AMPS Tutorial

This AMPS Tutorial covers AMPS basics, AMPS frequency spectrum, AMPS system specifications, AMPS frame structure and AMPS call setup procedure.

AMPS Basics

AMPS is the short form of Advanced Mobile Phone Service. This system was developed by AT & T and is regarded as 1G analog system and most commonly used in North America. It supports coverage of about 20 km and data rate of about 10kbps.

AMPS Frequency Spectrum and system specifications

AMPS spectrum allocated in North America comprised of total 50 MHz, 25 MHz in the downlink and 25 MHz in the Uplink. Downlink refers to Base station(BS) to Mobile station (MS) direction and Uplink refers to Mobile to Base station direction. Downlink RF carrier frequency is 869MHz to 894MHz and Uplink RF carrier frequency is 824MHz to 849MHz. One operator is allocated half of 25MHz (i.e. 12.5MHz band) both in the uplink and downlink. Channel bandwidth is about 30KHz, which gives about 833 total channels in 25MHz span. Hence each operator supports about 416 channels for traffic as well as control functions. 21 channels are dedicated for control signaling channels per operator and the rest is used for traffic purpose. In AMPS, voice traffic is modulated using FM modulation with peak deviation of about 12 KHz. Control channel information is modulated using FSK modulation with peak deviation of about 8 KHz. AMPS uses BCH as forward error correction technique. Supports BCH (48, 36, 5) and BCH (40, 28, 5) flavors.

AMPS Frame Structure

As shown in figure AMPS frame structure is different for forward (BS to MS) and reverse (MS to BS) control channels. There are about 21 each. During connected state, control information carried over normal voice channel used for conversation.

Reverse Control channel frame structure:

Precursor- Total length: 48 bits, composed of sync field(30 bit), word sync field(11bit) and digital color code(7bit). A sync field consists of alternate 1's and 0's. word sync field is fixed pattern of 11100010010. DCC is unique for each Base station and hence help deliver RCC to the correct Base station from MS.

Following the precursor, 1 to 6 words of data will be sent. Each word is of about 36 data bits and encoded to form 48 bits using BCH shortened version. Original BCH is of polynomial (63,51,5). To increase robustness of the air interface and make the link most reliable each word having same information is transmitted 5 times in each frame. For example w1 mentioned 5 times. Forward Control channel frame structure:

Forward control channel has bit sync (10 bts), word sync (11 bits) and two words of data bits. Each word of about 40 bits (including 28 bits of data and 12 redundant bits). For reliability of the frame each word is sent 5 times over the radio link.

AMPS Frame structure

AMPS Call set up procedure

AMPS call set up
Call set up procedure is outlined in the figure 2, as shown in the figure call is initiated by dialing telephone number of the called mobile(subscriber #2). The requested mobile (here Subscriber #1) is first authenticated by MTSO (Mobile Telephone Switching Office) and assigned traffic channels for further use. After this MTSO sends ring tone to SS #2 and in turn circuit connection is established between SS #1 and SS #2. The call disconnection can be initiated by either SS #1 or SS #2.

Frame structure of wireless standards, technologies

Frame structure of various wireless standards/technologies are mentioned below. It include WiMAX, WLAN, Zigbee, GSM, GPRS, UMTS, LTE, TD-SCDMA, GPS, SDH, 11ac WLAN, AMPS, Ethernet, VLAN etc.

WiMAX physical layer Frame Structure as per 802.16d and 802.16e standards
WiMAX MAC layer Frame Structure as per OFDM 802.16d standard
Zigbee RF4CE Frame Structure
Zigbee physical layer Frame Structure
Zigbee MAC layer Frame Structure
GPRS Frame Structure
GPS Frame Structure
LTE Frame Structure
TD-SCDMA Frame Structure
UMTS Frame Structure
SONET Frame Structure
SDH Frame Structure
802.11ac PHY Frame Structure
802.11ac MAC layer Frame Structure
WLAN Frame Structure as per 802.11a,11b,11n,11ac standards
AMPS Frame Structure
Ethernet Frame Structure
VLAN Frame Structure
GSM Frame Structure