CN114698089A - Terminal synchronous search detection method applied to next-generation Internet of things communication system - Google Patents
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Abstract
The invention discloses a terminal synchronous search detection method applied to a next generation Internet of things communication system, which comprises the steps of carrying out differential-based incoherent detection on NR-PSS, storing a differential accumulated multiplication factor sequence corresponding to a maximum value with the amplitude exceeding a threshold value, compensating an NR-SSS frequency domain received signal by using the stored differential accumulated multiplication factor sequence, and carrying out coherent detection on the NR-SSS. The invention completes the joint estimation of the cell ID group number and the integer frequency offset based on the PSS signal, and compensates the channel coefficient difference of the SSS by using the differential correlation result estimated by the PSS, thereby realizing the low-complexity high-performance coherent detection of the SSS, and saving half of the storage space of the NR-SSS by resource multiplexing when the circuit is realized.
Description
Technical Field
The invention relates to a terminal synchronous search detection method of a communication system, in particular to a terminal synchronous search detection method applied to a next generation Internet of things communication system.
Background
The next generation internet of things wireless communication system is a 5 GNR-based technical protocol. In contrast to LTE, the repetition period of NR varies from 5ms to 20 ms. This is because, in order to introduce the function of multi-beam transmission, that is, the terminal needs to search not only for a frequency domain carrier wave, but also for different spatial beams under the condition of initial access, so as to implement an optimal access for a certain beam direction, that is, implement an initial beam establishment function. Therefore, in this case, NR has a maximum of 64 sync resource blocks to repeat, each repetition resource block weighted for a different beam, compared to LTE with only one sync resource block per 5 ms. Since the overhead of the NR resource is significantly increased, the interval of two adjacent access synchronization blocks (SSBs) is increased to 20 ms. This requires that the terminal can complete the whole cell search and time-frequency synchronization process in one access block as much as possible.
In addition to the time domain case, the SSB distribution in the 5GNR frequency domain needs to be considered. Compared to LTE, the SSB of 5GNR includes resource blocks of primary and secondary synchronization signals and a Physical Broadcast Channel (PBCH) distributed over a larger bandwidth. The entire SSB is distributed in a region consisting of four consecutive OFDM symbols in the time domain, i.e., 240 subcarriers (Tones). The first symbol is the primary synchronization signal PSS, which occupies 12 RBs in the middle range of 20 RBs, i.e. 144 subcarriers Tones, wherein 127 subcarriers Tones in the middle part are effective signal parts, and 8/9 subcarriers Tones are left on the left and right sides respectively as guard intervals. The frequency domain position occupied by the secondary synchronization signal SSS is consistent with that of the PSS. The PBCH signal continues from the second symbol to the last symbol, which also contains DMRS pilots for PBCH demodulation.
To provide sufficient deployment flexibility for NRs, the number of physical layer cell identities (PCIDs) of NRs is extended to 1008 (504 in LTE). Each NR cell ID may be collectively represented by PSS/SSS.
Wherein,
the PSS includes a Binary Phase Shift Keying (BPSK) length-127 m-sequence based on the three frequency domains and the SSS corresponds to the length-127 m-sequence selected from 336. Both PSS and SSS signals are mapped to 127 contiguous subcarriers. The method has good cross-correlation sequence properties, and the performance of NR SS detection probability and missed detection probability is better than that of LTE. For each SS/PBCH block, the PSS, SSs and PBCH share the same single antenna port. It should be noted that the physical beams applied to the SS/PBCH block are transparent to the User Equipment (UE), since the UE sees only the equivalent terms potential precoding and/or subsequent SS and PBCH signals depending on the beamforming operation implementation of the network.
The signal sequence of NR-PSS is generated by the following formula,
pu(n′)＝1-2c([n′+43u]modM)，0≤n′≤M
where u ∈ {0, 1, 2}, M is the length of the NR-PSS sequence. The c sequence is a basic m sequence. Mapping NR-PSS to the frequency domain takes the following equation:
for the secondary synchronization signal NR-SSS, the generated sequence comprises 336M-point sequences with different combinations. It is defined as:
sg(n′)＝[1-2c0([n′+n0]modM)]×[1-2c1([n′+n1]modM)]，0≤n′≤M
wherein,
and n is1(gmod112) g ∈ {0, 1, 2, …, 335 }. Note that compared with NR-PSS, NR-SSS is obtained by multiplying two groups of m sequences with good orthogonality, namely c in the formula0And c1. NR-SSS is mapped to the frequency domain s in the following mannerg，(k)
Since the downlink cell search and time-frequency synchronization process is the first step of the whole terminal baseband processing, the terminal does not have any system time-frequency information and system information before the synchronization is completed. The conventional processing is shown in fig. 1:
firstly, the terminal carries out time domain difference correlation according to the symbol period structure of the Cyclic Prefix (CP) to obtain symbol timing, and meanwhile, preliminary fractional frequency offset estimation can be obtained. When this step is completed, the terminal may perform initial frequency offset correction and Fast Fourier Transform (FFT) based on the symbol timing and the frequency offset estimation result, thereby processing the above operation in the frequency domain.
It can be seen that for the transmitted signal of the SSB block described above, after the symbol timing of the CP is performed, the initial signal received by the terminal can be modeled as follows:
where υ denotes the normalized integer frequency offset (relative to the carrier spacing),. epsilon denotes the normalized fractional frequency offset, hqIs the response of the channel impulse and,
representing a linear convolution operation, Zq(n) additive Gaussian noise with zero mean and power of
NsThe number of sampling points corresponding to the length of a complete OFDM symbol is represented, the CP is removed from the time domain received signal and the frequency domain is changed,
wherein
Representing the complete frequency offset residual term. I isq(k) Representing an intercarrier interference term, Zq(k) Representing the noise term.
For the above received signals, the PSS and SSS perform detection in a manner where PSS is used to traverse through the three cell ID group numbers to obtain the group number
And integer frequency offset estimation, while the SSS needs to perform 336 sets of traversal searches to obtain the complete cell ID,
in the conventional PSS detection, under the condition of no integral frequency offset prior information and no prior information of a channel, a differential correlation method based on incoherent detection is generally adopted to eliminate the influence of the channel. As shown in the following formula,
wherein,
a term that is brought about by the inter-carrier interference,
a term brought to white noise. Based on the above formula, therefore, it can be obtained that the conventional PSS detection is obtained by first performing the autocorrelation with 1 point interval for the received signal
Then the correlation result Du (k) of the local sequence with a certain interval is subjected to cross-correlation operation to obtain the following expression,
wherein m searches the value range of all integer frequency offsets (upsilon) as [ -G G ], w belongs to the value range of {0, 1, 2} search group number (u), the final optimal estimation result is just,
after the PSS detection is completed and the estimated values of u and υ are obtained, the terminal needs to perform detection aiming at NR-SSS so as to complete the detection of the cell ID. Generally, since there is no channel prior information (channel estimation result) for NR-SSS, a non-coherent detection method based on differential correlation is often adopted.
Wherein, the value range of c is [ 0335 ]. Therefore, the estimated value of the number g in the cell group is shown by the following formula,
that is, as can be obtained from the above equation, based on the estimation process of the number g in the cell group, the terminal conventionally performs differential correlation at intervals on the SSS signal sequence located under the l +2 symbol, and traverses the complete 336 groups of local sequences, performs differential correlation at intervals on each group of local sequences, performs cross correlation on two differential correlation results, and selects the local sequence number with the largest correlation result amplitude value as the estimation result of the number g in the cell group.
Based on the conventional PSS and SSS initial synchronization estimation process, since both steps perform differential-based non-coherent detection, the detection performance is lower than that of coherent detection, especially at low snr, and the noise introduced by noise and interference terms is significantly increased compared to coherent detection, thus deteriorating the detection result of initial access. If a coherent detection algorithm is introduced, additional circuits or algorithms are required to introduce a channel estimation process, and the process greatly increases the complexity of a baseband algorithm.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a terminal synchronous search detection method applied to a next generation Internet of things communication system, which reduces algorithm complexity by adopting a mode of combining non-coherent detection and coherent detection based on NR-PSS and NR-SSS cooperative detection, and realizes coherent demodulation of NR-SSS signals without increasing any circuit overhead.
The technical scheme of the invention is as follows: a terminal synchronous search detection method applied to a next generation Internet of things communication system comprises the steps of carrying out differential-based incoherent detection on NR-PSS, storing a differential accumulative multiplication factor sequence corresponding to the maximum value with the amplitude exceeding a threshold value, compensating NR-SSS frequency domain received signals by using the stored differential accumulative multiplication factor sequence, and carrying out coherent detection on NR-SSS.
Further, the performing differential-based non-coherent detection on the NR-PSS comprises: based on the cyclic prefix symbol timing, obtaining NR-PSS symbol data according to the symbol; sequentially traversing the initial positions of the NR-PSS frequency domain symbols; traversing 3 local NR-PSS sequences aiming at each integer frequency offset, and carrying out corresponding negation accumulation operation on a difference sequence of the NR-PSS frequency domain signal according to a local NR-PSS sequence negation value; comparing the group number of the local PSS sequence corresponding to the maximum amplitude obtained by the negation accumulation operation with the integer frequency offset position, and judging whether the maximum amplitude exceeds a threshold value; if the peak value exceeds the threshold value, outputting a fraction time offset corresponding to the peak value phase corresponding to the maximum amplitude; and performing normalization output on the difference sequence, performing an inversion operation according to the value of the local NR-PSS sequence corresponding to the maximum amplitude, and then multiplying the operation result by a difference accumulation multiplication factor sequence Δ (k) delayed by one sample, where the difference accumulation multiplication factor sequence Δ (k) is an output result of the output sequence output by the difference sequence normalization operation of the NR-PSS frequency domain signal after an accumulation multiplication, where the accumulation multiplication is Y (k) ═ Y (k-1) × x (k), Y (0) ═ 1, Y (k) is an accumulation multiplication result, Y (k-1) is a previous accumulation multiplication result, x (k) is an input of the accumulation multiplication, and finally storing the difference accumulation multiplication factor sequence Δ (k).
Further, the difference sequence of the NR-PSS frequency domain signal is obtained by multiplying the sequence of the NR-PSS frequency domain signal and the replica sequence of the NR-PSS frequency domain signal delayed by one sample by a first multiplier, and the multiplication of the operation result and the difference cumulative multiplication factor sequence Δ (k) delayed by one sample is performed by the first multiplier.
Further, the coherently detecting the NR-SSS comprises: carrying out differential-based incoherent detection on NR-PSS to obtain an integer frequency offset to obtain a data initial position of an NR-SSS frequency domain signal; multiplying data symbols of the NR-SSS frequency-domain signal by the frequency-domain differential sequence bit-pairs; and performing cross-correlation operation on the alignment multiplication result and a local signal sequence after passing through a shift register, and obtaining a corresponding detection result by the maximum amplitude value of the result of the cross-correlation operation.
Further, the cross-correlation operation of the bit-aligned multiplication result and the local signal sequence after passing through the shift register includes: step one, traversing 112 groups of local sequences after the para-position multiplication result passes through a shift register, and executing negation operation according to the values of the 112 groups of local sequences; and step two, traversing 3 groups of local sequences, and performing negation and accumulation operation on the sequence subjected to the negation operation according to the values of the 3 groups of local sequences, wherein the maximum amplitude value of the accumulation operation is the maximum amplitude value of the result of the cross-correlation operation.
The invention provides a collaborative estimation method based on NR-PSS and NR-SSS signals, which is used for completing the joint estimation of cell ID group numbers and integer frequency offsets based on the NR-PSS signals and compensating the channel coefficient difference of the NR-SSS by using the differential correlation result estimated by the NR-PSS, thereby realizing the low-complexity high-performance coherent detection of the NR-SSS. In the circuit structure, because the detection process time of the NR-PSS and the NR-SSS has an interval of one OFDM symbol and the related processing mode can be multiplexed, the two circuits can be multiplexed to the maximum extent, thereby effectively reducing the area of a system; on the other hand, the NR-SSS is realized by multiplying two m sequences with better cross-correlation performance, and the invention adopts two-stage local cross-correlation processing, thereby realizing the effect of saving half of the storage space of the NR-SSS.
Drawings
Fig. 1 is a flow chart of a prior art synchronization signal detection process.
FIG. 2 is a schematic diagram of the NR-PSS detection process.
FIG. 3 is a schematic diagram of a circuit configuration for implementing the NR-PSS detection process.
Fig. 4 is a flow chart of the NR-SSS detection process.
Fig. 5 is a schematic circuit structure diagram for implementing the NR-SSS detection process.
Detailed Description
The present invention is further described in the following examples, which are intended to be illustrative only and not to be limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which would occur to persons skilled in the art upon reading the present specification and which are intended to be within the scope of the present invention as defined in the appended claims.
The terminal synchronous search detection method applied to the next generation Internet of things communication system in the embodiment of the invention designs a differential correlation structure based on NR-PSS, obtains a differential accumulated multiplication factor sequence, and realizes the coherent demodulation of NR-SSS signals under the condition of not increasing any circuit overhead by combining a scheme of compensating NR-SSS frequency domain signals. The principle is shown in the following formula, and considering that for an NR-PSS signal, the sequence cross-correlation of the difference of one point apart of the frequency domain received signal with the difference of one point apart of the local sequence can be expressed as follows (assuming that the integer frequency offset is v),
wherein,
when NR-PSS finds the maximum peak, i.e. the correct transmission sequence
And the correct integer frequency offset, can be obtained (the description is convenient, and the integer frequency offset is assumed to be 0)
And then passing the differential product sequence Λ through an accumulative multiplier, wherein the principle of the multiplier can be obtained by the following expression:
Y(k)＝Y(k-1)×X(k)，Y(0)＝1
after the Λ sequence passes through the accumulation multiplier and the coefficient normalization operation is performed, the following sequence of differential accumulation multiplication factors Δ (k) can be obtained, as shown in the following formula.
After 126 sequences of differential accumulated multiplication factors delta (k) are obtained in the NR-PSS, the factors are cached in a memory, and the sequences can be used for compensating the received signals during the processing of the NR-SSS.
Considering the received frequency domain NR-SSS signal sequence as shown below,
Yl+2(k)＝Hl+2(k)Xc(k)+I(k)+Z(k)
compensating the received signal by applying a sequence of differential cumulative multiplication factors delta (k) to obtain (without compensation for the first value of the NR-SSS received signal sequence)
Yl+2(k)≈Hl+2(k)×Xc(k)
……
The above derivation takes into account Hl+2(k) And Hl(k) The channels are substantially identical. It can be seen that the NR-SSS frequency domain received signal, compensated by applying a sequence of differential cumulative multiplication factors Δ (k), has its phase portion of the channel adjustedAre aligned (all are channels H corresponding to frequency domain received signals on the first NR-SSS)l+2(k) I.e., the effect of the radio channel on the NR-SSS frequency domain sequence phase has been eliminated. The local sequence X may be traversed at this pointcThe signals are cross-correlated to perform a coherent detection search of the NR-SSS.
Please refer to fig. 2 and fig. 3, the specific detection process for NR-PSS is as follows: after the symbol timing and fractional frequency offset estimation based on the CP is finished, the air interface receiving signal firstly executes fractional frequency offset compensation operation, then is converted into a frequency domain through FFT, and reads the initial position of the NR-PSS based on a control signal. Note that, considering the influence of the integer frequency offset, the start point and the end point of reading will be early and late for each M/2 carriers with respect to the subcarriers without the integer frequency offset position, so that M different carrier frequency offset results can be evaluated.
After the frequency domain NR-PSS symbol sequence is read out from the FFT module, it is sent to a multiplier, which is determined by a multiplexing unit controlled by two control signals. In the current step, the input equation of the multiplier is the signal sequence input by the FFT module and its replica sequence delayed by one sample, i.e. a differential multiplication calculation with 1 point interval is performed.
The result from the multiplier is input to a shift register of order 126+ M. Wherein, M order corresponds to the integer frequency offset number to be estimated.
After the signal sequence has passed through the 126+ M shift register delays, a correlation accumulation operation of 126 sets of data with the local differential sequence is performed. In each clock cycle, the sequence read out by 126 registers at the same time will be sequentially correlated and accumulated with the local three groups of sequences. Wherein, three groups of local differential sequences D are stored in the local memory 1u(k) A sequence of length 126 points, wherein
Wherein u is 0, 1 and 2 respectively.
Due to Du(k) The sequence takes on values of 1/-1, so the correlation accumulation operation can be equivalent to an inverse sum of the input values of each registerAccumulation operation, in which whether or not to invert by Du(k) The sequence is determined by taking the value of 1 as not negating and 1 as negating. The entire logic implementation can be implemented using LUT truth tables.
The NR-PSS processing for one OFDM symbol will perform M clock cycles (corresponding to M integer frequency offset estimates), and each clock cycle will perform 3 correlation accumulation operations (for 3 u values), so that finally 3M correlation accumulation results will be obtained. And comparing the amplitudes of the 3M results to find out the maximum amplitude, comparing the maximum amplitude with a threshold value, when an event exceeding the threshold occurs, indicating that the NR-PSS detection is successful, and finding out the number corresponding to the maximum amplitude in the 3M under the current condition, namely the estimated value of u and integer frequency offset. And simultaneously reads out phase information corresponding to the correlation peak value, thereby estimating the fractional time offset.
When the NR-PSS detection is successful, the corresponding control signal is triggered immediately. Now, normalization of the output values of the 126-step shift register is started, based on the estimated output values
The value of the sequence is inverted, and the inverted result is sent to the previous multiplier.
The multiplier is triggered by the control signal to switch to a multiplication operation of reading data from the inverter as a multiplicand, and the other end of the multiplier is connected to a delayed version of the output of the multiplier. Namely, the following operation is achieved.
Y(k)＝Y(k-1)×X(k)，Y(0)＝1
The sequences after the output of the accumulator are accumulated and buffered in the memory 2 for the NR-SSS detection.
It can be seen that by adding an accumulation multiplier to the differential structure and multiplexing the differential multipliers, a sequence of differential accumulation multiplication factors Δ (k) can be obtained without significantly increasing hardware overhead.
When the detection of the NR-PSS signal is successful, the detection processing process of the NR-SSS is started. Please refer to fig. 4 and 5, in the process, an FFT is first performed on the time domain signal after fractional frequency doubling offset compensation, and a data start position of the NR-SSS output by the FFT is obtained according to the integer frequency offset obtained by PSS estimation.
Secondly, with a structure similar to the NR-PSS, the signal output from the FFT module is bit-multiplied by the differential accumulated multiplication factor Δ (k) sequence stored in the memory 2. Thereby removing the influence of the phase due to the channel and adjusting the phase of the equivalent channel on each subcarrier to be uniform.
The output signal of the multiplier is passed through a 127-step shift register. When the signal sequence with length of 127 is completely inputted into the 127-step shift register, the operation of cross-correlation with the local signal sequence is performed. Since the local signal contains 336 sets, it is theoretically necessary to perform 336 sets of cross-correlations, while 336 sets of local sequences need to be extracted.
The two m-sequences are multiplied for the NR-SSS signal and each m-sequence is controlled by the following coefficients. Namely, it is
sg(n′)＝[1-2c0([n′+n0]modM)]×[1-2c1([n′+n1]modM)]，0≤n′≤M
The above-mentioned formula can be simplified to that,
sg(k)＝s0，g0(k)s1，g1(k)
wherein,
namely, cyclic shift values of two m sequences in the SSS sequences are respectively determined by g0 and g 1.
Because of the good cross-correlation property and circular auto-correlation property of the m-sequences, namely the good property that the cross-correlation and auto-correlation values under different offsets and delays are low, two groups of m-sequences can be separately detected (because the local m-sequence is composed of 1/-1, the correlation operation becomes the inverse accumulation operation, and the operation cost is low).
First of all for s1，g1(k) The sequence is correlation detected by traversing 112 sets of local sequences (stored in memory 3) and performing an inversion operation (without accumulation) based on the values of the local sequences.
Secondly, it is obtained for each group of local sequencesThe inverted sequence performs 3 sets of inverted accumulate operations, which correspond to s0，g0(k) And performing inversion operation (stored in the memory 4) of the sequence obtained by traversing the three values, and performing accumulation operation after the inversion is completed. The operation can be obtained by using LUT truth table lookup table.
Third, when comparing the amplitude values of all 336 groups (112 × 3) of accumulated results, the number corresponding to the largest amplitude is found, i.e. g0, g1, and based on the value, the intra-group number of the cell ID can be calculated.
Claims (5)
1. A terminal synchronous search detection method applied to a next generation Internet of things communication system is characterized by comprising the steps of carrying out differential-based incoherent detection on NR-PSS, storing a differential accumulated multiplication factor sequence corresponding to a maximum value with the amplitude exceeding a threshold value, compensating an NR-SSS frequency domain received signal by using the stored differential accumulated multiplication factor sequence, and carrying out coherent detection on the NR-SSS.
2. The method for synchronous search and detection of the terminal applied to the next generation internet of things communication system according to claim 1, wherein the differential-based incoherent detection of the NR-PSS comprises: based on the cyclic prefix symbol timing, obtaining NR-PSS symbol data according to the symbol; sequentially traversing the initial positions of the NR-PSS frequency domain symbols; traversing 3 local NR-PSS sequences aiming at each integer frequency offset, and carrying out corresponding negation accumulation operation on a difference sequence of the NR-PSS frequency domain signal according to a local NR-PSS sequence negation value; comparing the group number of the local PSS sequence corresponding to the maximum amplitude obtained by the negation accumulation operation with the integer frequency offset position, and judging whether the maximum amplitude exceeds a threshold value; if the peak value exceeds the threshold value, outputting a fraction time offset corresponding to the peak value phase corresponding to the maximum amplitude; and performing normalization output on the difference sequence, performing an inversion operation according to the value of the local NR-PSS sequence corresponding to the maximum amplitude, and then multiplying the operation result by a difference accumulation multiplication factor sequence Δ (k) delayed by one sample, where the difference accumulation multiplication factor sequence Δ (k) is an output result of the output sequence output by the difference sequence normalization operation of the NR-PSS frequency domain signal after an accumulation multiplication, where the accumulation multiplication is Y (k) ═ Y (k-1) × x (k), Y (0) ═ 1, Y (k) is an accumulation multiplication result, Y (k-1) is a previous accumulation multiplication result, x (k) is an input of the accumulation multiplication, and finally storing the difference accumulation multiplication factor sequence Δ (k).
3. The method for searching and detecting the terminal synchronization applied to the next generation internet of things communication system according to claim 2, wherein the difference sequence of the NR-PSS frequency domain signal is obtained by multiplying the sequence of the NR-PSS frequency domain signal and a replica sequence of the NR-PSS frequency domain signal delayed by one sample by a first multiplier, and the multiplying the operation result by a difference cumulative multiplication factor sequence Δ (k) delayed by one sample is performed by the first multiplier.
4. The method for synchronous search detection of a terminal applied to a next generation internet of things communication system according to claim 1, wherein the performing coherent detection on the NR-SSS comprises: carrying out differential-based incoherent detection on NR-PSS to obtain an integer frequency offset to obtain a data initial position of an NR-SSS frequency domain signal; multiplying data symbols of the NR-SSS frequency-domain signal by the frequency-domain differential sequence bit-pairs; and performing cross-correlation operation on the alignment multiplication result and a local signal sequence after passing through a shift register, and obtaining a corresponding detection result by the maximum amplitude value of the result of the cross-correlation operation.
5. The method as claimed in claim 4, wherein the cross-correlation operation of the bit-aligned multiplication result with the local signal sequence after passing through the shift register comprises: step one, traversing 112 groups of local sequences after a counterpoint multiplication result passes through a shift register, and executing negation operation according to the values of the 112 groups of local sequences; and step two, traversing 3 groups of local sequences, and performing negation and accumulation operation on the sequence subjected to the negation operation according to the values of the 3 groups of local sequences, wherein the maximum amplitude value of the accumulation operation is the maximum amplitude value of the result of the cross-correlation operation.
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| WO2024051056A1 (en) * | 2022-09-09 | 2024-03-14 | 京信网络系统股份有限公司 | Time-frequency synchronization method and apparatus, and device, storage medium and readable instruction product |
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