CN108616475A - A kind of sub-carrier indices differential modulation method for ofdm system - Google Patents

Abstract

The invention belongs to wireless communication technology field, specifically a kind of difference sub-carrier indices modulator approach for ofdm system.In being suggested plans, bit information is indexed by sub-carrier by sub-carrier indices and PSK symbol common transports and carries out differential modulation, and when detection no longer needs channel information.Find out from simulation result, the D IM ofdm system performances carried are better than traditional D ofdm systems, and compared with the performance loss that SIM OFDM have about 1.5dB or so, while the PAPR of D IM ofdm systems is less than OFDM and SIM ofdm systems.So scheme is in the case where retaining SIM OFDM performance advantages, while obtaining the advantages of DSM detections do not need channel information.

Description

A kind of sub-carrier indices differential modulation method for ofdm system

Technical field

The invention belongs to wireless communication technology field, the difference sub-carrier indices for ofdm system are particularly related to Modulator approach；The present invention relates to difference spatial modulation (Differential spatial modulation, DSM) and OFDM Technologies such as (Multiple Input Multiple Output, MIMO).

Background technology

OFDM (Orthogonal Frequency Division Multiplexing) technology is a kind of wireless communication High speed transmission technology, basic principle are that the data flow of high speed is resolved into the sub-data flow of many low rates, i.e., by signal point At many orthogonal subcarriers, transmission is carried out at the same time using these mutually orthogonal subcarriers.The technology utilizes subcarrier logarithm According to being modulated, the pulse width of symbol is extended, intersymbol interference (Inter-Symbol can be reasonably resistant to Interference, ISI), improve the performance to anti-multipath fading.It is multiplexed (Frequency Division with conventional frequency division Multiplexing, FDM) it compares, OFDM does not need special guard band.It is each although having overlapping between frequency spectrum It is mutually orthogonal between carrier wave.According to orthogonality principle it is found that being there is no interference, to carry significantly between each carrier wave The high utilization rate of frequency spectrum.

Recently, a kind of new multi-carrier communication mode --- modulate (Subcarrier Index based on sub-carrier indices Modulation, SIM) ofdm system be suggested.For SIM-OFDM systems, in addition to increase SIM modulation modules with Outside, other the step of and traditional ofdm system there is no any differences.Wherein, most crucial SIM modulation modules use son The thought of carrier wave piecemeal.Entire multicarrier is continuously divided into the identical multiple sub-blocks of size first, passes through rope in each sub-block Draw bit to select wherein several subcarriers (referred to as activating subcarrier) to carry out transmission data, and remaining subcarrier is not sent Data (are referred to as silent subcarriers).Since index bit itself is not sent, but lie in the position letter of activation subcarrier In breath, so index bit and being not take up frequency spectrum resource.In receiving terminal, by activating the position of subcarrier to be obtained with rope Draw the information of bit.Existing SIM-OFDM has many advantages, such as, such as SIM-OFDM compared with traditional ofdm communication method System peak average power ratio smaller, confrontation inter-sub-carrier interference performance is more preferable, the bit error rate is more low, by selecting different work( Rate allocation strategy can also save transmitter energy.The disadvantage is that as a result of the mode of piecemeal, SIM-OFDM systems are without the image of Buddha It is the same in ofdm system, pilot tone is simply inserted on fixed position to complete channel estimation.And pilot frequency locations misjudgment Tremendous influence will be generated to the channel estimating performance of SIM-OFDM systems.

Invention content

The purpose of the present invention, aiming at the above problem, based on traditional difference OFDM (Differential OFDM, D- OFDM) system proposes a kind of carry out differential modulation D-IM-OFDM (Differential index of sub-carrier index Modulation OFDM, D-IM-OFDM) transmission plan, the program remains traditional D-OFDM detection and do not need channel estimation Characteristic, and the performance of effective lifting system.

In order to make it easy to understand, difference spatial modulation (the Differential spatial used to the present invention Modulation, DSM) technology progress is as described below：

Difference space-modulation technique is a kind of Novel MIM O technologies using noncoherent detection based on space-modulation technique.Hair Penetrate transmission antenna matrix index and constellation symbol transmission information of the end using activation.Therefore it is empty to be modulated at reservation tradition for difference space Between modulation injection frequency characteristic outside, by transmitting terminal carry out differential encoding to receiving terminal can be in not channel information In the case of accurately recover the information of transmission.Because it does not all need channel information in transmitting terminal and receiving terminal, and can retain The characteristic of injection frequency causes extensive concern.Consider to introduce difference spatial modulation in SIM-OFDM, i.e. sub-carrier indexes Differential modulation is carried out, in the case where retaining SIM-OFDM performance advantages, while DSM detections is obtained and not needing the excellent of channel information Point.

Technical scheme is as follows：

A kind of sub-carrier indices differential modulation method for ofdm system, which is characterized in that include the following steps：

S1, an OFDM symbol with N number of subcarrier is divided into R OFDM-IM sub-block, each sub-block contains G= N/R subcarrier, each sub-block X (r)=[X₁(r) X₂(r) … X_g(r) … X_G(r)]^TIt indicates, wherein r=1,2 ..., R, and only there are one X_g(r) it is not 0；The matrix E that moves to right of G × G is defined as：

S2, for r≤G, each sub-block sends reference mark, i.e. X (r)=E (:, r), E (:, r) representing matrix E r Row；Obtain the DSM transmission vector set that length is Ga_kIt is a N_t× 1 dimensional vector, and only there are one Element is 1, and other elements are 0；

S3, to r>The transmitting information bit that length is B is divided into B by G₁And B₂Two parts；B₁=log₂(G) a bit is used for Select transmission vector a_k(q=1 ..., Q)；B₂=log₂(L) bit is used for modulating L-PSK constellation symbols (s₁,s₂...,s_L), L Indicate PSK modulation constellation sizes；Then the bit of each sub-block transmission is log₂Q+log₂L；Obtain the symbol of r-th of sub-block to Amount is：S (r)=a_q(r)s_l(r), r>G；

S4, the transmitting vector that r-th of sub-block is obtained by differential encodingFor：

X (r)=G [X (r-1)] S (r), r>G

For arbitrary vectorFunction G [α] is defined as follows：

S5, to all sub-blocks carry out differential encoding after, the OFDM symbol for obtaining differential encoding is：

[X(1)^T … X(r)^T … X(R)^T]^T。

Beneficial effects of the present invention are：Bit information is by sub-carrier indices and PSK symbol common transports, while by right Sub-carrier indices carry out differential modulation, and when detection no longer needs channel information.Find out from simulation result, the D-IM-OFDM carried System performance is better than traditional D-OFDM systems, compared with the performance loss that SIM-OFDM has about 1.5dB or so, while D-IM- The PAPR of ofdm system is less than OFDM and SIM-OFDM systems.

Description of the drawings

Fig. 1 is D-IM-OFDM system block diagrams；

Fig. 2 is sub-carrier number when being 1024, and D-IM-OFDM and tradition D-OFDM and SIM-OFDM system performances, which compare, to be shown It is intended to；

When Fig. 3 is sub-carrier number difference, D-IM-OFDM system performance contrast schematic diagrams.

Fig. 4 is D-IM-OFDM and OFDM and SIM-OFDM system PAPR contrast schematic diagrams.

Specific implementation mode

With reference to the accompanying drawings and examples, detailed description of the present invention technical solution：

With G=4, for BPSK modulation, then Q=4.Then the bit of each block of sub-carriers transmission is log₂Q+log₂L= 3bit。

Step 1：The reference mark of preceding 4 sub-blocks transmitting is obtained, That is matrix E.

Step 2：Obtain the RDSM transmission vector set that length is G：a₁=[1 00 0]^T, a₂=[0 10 0]^T, a₃= [0 0 1 0]^T, a₄=[0 00 1]^T.Assuming that the bit of the i-th=5 sub-block transmission isTransmitted bit is divided into B₁ =log₂Q=2 and B₂=log₂M=1 two parts.

Step 3：Preceding B₁=2 bitsFor selecting selection transmission antenna vectorB afterwards₂=1 bit (0)+1, i.e. s are modulated to through BPSK₁(5)=+ 1.It obtains

Step 4：Due toThenThe i-th=5 is obtained by differential encoding The transmitting vector of a sub-block is：

Assuming that the bit of the 6th sub-block isPreceding B₁=2 bitsFor select selection transmission antenna to AmountB afterwards₂=1 bit (1) is modulated to -1, i.e. s through BPSK₂(6)=- 1.ThenThe transmitting vector of i=6 sub-block is obtained by the identical method of from Step 2 to Step 4：

Step 5：After carrying out differential encoding soon to all subcarriers, the OFDM symbol for obtaining differential encoding is [X (1)^T … X(r)^T … X(R)^T]^T, i.e.,

Claims (1)

1. a kind of sub-carrier indices differential modulation method for ofdm system, which is characterized in that include the following steps：

S1, an OFDM symbol with N number of subcarrier is divided into R OFDM-IM sub-block, each sub-block contains G=N/R Subcarrier, each sub-block X (r)=[X₁(r) X₂(r) … X_g(r) … X_G(r)]^TIt indicates, wherein r=1,2 ..., R, and Only there are one X_g(r) it is not 0；The matrix E that moves to right of G × G is defined as：

S2, to r≤G, each sub-block sends reference mark, i.e. X (r)=E (:, r), E (:, r) representing matrix E r row；It obtains Length is the DSM transmission vector set of Ga_kIt is a N_t× 1 dimensional vector, and be only 1 there are one element, Other elements are 0；

S3, to r>The transmitting information bit that length is B is divided into B by G₁And B₂Two parts；B₁=log₂(G) a bit is used for selecting Transmission vector a_k(q=1 ..., Q)；B₂=log₂(L) bit is used for modulating L-PSK constellation symbols (s₁,s₂...,s_L), L is indicated PSK modulation constellation sizes；Then the bit of each sub-block transmission is log₂Q+log₂L；The symbolic vector for obtaining r-th of sub-block is： S (r)=a_q(r)s_l(r), r>G；

S4, the transmitting vector that r-th of sub-block is obtained by differential encodingFor：

X (r)=G [X (r-1)] S (r), r>G

For arbitrary vectorFunction G [α] is defined as follows：

S5, to all sub-blocks carry out differential encoding after, the OFDM symbol for obtaining differential encoding is：

[X(1)^T … X(r)^T … X(R)^T]^T。