CN101282321B - Transmission method capable of reducing self-adaption frequency-select block of back information - Google Patents

Abstract

The invention provides a self-adapting frequency selection blocking transmission method of reducing feedback information, comprising: (1) channels are grouped; (2) frequency is selected initially; (3) an inchoation processes signal mapping according to an adopted modulation mode, and gains a frequency domain form of awaiting sending information according to sub-channel group marker information, and converts back time domain and sends time domain signals; (4) the inchoation processes frequency domain equalization for the received signals according to the sub-channel group marker information, and converts back the time domain signals and finishes judgment; (5) the inchoation processes channel estimation or prediction to gain renewed channel state information, and determines if the sub-channel group marker information need to be renewed according to a self-adapting judgment rule. The invention better solves a problem of excessive the feedback information in the premise of guaranteeing system performance. A simulation result shows that the invention can guarantee that the bit error rate of the system is not more than 5*10<-3>, and the transmission rate of the system is not lower than 7.5Mbps, and the feedback information rate of reverse channels is not over than 100Kbps.

Description

An adaptive frequency-selective block transmission method to reduce backhaul information

technical field

The invention relates to a broadband digital communication transmission method and belongs to the technical field of broadband wireless communication.

Background technique

Communication technology has developed rapidly in recent decades, especially since the 1990s, and has had a profound impact on people's daily life and the development of the national economy. The future communication technology is developing towards broadband and high speed, so many broadband digital transmission technologies have received widespread attention, such as Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM: Orthogonal Frequency Division Multiplexing) and frequency domain balanced -FDE: Single Carrier with Frequency Domain Equalization) are two broadband digital transmission technologies that are valued by people. Become a supporting technology, such as: IEEE802.11a in Wireless Local Area Network (WLAN: Wireless Local Area Network); IEEE802.16 in Wireless Metropolitan Area Network (WMAN: Wireless Metropolitan Area Network); various high-speed digital users in wired data transmission Digital Subscriber Line (xDSL: Digital Subscriber Line) is a standard based on OFDM technology. SC-FDE has not been adopted by these standards, but it is jointly proposed as a physical layer transmission technology together with OFDM in IEEE802.16.

1. Information transmission method in time-varying channel

First a brief introduction to time-varying channels. In the mobile environment, the relative movement of the transmitter and receiver and the diversity of the ground make the mobile wireless channel often be modeled as a non-stationary stochastic time-varying linear system. This results in a Doppler shift of the arriving signal, the Doppler shift of the nth arriving signal is:

f _n = f _max cos α _n

Among them, f _max is the maximum Doppler frequency corresponding to the moving speed v, f _max = vf _c /c, f _c is the carrier frequency, α _n is the angle of arrival, which is defined as the angle between the signal arrival direction and the moving direction, and c is speed of light.

Due to the Doppler effect, the spectrum of the transmitted signal is broadened in frequency during transmission. This phenomenon is called frequency dispersion or Doppler spread. changes with the passage of time, resulting in time-selective fading. The degree of frequency scatter depends on the maximum Doppler frequency. In the time domain, the Doppler effect means that the impulse response of the channel is time-varying.

Since the effect of the Doppler effect is manifested by the time-varying characteristics of the channel, it is assumed that the duration of the signal is relatively short. In this relatively short period of time, if the characteristics of the channel do not change significantly, the time selectivity of the channel will Not obvious. Conversely, if the characteristics of the channel change significantly over the duration of the signal, the signal will be distorted. At present, the carrier frequency used in broadband wireless communication is getting higher and higher, and the mobility of wireless communication is further enhanced, which makes time-varying channel information transmission more and more concerned in broadband wireless communication.

2. Block transmission system with frequency selection

Both OFDM and SC-FDE belong to block transmission technology, and the system formed by them is called block transmission system.

The impact of the frequency selective channel on the block transmission system is mainly manifested in: the multipath propagation or delay spread of the signal will cause frequency selective fading, and the propagation of the signal in the frequency selective fading channel will cause some spectral components of the signal to be attenuated If the signal is very low, in the case of deep fading points in the channel, the signal will be more affected, so that the signal will be distorted, resulting in inter-symbol interference, which will affect the system performance.

In many important applications of OFDM and SC-FDE (such as WLAN, WMAN, xDSL, etc.), there is a reverse channel. At this time, the originator of the block transmission system can use the channel state information returned by the reverse channel and some adaptive techniques to improve overall system performance and efficiency.

The Chinese patent application with publication number CN1617530 discloses "A Single-Carrier Block Transmission Method with Frequency Selection Mode", and the block transmission method with frequency selection mode includes the following steps:

(1) After the sending and receiving parties establish communication, the receiving end finds M available sub-channels from the estimated N channel state information, and marks the available channels and forbidden channels respectively to form sub-channel marking information, and pass the reverse channel Send subchannel label information back to the originator;

(2) After receiving the sub-channel marking information sent back by the receiving end, the transmitting end changes the signal spectrum according to the information, and uses the available sub-channel to transmit the signal;

(3) After receiving the signal, the receiving end transforms the signal into the frequency domain, and then selects the signal on the available sub-channel according to the sub-channel label information, and then performs equalization and judgment on the selected signal, and finally obtains the transmitted data.

3. Block transmission system with adaptive frequency selection

In the broadband wireless mobile environment, the time-varying characteristics of the channel are the most important constraints on the system's bit error performance. For time-varying environments, the impact of time-selective fading must also be considered.

The Chinese patent application with publication number CN1777161 discloses an "Adaptive Frequency Selection and Blocking Transmission Method in Mobile Broadband Channel" for the time-varying characteristics of mobile channels, which can better solve frequency selectivity and The problem of time-selective fading. The implementation steps of the adaptive frequency selection block transmission method are as follows:

(1) Initial frequency selection. After the two parties establish communication, the receiving end obtains the channel state information of the current channel according to the agreed method; the receiving end selects according to the frequency domain sub-channel gain level according to the system error performance requirements and the current channel state information. The first M subchannels with high gain are available subchannels, and are marked with one bit information "0" or "1" to form subchannel label information, and these subchannel label information are sent to the sender through the reverse channel;

(2) The transmitting end performs symbol mapping according to the modulation method adopted to form a frame of M symbols to be transmitted, and performs orthogonal transformation on these M symbols to obtain M transform domain symbols, and converts the above M symbols according to the subchannel label information The transformation domain symbol is expanded into an N-dimensional vector, and the frequency domain form of the signal to be transmitted is obtained, and the time domain signal is transformed back to the time domain. When M is not an integer power of 2, the orthogonal transformation can be implemented in blocks, and different blocks can be with the same or different orthogonal transformations;

(3) The receiving end transforms the received sampling signal into the frequency domain, performs frequency domain equalization on the received signal according to the sub-channel label information, selects M useful signals on the available sub-channel, performs orthogonal inverse transformation, and transforms back to time domain signal and complete the judgment to obtain the information data. When M is not an integer power of 2, if the original orthogonal transformation is implemented in blocks, the orthogonal inverse transformation should also be implemented in blocks. Different blocks are based on their respective orthogonal transformations. Transform using the same or different orthogonal inverse transform;

(4) The receiving end performs channel estimation or prediction to obtain updated channel state information, and judges whether it is necessary to update the sub-channel marking information according to the adaptive judgment rule. If it needs to be updated, the receiving end updates the sub-channel marking information according to the requirements of the system error performance , and feed back to the originating end through the reverse channel; when sending a new frame of data, the originating end always performs signal transformation according to the latest received sub-channel label information.

4. Problems existing in the existing technology

In broadband wireless mobile communication, due to the influence of the time-varying characteristics of the channel, adaptive frequency-selective block transmission methods (including "Adaptive frequency-selective block transmission method in mobile broadband channels" disclosed by CN1777161) will be constantly updated Sub-channel status information causes a large amount of frequently returned information, which will lead to the problem that the amount of returned information is too large.

Contents of the invention

The present invention aims at the problem that the amount of returned information is too large in the existing adaptive frequency selection and block transmission method in the existing mobile broadband channel, and provides an adaptive frequency selection and block transmission method that can reduce the return information, which can be used in broadband mobile Under the premise of ensuring the system performance in the communication, it is better to solve the problem of excessive amount of returned information.

The self-adaptive frequency selection and block transmission method for reducing backhaul information of the present invention comprises the following steps:

(1) Channel grouping. After the sending and receiving parties establish communication, the receiving end obtains the channel state information of the current channel according to the agreed method, and then the receiving end determines the sub-channel grouping according to the agreed sub-channel grouping strategy and channel state information. For N frequency domains Sub-channels are grouped and bound to obtain T sub-channel groups, and K-bit sub-channel grouping strategy information is formed at the same time;

(2) Initial frequency selection, calculate the channel gain parameters of each sub-channel group, and then select the gain parameters according to the channel gain parameters of each sub-channel group according to the system bit error performance requirements and the sub-channel grouping strategy information of the current channel state The highest first U subchannel groups are available subchannel groups, and are marked with one bit information "0" or "1" to form subchannel group label information, and the subchannel group label information and subchannel grouping strategy information are sent to The sending end, wherein, the U available subchannel groups include M available subchannels;

(3) The transmitting end performs symbol mapping according to the modulation method adopted to form a frame of M symbols to be transmitted, and performs orthogonal transformation on these M symbols to obtain M transform domain symbols, and converts the above M symbols according to the sub-channel group label information Transform domain symbols are expanded into N-dimensional vectors to obtain the frequency domain form of the signal to be transmitted, transform back to the time domain and transmit the time domain signal, when M is not an integer power of 2, the orthogonal transformation is implemented in blocks, and different blocks use the same or different orthogonal transformations;

(4) The receiving end transforms the received sampling signal into the frequency domain, performs frequency domain equalization on the received signal according to the sub-channel group label information, selects M useful signals on the available sub-channels, performs orthogonal inverse transformation, and transforms back to The time-domain signal is judged and the information data is obtained. When M is not an integer power of 2, if the original orthogonal transformation is implemented in blocks, the orthogonal inverse transformation should also be implemented in blocks. Different blocks are based on their respective orthogonal transformations. The alternating transformation adopts the same or different orthogonal inverse transformation;

(5) The receiving end performs channel estimation or prediction to obtain updated channel state information, and judges whether it is necessary to update the sub-channel group label information according to the adaptive judgment rule. If it needs to be updated, the receiving end first updates the sub-channel grouping strategy information, and then Update subchannel group marking information according to subchannel grouping strategy information and system error performance requirements, and feed back to the originating end through the reverse channel; when sending a new frame of data, the originating end always receives the latest subchannel group Signature information and grouping policy information are signal transformed.

The specific implementation method of each step is as follows:

The method of obtaining the channel state information of the current channel in step (1) can be realized by different methods, for example, the channel state information can be obtained by using the channel estimation method based on the training frame, and the channel state information can also be estimated by inserting pilot symbols.

The sub-channel grouping strategy can adopt several different implementation methods according to the agreement of the sending and receiving parties, and these different grouping strategy schemes are respectively represented by K-bit information. For example, several adjacent frequency-domain sub-channels can be bound as a sub-channel group, different sub-channel groups use the same channel group length, and different channel group lengths are used as corresponding grouping strategies. The channel packet length can adopt several fixed packet lengths, and can also be determined according to the estimation of the time-domain delay spread. The longer the delay spread, the smaller the packet length; vice versa. The channel delay spread estimation method can be obtained by transforming the channel state information in the frequency domain to the time domain, or refer to relevant literature, which will not be discussed here.

The implementation method of the initial frequency selection in step (2):

For example, let the vector representing subchannel group label information be:

B={B(k), k=0, 1..., T-1},

B(k)=1 indicates that the kth subchannel group is an available subchannel group, B(k)=0 indicates that the kth subchannel group is an unavailable subchannel group, and the sending end can map according to the subchannel group label information and grouping strategy information Get all original subchannel label information. Record the labels of all U available subchannel groups as k _i , i=0, 1, ..., U-1, that is, B(k _i ) = 1, i = 0, 1, ..., U-1.

The channel gain parameter of the subchannel group is a parameter representing the overall channel gain of a subchannel group; for example, it may be the average channel gain of the subchannel group, or the overall equalized signal-to-noise ratio of the subchannel group, etc. . The calculation method of the channel gain parameter of the sub-channel group is as follows:

(a) The average channel gain of the sub-channel group is the average obtained after summing the gains of each sub-channel in the sub-channel group.

(b) The overall equalized signal-to-noise ratio of the sub-channel groups; suppose each sub-channel group contains P sub-channels, and the channel gains of the jth, j=0, 1..., T-1 sub-channel groups are respectively H(j ^p ) , p=0, 1..., P-1, taking zero-forcing equalization as an example to introduce the calculation of SNR after overall equalization of sub-channel groups, the influence of synchronization error is not considered here:

Due to the cyclic prefix, in the discrete time domain, the linear convolution of the signal and the channel impulse response can be transformed into a product in the discrete frequency domain. Let S′(j ^p ), W(j ^p ), R′(j ^p ) be the transmitted signal in the frequency domain of the sub-channel group, the noise and the received signal after removing the CP, where W(j ^p ) is the Gaussian noise, but:

R'(j ^p )=S'(j ^p )H(j ^p )+W(j ^p ), p=0,1,...,P-1

After zero-forcing equalization:

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; S</span>}}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

The overall equalized signal-to-noise ratio of the subchannel group:

${{\mathrm{<span\; class="notranslate">\; SNR</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}}}_{\mathrm{<span\; class="notranslate">\; eq</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

in, ${\mathrm{\&sigma;}}_{\mathrm{no}}^2=\mathrm{E.}\left({\left|W\left(j^p\right)\right|}^2\right),p=\mathrm{0,1},\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;,P-1$ is the noise power on each subchannel.

When selecting the available sub-channel group, first estimate the received signal-to-noise ratio and determine the modulation method according to the received signal-to-noise ratio. The modulation method can also be agreed by the two parties in advance. Under the premise of the code performance requirements, the number of available sub-channel groups is selected as much as possible. The bit error performance of the system is determined by the SNR of the system after equalization. The lowest SNR after equalization to achieve this bit error performance is called the expected SNR after equalization, and a certain margin is left for the SNR after equalization. .

Wherein, the calculation method of the receiving signal-to-noise ratio refers to relevant literature. Only take zero-forcing equalization as an example to briefly introduce the calculation of SNR after equalization, and the influence of synchronization error is not considered here:

Due to the cyclic prefix, in the discrete time domain, the linear convolution of the signal and the channel impulse response can be transformed into a product in the discrete frequency domain. Let S'(k), H(k), W(k), R'(k), k=0, 1, ..., N-1 respectively be the frequency domain transmission signal, channel complex gain, noise and after removing CP The received signal of , where W(k), k=0, 1, ..., N-1 is Gaussian noise, then:

R'(k)=S'(k)H(k)+W(k), k=0,1,...,N-1

After zero-forcing equalization:

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; S</span>}}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

The signal-to-noise ratio after equalization is:

${\mathrm{<span\; class="notranslate">\; SNR</span>}}_{\mathrm{<span\; class="notranslate">\; eq</span>}}<span\; class="notranslate">\; =</span>\frac{\frac{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}{\frac{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

in, ${\mathrm{\&sigma;}}_{\mathrm{no}}^2=\mathrm{E.}\left({\left|W\left(k\right)\right|}^2\right),k=\mathrm{0,1},\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;,N-1$ is the power of noise on each sub-channel; D={D(k), k=0, 1..., N-1} is all sub-channel label information vectors corresponding to vector B of sub-channel group label information.

In step (3), the specific method of expanding the M transform domain symbols into N-dimensional vectors according to the subchannel group label information is:

After receiving the sub-channel group marking information sent back by the receiving end, the sending end first maps all sub-channel marking information according to the agreed grouping strategy and the received channel grouping strategy information. The specific method is: the sub-channel group marking information is For a sub-channel group of 1, all corresponding sub-channel flag information is all 1; for a sub-channel group with sub-channel group flag information of 0, all corresponding sub-channel flag information is all 0. Assuming that all subchannel label information vectors corresponding to vector B representing subchannel group label information are:

D={D(k), k=0, 1..., N-1},

D(k)=1 represents that the kth sub-channel is an available sub-channel, D(k)=0 represents that the k-th sub-channel is an unavailable sub-channel, and marks all M available sub-channels as k _i , i=0, 1, . . . , M−1, that is, D(k _i )=1, i=0, 1, . . . , M−1.

Only M available sub-channels are used to transmit signals at the originating end, so M-block transmission system symbols s(n) in one frame, n=0, 1,..., M-1, are M-point orthogonally transformed into the transform domain :

S=Fs

Among them, F is the M-point orthogonal transformation matrix, s={s(n), n=0, 1...M-1} is the M block transmission system time-domain symbols, S={S(i), i= 0, 1..., M−1} are M transform domain symbols.

Expand M transform domain symbols S={S(i), i=0, 1...M-1} into N-dimensional vectors corresponding to D={D(k), k=0, 1...N-1} S'={S'(k), k=0, 1...N-1}, the process is as follows:

S'={S'(k), k=0, 1...N-1}'s k _i component S'(k _i ), the corresponding D(k _i )=1, place S(i), i =0, 1,..., M-1, for example, S'(k _i )=S(i), i=0, 1,..., M-1 can be set, and the remaining components are set to zero or filled with some non- information data.

Then do the inverse discrete Fourier transform (hereinafter referred to as IDFT: Inverse Discrete Fourier Transform) of N points to S'(k), k=0, 1, ..., N-1, and can pass the inverse fast Fourier transform (hereinafter referred to as IFFT: Inverse FastFourier Transform) algorithm implementation:

${\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="e\; j"\; filenames="S2008100166139E00011.png"\; state="\{\{state\}\}">e</figure-callout></span><figure-callout\; id="2"\; label="e\; j"\; filenames="S2008100166139E00011.png"\; state="\{\{state\}\}">\; </figure-callout>}}^{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

It becomes a time-domain signal. When oversampling, the number of IFFT points must be greater than N, and the high-frequency part is set to zero. After the D/A conversion is performed on the time-domain signal, it can be sent out after carrier modulation.

The specific implementation method of selecting the signal on the available sub-channel according to the sub-channel group label information in the (4) step is:

Same as the sending end, at the receiving end, the sub-channel group label information is first mapped into all sub-channel label information according to the grouping strategy information, and the corresponding all sub-channel label information vectors are D={D(k), k=0, 1...,N-1}.

Suppose the time-domain discrete signal received by the receiving end and removed from the CP is:

${\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

Do N-point FFT on it:

${\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="S2008100166139E00011.png"\; state="\{\{state\}\}">j</figure-callout></span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; nk</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

and:

R'(k)=S'(k)H(k)+W(k), k=0,1,...,N-1

In this way, signals R(i) on M available sub-channels can be selected according to all sub-channel label information, i=0, 1, ..., M-1

R(i)=R'(k _i ), where D(k _i )=1, i=0,1,...,M-1

Use the channel state information of the available sub-channels in the estimated channel state information to equalize the selected signal; one of the following three equalization methods can be selected:

1. Zero-forcing equilibrium;

2. Minimum mean square error equalization;

3. Mixed equalization, that is, some sub-channels are equalized by zero-forcing, while other sub-channels are equalized by minimum mean square error. Taking zero-forcing equalization as an example, the equalized signal is:

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; S</span>}}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

The equalized signal is transformed back to the time domain by M-point orthogonal inverse transformation:

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; S</span>}}}^{<span\; class="notranslate">\; \&prime;</span>}$

where F ^H is the conjugate transpose of F, which is the inverse transformation matrix of F.

The method of obtaining channel state information in step (5) can be realized by different methods, for example, the method of training frame plus decision feedback tracking or the method of decision feedback tracking plus pilot symbols can be used, channel prediction and channel blind estimation can also be used method etc.

There are many adaptive criteria for judging whether frequency reselection is required according to system bit error performance requirements, for example:

(a) Calculate the current equalized signal-to-noise ratio, record it as the actual equalized signal-to-noise ratio, make the difference with the expected equalized signal-to-noise ratio, set the upper and lower limits for this difference, if the obtained difference is in Between the set upper limit and lower limit, keep the current sub-channel group label information unchanged; if the obtained difference exceeds the upper limit or lower limit, re-select the frequency; this adaptive criterion can ensure that the bit error performance of the system is within the required In the range.

(b) If all channel state information can be obtained, that is, channel state information including available sub-channels and unused sub-channels; assuming that the noise power is constant, calculate the current equalized signal-to-noise ratio and record it as the actual equalized signal-to-noise ratio ratio; select the subchannel group that maximizes the SNR after equalization from all the subchannels after the channel state information is updated, and the number of subchannels is the number of currently available subchannels, and record the maximum SNR after equalization as the optimal SNR after equalization; make a difference between the actual SNR after equalization and the optimal SNR after equalization, and set upper and lower limits for the difference, if the obtained difference is between the set upper limit and lower limit During the period, keep the current sub-channel group label information unchanged; if the obtained difference exceeds the upper limit or lower limit, re-select the frequency. This adaptive criterion can also ensure that the bit error performance of the system is within the required range.

If frequency selection needs to be re-selected, the receiving end first updates the sub-channel grouping strategy information. The method is: the receiving end judges whether it is necessary to update the K-bit sub-channel grouping strategy information according to the estimation of channel time-domain delay expansion, and then The longer the extension, the smaller the packet length, and vice versa. The channel delay spread estimation method can be obtained by transforming the channel state information in the frequency domain to the time domain, or refer to relevant literature, which will not be discussed here.

Through the description of the above steps, a new system can be constructed, but it is necessary to explain the parameters that affect the bit error performance and spectral efficiency of the system:

1. Determination of the number of available sub-channel groups

The number of available subchannel groups U directly affects the number of available subchannels M, so the number of available subchannel groups is an important parameter that affects the performance of the new system. Looking at the above schemes, only the available sub-channels are used to transmit useful information, so there is a problem of how to determine the number of available sub-channels. For different channel types and different time-varying channels, this value is not a fixed value. According to different channel conditions, taking into account the spectrum efficiency and performance of the system, the ratio of the selected number of available sub-channels M to the total number of sub-channels N is between 5% and 100%.

2. Perform block orthogonal transformation on the signals on the available sub-channels

For most of the orthogonal transformation operations, there is a fast algorithm when the number of points is an integer power of 2, so when the number of orthogonal transformation points is not an integer power of 2, the block method can be used to improve the calculation efficiency.

The method is to divide an orthogonal transformation operation with a large number of points but not an integer power of 2 into several orthogonal transformation operations with a relatively small number of points; at most one of these orthogonal transformation operations with a small number of points is not an integer power of 2, But the number of points is very small, and the remaining ones are integer powers of 2, that is, block orthogonal transformation. There are many block methods. It is recommended to follow the following principles:

a. For blocks with a length greater than or equal to 16, the length must be an integer power of 2;

b. There is at most one block whose length is less than 16;

c. It is not recommended to use blocks with a length less than 4;

The same processing is done for the orthogonal inverse transform, and the operation efficiency of the system is improved after such block processing.

The present invention better solves the problem of excessive amount of feedback information on the premise of ensuring system performance. As can be seen from the simulation results provided in the embodiment, for a signal sampling rate of 10MHz, a single-antenna system with a radio frequency bandwidth of no more than 12MHz, the sum Doppler frequency of IMT 2000 mobile channel A reaches 100Hz-300Hz, and the channel grouping length 8. Under the condition that the average receiving signal-to-noise ratio is 13dB, the method proposed by the present invention can ensure that the bit error rate of the system is not higher than 5×10 ^-3 , the transmission rate of the system is not lower than 7.5Mbps, and the reverse channel The return information rate does not exceed 100Kbps. From the current literature, there is no published literature that can achieve such a result under the same conditions.

Description of drawings

Accompanying drawing is the system block diagram that realizes the method proposed by the present invention.

In the figure: 1. Source module, 2. Symbol mapping module, 3. FFT module (M point), 4. Signal spectrum transformation module, 5. IFFT module (N point), 6. Cyclic prefix (CP) module, 7. D/A module, 8. Intermediate frequency and radio frequency modulation module, 9. Channel, 10. Radio frequency and intermediate frequency demodulation module, 11. A/D module, 12. CP removal module, 13. FFT module (N points), 14. Signal spectrum inverse transformation module, 15. Equalization module, 16. IFFT module (M point), 17. Judgment and symbol inverse mapping module, 18. Channel estimation or prediction module, 19. Adaptive frequency selection judgment module, 20. Frequency selection (sub-channel group) module, 21, channel label information mapping module, 22, reverse channel, 23, synchronization module

Detailed ways

Example

The orthogonal transform used in the embodiment is an M-point discrete Fourier transform, and the corresponding orthogonal inverse transform is an M-point inverse discrete Fourier transform. The embodiment does not perform block processing on the M-point DFT and IDFT. The channel grouping method adopted in the embodiment is to bind adjacent frequency-domain sub-channels, and different sub-channel groups contain the same packet length; in the embodiment, the channel model does not change, so the estimation of channel time-domain delay extension is not considered, Only the results of fixed packet lengths are given, wherein the number of channel grouping policy information bits is 2 bits, where 00, 01, 10, and 11 represent four different channel grouping lengths of 2, 4, 8, and 16, respectively. The simulation results of the embodiment The channel grouping strategy information adopted in is 10, that is, the channel grouping length is 8. The channel gain parameter of the sub-channel group in the embodiment is the average channel gain of the sub-channel group.

Accompanying drawing has provided the system block diagram realizing the proposed method of the present invention, and each module effect is as follows:

Source module 1: a general module that generates data to be transmitted. According to the result sent back by the reverse channel 21 and the number of modulation systems used, data with a length corresponding to the selected number of available sub-channels M is generated.

Symbol mapping module 2: a general module, which maps the data generated by the source to the corresponding points of the constellation diagram according to the modulation method adopted.

M-point FFT transformation module 3: a general module, which transforms the M mapped signals of each frame into the frequency domain to obtain M-point frequency domain signals of the signal.

Signal spectrum transformation module 4: a unique module of this system, according to all the sub-channel label information obtained by the receiving end through the channel label information mapping module 21, place the M-point frequency domain signal output by module 3 into the spectrum points corresponding to M available sub-channels , and disable the sub-channels to set the corresponding spectrum points to zero, or fill in non-information data, to obtain a frequency-domain signal of an N-point block transmission system in a frame. This module needs to be programmed according to the detailed implementation method of step (3) in the summary of the invention, and is implemented by a general-purpose digital signal processing chip.

N-point IFFT module 5: a general module, which transforms the newly obtained frequency domain signal into the time domain.

Add CP module 6: a general module, adding a cyclic prefix to each frame of data obtained.

D/A module 7: general-purpose module, which converts digital signals into analog signals.

IF and RF modulation module 8: General module, if the system is used in a wireless environment, the signal needs to be modulated by RF to be sent to the antenna for transmission. Sometimes it is necessary to modulate the signal to the intermediate frequency for intermediate frequency amplification, then perform radio frequency modulation, and finally send the modulated signal to the antenna for transmission.

Channel 9: Universal module, broadband mobile channel for transmitting signals.

Radio frequency and intermediate frequency demodulation module 10: a general module, in a wireless environment, moves the spectrum of the signal received by the receiving antenna from radio frequency or intermediate frequency to low frequency. Before demodulation, it is necessary to use frequency synchronization data to correct the frequency deviation caused in the signal transmission process.

A/D module 11: a general module, which converts the demodulated analog signal into a digital signal. The A/D needs to sample the analog signal, and the crystal oscillator that provides the clock signal needs to have the same frequency as the crystal oscillator of the D/A module of the transmitter, otherwise it will cause a sampling rate error. Therefore, the sampling rate must be synchronized before the A/D.

Remove CP module 12: general module, and remove the cyclic prefix. At this time, there is a problem of judging when a frame of data starts, so timing synchronization is required before going to the CP.

N-point FFT module 13: a general module, transforming the CP-removed signal into the frequency domain.

Signal spectrum inverse transformation module 14: a unique module of this system, according to all the sub-channel label information sent by the channel label information mapping module 21, find out the frequency domain signals of M points carried by the available sub-channels in the received signal. This module needs to be programmed according to the detailed implementation method of step (4) in the summary of the invention, and is implemented by a general-purpose digital signal processing chip.

Equalization module 15 : a general module, which uses the channel state information sent by the channel estimation or prediction module 18 to equalize the signal selected by the signal spectrum inverse transformation module 14 . The equalization method can choose one of the following three equalization methods: zero-forcing equalization, minimum mean square error equalization, and mixed mode equalization.

M-point IFFT transformation module 16: a general module, transforming the M frequency domain signals of the equalized signal into the time domain.

Judgment and symbol inverse mapping module 17: a general module, which completes the judgment of the time-domain signal according to the modulation method adopted by the system.

Channel estimation or prediction module 18: a general module for acquiring channel state information. Different methods can be used to obtain channel state information, such as channel prediction, channel estimation method based on auxiliary data, decision feedback channel tracking method, etc. The embodiment provides the simulation results of two channel state acquisition methods, the two channel state acquisition methods are training frame plus decision feedback tracking method and decision feedback tracking plus pilot symbol method. The two methods are briefly described below:

(a) The method of training frame plus decision feedback tracking is to first send the training frame to estimate the channel, and the following data frames reconstruct the symbols after the decision according to the result of the decision:

根据发端采用的调制方式进行符号映射，得到重构后的符号仍然记为

利用M点正交变换将重构后的

变换到变换域得到

按照说明书详细步骤(3)介绍的方法，将扩张成一个N维向量，记为

这就是根据判决结果重构的频域符号，利用重构的频域符号跟踪信道的方法是：Assume that the received signal discrete time domain is r'(n), (n=0, 1, ..., N-1), transform it into the frequency domain to obtain R'(k), (k = 0, 1, ... , N-1), the time-domain symbol after the data frame decision is

Symbol mapping is performed according to the modulation method adopted by the transmitting end, and the reconstructed symbols are still recorded as

Using the M-point orthogonal transformation, the reconstructed

Transform into the transform domain to get

According to the method described in the detailed step (3) of the manual, the Expand into an N-dimensional vector, denoted as

This is the frequency domain symbol reconstructed according to the judgment result. The method of using the reconstructed frequency domain symbol to track the channel is:

$h^{\&prime;}\left(k_i\right)=R^{\&prime;}\left(k_i\right)/{\hat{S}}^{\&prime;}\left(k_i\right),$ Here D(k _i )=1, (i=0, 1, . . . , M-1)

Since only some of the subchannels have decision symbols, tracking is only performed on the available subchannels. When the adaptive frequency selection judgment module judges that frequency selection needs to be re-selected, the receiving end first requests the sending end to send a training frame, estimates the channel and obtains updated channel state information, then performs frequency selection, and passes the sub-channel group label information through the reverse channel module 22 sent to the originator. It should be noted that the tracking method does not use the reconstructed symbols on all available sub-channels, but only uses the frequency-domain symbols whose amplitude is greater than a certain threshold. For sub-channels whose amplitude is smaller than the threshold, the channel state The information is not updated, that is, the value at the previous moment remains unchanged. In this embodiment, the threshold used is the frequency domain average power of the signal.

(b) Judgment feedback tracking plus pilot symbol method:

The channel state information is obtained respectively by two channel estimation methods, and the average value of the two is taken.

The estimation method of the pilot symbol is: according to the Fourier transform relationship,

Fh=H

Where F is the Fourier transform matrix, h is the channel time-domain impulse response, and H is the channel frequency-domain response. According to different requirements for channel estimation accuracy, different numbers of pilot symbols can be inserted in the frequency domain. The minimum number of pilot symbols is the length of the channel time-domain impulse response. When more pilot symbols are inserted, higher channel estimation accuracy may be achieved. , but more transmit power and available spectrum will be wasted; less pilot symbols may affect the accuracy of channel estimation, but it can save transmit power and improve spectrum efficiency. The simulation result of this embodiment is that the number of pilot symbols equal to The cyclic prefix CP is obtained.

Adaptive frequency selection judgment module 19: a unique module of this system, according to the channel state information of each frame update sent by the channel estimation or prediction module 18, obtain the amplitude gain |H(k _i )| of the sub-channel, (i=0, 1, ..., M-1) and can be judged by subchannel group label information. Different judgment rules can be used. If the judgment result is that frequency selection needs to be re-selected, the frequency selection module 20 is controlled to work; when the sending end sends a new frame of data, it always works according to the latest obtained sub-channel group label information. Two implementation examples are given below:

1. Assuming that only the channel state information on the available sub-channels can be obtained, the judgment method used is: calculate the current equalized signal-to-noise ratio, that is, the actual equalized signal-to-noise ratio, and the difference between the expected equalized signal-to-noise ratio value, if the absolute value of the difference obtained is greater than the threshold, reselect the frequency, otherwise keep the current subchannel group label information unchanged; in the simulation of the embodiment, the threshold value is 3dB;

2. Assuming that the channel state information on all sub-channels can be obtained, the judgment method used is: calculate the actual SNR after equalization, the optimal SNR after equalization, and compare the actual SNR after equalization with the expected The equalized signal-to-noise ratio and the optimal equalized signal-to-noise ratio are respectively made a difference, the absolute values of the two are weighted and summed, and the frequency is reselected when the sum value is greater than the threshold. In the embodiment, the weighting values are respectively p and (1-p), where p is the ratio of the number of available sub-channels to the number of all sub-channels, and the threshold value in the simulation of the embodiment is 2.3dB.

Frequency selection (sub-channel group) module 20: a unique module of this system, which determines whether re-selection of frequencies is required based on the result of the adaptive frequency selection judgment module 19. If frequency selection needs to be re-selected, the module works to select an available sub-channel group. According to whether the sub-channel group is available, it is marked with 1-bit information ("0" or "1") to form sub-channel group marking information, and the sub-channel The group label information is sent to the channel label information mapping module 21 and the reverse channel 22 of the receiving end at the same time, and is sent back to the channel label information mapping module 21 of the sending end through the reverse channel; Method programming is implemented by a general-purpose digital signal processing chip.

Channel label information mapping module 21: a unique module of this system, one at the sending end and one at the receiving end. The sending end module is mapped into all subchannel marking information according to the subchannel group label information obtained by the reverse channel module 22, and then sent to the source module 1 and the signal spectrum conversion module 4 at the same time; The subchannel group label information is mapped into all subchannel label information, and then sent to the signal spectrum inverse transformation module 14 .

Reverse channel 22: a general module, which transmits subchannel group label information back to the originator.

Synchronization module 23: a general module, which obtains various synchronization data required by the system through parameter estimation. The synchronization module sends the frequency synchronization data to the radio frequency and intermediate frequency demodulation module 10 ; sends the sampling rate synchronization data to the analog-to-digital conversion module 11 ; and sends the timing synchronization data to the CP module 12 .

The simulation parameters of this embodiment:

Simulation environment: MATLAB R2007a

Total number of sub-channels: N=256

Modulation method: QPSK

CP length: 64

Channel Packet Length: 8

Number of channel grouping strategy information bits: K=2

The average received signal-to-noise ratio range selected by simulation: SNR=12, 13(dB)

Maximum Doppler frequency fd: 100Hz, 200Hz, 300Hz

Data sampling rate: 10MHz

Time-varying channel model:

ITU IMT2000 Vehicular Test Environment channel model A

Refer to RECOMMENDATION ITU-R M.1225

GUIDELINES FOR EVALUATION OF RADIO TRANSMISSION

TECHNOLOGIES FOR IMT-2000

The training frame used for channel estimation in the simulation has a 3dB higher signal-to-noise ratio than the normal data frame

In the simulation, the impact of synchronization errors (including carrier synchronization errors, sampling rate synchronization errors and frame timing synchronization errors) on the system is not considered, that is, it is assumed that the errors of all synchronization parameters are 0; the subchannel group flag information returned by the reverse channel is not considered The impact of transmission delay and transmission error, that is, it is assumed that the transmission delay and error are both 0; the influence of other non-ideal factors (such as the nonlinearity of the device, etc.) is not considered.

Simulation results:

Simulation result description:

In the simulation results in the above table, the reverse channel rate of the original method can be seen in the Chinese invention patent with publication number CN1777161, and the corresponding bit error rate is slightly different from the method disclosed in CN1777161.

To avoid confusion, some terms mentioned in this manual are explained as follows:

1. Symbol: refers to the data after information bits are modulated and mapped (also called symbol mapping). Usually a complex number whose real and imaginary parts are integers.

2. One frame signal: For OFDM, one frame signal refers to N symbols that undergo IFFT transformation at the sending end, and at the receiving end refers to N symbols that undergo FFT transformation after removing the CP. For SC-FDE, a frame signal refers to the N information symbols between two adjacent CPs at the sending end, and refers to the N symbols transformed by FFT after removing the CP at the receiving end. For the SC-FDE system realized by the method proposed by the present invention, a frame signal refers to M symbols that are transformed by FFT at the sending end, and refers to M symbols that are transformed by IFFT after equalization at the receiving end.

3. Sub-channel: For OFDM and SC-FDE baseband signals, a sub-channel refers to a frequency point after FFT at the receiving end. For a radio frequency channel, a subchannel refers to a section of frequency spectrum of the radio frequency channel.

5. Signal-to-noise ratio after equalization: the ratio of signal power to noise power after equalization.

6. Expected equalized signal-to-noise ratio: the lowest equalized signal-to-noise ratio that satisfies different bit error performance requirements.

Claims (7)

1. An adaptive frequency-selective block transmission method for reducing backtransmission information, comprising the steps of:

(1) grouping channels, wherein after a transceiver establishes communication, a receiving end acquires channel state information of a current channel according to an agreed mode, then the receiving end determines sub-channel grouping according to an agreed sub-channel grouping strategy and the channel state information, and performs grouping and binding on N frequency domain sub-channels to obtain T sub-channel groups and simultaneously form K-bit sub-channel grouping strategy information;

(2) the method comprises the steps of initially selecting frequency, calculating channel gain parameters of each subchannel group, then selecting the first U subchannel groups with high gain parameters as available subchannel groups according to the system error code performance requirements and subchannel grouping strategy information of the current channel state, marking the available subchannel groups by using bit information of 0 or 1 to form subchannel group marking information, and sending the subchannel group marking information and the subchannel grouping strategy information to a sending end through a reverse channel, wherein the U available subchannel groups comprise M available subchannels;

(3) a transmitting end carries out symbol mapping according to an adopted modulation mode to form a frame of M symbols to be transmitted, carries out orthogonal transformation on the M symbols to obtain M transformation domain symbols, expands the M transformation domain symbols into N-dimensional vectors according to sub-channel group mark information to obtain a frequency domain form of a signal to be transmitted, transforms the frequency domain form back to a time domain and transmits a time domain signal, when M is not an integer power of 2, the orthogonal transformation is realized in blocks, and different blocks are subjected to the same or different orthogonal transformations;

(4) the receiving end transforms the received sampling signal to the frequency domain, carries on the frequency domain equalization to the received signal according to the mark information of the sub-channel group, chooses M useful signals on the available sub-channel, does the orthogonal inverse transformation, changes back to the time domain signal and finishes the judgement, gets the information data, when M is not the integer power of 2, the original orthogonal transformation uses the block to realize, the orthogonal inverse transformation also needs the block to realize, different blocks use the same or different orthogonal inverse transformation according to the orthogonal transformation used respectively;

(5) the receiving end carries out channel estimation or prediction to obtain updated channel state information, judges whether the sub-channel group marking information needs to be updated or not according to a self-adaptive judgment rule, if the sub-channel group marking information needs to be updated, the receiving end firstly updates the sub-channel group strategy information, then updates the sub-channel group marking information according to the sub-channel group strategy information and the requirement of system error code performance, and feeds the sub-channel group marking information back to the transmitting end through a reverse channel; when a new frame of data is transmitted, the transmitting end always performs signal conversion according to the latest received sub-channel group mark information and grouping strategy information.

2. The adaptive frequency-selective block transmission method according to claim 1, wherein the method for obtaining the channel state information of the current channel in step (1) is to obtain the channel state information by a channel estimation method based on training frame or to insert pilot symbols to estimate the channel state information.

3. The adaptive frequency-selective block transmission method for reducing the feedback information according to claim 1, wherein the sub-channel grouping strategy in step (1) is to bind a plurality of adjacent frequency domain sub-channels as a sub-channel group, different channel groups use the same channel grouping length, and different channel grouping lengths are respectively used as the corresponding grouping strategy information.

4. The adaptive frequency-selective block transmission method according to claim 1, wherein the channel gain parameter of the sub-channel group in step (2) represents a parameter of the overall channel gain of a sub-channel group, which is the average channel gain of the sub-channel group or the overall equalized snr of the sub-channel group, and the calculation method is as follows:

(a) the average channel gain of the sub-channel group is obtained by summing the gains of all sub-channels in the sub-channel group and then averaging;

(b) overall equalized signal-to-noise ratio of a group of subchannels: let each subchannel group contain P subchannels, jth, where j equals 0, 1, …, and the channel gain of T-1 subchannel group is H (j) respectively^p) And P is 0, 1, …, P-1, and the calculation of the signal-to-noise ratio after the overall equalization of the subchannel group by adopting the zero-forcing equalization mode does not consider the influence of the synchronization error:

due to the cyclic prefix, in the discrete time domain, the linear convolution of the signal and the channel impulse response is converted into a product in the discrete frequency domain, and S' (j) is set^p)，W(j^p)，R′(j^p) Respectively transmitting signal, noise and receiving signal after removing cyclic prefix in frequency domain in sub-channel group, wherein W (j)^p) Gaussian noise, then:

R′(j^p)＝S′(j^p)H(j^p)+W(j^p)，p＝0，1，…，P-1

after zero forcing equalization:

<math><mrow><msup><mover><mi>S</mi><mo>~</mo></mover><mo>&prime;</mo></msup><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow><mo>=</mo><msup><mi>S</mi><mo>&prime;</mo></msup><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow><mo>+</mo><mfrac><mrow><mi>W</mi><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow></mrow><mrow><mi>H</mi><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow></mrow></mfrac><mo>,</mo><mi>p</mi><mo>=</mo><mn>0,1</mn><mo>,</mo><mo>.</mo><mo>.</mo><mo>.</mo><mo>,</mo><mi>P</mi><mo>-</mo><mn>1</mn></mrow></math>

overall equalized signal-to-noise ratio of a group of subchannels:

<math><mrow><msub><msup><mi>SNR</mi><mi>j</mi></msup><mi>eq</mi></msub><mo>=</mo><mfrac><mrow><mi>E</mi><mrow><mo>(</mo><munderover><mi>&Sigma;</mi><mrow><mi>p</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>P</mi><mo>-</mo><mn>1</mn></mrow></munderover><msup><mrow><mo>|</mo><msup><mi>S</mi><mo>&prime;</mo></msup><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow><mo>|</mo></mrow><mn>2</mn></msup><mo>)</mo></mrow></mrow><mrow><mi>E</mi><mrow><mo>(</mo><munderover><mi>&Sigma;</mi><mrow><mi>p</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>P</mi><mo>-</mo><mn>1</mn></mrow></munderover><msup><mrow><mo>|</mo><mfrac><mrow><mi>W</mi><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow></mrow><mrow><mi>H</mi><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow></mrow></mfrac><mo>|</mo></mrow><mn>2</mn></msup><mo>)</mo></mrow></mrow></mfrac><mo>=</mo><mfrac><mrow><mi>E</mi><mrow><mo>(</mo><munderover><mi>&Sigma;</mi><mrow><mi>p</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>P</mi><mo>-</mo><mn>1</mn></mrow></munderover><msup><mrow><mo>|</mo><msup><mi>S</mi><mo>&prime;</mo></msup><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow><mo>|</mo></mrow><mn>2</mn></msup><mo>)</mo></mrow></mrow><mrow><msubsup><mi>&sigma;</mi><mi>n</mi><mn>2</mn></msubsup><munderover><mi>&Sigma;</mi><mrow><mi>p</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>P</mi><mo>-</mo><mn>1</mn></mrow></munderover><msup><mrow><mo>|</mo><mfrac><mn>1</mn><mrow><mi>H</mi><mrow><mo>(</mo><msup><mi>j</mi><mi>p</mi></msup><mo>)</mo></mrow></mrow></mfrac><mo>|</mo></mrow><mn>2</mn></msup></mrow></mfrac><mo>,</mo><mi>j</mi><mo>=</mo><mn>0,1</mn><mo>,</mo><mo>.</mo><mo>.</mo><mo>.</mo><mo>,</mo><mi>T</mi><mo>-</mo><mn>1</mn></mrow></math>

wherein,

p-1 is 0, 1, …, and P-1 is the power of the noise on each subchannel.

5. The adaptive frequency-selective block transmission method for reducing backhaul information according to claim 1, wherein the specific method for expanding the M transform domain symbols into N-dimensional vectors according to the sub-channel group signature information in step (3) is:

after the sending end receives the sub-channel group mark information sent back by the receiving end, firstly mapping all sub-channel mark information according to the appointed grouping strategy and the received channel grouping strategy information, and the specific method is as follows: the sub-channel group with the sub-channel group mark information of 1, wherein all the corresponding sub-channel mark information is 1; for a subchannel group whose subchannel group flag information is 0, all the corresponding subchannel flag information is 0, and all the subchannel flag information vectors corresponding to the vector B indicating the subchannel group flag information are set as:

D＝{D(k)，k＝0，1，…，N-1}，

d (k) ═ 1 denotes that the k-th subchannel is an available subchannel, and d (k) ═ 0 denotes that the k-th subchannel is an unavailable subchannelLet the label of all M available sub-channels be k_iI-0, 1, …, M-1, i.e. D (k)_i)＝1，i＝0，1，…，M-1；

At the transmitting end, only M available sub-channels are used for transmitting signals, thus, M-point orthogonal transformation is carried out on a frame of M block transmission system symbols s (n), n is 0, 1, … and M-1, and the system symbols are transformed into a transformation domain:

S＝Fs

wherein F is an M-point orthogonal transform matrix, S ═ { S (n), n ═ 0, 1, …, M-1} is M time domain symbols of the block transmission system, S ═ { S (i), i ═ 0, 1, …, M-1} is M transform domain symbols;

expanding M transform domain symbols S ═ { S (i), i ═ 0, 1, …, M-1} into an N-dimensional vector S '═ { S' (k), k ═ 0, 1, …, N-1} corresponding to D ═ D (k), k ═ 0, 1, …, N-1} as follows:

k-th of S '{ S' (k), k ═ 0, 1, …, N-1}_iComponent S' (k)_i) Corresponding D (k)_i) Place S (i) 1, i 0, 1, …, M-1, let S' (k)_i) (i) 0, 1, …, M-1, and the rest of each component is set with zero or filled with some non-information data;

and then performing N-point inverse discrete Fourier transform on S' (k), k being 0, 1, … and N-1, and realizing the following steps by an inverse fast Fourier transform algorithm:

<math><mrow><msup><mi>s</mi><mo>&prime;</mo></msup><mrow><mo>(</mo><mi>n</mi><mo>)</mo></mrow><mo>=</mo><mfrac><mn>1</mn><mi>N</mi></mfrac><munderover><mi>&Sigma;</mi><mrow><mi>k</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></munderover><msup><mi>S</mi><mo>&prime;</mo></msup><mrow><mo>(</mo><mi>k</mi><mo>)</mo></mrow><msup><mi>e</mi><mrow><mi>j</mi><mfrac><mrow><mn>2</mn><mi>&pi;</mi></mrow><mi>N</mi></mfrac><mi>nk</mi></mrow></msup><mo>,</mo><mi>n</mi><mo>=</mo><mn>0,1</mn><mo>,</mo><mo>.</mo><mo>.</mo><mo>.</mo><mo>,</mo><mi>N</mi><mo>-</mo><mn>1</mn></mrow></math>

when the time domain signal is converted into a time domain signal, the IFFT points are more than N when the time domain signal is over-sampled, the high frequency part is set to zero, and the time domain signal is sent out after being subjected to D/A conversion and then subjected to carrier modulation.

6. The adaptive frequency-selective block transmission method according to claim 1, wherein the method for obtaining channel state information in step (5) uses a training frame plus decision feedback tracking method or a decision feedback tracking plus pilot symbol method or a channel prediction or channel blind estimation method.

7. The adaptive frequency-selective block transmission method for reducing the amount of feedback information according to claim 1, wherein the adaptive decision rule in step (5) for deciding whether to re-select frequency according to the system error performance requirement is one of the following two rules:

(a) calculating the current signal-to-noise ratio after equalization, recording as the actual signal-to-noise ratio after equalization, making a difference with the signal-to-noise ratio after expected equalization, setting an upper limit and a lower limit for the difference, and keeping the current sub-channel group marking information unchanged if the obtained difference is between the set upper limit and the set lower limit; if the obtained difference exceeds the upper limit or the lower limit, frequency is selected again;

(b) assuming that all channel state information is obtained, namely the channel state information comprises available sub-channels and unused sub-channels; assuming that the noise power is constant, calculating the current post-equalization signal-to-noise ratio, and recording as the actual post-equalization signal-to-noise ratio; selecting a subchannel group which enables the equalized signal-to-noise ratio to be maximum from all subchannels after channel state information updating, wherein the number of the subchannels is the number of currently available subchannels, and recording the maximum equalized signal-to-noise ratio as the optimal equalized signal-to-noise ratio; making a difference between the actual equalized signal-to-noise ratio and the optimal equalized signal-to-noise ratio, setting an upper limit and a lower limit for the difference, and keeping the current sub-channel group marking information unchanged if the obtained difference is between the set upper limit and the set lower limit; and if the obtained difference value exceeds the upper limit or the lower limit, the frequency is selected again.

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