A frequency hopping communication system and method based on RCM

Abstract

The present invention discloses a frequency hopping communication system and method based on RCM, belonging to the field of wireless communication technology. The system includes 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 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. The present invention applies RCM to a frequency hopping communication system, replaces modulation modes such as QPSK and QAM in traditional frequency hopping communication systems with RCM, and designs an RCM coding symbol allocation scheme. It can dynamically change the number of symbols carried by each carrier frequency point in units of single symbols according to channel conditions, realize adaptive changes in 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.

Description

Technical Field

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

[0002] Frequency-hopping communication distributes modulation symbols across multiple different carrier frequencies for transmission, and controls the rapid random changes in carrier frequencies through frequency hopping patterns, making them difficult to track and interfere with, resulting in higher anti-interference performance. Currently, most frequency-hopping systems use traditional modulation technologies such as QPSK and QAM. Each modulation symbol carries one or more bits of information, and other symbols no longer carry these bits of information. If interference is strong during transmission, the information corresponding to the bits of the symbol is completely lost, making it impossible to participate in decoding. The loss of a small amount of bit information can be resolved through 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 adopted for frequency-hopping communication systems, resulting in a large number of interfered carrier frequencies, it is very likely that decoding will be impossible. 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 technique. The transmitter generates coded symbols by weighted summing information bits using a sparse mapping matrix. The receiver iteratively decodes the received symbols using a Tanner graph-based belief propagation (BP) algorithm. Because RCM's receiver uses accumulated symbols for decoding, successful decoding is achieved as long as sufficient received symbols are accumulated under specific signal-to-noise ratio (SNR) conditions. Therefore, RCM does not require accurate and timely information about channel conditions. It can dynamically adjust the number of transmitted coded symbols to match changes in channel capacity, achieving smooth and adaptive transmission rate adjustment and near-capacity transmission efficiency over a wide range of SNRs (Signal-Noise Ratios). If RCM is applied to frequency-hopping communication systems, even if some RCM coded symbols are lost due to interference on the carrier frequency, correct demodulation can still be achieved using the remaining coded symbols under appropriate SNRs. 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 drops sharply when multiple carrier frequencies of the existing frequency hopping system are interfered with, and to improve the anti-interference ability of the frequency hopping system.

[0005] To achieve the above-mentioned objectives, the present invention provides a frequency hopping communication system based on RCM, including a transmitting end and a receiving end, the transmitting end including 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 including 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 transmitter, 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, the frequency hopping module performs the frequency hopping operation, and 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 to the symbol reconstruction unit, which sets the symbols carried by the interfered carrier frequency to 0 and restores the symbol order to obtain the received symbol vector Will receive a symbol vector Send it to the RCM demodulation unit for demodulation to obtain the demodulated signal vector Finally, yes The information vector obtained by channel decoding It is sent to the destination to complete the reception of the information.

[0008] Furthermore, the RCM modulation is specifically for the coding vector x={x1, x2, ..., x N}Weighted summation is performed to obtain the 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 as follows: every n symbols are uniformly 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 Demodulation obtains 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 transmitter, the information bit vector b generated by the source undergoes channel coding to generate a code vector x, which is then modulated by RCM to obtain an RCM code symbol vector s. Different symbols in the code symbol vector s are assigned to different carrier frequencies, which undergo frequency hopping to generate RF signals.

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

[0018] Through the above technical scheme conceived by the present invention, compared with the existing technology, the present invention applies RCM to the frequency hopping communication system, and replaces the modulation methods such as QPSK and QAM 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 degraded 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. It can dynamically change the number of symbols carried by each carrier frequency in units of a single symbol according to the channel conditions. Under a suitable signal-to-noise ratio, it can still use undisturbed coded symbols, or accumulate enough received coded symbols 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 This is a block diagram of the RCM-based frequency hopping communication system 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 comparing the performance of 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 objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining 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 may 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, while 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 technology. When the channel coding unit generates a coding vector x={x1,x2,...,x N}∈{0,1} NWhen the weighted summation of x is performed by 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 frequency points 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, this allocation scheme can dynamically change the number of symbols allocated to each carrier frequency based on the current channel conditions, using a single symbol as a unit, 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 frequency points that are interfered with by high-power noise, which are marked as gray parts in the figure, and the symbols of the other η-λ carrier frequency points are not subject to strong interference. The symbols carried by the λ carrier frequency points that are strongly interfered with are all 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 point 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 Under the condition of , the probability distribution of different encoding vectors x appears. N (2) represents a binary vector space of length N on the finite field {0,1}. Then, the demodulated signal vector Perform channel decoding 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 continuously iteratively updating soft information between symbol nodes and variable nodes. The demodulation result is then determined based on the output soft information. The RCM coding principle shows that each RCM coded symbol is obtained by weighted summation of multiple information bits. This means that for each bit, multiple RCM symbols carry its information. Even if some symbols are interfered with during signal transmission, 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 accurately recovered.

[0036] Example

[0037] The channel coding in this embodiment adopts Turbo code with code rate 1 / 2, and the generating polynomial is expressed as (13, 15) in octal. The length of the information bit vector b is 2048, and the code 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 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 without affecting the effectiveness of the method proposed in the present invention.

[0038] The coding vector x is RCM-encoded by the sparse mapping matrix H of size 4096×4096, and the RCM coding symbol vector s={s1,s2,...,s 4096 Each row of the matrix H contains L = 8 non-zero weight values, selected from the weight set W = {-4, -4, -2, -1, 1, 2, 4, 4} without duplication. Assume that in a frequency-hopping communication system, each message group is transmitted using η = 16 carrier frequencies. The 4096 coded symbols in the RCM coded symbol vector s are evenly distributed across the 16 carrier frequencies, with each carrier frequency 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, of which λ,λ∈{0,1,2,...,16} carrier frequencies may randomly suffer from high-power noise interference.

[0040] At the receiving end, all the symbols carried by the λ carrier frequencies that are strongly interfered with are set to 0. 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 Use BP algorithm to perform RCM demodulation to obtain the demodulated signal vector Then, Turbo decoding is performed to obtain the information bit vector Turbo decoding is performed by repeated iteration 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 following will be a simulation comparison of the present invention and the QPSK modulation technology often used in traditional frequency hopping communication systems. The results are as follows: 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 under 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 to be lost due to too many interfered carriers, and the bit error rate is around 10 -2 The above results show that there is an obvious error platform, and the bit 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 merely 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 scope of protection of the present invention.

Claims

1. A frequency hopping communication system based on RCM, characterized in that: The device comprises a transmitting end and a receiving end, wherein the transmitting end comprises 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 comprises 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 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; the carrier frequency is subjected to a frequency hopping operation by the frequency hopping module unit, and 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 Perform channel decoding to obtain the information vector The information vector It is sent to the destination to complete the reception of the information.

2. The frequency hopping communication system according to claim 1, wherein: The RCM modulation is specifically for the coding vector x={x1, x2, ..., x N }Weighted summation is performed to obtain the coding symbol vector s={s1,s2,...,s M }, expressed as: s T =Ηx T Wherein, 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, wherein: 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, wherein: The symbol reconstruction unit sets all the symbols carried by the λ interfered carrier frequency points to 0, and extracts the symbols of each carrier frequency point in turn to form the received symbol vector 5. The frequency hopping communication system according to claim 4, wherein: The RCM demodulation unit uses the BP algorithm to receive the symbol vector Demodulation obtains the demodulated signal vector 6. The frequency hopping communication system according to claim 5, wherein: 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 transmitter, the information bit vector b generated by the source undergoes channel coding to generate a code vector x, which is then modulated by RCM to obtain an RCM code symbol vector s. Different symbols in the code symbol vector s are assigned to different carrier frequencies, which undergo frequency hopping to generate RF signals. At the receiving end, the received RF signal is frequency de-hopped, the symbols carried by the interfered carrier frequency in the de-hopped RF signal are set to 0, and the symbol order is restored to obtain the received symbol vector Will receive a symbol vector Demodulate and obtain the demodulated signal vector right Perform channel decoding to obtain the information vector The information vector It is sent to the destination to complete the reception of the information.

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