CN112787758B - Serial interference elimination uplink multiple access system of mass medium modulation equipment - Google Patents

Serial interference elimination uplink multiple access system of mass medium modulation equipment Download PDF

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CN112787758B
CN112787758B CN202110053140.5A CN202110053140A CN112787758B CN 112787758 B CN112787758 B CN 112787758B CN 202110053140 A CN202110053140 A CN 202110053140A CN 112787758 B CN112787758 B CN 112787758B
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CN112787758A (en
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�乔力
梅逸堃
高镇
张军
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Beijing Institute of Technology BIT
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0047—Decoding adapted to other signal detection operation
    • H04L1/0048—Decoding adapted to other signal detection operation in conjunction with detection of multiuser or interfering signals, e.g. iteration between CDMA or MIMO detector and FEC decoder
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0047—Decoding adapted to other signal detection operation
    • H04L1/005—Iterative decoding, including iteration between signal detection and decoding operation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0054—Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0071—Use of interleaving
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
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Abstract

The invention discloses a mass media modulation equipment multi-access system capable of self-adapting serial interference elimination, wherein a transmitting end comprises a data packet generating module, a first channel coding module and a first media modulation module; the transmitting terminal inserts the characteristic sequence b into the data to be transmitted by using the data packet generating modules(ii) a The receiving end comprises a non-coding detection algorithm module, a likelihood ratio calculation module, a soft decoding module, a decoding accuracy judgment module, a second channel coding module, a second medium modulation module and an interference elimination module; the decoding accuracy judging module calculates the decoding result of the characteristic sequence
Figure DDA0002899732690000011
With the true signature sequence bsThe Hamming distance of the mobile terminal is only subjected to interference elimination on effective data of active equipment with the Hamming distance smaller than a preset value. The invention can further improve the data demodulation accuracy of the multiple access of the mass media modulation equipment in the channel coding system.

Description

Serial interference elimination uplink multiple access system of mass medium modulation equipment
Technical Field
The invention relates to the field of data transmission in wireless communication, in particular to an uplink authorization-free multiple access system of mass medium modulation equipment with self-adaptive serial interference elimination.
Background
The Internet of things has the advantages of saving cost, increasing income sources, improving efficiency and the like, and plays an important role in various vertical fields. A typical feature of the internet of things is a large number of low power devices. The 6G white paper of samsung indicates that by 2030, the number of internet of things devices accessing a cellular network will be as high as 500 billion, which is 59 times the total number of people at that time, which requires that future base stations can achieve massive connections with hundreds of billions of devices. Although mass Machine-Type Communications (mtc) has been listed as one of three 5G application scenarios, low latency and high reliability for supporting mass device access is still very challenging for current networks.
Mass device multiple access protocols can generally be divided into two categories: an authorization-based approach and an authorization-free approach. In the future scenario of massive connections, the multiple access protocol based on authorization generally requires complex access scheduling, thereby generating intolerable access delay. As a promising alternative, unlicensed multiple access protocols have recently attracted considerable attention in both the academic and industrial sectors. In an authorization-free multiple access protocol, a user needing to access a network can directly send pilot frequency and data to a base station in an uplink mode without base station authorization; and the base station performs user identification and data detection according to the received signal.
In order to further improve the spectrum efficiency and energy efficiency of the mass connection of the internet of things, the scheme that the internet of things equipment adopts spatial modulation is also widely discussed and researched. Spatial modulation is a low complexity, high energy efficiency multiple antenna technique with a single rf or fewer rf than the number of transmit antennas. A typical spatial modulation scheme is equipped with multiple transmit antennas and a single radio frequency link at the transmit end, and the input bit stream is divided into spatial domain information bits and symbol domain information bits at each time slot: the former decides which transmitting antenna in the time slot is activated, called as "active antenna", and other transmitting antennas keep silent in the time slot; the latter determines the constellation symbols that need to be transmitted and is transmitted by the active antennas in this time slot. The receiving end detects the subscript and the constellation symbol of the active antenna through a corresponding detection scheme, and then the transmitted bit information can be obtained through demapping. The above process is repeated in the next symbol period, and the time slots are independent from one another, and the information bits between different time slots are independent from one another. Therefore, the single radio frequency link configuration of the typical spatial modulation technology is beneficial to reducing the size of a transmitter, reducing the energy consumption and improving the energy efficiency; the transmission of the spatial domain symbols can compensate for the rate loss caused by a single radio frequency, thereby obtaining a better compromise between spectral efficiency and energy efficiency.
In recent years, many new modulation techniques have evolved in variety, such as: generalized spatial modulation, medium modulation, and meta-surface modulation, etc., which preserve the low complexity and high energy efficiency characteristics of typical spatial modulation techniques while achieving higher spectral efficiency. Among them, the problem of mass access based on media modulation becomes a hotspot in academia and industry. In particular, medium modulation employs a single radio frequency link, a single transmit antenna, and a plurality of low cost, low overhead radio frequency mirrors. Wherein each radio frequency mirror can have two states of ON/OFF, and the combination of different ON/OFF states of a plurality of radio frequency mirrors can generate different radiation patterns ON the transmission signal of the transmitting antenna. Therefore, the spatial information can be coded ON the ON/OFF state combination of the radio frequency mirror surface, and the receiving end can demodulate the spatial information by detecting different radiation patterns. Unlike typical spatial modulation, the number of spatial bits of the medium modulation depends on the number of radiation patterns that can be distinguished, and thus it is expected to encode more spatial bits, thereby further improving spectral efficiency. Due to the above superiority of media modulation, mass access based on media modulation is widely studied as an improvement based on spatial modulation scheme, and many active user detection and media modulation data demodulation algorithms based on compressed sensing are emerging. However, for the above uplink unlicensed access scenario of the massive media modulation device, the existing schemes are designed at the transmitting and receiving ends without channel coding, and further research is needed for the scheme design at the transmitting and receiving ends with channel coding system.
Disclosure of Invention
In view of this, the present invention provides a mass media modulation device multiple access system with adaptive serial interference cancellation, so as to further improve the data demodulation accuracy of the mass media modulation device multiple access in the channel coding system.
In order to solve the above-mentioned technical problems, the present invention has been accomplished as described above.
A mass medium modulation equipment multiple access system of self-adaptive serial interference elimination comprises a transmitting end and a receiving end;
the transmitting terminal comprises a data packet generating module, a first channel coding module and a first medium modulating module;
the data packet generating module is used for generating a transmission data packet of equipment in a multi-access system of the mass media modulation equipment; inserting a known special character of a transmitting and receiving end into a transmitting data packetSign sequence bs；
The first channel coding module is used for carrying out channel coding on the sending data packet generated by the data packet generating module;
the first medium modulation module is used for performing medium modulation on the transmission data packet coded by the first channel coding module and transmitting the transmission data packet in a medium modulation symbol form;
the receiving end designs a medium modulation signal iterative decoder, and part of equipment is adaptively selected to eliminate serial interference based on a decoded characteristic sequence in each iteration; the receiving end comprises a non-coding detection algorithm module, a likelihood ratio calculation module, a soft decoding module, a decoding accuracy judgment module, a second channel coding module, a second medium modulation module and an interference elimination module;
the non-coding detection algorithm module is used for detecting the active equipment according to an observation matrix formed by the received signal and the estimated channel state information, and simultaneously obtaining the posterior probability of the medium modulation symbol sent by the active equipment;
the likelihood ratio calculation module is used for calculating the likelihood ratio information of each data bit according to the posterior probability of the medium modulation symbol;
a soft decoding module for performing soft decoding on the likelihood ratio information of the active device according to the channel coding mode of the transmitting terminal, wherein the soft decoding result comprises the decoding result of the characteristic sequence
Figure BDA0002899732670000031
A decoding accuracy judgment module for calculating the decoding result of the characteristic sequence
Figure BDA0002899732670000032
With the true signature sequence bsIf the hamming distance is smaller than the preset value, the effective data of the active device is considered to be used for interference elimination, and then the second channel coding module, the second medium modulation module and the interference elimination module are informed to execute interference elimination work; otherwise, the subsequent interference elimination step is not executed, and finally the self-adaptive string is realizedEliminating line interference;
the second channel coding module is used for coding the demodulation data of the active equipment to be subjected to interference elimination by adopting the same channel coding mode as the first channel coding module at the transmitting end;
the second medium modulation module is used for performing medium modulation on the coded data obtained by the second channel coding module by adopting the same medium modulation parameters as the first medium modulation module at the transmitting end to obtain a medium modulation symbol;
and the interference elimination module is used for eliminating interference on the active equipment judged by the decoding accuracy judgment module by utilizing the medium modulation symbol generated by the second medium modulation module, respectively updating the received signal and the observation matrix of the no-code detection algorithm module, and returning to the no-code detection algorithm module for iteration.
Preferably, a block interleaver is added between a first channel coding module and a first medium modulation module at the transmitting end, and the channel coding module, the block interleaver and the first medium modulation module form a 'bit interleaving coded medium modulation' module; the width of the block interleaver is equal to the number of effective radiation patterns of the first medium modulation module, and the depth of the block interleaver is determined by the length of the coded data packet, so that the channel space selective fading of the medium modulation symbol can be effectively coped with;
meanwhile, a de-interleaver corresponding to the transmitting end is added between the likelihood ratio calculation module and the soft decoding module of the receiving end, and a block interleaver same as the transmitting end is added between the second channel coding module and the second medium modulation module.
Preferably, the signature sequence bsA pseudo-random 0-1 sequence is employed.
Preferably, the no-code detection module adopts a joint structured approximate message passing (JS-AMP) algorithm to realize the detection of the active device and the computation of the posterior probability of the medium modulation symbol sent by the active device.
Preferably, the no-code detection module adds a dispersion normalization operation to the activity factor when executing the JS-AMP algorithm.
Preferably, the receiving end is implemented asIterative procedure for adaptive successive interference cancellation using a defined set omega0、Ω1、Ω2、Ω3The realization specifically is that:
for the no-code detection algorithm module, defining the activity factor of the kth equipment as akE {0,1}, K ═ 1,2, …, K }, where K is the total number of media modulation devices at the transmitting end, and 0 and 1 respectively represent inactive and active; an estimated value of an activity factor for defining the output of the JS-AMP algorithm is
Figure BDA0002899732670000041
For the estimated active factor
Figure BDA0002899732670000042
Is obtained by dispersion standardization
Figure BDA0002899732670000043
The dispersion standardization operation specifically comprises the following steps:
Figure BDA0002899732670000044
the definitional symbols min (-) and max (-) denote the operations of taking the minimum and maximum values of the vector elements, respectively; will be provided with
Figure BDA0002899732670000045
Judging that the medium element is greater than 0.5 as active equipment, and recording the set of the active equipment as omega0(ii) a In subsequent iterations, the set of active devices Ω0Updating is not carried out, and the iterative process aims at reducing the error rate of active equipment;
define the set omega1Indicating a set of active devices that have not been interference canceled; on the first iteration, value Ω is assigned1＝Ω0Each subsequent iteration is from Ω1Subtracting the device number which is eliminated by interference until omega1Changing into an empty set;
define the set omega2Represents the set omega1With the greatest median activity factor
Figure BDA0002899732670000052
Number set of individual active devices, set omega2The active equipment in the system is subjected to decoding accuracy judgment in the iteration by a decoding accuracy judgment module;
Figure BDA0002899732670000054
is a set constant when Ω1The number of middle elements is less than
Figure BDA0002899732670000053
In time, let omega2＝Ω1；
Decoding accuracy judgment module comparison set omega2Decoded signature sequences for mid-active devices
Figure BDA0002899732670000051
With the true signature sequence bsHamming distance therebetween; for the devices with Hamming distance smaller than the preset value, the set of the active devices is recorded as omega3Will be omega3Sending to a second channel coding module, and matching omega by the second channel coding module and subsequent modules thereof3The device in (1) performs interference cancellation; the equipment with the Hamming distance larger than the preset value does not carry out subsequent operation; if there is no device with Hamming distance less than the preset value, i.e. Ω3If the data is an empty set, terminating iteration and directly outputting soft decoding data of the rest active devices;
the interference elimination step of the interference elimination module comprises the following steps: subtracting the set omega from the received signal3Updating the observation matrix formed by the channel state information from the set omega1Mid-subtraction of interference-cancelled omega3In part, will new Ω1And the observation matrix informs the non-coding detection algorithm module to carry out the next iteration.
Has the advantages that:
(1) by designing the data packet structure of the transmitting terminal, the invention can judge the decoding accuracy of the effective data at the receiving terminal according to the decoding accuracy of the characteristic sequence, thereby providing a basis for the subsequent self-adaptive serial interference elimination operation. Meanwhile, by designing an active device detection and medium modulation signal iteration decoder at a receiving end, the invention can adaptively select a small number of devices to perform serial interference elimination or not perform interference elimination based on the characteristic sequence in each iteration, thereby reducing error propagation of serial interference elimination, effectively improving the demodulation precision of the medium modulation signal and reducing the error rate.
(2) The invention adds the bit interleaving code before the medium modulation of the transmitting end to form the medium modulation mode of the bit interleaving code, and can effectively resist the channel space selective fading of the medium modulation signal.
(3) According to the method, the step of dispersion standardization (min-max standardization) is added to the estimated active factor in the joint structured approximate message passing (JS-AMP) algorithm, so that the detection performance of the active equipment of the original algorithm under the condition of low signal to noise ratio can be remarkably improved. (for JS-AMP algorithm, see the literature "translation name: Joint active device and data detection in massive machine type communication based on spatial modulation", author, English name and convention "L.Qiao and Z.Gao", "Joint active device and data detection for massive MTC reproduction on spatial modulation", "2020IEEE Wireless Communications and network interference reference kshos (WCNCW), Seoul, Korea (south)", 2020, pp.1-6. ").
Drawings
Fig. 1 is a schematic diagram of uplink unlicensed access of a typical massive media modulation device.
Fig. 2 is a flowchart of an implementation of the multiple access scheme of the massive media modulation device based on adaptive successive interference cancellation of the present invention, in which the media modulation module of the proposed bit interleaving coding and the adaptive successive interference cancellation module are highlighted.
FIG. 3 is a comparison graph of the performance evaluation of the ADER (Activity Detection Error Rate) of the JS-AMP algorithm before and after adding dispersion normalization (min-max normalization) according to the change of the signal-to-noise ratio.
Fig. 4 is a graph comparing SER (Symbol Error Rate) performance evaluation of different uplink unlicensed access transceiving schemes of a medium modulation device as a function of a signal-to-noise ratio.
Fig. 5 is a comparison graph of BER (Bit Error Rate) performance evaluation of the uplink unlicensed access transceiving scheme of different medium modulation devices as a function of signal-to-noise ratio.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
The invention provides a mass media modulation equipment multiple access system with self-adaptive serial interference elimination, which has the basic idea that a receiver can judge the decoding accuracy of equipment by utilizing a known characteristic sequence, further carries out interference elimination on the equipment with accurate decoding, and can improve the overall decoding accuracy of active equipment through multiple iterations. The introduction of the characteristic sequence can effectively reduce error propagation possibly caused by interference elimination under low signal-to-noise ratio. In addition, the transmitting end adopts a medium modulation mode added with bit interleaving, so that a space selective fading channel in the medium modulation symbol propagation can be effectively resisted, and the error rate is further reduced.
The invention is described in detail below by way of example with reference to the accompanying drawings.
The invention considers that a typical large-scale MIMO base station serves mass media to modulate uplink authorization-free data transmission of Internet of things equipment, as shown in figure 1. In the system, a receiving end adopts a typical all-digital architecture and has NrMassive MIMO with > 1 antennas, serving K medium modulation devices, with K at the same timea(K＞＞Ka) Several devices are transmitting uplink data, i.e. are active, each device using a single radio frequency link, a single antenna and NRFAnd the medium modulation is composed of a low-cost radio frequency mirror. Wherein the RF mirror of each medium modulation device has two controllable states of ON/OFF, so that NRFA radio frequency mirror can be formed
Figure BDA0002899732670000071
Combinations of species, also known as NtMirror Activation Patterns (MAPs), corresponding to NtA different channel implementation. Taking a single device as an example, assuming that M-ary quadrature amplitude modulation (M-QAM) is used, thenEach media modulation symbol may carry η log2M+NRFInformation of bits, log thereof2M bits carried by M-QAM symbols, NRF＝log2NtBit modulation at NtThe selection of different media modulation channels is referred to as media modulation space symbol. Without loss of generality, it is assumed that uplink data of active devices is transmitted by using a frame formed by adjacent J slots (J medium modulation symbols) as a basic unit, and frames and slots of K devices are perfectly synchronized. Therefore, without loss of generality, we take any data frame as an example, and the base station end is at j th of the data frame
Figure BDA0002899732670000072
Signals received in one time slot
Figure BDA0002899732670000073
Can be expressed as
Figure BDA0002899732670000074
Wherein the active factor akE {0,1} equals 1 indicating that the device is active, and equals 0 indicating that the device is inactive; the symbol of M-QAM of the kth device is denoted as sk,j；
Figure BDA0002899732670000075
Is NtMedium-modulated spatial symbols of dimension, where only one element is 1 and the other elements are 0, represent from NtSelecting one channel from different medium modulation channels;
Figure BDA0002899732670000076
represents the equivalent transmitted signal of the kth device;
Figure BDA0002899732670000077
representing a MIMO channel between the kth device and the base station;
Figure BDA0002899732670000078
representing additive white gaussian noise generated by the receiver;
Figure BDA0002899732670000079
a MIMO channel matrix representing the combination of K users;
Figure BDA00028997326700000710
representing the equivalent transmitted signal of the K users in combination.
Without loss of generality, we assume that channel estimation is already completed, channels between all K devices and the base station are estimated, and only the subsequent active device and medium modulation symbol joint detection steps are considered. The sparsity due to the number of active devices at a time being much smaller than the total number of devices, and the inherent structural sparsity of the medium modulation symbols, problem (1)
Figure BDA0002899732670000081
The recovery can be regarded as a single-vector observed sparse signal recovery problem, and a low-complexity receiver detection algorithm can be realized by utilizing and improving a compressed sensing method, such as a greedy algorithm or an approximate message passing-based algorithm. As the devices in one data frame have the same activity, J single-vector observation problems (1) in one data frame can be jointly considered into a multi-vector observation problem, and the detection accuracy of active users can be greatly improved.
The transmitting end comprises a data packet generating module, a channel coding module and a medium modulation module. The data packet generating module is used for generating a transmission data packet of each medium modulation device in a mass medium modulation device multiple access system; a characteristic sequence b known by a transmitting and receiving end is inserted into a transmitting data packets(ii) a The first channel coding module is used for carrying out channel coding on the sending data packet generated by the data packet generating module; and the first medium modulation module is used for performing medium modulation on the transmission data packet coded by the first channel coding module and transmitting the transmission data packet in a medium modulation symbol form. Inserting characteristic sequence b in transmitting data packetsIs aimed at receivingAnd comparing the decoded end, and judging whether to carry out interference elimination operation on corresponding equipment according to the accuracy. Thus, for the characteristic sequence bsAs long as it is known to both the transceiver, signature sequence bsMay be a pseudo-random 0-1 sequence.
In a preferred embodiment, a block interleaver is added between a channel coding module and a medium modulation module at a transmitting end, and the channel coding module, the block interleaver and the medium modulation module form a 'bit interleaving coded medium modulation' module; the width of the block interleaver is equal to the number of effective radiation patterns of the first medium modulation module, and the depth of the block interleaver is determined by the length of the encoded data packet, thereby effectively coping with the channel space selective fading of the medium modulation symbol.
The transmitting end is described in detail below. We consider a coded system where the transmitted signal for each data frame is generated by modulation of the channel coded bit stream through a bit interleaved coded medium, as shown in fig. 2. It can be seen that the transmitting end is composed of a data packet generating module and a bit interleaved encoded media modulation module. Wherein the data packet generation module generates a bit stream with length L, including LsLong signature sequences bsAnd LdThe long transmit data bits constitute a transmit data frame. Then, the binary data frame is subjected to a medium modulation module of bit interleaving coding, which comprises three steps of channel coding, bit interleaving and medium modulation, so as to form a transmitting signal. Assuming that the encoded data has L ' bits without loss of generality, the block interleaver adopts a block interleaver with width η and height J ═ L '/η (assuming without loss of generality that L ' can be divided by η), and the bit stream is read in column by column and read out row by row to complete bit-level interleaving; the medium modulation part modulates eta bits output by each line of the interleaver into a medium modulation symbol, including log2M bits modulated on M-QAM symbols, and NRFThe bits are modulated on the medium modulation space symbols. It can be seen that L-length bit streams for each active device are modulated into J medium modulation symbols, constituting J adjacent slots. KaAll the active devices adopt the transmission scheme and simultaneously carry out authorization-freeAnd transmitting the weighted uplink data (transmitting symbols).
At the base station, the receiving detector is an iterative detector that can be divided into eight modules, as shown in fig. 2, including: the device comprises a non-coding detection algorithm module, a likelihood ratio calculation module, a de-interleaving module, a soft decoding module, a decoding accuracy judgment module, a channel coding module, a block interleaver module and an interference elimination module. If the transmitting end has no block interleaver, the receiving detector has no deinterleaving module and no block interleaver module. In the following, we will use any one-time detection as an example to describe in detail the specific functions of each module and how the receiver performs iterative detection.
1. A no-code detection algorithm module: the module is used for recovering the number of the active transmitting equipment and the corresponding transmitting medium modulation symbol according to an observation matrix H formed by the received signal Y and the estimated channel state information. Note that in the first iteration, there is a received signal
Figure BDA0002899732670000091
And observation matrix
Figure BDA0002899732670000092
Both Y and H are continuously updated in subsequent iterations. Since this process is a typical sparse signal recovery problem, a compressed sensing algorithm may be employed.
In order to calculate the soft information of the Log Likelihood Ratio (LLR) in the next step, a JS-AMP algorithm improvement based on approximate message passing is adopted, but the module can also be other joint device detection and data demodulation algorithms which can output the soft information. The output of the JS-AMP algorithm here is the posterior probability q (x) of the medium modulation symbolsk,j|yj) To a
Figure BDA0002899732670000093
And an estimated value of an activity factor corresponding to each device
Figure BDA0002899732670000094
For the estimated active factor
Figure BDA0002899732670000095
Is obtained by dispersion standardization
Figure BDA0002899732670000096
Judging that the medium element is greater than 0.5 as active equipment, and recording the set of the active equipment as omega0. By the dispersion standardization operation, the separability of the active factors of the active devices and the active factors of the inactive devices is more obvious, and the error of the activity judgment can be effectively reduced under the condition of low signal to noise ratio. Specifically, dispersion normalization operates as follows:
Figure BDA0002899732670000101
the definitional symbols min (-) and max (-) denote the minimum and maximum operations, respectively. In subsequent iterations, the set of active devices is no longer updated, and the iterative process aims to reduce the bit error rate of the active devices.
Define the set omega1Representing the active set of devices for which interference cancellation has not yet been performed. On the first iteration, let Ω1＝Ω0Each subsequent iteration is from Ω1Subtracting the device number which is eliminated by interference until omega1Becoming an empty set.
Define the set omega2Represents the set omega1With the greatest median activity factor
Figure BDA00028997326700001015
Number set of individual active devices, set omega2The active device in (2) will make a decoding accuracy decision in this iteration. Empirically, the closer the JS-AMP algorithm gets to 1 the activity factor, indicating a higher decoding accuracy of the device, and thus the Ω2The obtaining of (c) may be based on the activity factor.
Figure BDA0002899732670000102
Is a constant and can be freely designed according to the actual system. When omega is higher than1The number of middle elements is less than
Figure BDA0002899732670000103
In time, let omega2＝Ω1。
2. Likelihood ratio calculation module: for calculating likelihood ratio information for each data bit based on the a posteriori probabilities of the medium modulation symbols.
The module obtains the posterior probability q (x) of the medium modulation symbol according to the previous modulek,j|yj) The set Ω can be calculated2LLR information of the bit stream of the corresponding active device. For medium modulation symbol xk,j，
Figure BDA0002899732670000104
Its corresponding medium modulation space symbol bit
Figure BDA0002899732670000105
And corresponding M-QAM symbol bits
Figure BDA0002899732670000106
Can be expressed as LLR
Figure BDA0002899732670000107
Figure BDA0002899732670000108
Wherein, belong to the set
Figure BDA0002899732670000109
Or
Figure BDA00028997326700001010
X ofk,jSuch that the medium modulates the spatial symbol bits
Figure BDA00028997326700001011
Is 1 or 0; belong to a set
Figure BDA00028997326700001012
Or
Figure BDA00028997326700001013
X ofk,jMaking M-QAM symbol bits
Figure BDA00028997326700001014
Is 1 or 0.
3. A de-interleaving module: the module is a deinterleaver corresponding to a block interleaver of the transmitting end. Set omega in any one2For example, the LLR information stream of L 'length obtained by the previous module corresponds to the bit stream of L' length after encoding at the transmitting end. The de-interleaving module also adopts a structure with the width eta and the height J ═ L'/eta, the information flow is read in line by line and read out column by column, and the de-interleaving of the LLR information flow is completed.
4. A soft decoding module: the device is used for carrying out soft decoding on the likelihood ratio information of the active device according to the channel coding mode of the transmitting end, and the soft decoding result comprises the decoding result of the characteristic sequence
Figure BDA0002899732670000111
5. A decoding accuracy decision module: the module calculates the characteristic sequence after the active device decodes
Figure BDA0002899732670000112
With the true signature sequence bsIf the hamming distance is smaller than a preset value, the effective data of the active device is considered to be used for interference elimination, and then a subsequent module can be executed for the active device, otherwise, a subsequent interference elimination step is not executed, and finally, the self-adaptive serial interference elimination is realized.
In particular, the purpose of this module is to further judge the set Ω2The decoding accuracy of the device in (1), and then decide whether to perform interference cancellation and set omega2Which devices perform interference cancellation. First compare the set omega2Hamming distance between decoded signature sequence and the true signature sequence of the active device. For devices with Hamming distances less than a preset value, these settings will be set as followsThe medium modulation symbol reconstruction and interference elimination are carried out, and the set of the active devices is recorded as omega3. And the equipment with the Hamming distance larger than the preset value does not carry out subsequent operation. If no equipment with the Hamming distance smaller than the preset value exists, namely: omega3And if the data is an empty set, terminating the iteration and directly outputting the soft decoding data of the rest active devices. Note that the hamming distance preset value for the decision can be designed according to the actual system.
6. A channel coding module: the method is used for encoding the demodulation data of the active equipment to be subjected to interference elimination by adopting the same channel encoding mode as the first channel encoding module of the transmitting terminal.
7. The medium modulation module: and the medium modulation module is used for performing medium modulation on the coded data obtained by the second channel coding module by adopting the same medium modulation parameters as the first medium modulation module at the transmitting end to obtain a medium modulation symbol.
At each iteration, suppose Ω3If not, the step is executed. Specifically, the module uses the same channel coding mode as the transmitting end, firstly, the demodulation data of the active device to be subjected to interference cancellation is coded, and the coded bits are subjected to medium modulation symbol reconstruction through the same interleaver and the medium modulation module with the same parameters as the transmitting end.
8. An interference elimination module: and the medium modulation symbol generated by the second medium modulation module is used for eliminating interference on active equipment judged by the decoding accuracy judgment module, updating a received signal matrix and an observation matrix of the no-code detection algorithm module respectively, and returning to the no-code detection algorithm module for iteration.
At each iteration, suppose Ω3If not, the step is executed. The main purpose of this step is to eliminate omega from the received signal3To the corresponding part of the device. In the next iteration, the number of the support sets of the sparse signals is reduced, and the observation dimensionality is unchanged, so that the detection performance of the medium modulation signals is improved. In particular, the set Ω is subtracted from the received signal Y3The signal components corresponding to the devices are updated, and the observation matrix H is updated from the set omega1Middling is interfered with and eliminatedOmega of division3And (4) partial. If updated omega1The received signal Y and the observation matrix H that are not updated for the empty set will be fed back to step 1 to start the next iterative decoding.
The present invention discloses a multiple access scheme of mass medium modulation equipment for adaptive serial interference cancellation.
In order to illustrate the superiority of the improved JS-AMP algorithm based on dispersion normalization (min-max normalization) proposed by the present invention over the original JS-AMP algorithm in active device detection, the effect of the present invention is illustrated with fig. 3. Considering that the total number of the medium modulation devices is 500, wherein the number of the active devices is 50, the channel obeys a Rayleigh MIMO channel, the devices adopt 4QAM modulation and carry 2bit information, the number of the mirror surfaces of the medium modulation is 2, the 2bit spatial information can be coded, considering that one data frame comprises 12 time slots, and the maximum iteration number of the JS-AMP algorithm is 15. ADER is defined as: (false alarm device count + missed detection device count) ÷ potential device total count. As can be seen from fig. 3, the JS-AMP algorithm modified with min-max normalization significantly improves the ADER performance for signal-to-noise ratios below 3 dB.
In order to illustrate the advantages of the adaptive serial interference cancellation method based on the signature sequence and the media modulation method of the bit interleaving coding at the transmitting end in improving the decoding accuracy, fig. 4 and 5 are used to illustrate the effects of the present invention. The specific contents of the comparison algorithm illustrated in fig. 4 and 5 are shown in table 1. It is noted that the coding scheme 3 has no signature sequence, and the Serial Interference Cancellation (SIC) at the receiving end is based on the size of the active factor, and the active factor is larger for each cancellation
Figure BDA0002899732670000121
(it is assumed here that
Figure BDA0002899732670000122
) And (4) corresponding signals of the devices until the data of all the active devices are demodulated. In order to ensure the fairness of comparison, all the schemes adopt a data packet with the length of 120 bits, wherein if a characteristic sequence exists, the characteristic sequence is a random 0-1 sequence with the length of 20 bits, and the characteristic sequence is adoptedThe code rate is 1/3, the tail code is 12bit Turbo coding, the length of the coded data packet is 372 bit. Considering that the total number of the medium modulation devices is 500, wherein the number of active devices is 50, the channel complies with a rayleigh MIMO channel, the device adopts 4QAM modulation and carries 2bit information, the number of mirror surfaces of the medium modulation is 2, and 2bit spatial information can be encoded, so that the encoded data packet can be modulated on continuous 93 medium modulation symbols to form a data frame (93 adjacent time slots). Furthermore, we define SER as: (number of medium modulation symbols of missed detection equipment + number of error medium modulation symbols of correct detection equipment) ÷ total number of medium modulation symbols of active users, wherein detection error of one medium modulation symbol indicates error of a corresponding QAM symbol or space symbol; the BER is defined as: (total number of bits of undetected devices + number of error bits of correct detection devices) ÷ total number of transmission bits of active users. And the preset Hamming distance value of the demodulation accuracy judgment module is set to be 0.
Table 1 corresponds to the scheme illustrated in the diagrams of FIGS. 4 and 5
Figure BDA0002899732670000131
Specifically, as can be seen from fig. 4, the SER performance of the no-coding scheme is the worst of all schemes, and the coding scheme 1 greatly improves the SER performance of the system by using Turbo channel coding. It can be seen that the SER performance of coding scheme 2 is further improved compared to coding scheme 1, which illustrates that the block interleaving module can effectively combat channel space-selective fading. The SER performance of coding scheme 3 has a significant advantage over coding scheme 2 at high signal-to-noise ratio (SNR >2dB), indicating that the receiver side successive interference cancellation can significantly improve the decoding performance. However, at low signal-to-noise ratios (SNR < -2.5dB), the SER performance of coding scheme 3 deteriorates, worse than that of coding scheme 1, due to error propagation for successive interference cancellation. It can be seen that the overall advantage of the proposed scheme over all other comparison schemes indicates that the introduction of the signature sequence can significantly reduce the error propagation that may be present in successive interference cancellation. Fig. 5 compares the BER performance of the proposed scheme with other comparative schemes as a function of SNR, and a conclusion similar to fig. 4 can be drawn that the proposed scheme has better BER performance.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A mass medium modulation equipment multiple access system of self-adaptive serial interference elimination comprises a transmitting end and a receiving end; the method is characterized in that:
the transmitting terminal comprises a data packet generating module, a first channel coding module and a first medium modulating module; wherein the content of the first and second substances,
the data packet generating module is used for generating a transmission data packet of equipment in a multi-access system of the mass media modulation equipment; a characteristic sequence b known by a transmitting and receiving end is inserted into a transmitting data packets；
The first channel coding module is used for carrying out channel coding on the sending data packet generated by the data packet generating module;
the first medium modulation module is used for performing medium modulation on the transmission data packet coded by the first channel coding module and transmitting the transmission data packet in a medium modulation symbol form;
the receiving end designs a medium modulation signal iterative decoder, and part of equipment is adaptively selected to eliminate serial interference based on a decoded characteristic sequence in each iteration; the receiving end comprises a non-coding detection algorithm module, a likelihood ratio calculation module, a soft decoding module, a decoding accuracy judgment module, a second channel coding module, a second medium modulation module and an interference elimination module;
the non-coding detection algorithm module is used for detecting the active equipment according to an observation matrix formed by the received signal and the estimated channel state information, and simultaneously obtaining the posterior probability of the medium modulation symbol sent by the active equipment;
the likelihood ratio calculation module is used for calculating the likelihood ratio information of each data bit according to the posterior probability of the medium modulation symbol;
a soft decoding module for performing soft decoding on the likelihood ratio information of the active device according to the channel coding mode of the transmitting terminal, wherein the soft decoding result comprises the decoding result of the characteristic sequence
Figure FDA0002899732660000011
A decoding accuracy judgment module for calculating the decoding result of the characteristic sequence
Figure FDA0002899732660000012
With the true signature sequence bsIf the hamming distance is smaller than the preset value, the effective data of the active device is considered to be used for interference elimination, and then the second channel coding module, the second medium modulation module and the interference elimination module are informed to execute interference elimination work; otherwise, the subsequent interference elimination step is not executed, and finally the self-adaptive serial interference elimination is realized;
the second channel coding module is used for coding the demodulation data of the active equipment to be subjected to interference elimination by adopting the same channel coding mode as the first channel coding module at the transmitting end;
the second medium modulation module is used for performing medium modulation on the coded data obtained by the second channel coding module by adopting the same medium modulation parameters as the first medium modulation module at the transmitting end to obtain a medium modulation symbol;
and the interference elimination module is used for eliminating interference on the active equipment judged by the decoding accuracy judgment module by utilizing the medium modulation symbol generated by the second medium modulation module, respectively updating the received signal and the observation matrix of the no-code detection algorithm module, and returning to the no-code detection algorithm module for iteration.
2. The system of claim 1, wherein a block interleaver is added between the first channel coding module and the first medium modulation module at the transmitting end, and the channel coding module, the block interleaver and the first medium modulation module form a "bit interleaved coded medium modulation" module; the width of the block interleaver is equal to the number of effective radiation patterns of the first medium modulation module, and the depth of the block interleaver is determined by the length of the coded data packet, so that the channel space selective fading of the medium modulation symbol can be effectively coped with;
meanwhile, a de-interleaver corresponding to the transmitting end is added between the likelihood ratio calculation module and the soft decoding module of the receiving end, and a block interleaver same as the transmitting end is added between the second channel coding module and the second medium modulation module.
3. The system of claim 1, wherein the sequence of features bsA pseudo-random 0-1 sequence is employed.
4. The system of claim 1, wherein the codeless detection algorithm module employs a joint structured approximate messaging (JS-AMP) algorithm to achieve a posteriori probability computation of active device detection and media modulation symbols sent by active devices.
5. The system of claim 4, wherein the no-code detection algorithm module, when executing the JS-AMP algorithm, adds a dispersion normalization operation to the activity factor.
6. The system of claim 4, wherein the receiving end implements an iterative process of adaptive successive interference cancellation using a defined set Ω0、Ω1、Ω2、Ω3The realization specifically is that:
for the no-code detection algorithm module, defining the activity factor of the kth equipment as akE {0,1}, K ═ 1,2, …, K }, where K is the total number of media modulation devices at the transmitting end, and 0 and 1 respectively represent inactive and active; an estimated value of an activity factor for defining the output of the JS-AMP algorithm is
Figure FDA0002899732660000031
For the estimated active factor
Figure FDA0002899732660000032
Is obtained by dispersion standardization
Figure FDA0002899732660000033
The dispersion standardization operation specifically comprises the following steps:
Figure FDA0002899732660000034
the definitional symbols min (-) and max (-) denote the operations of taking the minimum and maximum values of the vector elements, respectively; will be provided with
Figure FDA0002899732660000035
Judging that the medium element is greater than 0.5 as active equipment, and recording the set of the active equipment as omega0(ii) a In subsequent iterations, the set of active devices Ω0Updating is not carried out, and the iterative process aims at reducing the error rate of active equipment;
define the set omega1Indicating a set of active devices that have not been interference canceled; on the first iteration, value Ω is assigned1＝Ω0Each subsequent iteration is from Ω1Subtracting the device number which is eliminated by interference until omega1Changing into an empty set;
define the set omega2Represents the set omega1With the greatest median activity factor
Figure FDA0002899732660000036
Number set of individual active devices, set omega2The active equipment in the system is subjected to decoding accuracy judgment in the iteration by a decoding accuracy judgment module;
Figure FDA0002899732660000037
is a set constant when Ω1The number of middle elements is less than
Figure FDA0002899732660000038
In time, let omega2＝Ω1；
Decoding accuracy judgment module comparison set omega2Decoded signature sequences for mid-active devices
Figure FDA0002899732660000039
With the true signature sequence bsHamming distance therebetween; for the devices with Hamming distance smaller than the preset value, the set of the active devices is recorded as omega3Will be omega3Sending to a second channel coding module, and matching omega by the second channel coding module and subsequent modules thereof3The device in (1) performs interference cancellation; the equipment with the Hamming distance larger than the preset value does not carry out subsequent operation; if there is no device with Hamming distance less than the preset value, i.e. Ω3If the data is an empty set, terminating iteration and directly outputting soft decoding data of the rest active devices;
the interference elimination step of the interference elimination module comprises the following steps: subtracting the set omega from the received signal3Updating the observation matrix formed by the channel state information from the set omega1Mid-subtraction of interference-cancelled omega3In part, will new Ω1And the observation matrix informs the non-coding detection algorithm module to carry out the next iteration.
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