TABLE 1.1 Parameters of Some First-Generation Cellular Standards

Parameters	AMPS	C450	NMT 450	NTT	TACS
Tx Frequency (MHz)
Mobile	824–849	450–455.74	453–457.5	925–940	890–915
Base Station	869–894	460–465.74	463–467.5	870–885	935–960
Channel bandwidth	30	20	25	25	25
(kHz)
Spacing between	45	10	10	55	45
forward and reverse
channels (MHz)
Speech signal	±12	±5	±5	±5	±9.5
FM deviation
Control signal data	10	5.28	1.2	0.3	8
rate (kbps)
Handoff decision is	Power received	Round-trip	Power received	Power received	Power received
based on	at base	delay	at base	at base	at base

While a call is in progress on voice channels, the MSC issues several blank-and-burst commands to transmit signaling information using binary FSK at a rate of 10 kbps. In this mode, voice and SAT are temporarily replaced with this wideband FSK data. The signaling information is used to initiate handoff, to change mobile power level, and to provide other data as required.

The handoff decision is taken by the MSC when the signal strength on RVC falls below threshold or when the SAT experiences interference level above a predetermined value. The MSC uses scanning receivers in nearby base stations to determine the signal level of a mobile requiring handoff.

The termination of a call by a mobile is initiated using a signaling tone (ST). ST is a 10-kbps data burst of 1 and 0 s. It is sent at the end of a message for 200 ms indicating “end-of-call.” It is sent along with SAT and indicates to the base station that the mobile has terminated the call instead of the call dropping out or prematurely terminating. It is sent automatically when a mobile is switched off.

1.3.3Narrowband Advanced Mobile Phone Service, European Total Access Communication System, and Other Systems

A narrowband AMPS (N-AMPS) was developed by Motorola to provide three 10-kHz channels using FDMA in a 30-kHz AMPS channel. By replacing one AMPS channel by three N-AMPS channels at a time, the service providers are able to increase the system capacity by three times. It uses SAT, ST, and blank-and-burst similar to AMPS. Because it uses 10-kHz channels, FM deviation is smaller compared with AMPS and hence it has a lower signal to noise plus interference ratio (SNIR) resulting in degradation of audio quality. It has taken measures to compensate this degradation.

The European Total Access Communication Systems (ETACS) is identical to AMPS except that it uses 25-kHz wide channels compared with 30-kHz channels used by AMPS. It also formats its MIN differently to AMPS to accommodate different country codes in Europe. Parameters for some other popular analog systems are shown in Table 1.1.

1.4 Second-Generation Systems

In contrast to the first-generation analog systems, second-generation systems are designed to use digital transmission and to employ TDMA or CDMA as a multiple access scheme. These systems include North American dual-mode cellular system IS-54, North American IS-95 systems, Japanese Personal Digital Cellular (PDC) systems, and European GSM and DCS 1800 systems. GSM, DCS 1800, IS-54, and PDC systems use TDMA and FDD whereas IS-95 is a CDMA system and also uses FDD for a duplexing technique. Other parameters for these systems are shown in Table 1.2. In this section a brief description of these systems is presented [1].

© 2002 by CRC Press LLC

TABLE 1.2 Parameters of Some Second-Generation Cellular Standards

Parameters	IS-54	GSM	IS-95	PDC
TX frequencies (MHz)
Mobile	824–849	890–915	824–849	940–956 and 1429–1453
Base station	869–894	935–960	869–894	810–826 and 1477–1501
Channel bandwidth (kHz)	30 kHz	200 kHz	1250 kHz	25 kHz
Spacing between forward	45	45	45	30/48
and reverse channels
(MHz)	π/4			π/4
Modulation		GMSK	BPSK/QPSK
	DQPSK			DQPSK
Frame duration (ms)	40	4.615	20	20

1.4.1 United States Digital Cellular (Interim Standard-54)

United States Digital Cellular (IS-54) is a digital system and uses TDMA as a multiple access technique compared with AMPS, which is an analog system and uses FDMA. It is referred to as a dual-mode system because it was designed to share the same frequency, frequency-reuse plan, and base stations with AMPS. It was done so that the mobile and base stations can be equipped with AMPS and IS-54 channels within the same equipment to help migrate from an analog to a digital system and simultaneously to increase system capacity. In this system each frequency channel of 30 kHz is divided into six time slots in each direction. For full-rate speech, three users equally share six slots where two slots are allocated per user. For half-rate speech, each user only uses one slot. Thus, the system capacity is three times more than that of the AMPS for full-rate speech and double that for the half-rate speech. This system also uses the same signaling (FSK) technique as that of AMPS for control whereas it uses π/4 DQPSK for the voice.

It was standardized as IS-54 by the Electronic Industries Association and Telecommunication Industry Association (EIA/TIA) and was later revised as IS-136. The revised version has digital control channels (DCCs) that provide an increased signaling rate as well as additional features such as transmission of point-to-point short messages, broadcast messages, group addressing, and so on.

As was discussed in the previous section, AMPS has 42 control channels. The IS-54 standard specifies these as primary channels and additional 42 channels as secondary channels. Thus, it has twice the control channels as that of AMPS and is able to carry twice the control traffic in a given area. The secondary channels are not monitored by AMPS users and are for the exclusive use of IS-54 users.

Each time slot in each voice channel has one digital traffic channel (DTC) for user data and digitized speech and three supervisory channels to carry control information.

A full duplex DTC consists of forward DTC to carry data from the base station to the mobile and reverse DTC to carry data from the mobile to the base station. The three supervisory channels are coded digital verification color code (CDVCC), slow associated control channel (SACCH), and fast associated control channel (FACCH).

The CDVCC is a 12-b message transmitted every slot containing 8-b color code number between 1 and 255. The 12-b message is generated using shortened Hamming code. It has a similar function to SAT in AMPS. A station transmits this number on CDVCC channels and expects a handshake from each mobile that must retransmit this value on a reverse voice channel. If the number is not returned within a specified time, the time slot is relinquished.

The SACCH is a signaling channel and carries control information between base and mobile while a call is in progress. It is sent with every slot carrying information about power level change, handoff, and so on. Mobiles use this channel to send signal strength measurement of neighboring base stations so that the base may implement mobile-assisted handoff (MAHO).

The FACCH is a second signaling channel to carry control information when the call is in progress. It does not have a dedicated time during each slot as is the case for CDVCC and SACCH. It is similar to

© 2002 by CRC Press LLC