Advanced Mobile Phone System (AMPS)
AMPS facts
- Analog FM modulation
- RF bandwidth 30 kHz. The band can accommodate 832 duplex channels,
among which 21 are reserved for call setup, and the rest for voice communication.
- Frequency allocated by FCC on 824-849 MHz for downlink
and 869-894 MHz for uplink traffic.
- Uses the same system throughout the US
- Available in U.S., Canada, Hong Kong, New Zealand, Thailand
- A narrowband versus exists with a 10 kHz channel spacing, such that 2496 channels can be assigned, in stead of 832 for the normal AMPS mode.
Digitization of AMPS
The uniformity of the analogue AMPS system throughout the US highly contributed to
its success of capturing 2/3 of the analog cellular subscribers worldwide. Around 1995, AMPS
had an estimated 13 Million subscribers in the U.S..
US manufacturers and operators have
been divided about the operational merits of various technologically advanced
options for radio channel access and digital modulation, in particular the
choice between Code Division Multiple Access (CDMA) and Time Division Multiple
Access (TDMA) transmission formats for cellular telephony. For the
migration towards all-digital operation, the objective of the Federal
Communication Commission (FCC) has been to introduce a digital system that
was fully compatible with the existing analog AMPS system, i.e., the FCC was
looking for a new system that uses the same radio spectrum as the old analog
system, but at least ten times more efficient in spectrum use. By 1988, the Cellular Telecommunications Industry Association
(CTIA) defined a full set of User Performance Requirements (UPR).
Two different solutions have come up. US cellular network operators
are implementing a narrowband TDMA version of AMPS, known as IS-54. Meanwhile,
the Californian company Qualcomm promotes a CDMA concept, presenting
scientific and experimental evidence to academic fora about the technical
superiority of CDMA over TDMA. Experimental CDMA systems are in operation in several cities, based on the
IS-95 standard.
Expectations are that AMPS product shipments reached its top in 1996
with Motorola, Nokia, NEC and Ericsson dominating the market.
Digital systems including PCS are expected to become cost effective with analog AMPS in the time frame 1997-2000.
PCS: AMPS 1900
A 1900 MHz version of AMPS has been developed, which allows dual-band/dual-mode 800/1900 MHz systems.
It allows operators to provide identical PCS applications and services in both bands. Seamless inter-working between 800 and
1900 MHz networks is possible through dual-band/dualmode mobile stations.
Subscribers on a D-AMPS 1900 channel can handoff both to/from a D-AMPS channel on
800 MHz as well as to/from an analog AMPS channel.
Existing 800 MHz D-AMPS operators can use the 1900 MHz spectrum to increase capacity and develop new user segments in their 800 MHz networks. For example, 800 MHz cells can provide wide-area coverage (through macro-cells) and act as umbrellas for 1900 MHz micro- and picocells. The small cells can cover the indoor office environment, shopping malls, airports and hot spot coverage. The umbrella cells would carry the signals for fast-moving subscribers and fill in gaps in between two isolated microcells.
D-AMPS 1900 mobile phones will be marketed initially in single-band 1900 MHz as well as dual-band 800/1900 MHz versions. In the long run, dual-band versions may prove themselves able to replace single-band versions at both 800 and 1900 MHz.
The D-AMPS 800/1900 system architecture is similar to most other cellular system architectures (e.g. GSM network architecture). It contains a Switching System, an Operation and Support System, base stations and
mobile station.
The switching system
The Switching System contains five main functional entities:
- The Mobile Switching Center (MSC) performs the telephony switching functions for the network. It controls calls to and from other telephone and data communications networks such as Public Switched Telephone Networks (PSTN), Integrated Services Digital Networks (ISDN), Public Land Mobile Networks (PLMN) and Public Data Networks.
- The Visitor Location Register (VLR) database contains all temporary subscriber information needed by the MSC to serve visiting subscribers who are temporarily in the area of the MSC.
- The Home Location Register (HLR) database stores and manages user subscriptions. It contains all permanent subscriber information including the their service profile, location information and activity status.
- The Authentication Center (AC) supports authentication and encryption functionality. It verifies the user’s identity (by authitication) and ensures the confidentiality of each call
(by encryption) . This protects network operators against fraud.
- The Message Center (MC) supports messaging services.
The base station
The Base Station is the radio equipment needed to serve each cell in the network. One base station site may serve more than one cell.
The Operation and Support System
The Operation and Support System supports operation and maintenance activities in the network to allow for reliable and cost-efficient operation.
The mobile station
