igital transmission scheme multiplexes three signals over a single channel. Each of the carrier frequencies is divided in time, using a TDMA scheme, into eight time slots, as shown in Figure 1-29. One time slot is used for transmission by the mobile and one for reception. They are separated in time so that the mobile unit does not receive and transmit at the same time, a fact that simplifies the electronics. TDMA enables several users to share the same channel. Each of the users, sharing the common channel, is assigned his or her own burst Figure 1-28 FDMA. User 3 Channel 3 User 2 Channel 2 User 1 Channel 1 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to GSM Chapter 1 Figure 1-29 TDMA. Ch 2 01234567 Ch 01234567 within a group of bursts called a frame. Usually, TDMA is used with an FDMA structure. In addition to increasing the efficiency of transmission, TDMA offers a number of other advantages over standard cellular tech- nologies. First and foremost, it can be easily adapted to the transmission of data as well as voice communication. TDMA offers the capability to carry data rates of 64 Kbps to 120 Mbps (expandable in multiples of 64 Kbps). This enables operators to offer personal communication-like services including fax, voice band data, and Short Message Services (SMSs) as well as bandwidth-intensive applications such as multimedia and videoconfer- encing. Unlike spread-spectrum techniques that can suffer from interfer- ence among the users all of whom are on the same frequency band and transmitting at the same time, TDMA's technology, which separates users in time, ensures that they will not experience interference from other simultaneous transmissions. CDMA is characterized by high capacity and small cell radius, which employs spread-spectrum technology and a special coding scheme. CDMA is the dynamic allocation of bandwi