Baseband Interface
VBAP
Signal Conditioning
Analog Cellular

IS-54B Overview

IS-54B, A.K.A. D-AMPS, is a North American digital cellular standard developed in the late 80's by the Cellular Telecommunications Industry Association (CTIA). IS-54B was the first North American dual mode digital cellular standard. It was released in March of 1990.

It is interesting to compare the driving forces behind the development of North America's digital cellular standard (IS-54B) and that of Europe's digital cellular standard (GSM). The development of the North American standard was basically driven by the need for added capacity within the existing AMPS spectrum. The North American standard not only had to be compatible with the existing AMPS infrastructure, but also support AMPS operation, I.E. provide dual mode service. Europe's standard on the other hand was driven purely by the need for a common compatible system for all of Europe. Prior to GSM, Europe had many incompatible analog cellular standards making it very difficult to communicate via cellular when traveling across Europe. The European standard had to provide service to all of Europe, and unlike North America, Europe allocated spectrum specifically for the implementation of GSM.

IS-54B is a Time Division Multiple Access (TDMA) cellular standard.

The specs are as follows:

• 832 channels per carrier in the 800 MHz range (1664 total channels)
• 824 - 849 MHz reserved for mobile transmit
• 869 - 894 MHz reserved for mobile receive
  Note: Carrier (A) assigned frequencies (25 MHz)
• 824-835, 845-846.5 MHz reserved for mobile transmit
• 869-880, 890-891.5 MHz reserved for mobile receive
  Note: Carrier (B) assigned frequencies (25 MHz)
• 835-845, 846.5-849 MHz reserved for mobile transmit
• 880-890, 891.5-894 MHz reserved for mobile receive
• Each radio channel is 30 KHz and is segmented in time into 6 slots (2 slots make up one voice circuit) using TDMA. The data rate is 48.6 Kbits/s, with each slot transmitting 324 bits in 6.67 ms.

Example: Single 30 KHz channel

|<-------------------------------- 40 ms ------------------------------>|

--------------------------------------------------------------------------

|     1     |     2     |     3     |     4     |     5     |     6     |

--------------------------------------------------------------------------

|<--------->|
   6.67 ms 

• Duplex separation: 45 MHz (Forward channel and corresponding reverse channel are separated by 45 MHz)
• Speech is compressed into 7.95 KBits/s using VSELP (Vector Sum Excited Linear Predictive) compression
• The RF wave modulation is Pi/4 DQPSK (Differential Phase Shift Keying) modulation
• Dual mode standard that can operate in either digital or analog mode. Operates in the same spectrum allocated for AMPS and is 100% compatible with AMPS.
• Currently provides 3X the capacity of AMPS. With a 1/2 rate vocoder will provide 6X the capacity of AMPS.
• 21 dedicated analog control channels per carrier system. Control channels are used for mobile registration, mobile paging, mobile access, and mobile handoffs, I.E. non-conversational channels.
• No direct fax or data communication support. Can purchase add-ons to handle fax and data communication support.
• Mobile units transmit up to 0.6 and 3.0 watts