Cellular Telephony

Cellular Telephony Four popular cellular telephony networks are: 1. 2. 3. 4. Advanced Mobile Phone Service (AMPS) Global System for Mobile Communication (GSM) EIA/TIA IS-136 Digital Cellular System EIA/TIA IS-95 Digital Cellular System Advanced Mobile Phone Service (AMPS): AMPS was the first cellular system, which was developed during the 1970s by Bell Lab. From 1974 to 1978, a large scale AMPS trial was conducted in Chicago. Commercial AMPS service has been available since 1983. It 1s based on frequency division multiple access (FDMA), AMPS was designed as a high capacity system based on a frequency reuse scheme. A total of 50 MHz in the 824-849 MHz and 869-894 MHZ bands is allocated for AMPS. This spectrum is divided into 832 full-duplex channels using 1664 discrete frequencies, that is, 832 downlinks and 832 uplinks. In AMPS, the typical frequency reuse plan employs either a 12-group frequency cluster using omni-directional antennas or a 7-group cluster using three sectors per base stations. Thus, there are about 50 channels per cell. Global System for Mobile Communication (GSM) GSM is a digital cellular system developed by Groups Special Mobile of Conference Europeenne des Postes et Telecommunications (CEPT) and its successor European Telecommunications Standard Institute (ETSI). GSM combines time division multiple access (TDMA) and FDMA. With TDMA, the radio hardware in the base station can be shared among multiple users. In GSM the frequency carrier is divided into eight time slots where the speech coding rate is 13 Kbps. In a GSM base station, every pair of radio transceiver-receiver supports eight voice channels, whereas an AMPS base station needs one such pair for every voice channel. The GSM MSs control their RF output power to maintain interference at low levels. The GSM air interface has been evolved into Enhanced Data Rate for GSM Evolution (EDGE) with variable data rate link adaptation. EDGE utilizes highly spectrum –efficient modulation for bit rates higher than existing GSM technology. The GSM development process was similar to that of AMPS, except that no large scale trial was conducted. GSM Architecture In this architecture, mobile station (MS) communicates with a base station system (BSS) through the radio interface. The BSS is connected to the network and switching subsystem (NSS) by communicating with a mobile switching center using the A interface. Figure: GSM architecture The MS consists of two parts: the subscriber identity module (SIM) and the mobile equipment (ME). In a broader definition, the MS also includes a third part called terminal equipment (TE), which can be a PDA or PC connected to the ME. The SIM is protected by a personal identity number (PIN) between four to eight digits in length, The PIN is initially loaded by the network operator at the subscription time. This PIN can be deactivated or changed by the user. EIA/TIA S-136 Digital Cellular System This system is also referred to as digital AMPS (DAMPS), American Digital Cellular (ADC), or North American TDMA (NA-TDMA), IS-136, the successor to IS-54, supports a TDMA air interface similar to that of GSM. IS-54 was renamed IS-136 when it reached revision C. It supports three voice channels, where the speech coding rate is 7.95 Kbps. IS-136 capacity is around three times that of AMPS. An existing AMPS system can be easily upgraded to IS-136 on a circuit-by-circuit basis. ElA/TIA IS-95 Digital Cellular System This digital cellular system was developed by Qualcomm, and has been operating in USA since 1996. IS-95 is based on Code Division Multiple Acess (CDMA) technology. It allows many users to share a common frequency/time channel for transmission. The channel bandwidth used by IS-95 is 1. 25 Miz. which has been extended to 5 MHz in the third generation wideband CDMA proposal. The speech coding rate for IS-95 is 13 Kbps or 8 Kbps. IS-95's capacity is estimated to be 10 times that of AMPS.