Chapter 8
Examples of air-interface standards: GSM, IS-95, WiFi
In this chapter we examine physical layer and link layer aspects of the most popular commercial wireless personal communications systems. We begin in Section 8.1 with GSM, the predominant TDMA-based second-generation system. We then discuss the second-generation IS-95 CDMA system in Section 8.2. The third standard we survey here is IEEE 802.11, in Section 8.3.
In a cellular system with multiple uplink transmissions (from mobiles to base stations) and downlink transmissions (from base stations to mobiles) occurring simultaneously, it is crucial in designing standards to carefully consider various separation problems. By separation, we mean avoiding or minimizing interference between signals from different transmissions. We consider five separation problems (Table 8.1):
1. Consider a base station that is serving multiple mobile stations. How are the signals it sends to these mobile stations separated from one another?
2. Again, consider a base station that is serving multiple mobile stations. How are the signals from these multiple mobile stations to this base station separated?
3. In the larger context, the cellular system would have multiple base stations. How are signals from these multiple base stations separated from those transmitted by other base stations?
4. How is a signal from a mobile station to its base station separated from the signals that other base stations are trying to receive from their mobile stations? ...
