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Outline
2.5.1 Introduction
2.5.2 OFDM Basics
2.5.3 Performance Sensitivity for Imperfect Circuit
2.5.4 Timing and Frequency Synchronization
2.5.5 Example Coherent Detection and Channel
Estimation
2.5.6 The Peak Power Problem
2.5.7 Summary
References
Problems
Wireless Communication Technologies 2.5.1
1
Performance sensitivity for imperfect circuit
 OFDM is sensitivity to many effects of imperfect circuit,
including (1) the phase noise, (2) the carrier frequency offset,
(3) the timing errors, (4) the I/Q imbalance, and (5) the power
gain compression.
 These impairments may destroy orthogonality and cause
intercarrier interference (ICI), and then result in the
degradation in performance.
 For single-carrier systems, these imperfect effects only give a
degradation in the received SNR, rather than introducing
interference.
 This is the reason that the sensitivity to these impairments are
often mentioned as disadvantages of OFDM relative to singlecarrier systems.
Wireless Communication Technologies 2.5.3
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Performance sensitivity for imperfect circuit
 In this section, we will discuss the impairments of (1) to (4),
the impairment (5) of power amplifier in the transmitter is
discussed in section 2.5.6.
 Note that the impairments of (1) the phase noise can not be
reduced by any signal processing technique. To improve the
performance, it only can do is make a good phase-locked loop
(PLL) to generate a stable reference frequency.
 By using the cyclic prefix or special OFDM training symbols,
the degradation of the impairments of (2) to (4), can be kept to
a minimum, some topics are presented in section 2.5.4.
 And, by various methods to reduce the peak-to-average power
ratio, the required backoff of a RF power amplifier may be
reduced, and hence improves the power efficiency.
Wireless Communication Technologies 2.5.3
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