KR20020055451A - Methods and apparatus for signal searching using correlation - Google Patents

Abstract

The signal searcher for the CDMA communication system has a correlator that correlates the reference signal with the received signal in a short (signal-coherent) correlation interval with the reference signal generator. The code phase of the reference signal is changed through all N possible code phases in the N consecutive correlation intervals constituting one signal scanning cycle. Correlation results for the same code phase for multiple correlation intervals are accumulated over successive signal scanning cycles using a combiner and a buffer, and the presence of one or more desired signals in the received signal and the correlation of the code phases are accumulated. It is determined by the decision unit depending on the result. In one embodiment all correlation results are accumulated and in other embodiments the memory requirements are reduced by accumulating only those values where the correlation results are large.

Description

Methods and apparatus for retrieving signals using correlation {METHODS AND APPARATUS FOR SIGNAL SEARCHING USING CORRELATION}

Communication systems using CDMA signals have advantages for capacity, frequency planning, communication quality, security from unauthorized access, and immunity to interference. However, there is a significant challenge in CDMA system design since there is a need to achieve precise synchronization between the locally generated signal and the desired signal contained in the received signal. The first step in this synchronization is that one or more parameters, such as the frequency and code phase of the pseudo-noise (PN) signal that make up the reference signal, are changed and the assumptions about the presence of the desired signal are gradually evaluated. Signal search processing. This uses significant time and hardware resources of the CDMA system receiver.

More specifically, for each set of possible values for the parameter of the reference signal, referred to as the offset position or state of the reference signal, correlation is performed with the received signal, and the resulting correlation value is determined with each offset or position. It is evaluated to determine the presence of a signal.

Signals communicated in a CDMA wireless cellular communication system are known to be faded, so that reduced RF signal amplitude and phase changes are known to cause substantial degradation of signal retrieval processing.

To eliminate fast signal phase dispersion or fast fading, see, for example, "DS-SS Code Acquisition in a Rapid Fading Environment" by Manabu Mukai and Mutsumu Serizawa, IEEE 0-7803 From -2742-X / 95, p 281-285, 1995 it is known to divide the accumulation interval (TA) into several consecutive short intervals (TCOH) such that TA = mTCOH. The duration of each interval TCOH is chosen small enough so that the signal phase does not change noticeably during this interval, so it is called the signal coherence interval. During the accumulation interval TA, the correlation result for each offset or position of the reference signal is accumulated without interference. However, slow fading causes the accumulated correlation result used to determine the presence of the desired signal at each offset to be clearly different from the long term value, thus increasing the probability of missing or false signal detection. In order to reduce such inconvenience, reducing the length of the accumulation interval TA undesirably increases the signal retrieval time.

The effects of slow fading can be achieved using a diversity method, e.g., spatial diversity techniques in which signals with relatively independent fading characteristics are received by two or more spaced antennas and the correlation results for these signals are combined. Can be reduced. However, this undesirably increases the complexity of the receiver, and the use of multiple antennas with space, especially in small portable receivers, is not practical.

US Patent No. entitled “Sync Acquisition and Tracking Circuit for DS / CDMA Receiver” issued August 27, 1996. 5,550, 811 describes a time diversity arrangement to compensate for slow fading that feeds each combiner periodically a correlation result for each position or set of parameters so that the selector switch performs uninterrupted accumulation. Since the switching period is determined according to the fading period, the accumulated correlation result is averaged over the signal fading. This arrangement is complex to implement and has the inconvenience of requiring a selector switch and its control arrangement, and also requiring a combiner by as many parameter sets or positions. For example, in an IS-95 CDMA wireless cellular communication system, there are N = 32769 possible PN code phases or positions for a mobile station to retrieve a pilot signal from a base station.

Andrew J. Viterbi's "CDMA Principles of Spread Spectrum Communication", Addison-Wesley Communication Series, 1995, Section 3.4.1, "Single-Pass Serial Search" A signal retrieval method is described in which m correlation estimates of consecutive adjacent signal coherence intervals (TCOH) are accumulated during an accumulation interval TA = mTCOH. In an IS-95 CDMA system having a signal bandwidth of 800 MHz to 1.25 MHz, the Rayleigh fading period is about 20 to 50 ms, while the length of the access channel signal accumulation interval can be 1.2 to 2.4 ms. Thus, a substantial change in signal amplitude due to fading can occur within the accumulation interval TA, thereby increasing the probability of signal loss and false signal detection.

The present invention relates to a method and apparatus for retrieving a signal using a correlation of a reference signal and a received signal, in particular the presence of wideband signals using CDMA in a code division multiple access (CDMA) wireless cellular communication system. And a method and apparatus for detecting code phases.

1 is a block diagram of a known signal searcher.

2 is a block diagram of a known correlator used in the signal finder of FIG.

3 is a timing diagram illustrating signal fading.

4 is a timing diagram illustrating the operation of the signal searcher of FIG.

5 is a block diagram of a signal searcher according to a first embodiment of the present invention.

FIG. 6 illustrates a serial buffer in the signal finder of FIG. 5. FIG.

7 is a timing diagram illustrating the operation of the signal searcher of FIG.

8 is a block diagram of a signal searcher according to a second embodiment of the present invention.

FIG. 9 illustrates a buffer memory in the signal finder of FIG. 8; FIG.

10 is a flow diagram illustrating a data update algorithm.

11 and 12 illustrate data updates in the operation of the signal finder of FIG.

13 is a graph comparing the signal searcher of FIG. 1 and the signal searcher of FIG. 8.

14 is a block diagram of a signal searcher according to a third embodiment of the present invention.

FIG. 15 illustrates a serial buffer in the signal finder of FIG. 14. FIG.

FIG. 16 illustrates a maximum searcher in the signal searcher of FIG. 14; FIG.

FIG. 17 illustrates a comparison and combination unit in the signal finder of FIG.

FIG. 18 is a flowchart for explaining the operation of the signal searcher of FIG.

It is an object of the present invention to provide a method and apparatus that can facilitate signal retrieval in a communication system such as a CDMA system.

In accordance with an aspect of the present invention, the signal searcher for a CDMA communication system generates at least one reference signal and generates each reference signal at a sufficiently short correlation interval so that the phase of the received signal does not change significantly during the correlation interval. Correlate with the received signal. Correlation results for the same code phase are accumulated over the plurality of correlation intervals, and the presence and code phase of one or more desired signals in the received signal are determined depending on the accumulated correlation results. The code phase of the reference signal is changed through all N possible code phases in N consecutive correlation intervals constituting one signal scanning cycle, and the correlation result is stored to accumulate over a plurality of signal scanning cycles. This feature of the invention also provides means for performing these functions, for example a digital signal processor.

Another characteristic of the invention is that the received signal is correlated with the reference signal and at least one parameter of the reference signal is changed so that each correlation result for different offsets of the N possible offsets between the received signal and the reference signal. A signal retrieval method is provided, wherein each of N possible offsets from a correlation between a received signal and a reference signal having a separate offset during each correlation interval in which the phase of the received signal does not change significantly in one scan cycle. Generating an individual correlation result for; And accumulating correlation results for the plurality of correlations with corresponding offsets in successive scan cycles so that the presence and offset of a desired signal can be determined from the accumulated correlation results. The parameter is changed between successive ones of the correlations.

In one embodiment of the method, correlation results are accumulated for all N possible offsets between the received signal and the reference signal. In another embodiment, the method includes determining the largest correlation result for L of N possible offsets in the scan cycle, where L is an integer less than N and the correlation result is L Accumulate only for offset. Another embodiment includes determining the largest correlation result for each of the L groups with J of each of the N possible offsets in the scanning cycle, where L = N / J, and the correlation result is L Only for the largest correlation result in each of the groups. In each of these two later embodiments, an identification of each offset, eg a position count, may be stored in association with each accumulated correlation result.

Yet another aspect of the present invention provides a method for detecting the presence of a desired signal and a PN code phase in a received signal of a CDMA communication system, wherein N possible PN code phases in consecutive ones of N correlation intervals in one scanning cycle Generating a reference signal with different phases; Correlating a reference signal and a received signal during the correlation interval to generate respective correlation results; Accumulating at least some of the correlation results over successive scan cycles; And determining the presence of the desired signal and the code phase from the accumulated correlation results.

Correlation results can be accumulated for all N correlation intervals in each scan cycle. Alternatively, correlation results can be accumulated only for the L correlation intervals with the largest correlation in the scanning cycle, where L is an integer less than N, and the method determines and accumulates the largest correlation. Storing an identification of each of the L correlation intervals associated with each correlation result. Alternatively, the correlation interval may comprise L groups each having J correlation intervals in each scan cycle, where L and J are integers L = N / J, and the correlation result is a scan Only one of the correlation intervals within each group of J correlation intervals that provides the largest correlation in the cycle can be accumulated, and the method also determines the largest correlation and correlates with each accumulated correlation result. Storing an identification of each correlation interval that is associated and provides the largest correlation among each group of J correlation intervals.

The present invention also provides a signal finder for a CDMA communication system, comprising: a control unit; A reference signal generator controlled by the control unit to generate a reference signal in a different phase of the N code phases in each of the N consecutive correlation intervals within the scan cycle; A correlator for correlating the reference signal and the received signal at successive correlation intervals to produce respective correlation results; And a control unit for accumulating correlation results from the correlator for each of a plurality of corresponding correlation intervals in the plurality of scan cycles to produce an accumulated individual correlation result in which the presence and code phase of the desired signal in the received signal can be determined. And an accumulator responsive to each, and each correlation interval is short enough so that the phase of the received signal does not change significantly during the correlation interval.

In a first embodiment of the searcher described later, the accumulator includes a buffer that stores the accumulated correlation results for each of the N code phases. In a second embodiment, the signal searcher includes a unit for determining the largest correlation result for L of N code phases in a scanning cycle, and the accumulator includes accumulated correlation results for each of the L code phases and And a buffer that stores an associated count that identifies each code phase, where L is an integer less than N.

In a third embodiment, the correlation interval comprises L groups each having J correlation intervals in each scan cycle, where L and J are integers L = N / J, and the signal retriever is also a scan cycle. A searcher that determines the largest correlation result for each group of J correlation intervals and provides a count that identifies the corresponding correlation interval in each group, wherein the accumulator correlates for each of the L groups A buffer for storing the result and the count associated therewith, and a combiner for incrementing the stored correlation result for each of the L groups in at least one subsequent scan cycle by the correlation result for the same code phase identified by the count. do. In this case, the combiner is stored in each subsequent scan cycle only if the detector determines that the correlation result for the same code phase identified by the count is the largest correlation result for each group of J correlation intervals. May be arranged to increase correlation results.

The signal searcher may include a determining unit that determines a maximum of one or more correlation results accumulated to determine the presence and the code phase of one or more desired signals in the received signal.

Embodiments of the present invention may provide significant advantages over the prior art discussed above. In particular, they are simple to implement and can provide a significant improvement in the probability of detecting lost and false signals, and because of their relative immunity to fading environments, many such as pilot signals from multiple base stations in a CDMA cellular communication system. The detection of a desired signal can be facilitated. The second and third embodiments described below also reduce memory requirements, and are therefore particularly important when the number N of code phases is very large.

Referring to the drawings, FIG. 1 describes a known wideband signal searcher for detecting signals, for example, in a CDMA cellular communication system. The signal searcher includes a reference pseudo-noise signal generator 10, a correlator 12, an accumulator 14, a determination unit 16, and a timing control unit 18.

The signal finder operates to detect the desired RF signal supplied to the input 20 of the correlator 12, the RF signal having a nominal carrier frequency f0 and the sum of the two components I and Q in quadrature phase. Wherein these components are modulated with PNI and PNQ, respectively, by spreading the PN sequence or PN code.

Typically, as assumed in the following description, the PN code phase is assumed to be the timing parameter by which the signal search is performed. However, it is contemplated that additional parameters such as input signal frequency f may be included. In any case, in order to perform a signal search, a plurality of N offsets, positions, or states (simply referred to as balances in position) are provided for each parameter set in the search range or the uncertainty area, respectively, In the case of a PN code phase search, each PN code phase value corresponds to each position, and the distance between PN code phases of adjacent ones of the N positions is merely one basic symbol or chip of the communication system. The reference signal generator 10 forms the PN code sequences PNI and PNQ and the reference frequency signal cos2? F0t and supplies them to the correlator 12, where t represents the time according to the timing pulse supplied from the timing control unit 18.

Referring to FIG. 2, correlator 12 includes multipliers 22, 24, 26, 28, 30, 32, quadrature phase shifters 34, low pass filters (LPFs) 36, 38, Inverter 40, accumulation combiners 42, 44, square units 46, 48, and combiner 50. The reference frequency signal cos2 f0t is multiplied by the signal from the input 20 in the multiplier 22 and phase shifted by the phase shifter 34, and the result is the signal from the input 20 in the multiplier 24. Multiplied, the outputs of these multipliers are lowpass filtered by LPFs 36 and 38, respectively, to produce I and Q demodulated channel signals. These signals are supplied to the first input of the multipliers 26 and 38 and the first input of the multipliers 28 and 32, respectively, and the PN code sequence PNI is supplied to the second input of the multiplier 26, and each multiplier (8 The PN code sequence PNQ is supplied to the second input of 30, and the PN code sequence PNQ is supplied to the second input of the multiplier 32 after being converted by the inverter 40.

In each case, the outputs of the multipliers 26 and 28 are combined and accumulated by the accumulator combiner 42 to provide correlation values YI and YQ over the signal coherence interval TCOH, which will be described later. , 28 are combined and accumulated by the accumulation combiner 44. These correlation values are squared by square units 46 and 48, respectively, and the squared values are added by combiner 50 to correlate estimate Y (Y = Y) for signal coherence interval (TCOH). YI2 + YQ2).

Correlation estimates Y for m consecutive coherence intervals are accumulated in a (non-coherent) accumulator 14 (FIG. 1), signaling the decision result as to whether a desired signal has been detected. The accumulated value Z, which is supplied to the determining unit 16 (eg, compared to the limit value), is made to provide at the output of the searcher. If the desired signal has not been detected, via the timing control unit 18, the parameter of the reference signal generator 10 is changed to the next position, and the above described search process is repeated. This process continues in sequence for each of the N positions to produce successive values Z1 to ZN, which are then repeated cyclically until the desired signal is detected.

Figure 3 illustrates the amplitude of the desired signal in a fading environment as a curve 52 as a function of time, expressed as a small continuous signal coherence interval (TCOH) with respect to the fading ratio. On the same time scale, Figure 4 shows values Z1 and Z2 at N consecutive accumulation periods, each of which corresponds to m consecutive signal coherence intervals TCOH during the period NTA of the total scan cycle. Explain the time interval for determining ZN. 4 illustrates this for the case of m = 6.

A disadvantage of the known signal finders and methods described above is that Z for each of the N positions is determined over m consecutive signal coherence intervals. In a fading environment such as a CDMA cellular communication system, signal fading severely adversely affects the determination within these consecutive intervals, so that a significant random change in the determined value Z is possible, resulting in increased probability of missing and false signal detection. Let's do it. To reduce this, it is necessary to increase the value m, which in turn increases the signal search time and the scan cycle duration. This increases the system access time and decreases the system capacity by increasing the intrasystem interference in the CDMA cellular communication system.

In Fig. 5 a signal searcher according to a first embodiment of the present invention is described, which can be operated as described above with reference signal generator 10 and correlator 12, combiner 62 and serial buffer 64. Recycle accumulator 60, a determination unit 66, and a timing control unit 68. In contrast to the timing control unit 18 of FIG. 1, which provides an output pulse to change the parameters of the reference signal generator 10 once every m intervals TCOH, the timing control unit 68 is a signal coherer every time. At every run interval, an output pulse is provided at each interval (TCOH) to change the parameters of the reference signal generator thereafter, so that a scan cycle through all N positions or states is completed at every N intervals (TCOH). The output pulse of the timing control unit 68 is also supplied to the clock input C of the serial buffer 64.

The correlation estimate Y given to the output of the correlator 12 at each signal coherence interval TCOH is supplied to one input, and the output ZOUT of the serial buffer 64 is supplied to the second input of the combiner 62, Are summed to provide the resulting ZIN that is supplied at the output to the input of the serial buffer 64. 6 illustrates a serial buffer 64, which is clocked together by pulses that are each connected in series in a shift register manner to store correlation sums and are supplied to clock input C with a periodicity of interval TCOH. N buffer stages 701 to 70N are included. The output of the final buffer stage 70N constitutes the output ZOUT of the serial buffer 64.

FIG. 7, which may be compared to FIG. 4 described above, illustrates the resulting operation of the signal retriever of FIG. 5. In each of the m scan cycles, each having a period NTCOH, including N signal coherence intervals, the reference signal generator 10 changes through all N positions, and the contents of the stage 70 of the serial buffer 64 are buffered. Cyclically shifted through to be supplemented by having a current correlation estimate Y for each reference signal generator position summed by combiner 62 in each case. The contents of the buffer stage 70 of the serial buffer 64 may initially be set to zero, after which m scan cycles are accumulated for m signal coherence intervals. However, as shown in FIG. 7, this accumulation to determine the corresponding value Zi (i = 1 to N) occurs over non-adjacent signal coherence intervals, so the signal fading effect as shown in FIG. 3. Is significantly reduced by averaging. The accumulated these correlation values Zi are conveniently supplied sequentially from the serial buffer 64 to the output ZOUT, the maximum or maximum of these values being determined in the determination unit 66 to determine the presence and offset of one or more desired input signals (code Phase) to compare the threshold.

Instead of being supplied in series from the buffer 64 to the determination unit 66, it is contemplated that the value Zi can be supplied in parallel (for an appropriate N value), or in a combination of series and parallel. Furthermore, instead of running the search cycles in a discrete group of m scan cycles each having N signal coherence intervals, the value Zi is repeated in an ongoing manner in each scan cycle of the N signal coherence intervals. It is believed that it can be updated. In this case, the signal ZOUT fed back to the combiner 62 can be reduced by weighting in a known manner. In any case, the averaging of the accumulation correlation value Zi provided by the searcher of FIG. 5 is believed to reduce the inconveniences due to the signal fading discussed above.

8 illustrates a signal searcher according to a second embodiment of the present invention, which is a reference signal generator 10, a correlator 12, a combiner 62, and a timing control unit that can be operated as described above. 68, and a counter 72, a buffer memory 74, a data update unit 76, and a determination unit 78. As described above, the timing control unit 68 provides an output pulse for each interval TCOH to change the parameters of the reference signal generator thereafter every signal coherence interval, thus providing a change in all N positions. Over scan cycles are completed every N intervals (TCOH). The output pulse of the timing control unit 68 also receives a position count i representing the current position in one scan cycle via the clock input C of the data update unit 76 and the output connected to the data update unit 76. Supplied to the input of a counter 72, which is a modulo-N counter that counts these pulses to provide.

Buffer memory 74 is shown in more detail in FIG. In contrast to the serial buffer 64 with N stages described above, the buffer memory 74 typically includes even fewer L stages 801 to 80N, each of which has L correlation values Z1. Has two memory fields for one of to ZL and the associated position counts i1 to iL. Each memory field of the stage 80 is connected in series with each other between the inputs ZIN and iIN of the respective signals and the outputs ZOUT and iOUT of the respective signals, but individually by the clock signals C1 to CL supplied from the data update unit 76. It is clocked and supplies each of the signals Z1 to ZL to the data update unit 76. The data update unit 76 is also supplied with the signals ZOUT and iOUT from the buffer memory 74 to provide a line 82 with a signal which becomes zero or a correlation value ZOUT as will be described later. The signal on line 82 is supplied to the second input of combiner 62, and the first input of the combiner is supplied with a current correlation estimate Y as described later, and its output is a signal to buffer memory 74. Configure ZIN. The signal iIN for the buffer memory 74 consists of the current position count i from the counter 72. The current correlation estimate Y is also supplied to the data update unit 76.

As will be described later, L can be one fifth or one tenth of the position number N, so that the capacity of the buffer memory 74 can be much smaller than the serial buffer 64. This is especially important for large N values.

The operation of the signal finder of FIG. 8 refers to the flowchart of FIG. 10 including steps 81 to 87, and the data update diagrams of FIGS. 11 and 12, wherein the top and bottom portions respectively represent the contents of the buffer memory stage before and after the data update. As will be described later.

In step 81, the data update unit 76 determines the minimum (non-zero) Zn of the correlation values currently stored in the buffer memory 74, and determines its position. If there is more than one of the same minimums, any of those minimums and positions are used. It is contemplated that this determination can only be performed during the interval TCOH at which the current correlation estimate Y is being provided since it contains only stored data.

In a subsequent step 82, the unit 76 determines from the output of the buffer memory 74 whether the current position count i is equal to the position iOUT (= iL). If not, such as during the first scan cycle through the N position, in step 83, unit 76 determines whether the current correlation estimate Y is less than or equal to the decision minimum value Zn stored in buffer memory 74. . In that case, the data for the current position count i is not updated and exits from the flowchart of FIG. 10.

If it is determined in step 83 that Y> Zn, steps 84 and 85 are performed to update data in the buffer memory 74 in the manner shown in FIG. In FIG. 11 it is assumed, for example, that n = 4, ie Z4, is the minimum determined in step 81. In this case, unit 76 provides a zero signal at line 82, so as shown by step 84, combiner 62 outputs the current correlation estimate Y with correlation value ZIN. As indicated by 85, this value and its position count iIN = i are stored in the first stage 801 of the buffer memory, and the contents of the buffer memory stages 801 to 80n-1 are clock pulses C1 to Cn. Are shifted to stages 802 to 80n respectively. The previous contents of the buffer memory stage 80n = 804 are overwritten, and the contents of the buffer memory stage 80n + 1 to 80L do not change since no clock pulses Cn + 1 to CL are given. In this way, in the first scanning cycle of the N signal coherence interval TCOH, the L largest correlation estimates Y and their positions i are stored in the L stage of the buffer memory 74.

If it is determined in step 82 that the current position count i from the output of the buffer memory 74 is equal to the position iOUT (= iL), then the step is performed to update the data in the buffer memory 74 in the manner shown in FIG. 86, 87). In this case, unit 76 provides a correlation value ZOUT at line 82, so that combiner 62 has a correlation value ZIN and a correlation value Y as the correlation value ZIN, as indicated by step 86. Output the sum of ZOUT. As indicated by step 87, all stages of the buffer memory are then updated as they are shifted by providing clock pulses Cl to CL. In this case, the arrangement acts substantially as a recycling accumulator for the correlation values Z1 to ZL and their positions i1 to iL stored in the buffer memory 74.

After a few m desired scan cycles in which the parameters of the reference signal generator 10 are subsequently changed at every interval TCOH to provide the same advantages for fading as described above in the first embodiment. The memory 74 includes a maximum correlation value substantially accumulated for L locations among a total of N locations, and the location i of these locations. These accumulated correlation values Z1 to ZL and their positions i1 to iL are then determined in series from the buffer memory 74 as shown in FIG. 8, or in parallel or in series-parallel in a manner similar to that discussed above. 78 is supplied. Determination unit 78 determines the maximum or maximum of these values, for example by comparing it with a threshold to detect the presence and offset (code phase) of one or more desired input signals, and position the resulting correlation value (if desired). Information i is fed to its output.

As indicated above, the fact that the continuous correlation estimates accumulated and stored for each position are divided in each case into N signal coherence intervals (TCOH) reduces the fading effect in the operation of the signal retriever of FIG. 8. Let's do it. However, since the first scan cycle is used to determine where the correlation estimates accumulate, the probability of lost detection is increased, which depends on the ratio between the position number N and the buffer memory capacity L. Figure 13 illustrates the computer simulation results for this, which shows the loss detection probability as a function of m for a Rayleigh fading channel where N = 675. Top curve 88 represents the performance of the known signal retriever of FIG. 1, and three bottom curves 90 represent substantially improved performance for the signal retriever of FIG. 8 at different ratios from L to N. FIG. As can be appreciated from these curves, the signal retriever of FIG. 8 provides a substantial improvement in the lost signal detection probability, which does not significantly degrade at L values above about N / 10, thus significantly reducing the buffer memory capacity. Can be.

FIG. 14 illustrates a signal searcher according to a third embodiment of the present invention, in which the position counter 72 is a modulo-J counter, where J is an integer as will be described later, and the positioning of the determination unit 78. It includes a reference signal generator 10, a correlator 12, a timing control unit 68, a position counter 72, and a determination unit as described above, except that it is modified as will be described later. . As described above, the timing control unit 68 provides an output pulse during each interval TCOH to change the parameter of the reference signal generator 10 thereafter every signal coherence interval. The position counter 72 counts these pulses on the clock pulse line C, and provides an output pulse on the clock pulse line C1 after every J pulses. Alternatively, the pulse on this line C1 can be provided directly from the timing control unit 68.

The signal retriever of FIG. 14 also includes a maximum retriever 92 and a recycle accumulator 94 that includes a comparison and combination unit 94 and a serial buffer 96. As shown in Fig. 15, the serial buffer 98 is composed of L stages each having two memory fields for one of the L correlation values Z1 to ZL and their associated position counts j1 to jL. 1001 to 100L). Each memory field of the stage 100 is connected in series between each other between an input for each signal ZIN and jIN and an output for each signal ZOUT and jOUT, and is clocked in common by a clock signal on the clock pulse line C1. do.

The signal searcher of FIG. 14 is particularly advantageous when N is very large, for example when N = 32768, and for searching if, for example, multiple signals need to be detected, for example to detect pilot signals of several base stations. Is advantageous to. In the latter case, the PN code phase of another pilot signal is separated into J out of N positions. For example, for a PN code chip in the forward pilot channel of an IS-95 cellular communication system, J = 64. The integers J, L, and N are related to the formula J = N / L, and the value of N is increased to ensure that J and L are integers if necessary.

In the signal detector of FIG. 14, the maximum detector 92 has a correlation estimate Y from the correlator 12 during each signal coherence interval TCOH, and a clock pulse C from the timing control unit 68. The position count j is supplied from the counter 72, and the maximum value YMAX of the correlation estimate Y is determined in each subset of the N positions retrieved, and at its output, the maximum correlation estimate YMAX and It provides the value jMAX of the position count j for the maximum value.

To this end, as shown in FIG. 16, the maximum detector detects a comparator 102, a memory cell 104 for storing a correlation estimate Y, and a memory cell 106 for storing an associated position count j. Include. Memory cell 106 is required to store only numbers up to J, and requires relatively few bits compared to the number of bits required to store location counts up to N (e.g., compared to 15 bits for N = 32768). 6 bits for J = 64). This is applied to the fields j1 to jL in the L stage 100 of the serial buffer 98, thereby significantly reducing the memory capacity required to store the position count.

Comparator 102 has an input coupled to the output and input of memory cell 104 and compares each input correlation estimate Y with the current contents YMAX of memory cell 104. For Y> YMAX, comparator 102 supplies an output to enable input E of memory cells 104 and 106, with a larger correlation estimate Y stored in memory cell 104 and its position count j Writes the input W to which the clock pulse C is supplied so that is stored in the memory cell 106. After J signal coherence intervals (TCOH) defining each position subset, the stored maximum value YMAX and its position jMAX, if necessary, via unit 96 of recycle accumulator 94 through a clocked buffer, not shown. Supplied to.

The signals ZOUT and jOUT from the output of the serial buffer 98 and the signals YMAX and jMAX from the maximum detector 92 are supplied to the unit 96 in the form shown in FIG. As shown in FIG. 17, unit 96 has a selector having an output for signals ZIN and jIN at the inputs of comparators 108, 110, switch 112, combiner 114, and serial buffer 98. 116). 18 shows a flowchart of the operation of unit 96 including steps 121-125.

The comparator 108 is supplied with position counts jMAX and jOUT, and if they are the same as determined in step 121, the correlation estimate is at one input of the combiner 114, which is another input supplied with the correlation value ZOUT. The switch 112 is closed to supply YMAX. Combiner 114 sums its inputs and provides an output Z1. The selector 116 supplies Z1 or YMAX with signal ZIN and jOUT or jMAX with signal jIN under the control of comparator 110 comparing YMAX and ZIN. The selector 116 has the switch position shown in FIG. 17 except when the comparator 116 determines that YMAX > Z1. Thus, in this case, as shown by block 122 in FIG. 18, the selector 116 may select the switch position shown to provide outputs ZIN = Z1 = ZOUT + YMAX and jIN = jOUT (also equal to jMAX). Have As a result, when the maximum correlation estimate YMAX is generated with the same position count jMAX in the same position subset in repeated scan cycles, these correlation estimates are accumulated in a manner similar to that described above.

If it is determined at step 121 that jMAX is not equal to jOUT, switch 112 remains open and combiner 114 provides signal Z1 = ZOUT. In this case, the comparator 110 determines whether or not YMAX > Z1 in step 123, and in that case, a switch position that delivers signals YMAX and jMAX to its outputs ZIN and jIN, respectively, as indicated by step 124. The selector 116 is controlled to alternately adopt. Otherwise, comparator 112 controls selector 116 to adopt a switch position that delivers signals Z1 = ZOUT and jOUT to outputs ZIN and jIN, respectively, as indicated by step 125 in FIG.

After m scan cycles, each of which is an N signal coherence interval (TCOH) as described above, the contents of the serial buffer 98 are supplied in series to the determining unit 78 and one or more signals to be detected. One or more maximum values ZI, where I is an integer between 1 and L representing the corresponding buffer stage 100, is determined and compared with the threshold value to determine the presence of. The code phase or position of each of these signals is J (I-1) + jI, where jI is the position count or value jOUT associated with the determined maximum.

As described above, each correlation result stored in the serial buffer 98 is incremented only when the angular position count jMAX is equal to the stored position count jOUT, but this need not be the case. Instead, the maximum correlation result YMAX and its position jMAX may be determined by the maximum determiner 96 as described above in the first signal scan cycle, and in subsequent ones of the m signal scan cycles, the group within each scan cycle. The correlation result Y for each position count jMAX in each group can be accumulated regardless of whether or not it is a maximum correlation result for. However, since the determination of the maximum position in each subset is based solely on the first scan cycle and no accumulation is used, it is expected that a significant degradation in detection probability will occur.

Although embodiments of the present invention have been described above with respect to particular physical devices such as counters and comparators, they may be substituted and embodiments of the present invention may be more easily implemented by one or more digital signal processors or special purpose integrated circuits. It is thought to be.

In addition, it is contemplated that various other changes, modifications, and modifications may be made to certain embodiments of the invention described through the examples above without departing from the scope of the claims.

According to the present invention, when searching for a signal in a communication system such as a CDMA system, it is possible to considerably reduce the probability of detecting a lost signal and a wrong signal, and due to the relative immunity to a fading environment, many base stations in a CDMA cellular communication system Can facilitate the detection of multiple desired signals, such as pilot signals.

Claims (21)

The received signal is correlated with the reference signal and at least one parameter of the reference signal is changed to produce respective correlation results for different offsets of the N possible offsets between the received signal and the reference signal. In the signal search method, In one scan cycle, each of the N possible offsets from the correlations between the received signal and the reference signal having a separate offset during each correlation interval where the phase of the received signal does not change significantly. Generating an individual correlation result for each; And Accumulating the correlation results for the plurality of correlations with corresponding offsets in successive scan cycles so that the presence and offset of a desired signal can be determined from the accumulated correlation results. Including, The at least one parameter is varied between successive ones of the correlations Signal search method, characterized in that. The method of claim 1, Wherein said correlation results are accumulated for all N possible offsets between said received signal and said reference signal. The method of claim 1, Determining the largest correlation results for L of the N possible offsets, where L is an integer less than N, in one scan cycle, wherein the correlation results accumulate only for the L offsets. Signal search method. The method of claim 3, Storing an identity of each of the L offsets in association with each accumulated correlation result. The method of claim 3, N / L is about 5 to about 10, characterized in that the signal retrieval method. The method of claim 1, Determining the largest correlation result for each group of L each having J of the N possible offsets, wherein L = N / J, in one scan cycle, the correlation results being the L And accumulating only for the largest correlation result for each of the dog groups. The method of claim 6, Storing an identification of each of the largest correlation results in association with each accumulated correlation result. The method of claim 1, Determining at least a maximum correlation result of the accumulated correlation results to determine the presence and offset of a desired signal. A method for detecting the presence of a desired signal and a PN code phase in a received signal of a CDMA communication system, Generating a reference signal with different phases of N possible PN code phases in successive correlation intervals of N correlation intervals in one scan cycle; Correlating the reference signal and the received signal during the correlation intervals to produce respective correlation results; Accumulating at least some of the correlation results over successive scan cycles; And Determining the presence and offset of a desired signal from the accumulated correlation results Detection method comprising a. The method of claim 9, Wherein said correlation results accumulate for all N correlation intervals in each scan cycle. The method of claim 9, The correlation results are accumulated only for correlation intervals of L having the largest correlations in one scan cycle, where L is an integer less than N, and associated with each accumulated correlation result and having the largest correlation And determining an identification of each of the L correlation intervals. The method of claim 9, The correlation intervals comprise L groups each having J correlation intervals in each scan cycle-L and J are integers and L = N / J-and the correlation results are the largest correlation in one scan cycle. Accumulate only for one of the correlation intervals in each group of J correlation intervals providing a relationship, and are associated with each accumulated correlation result to determine the largest correlations and having J correlation intervals. And storing an identification of each correlation interval that provides the largest correlation of each group. A signal finder for a code division multiple access (CDMA) communication system, Control unit; A reference signal generator controlled by the control unit to generate a reference signal in a different phase of the N code phases in each of the N consecutive correlation intervals within one scan cycle; A correlator for correlating the reference signal and the received signal at the successive correlation intervals to produce respective correlation results; And Accumulate the correlation results from the correlator for each of a plurality of corresponding correlation intervals in multiple scan cycles to produce accumulated individual correlation results in which the presence and code phase of the desired signal in the received signal can be determined. An accumulator responsive to the control unit Including, Each correlation interval is short enough so that the phase of the received signal does not change significantly during the correlation interval. Signal finder, characterized in that. The method of claim 13, And said accumulator comprises a buffer for storing accumulated correlation results for each of said N code phases. The method of claim 13, A unit for determining the largest correlation results for L of the N code phases, where L is an integer less than N, in one scan cycle, and the accumulator accumulated accumulated for each of the L code phases. And a buffer for storing a result and an associated count that identifies each code phase. The method of claim 15, N / L is about 5 to about 10 signal detector. The method of claim 13, The correlation intervals comprise L groups each having J correlation intervals in each scan cycle—L and J are integers and L = N / J—and the signal retriever has J correlations in one scan cycle. A detector that determines the largest correlation result for each group of intervals and provides a count that identifies a corresponding correlation interval in each group, and at least one of the correlation results for the same code phase identified by the count. And a combiner for incrementing the stored correlation result for each of the L groups in a subsequent scan cycle, wherein the accumulator includes a buffer for storing the correlation result and a count associated therewith for each of the L groups. Signal finder, characterized in that. The method of claim 17, The combiner is stored in each subsequent scan cycle only if the detector determines that the correlation result for the same code phase identified by the count is the largest correlation result for each group of J correlation intervals. And a signal retriever arranged to increase the correlation result. The method of claim 17, A signal retriever characterized in that N = 32768 and J = 64. The method of claim 13, And a determining unit for determining a maximum of one or more of the accumulated correlation results to determine the presence and the code phase of one or more desired signals in the received signal. In the signal finder for a CDMA communication system, Means for generating at least one reference signal, means for correlating the received signal with the reference signal at the correlation intervals short enough so that the phase of the received signal does not significantly change during the correlation interval, the plurality of correlation intervals Means for accumulating correlation results for the same code phase for < RTI ID = 0.0 > and < / RTI > means for determining the code phase and the presence of one or more desired signals in the received signal depending on the accumulated correlation results. Including, Control means for varying the code phase of the reference signal through all N possible code phases in N consecutive correlation intervals constituting one signal scanning cycle, wherein the correlation results are applied to a plurality of signal scanning cycles. Stored to accumulate over Signal finder, characterized in that.