CN101005303B - Selective and adaptive modulation method for transmitting antenna in multiple input and multiple output orthogonal frequency division multiplex system - Google Patents

Selective and adaptive modulation method for transmitting antenna in multiple input and multiple output orthogonal frequency division multiplex system Download PDF

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CN101005303B
CN101005303B CN2006100016359A CN200610001635A CN101005303B CN 101005303 B CN101005303 B CN 101005303B CN 2006100016359 A CN2006100016359 A CN 2006100016359A CN 200610001635 A CN200610001635 A CN 200610001635A CN 101005303 B CN101005303 B CN 101005303B
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transmitting antenna
noise ratio
antenna
transmit antennas
modulation
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蒋小奎
王强
张力
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ZTE Corp
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Abstract

The method includes steps: first, receiver estimates channel impulse response corresponding to each sub carrier; then, filtering the received signal to obtain filtering matrix corresponding to each sub carrier; estimating detected output SNR of each transmitting antenna corresponding to each carrier in each combination of transmitting antenna; estimating average detected output SNR in whole bandwidth range of spatial channel corresponding to each transmitting antenna; selecting modulation mode based on the said average detected output SNR, and relation between SNR thresholds under each possible modulation mode; calculating system throughput under each combination of transmitting antennae; selecting one set of transmitting antenna with largest throughput and corresponding modulation mode as final transmission mode. In MIMO OFDM system, the invention realizes selection of transmitting antenna, and adaptive modulation.

Description

The emitting antenna selecting of ofdm system and self-adaptive modulation method
Technical field
The present invention relates to OFDM (OFDM) wireless communication system of a kind of multiple-input and multiple-output (MIMO), relate in particular to a kind of emitting antenna selecting and self-adaptive modulation method in the spatial multiplexing MIMO ofdm system.
Background technology
Along with development of wireless communication devices, the user has proposed higher requirement for large-capacity data emission and fast data transmission, therefore, need effectively utilize the wireless communication system resource, improves the performance and the efficient of wireless communication system.Yet in the mobile communication system in future, multipath fading and bandwidth efficiency will be to hinder the major technique factor that communication system is greatly developed.How overcoming this two big difficulty, is the core of next generation wireless communication research.Multicarrier treatment technology based on OFDM (OFDM) can be by being converted into flat channel with the frequency selectivity multidiameter fading channel in frequency domain, thereby reduced the influence of multipath fading, and multiple-input and multiple-output (MIMO) technology can increase the spectrum utilization efficiency of system under the condition that does not increase system bandwidth, so OFDM and MIMO technology will become the core of physical layer process in the next generation wireless communication system.Further, the MIMO ofdm system that MIMO and OFDM technology are combined just can make full use of Radio Resource in time domain, frequency domain and spatial domain, and reaches stronger reliability and very high transmission rate by diversity.
The proposition of multiple-input and multiple-output (MIMO) technology is that Modern wireless communication has been opened up a brand-new field, it gives following mobile communication system, particularly the business that high-speed data is inserted provides a kind of means that can greatly improve system data rate and spectrum efficiency under the situation that does not increase bandwidth.
In the spatial multiplexing MIMO system, different separate the transmitting of antenna emission that is to say that the data of launching at each frame all must obtain correct demodulation at receiving terminal.But, actual wireless channel environment is protean and quite complicated, if the state of certain channel is relatively poor, the cost that the signal that will cause respective antenna to be launched can not obtain correct demodulation or demodulation is too big, this just means losing of the corresponding transmission information of all antennas, and to be that we are extremely unwilling see for this.There are some researches show, under the low rank channel environment, adopt less antenna can obtain the improvement of channel capacity on the contrary.Its solution is judged channel condition information exactly, antenna by sky line options choice of technology channel status better (can be accepted) sends the corresponding service signal, and the antenna of other channel statuss bad (can not be accepted) cuts out or just is used for sending pilot tone and do not send service signal, like this, in the worst case, at least can guarantee an antenna transmission service signal, thereby the link of the system of assurance is unimpeded.
In the Chinese patent CN 1578192 (publication number) " transmission diversity apparatus in the mobile communication system and method " of application on July 8th, 2004, a kind of emitting antenna selecting method has just been described.Receiver calculates the signal to noise ratio (snr) of the forward channel relevant with every transmit antennas to carry out the BLAST decoding from the received signal of many reception antennas, to determine the channel characteristics of the forward channel of every transmit antennas correspondence in many transmit antennas.And with this channel status feature as the selection feedback information of transmitting antenna to transmitter, by transmitter according to this Information Selection state preferably transmitting antenna come the transmitting business signal.But, do not illustrate in this patent and judge the foundation of selecting several transmit antennas.
At IEEE International Conference on Communications 2002, announce the paper that is entitled as " StatisticalMIMO Antenna Sub-Set Selection with Space-Time Coding " that Gore D and Paulraj A write on the 641st～645 page of the first volume of ICC 2002, in this piece paper, described a kind of antenna selecting method that minimizes criterion based on the channel average error bit rate.But this method is just at mimo system, and the hypothesis mimo channel has the characteristics of flat fading, is not suitable for the MIMO ofdm system with frequency selective fading channels characteristic.
Summary of the invention
Technical problem to be solved by this invention is to provide emitting antenna selecting and the self-adaptive modulation method in a kind of multi-input multi-output orthogonal frequency division multiplexing system, in having the MIMO ofdm system of frequency selective fading channels characteristic, realize the selection and the Adaptive Modulation of transmitting antenna.
For solving the problems of the technologies described above, the invention provides emitting antenna selecting and self-adaptive modulation method in a kind of multi-input multi-output orthogonal frequency division multiplexing system, 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, kH wherein C, kThe channel impulse response of representing c subcarrier correspondence in the k kind emitting antenna combination;
(2) utilize described estimated channel impulse response H C, kCarry 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.
Wherein, if the emitting antenna combination with maximum throughput, is then selected wherein that maximum group of number of antennas more than one group.
The method of emitting antenna selecting of the present invention and Adaptive Modulation, the principle throughput-maximized according to system transmissions merges into one emitting antenna selecting in the spatial multiplexing MIMO system and the Adaptive Modulation in the ofdm system dexterously, made full use of the frequency domain and the spatial domain resource of MIMO OFDM wireless communication system.And antenna selecting method of the present invention, needs are selected the total number of transmitting antenna definite process, select the deterministic process of which transmit antennas to get in touch naturally together, thereby strengthened the use flexibility of day line options technology.
Description of drawings
Fig. 1 is according to the schematic flow sheet of realizing emitting antenna selecting and Adaptive Modulation in the described MIMO ofdm system of the embodiment of the invention.
Embodiment
In multiple-input and multiple-output (MIMO) and OFDM (OFDM) system, it line options and Adaptive Modulation are to improve two technology of systematic function, wherein Adaptive Modulation is exactly according to the channel variation on each subcarrier, select suitable modulation system for each subcarrier, make the information rate of whole OFDM system maximize.And a day line options is exactly all to have disposed in the mimo system of many antennas at transmitting terminal and receiving terminal, selects a subclass and realize transmitting and receiving function from numerous transmitting antennas or reception antenna.
The possible modulation system that system of the present invention adopts, can but to be not limited to be BPSK (binary phase shift keying), QPSK (quadriphase PSK), 16QAM (16 quadrature amplitude modulation), 64QAM (64 quadrature amplitude modulation).
Have in hypothesis under the situation of 4 transmit antennas, we can be designated as 1,2,3,4 respectively with the call number of antenna, for convenience, all transmission antenna group are share a S set to be described (because the present invention only relates to emitting antenna selecting, therefore when describing combination of antennas, just at 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)}，
These 14 kinds combination difference index of reference q=1,2 ..., 14 represent.Wherein q=1 represents just to utilize the 1st transmit antennas to launch, and is described as (1) in set; Q=2 represents that system just selects for use the 1st, 2 antenna to launch, and is described as (1,2) in set; The rest may be inferred for the implication of other combinations.Like this, the modulation system that each subcarrier may be supported has 4 kinds, and possible antenna configurations mode has 14 kinds.
As shown in Figure 1, suppose in the MIMO ofdm system, to have disposed M transmit antennas and N root reception antenna, the subcarrier of system is C, then realizes the method for emitting antenna selecting and Adaptive Modulation in the described MIMO ofdm system of the embodiment of the invention, comprises the steps:
Step 101:, utilize the pilot frequency information that receives to estimate the channel impulse response H of each subcarrier correspondence at receiving terminal c, subscript c=1 wherein, 2 ..., C represents subcarrier.
Step 102: utilize estimated channel impulse response H in the step 101 cCarry out filtering to received signal, obtain the filtering matrix G of each subcarrier correspondence (c)Here, ZF (ZF) or least mean-square error (MMSE) detection algorithm during structure (V-BLAST) was handled when this filtering matrix can be by the Bell Laboratory vertical layered space obtain, that is:
G ZF ( c ) = ( H c , k H H c , k ) - 1 H c , k H , G MMSE ( c ) = ( H c , k H H c , k + N 0 / E s - I N k ) - 1 H c , k H .
And filtering matrix meets the following conditions, that is: G (c)H C, k=I.H wherein C, kRepresent that k kind transmission antenna group is combined in c the channel response matrix under the subcarrier, N kRepresent in the k kind emitting antenna combination number of transmit antennas (always total K kind emitting antenna combination, i.e. k=1,2 ..., K is if number of transmit antennas is M=4, then K=14),
Figure G06101635920060126D000053
The expression dimension is N kUnit matrix, E sBe signal power (W), N 0Be the power (W) of white Gaussian noise, subscript H represents the Hermitian transposition, the inverse operation of subscript (1) representing matrix.
Step 103: utilize filtering matrix, estimate each subcarrier detection output signal-to-noise ratio corresponding to every transmit antennas in every kind of emitting antenna combination.
Use formula 1, suppose g kBe filtering matrix G (c)K capable, h kBe channel matrix H C, kK row, then can obtain the SNR that the detection of k sub data flow correspondence is exported.
γ m , c , k = E s | g k h k | 2 N k N 0 | | g k | | 2 + E s Σ j ≠ k | g k h j | 2 Formula 1
Step 104: use formula 2, estimate the average detected output signal-to-noise ratio of every transmit antennas spatial channel corresponding in the entire belt wide region.
γ m , k = 1 C Σ c = 1 C γ m , c , k Formula 2
Step 105:, be every transmit antennas selecting modulation mode according to the average detected output signal-to-noise ratio of every transmit antennas correspondence and the relation between the signal-noise ratio threshold under the various possibility modulation system.
In concrete application process, select modulation levels according to average detected output signal-to-noise ratio and the required SNR thresholding of predetermined employing different modulating mode.This method is at R Grunheid, EBolinth, being entitled as in " A Blockwise Loading Algorithm for theAdaptive Modulation Technique in OFDM Systems " that H Rohling writes has introduction, and this piece paper publishing is on second volume the 948th～951 page number of IEEE Vehicular Technology Conference in October calendar year 2001 (VTC).
For example, when given target bit (BER) is 10-3, can obtain the required SNR thresholding of different modulating mode according to the BER curve in the white Gaussian noise channel:
Modulation scheme SNR thresholding (dB)
Do not use ＜8
Binary phase shift keying (BPSK) 8
Quadriphase PSK (QPSK) 10
16 quadrature amplitude modulation (16QAM) 18
64 quadrature amplitude modulation (64QAM) 24
Step 106: under the modulation system that every transmit antennas is selected, calculate the throughput of system under each emitting antenna combination.This throughput is defined as the summation of system's transmitted bit on each subcarrier.
In this step, each group transmitting antenna throughput of system down, be every antenna in this group transmitting antenna all use calculating under the situation of its modulation system that is determined separately transmission and.
Step 107: select that group antenna of throughput maximum in all emitting antenna combination, and each self-corresponding modulation system is as final transmission means.If there is the throughput of two groups of combination of antennas correspondences identical, then select wherein that maximum group of number of antennas.
Owing in step 105, determined modulation system separately for every transmit antennas, therefore, determined to have one group of transmitting antenna of maximum throughput by step 107 after, the modulation system of every antenna correspondence also is that nature is determined in this group antenna.Just be to say, the present invention has determined every transmit antennas modulation system separately earlier, and then determines to use which root antenna.
Certainly; embodiment provided by the invention is just for the method that realizes Adaptive Modulation in the MIMO ofdm system that provides according to content of the present invention at large is provided; thereby all be exemplary execution mode; it can not be regarded as for restriction of the present invention; and every conspicuous modification within aim of the present invention is also due within protection scope 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, kH wherein C, kThe channel impulse response of representing c subcarrier correspondence in the k kind emitting antenna combination;
(2) utilize described estimated channel impulse response H C, kCarry 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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