Mobile Data Systems The design aspect of developing a mobile data system is different from that of developing a cellular voice system, although the mobile radio environment is the same. The quality of a voice channel has to be determined based on a subjective test. The quality of a data transmission is based on an objective test. In a data transmission, the bit error rate and the word error rate are the parameters to be used to measure the performance at any given carrier-to-interference ratio(C/I). The burst errors caused by the multipath fading and the intersymbol inter- ence caused by the time delay spread are the major concerns in receiving the mobile data. The burst errors can be reduced by interleaving and coding. The intersymbol interference can be reduced by using equalizers or lowering the symbol rate or applying diversity. The wireless data transmission can be sent via a circuit switched network or a packet switched network. Also, mobile data transmission can be implemented on cellular systems or on a stand-alone syste ARDIS* Transmission rate 4.8 kbps and 19.2 kbps Transmission rate Transmit power 1 Transmit power Packet radio Cellular Plan ll Cellular Modems Transmission rate 19.2 kb Transmission rate Transmit power 0.6-1.2 w Transmission Channel Packet cellular cellular, carry data over cellular AT&T PowerTek vital ARDIS advanced radio data RAM= mobile data service Personal Communication Service Systems In June 1990, the FCC started to ask the wireless communication industry to study the development of future rsonal communication service(PCS)systems. (In late 1994, the FCC started to auction off two of the six ectral bands for over 7 billion dollars. In 1996, Band C was auctioned off for over 4 billion dollars. ) PCS systems need to have more capacity than cellular systems. The technologies of increasing the capacity not only apply to Gsm, but also apply to CDMA( code division multiple access)and the new microcell system. CDMA A San Diego field test held in 1991 showed that a cellular CDMa scheme can provide higher capacity than cellular TDMA (time division multiple access). A cellular CDMA system [Lee, May 1991] does not require a frequency reuse scheme. All the CDMA cells share the same radio channel. Therefore, the capacity of a cellular CDMA system is higher than either cellular FDMA(frequency division multiple access)or cellular TDMA systems. ssume that a spectral bandwidth of 1.2 MHz can be divided into 120 radio channels with a channel bandwidth of 10 kHz. This is an FDMA scheme. A spectral bandwidth of 1.2 MHz can also be divided into 40 radio channels with a radio channel bandwidth of 30 kHz but each radio channel carries three time slots herefore, a total of 120 time-slot channels is obtained. This is a TDMA scheme. A spectral bandwidth of 1.2 MHz can also be used as one radio channel but provide 40 code-sequence traffic channels for each sector of a cell. a cell of three sectors will have a total of 120 traffic channels this is a cdma scheme. now we can visualize that as far as channel efficiency is concerned, TDMA, FDMA, and CDMa provide the same number of traffic channels. However, in FDMA or TDMA, frequency reuse has to be applied. Let the frequency reuse factor K=7 maintain a required C/2 18 dB; then the total channels will be divided by 7 as: 17 channels/cell (in TDMA or FDMA) c 2000 by CRC Press LLC© 2000 by CRC Press LLC Mobile Data Systems The design aspect of developing a mobile data system is different from that of developing a cellular voice system, although the mobile radio environment is the same. The quality of a voice channel has to be determined based on a subjective test. The quality of a data transmission is based on an objective test. In a data transmission, the bit error rate and the word error rate are the parameters to be used to measure the performance at any given carrier-to-interference ratio (C/I). The burst errors caused by the multipath fading and the intersymbol inter￾ference caused by the time delay spread are the major concerns in receiving the mobile data. The burst errors can be reduced by interleaving and coding. The intersymbol interference can be reduced by using equalizers or lowering the symbol rate or applying diversity. The wireless data transmission can be sent via a circuit switched network or a packet switched network. Also, mobile data transmission can be implemented on cellular systems or on a stand-alone system. Personal Communication Service Systems In June 1990, the FCC started to ask the wireless communication industry to study the development of future personal communication service (PCS) systems. (In late 1994, the FCC started to auction off two of the six spectral bands for over 7 billion dollars. In 1996, Band C was auctioned off for over 4 billion dollars.) PCS systems need to have more capacity than cellular systems. The technologies of increasing the capacity not only apply to GSM, but also apply to CDMA (code division multiple access) and the new microcell system. CDMA A San Diego field test held in 1991 showed that a cellular CDMA scheme can provide higher capacity than cellular TDMA (time division multiple access). A cellular CDMA system [Lee, May 1991] does not require a frequency reuse scheme.All the CDMA cells share the same radio channel. Therefore, the capacity of a cellular CDMA system is higher than either cellular FDMA (frequency division multiple access) or cellular TDMA systems. Assume that a spectral bandwidth of 1.2 MHz can be divided into 120 radio channels with a channel bandwidth of 10 kHz. This is an FDMA scheme. A spectral bandwidth of 1.2 MHz can also be divided into 40 radio channels with a radio channel bandwidth of 30 kHz but each radio channel carries three time slots. Therefore, a total of 120 time-slot channels is obtained. This is a TDMA scheme. A spectral bandwidth of 1.2 MHz can also be used as one radio channel but provide 40 code-sequence traffic channels for each sector of a cell. A cell of three sectors will have a total of 120 traffic channels. This is a CDMA scheme. Now we can visualize that as far as channel efficiency is concerned, TDMA, FDMA, and CDMA provide the same number of traffic channels. However, in FDMA or TDMA, frequency reuse has to be applied. Let the frequency reuse factor K = 7 maintain a required C/I ³ 18 dB; then the total channels will be divided by 7 as: ARDIS* RAM* Transmission rate 4.8 kbps and 19.2 kbps Transmission rate 8 kbps Transmit power 1 W Transmit power 4 W Channel Packet radio Channel Packet radio Vendors IBM/Motorola Vendor Ericsson Cellular Plan II Cellular Modems Transmission rate 19.2 kbps Transmission rate 38.4 kbps Transmit power 0.6–1.2 W Transmission 3 W Channel Packet cellular Channel Circuit cellular, carry data over cellular voice channels Modem vendor AT&T, PowerTek, Vital *ARDIS = advanced radio data *RAM = mobile data service 120 7 = 17 channels/cell (in TDMA or FDMA)