CN108712234B - Frequency offset detection method under interleaved multiple access technology combined with coordinate descent method - Google Patents

Frequency offset detection method under interleaved multiple access technology combined with coordinate descent method Download PDF

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CN108712234B
CN108712234B CN201810501444.1A CN201810501444A CN108712234B CN 108712234 B CN108712234 B CN 108712234B CN 201810501444 A CN201810501444 A CN 201810501444A CN 108712234 B CN108712234 B CN 108712234B
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何燃燃
肖悦
康洁思
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University of Electronic Science and Technology of China
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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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/391—Modelling the propagation channel
    • 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
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    • 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
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    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/2628—Inverse Fourier transform modulators, e.g. inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators
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    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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    • H04L27/26—Systems using multi-frequency codes
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Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a frequency offset detection method based on an interleaving multiple access technology. Because an orthogonal frequency division multiplexing (OFDM-IDMA) system based on interleaved multiple access suffers from multiple frequency offsets caused by doppler shift or different crystal oscillator accuracies of the transmitting and receiving terminals, a conventional frequency offset suppression method in the OFDM system is not suitable for the OFDM-IDMA system, and thus a multi-frequency offset suppression method in the OFDM-IDMA system needs to be researched. The method of the invention is that a coordinate reduction (CDM) frequency offset detection algorithm is adopted to restrain the frequency offset in the OFDM-IDMA system. And after the frequency offset detection is carried out, the frequency offset detection is promoted.

Description

Frequency offset detection method under interleaved multiple access technology combined with coordinate descent method
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a frequency offset detection method based on an interleaving multiple access technology. The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) -based interlace-Division Multiple Access (IDMA) and Coordinate reduction (CDM) Frequency offset detection algorithm.
Background
Multiple access technology is the basis for forming wireless communication networks, and is also one of the more recent indicators of wireless communication. Multiple access techniques refer to how all the resources (time, frequency, and space) of the system are allocated to all users in a cell, thereby enabling multiple users to access a common channel for simultaneous communication. In order to meet the high-speed increasing wireless network application requirement, support mass equipment connection, and achieve higher frequency spectrum efficiency, faster data rate and larger channel capacity, a novel multiple access technology becomes one of the hot spots of the next generation mobile communication system 5G network research.
The Interleave Division Multiplexing (IDM) technology adopts different interleavers to distinguish different data streams, and has been proposed as a Multiple Access method, namely, the basic idea of Interleave-Division Multiple Access (IDMA) IDMA is to allocate a unique interleaver to each user, and distinguish users by different interleavers, unlike the traditional Code-Division Multiple Access (CDMA) technology which adopts spreading codes to distinguish users. When the interleavers for all users are generated randomly and independently, the interleaved chip sequences are almost uncorrelated. IDMA inherits many advantages of CDMA such as diversity against fading, interference cancellation between cells, dynamic channel sharing, etc. Meanwhile, since the IDMA uses the entire spread spectrum bandwidth for channel coding of a low code rate, it is possible to maximize coding gain and obtain higher spectral efficiency than CDMA. In addition, IDMA performs better than CDMA and has a low complexity iterative detection method. Receivers of IDMA systems typically employ low complexity iterative multi-user detection methods, such as a conventional Elementary Signal Estimator (ESE).
Orthogonal Frequency Division Multiplexing (OFDM) technology plays an important role in fourth generation mobile communication systems. Because the OFDM technology has higher frequency spectrum utilization rate and the capability of overcoming frequency selective fading. In order to reduce the complexity of detection in multipath channels and overcome frequency selective fading, IDMA may be combined with OFDM, an orthogonal frequency division multiplexing (OFDM-IDMA) technique based on interleaved multiple access to achieve greater throughput and reliability.
Because the OFDM-IDMA system suffers from a plurality of frequency offsets caused by different doppler shifts or different crystal oscillator accuracies of the transmitting and receiving terminals, the conventional frequency offset suppression method in the OFDM system is not suitable for the OFDM-IDMA system, and therefore, a multi-frequency offset suppression method in the OFDM-IDMA system needs to be researched. The technical scheme of the invention provides a CDM frequency offset detection algorithm based on an OFDM-IDMA technology.
Disclosure of Invention
The invention aims to provide a frequency offset detection algorithm suitable for an OFDM-IDMA system.
The transmitter structure of the uplink OFDM-IDMA system is shown in fig. 1, which includes K users. For the firstk users, first data sequence dkCarrying out low-rate coding, including two steps of FEC coding and spread spectrum; then the coded codeword sequence ckInto the user-specific chip-level interleaver pikGenerating an interleaved chip sequence xkThereby completing the processing of the IDMA portion in the transmitter. The signal is then transformed into the time domain by Inverse Fast Fourier Transform (IFFT) and insertion of a cyclic prefix, and the time domain signal of the kth user can be represented as
Figure BDA0001670471480000021
Wherein N represents the total number of subcarriers, NgIndicating the length of the cyclic prefix.
The receiver structure of the OFDM-IDMA system is shown in fig. 2. The received signal is first subjected to a Fast Fourier Transform (FFT) to Transform the time domain received signal to the frequency domain, and then iterative multi-user signal detection is performed.
The time domain received signals from all users can be represented as,
Figure BDA0001670471480000022
wherein,
Figure BDA0001670471480000023
represents a convolution operation, hk(u) represents the temporal impulse response of the kth user at the time of the u. w is a mean of 0 and a variance of σ2White Gaussian Noise (AWGN).
In an actual OFDM-IDMA system, due to the difference of crystal oscillator precision of the transmitting and receiving terminals and the influence of doppler shift, the receiver will be influenced by carrier frequency deviation from different users, as shown in fig. 3, after passing through a multipath fading channel, the time domain received signal influenced by multiple frequency offset becomes:
Figure BDA0001670471480000024
wherein epsilonkRepresents the normalized frequency offset value, h, of the k-th userjkIndicating the channel time domain impulse response between the jth receiving antenna and the kth user. w is anIs AWGN.
Receiving a signal r in the time domainj,CFO(u) removal of CP and then conversion to the frequency domain, which can be expressed as
Figure BDA0001670471480000031
Wherein Si(k) The frequency offset factor representing the kth user on the nth subcarrier can be expressed by the following formula:
Figure BDA0001670471480000032
the following will propose a detection method for suppressing multiple frequency offsets in an uplink OFDM-IDMA system. Firstly, respectively adopting a single-user frequency offset correction method to carry out coarse synchronization on each user in a time domain so as to inhibit the self frequency offset of each user; then, the received signal of each user is transformed to the frequency domain through FFT, finally, an iterative interference elimination method is adopted in the frequency domain to restrain the residual frequency offset of other users, and the signal of each user is detected.
After the frequency offset compensation value, the signal on the nth subcarrier of the jth receiving antenna may be represented as:
Figure BDA0001670471480000033
wherein
Figure BDA0001670471480000034
The residual frequency offset factor after CFO compensation is expressed by the following formula:
Figure BDA0001670471480000035
the technical scheme of the invention is as follows:
the CDM detector is organically combined with the IDMA system, if M-PSK or M-QAM modulation is adopted, B represents the number of receiving antennas, U represents the number of users, and the information of the mu user can be represented as
Figure BDA0001670471480000036
The CDM algorithm then comprises the following steps:
s1, setting IDMA system parameters, including assigning the number of users U and the number of antennas B, setting the number of constellation points adopted by each user as M and setting the maximum iteration times tmax；
S2, initialization: we first assume that the probability at iteration 1 is
Figure BDA0001670471480000041
Wherein
Figure BDA0001670471480000042
Let us assume that the amplitude of each user signal is initialized to 1 and the phase is initialized to 0, i.e.
Figure BDA0001670471480000043
Figure BDA0001670471480000044
S3, entering message iteration updating, judging whether t exceeds the maximum iteration number set in the step S1, if t is less than or equal to tmaxThen the flow proceeds to step S4, if t>tmaxIf yes, the iterative update of the message is terminated and the step S8 is proceeded, and whether mu exceeds the number of users set in the step S1 is judged, if mu is less than or equal to U, the step S4 is proceeded, if mu is less than or equal to U>U, terminating the updating of the user message and entering step S7;
s4, updating the amplitude and the phase of the user, specifically;
s41, calculating frequency offset residual factor
Figure BDA0001670471480000045
Wherein epsilonμIndicating the frequency offset value of the mu user, N is the data length of each user, and the optimal compensation value epsilon0Is composed of
Figure BDA0001670471480000046
S42, updating the amplitude and phase of the mu user signal by the following two formulas
Figure BDA0001670471480000047
Figure BDA0001670471480000051
Wherein HbμRepresents the channel matrix H ∈ CB×UThe (b, μ) th element of (a), SbμDenotes S ∈ CB×UThe (b, μ) th element of (a), ybRepresents the signal vector y ∈ C received by the receiving endB×1The b-th element of (1).
S5, estimating the signal of the mu user by the following formula:
Figure BDA0001670471480000052
s6, setting the user number mu as mu +1, returning to S2 until the signal updating of U users is completed
S7, setting t to t +1, returning to S2 until the iteration loop is completed
And S8, completing multi-user detection by using the updated probability distribution, and outputting soft decision to the user.
Drawings
FIG. 1 is a basic model of an OFDM-IDMA system transmitter;
FIG. 2 is a basic model of an OFDM-IDMA system receiver;
FIG. 3 is a diagram of an OFDM-IDMA system architecture affected by multiple frequency offsets;
FIG. 4 is a simulation diagram of frequency offset suppression comparison of a single-transmission four-reception 2-user OFDM-based CDM detection method using QPSK modulation;
Detailed Description
The technical scheme of the invention is described in detail in the following with reference to the accompanying drawings and embodiments:
in this embodiment, a Matlab simulation platform is used for the experiment.
The object of the present example is achieved by the steps of:
s1, setting IDMA simulation parameters, wherein the system parameters in the example are as follows: the number of users U is 2, the number of receiving antennas B is 4, and the number of iterations tmaxQPSK modulation is adopted, that is, M is 4, turbo code of 1/6 is adopted for encoding, and the simulation channel is TDL-C channel;
s2, generating initial data of two groups of users, respectively and sequentially coding and interleaving, carrying out QPSK modulation and then carrying out fast inverse Fourier transform;
s3, after passing through a channel, adding frequency offset and Gaussian white noise to the signal, then carrying out fast Fourier transform and sending the signal to a receiving end;
s4, at the receiving end, after the data on the 4-path receiving antenna is combined in the maximum ratio, the CDM-based frequency offset detection, the de-interleaving, the de-spreading and the decoding are carried out to complete the iterative loop;
and S5, comparing the detected recovery data with the initial data and counting to obtain the BER.
As can be seen from fig. 4, the simulation result shows that the performance of the OFDM-IDMA-CDM system is reduced by about 5dB due to the existence of the frequency offset, and the performance of the system is improved after the frequency offset compensation detection is performed at the detection end.

Claims (1)

1. A frequency deviation detection method under the interleaving multiple access technology combined with a coordinate descent method is characterized by comprising the following steps:
s1, setting IDMA system parameters:
M-PSK or M-QAM is adopted for modulation, the number of receiving antennas is B, the number of users is U, and the information of the mu user is represented as
Figure FDA0002811178850000011
The user number U and the antenna number B are assigned, the number of constellation points adopted by each user is set to be M, and the maximum iteration number t is setmax；
S2, initialization: assume that the probability at iteration 1 is
Figure FDA0002811178850000017
Wherein
Figure FDA0002811178850000012
i＝1,...,U；
Figure FDA0002811178850000013
While assuming that the amplitude of each user signal is initialized to 1 and the phase is initialized to 0, i.e.
Figure FDA0002811178850000014
S3, entering message iteration updating, judging whether t exceeds the maximum iteration number set in the step S1, if t is less than or equal to tmaxThen the flow proceeds to step S4, if t>tmaxIf yes, the iterative update of the message is terminated and the step S8 is proceeded, and whether mu exceeds the number of users set in the step S1 is judged, if mu is less than or equal to U, the step S4 is proceeded, if mu is less than or equal to U>U, terminating the updating of the user message and entering step S7;
s4, updating the amplitude and the phase of the user, specifically:
s41, calculating frequency offset residual factor
Figure FDA0002811178850000015
Where n denotes the nth subcarrier,. epsilonμIs shown asFrequency offset values of mu users, N being the data length of each user, optimum compensation value epsilon0Is composed of
Figure FDA0002811178850000016
S42, updating the amplitude and phase of the μ -th user signal using the following two equations:
Figure FDA0002811178850000021
Figure FDA0002811178850000022
wherein HbμRepresents the channel matrix H ∈ CB×UThe (b, μ) th element of (a), SbμDenotes S ∈ CB×UElement (b, mu) of (a), ybRepresents the signal vector y ∈ C received by the receiving endB×1The b-th element of (1);
s5, estimating the signal of the mu user by the following formula:
Figure FDA0002811178850000023
s6, setting the user number mu as mu +1, and returning to S2 until the signal updating of U users is completed;
s7, setting t as t +1, and returning to S2 until the iteration loop is completed;
and S8, completing multi-user detection by using the updated signals of the U users, and outputting soft decision to the users.
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