WO2007104203A1

WO2007104203A1 - Multi-antenna transmitting method in orthogonal frequency division multiplexing system and an apparatus thereof

Info

Publication number: WO2007104203A1
Application number: PCT/CN2006/003720
Authority: WO
Inventors: Lina Chen; Peigang Jiang; Jianghua Liu
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2006-03-15
Filing date: 2006-12-30
Publication date: 2007-09-20

Abstract

A multi-antenna transmitting method in orthogonal frequency division multiplexing system and an apparatus thereof. In present invention, the frequency-domain signals are multiplied by different phase sequences before modulation of orthogonal frequency division multiplexing, then modulated in each path and transmitted with antenna diversity, wherein the phase sequence can be random determined or designed on demand, the related bandwidth of channel and the accuracy of the channel characteristic estimation of the reception can be ensured not to change within n subcarriers by setting the phase sequence to vary each n (n is positive integer) subcarriers.

Description

Multi-antenna transmission method and device for orthogonal frequency division multiplexing system The present application claims to be submitted to the Chinese Patent Office on March 15, 2006, application number 200610067776.0, and the invention name is "multi-antenna transmission of orthogonal frequency division multiplexing system" The priority of the Chinese Patent Application, the entire disclosure of which is hereby incorporated by reference. Technical field

The present invention relates to the field of wireless communication technologies, and in particular, to radio frequency technology, and more particularly to a multi-antenna transmission method and apparatus for an orthogonal frequency division multiplexing system. Background technique

With the development of wireless mobile communication, users have put forward higher and higher requirements for the rate of wireless communication and the quality of monthly communication. As a multi-carrier communication technology of the future mobile communication core technology, Orthogonal Frequency Division Multiplexing (OFDM), it can overcome the multipath characteristics of the wireless channel and is more efficient than the single carrier spectrum. Become a hot spot of current research. In addition, the multi-input multi-output (MIMO) technology that has emerged in recent years has attracted much attention because it can increase the spectral efficiency and reliability of wireless communication systems, and has been applied to practical communication systems. .

As a multi-carrier digital modulation technique, OFDM encodes data and transmits it in the frequency domain. OFDM simultaneously transmits multiple high speed signals over a specially calculated orthogonal frequency. OFDM, in turn, acts as a multiplexing technique that multiplexes multiple signals onto different orthogonal subcarriers. The required bandwidth is much less. Due to the use of interference-free orthogonal carrier technology, no guard bands are required between individual carriers. This makes the available spectrum more efficient to use. In addition, OFDM technology can dynamically allocate data on subchannels. For maximum data throughput, multi-carrier modulators can intelligently allocate more data to sub-channels with less noise.

OFDM encodes the data to be transmitted as frequency domain information, modulates it into a time domain signal, and transmits it on the channel, and performs inverse process demodulation at the receiving end. Figure 1 shows the various components of an OFDM communication system. Wherein, the data is first encoded at the transmitting end, and then digitally modulated, where the digital modulation is a common modulation, such as Quadrature Amplitude Modulation (QAM), and then the data stream is segmented and converted in parallel, When each piece of data is obtained by fast inverse Fourier transform (IFFT, Inverse Fast Fourier Transform) The domain information is then subjected to parallel and serial conversion, and the cyclic prefix CP is added, and then sent to the communication channel through the transmitting module; on the receiving end, the signal is received first by the receiving module, followed by de-CP, serial-to-parallel conversion, fast Fourier transform. (FFT, Fast Fourier Transform), parallel-to-serial conversion, digital demodulation, decoding.

Multiple Input Multiple Output MIMO technology is a multi-input multi-antenna multi-antenna technology, in which multiple antennas are placed at the transmitting end and the receiving end of the communication system. Together with Space Division Multiplex (SDM), it is one of the cutting-edge communication technologies currently in development. In theory, it has been proved that multiple transmit antennas can divide the wireless channel into multiple parallel narrowband channels, which has the potential to improve the channel bit transmission rate, and the research results show that the channel capacity increases linearly with the increase of the number of antennas.

One of the key applications of MIMO technology is diversity, which can achieve spatial diversity gain to improve system performance.

The prior art Cyclic Shift Diversity (CSD) is a multi-antenna transmit diversity method based on OFDM systems. The frequency diversity gain is obtained by performing different cyclic shifts of the same OFDM symbols in the time domain and then transmitting them from a plurality of transmitting antennas, the specific transmitter system structure, as shown in FIG.

There are a total of M transmit antennas in the system. The OFDM symbols processed by IFFT are respectively copied on M transmit antennas, the first antenna is not shifted (delay is 0), and the OFDM symbols are needed on the second to Mth antennas. The cyclic shifts of unequal lengths are sequentially performed, and the number of bits shifted on different antennas is expressed as, " ₂ = 1, 2, ...^, where = 0. Assume that the length of IFFT is N, cyclically shifted The number of bits should satisfy o ≤ „ ≤ N - 1. After cyclic shifting, according to the communication principle of OFDM, the OFDM symbols on each antenna need to be added with a cyclic prefix CP, and then simultaneously transmitted out from different antennas to implement space division multiplexing. The length of the CP should be greater than the maximum multipath delay of the channel.

Since each antenna transmits a cyclic shift of the same OFDM symbol in the time domain, the signal of the OFDM symbol in the time domain is x(«), (o≤«≤N - 1), The signal of each carrier pair in the frequency domain is; ^ = o ..N - 1 , according to the condition that the CP length satisfies, it can be seen that the orthogonality of the subcarriers will not change. It can be seen from the nature of the FFT that cyclic shift in the time domain is equivalent to adding a phase rotation to the symbols in the frequency domain. After the time domain rotation, the signal obtained in the frequency domain is: Z(k) = X, k]e-, k = 0, --- Nl

The expression in the formula is the number of bits of the cyclic shift in the time domain. According to the above shift relationship, the signal of each antenna on each subcarrier in the frequency domain can be obtained as follows:

Z _m (k) =

, k = 0, -Nl;m = l,---M Assuming that the number of receiving antennas at the receiving end is 1, the receiving signal of the receiving end in the frequency domain is:

M M

Y{k) = H _m {k)Z _m (k) + N(k) = W∑ H _m k)e-^' ^IN + N(k), k = 0 N-\ where ^y W^3⁄4r Is the received signal at the first subcarrier, indicating the frequency domain channel response between the first transmit antenna and the receive antenna on the first subcarrier. Indicates additive white Gaussian noise.

From the results of the above formula, the multi-antenna system above 4 bar is equivalent to a single antenna system, which is expressed as:

Y(k) = H _e (k)X(k) + N(k), k = 0,---Nl, the equivalent channel can be expressed as

M m=l

From the final equivalent results, it can be seen that the cyclic shift of different antennas in the time domain is equivalent to introducing multipath in the time domain, and the performance in the frequency domain is enhanced by frequency selectivity, so that the OFDM modulation is used. The channel coding can obtain the frequency diversity gain. Compared with the single antenna system, this cyclic shift method can obtain more frequency diversity gain under the same channel coding and interleaving.

The advantage of CSD is that regardless of the number of antennas, its encoding rate is always 1. In addition, the implementation of CSD for different antenna numbers is simple, and its transmission and reception algorithms are similar for different antenna numbers.

However, its disadvantage is that, first of all, the method is prone to frequency puncturing, resulting in a decrease in the reliability of the wireless channel. It is noted that the diversity channel is formed by superimposing a plurality of subchannels after a fixed phase shift. Due to the uncertainty or randomness of the transmission characteristics of the subchannels, once the subchannel transmission characteristics themselves satisfy a certain relationship, such as a common divisor relationship , it will cause some equally spaced frequency blind spots on the resulting diversity channel, and the signal can not be transmitted at these frequency points, which is called frequency puncturing effect. Obviously, the appearance of the frequency puncturing effect will greatly reduce the channel transmission performance. Especially when the coding method such as interleaving code is adopted, the transmission signal itself is regularly interleaved in the transmission code. In the stream, if the signal appears on the blind spot of frequency, it will have serious consequences. It can be seen that the diversity method has a reliability problem and may cause deterioration of channel transmission performance. Secondly, the method reduces the correlation bandwidth of the channel by speeding up the frequency domain channel transform speed. When the receiver needs to estimate the fading characteristics of the signal and the interference within the relevant bandwidth, the estimation accuracy is reduced. In practical applications, the frequency selectivity is completely determined by one parameter of the delay, and the selectivity cannot be flexibly controlled. Due to the adoption of the fixed cyclic shift mechanism to achieve multi-antenna diversity, the additional fixed phase shift of different sub-channels of OFDM is not Appropriate delay value will cause the frequency response of some interval to be zero, which will produce the punching effect, affect the performance of the decoder and reduce the transmission reliability. Summary of the invention

The main object of the present invention is to provide a multi-antenna transmission method and apparatus for an orthogonal frequency division multiplexing system, so that an OFDM system realizes multi-antenna transmit diversity, obtains frequency diversity gain, improves transmission reliability, and effectively overcomes CSD. Disadvantages.

An embodiment of the present invention provides a multi-antenna transmission method for an orthogonal frequency division multiplexing system, where the orthogonal frequency division multiplexing system is provided with at least two transmitting antennas, and the method includes the following steps:

The transmitting end multiplies each frequency domain signal to be transmitted by a phase sequence corresponding to each transmitting antenna;

Performing orthogonal frequency division multiplexing modulation on the multi-channel frequency domain signals multiplied by the phase sequence to obtain a time domain signal;

The time domain signals are appended with cyclic prefixes and transmitted on respective corresponding transmit antennas. Preferably, the method further comprises the steps of:

Receiving, by the receiving end, the phase sequence information from the transmitting end;

The receiving end demodulates the received signal according to the received phase sequence information. The multiplexed frequency domain signals multiplied by the phase sequence corresponding to the same transmitting antenna are added before the orthogonal frequency division multiplexing modulation is converted into the time domain signal.

An embodiment of the present invention further provides a multi-antenna transmitting apparatus for an Orthogonal Frequency Division Multiplexing system, including a phase multiplying module, an orthogonal frequency division multiplexing modulation module, a cyclic prefix module, and at least two transmitting antennas.

The phase multiplication module is configured to multiply each channel-coded and modulated frequency domain signal by a phase sequence corresponding to the transmit antenna; The orthogonal frequency division multiplexing modulation module is configured to perform orthogonal frequency division multiplexing modulation on a signal from the phase multiplication module to obtain a time domain signal;

a cyclic prefix module, configured to add a cyclic prefix to the time domain signal from the orthogonal frequency division multiplexing modulation module;

The transmitting antenna is configured to send a signal from a cyclic prefix module.

More suitably, the device further comprises:

An adding module, configured to add phase-multiplied multiplex data corresponding to the same transmitting antenna;

The orthogonal frequency division multiplexing modulation module performs orthogonal frequency division multiplexing modulation on the signal from the adding module to obtain a time domain signal, and then sends the cyclic prefix module to the cyclic prefix module.

In the technical solution provided by the embodiment of the present invention, after multiplying the frequency domain signal by a different phase sequence before orthogonal frequency division multiplexing modulation, the sub-channel is modulated by orthogonal frequency division multiplexing and is applied to each antenna. The diversity transmission realizes the frequency diversity gain and obtains a high coding rate; wherein the phase sequence can be designed according to specific rules according to requirements, effectively avoiding the frequency puncturing effect and improving the channel transmission reliability; and, by setting the phase sequence every n (n is A positive integer) subcarrier changes once, which can ensure that the relevant bandwidth of the channel is constant within the range of n subcarriers, and the accuracy of the channel characteristic estimation by the receiving end is guaranteed to be unchanged. Furthermore, the phase sequence can also be adaptively adjusted according to the transmission quality evaluation and feedback at the receiving end, thereby improving the system robustness; the free setting of the phase sequence greatly improves the flexibility of the multi-antenna diversity transmitting system.

By multiplying different phase sequences before orthogonal frequency division multiplexing modulation to achieve frequency domain multi-antenna transmit diversity, the diversity gain of coding rate 1 is realized under any multiple antennas, and the transmission performance of the wireless channel is improved, which is achieved by directly multiplying the phase. More flexible control of the final channel response, increased system flexibility, and by avoiding frequency puncturing effects by setting the phase sequence as required, either time-varying or non-time-variant, random or ordered, adaptively adjusted, etc. , thereby improving the performance of the system decoder and improving the reliability of wireless communication. DRAWINGS

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

2 is a schematic structural diagram of a transmitter system of cyclic shift diversity;

3 is a schematic structural diagram of a diversity transmitting apparatus according to an embodiment of the present invention; 4 is a schematic structural diagram of a diversity transmitting apparatus according to another embodiment of the present invention. detailed description

The present invention will be further described in detail below with reference to the accompanying drawings.

In order to achieve fully flexible and customized phase multiplication, the present invention selects the OFDM modulated signal before the orthogonal frequency division multiplexing modulation transform, and separately performs phase multiplication, and then respectively modulates and adds the loop by orthogonal frequency division multiplexing. The prefix CP is simultaneously transmitted on the antenna in diversity. In addition, the selection or design of the phase sequence is a key factor in determining the diversity performance. It may be generated by the system using some kind of pseudo-random code or according to a fixed law, which may be changed with time or statically, and may be adaptively adjusted according to feedback. and many more. The basic innovations are: Setting phase sequence multiplication prior to Orthogonal Frequency Division Multiplexing modulation makes these completely free and flexible configurations possible, and provides the basis for improving or optimizing the diversity channel.

In the process of orthogonal frequency division multiplexing OFDM modulation, the encoded data to be transmitted needs to be used as frequency domain information, and then modulated into a time domain signal. Here, the fast data to be transmitted is usually subjected to fast inverse Fourier transform IFFT, and other transforms may be adopted. In this way, get time domain information. The frequency diversity gain is obtained by performing different cyclic shifts in the time domain and then transmitting them from multiple transmit antennas.

It can be seen from the principle of the foregoing CSD that CSD can be equivalent to multiplying the data on the frequency i or each subcarrier by different phases on the antenna. The CSD signal expression is as follows:

Z _m , k, = X(jc)e- ^{jl7ksj N} , k = 0, · · · N - ^lm2 , · · · M

It can be clearly seen that this phase is linear with the cyclic delay and the number of the subcarriers, ie _{% m =} -3⁄4L, where N is the length of the IFFT, = 1, 2, ... N represents the number of the subcarrier. Is the cyclic delay on the first transmit antenna. Embodiments of the present invention utilize this equivalent characteristic to replace the cyclic delay of the time domain by adding phase shifting in the frequency domain.

In the first embodiment of the present invention, the multi-antenna transmit diversity device of the orthogonal frequency division multiplexing system of this configuration is multiplied by the phase sequence before the orthogonal frequency division multiplexing modulation, as shown in FIG.

The device includes a source-to-channel coding module and an OFDM modulation module. According to the principle of the foregoing OFDM system, the channel coding module is configured to encode and transmit the information to be transmitted to the OFDM modulation module, and the OFDM modulation module is used for future confidence. The coded signal of the channel coding module is OFDM-modulated to obtain a frequency domain signal. In addition, the single signal from the OFDM modulation module is split into signals corresponding to the respective antennas, and each of the signals passes through: a phase multiplication module, an orthogonal frequency division multiplexing modulation module, a CP module, and a transmitting antenna. The phase multiplication module is configured to multiply the frequency domain OFDM modulated signal modulated by the OFDM modulation module by the phase sequence corresponding to the transmit antenna; the orthogonal frequency division multiplexing modulation module is configured to use the frequency from the phase multiplication module. The domain signal is subjected to orthogonal frequency division multiplexing modulation to obtain a time domain signal; the cyclic prefix module is configured to add a cyclic prefix to the time domain signal from the orthogonal frequency division multiplexing modulation module, and finally send the respective transmit antennas, which is Implement frequency domain diversity transmission.

It can be seen from Fig. 3 that the data to be transmitted is channel-coded and modulated and then copied into M parts and mapped onto the M卞 antenna. The modulated symbols are multiplied by a phase sequence c on each day, C _m = { e ^M "' e ^Jd '"' ---, e ^je "'' ^T ), and then OFDM is added and cyclic prefix is added to transmit on the antenna.

At this time, the frequency domain signal transmitted by the antenna m can be expressed as:

Z _m (k) = X(k)e ^jem ' ^k ,k = 0,---,Nl;m = l,---,M Assuming that the number of antennas at the receiving end is 1, then the receiving antenna is received in the frequency domain. The channel can represent (t) H _m {k)e ^je -' ^k + N(k), k = 0,---Nl

At this point, the equivalent channel in the frequency domain can be expressed as:

It can be seen from the above that by randomly superimposing the channels on the plurality of antennas by using different phase sequences on the respective antennas, the equivalent channel frequency selectivity can be made stronger, thereby increasing the frequency diversity gain. In addition, the transmitting end can also notify the receiving end of the phase sequence multiplied in the frequency domain on each antenna by broadcasting or other means, and the receiving end can demodulate the data.

First, the transmitting end multiplies the frequency domain modulated signals to be transmitted by the phase sequence corresponding to each transmitting antenna; and then performs orthogonal frequency division multiplexing modulation to obtain a time domain signal; finally, the time domain signal is added with a cyclic prefix, and Each is transmitted simultaneously on the corresponding transmit antenna. At the same time, the transmitting end also notifies the receiving end of the phase sequence information, so that the receiving end demodulates the received signal.

In the embodiment of the present invention, a manner of completely freely customizing the phase sequence is provided, so the channel Transmission effects, reliability, performance, etc. all depend on the design of the phase sequence. For different OFDM symbols, the phase sequence multiplied by each antenna in the frequency domain may be varied or constant. The phase sequence can be a pseudo-random sequence, and has a certain rule, when each element of the phase sequence takes a value

The present invention is equivalent to the effect of the CSD, T _m CSD i.e. the cyclic delay.

In a specific embodiment of the present invention, the transmission characteristics of each subchannel corresponding to the transmitting antenna are random, so the phase sequence can be generated by the system through the pseudo random code, which can significantly reduce the probability of frequency domain puncturing in the finally synthesized channel. , improve reliability;

Secondly, the system can set the transform period of the phase sequence to n (n is a positive integer) subcarriers; ensure that the relevant bandwidth of the channel is not affected in n subcarriers, and guarantee the performance of channel estimation and interference cancellation;

Again, the real channel tends to change over time, so the system can regenerate the phase sequence over time;

Finally, a feedback mechanism can be established to implement adaptive adjustment. For example, the receiving end evaluates and feeds back channel transmission performance information according to the received demodulation signal, and the transmitting end automatically adjusts the phase sequence according to the feedback information, so that the performance of the channel tends to be optimal, and the specific There are many ways to adjust. In addition, it is also possible to combine space-time coding into the above-described orthogonal frequency division multiplexing system, combining their respective advantages.

A diversity transmitting device architecture according to another embodiment of the present invention is shown in FIG. There are multiple sets of data sending units in the system, which can send multiple data streams at the same time.

Based on the MIMO principle, when there are multiple transmit antennas and multiple receive antennas, multiple data streams can be simultaneously transmitted on different antennas, that is, spatial multiplexing. In this case, the method described in the foregoing embodiment can be implemented for each data stream. Each data stream is copied into the same data in the frequency domain. Each branch is multiplied by a different phase sequence, and the same branches of different data streams are added to perform orthogonal frequency division multiplexing modulation and adding cycles. After the prefix CP is operated, it is sent on M antennas.

The plurality of data streams may be data streams generated from different sources and encoded and modulated by different channels, or may be generated by the same source through the same channel coding and modulation and then serial-to-parallel conversion. Combining spatial multiplexing with the technical solutions described in the foregoing embodiments can be obtained simultaneously The spatial multiplexing gain, that is, the simultaneous transmission of multiple data streams increases the transmission rate, and simultaneously obtains the frequency diversity gain for each data stream, thereby improving the reliability of the transmission.

In addition, as can be seen from the above, the cyclic delay diversity CSD is equivalent to multiplying the data on each subcarrier by a phase in the frequency domain, so that the equivalent channel change of the signal passes faster, that is, the correlation bandwidth of the channel becomes smaller, thereby obtaining Frequency diversity gain.

When the receiver uses the interference cancellation receiver, in order to estimate the interference characteristics more accurately, the estimated value needs to be averaged over the n subcarriers in the frequency domain. At this time, the number of subcarriers n is proportional to the correlation bandwidth.

If the data on each subcarrier is multiplied by a different phase when the present invention is applied, the fluctuation of the equivalent channel is large. If the estimated value is still averaged over n subcarriers, the estimation accuracy will decrease. At this time, only the number of subcarriers n averaged will be reduced, which will also cause the estimation accuracy to decrease. In order to avoid this effect, the phase sequence change period on each antenna is set to n, that is, on the adjacent n subcarriers, the multiplied phases are the same, and the phase is different every n subcarriers. This ensures that the accuracy of the n subcarriers with the same phase is not reduced when averaging the estimated values, and the channel variation can be accelerated every n subcarriers to obtain the frequency diversity gain.

It should be understood that, in the description of the foregoing embodiments, specific examples and details of the implementations are given for clarity of description. In a specific application, the preferred manner may be selected according to actual conditions to achieve the object of the invention, which does not affect the present invention. The substance and scope.

While the invention has been illustrated and described with reference to the preferred embodiments embodiments The spirit and scope of the invention.

Claims

Rights request

A multi-antenna transmission method for an Orthogonal Frequency Division Multiplexing (OFDM) system, the Orthogonal Frequency Division Multiplexing (OFDM) system is provided with at least two transmitting antennas, and the method includes the following steps:

The time domain signals are appended with cyclic prefixes and transmitted on respective corresponding transmit antennas.

2. The multi-antenna transmission method according to claim 1, further comprising the following steps:

The receiving end demodulates the received signal according to the received phase sequence information.

The multi-antenna transmission method according to claim 1 or 2, wherein the phase sequence is generated by a formula or a pseudo-random sequence is used.

The multi-antenna transmission method according to claim 2, wherein the phase sequence satisfies different path frequencies i on the same antenna or different phase sequences of signals, and corresponding phases of signals in the same frequency domain on different antennas The sequence is different.

The multi-antenna transmission method according to claim 2, further comprising the following steps:

The transmitting end multiplies the frequency domain orthogonal frequency division multiplexing modulated signal by a different phase sequence at different times.

The receiving end evaluates and feeds back channel transmission performance information according to the received demodulation signal, and the transmitting end adjusts the phase sequence according to the feedback information.

The multi-antenna transmission method according to claim 1, further comprising: before the converting the orthogonal frequency division multiplexing modulation into a time domain signal, the passing and phase corresponding to the same transmitting antenna The multiplied frequency domain signals of the sequence multiplication are added.

The multi-antenna transmission method according to claim 1, wherein the frequency domain is adjusted When the signal is multiplied by the phase sequence corresponding to each transmitting antenna,

According to the frequency domain change period of the phase sequence on each antenna is preset, the same phase is multiplied on adjacent integer n subcarriers, and the separated subcarriers are multiplied by different phases.

A multi-antenna transmitting apparatus for an Orthogonal Frequency Division Multiplexing system, comprising: a phase multiplying module, an orthogonal frequency division multiplexing modulation module, a cyclic prefix module, and at least two transmitting antennas, wherein the phase a multiplying module, configured to multiply each channel-coded and modulated frequency domain signal by a phase sequence corresponding to the transmitting antenna;

The orthogonal frequency division multiplexing modulation module is configured to perform orthogonal frequency division multiplexing modulation on a signal from the phase multiplying module to obtain a time domain signal;

The multi-antenna transmitting apparatus according to claim 9, further comprising: an adding module, configured to add phase-multiplied multiplex data corresponding to the same transmitting antenna; The signal from the adding module is subjected to orthogonal frequency division multiplexing modulation by the modulation module to obtain a time domain signal, which is then sent to the cyclic prefix module.

The multi-antenna transmitting apparatus according to claim 9, further comprising a transmitting module, wherein the transmitting end notifies the receiving end of the phase sequence information, so that the receiving end solves the received signal. Tune.

12. Multi-antenna transmitting apparatus according to claim 9 or 10 or 11, wherein the phase sequence is regenerated by the system over time.