阅读说明：本技术 一种泛在感知网络编码mpsk信号的低复杂度检测方法 (Low-complexity detection method for ubiquitous sensing network coding MPSK signal ) 是由 张高远 李海琼 韩瑽琤 马聪芳 唐杰 宋欢欢 文红 张晓辉 冀保峰 王雨凡 黄旭 于 2021-07-16 设计创作，主要内容包括：一种泛在感知网络编码MPSK信号的低复杂度检测方法,对MPSK扩频信号进行解析处理,提取出随机发送数据符号对应的样值序列；根据样值序列得出无需信道状态信息的比特对数似然比信息；利用提取出的比特对数似然比信息,采用无需信道状态信息的译码方法进行译码,得出检测结果。本发明可靠性高、鲁棒性强,且计算复杂度低,能够降低网络节点的能耗。(A low complexity detection method of a ubiquitous sensing network coding MPSK signal is provided, which comprises the steps of analyzing an MPSK spread spectrum signal, and extracting a sample value sequence corresponding to a random transmission data symbol; obtaining bit log likelihood ratio information without channel state information according to the sample value sequence; and decoding by using the extracted bit log-likelihood ratio information and adopting a decoding method without channel state information to obtain a detection result. The invention has high reliability, strong robustness and low computation complexity, and can reduce the energy consumption of network nodes.)

1. A low complexity detection method of ubiquitous sensing network coding MPSK signal, the transmitting end codes the binary bit sequence generated by the information source, the coded binary bit sequence is grouped, each group contains 4 bit, each group forms a transmitting symbol after MPSK spread spectrum modulation and pulse forming, the transmitting symbol is transmitted to the channel through the radio frequency antenna, the receiving end detects the transmitting symbol, the method is characterized in that: the detection method adopted by the detector at the receiving end comprises the following steps:

s1: performing matched filtering sampling on the MPSK spread spectrum signal to obtain a discrete received sample value sequence;

s2: extracting bit LLR without CSI according to the discrete sample value sequence;

s3: and decoding by using the extracted bit LLR information and adopting a decoding method without CSI to obtain a detection result.

2. A method of low complexity detection of a ubiquitous-aware network-coded MPSK signal as claimed in claim 1, wherein: the specific implementation method of step S1 is that, in the discrete received sample sequence obtained after performing matched filtering sampling on the MPSK spread spectrum signal, the sequence corresponding to the kth symbol period is:i.e. containing 16 discrete samples, where s^(k)Indicating the spreading chip sequence corresponding to the k-th symbol period, is the jth chip of the yth spreading code sequence, j being 1, 2 … … 16, η_k,jIs discrete, circularly symmetric, has a mean of zero and a variance of sigma²Complex gaussian random variables.

3. A method of low complexity detection of a ubiquitous-aware network-coded MPSK signal as claimed in claim 1, wherein: the specific implementation method of the step S2 is

Wherein the content of the first and second substances,representing bit LLRs that do not require CSI,indicating the ith code bit corresponding to the kth symbol period,to representTime-corresponding spreading code sequence s^(k)，To representTime-corresponding spreading code sequence s^(k)Denotes a complex conjugate operation.

4. A method of low complexity detection of a ubiquitous-aware network-coded MPSK signal as claimed in claim 1, wherein: the decoding method in the step S3 is a minimum sum algorithm of low density parity check codes or a soft output viterbi algorithm of convolutional codes.

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a low-complexity detection method for a ubiquitous sensing network coded MPSK signal.

Background

At present, in order to accelerate the construction pace of modern cities, improve the urban treatment efficiency and the quality of life of citizens, the state continuously issues policies, the supporting force for the construction of smart cities is increased, and the development of the smart cities is promoted. The world second major market research institute marks and marks published reports that the world smart city market size was 3080 billion dollars in 2018, the number is expected to grow to 7172 billion dollars by 2023, and the annual composite growth rate in the forecast period (2018 and 2023) is 18.4%.

Along with the continuous promotion of wisdom city construction process, novel wisdom city gradually gets into masses' field of vision. The novel smart city presents four new characteristics on the construction and the service: comprehensive and thorough perception, broadband ubiquitous interconnection, intelligent fusion application and human-oriented sustainable innovation. The wide-spread information-aware network is the basis of the smart city. Information resources owned by any city are massive, and in order to acquire city information more timely and comprehensively and judge the city condition more accurately, a central system of a smart city needs to have the capability of various elements of the city to exchange required information. The information perception network of the novel smart city can cover all dimensions of time, space, objects and the like of the city and can collect information with different attributes, different forms and different densities.

The Internet of things comprises a sensing layer, a network layer, a platform layer and an application layer. The perception layer at the bottom layer is the skin and five sense organs of the Internet of Things (IoT), is a link for connecting the physical world such as the smart city and the information world, and is responsible for identifying objects in the smart city, collecting data and primarily transmitting information. On the premise that the network layer accurately and timely transmits data, the accuracy of processing data by the application layer and the accuracy of data mining conclusions depend on the quality of the data of the perception layer. And the three basic characteristics of the internet of things are comprehensive perception, reliable transmission and intelligent processing. Therefore, the actual application value of the Internet of things system in the smart city is determined by the accuracy of the perception data, the perception layer is the core of the Internet of things, and the reliable transmission of the data of the perception layer is one of the most key technologies.

The IEEE 802.15.4c protocol published in 2009 is a physical layer specification customized for china low-power short-range wireless personal area networks. Aiming at different speed requirements, the protocol provides two physical layer structures of Offset-quadrature Phase Shift Keying (O-QPSK) and multi-Phase Shift Keying (MPSK) for the China low-power short-distance wireless personal area network. The MPSK modulation physical layer has the best ability to provide a solid guarantee for reliable and fast transmission of the smart city sensing data. Therefore, the research on the MPSK signal strong robustness detection technology conforming to the characteristics of the wireless personal area network is one of the most basic starting points for ensuring that the sensing data accurately reaches the application layer, and is also one of the problems that the technology of the internet of things needs to be solved urgently when being applied to the smart city.

As shown in fig. 10, the IEEE 802.15.4c protocol uses different modulation schemes and data transmission rates on different carrier frequency bands. As shown in fig. 11, the 780MHz band is shared by two modulation schemes of O-QPSK and MPSK, and there are 8 channels in the 779-787MHz band. Wherein, the channels 0-3 adopt O-QPSK modulation mode, and the channels 4-7 adopt MPSK modulation mode. The modulation mode of the invention adopts MPSK modulation, and the carrier frequency adopts the maximum frequency on the 780MHz frequency band, namely 786 MHz.

As shown in fig. 12, the IEEE 802.15.4c physical layer protocol data unit (PPDU) is mainly composed of three parts, a Synchronization Header (SHR), a physical layer header (PHR), and a physical layer (PHY) payload. The SHR of the PPDU includes two parts, a preamble and a Start of Frame (SFD), which primarily function to allow a receiving device to synchronize and lock onto a bitstream. The preamble field is 4 bytes, and is 32 all-zero bits. The Start of Frame Delimiter (SFD) field takes 1 byte and its value is fixed to 0xA7, indicating the start of a physical frame. The PHR field of the PPDU takes 1 byte. Wherein, the lower 7 bits represent the frame length, and the value is the length of the physical frame load, so the length of the physical frame load cannot exceed 127 bytes; the upper 1 bit is a reserved bit. The PHY payload of a PPDU, also known as a physical layer service data unit (PSDU), is variable in length and is typically used to carry Medium Access Control (MAC) frames.

As shown in fig. 13, the transmitting end sequentially processes binary data from the PPDU through modulation and spreading functions, starting from a Preamble (Preamble) field in fig. 12 and ending at the last byte of the PSDU. The lower 4 bits of each byte of the PPDU are mapped to one data symbol and the upper 4 bits are mapped to the next data symbol, and each data symbol is further mapped to a length 16 pseudo-random (PN) chip sequence, respectively.

As shown in fig. 1, in the 780MHz band, the MPSK physical layer selects 1 of 16 PN chip sequences to be transmitted in each data symbol period by 4 information bits, i.e. each 4 bits of data can be converted into a PN chip sequence with a length of 16 after being modulated and spread.

The existing research on the physical layer of the IEEE 802.15.4c MPSK modulation focuses on a waveform detection method when channel coding is not adopted. Although the uncoded modulation system is simple to implement, the uncoded modulation system has the disadvantage of insufficient detection performance and is not suitable for application scenarios with high reliability requirements. For a coded MPSK modulation system, the Log-likelihood Ratio (LLR) information is a bridge between the demodulator and the decoder. The quality of LLR is one of the key factors that determine the final detection performance of the system. The conventional precise form of LLR calculation method requires Channel State Information (CSI). In practical application, the estimation process of the CSI involves high implementation complexity, high energy consumption and high cost. This is contrary to the low complexity and low cost features of IEEE 802.15.4 c. Moreover, when there is an error in the estimation of CSI, the performance of the entire coding system will be drastically degraded. I.e. a detection system using accurate CSI is not robust to CSI. The technical defects limit the depth and the breadth of the application of the Internet of things communication technology in the ubiquitous sensing network of the novel smart city in China to a certain extent.

Disclosure of Invention

In order to solve the defects of the prior art, the invention aims to provide a low-complexity detection method for a ubiquitous sensing network coding MPSK signal, which has the characteristics of low computational complexity, strong robustness and high reliability.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a low complexity detection method of a ubiquitous sensing network coding MPSK signal is characterized in that a sending end codes a binary bit sequence generated by a signal source, the coded binary bit sequence is grouped, each group comprises 4 bit positions, each group forms a sending symbol after MPSK spread spectrum modulation and pulse forming, the sending symbol is sent to a channel through a radio frequency antenna, a receiving end detects the sending symbol, and a detection method adopted by a detector of a receiving end comprises the following steps:

s1: performing matched filtering sampling on the MPSK spread spectrum signal to obtain a discrete received sample value sequence;

s2: extracting bit LLR without CSI according to the discrete sample value sequence;

s3: and decoding by using the extracted bit LLR information and adopting a decoding method without CSI to obtain a detection result.

The specific implementation method of step S1 in the present invention is that, in the discrete received sample sequence obtained after performing matched filtering sampling on the MPSK spread spectrum signal, the sequence corresponding to the kth symbol period is:i.e. containing 16 discrete samples, where s^(k)Indicating the spreading chip sequence corresponding to the k-th symbol period, is the jth chip of the yth spreading code sequence, j being 1, 2 … … 16, η_k,jIs discrete, circularly symmetric, has a mean of zero and a variance of sigma²Complex gaussian random variables.

The step S2 is realized by the method

Wherein the content of the first and second substances,representing bit LLRs that do not require CSI,indicating the ith code bit corresponding to the kth symbol period,to representTime-corresponding spreading code sequence s^(k)，To representTime-corresponding spreading code sequence s^(k)Denotes a complex conjugate operation.

The decoding method in step S3 of the present invention is the minimum sum algorithm of the low density parity check code or the soft output viterbi algorithm of the convolutional code.

The invention has the beneficial effects that: the low-complexity detection method for the ubiquitous sensing network coding MPSK signal has the advantages of being high in reliability, strong in robustness and low in calculation complexity. The concrete aspects are as follows:

the log-likelihood ratio extraction scheme disclosed by the invention can completely meet the requirement of an IEEE 802.15.4c protocol on detection performance;

compared with the precise LLR extraction scheme, the scheme provided by the invention has the advantages of low performance loss, no need of channel state information, low implementation complexity, low cost and strong robustness on the channel state information.

Drawings

FIG. 1 is a diagram of a data spreading mapping mode of an MPSK physical layer;

FIG. 2 is a diagram showing comparison of BER performance in different LLR extraction methods and different decoding methods;

FIG. 3 is a graph showing the comparison of SER performance for different LLR extraction methods and different decoding methods;

FIG. 4 is a graph showing performance comparison of PER for different LLR extraction methods and different decoding methods;

FIG. 5 is a chart of channel noise variance robustness BER under the Belief Propagation (BP) algorithm, a method of exact LLR extraction, where Δ σ²＝ασ²；

FIG. 6 is a SER graph of channel noise variance robustness under the exact LLR extraction method, BP algorithm, where Δ σ²＝ασ²；

FIG. 7 is a PER graph of channel noise variance robustness under the exact LLR extraction method, BP algorithm, where Δ σ²＝ασ²；

FIG. 8 is an H matrix diagram of an LDPC code (1008,504);

fig. 9 is a flowchart of the operation of the communication system in the embodiment of the present invention;

FIG. 10 is a diagram of basic parameter characteristics of two frequency bands of the physical layer of the IEEE 802.15.4 protocol;

FIG. 11 is a channel structure diagram of the physical layer of the IEEE 802.15.4 protocol;

FIG. 12 is a diagram of an IEEE 802.15.4 protocol physical layer frame structure;

FIG. 13 is a diagram of a physical layer data modulation process of the 786MHz band of the IEEE 802.15.4 protocol.

Detailed Description

The following specific examples are given to further clarify, complete and detailed the technical solution of the present invention. The present embodiment is a preferred embodiment based on the technical solution of the present invention, but the scope of the present invention is not limited to the following embodiments.

This embodiment is described by taking an IEEE 802.15.4 system as an example, and its communication environment is 780MHz band, the carrier center frequency of the channel is 786MHz, the data length of the PSDU is 22 bytes, and the chip transmission rate is 1 × 10⁶chip/s, MPSK as modulation mode, LDPC (1008,504) as coding mode, check matrix as shown in fig. 8, and maximum iteration number 10.

As shown in fig. 9, at the transmitting end, the working process of the system is as follows: the LDPC code or convolutional code encoder encodes the binary information bit sequence alpha generated by the source to generate a coded bit sequence c. And then, after mapping from bit data to symbols and mapping from symbols to chips in sequence, MPSK modulation is carried out to send MPSK spread spectrum signals to a receiving end.

After receiving MPSK spread spectrum signals, the receiving end extracts LLR according to the method of the invention, and the specific process is as follows:

a low-complexity detection method for a ubiquitous sensing network coded MPSK signal comprises the steps that a sending end codes a binary bit sequence generated by an information source, the coded binary bit sequence is grouped, each group comprises 4 bit positions, each group forms a sending symbol after MPSK spread spectrum modulation and pulse forming, and the sending symbol is sent to a channel through a radio frequency antenna. And the receiving end detects the signal. The detection method adopted by the detector comprises the following steps:

s1: performing matched filtering sampling on the MPSK spread spectrum signal to obtain a discrete received sample value sequence;

s2: extracting bit LLR without CSI according to the discrete sample value sequence;

s3: and decoding by using the extracted bit LLR information and adopting a decoding method without CSI to obtain a detection result.

Further, the step S1 specifically includes:

in a discrete received sample sequence obtained after performing matched filtering sampling on the MPSK spread spectrum signal, the sequence corresponding to the kth symbol period is as follows:i.e. containing 16 discrete samples. Wherein s is^(k)Indicating the spreading chip sequence corresponding to the k-th symbol period, is the jth chip of the yth spreading code sequence, j being 1, 2 … … 16, η_k,jIs discrete, circularly symmetric, has a mean of zero and a variance of sigma²Complex gaussian random variables.

Further, the step S2 specifically includes:

wherein the content of the first and second substances,representing bit LLRs that do not require CSI,indicating the ith code bit corresponding to the kth symbol period,to representTime-corresponding spreading codesSequence s^(k)，To representTime-corresponding spreading code sequence_s ^(k)Denotes a complex conjugate operation.

Further, the decoding method in step S3 may be a Minimum Sum (MS) Algorithm of a Low-Density Parity-Check (LDPC) code, or a Soft Output Viterbi Algorithm (SOVA) of a convolutional code.

As shown in fig. 2, fig. 3 and fig. 4, the detection method corresponding to the precise LLR extraction method is taken as a boundary and compared with the detection method corresponding to the simplified LLR extraction method of the present invention. It can be seen from the figure that the gap between the detection performance of the simplified scheme and the accurate scheme is small. In particular, when PER is 1 × 10^-3When compared with the exact scheme, the performance loss of the simplified scheme using BP coding is only 0.07dB, and the performance loss of the simplified scheme using MS coding is only 0.2 dB. The above results show that the simplified scheme using MS decoding suffers little performance loss, but has low implementation complexity since no estimation of the channel state information is required. Therefore, better balanced matching between detection performance and realization complexity is achieved, and the method is particularly suitable for being used in an IEEE 802.15.4c coding MPSK system.

Further, in fig. 5, fig. 6 and fig. 7, simulation performances under different CSI estimation errors, precise LLR extraction method and BP algorithm are given, and compared with performances under the simplified LLR extraction method and MS algorithm of the present invention. As can be seen from fig. 5 to 7, when the variance estimation error for the channel noise is large, the detection performance using the exact-form LLR calculation method is degraded severely. Namely, the precise form LLR calculation method is not robust to CSI. The simplified LLR calculation method using MS decoding does not need CSI, so that the method has better robustness.

The intrinsic theoretical basis of equation (1) is described below.

First, the probability domain likelihood function can be expressed as:

the exact form of LLR can be expressed as:

it is assumed here that the coded bits are a priori equi-probable, i.e.

As shown in the formula (2), the computation method of the full form LLR involves multiple exponential operations and modulo operations, and requires to know the state information σ of the white Gaussian noise channel in advance². The implementation complexity is high and is not suitable for application in IEEE 802.15.4c featuring low complexity and low cost. The reduction of the implementation complexity of the formula (2) has theoretical and practical engineering significance and value.

Using approximation formula

ln[exp(δ₁)+…+exp(δ_J)]≈max(δ₁,…,δ_J)

＝max(ln exp(δ₁),…,ln exp(δ_J))

＝ln[max(exp(δ₁),…,exp(δ_J))]

The method (2) can be simplified, and the specific method is as follows:

the formula (3) does not involve complicated exponential operation and modular operation, and only comprises simple conjugate multiplication, a real part and a minimum operation. And isAs a constant term, MS algorithm for LDPC codes, or convolutional codesFor the SOVA algorithm of (1), removing LLRThe decoding result is not affected. Therefore, the following formula (3)After elimination, formula (1) is obtained.

In summary, the low-complexity detection method for coding the MPSK signal in the ubiquitous sensor network has the characteristics of high reliability, strong robustness and low computational complexity.

The principal features, principles and advantages of the invention have been shown and described above. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to explain the principles of the invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the invention as expressed in the following claims. The scope of the invention is defined by the appended claims and equivalents thereof.