rrier pair (m' = N - m) will carry the same data information. This signal redundancy renders it possible to improve the ICI mitigation performance through a coherent combining technique: (1.22) where HH,HN-MSYM, and YN-m are the channel frequency response (CFR) and the received signals at subcarrier m and its corresponding subcarrier pair (m' = N - m), respectively. Note that Eq. (1.22) is essentially maximum ratio combining (MRC). 1.4.1.1 MSR Scheme For MSR scheme, the conversion operation is applied, which can be represented as O(x) = -X. The 0-th and N/2-th subcarriers are vacant in order to meet the oppo- site polarity condition. The transmitted data symbols in the frequency-domain (FD) after the ICI self-canceling = = = X2, XN/2-1 = = and = According to Eq. (1.22), the decision variable at the m-th subcarrier (m E {1, N/2 - 1}) becomes = (So|Hml2 So|HN-ml' S-2mHmHN-m N/2-1 k=1,k#m The factor removed from the decision variable expression, as it does not affect the CIR value. The CIR at the m-th subcarrier can be expressed as 1.4 ICI Cancellation Techniques CIRMSR(m) N/2-1 k=1,k#m For the flat fading channel, i.e. L = 1, the CIR becomes 1250-S2m-S-2ml (1.23) k=1,k#m See Ref. [15] for proof. As Sk + S_k 22 0, the CIR of the MSR scheme can be markedly improved. The CIR under the multipath Rayleigh fading channel and the detailed deriva- tion are available in [15]. The average CIR of the MSR scheme is then given by (1.24) 1.4.1.2 MCSR Scheme For the MCSR scheme, conjugate operation is adopted, which can be represented as O(x) = x*. Accordingly, we = = = = ..., = and = 0. From Eq. (1.22), the decision variable at the m-th subcarrier is given by k=1,k#m k=N/2+1 Then, the CIR of the MCSR scheme can be expressed as CIRMCSR(m) : (1.25) k=1,kg{m,N/2} For the flat fading channels, it can be readily verified that the CIR of the MCSR scheme CIRMCSR(m) (1.26) Sk+S-kl2 k=1,k#|N/2-m,N-m} As Sk+S-k~ 0, the CIR of the MCSR scheme is improved compared with that of the plain OFDM. The CIR under the multipath Rayleigh fading chan