The Effect of Imperfect Channel Estimation

For the previous simulations, the channel estimation is assumed to be perfect, and we discuss the effect of imperfect channel estimation. The BER performance versus channel estimation error with different Eb/N0 over a six-path channel is shown in Fig. 4.12. The parameter α is defined as α =( /ε E_total) 100%× , where ε is the power of channel estimation error and E_total is the total channel power. Then the estimation value of the actual complex fading gain a_p^{j l,} mentioned in Eq.(3.7) is modeled as aˆ_p^{j l,} =a_p^{j l,} + ε/Pρ_p^{j l,} , where P is the total number of paths between a transmitter and receiver, and ρ is a random _p^{j l,} variable which is complex Gaussian distribution with zero mean and unit variance.

In Fig. 4.12, we can observe that the performance degradation is more obvious in the higher SNR region where the proposed method provides better performance. Thus the performance of our proposed method is very sensitive to the accuracy of channel estimation.

Fig. 4.12: The BER performance versus channel estimation error with different Eb/N0 over a six-path fading channel.

( Tx = 3, Rx = 4, K=256)

Chapter 5 Conclusions

For the future generation of wireless communication systems, high data rate transmission is a major demand. In this thesis, spatial multiplexing is applied in MIMO MC-CDMA system to increase spectral efficiency, and we propose iterative multilayered detection methods to suppress the interference which is induced by multi-layered transmission and multipath environment. At receive end, a simple adaptive MMSE equalizer is employed at first, and LAIC scheme reduces the interference in the received signals. MPIC technique is used to combine the path diversity over multipath channel. In Chapter 3, we present two interference cancellation procedures, successive interference cancellation (SIC) and parallel interference cancellation (PIC). In simulation results, it is shown that SIC ( Tx = 4 and Rx = 4) and PIC ( Tx = 3 and Rx = 4) can achieve the performance of perfect LAIC and MPIC. Thus SIC can supply of the spectral efficiency of 8 bits/sec/Hz which is four times that of the system with single transmitter and single receiver, and PIC supplies the spectral efficiency of 6 bits/sec/Hz.

But considering processing time, we adopt PIC to employ the iterative multi-layered detection method with soft interference cancellation.

In order to improve the reliability of interference cancellation and adjust adaptive MMSE

information helps not only interference cancellation and equalizer adjustment, but also symbol demapping. It is also shown that the parallel iterative multilayered detection method with BICM achieves better power efficiency than the system without BICM and provides the same spectral efficiency. It is also shown that our proposed system is sensitive to channel estimation error.

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