Frequency hopping communication system and method based on RCM

Abstract

The invention discloses a frequency hopping communication system and method based on RCM, and belongs to the technical field of wireless communication. The system comprises a transmitting end and a receiving end, the transmitting end comprises a channel coding unit, an RCM modulation unit, a symbol distribution unit, a frequency hopping module unit and a radio frequency transmitting unit which are connected in sequence, and the receiving end comprises a radio frequency receiving unit, a frequency hopping module unit, a symbol reconstruction unit, an RCM demodulation unit and a channel decoding unit which are connected in sequence. The RCM is applied to the frequency hopping communication system and replaces modulation modes such as QPSK and QAM in a traditional frequency hopping communication system, an RCM coding symbol distribution scheme is designed, the number of symbols borne by each carrier frequency point can be dynamically changed with a single symbol as a unit according to channel conditions, self-adaptive change of the transmission rate is achieved, and the transmission efficiency is improved. Therefore, the complex and changeable frequency hopping communication environment is dealt with, the loss of bit information under strong interference is reduced, and the anti-interference capability of the frequency hopping system is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communication, and more specifically, relates to a frequency hopping communication system and method based on RCM. Background Art

[0002] Frequency hopping communication distributes modulation symbols to multiple different carrier frequencies for transmission, and controls the rapid random changes of carrier frequencies through frequency hopping patterns, making it difficult to track interference and achieving higher anti-interference performance. At present, most frequency hopping systems use traditional QPSK, QAM and other modulation technologies, each of which carries one or more bits of information, and other symbols no longer carry these bits of information. Once the interference is strong during the transmission process, the information of the bits corresponding to the symbol is completely missing, and thus cannot be decoded. The missing of a small amount of bit information may be solved by the error correction capability of channel coding, but the error correction capability of channel coding is limited. If interference strategies such as tracking interference are used for frequency hopping communication systems, it is likely that decoding will not be possible when there are many interfered carrier frequencies, and this problem cannot be solved by increasing the transmit signal power and thus improving the signal-to-noise ratio.

[0003] RCM (Rate Compatible Modulation) is a rate-adaptive modulation technology. The transmitter generates coded symbols by weighted summing of information bits through a sparse mapping matrix, and the receiver iteratively decodes the received symbols through a belief propagation algorithm (BP) based on a Tanner graph. Since the receiver of RCM uses accumulated symbols for decoding, under specific signal-to-noise ratio conditions, successful decoding can be achieved as long as enough received symbols are accumulated. Therefore, RCM does not require accurate and timely channel condition information, and can dynamically change the number of coded symbols sent to match the change of channel capacity, realize adaptive and smooth adjustment of the transmission rate, and obtain transmission efficiency close to the capacity limit under a wide range of SNR (Signal Noise Ratio). If RCM is applied to a frequency hopping communication system, when the carrier frequency is interfered and some RCM coded symbols are lost, the undisturbed coded symbols can still be used to complete correct demodulation under a suitable signal-to-noise ratio. Therefore, RCM has the potential to improve the anti-interference performance of frequency hopping communication systems. Summary of the invention

[0004] In view of the defects of the prior art, the purpose of the present invention is to provide a frequency hopping communication system and method based on RCM, aiming to solve the problem that the performance of traditional modulation in the existing frequency hopping system drops sharply when multiple carrier frequencies are interfered, and to improve the anti-interference ability of the frequency hopping system.

[0005] To achieve the above-mentioned purpose, the present invention provides a frequency hopping communication system based on RCM, including a transmitting end and a receiving end, the transmitting end includes a channel coding unit, an RCM modulation unit, a symbol allocation unit, a frequency hopping module unit, and a radio frequency transmitting unit, and the receiving end includes a radio frequency receiving unit, a frequency hopping module unit, a symbol reconstruction unit, an RCM demodulation unit, and a channel decoding unit.

[0006] At the transmitting end, the information bit vector b generated by the source is channel-coded by the channel coding unit to generate the coding vector x; then, x is sent to the RCM modulation unit to obtain the RCM coding symbol vector s; according to the symbol allocation scheme, the symbol allocation unit allocates different symbols in s to different carrier frequencies; finally, after the frequency hopping module performs the frequency hopping operation, the RF transmitting unit performs wireless transmission.

[0007] At the receiving end, the received RF signal first passes through the frequency hopping module for frequency de-hopping. The de-hopping signal is input into the symbol reconstruction unit, which sets the symbols carried by the interfered carrier frequency points to 0 and restores the symbol order to obtain the received symbol vector Will receive the symbol vector Send it to the RCM demodulation unit for demodulation to obtain the demodulated signal vector Finally, The information vector obtained by channel decoding It is sent to the destination to complete the reception of information.

[0008] Furthermore, the RCM modulation is specifically for a coding vector x={x1, x2, ..., x N}Weighted summation yields a coding symbol vector s={s1,s2,...,s M}, expressed as:

[0009] s T = Ηx T

[0010] Wherein, H is a sparse mapping matrix of size M×N, and each row of H has N non-zero weight values.

[0011] Furthermore, the symbol allocation unit is used to allocate different symbols in s to different carrier frequencies: every n symbols are evenly allocated to n carrier frequencies in turn, each carrier frequency is allocated M / n RCM coded symbols, and the position of the jth symbol allocated to carrier frequency i in the RCM coded symbol vector s can be expressed as s i,j =i+η(j-1),i∈{1,2,...,η},j∈{1,2,3,...,M / η}.

[0012] Furthermore, the symbol reconstruction unit sets all the symbols carried by the λ interfered carrier frequency points to 0, and sequentially extracts the symbols of each carrier frequency point to form a received symbol vector

[0013] Furthermore, the RCM demodulation unit uses the BP algorithm to receive the symbol vector Demodulate and get the demodulated signal vector

[0014] Furthermore, the channel decoding unit demodulates the signal vector Decoding to obtain information bit vector Use Turbo codes, convolutional codes, low-density parity-check codes or polar codes.

[0015] The present invention also provides a frequency hopping communication method based on RCM, comprising the following steps:

[0016] At the transmitting end, the information bit vector b generated by the source is channel-coded to generate a coding vector x, and the x is modulated by RCM to obtain an RCM coding symbol vector s; different symbols in the coding symbol vector s are assigned to different carrier frequencies; the carrier frequencies are frequency-hopped to generate radio frequency signals;

[0017] At the receiving end, the received RF signal is frequency de-hopped, the symbols carried by the interfered carrier frequency points in the de-hopped RF signal are set to 0, and the symbol order is restored to obtain the received symbol vector Will receive the symbol vector Demodulate and obtain the demodulated signal vector right Channel decoding is performed to obtain the information vector The information vector It is sent to the destination to complete the reception of information.

[0018] Through the above technical scheme conceived by the present invention, compared with the prior art, the present invention applies RCM to a frequency hopping communication system, and replaces QPSK, QAM and other modulation methods in the traditional frequency hopping communication system with RCM. When a large number of carrier frequencies in the frequency hopping system are subjected to high-power interference, resulting in the loss of some RCM coded symbols, the performance of the traditional modulation method is seriously reduced and an error platform occurs. The present invention combines the matrix structure characteristics of RCM and designs an RCM coded symbol allocation scheme without affecting the RCM performance. The number of symbols carried by each carrier frequency can be dynamically changed in units of a single symbol according to the channel conditions. Under a suitable signal-to-noise ratio, undisturbed coded symbols can still be used, or sufficient received coded symbols can be accumulated for correct demodulation, thereby realizing adaptive changes in the transmission rate, thereby coping with complex and changeable frequency hopping communication environments, reducing the loss of bit information under strong interference, and enhancing the anti-interference ability of the frequency hopping system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a block diagram of a frequency hopping communication system based on RCM provided by the present invention.

[0020] Figure 2 It is a schematic diagram of the transmission process of RCM coded symbols in a frequency hopping communication system.

[0021] Figure 3 It is a schematic diagram showing the performance comparison between the RCM-based frequency hopping communication system provided by the present invention and the traditional frequency hopping communication system. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] The present invention proposes a frequency hopping communication system based on RCM, including a transmitting end and a receiving end, such as Figure 1 The transmitting end includes a channel coding unit, an RCM modulation unit, a symbol allocation unit, a frequency hopping module unit, and a radio frequency transmitting unit, and the receiving end includes a radio frequency receiving unit, a frequency hopping module unit, a symbol reconstruction unit, an RCM demodulation unit, and a channel decoding unit.

[0024] RCM is a rate modulation technique. When the channel coding unit generates a coding vector x={x1,x2,...,x N}∈{0,1} NWhen x is weighted and summed through the sparse mapping matrix H of size M×N, the coding symbol vector s={s1,s2,...,s M}, expressed as

[0025] s T = Ηx T (1)

[0026] Each row of the matrix H has L non-zero weight values, from the weight set w = {w1, w2, ..., w L} are selected without repetition, where L=N.

[0027] The RCM coded symbols generated by the RCM modulation unit need to be allocated to different carrier frequencies for transmission, such as Figure 2 Assume that in a frequency hopping communication system, each group of information is transmitted using η carrier frequencies, and the RCM coding symbol vector s = {s1, s2, ..., s M The allocation scheme of the M coded symbols in} is shown in Table 1. In Table 1, the number after "Symbol" in the title row represents the symbol sequence number allocated to the carrier frequency point, and the table body content is the position of the symbol allocated to each carrier frequency point in the RCM coding symbol vector s, that is, the symbol subscript of the symbol in the RCM coding symbol vector s. It can be seen from Table 1 that starting from the first symbol s1, every η symbols are uniformly allocated to η carrier frequencies in turn, and each carrier frequency point is allocated M / η RCM coding symbols. The position of the jth symbol allocated to carrier frequency point i in the RCM coding symbol vector s can be expressed as s i,j =i+η(j-1), i∈{1,2,...,η}, j∈{1,2,3,...,M / η}. Since each retransmission of η symbols can be evenly distributed to each carrier frequency point, this allocation scheme can dynamically change the number of symbols allocated to each carrier frequency point in units of a single symbol according to the current channel conditions, thereby achieving adaptive changes in the transmission rate.

[0028] Table 1

[0029]

[0030] like Figure 2 As shown in the figure, it is assumed that during the transmission process, there are λ,λ∈{0,1,2,...,η} carrier frequencies interfered by high-power noise, which are marked as gray parts in the figure, and the symbols of the other η-λ carrier frequencies are not subject to strong interference. All the symbols carried by the λ strongly interfered carrier frequencies are set to 0, and the information carried by the symbols set to 0 is completely lost, which is equivalent to reducing the number of symbols participating in RCM demodulation by λ·M / η. Then, the symbols are reconstructed according to the RCM coding symbol allocation scheme in Table 1, that is, according to the vertical direction of the table, the symbols of each carrier frequency are taken out in turn to form the received symbol vector For example, Figure 2 Assume that the second carrier frequency is interfered by high-power noise, then the received symbol vector In the example, all symbols carried by the second carrier frequency will be set to 0 (marked in gray in the figure).

[0031] After passing through the channel, the received symbol vector input to the RCM demodulation unit It can be expressed as:

[0032]

[0033] Where n is the channel noise vector, and the receiver decodes by solving the maximum a posteriori probability problem.

[0034]

[0035] Where P represents the received symbol vector The probability distribution of different encoding vectors x under the condition of . N (2) represents a binary vector space of length N over the finite field {0,1}. Then, the demodulated signal vector Channel decoding is performed to obtain the information bit vector RCM generally uses the efficient and low-complexity BP (Belief Propagation) algorithm to solve the maximum a posteriori probability problem in equation (3). The credibility is gradually improved by iteratively updating the soft information between the symbol node and the variable node, and then the demodulation result is obtained based on the output soft information. According to the RCM coding principle, each RCM coded symbol is obtained by weighted summation of multiple information bits, which means that for each bit, there will be multiple RCM symbols carrying its information. Even if some symbols are interfered during the signal transmission process, as long as the remaining number of symbols can meet the RCM demodulation and channel decoding requirements under the current channel conditions, the information bits can still be recovered correctly.

[0036] Example

[0037] The channel coding in this embodiment adopts Turbo code with code rate 1 / 2, and the generating polynomial is represented by octal as (13, 15). The length of the information bit vector b is 2048, and the length of the coded vector x = {x1, x2, ..., x 4096}∈{0,1} 4096It should be noted that the present invention has no restrictions on the channel coding scheme and the coding rate. Coding schemes such as convolutional code, low-density parity check code (LDPC Code), polar code, etc. can be used, and the code rate can also be selected and designed accordingly as needed, which does not affect the effectiveness of the method proposed in the present invention.

[0038] The sparse mapping matrix H of size 4096×4096 performs RCM encoding on the code vector x, and obtains an RCM code symbol vector s={s1,s2,...,s 4096}, each row of the matrix H has L = 8 non-zero weight values, which are selected from the weight set W = {-4, -4, -2, -1, 1, 2, 4, 4} without duplication. Assume that in the frequency hopping communication system, each group of information is transmitted using η = 16 carrier frequencies, and the 4096 coded symbols in the RCM coded symbol vector s are evenly distributed to the 16 carrier frequencies, and each carrier frequency is allocated M / η = 256 RCM coded symbols.

[0039] The wireless channel model is an AWGN channel. Each group of information is transmitted by η=16 carrier frequencies, among which λ,λ∈{0,1,2,...,16} carrier frequencies may be randomly interfered by high-power noise.

[0040] At the receiving end, all the symbols carried by the λ carrier frequencies with strong interference are set to 0, and the information carried by the symbols set to 0 is completely lost, which is equivalent to reducing the number of symbols involved in RCM demodulation by 256×λ. Then, the symbols are reconstructed according to the RCM coding symbol allocation scheme to form the received symbol vector Using the received symbol vector The BP algorithm is used to perform RCM demodulation to obtain the demodulated signal vector After that, Turbo decoding is performed to obtain the information bit vector Turbo decoding is performed by repeated iterations until the decoding converges or the predetermined number of decoding iterations (6 times) is reached and then the decoding is terminated.

[0041] In order to illustrate the effectiveness of the present invention, the present invention and the QPSK modulation technology often used in the traditional frequency hopping communication system are simulated and compared. Figure 3 shown.

[0042] like Figure 3The figure shows the bit error rate of the frequency hopping communication system when 7 to 11 subcarriers (the total number of subcarriers is 16) are randomly interfered with in the two modulation modes of QPSK and RCM. The TQPSK in the figure represents the bit error rate of Turbo+QPSK, TRCM represents the bit error rate of Turbo+RCM, and the number -λ behind it represents the random interference of λ carrier frequencies. As can be seen from the figure, when 7 or more carrier frequencies are interfered with, the frequency hopping communication system using traditional modulation QPSK will cause a large amount of bit information loss due to too many interfered carriers, and the bit error rate is around 10 -2 As shown above, there is an obvious error platform, and the error rate will not decrease with the improvement of SNR. However, the frequency hopping communication system using RCM can still correctly decode even when the number of interfered subcarriers reaches 11, and there is no error platform.

[0043] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A frequency hopping communication system based on RCM, characterized in that: It includes a transmitting end and a receiving end, wherein the transmitting end includes a channel coding unit, an RCM modulation unit, a symbol allocation unit, a frequency hopping module unit, and a radio frequency transmitting unit connected in sequence, and the receiving end includes a radio frequency receiving unit, a frequency hopping module unit, a symbol reconstruction unit, an RCM demodulation unit, and a channel decoding unit connected in sequence; At the transmitting end, the information bit vector b generated by the information source is channel-coded by the channel coding unit to generate a coding vector x, and the x is RCM modulated by the RCM modulation unit to obtain an RCM coding symbol vector s; the symbol allocation unit is used to allocate different symbols in s to different carrier frequencies; after the carrier frequency is subjected to the frequency hopping operation by the frequency hopping module unit, the generated radio frequency signal is wirelessly transmitted by the radio frequency transmitting unit; At the receiving end, the received RF signal is frequency de-hopped by the frequency hopping module unit, and the symbol reconstruction unit is used to set the symbols carried by the interfered carrier frequency points in the de-hopped RF signal to 0 and restore the symbol order to obtain the received symbol vector The RCM demodulation unit is used to receive the symbol vector Demodulate and obtain the demodulated signal vector The channel decoding unit is used to Channel decoding is performed to obtain the information vector The information vector It is sent to the destination to complete the reception of information.

2. The frequency hopping communication system according to claim 1, characterized in that: The RCM modulation is specifically for a coding vector x={x1, x2, ..., x N }Weighted summation obtains the coded symbol vector s={s1,s2,...,s M }, expressed as: s T =Ηx T Among them, H is a sparse mapping matrix of size M×N, and each row of H has N non-zero weight values.

3. The frequency hopping communication system according to claim 2, characterized in that: The symbol allocation unit is used to allocate different symbols in s to different carrier frequencies. Specifically, every n symbols are evenly allocated to n carrier frequencies in turn, and each carrier frequency is allocated M / n RCM coded symbols. The position of the jth symbol allocated to carrier frequency i in the RCM coded symbol vector s can be expressed as s i,j =i+η(j-1),i∈{1,2,...,η},j∈{1,2,3,...,M / η}.

4. The frequency hopping communication system according to claim 3, characterized in that: The symbol reconstruction unit sets all the symbols carried by the λ interfered carrier frequency points to 0, and sequentially extracts the symbols of each carrier frequency point to form a received symbol vector 5. The frequency hopping communication system according to claim 4, characterized in that: The RCM demodulation unit uses the BP algorithm to receive the symbol vector Demodulate and get the demodulated signal vector 6. The frequency hopping communication system according to claim 5, characterized in that: The channel decoding unit demodulates the signal vector Decoding to obtain information bit vector Use Turbo codes, convolutional codes, low-density parity-check codes or polar codes.

7. A frequency hopping communication method based on RCM, characterized in that: The following steps are involved: At the transmitting end, the information bit vector b generated by the source is channel-coded to generate a coding vector x, and the x is modulated by RCM to obtain an RCM coding symbol vector s; different symbols in the coding symbol vector s are assigned to different carrier frequencies; the carrier frequencies are frequency-hopped to generate radio frequency signals; At the receiving end, the received RF signal is frequency de-hopped, the symbols carried by the interfered carrier frequency points in the de-hopped RF signal are set to 0, and the symbol order is restored to obtain the received symbol vector Will receive the symbol vector Demodulate and obtain the demodulated signal vector right Channel decoding is performed to obtain the information vector The information vector It is sent to the destination to complete the reception of information.

Images