CN100521673C - Down link frequency division multiple access switching in method of frequency selecting block transmitting system - Google Patents

Abstract

A method for switching in downlink TDMA of frequency selection unblocking transmission system includes initializing distribution of subchannel set, sending an auxiliary data to mobile table switched in current base station ( BS ) by BS, selecting flag information and sending it to BS by mobile table, carrying out orthogonal transform on modulated signal of mobile table and setting up downlink of communication from BS to mobile table by BS, transforming sampled signal to frequency domain and selecting out usable signal by mobile table, changing subchannel set by BS according to requirement and carrying out communication with BS by mobile table according to received information.

Description

A Downlink Frequency Division Multiple Access Method for Frequency Selective Block Transmission System

(1) Technical field

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

(2) Background technology

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 extensive attention. -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.

The following briefly introduces the mathematical model of the traditional SC-FDE system.

A frame of discrete time-domain signals sent by the SC-FDE system at the sending end is s(n), (n=0, 1, ..., N-1), through a multipath channel, where the impulse response of the channel is h(n) , (n=0, 1,...L-1), the signal transmission process is interfered by additive white Gaussian noise (AWGN: Additive White Gaussian Noise), let the noise be w(n), (n=0, 1, ..., N-1), after removing the CP, the received time-domain signal r(n) is:

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

表示循环卷积运算。in,

Represents a circular convolution operation.

At the receiving end, the discrete Fourier transform (hereinafter referred to as DFT: Discrete Fourier Transform) is performed on the signal to the frequency domain. According to the time domain convolution theorem of DFT, the obtained frequency domain signal is:

R(k)=S(k)H(k)+W(k), (k=0, 1,..., N-1) (2)

Among them, R(k), S(k), H(k), W(k) are respectively r(n), s(n), h(n), w(n) in the frequency domain obtained by doing N-point DFT symbols, and, H(k), (k=0, 1, . . . , N-1) is the frequency domain response of the channel. After zero-forcing equalization, the frequency domain signal is:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; S</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">\; (</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">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</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">\; \&Center\; Dot;</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>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Finally, the signal is transformed back to the time domain by inverse discrete Fourier transform (hereinafter referred to as IDFT: Inverse Discrete Fourier Transform) for judgment, and the data transmitted by the sender is obtained.

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

Broadband mobile communication channels generally exhibit severe frequency-selective fading. The impact of frequency-selective channels on block transmission systems is mainly manifested in: multi-path propagation or delay extension of signals will cause frequency-selective fading. Signals in frequency Propagation in selective fading channels will cause certain spectral components of the signal to be attenuated very low. In the case of deep fading points in the channel, the signal will be affected more, 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 and future broadband mobile communications, etc.), there is a reverse channel. At this time, the sender of the block transmission system can use the channel state information returned by the reverse channel And some adaptive techniques to improve the performance and efficiency of the whole system.

The Chinese invention patent with the application number of 200410036439.6 provides a frequency-selective single-carrier block transmission method, which 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 the subchannel label information back to the sender;

(2) After receiving the sub-channel marking information sent back by the receiving end, the sending 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.

For detailed steps, refer to "A Single-Carrier Block Transmission Method with Frequency Selection Mode" (Chinese invention patent has been applied for, patent application number: 200410036439.6), and will not be repeated here.

In a mobile communication system, an effective multiple access technology must be used. The basic types of multiple access technology are frequency division multiple access FDMA (Frequency Division Multiple Access), time division multiple access TDMA (Time Division Multiple Access) and code division multiple access CDMA (Code Division Multiple Access). FDMA and TDMA are simple to implement but need to leave guard bands in the frequency domain and time domain respectively, which is inefficient. As a multiple access technology, CDMA has significantly higher user capacity than TDMA and FDMA, but it is complex to implement; multi-carrier CDMA (MC-CDMA) also has the same problems as ordinary CDMA. The carrier sense/collision avoidance technology in WLAN is very inefficient.

Orthogonal Frequency Division Multiple Access, OFDMA (Orthogonal Frequency Division Multiple Access), is a new broadband multiple access technology that has attracted attention in recent years. It is a multiple access technology based on OFDM, which can be regarded as It is a new type of frequency division multiple access technology. OFDMA divides the entire bandwidth into a large number of narrowband sub-channels, and a user allocates one or several sub-bands (sub-channel groups), and each sub-band contains a certain number of sub-channels. OFDMA is simple to implement and has high spectrum utilization. In the downlink, there is no multi-user interference. There are generally two schemes for establishing subbands in OFDMA. One is that a certain number of adjacent subchannels form subbands, and the second scheme is that all subchannels of a subband are scattered randomly or at certain intervals in the entire bandwidth. Compared with the first scheme, the second scheme has advantages, especially in frequency selective fading channels. In order to make full use of channel state information, a large number of adaptive OFDMA techniques have been proposed, but the complexity is too high. Although the above-mentioned second scheme is better in frequency selective fading channels, it is still greatly affected by frequency selective fading. Generally, it is necessary to combine error correction codes with strong error correction capabilities to control the bit error rate of the system. At a relatively low level (for example below 10 ⁻⁴ ), the coding rate of such error correction codes is generally very low, for example generally 1/2, 1/3 or even lower, which greatly reduces the efficiency of the entire system.

(3) Contents of the invention

Aiming at the problems existing in the prior art, the present invention proposes a downlink frequency division multiple access method of a frequency-selective block transmission system, which can greatly improve the bit error performance of the system with little increase in complexity , which can significantly improve the spectral efficiency of the system.

Since the access method of the base station to each mobile station is the same, for the convenience of description, the downlink communication of a certain mobile station U will be described below.

The method includes the following steps:

(1) initial sub-channel group allocation, the base station allocates a group of sub-channels for each mobile station connected to the current base station, and notifies each mobile station of the sub-channel group it is assigned to;

(2) The base station sends a frame of auxiliary data for channel estimation to the mobile station connected to the current base station, and each mobile station estimates the channel state information of the subchannel group used by the mobile station. According to the sub-channel gain level in the group, select the first M ones with high gain as available sub-channels to form sub-channel label information, and send the sub-channel label information of the sub-channel group of the mobile station to the base station;

(3) The base station performs orthogonal transformation on the modulated signal of each mobile station according to the received subchannel label information of each subchannel group, expands it into an N-dimensional vector, changes it back to the time domain transmission, and establishes the downlink from the base station to the mobile station communication link;

(4) The mobile station transforms the received sampled signal into the frequency domain, performs frequency domain equalization on the received signal according to the subchannel label information of the subchannel group of the mobile station U, and selects useful signals on the available subchannels, and converts back to the time Domain and complete the judgment, get the information data;

(5) According to needs, the base station can change the sub-channel group u to other sub-channel groups during the communication process, or the mobile station keeps the sub-channel group u unchanged, and only changes the sub-channel label information in the sub-channel group u; make After the change, the base station sends the identification information of the changed sub-channel group to the mobile station or the mobile station sends the sub-channel label information of the changed sub-channel group u to the base station, and the mobile station always uses the latest received sub-channel group u Identification information The base station communicates or the base station always communicates with the mobile station according to the most recently received subchannel identification information of the subchannel group u.

detailed steps:

First, the symbols involved are explained as follows:

k: The overall label of the subchannel, 0≤k≤N-1. In the block transmission system, the communication parties divide the entire available frequency band into N sub-channels. In the block transmission system based on FFT, k is also the label of the frequency domain variable.

m: The local label of the subchannel, which is the mth subchannel label in the same subchannel group, and m is called the local label in the subchannel group.

I _u : the identification information of the sub-channel group u. According to I _u , both the base station and the mobile station can obtain the overall labels of all sub-channels in the sub-channel group u.

D _B (k): N-dimensional vector, N is the number of all available sub-channels of the base station, if D _B (k)=u, 1≤u≤U _max , it means that the k-th sub-channel belongs to the sub-channel of the U-th mobile station The channel group u, U _max represents the maximum number of users that the base station allows to access.

D _u (m): array of subchannel labels of subchannel group u. D _u (m)=k means that the global index of the subchannel with the local index m of the subchannel group u is k. This array is stored in both the base station and the mobile station U. The base station can obtain D _u (m) according to D _B (k), and the mobile station U can obtain D _u (m) according to the identification information I _u of the subchannel group u transmitted from the base station. .

A _u (m): subchannel flag information of subchannel group u. A _u (m) = 0, indicating that the subchannel with the local label m in the subchannel group u is an unavailable subchannel; A _u (m) = 1, indicating that the subchannel with the local label m in the subchannel group u are available subchannels.

Step (1), the initial sub-channel group allocation, the base station allocates a group of sub-channels for each mobile station connected to the current base station, and notifies each mobile station of the sub-channel group situation it is assigned to;

In the block transmission system, the base station divides the entire available frequency band into several sub-channels. Since the block transmission system needs to remove the discrete time domain signal of the CP, it is transformed into the discrete frequency domain by using DFT. In the discrete frequency domain, the base station’s The total number of sub-channels is equal to the number of DFT points, and each sub-channel corresponds to a point or component of DFT. The number of sub-channels included in each sub-channel group may vary according to different services. The distribution of the sub-channels in the same sub-channel group in the entire frequency band can be selected in many ways. For example, the sub-channel groups of multiple users can each occupy a continuous spectrum, or the sub-channel groups of each user can be scattered throughout the entire frequency band. within the frequency band.

The base station allocates a group of sub-channels to the mobile station U according to its business needs and available spectrum resources, denoted as sub-channel group u, and forms the sub-channel identification information I _u of the sub-channel group u. For example, the base station can assign sub-channel groups to sixty-four mobile stations at most according to the protocol, and each sub-channel group needs six bits to be identified, and the identification information I _u of the sub-channel group u transmitted to the mobile station is the label of the sub-channel group u ; The number of sub-channels in these sub-channel groups can be the same or different; when the sub-channels in the sub-channel group u are completely randomly scattered in the whole frequency band, the identification information I _u of the sub-channel group u needs N bit information, that is, the base station needs to send N-bit information to the mobile station.

Let D _B be the vector used by the base station to represent the label information of the subchannel group u, namely:

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

D _B (k)=u, 1≤u≤U _max , indicating that the kth subchannel belongs to the uth subchannel group, and the uth subchannel group has B _u subchannels, D _u (m)=k, (m= 0, 1, . . . , B _u -1) indicates that the global label of the subchannel with the partial label m of the subchannel group u is k.

After the mobile station U receives the identification information I _u of the sub-channel group u, it knows D _u (m)=k, (m=0, 1, . . . , B _u -1).

In step (2), the base station sends a frame of auxiliary data for channel estimation to the mobile station connected to the current base station, and the mobile stations respectively estimate the channel state information of the subchannel group used. According to the sub-channel gain level, select the first M with high gain as available sub-channels, form sub-channel label information, and send the sub-channel label information of the sub-channel group of the mobile station to the base station;

There are many methods of channel estimation, such as the channel estimation method based on training frames, the method of inserting pilot symbols and so on.

After obtaining the channel state information, perform frequency selection. After the mobile station obtains the channel state information of each subchannel group, it selects the available subchannel according to the system performance requirements and the current channel state information, and marks it with a bit information "0" or "1" to form the subchannel label information. Send these sub-channel marking information to the base station on the channel. The number of available sub-channels selected by each mobile station can be different, which is determined by the link conditions and service requirements between the base station and different mobile stations.

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

A _u = {A _u (m), m = 0, 1, . . . , B _u -1},

A _u (m)=1, it means that the sub-channel with the local label m in the sub-channel group u is an available sub-channel; A _u (m)=0, it means that the sub-channel with the local label m in the sub-channel group u is Unavailable sub-channels, record the number of available sub-channels in all sub-channel groups u as M, and M can be changed during the communication process, for example, when re-selecting frequency each time, the selected number of available sub-channels M is generally are not the same. When selecting available sub-channels, 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. The criterion for selecting available sub-channels is to meet the bit error performance of the system. Under the premise of requirements, the number of available sub-channels is selected as much as possible. The bit error performance of the system is determined by the SNR of the system after equalization, and the lowest SNR after equalization to achieve this bit error performance is called the expected SNR after equalization, and a certain margin is left.

Wherein, the calculation method of the receiving signal-to-noise ratio refers to relevant literature. Assume that the overall number of the M available subchannels currently selected by the mobile station is k _m , (m=0, 1, . . . , M−1), and they are all subchannels in the subchannel group u. The following only takes zero-forcing equalization as an example to briefly introduce the calculation of the signal-to-noise ratio 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 _u (k), W(k), R′(k), (k=0, 1, ..., N-1) be frequency domain transmission signal, channel complex gain, noise and The received signal in the frequency domain after removing the CP, where W(k), (k=0, 1, ..., N-1) is Gaussian noise, then:

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

After performing zero-forcing equalization on the M available sub-channels in the sub-channel group u:

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

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{\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</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>}}_{\mathrm{<span\; class="notranslate">\; m</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">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</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>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</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">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</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>}}_{\mathrm{<span\; class="notranslate">\; m</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">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</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>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</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=0, 1, . . . , N-1) is the power of noise on each subchannel.

In step (3), the base station performs orthogonal transformation on the modulated signal of each mobile station according to the received subchannel label information of each subchannel group, expands it into an N-dimensional vector, and sends it back to the time domain to establish the base station to mobile station the downlink communication link;

The base station performs symbol mapping on the service data of each mobile station according to the modulation method adopted by each mobile station, and then transforms the service data after symbol mapping according to the subchannel label information of the subchannel group of the mobile station. Take the transformation of business data as an example to illustrate:

The base station performs symbol mapping on its business data according to the modulation method adopted by the mobile station U to form a frame of M symbols to be transmitted, and performs orthogonal transformation on the M symbols to obtain M transform domain symbols, according to the subchannel label information The above M transform domain symbols are expanded into N-dimensional vectors to obtain the frequency domain form of the signal to be transmitted.

The transmitted signals of each mobile station are non-overlapping in the frequency domain. These non-overlapping N-dimensional vectors are combined into one N-dimensional vector, that is, the frequency domain form of the signal to be transmitted by the base station is changed to the time domain plus CP transmission.

Among them, the specific method of expanding the M transform domain symbols into N-dimensional vectors according to the sub-channel label information is:

After the base station receives the subchannel label information sent back by the mobile station U, it only uses M available subchannels to transmit signals, so that the system symbol s(n) is transmitted in M blocks in one frame of the mobile station U, (n= 0, 1, ..., M-1), make M-point orthogonal transformation to 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 time-domain symbol of M block transmission system, S={S(i), i= 0, 1..., M−1} are M transform domain symbols.

Expand the M-dimensional transform domain symbol S={S(i), i=0, 1...M-1} into an N-dimensional vector S'={S'(k), k=0, 1...N-1}, Among them, the M transform domain symbols correspond to the M available subchannels of the subchannel group u one by one, for example, S corresponds to the M available subchannels according to the order of the overall labels:

Let S'={S'(k), k=0, 1, ..., N-1} the k _mth component is equal to S(m), and set zero or Place some non-information data; set all zeros on the sub-channels that do not belong to the sub-channel group u.

Here k _m , (m=0, 1, . . . , M−1) is the overall label of the M available sub-channels in the sub-channel group U. All the data groups of all mobile stations are converted by the above process, and the frequency domain signal S'={S'(k),k=0,1,...,N-1} of a frame block transmission system is obtained, and then To S'(k), (k=0, 1, ..., N-1) do N-point Inverse Discrete Fourier Transform (hereinafter referred to as IDFT: Inverse Discrete Fourier Transform), which can be performed by Inverse Fast Fourier Transform (hereinafter referred to as IFFT: Inverse Fast Fourier 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="C200610043964E00161.png"\; state="\{\{state\}\}">e</figure-callout></span><figure-callout\; id="2"\; label="e\; j"\; filenames="C200610043964E00161.png"\; state="\{\{state\}\}">\; </figure-callout>}}^{\mathrm{<span\; class="notranslate">\; </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">\; \&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>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</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.

When the number of available sub-channels of each mobile station is not an integer power of 2, the orthogonal transformation can be implemented in blocks, and different blocks can use the same or different orthogonal transformations;

In step (4), the mobile station transforms the received sampling signal into the frequency domain, performs frequency domain equalization on the received signal according to the subchannel label information of the subchannel group of the mobile station U, and selects useful signals on available subchannels , change back to the time domain and complete the judgment, and get the information data;

When the number of available sub-channels of each mobile station is not an integer power of 2, if the original orthogonal transformation is implemented in blocks, the inverse orthogonal transformation should also be implemented in blocks, and different blocks use the same or different inverse orthogonal transformations;

Wherein, the specific implementation method of selecting the signal on the available sub-channel of the mobile station according to the sub-channel label information is, taking the mobile station U as an example:

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

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

Do N-point DFT on it:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="C200610043964E00161.png"\; state="\{\{state\}\}">j</figure-callout></span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; nk</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

and:

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

In this way, signals R(m), (m=0, 1, ..., M-1) on M available sub-channels can be jointly selected according to the label information of the sub-channel group u and the corresponding sub-channel label information, for example For the aforementioned spectral transformation methods, there are:

R(m)=R'(k _m ), where k _m , (m=0, 1, . . . , M-1) is the overall index of the M available sub-channels.

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.

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

r = F ^H R

where F ^H is the conjugate transpose of F, which is the inverse transformation matrix of F. When M is not an integer power of 2, if the original orthogonal transformation is implemented in blocks, the inverse orthogonal transformation should also be implemented in blocks, and different blocks use the same or different inverse orthogonal transformations according to their respective orthogonal transformations. ;

Step (5), as needed, the base station can change the sub-channel group u to other sub-channel groups during the communication process, or the mobile station keeps the sub-channel group u unchanged, and only changes the sub-channel label in the sub-channel group u information; after making a change, the base station sends the identification information of the changed sub-channel group to the mobile station or the mobile station sends the sub-channel label information of the changed sub-channel group u to the base station, and the mobile station always uses the latest received Sub-channel group identification information The base station communicates or the base station always communicates with the mobile station according to the most recently received sub-channel identification information of the sub-channel group u.

When the channel state information changes, or the system needs to optimize the sub-channel group of multiple users, the base station can change the identification information of the sub-channel group u, that is, replace the sub-channel group u with other sub-channel groups, or the mobile station can keep the sub-channel group u The identification information of the channel group u remains unchanged, and only the sub-channel label information in the sub-channel group u is changed. At this time, the previous channel label information will be inaccurate, which will affect the system performance. At this time, it is necessary to re-select the frequency and repeat the second step and the third step.

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-channels

The number of available subchannels is an important parameter affecting the performance of the new system. Looking at the above schemes, if only available sub-channels are used to transmit useful information, there is a problem of how to determine the number of available sub-channels, which is not a fixed value for different channel types and time-varying channels at different times. 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 number of sub-channels _Bu in the sub-channel group u is generally 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 invention better solves the access problem of the downlink in the time-varying environment under the premise of ensuring the system performance. As can be seen from the simulation results given in the embodiment, for a signal sampling rate of 40MHz, a single-antenna system in which the RF bandwidth of the signal is no more than 46MHz, the IMT2000 mobile channel A and the Doppler frequency reach 100Hz-300Hz, and the receiving signal-to-noise ratio is 14dB Under the condition of applying 16QAM, the method proposed by the present invention can obtain the uplink transmission rate of the system not lower than 10.0Mbps for mobile stations occupying 128 sub-channels under the condition that the bit error rate of the system is guaranteed to be lower than 5×10 ^-3 , and the return information rate of the reverse channel does not exceed 500Kbps. From the current literature, there is no published literature that can achieve such a result under the same conditions.

(4) 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 points), 4. Signal spectrum transformation module, 5. Merging module, 6. IFFT module (N points), 7. Adding cyclic prefix (CP) module, 8. D/A module, 9. IF and RF modulation module, 10. Channel, 11. RF and IF demodulation module, 12. A/D module, 13. Remove CP module, 14. FFT module (N point), 15, signal spectrum inverse transformation module, 16, equalization module, 17, IFFT module (M point), 18, decision module, 19, channel estimation module, 20, adaptive frequency selection judgment module, 21, selection Frequency module, 22, reverse channel, 23, synchronization module, 24, multiple access control module.

(5) Specific implementation methods

Example:

The orthogonal transform adopted in the embodiment is an M-point discrete Fourier transform, and the corresponding inverse orthogonal transform is an M-point inverse discrete Fourier transform. The embodiment does not perform block processing on the M-point DFT and IDFT.

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 results returned by the multiple access module 24 and the reverse channel 22, data groups with a length corresponding to the number of available sub-channels selected by each mobile station are respectively 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 performs DFT transformation on the mapped signals of each mobile station U respectively.

Signal spectrum conversion module 4: a unique module of this system, the base station sends back the subchannel label information through the multiple access module 24 and the reverse channel 22, and places the M-point frequency domain signals output by module 3 into M available subchannels corresponding At the spectrum point, and the corresponding spectrum point of the disabled sub-channel is set to zero, or filled with non-information data, a new frequency-domain signal of a frame N-point block transmission system is obtained. This module needs to be programmed according to the method described in step (3) in the summary of the invention, and is implemented by a general-purpose digital signal processing chip.

Signal merging module 5: directly superimpose the frequency domain signals of all mobile stations to obtain a data frame containing data of all mobile stations.

N-point IFFT module 6: a general module, which transforms the newly obtained frequency domain signal into the time domain.

Add CP module 7: a general module, adding a cyclic prefix to each frame of data obtained.

D/A module 8: a general module, which converts digital signals into analog signals.

IF and RF modulation module 9: 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 10: general module, a broadband mobile channel through which signals are transmitted.

Radio frequency and intermediate frequency demodulation module 11: general module, in the wireless environment, the spectrum of the signal received by the receiving antenna is moved 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 12: a general module, which converts the demodulated analog signal into a digital signal. The A/D module 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.

Go to CP module 13: 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 14: a general module, transforming the CP-removed signal into the frequency domain.

Signal spectrum inverse transformation module 15: a unique module of this system, according to the subchannel label information sent by the multiple access module 24 and the channel estimation module 19, find out the frequency domain signals of M points carried by available subchannels in the received signal to form frequency domain signal. This module needs to be programmed according to the method described in step (4) in the summary of the invention, and is implemented by a general-purpose digital signal processing chip.

Equalization module 16: a general module, which equalizes the signal selected by the signal spectrum inverse transformation module 15 by using the available sub-channel parameters sent by the channel estimation module 19, that is, channel state information (CSI). 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 17: a general module, transforming the M frequency domain signals of the equalized signal into the time domain.

Judgment module 18: a general module, which completes the judgment of the time-domain signal according to the modulation method adopted by the system.

Channel estimation module 19: a general module for acquiring channel state. 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 that the channel state acquisition method is training frame plus decision feedback tracking. This method is briefly described below:

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:

(m＝0，1，…，M-1)，根据移动台采用的调制方式进行符号映射，得到重构后的符号

(m＝0，1，…，M-1)，对

(m＝0，1，…，M-1)进行M点正交变换，得到(m＝0，1，…，M-1)，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：Suppose the received discrete time domain signal is r'(k), (k=0, 1, ..., N-1), transform it into frequency domain to get R'(k), (k=0, 1, ... , N-1), the time-domain symbol after the data frame decision is

(m=0, 1, ..., M-1), perform symbol mapping according to the modulation method adopted by the mobile station, and obtain the reconstructed symbols

(m=0,1,...,M-1), for

(m=0, 1, ..., M-1) carry out M-point orthogonal transformation to obtain (m=0, 1, ..., M-1), this is the frequency domain symbol reconstructed according to the decision result, the method of using the reconstructed frequency domain symbol to track the channel is:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>& {<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\mathrm{<span\; class="notranslate">\; threshold</span>}\\ \mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>& {<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; threshold</span>}\end{array}\right.$

Wherein, H(k _m ) is the channel state information of the system in the previous frame, and threshold is the threshold. Here k _m , (m=0, 1, . . . , M-1) is the overall index of the M available sub-channels.

Since there are only decision symbols on some subchannels, tracking is only performed on available subchannels. After a period of time, resend the training frame to eliminate the error accumulation caused by tracking. 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 power is greater than a certain threshold, that is, the threshold. For sub-channels whose amplitude is smaller than the threshold, the frequency-domain CSI No update, that is, keep the value at the previous moment unchanged. In this embodiment, the threshold used by 16QAM is half of the average power in the frequency domain of the signal, and the threshold used by QPSK is the average power in the frequency domain of the signal.

Adaptive frequency selection judgment module 20: a unique module of this system, according to the updated CSI of each frame from the channel estimation 19, obtain the amplitude gain |H(k _i )| of the sub-channel, (i=0, 1, ..., M -1) and can be judged by sub-channel 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 21 is controlled to work; when the sending end sends a new frame of data, it always works according to the latest obtained sub-channel label information. An implementation example is given below:

After obtaining the CSI on the sub-channel, the judgment method used is: calculate the current equalized signal-to-noise ratio, that is, the actual equalized signal-to-noise ratio, and make the difference with the expected equalized signal-to-noise ratio, if the obtained difference If the absolute value is greater than the threshold, re-select the frequency, otherwise keep the current channel label information unchanged; in the simulation of the embodiment, the threshold value is 1dB;

Frequency selection module 21: a unique module of this system, the channel state information of the sub-channel group u obtained by the channel estimation module 19, selects the available sub-channel, and uses 1-bit information ("0" or "1") according to whether the channel is available Marking, forming sub-channel marking information, sending the sub-channel marking information to the signal spectrum inverse conversion module 15 and the reverse channel 22 at the same time, and sending back the signal spectrum conversion module 4 of the mobile station through the reverse channel; this module needs to follow the background technology The method programming introduced in the mentioned Chinese invention patent with application number 200410036439.6 is implemented by a general-purpose digital signal processing chip.

Reverse channel 22: a general module, which transmits the sub-channel label information back to the base station.

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 11 ; sends the sampling rate synchronization data to the A/D module 12 ; and sends the timing synchronization data to the CP module 13 .

Multiple access control module 24: when communication is established, the base station obtains channel state information of each user from the channel estimation module 19, and assigns subchannel group u to each user. The scheme of establishing sub-channel group u is that all sub-channels of sub-channel group u are scattered in the whole bandwidth according to a certain interval, the size of this interval is equal to the number of users, and the number of sub-channels of all sub-channel groups u is the same.

The simulation parameters of this embodiment:

Simulation environment: Matlab7.0.1

Total number of sub-channels: N=1024

Modulation method: QPSK, 16QAM

CP length: 128

Data sampling rate: 40M

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

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 impact of synchronization errors (including carrier synchronization errors, sampling rate synchronization errors, and frame timing synchronization errors) on the system is not considered in the simulation, that is, the errors of all synchronization parameters are assumed to be 0; The influence of transmission delay and transmission bit error, that is, it is assumed that the transmission delay and bit error are both 0; the influence of other non-ideal factors (such as the nonlinearity of the device, etc.) is not considered.

Simulation results:

1.128 sub-channel users, sub-channel group: 1mod(8)

2.16 sub-channel users, sub-channel group: 1mod(64)

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

1 Symbol: refers to the data after the 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 base station refers to N symbols that undergo FFT transformation after removing the CP. For SC-FDE, a frame signal refers to N information symbols between two adjacent CPs at the sending end, and refers to N symbols transformed by FFT after the CP is removed at the base station. 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 base station.

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

4 Subchannel group: A collection of subchannels assigned to a user.

5 Signal-to-noise ratio: the ratio of signal power to noise power, wherein the signal-to-noise ratio mentioned in the summary of the invention and the claims is not logarithmic and has no unit; the signal-to-noise ratio mentioned in the embodiments is a logarithmic signal-to-noise ratio Ratio, the unit is dB.

6 SNR after equalization: The ratio of signal power to noise power after equalization.

7 Expected equalized signal-to-noise ratio: the lowest equalized signal-to-noise ratio required by different bit error performance.

Claims (4)

1. A downlink frequency division multiple access method of a frequency selective block transmission system, the method comprising the steps of:

(1) initial sub-channel group allocation, wherein the base station allocates a group of sub-channels for each mobile station accessed to the current base station and informs each mobile station of the sub-channel group condition to which the mobile station is allocated;

(2) the base station sends a frame of auxiliary data for channel estimation to a mobile station accessed to the current base station, the mobile stations respectively estimate the channel state information of a subchannel group used by the mobile station, the mobile station selects the first M subchannels with high gains as available subchannels in the subchannel group of the mobile station according to the gain of the subchannels to form subchannel marking information, and sends the subchannel marking information of the subchannel group of the mobile station to the base station;

(3) the base station carries out orthogonal transformation on the modulated signals of each mobile station according to the received subchannel marking information of each subchannel group, expands the orthogonal transformation into N-dimensional vectors, returns the N-dimensional vectors to a time domain for transmission, and establishes a downlink communication link from the base station to the mobile station, wherein N is the number of all available subchannels of the base station;

(4) the mobile station transforms the received sampling signal to a frequency domain, performs frequency domain equalization on the received signal according to the subchannel marking information of the subchannel group of the mobile station U, selects a useful signal on an available subchannel, transforms the useful signal back to a time domain and completes judgment to obtain information data;

(5) according to the requirement, the base station changes the sub-channel group u to other sub-channel groups in the communication process, or the mobile station keeps the sub-channel group u unchanged and changes the sub-channel mark information in the sub-channel group u; after the change, the base station sends the identification information of the changed sub-channel group to the mobile station or the mobile station sends the sub-channel marking information of the changed sub-channel group u to the base station, and the mobile station always communicates with the base station according to the recently received sub-channel group identification information or the base station always communicates with the mobile station according to the recently received sub-channel marking information of the sub-channel group u.

2. The downlink frequency division multiple access method of a frequency selective block transmission system according to claim 1, wherein: in the step (3), the base station performs symbol mapping on the service data according to the modulation mode adopted by the mobile station U to form a frame of M symbols to be transmitted, performs orthogonal transformation on the M symbols to obtain M transform domain symbols, and expands the M transform domain symbols into N-dimensional vectors according to the subchannel marking information to obtain the frequency domain form of the signal to be transmitted;

the transmission signals of each mobile station are not overlapped in the frequency domain, and the non-overlapped N-dimensional vectors are combined into an N-dimensional vector, namely the frequency domain form of the signals to be transmitted of the base station is changed into the time domain and the cyclic prefix CP for transmission;

the specific method for expanding the M transform domain symbols into N-dimensional vectors according to the subchannel flag information is as follows:

after receiving the subchannel marking information sent back by the mobile station U, the base station transmits signals by using only M available subchannels, so that M-point orthogonal transformation is performed on a frame of M blocks of the mobile station U, wherein n is 0, 1, … and M-1, to a transform domain:

S＝Fs

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

expanding M-dimensional transform domain symbols S ═ { S (i), i ═ 0, 1 … M-1} into N-dimensional vectors S '═ { S' (k), k ═ 0, 1 … N-1}, wherein M transform domain symbols correspond one-to-one to M available subchannels of subchannel set u, and S sequentially corresponds to M available subchannels in order of their overall index:

let S '{ S' (k), k ═ 0, 1, …, N-1} th k_mOne component is equal to S (m), and zero or some non-information data is placed on the components corresponding to other sub-channels of the sub-channel group u; all the sub-channels which do not belong to the sub-channel group u are set to be zero;

where k is_mM-0, 1, …, M-1, is an overall index of the M available subchannels in the subchannel set u;

wherein: d_u(m): subchannel label array, D, for subchannel group u_uWhere k denotes the overall index k of the subchannel of subchannel set U, with local index m, this array being stored both at the base station and at the mobile station U, the base station being dependent on D_B(k) To obtain D_u(m), the mobile station U is based on the identification information I of the sub-channel group U transmitted from the base station_uTo obtain D_u(m)；

D_B(k) The method comprises the following steps Vector of N dimension, N is the number of all available sub-channels of the base station, if D_B(k)＝u，1≤u≤U_maxIndicates that the kth sub-channel belongs to the sub-channel group U, U of the Uth mobile station_maxRepresenting the maximum number of users allowed to be accessed by the base station;

A_u(m): sub-channel marking information, A, of a sub-channel group u_u(m) ═ 0, indicating that the subchannel in subchannel group u, which is locally labeled m, is an unavailable subchannel; a. the_u(m) ═ 1, indicating that the subchannel in subchannel group u, which is locally labeled m, is an available subchannel;

the above process is performed on the data sets of all the mobile stations, so as to obtain the frequency domain signal S ' ═ { S ' (k), k ═ 0, 1, …, N-1} of a frame of block transmission system, and then the inverse discrete fourier transform of N points is performed on S ' (k), k ═ 0, 1, …, N-1, and the implementation is realized through an inverse fast fourier transform algorithm:

<math> <mrow> <mi>s</mi> <mo>&prime;</mo> <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> <mi>S</mi> <mo>&prime;</mo> <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> </mrow></math> n＝0，1，…，N-1

the time domain signal is changed 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 be zero, and the time domain signal is sent out after being subjected to D/A conversion and then subjected to carrier modulation.

3. The downlink frequency division multiple access method of a frequency selective block transmission system according to claim 1, wherein: the specific implementation method for selecting the signal on the subchannel available to the mobile station according to the subchannel flag information in the step (4) is as follows:

the time domain discrete signal of the signal received by the receiving end and the cyclic prefix CP is set as follows:

<math> <mrow> <mi>r</mi> <mo>&prime;</mo> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>s</mi> <mo>&prime;</mo> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>&CircleTimes;</mo> <mi>h</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>+</mo> <mi>w</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>,</mo> </mrow></math> n＝0，1，…，N-1

and performing N-point DFT on the obtained data:

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

and:

R′(k)＝S′(k)H(k)+W(k)，k＝0，1，…，N-1

wherein:

h (N), wherein N is 0, 1, … N-1 is the impulse response of the channel;

w (N), N is 0, 1, …, and N-1 is additive white Gaussian noise;

represent a circular convolution operation ";

h (k), W (k) are h (N) and w (N) respectively, and frequency domain symbols obtained by performing N-point DFT are obtained;

h (k), k ═ 0, 1, …, N-1 is the frequency domain response of the channel;

where k is_mM-0, 1, …, M-1, is an overall index of the M available subchannels in the subchannel set u;

wherein: d_u(m): subchannel label array, D, for subchannel group u_uWhere k denotes the overall index k of the subchannel of subchannel set U, with local index m, this array being stored both at the base station and at the mobile station U, the base station being dependent on D_B(k) To obtain D_u(m), the mobile station U is based on the identification information I of the sub-channel group U transmitted from the base station_uTo obtain D_u(m)；

D_B(k) The method comprises the following steps Vector of N dimension, N is the number of all available sub-channels of the base station, if D_B(k)＝u，1≤u≤U_maxIndicates that the kth sub-channel belongs to the sub-channel group U, U of the Uth mobile station_maxRepresenting the maximum number of users allowed to be accessed by the base station;

A_u(m): sub-channel marking information, A, of a sub-channel group u_u(m) ═ 0, indicating that the subchannel in subchannel group u, which is locally labeled m, is an unavailable subchannel; a. the_u(m) ═ 1, indicating that the subchannel in subchannel group u, which is locally labeled m, is an available subchannel;

<math> <mrow> <mi>s</mi> <mo>&prime;</mo> <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> <mi>S</mi> <mo>&prime;</mo> <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> </mrow></math> n＝0，1，…，N-1；

this enables signals r (M) on M available subchannels to be jointly selected on the basis of the label information of the subchannel set u and its corresponding subchannel label information, M being 0, 1, …, M-1.

4. The downlink frequency division multiple access method of a frequency selective block transmission system according to claim 1, wherein: selecting the number of available sub-channels M occupying the number of sub-channels B in the sub-channel group u in the step (4)_uBetween 5% and 100%.

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