y Fast Fourier Transform (FFT) techniques. These mathematical operations are widely used for transforming data between the time- domain and frequency-domain. These transforms are interesting from the OFDM perspective because they can be viewed as mapping data onto orthogonal sub-carriers. The details on Fourier Transforms can be found in [6]. Consider a data block x(n), where n is the block index, consists of n data symbols that is, x(n) = [xo(n)x1(n) (2.1) A conventional OFDM modulation is employed at the transmitter. The baseband transmitted signal Xk at the output of the IFFT can be written as [7]: Xk = exp(j2rnk)/N (2.2) k = 0, 1, 2, ..., N - 1 where X* is the data symbol, and e(j2rnk)/N , k = 0, 1, 2, N - 1, represents the corresponding orthogonal frequencies of N sub-carriers. Thus, a group of n different data symbols is mapped onto N sub-carriers via the IFFT processor. Note that IFFT has TOFDM seconds to complete its operation. The duration TOFDM for an OFDM symbol is N.Ts, where Ts is the time period of a data symbol [3,7]. Next Generation Mobile Communications Ecosystem At the receiver, the OFDM signal is mixed with a local oscillator signal. Assuming it is Af above the carrier frequency of the received OFDM signal due to a frequency estimation error or Doppler velocity, the baseband FFT demodulator output is given by: dm1/NYrtexp(-j2rmk)/N (2.3) m=0,1,2, , N 1 where + Wk represents the received signal at the input to the FFT processor, Wk is the AWGN (Additive White Gaussian Noise), and dm is the output of the FFT processor. The term e(j2k/N)AfT N - 1, represents the corresponding frequency offset of the received signal at the sampling instants, and AfT is the frequency offset to subcarrier frequency spacing ratio [7]. 2.4 OFDM Advantages OFDM has a number of advantages that work well in providing high speed data services for NGMN [2,5]. High Spectral Efficiency: OFDM achieves high spectral efficiency by using orthogonal sub-carriers. Orthogonality allows sub-carriers' spectra to overlap which in turn 