s the frequency offset. It can be seen that the ICI increases with the increase of the OFDM symbol duration (or alternatively decrease of sub-carrier spacing) and the frequency offset. The effects of timing offset are typically less than that of the frequency offset, provided that the cyclic prefix is sufficiently large. The impact of local oscillator phase noise on the performance of an OFDM system. It has been concluded that the oscillator phase noise may have significant effects on close sub-carrier spacing (large OFDM symbol duration in time). Long symbol duration is required for implementing a long guard interval that can mitigate long multipath delay in single frequency operation without excessive reduction of data throughput. Extensive studies suggest that phase noise in OFDM can result in two effects: a common sub-carrier phase rotation on all the sub-carriers; and a thermal-noise-like sub- carrier de-orthogonality. The common phase error, i.e., constellation rotation, on all the demodulated sub-carriers is caused by the phase noise spectrum from DC up to the frequency of sub-carrier spacing. This low-pass effect is due to the long integration time of the OFDM symbol duration. This phase error can, in principle, be corrected by using pilots within the same symbol (in-band pilots). The phase error causes sub-carrier constellation blurring rather than rotation. It results from the phase noise spectrum contained within the system bandwidth. This part of the phase noise is more crucial, since it cannot be easily corrected. In brief, an OFDM system has the following advantages: It is sufficiently flexible in meeting various design requirements such as low complexity, bandwidth efficiency and scalability, spectrum shaping, and low sensitivity to various impairments. CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) OFDM is well-suited to multi-antenna transmission schemes. It requires no adaptation to instantaneous channel response for low-order modulations. It is robust to impulse interference and channel va