparatus, and it is only necessary to change the software for the control unit. For this reason, the circuit scale can be kept relatively small.
As described above, according to the spread spectrum receiver of the present invention, power consumption can be suppressed in terms of circuit scale and appropriate DLL operation. In particular, the third generation mobile communication system It can be applied to a receiving system.
[0044]
【The invention's effect】
Since the spread spectrum receiving apparatus of the present invention has the above-described configuration, the following effects can be obtained.
[0045]
That is, according to the spread spectrum receiver of the present invention, in the synchronization loss monitoring of the DLL in charge of synchronization tracking, which is an important element technology in the CDMA reception system, timing information from a searcher generally used for synchronization acquisition, The timing information of the DLL used for synchronization tracking is compared to determine whether or not synchronization is established.
Therefore, compared to the conventional technique that has a long operation cycle and uses correlation power, not only is it resistant to fading, but also the additional circuit can be made relatively small, resulting in reduced power consumption. it can.
[0046]
Further, according to the spread spectrum receiver of the present invention, the synchronization loss determination is performed based on the timing information obtained from the searcher of the common channel or the communication channel.
Therefore, it can be applied particularly to the third generation mobile communication system, and accurate synchronization determination according to the system can be performed, and the circuit scale can be reduced to contribute to low power consumption.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a spread spectrum receiver according to an embodiment of the present invention.
FIGS. 2A and 2B are explanatory diagrams of a transmission signal format in a spread spectrum receiving apparatus according to an embodiment of the present invention, where FIG. .
FIG. 3 is a block diagram showing a configuration of a known DLL in CDMA reception.
FIG. 4 is a block diagram showing a schematic configuration of a reception synchronization circuit in the prior art.
[Explanation of symbols]
101, 102, 103 DLL
104 RAKE synthesis circuit
105 Searcher
106 Timing controller
107 Control unit
S100 Receive signal
S108 Synchronization acquisition timing signal
S109 Demodulated data
S110 DLL operation instruction
S111 Synchronization tracking timing signal
S112, S113, Sll4 Synchronization tracking signal
301 Received signal
302, 303, 304 Correlation circuit
305 Difference output circuit
306 Loop filter
307 Spreading code generator
308, 309 delay circuit
310 Demodulated data
311 Timing signal generator
312 Operation start signal
313 DLL synchronization signal
411 Synchronization acquisition unit
412 Allocation control unit
413, 414, 415 Synchronization follower
S400 Received signal
S411A Acquisition synchronization position
S412A, S412B, S412C Allocation synchronization position
S412D Synchronization acquisition unit operation start signal
S413A, S414A, S415A Tracking synchronization position
S413B, S414B, S415B Follow-up correlation power value

Claims (3)

In a spread spectrum receiver employing a CDMA system,
A searcher for searching for a correlation peak position from a correlation profile obtained by taking a correlation with a spread spectrum received signal while changing a phase of a spread code, and outputting timing information thereof,
A control unit for receiving timing information from the searcher and controlling the operation of the timing controller;
A timing controller for providing an operation timing signal for the subsequent DLL;
Receiving the operation timing signal, despreading the spread spectrum received signal using a code sequence, and a DLL for performing synchronization tracking and demodulation,
The timing controller receives the synchronization tracking signal of the DLL and outputs a synchronous follow-up timing signal to the control unit, also outputs the operation start pulse to the searcher,
The control unit compares the synchronization timing expected from the timing information of the searcher with the timing signal from the DLL that is actually following the synchronization, and determines that the timing difference is equal to or greater than a certain value. The spread spectrum is characterized in that it is determined that the DLL operating at the time is a synchronization loss, and the operation of the DLL is stopped or the re-operation start timing of the DLL is given from another peak timing detected by the searcher. Receiver device.   2. The spread spectrum receiver according to claim 1, wherein a target signal to be path-searched by the searcher is determined as a common pilot channel used for propagation path estimation, and the synchronization loss determination of the DLL is performed.   2. The spread spectrum according to claim 1, wherein a target signal to be path-searched by the searcher is determined as a communication channel of a system that performs channel estimation using a dedicated pilot of the communication channel, and the synchronization loss determination of the DLL is performed. Receiver device.

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