Wireless Communications Systems Design

5Wireless Channel Impairment Mitigation Techniques

We realized wireless channels cause many types of wireless channel impairments such as noise, path loss, shadowing, and fading, and wireless communication systems should be designed to overcome these wireless channel impairments. There are many techniques to mitigate wireless channel impairments. For example, for the purpose of managing shadowing effects, the location of a base station is carefully selected to avoid shadowing effects. A power control scheme is also used to make a good radio link between a mobile station and a base station. For the purpose of mitigating delay spreads, Global System for Mobile Communications (GSM) system uses adaptive channel equalization techniques and Code Division Multiple Access (CDMA) system uses a rake receiver. For the purpose of mitigating the Doppler spreads, the signal bandwidth of GSM is designed to be much greater than the Doppler spread. GSM also uses a frequency correction feedback. CDMA system uses pilot channels for channel estimation. In Long-Term Evolution (LTE), a symbol time is designed to be less than channel coherence time. In Wireless Local Area Network (WLAN), the Doppler spread is not a big problem due to a low mobility. Thus, the wireless channel impairment mitigation techniques should be adopted according to system requirements and channel environments. In this chapter, fundamentals of wireless channel impairment mitigation techniques are investigated.

5.1 Diversity ...