nough to compare dif- ferent schemes [7]. Thus, the approximate average CIR is utilized in this chapter. Then, the CIR of the OFDM system is CIROFDM (1.19) k=0,km Owing to the periodic property of Sk and the identities = = and N-1 |Skl2 = 1, Eq. (1.19) can be simplified as (1.20) From Eqs. (1.17) and (1.20), an accurate approximation of the CIR can be obtained for a sufficiently large value of N as CIROFDM sinc^(e)/(1-sinc^(e)). - It is clear that the CIR of the OFDM system is very sensitive to the CFO. 1.4 ICI Cancellation Techniques 1.4 ICI Cancellation Techniques ICI can seriously degrade the performance of OFDM systems. To tackle this problem, sev- eral ICI countermeasures have been proposed over the past few years. These techniques can be generally classified into three categories. In the first category, the basis expansion model (BEM) is considered for ICI mitigation [8-10]. In the second category, the ICI is treated explicitly by first estimating the ICI coefficients followed by various ICI cancellation algo- rithms (see e.g. [11-14]). In the third category, a low-complexity strategy, is taken to treat ICI implicitly. The adjacent-mapping-based ICI cancellation method proposed by Zhao and Haggman [6] is a representative where each data symbol is transmitted over two adjacent subcarriers. Depending on the conversion or the conjugate relation between adjacent sub- carrier pairs carrying the same information, there are the adjacent symbol repetition (ASR) scheme and the adjacent conjugate symbol repetition (ACSR) scheme. These schemes implicitly cancel ICI by combining received signals on adjacent subcarrier pairs. This section introduces four ICI cancellation schemes belonging to the third category, called mirror symbol repetition (MSR), mirror conjugate symbol repetition (MCSR), mir- ror conversion transmission (MCVT), and mirror conjugate transmission (MCJT). Based on the interesting relationship between the interference from a mirror subcarrier pair, they apply data repetition within OFDM symbols accordin