CN101005303B - Transmitting Antenna Selection and Adaptive Modulation Method for OFDM Systems - Google Patents

Abstract

The invention discloses a transmitting antenna selection and adaptive modulation method in a multiple-input multiple-output orthogonal frequency division multiplexing system. First, the receiver estimates the channel impulse response corresponding to each subcarrier; then filters the received signal to obtain The filter matrix corresponding to each subcarrier; estimate the detection output signal-to-noise ratio of each subcarrier corresponding to each transmitting antenna in each transmitting antenna combination; estimate the average detection output signal of each transmitting antenna corresponding to the spatial channel in the entire bandwidth range Noise ratio; select a modulation method according to the relationship between the average detection output signal-to-noise ratio corresponding to each transmitting antenna and the signal-to-noise ratio threshold under various possible modulation methods; calculate the system throughput under each combination of transmitting antennas ; Select a group of transmitting antennas with the largest throughput and their corresponding modulation modes as the final transmission mode. The invention realizes the selection and self-adaptive modulation of the transmitting antenna in the MIMO OFDM system.

Description

Transmitting Antenna Selection and Adaptive Modulation Method for OFDM Systems

technical field

The present invention relates to a multiple-input multiple-output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) wireless communication system, in particular to a transmitting antenna selection and adaptive modulation method in the spatial multiplexing MIMO OFDM system.

Background technique

With the development of wireless communication technology, users put forward higher requirements for large-capacity data transmission and fast data transmission. Therefore, it is necessary to effectively use wireless communication system resources to improve the performance and efficiency of the wireless communication system. However, in future mobile communication systems, multipath fading and bandwidth efficiency will be the main technical factors that hinder the development of communication systems. How to overcome these two difficulties is the core of next generation wireless communication research. The multi-carrier processing technology based on Orthogonal Frequency Division Multiplexing (OFDM) can reduce the influence of multipath fading by converting the frequency-selective multipath fading channel into a flat channel in the frequency domain, while the multiple-input multiple-output (MIMO ) technology can increase the spectrum utilization efficiency of the system without increasing the system bandwidth, so OFDM and MIMO technology will become the core of physical layer processing in the next generation wireless communication system. Furthermore, the MIMO OFDM system that combines MIMO and OFDM technology can make full use of wireless resources in the time domain, frequency domain and air domain, and achieve strong reliability and high transmission rate through diversity.

The proposal of multiple-input multiple-output (MIMO) technology has opened up a new field for modern wireless communication. It provides a future mobile communication system, especially for high-speed data access services, without increasing the bandwidth. It can greatly improve the means of system data rate and spectral efficiency.

In a spatial multiplexing MIMO system, different antennas transmit mutually independent transmission signals, that is to say, the data transmitted for each frame must be correctly demodulated at the receiving end. However, the actual wireless channel environment is varied and quite complex. If a certain channel is in a poor state, the signal transmitted by the corresponding antenna will not be demodulated correctly or the cost of demodulation will be too high, which means With the loss of information sent by all antennas, this is something we are extremely reluctant to see. Existing studies have shown that in a low-rank channel environment, channel capacity can be improved by using fewer antennas. The solution is to judge the channel state information, select the antenna with better channel state (can be accepted) through antenna selection technology to send the corresponding service signal, and turn off other antennas with bad channel state (unacceptable) or just It is used to send pilots instead of service signals, so that, in the worst case, at least one antenna can be guaranteed to send service signals, thus ensuring the smooth link of the system.

In the Chinese patent CN 1578192 (publication number) "transmitting diversity equipment and method in mobile communication system" applied on July 8, 2004, a kind of transmitting antenna selection method has just been described. The receiver performs BLAST decoding on the received signals from multiple receiving antennas, and calculates the signal-to-noise ratio (SNR) of the forward channel associated with each transmitting antenna to determine the forward channel corresponding to each transmitting antenna among the multiple transmitting antennas channel characteristics. The channel state feature is fed back to the transmitter as the selection information of the transmitting antenna, and the transmitter selects a transmitting antenna with a better state according to the information to transmit the service signal. However, the patent does not explain the basis for judging the selection of several transmitting antennas.

In the IEEE International Conference on Communications 2002, the first volume of ICC 2002, pages 641-645, published a paper entitled "StatisticalMIMO Antenna Sub-Set Selection with Space-Time Coding" written by Gore D and Paulraj A. In this The paper describes a method of antenna selection based on the criterion of minimizing the average channel bit error rate. However, this method is only for the MIMO system, and it is assumed that the MIMO channel has the characteristics of flat fading, and it is not suitable for the MIMO OFDM system with the characteristics of the frequency selective fading channel.

Contents of the invention

The technical problem to be solved by the present invention is to provide a transmission antenna selection and adaptive modulation method in a multiple-input multiple-output orthogonal frequency division multiplexing system, in a MIMO OFDM system with frequency selective fading channel characteristics, to realize the transmission antenna selection and adaptive modulation.

In order to solve the above technical problems, the present invention provides a transmit antenna selection and adaptive modulation method in a MIMO system, comprising the following steps:

(1) At the receiving end, use the received pilot signal to estimate the channel impulse response Hc _,k corresponding to each subcarrier; where Hc _,k represents the channel impulse corresponding to the cth subcarrier in the kth transmit antenna combination response;

(2) Utilize the estimated channel impulse response H _{c, k} to filter the received signal, obtain the filter matrix G ^(c) corresponding to each subcarrier; wherein G ^(c) represents the filter matrix corresponding to the c subcarrier;

(3) Using the filter matrix G ^(c) and the channel impulse response _Hc,k to estimate the detection output signal-to-noise ratio of each subcarrier corresponding to each transmit antenna in each transmit antenna combination;

(4) According to the detection output signal-to-noise ratio, estimate the average detection output signal-to-noise ratio of each transmitting antenna corresponding to the spatial channel within the entire bandwidth range;

(5) According to the relationship between the average detection output signal-to-noise ratio corresponding to each transmitting antenna and the signal-to-noise ratio threshold under various possible modulation modes, select a modulation mode for each transmitting antenna;

(6) Under the modulation mode selected by each transmitting antenna, calculate the system throughput under each transmitting antenna combination;

(7) Select a group of transmitting antennas with the largest throughput and a modulation mode corresponding to each antenna in the group of transmitting antennas as the final transmission mode.

Wherein, if there are more than one group of transmit antenna combinations with the maximum throughput, the group with the largest number of antennas is selected.

The method of transmitting antenna selection and adaptive modulation in the present invention skillfully integrates the transmitting antenna selection in the spatial multiplexing MIMO system and the adaptive modulation in the OFDM system according to the principle of maximizing the system transmission throughput, fully The frequency domain and air domain resources of the MIMO OFDM wireless communication system are utilized. Moreover, the antenna selection method of the present invention naturally links together the determination process of the total number of transmitting antennas to be selected and the judging process of which transmitting antennas to select, thereby enhancing the flexibility of the antenna selection technology.

Description of drawings

FIG. 1 is a schematic flow diagram of implementing transmit antenna selection and adaptive modulation in a MIMO OFDM system according to an embodiment of the present invention.

Detailed ways

In Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) systems, antenna selection and adaptive modulation are two techniques to improve system performance, where adaptive modulation is based on channel changes on each subcarrier, Selecting an appropriate modulation scheme for each subcarrier maximizes the information rate of the entire OFDM system. Antenna selection is to select a subset from numerous transmitting antennas or receiving antennas to implement transmitting and receiving functions in a MIMO system in which multiple antennas are configured at both the transmitting end and the receiving end.

The possible modulation modes adopted by the system of the present invention can be, but not limited to, BPSK (binary phase shift keying), QPSK (quadrature phase shift keying), 16QAM (16-point quadrature amplitude modulation), 64QAM (64 point positive cross-amplitude modulation).

Under the assumption that there are 4 transmitting antennas, we can record the index numbers of the antennas as 1, 2, 3, and 4 respectively. For the convenience of description, all transmitting antenna combinations are described by a set S (because the present invention only It involves the selection of the transmitting antenna, so when describing the antenna combination, it is only for the transmitting antenna), that is:

S={(1), (2), (3), (4), (1, 2), (1, 3), (1, 4), (2, 3), (2, 4), ( 3,4),(1,2,3),(1,2,4),(2,3,4),(1,2,3,4)},

The 14 combinations are respectively represented by index numbers q=1, 2, . . . , 14. Among them, q=1 means that only the first transmitting antenna is used for transmission, which is described as (1) in the set; q=2 means that the system only uses the first and second antennas for transmission, and is described as (1, 2) in the set ; The meaning of other combinations can be deduced accordingly. In this way, each subcarrier may support 4 modulation modes, and there are 14 possible antenna configuration modes.

As shown in Figure 1, assuming that M transmit antennas and N receive antennas are configured in the MIMO OFDM system, and the number of subcarriers in the system is C, then the MIMO OFDM system described in the embodiment of the present invention realizes transmit antenna selection and automatic A method for adapting modulation, comprising the steps of:

Step 101: At the receiving end, use the received pilot information to estimate the channel impulse response H _c corresponding to each subcarrier, where the subscript c=1, 2, . . . , C represents the subcarrier.

Step 102: Use the channel impulse response H _c estimated in step 101 to filter the received signal to obtain a filter matrix G ^(c) corresponding to each subcarrier. Here, the filter matrix can be obtained by the zero-forcing (ZF) or minimum mean square error (MMSE) detection algorithm in Bell Labs vertical layered space-time structure (V-BLAST) processing, namely:

${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; ZF</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; ,</span>$ ${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; MMSE</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; .</span>$

表示维度是N_k的单位阵，E_s为信号功率(W)，N₀为高斯白噪声的功率(W)，上标H表示Hermitian转置，上标(-1)表示矩阵的逆运算。Moreover, the filter matrix satisfies the following condition, namely: G ^(c) H _c,k =I. Where Hc _{, k} represent the channel response matrix of the kth transmit antenna combination under the cth subcarrier, and N _k represents the number of transmit antennas in the kth transmit antenna combination (there are K transmit antenna combinations in total, that is, k=1 , 2,..., K, if the number of transmit antennas is M=4, then K=14),

Indicates the unit matrix whose dimension is N _k , E _s is the signal power (W), N ₀ is the power of Gaussian white noise (W), the superscript H indicates the Hermitian transpose, and the superscript (-1) indicates the inverse operation of the matrix.

Step 103: Using the filter matrix, estimate the signal-to-noise ratio of the detection output of each subcarrier corresponding to each transmit antenna in each transmit antenna combination.

Using Equation 1, assuming that g _k is the kth row of the filter matrix G ^(c) , and h _k is the kth column of the channel matrix Hc _,k , then the SNR of the detection output corresponding to the kth sub-data stream can be obtained.

${\mathrm{\&gamma;}}_{m,c,k}=\frac{{\mathrm{E.}}_{\mathrm{the\; s}}{\left|g_k{h}_k\right|}^2}{N_k{N}_0{\left|\right|g_k\left|\right|}^2+{\mathrm{E.}}_{\mathrm{the\; s}}{\mathrm{\&Sigma;}}_{j\&NotEqual;k}{\left|g_k{h}_j\right|}^2}$ Formula 1

Step 104: Using Formula 2, estimate the average detection output signal-to-noise ratio of the spatial channel corresponding to each transmitting antenna within the entire bandwidth range.

${\mathrm{\&gamma;}}_{m,k}=\frac{1}{C}\underset{c=1}{\overset{C}{\mathrm{\&Sigma;}}}{\mathrm{\&gamma;}}_{m,c,k}$ Formula 2

Step 105: Select a modulation mode for each transmitting antenna according to the relationship between the average detected output SNR corresponding to each transmitting antenna and the SNR thresholds under various possible modulation modes.

In a specific application process, the modulation level is selected according to the average detection output signal-to-noise ratio and the predetermined SNR threshold required for adopting different modulation modes. This method is described in "A Blockwise Loading Algorithm for the Adaptive Modulation Technique in OFDM Systems" written by R Grunheid, E Bolinth, and H Rohling, which was published in October 2001 at the IEEE Vehicular Technology Conference (VTC). Volume 2, pp. 948-951.

For example, when the given target bit error rate (BER) is 10-3, according to the BER curve in the Gaussian white noise channel, the SNR thresholds required for different modulation methods can be obtained:

modulation scheme SNR Threshold (dB) Do not use ＜8 Binary Phase Shift Keying (BPSK) 8 Quadrature Phase Shift Keying (QPSK) 10 16-point quadrature amplitude modulation (16QAM) 18 64-point quadrature amplitude modulation (64QAM) twenty four

Step 106: Under the modulation mode selected by each transmit antenna, calculate the system throughput under each transmit antenna combination. The throughput is defined as the sum of bits transmitted by the system on each subcarrier.

In this step, the system throughput under each group of transmitting antennas is calculated under the condition that each antenna in the group of transmitting antennas uses its respective determined modulation mode for transmission.

Step 107: Select the group of antennas with the highest throughput among all the combinations of transmitting antennas and their corresponding modulation modes as the final transmission mode. If there are two groups of antenna combinations corresponding to the same throughput, the group with the largest number of antennas is selected.

Since in step 105, the respective modulation modes have been determined for each transmitting antenna, therefore, after a group of transmitting antennas with maximum throughput is determined in step 107, the modulation mode corresponding to each antenna in the group of antennas is also Naturally determined. That is to say, the present invention firstly determines the respective modulation modes of each transmitting antenna, and then determines which antennas to use.

Of course, the embodiments provided by the present invention are only to illustrate in detail the method for realizing adaptive modulation in the MIMO OFDM system provided according to the contents of the present invention, and therefore they are all exemplary implementations, and it cannot be regarded as a reference to the present invention. Moreover, any obvious modifications within the gist of the present invention should also fall within the scope of protection of the present invention.

Claims (5)

1. the emitting antenna selecting of an ofdm system and self-adaptive modulation method, this ofdm system are multiple-input and multiple-output, it is characterized in that, comprise the steps:

(1), utilize the pilot signal that receives to estimate the channel impulse response H of each subcarrier correspondence at receiving terminal _{C, k}H wherein _{C, k}The channel impulse response of representing c subcarrier correspondence in the k kind emitting antenna combination;

(2) utilize described estimated channel impulse response H _{C, k}Carry out filtering to received signal, obtain the filtering matrix G of each subcarrier correspondence ^(c)G wherein ^(c)The filtering matrix of representing c subcarrier correspondence;

(3) utilize described filtering matrix G ^(c)With channel impulse response H _{C, k}, estimate each subcarrier detection output signal-to-noise ratio corresponding to every transmit antennas in every kind of emitting antenna combination;

(4), estimate the average detected output signal-to-noise ratio of every transmit antennas spatial channel corresponding in the entire belt wide region according to described detection output signal-to-noise ratio;

(5) according to the average detected output signal-to-noise ratio of described every transmit antennas correspondence and the relation between the signal-noise ratio threshold under the various possibility modulation system, be every transmit antennas selecting modulation mode;

(6) under the modulation system that every transmit antennas is selected, calculate the throughput of system under each emitting antenna combination;

(7) one group of transmitting antenna of the described throughput maximum of selection, and this modulation system of organizing every antenna correspondence in transmitting antenna is as final transmission means.

2. the method for claim 1 is characterized in that, selects the step of one group of transmitting antenna of throughput maximum described in the step (7), further comprises:

If the emitting antenna combination with maximum throughput, is then selected wherein that maximum group of number of antennas more than one group.

3. the method for claim 1 is characterized in that, filtering matrix G described in the step (2) ^(c), be that the ZF in the structure treatment or least mean-square error detection algorithm obtain during by the Bell Laboratory vertical layered space.

4. the method for claim 1 is characterized in that, the signal-noise ratio threshold under the described different modulating mode of step (5) is predetermined.

5. the method for claim 1 is characterized in that, the described throughput of step (6) is the summation of system's transmitted bit on each subcarrier.

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