AMPS Radio System

• To increase the capacity in large AMPS markets, Motorola developed an AMPS- like system called N- AMPS (narrowband AMPS) in 1991.
• N-AMPS were a useful transition technology before 2 G equipment became available. N AMPS provided three users in a 30 kHz AMPS channel by using FDMA and 10 kHz channels, and provided three times the capacity of AMPS.
• By replacing AMPS channels with three N- AMPS channels at one time, service providers were able to provide more trunked radio channels (and thus a much better grade of service) at base stations in heavily populated areas.
• N- AMPS used the SAT and ST signalling and blank and burst functions in exactly the same manner as AMPS, except the signalling was done by using sub-audible data streams.
• Since 10 kHz channels are used, the FM deviation is decreased in N-AMPS. This I turn reduces the S/ (N+1) which degrade the audio quality with respect to AMPS. To counteract this, NAMPS uses voice companding to provide a synthetic voice channel quieting.
• Ti counteracts this, N-AMPS, except the signalling was done by using sub-audible data streams.
• N-AMPS specify a 300Hz high pass audio filter for each voice channel so that supervisory and signalling data may be sent without blanking the voice.
• The SAT and ST signalling is sent using a continuous 200 bps NRZ data stream that is FSK modulated. SAT and ST are called as DSAT and DST in N- AMPS because they are sent digitally and repetitiously in small, predefined code blocks.

IS - 95B

• The interim data solution of CDMA is called IS-95B. Like GPRS, IS-95B is already being deployed worldwide, and provides high speed packet and circuit switched data access on a common CDMA radio channel by dedicating multiple orthogonal user channels (Walsh functions) for specific users and specific purposes.
• Each IS-95 CDMA radio channel supports up to 64 different user channels. The original IS-95 throughput rate specification of 9.6 kbps was not implemented in practice but was improved to the current rate of 14.4 kbps as specified in IS-95A.
• The 2.5G CDMA solution, IS-95B supports medium data rate (MDR) service by allowing a dedicated user to command up to 8 different user Walsh codes simultaneously and in parallel for an instantaneous throughput of 115.2 kbps per user (8*14.4 kbps).
• However, only about 64 kbps of practical throughput is available to a single user in IS-95B due to the slotting techniques of the air interface.
• IS-95B also specifies hard hand-off procedures that allow subscriber units to record different radio channels in the network without instructions from the switch so that the subscriber.

GSM

• Second Generation Cellular Technology
• Introduced in the year 1990 by Europe
• Multiple Access used is TDMA
• Modulation Technique used is GMSK
• Duplexing used is FDD
• Reverse Link :- 890 to 915 MHz
• Forward Link :- 935 to 960 MHz
• Spacing between forward & reverse channel pair :- 45MHz
• Bandwidth of channel :- 200 kHz
• No of Duplex RF channels – 125
• Introduced in US as PCS (Personal Communication System)

• Further Generations are

  HSCSD (2.5th Generation)

  GPRS (2.5th Generation)

  EDGE (2.5th Generation)