 ACCESS (TDMA) TDMA is the most common technology in the second generation of mobile communication systems, the digital systems. The available spectrum in TDMA is divided into physical channels of equal bandwidth. See Figure 13.19. The subscriber is allocated a time slot. The originally continuous subscriber information (speech/data/signalling) is divided into blocks. In GSM a voice block is 20 ms long and sent in bursts when the assigned time slot is available. TDMA requires strict timing of the burst transmission in order to avoid overlapping of adjacent time slots. In cellular systems with large cells the varying time delay for terminals with different distances to the base station must be compensated. A precise synchronization between the mobile station and the radio base station is required. 13.10.3 CODE DIVISION MULTIPLE ACCESS (CDMA) The basic concept of CDMA is to simultaneously handle several users' mobile stations without dividing the radio carrier into time slots. This is achieved by using codes to distinguish between different signals to enable many users to share the same radio channel. The information for each user is spread with a unique code, called chip. Spreading of the information means that the information is 'multiplied' with the codes. CDMA is also known as a spread spectrum technology. Frequency 1, Uplink 01234567 Frequency 2, downlink 01234567 Figure 13.19 TDMA principle Understanding Changing Telecommunications - Building a Successful Telecom Business The CMDA Cocktail Party What do YOU hear A) If you only speak Japanese? B) If you only speak English? C) If you only speak Italian? D) If you only speak Japanese, but the Japanese-speaking person is all the way across the room? E) If you only speak Japanese, but the Power Spanish-speaking person is talking very loudly? Figure 13.20 The CDMA cocktail party The information for several mobile stations is transmitted downlink at the same time. Functions in each mobile station can then be used to analyse the information and to decode only the inf