CHAPTER 8

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1. (a) Mobile communication systems based on GSM standards use FDMA/ TDMA. (b) A Bluetooth radio system uses frequency hopping. (c) 802.11 wireless local area network uses frequency hopping. (d) HiperLAN uses TDMA-TDD. (e) A digital enhanced cordless telecommunications (DECT) system uses TDMA-TDD.

2. In satellite communication systems, TDM-TDM, TDMA, and CDMA technologies are used. The details are given in Chapter 13.

3. In GSM, the service area is divided into small regions called cells. Each cell is assigned a number of channels that are shared by the mobile phones in that cell. Hence, FDMA is used. In addition, each channel is time-shared by eight mobile phones. Hence, TDMA is also used. So, the multiple access technique is referred to as FDMA/TDMA. Each radio channel has a pair of frequencies—one for uplink and one for downlink. Hence, the TDMA scheme is TDMA-FDD.

4. In a TDMA system, each station will give a small time slot during which it has to pump its data. However, the source will generate the data continuously. Hence, the source has to buffer the data and send it fast over the channel when it gets its time slot. For instance, the user talks into his mobile phone continuously. But the mobile phone gets its time slot only at regular intervals. Hence, the mobile device has to buffer the digitized voice and send it in its time slot.

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