rth-generation Networks (All-IP) The fundamental reason for the transition to the All-IP is to have a common platform for all the technologies that have been developed so far, and to harmonise with user expectations of the many services to be provided. The fundamental difference between the GSM/3G and All-IP is that the functionality of the RNC and BSC is now distributed to the BTS and a set of servers and gateways. This means that this network will be less expensive and data transfer will be much faster. 1.3 INFORMATION THEORY 1.3.1 Multiple-access Techniques The basic concept of multiple access is to permit transmitting stations to transmit to receiving stations without any interference. Sending the carriers separated by frequency, time and code can achieve this (Figure 1.2). Spreading codes Frequency Figure 1.2 Generic multiple-access methods Frequency-division Multiple Access (FDMA) This is the most traditional technique in radio communications, relying on separation of the frequencies between the carriers. All that is required is that the transmitters should transmit INFORMATION THEORY on the different frequencies and their modulation should not cause the carrier bandwidths to overlap. There should be as many users as possible utilising the frequencies. This multiple access method is used in the first-generation analogue cellular networks. The advantage of the FDMA system is that transmission can be without coordination or synchronisation. The constraint is the limited availability of frequencies. Time-division Multiple Access (TDMA) As mobile communications moved on to the second generation, FDMA was not considered an effective way for frequency utilisation, so time-division multiple access was introduced. Thus, as shown in Figure 1.2, many users can use the same frequency as each frequency can be divided into small slots of time called time slots, which are generated continuously. Code-division Multiple Access (CDMA) By utilising the spread spectrum technique, code-division multiple access combines modula-