CN103259758B - A kind of ofdm communication system based on companding and method - Google Patents

Abstract

The present invention proposes an OFDM communication system and method based on compression and expansion. The bit stream input in the transmitting device forms an OFDM signal after baseband mapping and IFFT. The amplified signal is mapped to the sending unit for transmission; the receiving device converts the received time-domain signal through serial-to-parallel conversion, performs the first FFT transformation on the time-domain signal into a frequency-domain signal, obtains channel information through channel estimation, and analyzes the received The channel equalization is performed on the frequency domain signal, and the equalized signal is converted to the time domain by IFFT, then extended and transformed, and then sent to the FFT module for demodulation and decoding, and finally the required bit stream is obtained by baseband inverse mapping. The communication system provided by the present application can effectively overcome the constellation diagram diffusion problem of the traditional companded OFDM communication system under multi-path channels, and can effectively reduce the EVM value and the bit error rate.

Description

An OFDM communication system and method based on compression and expansion

technical field

The present invention relates to the field of communication technology, in particular to a communication system and method of OFDM (Orthogonal Frequency Multiplexing) technology.

Background technique

The emergence of Orthogonal Frequency Division Multiplexing (OFDM) technology has solved the frequency selective fading of wireless channels well, and it is considered to be one of the core technologies of the fourth generation of mobile communication 4G. One of the main disadvantages of the OFDM system is that it has a large peak-to-average ratio (PAPR), which directly affects the operating cost and efficiency of the entire system. When the signal exceeds the dynamic range of the power amplifier and cannot be put in linearly, it will cause serious signal distortion and destroy the orthogonality between the subcarriers. Causes in-band signal distortion and out-of-band spectrum dispersion.

At present, many methods to reduce the peak-to-average ratio of OFDM signals have been proposed, including clipping method, partial transmission sequence (PTS) method, selective mapping (SLM) method, interleaving (Interleaving) method, coding (coding) method , Companding method, Active Constellation method, etc. These methods provide effective solutions for reducing the peak-to-average ratio of OFDM signals at different costs. For example, the PTS method and the SLM method will increase the complexity of the system and generate redundant information; the limiting method and the companding method will cause spectrum distortion; the coding method will reduce the information transmission rate and so on.

FIG. 1 is a schematic structural diagram of an existing OFDM communication system. In the existing OFDM communication system structure, the signal flow at the receiving end is as follows: the received signal is first subjected to expansion transformation, and then transformed to the frequency domain through the FFT module. Such a method achieves better performance in the additive Gaussian white noise channel. However, under multi-path channels, since the received signal is the delayed superposition of each path of the transmitted signal, the traditional extended transformation algorithm will cause serious distortion of the signal and reduce the receiving performance of the entire system. The invention proposes a new signal flow and a processing method to solve the problem of constellation diagram diffusion caused by the companding and spreading method in the multipath channel environment.

Contents of the invention

In view of the above-mentioned defects of the prior art, the present invention proposes an OFDM communication system and method to solve the problem of constellation diagram diffusion in a multi-path channel environment caused by the compression and expansion method of the existing OFDM communication system,

The technical solution of the present invention to solve the above-mentioned technical problems is to propose an OFDM communication system based on companding and expansion, which is characterized in that it includes: a wired or wireless communication channel, a sending device and a receiving device, and the sending device includes a peak-average suppressing OFDM signal Ratio compression transformation module, the compression transformation module compresses and transforms the signal and sends it to the receiving device through a wired or wireless communication channel, and the receiving device restores the OFDM signal at the sending end according to the received compressed signal.

The receiving device comprises an FFT unit for the first time, a channel equalization unit, an IFFT unit, an extension transformation unit, an FFT unit for the second time, a parallel-to-serial conversion unit and a decoding unit; The frequency domain signal is obtained by FFT transformation, and the channel equalization unit performs channel equalization processing on the frequency domain signal and sends it to the IFFT unit; the IFFT unit performs IFFT processing on the signal after channel equalization processing and converts it to the time domain, and the expansion transformation unit The time-domain signal transformed by IFFT is extended and transformed and sent to the second FFT unit, and the time-domain signal is transformed into a frequency-domain signal by the second FFT unit, and sent to the parallel-serial conversion unit, and the parallel-serial conversion unit passes the frequency The domain signal is converted from parallel to serial, and sent to the decoding unit for decoding to obtain OFDM signal. The compression transformation module in the sending device calculates the time domain sequence {x _n } of the OFDM signal, obtains the average amplitude v of the OFDM signal in the time domain, determines the companding coefficient μ, and calls the formula: The OFDM signal is compressed and transformed, and the compressed and transformed signal is obtained as S(n), where v is the average amplitude of the OFDM signal x _n . The extended transformation unit in the receiving device is used for the time-domain signal Perform expansion transformation, according to the formula: The expanded and transformed signal y(n) is obtained, where μ is the compression coefficient, and v is the average amplitude of the OFDM signal in the time domain.

The present invention also proposes an OFDM communication method based on compression and expansion. The sending device compresses and transforms the signal and sends it to the receiving device through a wired or wireless communication channel. After receiving the compressed signal, the receiving device performs conversion processing to restore the OFDM signal at the sending end; The transformation processing of the receiving device includes that the first FFT unit in the receiving device performs the first FFT transformation on the received compressed signal to obtain the frequency domain signal and sends it to the channel equalization unit, and the channel equalization unit performs frequency domain optimization on the frequency domain signal. channel equalization processing; the IFFT unit performs IFFT conversion to the time domain through the signal after the channel equalization unit; The second FFT transformation is performed to obtain the second frequency domain signal, and the parallel-serial conversion unit performs parallel-serial conversion on the second frequency domain signal, and sends it to the decoding unit for decoding.

In the OFDM communication system provided by the present invention, FFT transformation is performed on the received signal at the receiving end, and after channel equalization in the frequency domain is completed, the signal after channel equalization is converted into a time domain signal by IFFT for down-spread transformation, and the extended-transformed The signal is sent to the FFT module, and finally the final bit stream information is obtained through baseband demodulation and decoding. It can effectively reduce the diffusion problem of the compression and expansion algorithm constellation diagram caused by the multipath channel, reduce the bit error rate, and improve the system reliability.

The present invention also has the following advantages:

(a) Do not change the signal processing process at the sending end;

(b) The receiving end preferentially performs FFT transformation, equalization and IFFT transformation, which effectively eliminates the influence of multipath effects on the signal;

(c) The method proposed by the present invention is not fixed for the method of companding transformation, so a flexible companding algorithm can be used to compress and expand the signal, rather than being limited to the traditional μ-rate compression algorithm adopted in the present invention ;

Description of drawings

FIG. 1 is a schematic structural diagram of an existing OFDM communication system;

Fig. 2 is a schematic structural diagram of an OFDM communication system provided by an embodiment of the present invention.

detailed description

The present invention proposes an OFDM communication system based on compression and expansion, including: a wired or wireless communication channel, a sending device, and a receiving device. ; The receiving device restores the signal of the sending end according to the received signal.

The receiving device comprises an FFT unit for the first time, a channel equalization unit, an IFFT unit, an extension transformation unit, a second FFT unit, a parallel-to-serial conversion unit and a decoding unit; For the first FFT transformation, the channel equalization unit performs channel equalization processing in the frequency domain on the frequency domain signal after the first FFT unit; the IFFT unit performs IFFT conversion to the time domain on the signal after the channel equalization unit; The transformation unit performs extended transformation processing on the signal after passing through the IFFT unit; the second FFT unit performs a second FFT transformation on the signal after passing through the extended transformation unit; The domain signal is subjected to parallel-serial conversion; the decoding unit decodes the signal after passing through the parallel-serial conversion unit.

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

An embodiment of the present invention provides an OFDM communication system based on compression and expansion. FIG. 2 is a schematic structural diagram of the system. Wherein, the sending device 21 includes: an encoding unit 211, a modulating unit 212, a serial-to-parallel conversion unit 213, an IFFT unit 214, and a compression transform unit 215, and the receiving device 22 includes a first-time FFT unit 221, a channel equalization unit 222, and an IFFT unit 223, An extension transformation unit 224 , a second FFT unit 225 , a parallel-to-serial conversion unit 226 , a demodulation unit 227 , and a decoding unit 228 .

In this embodiment, the transmitting end completes the signal transmission according to the existing OFDM signal generation process based on the compressed PAPR suppression method.

(1) The encoding unit 211 encodes the input bit stream;

(2) Modulation unit 212 modulates the encoded signal, here adopts quadrature phase shift keying (QPSK) modulation to obtain serial modulation signal X _S ;

(3) The serial-to-parallel unit 213 performs serial-to-parallel conversion on X _S to obtain a parallel modulation signal X _k , where k=0,1,...,N-1, N represents the number of subcarriers of the OFDM signal;

(4) The IFFT unit 214 performs IFFT transformation on X _k to obtain a time-domain signal x _n , where n=0,1,...,N-1;

(5) The compression transformation unit 215 calculates the time domain sequence {x _n } of the OFDM signal to obtain the average amplitude v of the OFDM signal in the time domain; according to the requirements of the OFDM system, determine the companding coefficient μ; for the OFDM signal Perform compression transformation to obtain the signal after companding transformation as S(n), and the companding transformation method can be compressed by μ rate, and can be compressed by the following compression formula:

$\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; vx</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; |</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; )</span>$

Where v is the average amplitude of OFDM signal x _n , and μ is the compression factor; the compressed signal S(n) is converted to parallel and sent to the power amplifier, and the high-power signal generated by the amplifier is transmitted to the radio frequency circuit for signal transmission. The signal can also be compressed in other ways known to those skilled in the art.

The receiving method proposed by the present invention is adopted at the receiving end.

(1) The time domain signal received by the receiving end is Through the first FFT unit 221, the Convert to frequency domain signal k=0,1,...,N-1, N is the number of subcarriers of OFDM signal;

(2) Channel equalization unit 222 pairs Do channel equalization to get the equalized signal

(3) IFFT unit 223 pair signal Perform IFFT transformation to obtain the time domain signal

(4) The extended transformation unit 224 obtains the time-domain signal Carry out extended transformation, the transformation formula is as follows:

$\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; vy</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; E.</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; |</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \}</span>$

in is the time domain signal, v is The average amplitude of , μ is the compression factor;

(5) The second FFT unit 225 performs FFT transformation on the expanded and transformed signal y(n) to obtain a frequency domain sequence;

(6) The parallel-to-serial unit 226 performs parallel-to-serial conversion on the sequence, and then performs QPSK modulation through the demodulation unit 227, and finally the decoding unit 228 decodes the demodulated information to restore the data bit stream at the sending end (OFDM Signal).

By comparing and analyzing the existing OFDM communication system based on companding and the OFDM communication system proposed by the present invention, it can be found that the present invention can improve the problem of constellation diagram diffusion in a multipath environment, and the implementation process is simple.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Accordingly, the present invention shall not be limited to the Examples shown herein.

Claims (6)

1. the ofdm communication system based on companding, it is characterized in that, comprise: wired or wireless communication channel, dispensing device and receiving system, described dispensing device comprises the compressed transform module suppressing ofdm signal peak-to-average force ratio, compressed transform module is sent to receiving system by wired or wireless communication channel after carrying out compressed transform to signal, receiving system restores transmitting terminal ofdm signal according to the compressed signal received, described receiving system comprises first time FFT unit, channel equalization unit, IFFT unit, transform expansion unit, second time FFT unit, parallel serial conversion unit and decoding unit, first time, FFT unit carried out first time FFT conversion acquisition frequency-region signal to the compressed signal received, and channel equalization unit sends into IFFT unit to the channel equalization that this frequency-region signal does on frequency domain, IFFT unit carries out IFFT process to the signal after channel equalization and is transformed into time domain, transform expansion unit is carried out transform expansion to the time-domain signal converted by IFFT and sends into second time FFT unit, this time-domain signal is transformed to frequency-region signal through second time FFT unit, send into parallel serial conversion unit, parallel serial conversion unit does parallel-serial conversion to this frequency-region signal, sends into decoding unit and carries out decoding acquisition ofdm signal.

2. system according to claim 1, is characterized in that, in dispensing device, compressed transform module is to the time domain sequences { x of ofdm signal _ncalculate, draw the average amplitude v of ofdm signal in time domain, determine companding coefficient μ, call formula: $S\left(n\right)=C\left\{x_n\right\}=\frac{{\mathrm{vx}}_n}{ln(1+u)\left|x_n\right|}ln(1+\frac{u}{v}|x_n\left|\right)$ Carry out compressed transform to ofdm signal, obtaining the signal after compressed transform is S (n), and wherein v is ofdm signal x _naverage amplitude.

3. system according to claim 1, is characterized in that, in receiving system, transform expansion unit is to time-domain signal carry out transform expansion, according to formula: obtain signal y (n) after transform expansion, wherein, μ is the compressed coefficient, and v is the average amplitude of ofdm signal in time domain.

4. the ofdm communication method based on companding, it is characterized in that, dispensing device is carried out compressed transform to signal and is sent to receiving system by wired or wireless communication channel, and receiving system receives the ofdm signal that the laggard line translation process of compressed signal restores transmitting terminal; Described receiving system carries out conversion process and comprises, in receiving system, FFT unit carries out first time FFT conversion acquisition frequency-region signal feeding channel equalization unit to the compressed signal received for the first time, and channel equalization unit does the channel equalization on frequency domain to this frequency-region signal; IFFT unit is transformed into time domain by carrying out IFFT by the signal after channel equalization unit, transform expansion unit carries out transform expansion to by the time-domain signal after IFFT unit, second time FFT unit converts acquisition second frequency-region signal to being second time FFT by the signal after transform expansion, parallel serial conversion unit does parallel-serial conversion to the second frequency-region signal, sends into decoding unit and carries out decoding.

5. method according to claim 4, is characterized in that, in dispensing device, compressed transform unit is to the time domain sequences { x of ofdm signal _ncalculate, draw the average amplitude v of ofdm signal in time domain, determine companding coefficient μ, call formula: $S\left(n\right)=C\left\{x_n\right\}=\frac{{\mathrm{vx}}_n}{ln(1+u)\left|x_n\right|}ln(1+\frac{u}{v}|x_n\left|\right)$ Carry out compressed transform to ofdm signal, obtaining the signal after companding transform is S (n), and wherein v is ofdm signal x _naverage amplitude.

6. method according to claim 4, is characterized in that, transform expansion unit is to obtaining time-domain signal carry out transform expansion, according to formula: obtain signal y (n) after transform expansion, wherein, μ is the compressed coefficient, and v is the average amplitude of ofdm signal in time domain.