Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) are promising multiple subcarriers high data rate transmission schemes, which are referred to as ‘OFDM-like technology’ uniformly hereinafter. The basic idea is to convert high speed serial data into branches of relatively low speed parallel data, and then modulate the orthogonal carriers. By using OFDM-like technology, the spectral utilization rate will be greatly enhanced, and the system becomes much stronger against Multipath Fading and narrowband interference. OFDM-like technology is considered as one of the core technologies of the fourth generation mobile communication, and is widely used in high speed wireless data telecommunication systems such as World Interoperability for Microwave Access (WiMAX).
Multi-input Multi-output (MIMO) system is a telecommunication system whose receiver and transmitter are both configured with multiple antennas, so that it is possible to provide high speed wireless data transmission. In a flat fading channel with lower SNR but less influence to the Bit Error Rate, MIMO system can provide important data rate gain or diversity gain. In practice, there are ways to implement MIMO, such as: Space-Time Coding (STC) based on Alamouti code and spatial multiplexing.
Obviously, the combination of OFDM and MIIMO can bring us better data transmission scheme with high speed.
See FIG. 1, FIG. 1 shows the schematic view of a typical sending means in a telecommunication network combining OFDM-like technology and MIMO.
Hereinafter, the signal processing flow in the sending means will be described, wherein, the MIMO system is applied with the Partial Usage of SubChannel (PUSC) mode; the modulation is QPSK; the rate of channel coding is 1/2; STBC is used.
1) Source bit stream b0 . . . b47 are channel coded, so that the channel coded bit stream c0 . . . c95 is generated.
2) Channel coded bit stream enters the interleaver for interleaving (not shown), and then will be mapped to the constellation of the QPSK modulator, so as to generate modulated symbol stream s0 . . . s47, say {Sn}(each modulated symbol comprising two channel coded bits). Hereunder, without specific statement, modulated symbols stand for the symbols generated after digital modulation in this step;
3) When using Space-Time coding, the MIMO coder will perform Space-Time coding on the input modulated symbol stream. Here, since the aim of Space-Time coding is to realize MIMO, it is also called MIMO coding. The MIMO symbol stream generated can be in the form of: {s0, s1},{s2, s3}, . . . , {s46, s47} and {−s1*, s0*},{−s3*, s2*}, . . . , {−s47*, s46*};
4) Before IFFT, N (let N=1024) subcarriers are numbered as 0, 1,. . . , 1023 from low frequency to high frequency, as the physical address of subcarriers. By eliminating the number zero subcarrier and the virtual subcarriers therefrom, the remained subcarriers are numbered again, as their first level logical address. Then, the subcarriers with first level logical address are classified into clusters, so that each cluster will comprise physical subcarriers as shown in FIG. 2. And the pilot subcarriers shall be allocated according to the manner shown in FIG. 2.
5) After the allocation of pilot subcarriers, other subcarriers are called data subcarriers. Then, a permutation will be done with respect to the data subcarriers, and then they will be further numbered as I1, I2, . . . , I840, as the second level logical address of the data subcarriers in correspondence with the discrete physical address.
6) Then, the subcarrier mapping module is responsible for mapping the MIMO symbol stream to the data subcarriers with the second level logical address. It is easy to understand that, for a sending means using spatial multiplexing (no need of MIMO coding), the subcarrier mapping module will map the modulated symbol stream generated in the step 2) to the data subcarriers.
In existing sending means using spatial multiplexing, after the aforesaid steps, mapping the modulated symbol stream s0 . . . s47 to data subcarriers is shown in Table. 1. Wherein, a sending means with 2 transmitting antennas is taken as an example. However, it should be understood that, the present invention is not limited to systems with 2 transmission antennas.
TABLE 1Spatial multiplexing, 2 antennasAntenna 0Antenna 1s0s1s2s3s4s5s6s7s8s9s10s11s12s13s14s15s16s17s18s19s20s21s22s23s24s25s26s27s28s29s30s31s32s33s34s35s36s37s38s39s40s41s42s43s44s45s46s47
Wherein, the symbols in the same row are mapped to the same data subcarrier, say their mapping objects have the same physical address. Then, the Inverse Fast Fourier Transform (IFFT) modules, corresponding to the two transmitting antennas respectively, will perform IFFT process on the signals in correspondence with the antennas, so that two OFDM symbols will be generated, realizing the conversion from frequency domain to time domain. Wherein, the modulated symbols mapped to the same data subcarrier will be located at the same position in the two OFDM symbols. s0 . . . s47 are the modulated symbols generated by the digital modulator shown in FIG. 1 (using QPSK etc. modulation method) in the first time slot.
From Table 1, it can be seen that, in prior art, the modulated symbols mapped to the same data subcarrier correspond to adjacent symbols in s0 . . . s47. Therefore, when the channel is in deep fading, the terminal has moved into deep fading zones like a jungle, since the decoder at the receiver cannot decode successfully, s0 and s1 will be deemed as wrong. Since s0 and s1 are adjacent symbols in the modulated symbol sequence, and comprise adjacent coded bits such as c0, c1, c2 and c3 in the coded bit stream c0 . . . c95, hence, there is a burst error.
In a telecommunication system, burst errors are always undesired. Hence, a solution is needed to avoid burst errors in the aforesaid OFDM-like MIMO system.
For conciseness, FIG. 1 has not shown all means (modules) of the telecommunication system for implementing the combination of OFDM-like technology and MIMO technology. However, those skilled in this art can know well, with the aid of FIG. 1 and the description above, the technical problems existing in the prior art to be solved by the present invention. Also, those skilled in this art will have a good understanding of the solution provided by the present invention by reading the description below with reference to the drawings.