A signal receiving method for a hybrid cyclic prefix single carrier frequency domain equalization system

Abstract

The present invention belongs to the field of wireless communication technology, and specifically relates to a signal receiving method of a hybrid cyclic prefix single carrier frequency domain equalization system. The present invention first separates the odd and even frames of the received signal, removes the CP of the even frame and transforms it to the frequency domain, and performs frequency domain iterative equalization; then estimates the ISI received by the odd frame and the discarded tail according to the LLR of the even frame, compensates the odd frame, transforms the compensated odd frame to the frequency domain, and performs frequency domain iterative equalization; finally, the decoder outputs of the odd and even frames are connected in series according to the transmitter order, and the output results of the decoder are judged to obtain the received bits. The present invention can effectively counteract the interference of the CP-free frame and improve the system bit error rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to a signal receiving method of a hybrid cyclic prefix single carrier frequency domain equalization (HP-SCFDE) system. Background Art

[0002] The Single Carrier Frequency Domain Equalization (SCFDE) technology converts the received signal into the frequency domain for channel equalization. By adding a cyclic prefix (CP) before each frame of the transmitted signal, it can effectively resist inter-symbol interference (ISI) and improve the ability to resist multipath fading. Compared with time domain equalization (TDE), frequency domain equalization has lower complexity when the channel multipath delay is long.

[0003] The basic idea of ​​hybrid cyclic prefix single carrier frequency domain equalization is to add the cyclic prefix to the front of the transmitted frame at intervals, that is, one of every two frames has a cyclic prefix added, thereby improving the utilization of spectrum resources. Figure 1 As shown. The receiver uses a decision feedback mechanism to compensate for odd frames without cyclic prefixes, which can significantly improve the bit error rate performance of odd frames. Bai Wenling et al. published "A low-transmit power single-carrier frequency domain equalization structure" (Bai Wenling, Xiao Yue, Li Shaoqian. A low-transmit power single-carrier frequency domain equalization structure [J]. Journal of University of Science and Technology of China, 2009, 39(10): 1102-1106, hereinafter referred to as "reference [1]") introduced the design of HP-SCFDE and proposed a receiver structure based on hard information compensation.

[0004] When compensating odd symbols, using soft information can make better use of received information than using hard information. On the other hand, due to the errors in the decision results of even symbols, odd symbols will still have residual inter-symbol interference after compensation and equalization. Summary of the invention

[0005] In view of the above problems, the present invention proposes a novel signal receiving method, which performs soft compensation on frames without prefixes and uses an iterative equalization method to further offset ISI, thereby improving the bit error rate performance of the system.

[0006] In the HP-SCFDE system, no CP is added before odd frames, and a CP is added before even frames. Since odd frames do not have a CP, the transmission performance is affected by two additional factors compared to even frames. (2i+1) On the one hand, x (2i) The tail after the delay multipath channel does not fall into the protection interval, but directly falls into the information segment. (2i+1) On the other hand, x (2i+1) The tail of (2i+2) During the guard interval, it is discarded in the receiver, resulting in signal energy loss. For even frames, this loss is compensated by the tail of its own CP.

[0007] According to the above description, we can deduce that x (2i-1) The signal y that reaches the receiver after passing through the channel (2i-1) The expression of y (2i-1) The signal of the nth time slot is:

[0008]

[0009] In the above formula is additive white Gaussian noise, It represents the signal after a frame with complete CP passes through a multipath channel; Corresponding to y (2i-1) The signal is lost because it falls into the guard interval of the following frame; It corresponds to the interference of the tail of the previous frame, where N is the frame length, that is, the number of modulation symbols in a frame, L represents the length of the channel time domain impact, τ l Represents the multipath delay of the lth path.

[0010] For even frames x of a complete CP (2i) , the signal y that reaches the receiver after passing through the channel (2i) The signal of the nth time slot is:

[0011]

[0012] The signal receiving method includes:

[0013] S1. Detect even-numbered frames:

[0014] Perform channel equalization and soft demodulation on even frames, and iterate the obtained soft information between the equalizer and the decoder to obtain the output soft information;

[0015] S2. Estimate the inter-symbol interference of odd frames:

[0016] Define the soft information of the 2ith frame as S 2i , according to S 2iCalculate the mean value E of each symbol in the 2ith frame 2i and variance V 2i , then for the 2i+1th frame, the estimated ISI is α 2i+1,2i :

[0017]

[0018] The transmission error is γ 2i+1,2i :

[0019]

[0020] Among them, N is the frame length, L represents the length of the channel time domain impact, τ l represents the multipath delay of the lth path, and the subscript k represents the kth element of the vector;

[0021] S3, estimate the tail of the discarded odd frames:

[0022] According to S 2i+2 Calculate the mean value E of each symbol in the 2i+2th frame 2i+2 and variance V 2i+2 , for the 2i+1th frame, the estimated tail is α 2i+1,2i+2 :

[0023]

[0024] The transmission error is γ 2i+1,2i+2 :

[0025]

[0026] where τ m Indicates the maximum multipath spread of the channel, cp 2i+2 Indicates the CP part of the 2i+2th frame, N 0 is the power of additive noise;

[0027] S4. Compensate for odd frames:

[0028] For the 2i+1th frame, the received signal y is calculated based on the estimated ISI and tailing. (2i+1) After correction, the corrected mean is α 2i+1 =y (2i+1) +α 2i+1,2i +α 2i+1,2i+2 , the variance of the total additive noise is γ 2i+1 =N 0 +γ 2i+1,2i +γ 2i+1,2i+2 ;

[0029] S5. Detect the compensated odd-numbered frames:

[0030] Using alpha2i+1 and γ 2i+1 Channel equalization and soft demodulation are performed, and the obtained soft information is iterated between the equalizer and the decoder to further offset the residual ISI and obtain the output soft information.

[0031] The beneficial effect of the present invention is that it can effectively resist the interference of CP-free frames and improve the system bit error rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the transmitter block diagram of the HP-SCFDE system;

[0033] Figure 2 is the proposed receiver block diagram;

[0034] Figure 3 This is a comparison chart of the bit error rate of the CP-free frame obtained by the proposed receiver method without iteration under QPSK modulation and the method in reference [1].

[0035] Figure 4 It is a comparison chart of the bit error rate of the CP-free frame without iteration and with two iterations under QPSK modulation. DETAILED DESCRIPTION

[0036] The present invention is described below in conjunction with the accompanying drawings and simulation examples.

[0037] In the HP-SCFDE system, the transmission data is first encoded with a 1 / 2 code rate convolutional code and QPSK modulated into odd frames and even frames, and a cyclic prefix is ​​inserted only before the even frames, and then the obtained transmission signal is transmitted; the signal reception process is as follows Figure 2 As shown, first, the odd and even frames of the received signal are separated, and the even frames are transformed to the frequency domain after removing the CP, and the frequency domain iterative equalization is performed, wherein the equalizer adopts the MMSE criterion, and the soft information output is the log likelihood ratio (LLR) calculated by the Log-MAP method; then, the ISI received by the odd frame and the discarded tail are estimated according to the LLR of the even frame, and the odd frame is compensated, and the compensated odd frame is transformed to the frequency domain, and the frequency domain iterative equalization is performed. The equalizer adopts the MMSE criterion, and the soft information output is the LLR calculated by the Log-MAP method; finally, the decoder outputs of the odd and even frames are connected in series according to the transmitter order, and the decoder output results are judged to obtain the received bits.

[0038] Simulation example:

[0039] The simulation conditions are set as follows: the channel is a CDL-C channel, the RMS delay is 6us, the bandwidth is 15.36MHz, the transmission signal frame length is 1024, the modulation mode is QPSK modulation, the cyclic prefix is ​​inserted only before the even symbols, and its length is 798, and the number of iterations between the equalizer and the decoder is 2. The simulation is performed using the traditional method and the method of the present invention respectively, and the simulation results are shown as follows: Figure 3 and 4 As shown, the soft compensation receiver method proposed by the present invention can obtain better bit error rate performance advantage than the hard compensation method, and after two iterations of equalization, better bit error rate performance advantage can be obtained than without iteration.

Claims

1. A signal receiving method for a hybrid cyclic prefix single carrier frequency domain equalization system, in which no CP is added before odd frames and a CP is added before even frames, characterized in that: The signal receiving method comprises: S1. Detect even-numbered frames: Perform channel equalization and soft demodulation on even frames, and iterate the obtained soft information between the equalizer and the decoder to obtain the output soft information; S2. Estimate the inter-symbol interference of odd frames: Define the soft information of the 2ith frame as S 2i , according to S 2i Calculate the mean value E of each symbol in the 2ith frame 2i and variance V 2i , then for the 2i+1th frame, the estimated ISI is α 2i+1,2i : The transmission error is γ 2i+1,2i : Among them, N is the frame length, L represents the length of the channel time domain impact, τ l represents the multipath delay of the lth path, and the subscript n represents the nth element of the vector; S3, estimate the tail of the discarded odd frames: According to S 2i+2 Calculate the mean value E of each symbol in the 2i+2th frame 2i+2 and variance V 2i+2 , for the 2i+1th frame, the estimated tail is α 2i+1,2i+2 : The transmission error is γ 2i+1,2i+2 : where τ m Indicates the maximum multipath spread of the channel, cp 2i+2 represents the CP part of the 2i+2th frame, N0 is the power of the additive noise; S4. Compensate for odd frames: For the 2i+1th frame, the received signal y is calculated based on the estimated ISI and tailing. (2i+1) After correction, the corrected mean is α 2i+1 =y (2i+1) +α 2i+1,2i +α 2i+1,2i+2 , the variance of the total additive noise is γ 2i+1 =N0+γ 2i+1,2i +γ 2i+1,2i+2 ; S5. Detect the compensated odd-numbered frames: Using alpha 2i+1 and γ 2i+1 Channel equalization and soft demodulation are performed, and the obtained soft information is iterated between the equalizer and the decoder to further offset the residual ISI and obtain the output soft information.

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