Real-Time I/Q Baseband Generator User’s and Programming Guide
1-9
ESG Family Signal Generators
Overview of Modulation Formats
Options UN8 and 202
NADC
NADC
The North American Digital Cellular digital communications standard defines a voice and
data over-air interface between a mobile radio and the system infrastructure. This
standard was designed as the basis for a private radio communications system. A central
control center is linked to multiple base station sites which provide the required coverage.
The NADC digital communications standard employs a 6:1 Time Division Multiple Access
(TDMA) allowing six channels to use one carrier frequency simultaneously. The raw bit
rate, 48.6 kbits/second, is modulated using a system known as
π
/4 Differential Quadrature
Phase Shift Keying (
π
/4DQPSK). This standard defines the channel separation as 30 kHz
at carrier frequencies between 824 and 849 MHz (uplink transmissions) and 869 to
894 MHz (downlink transmissions) at a power level ranging from 2.2 mW to 6W (mobile
station).
The NADC framing structure is based on a hierarchical system consisting of timeslots,
TDMA frames, multiframes, and hyperframes. One Normal Uplink Burst (from mobile to
base station) consists of 324 modulated bits consisting of guard, ramp, synchronization
word, slow associated control channel, color code, and data bits. Six of these bursts make
up one TDMA frame. Eighteen TDMA frames make up one multiframe. Frame 18 in the
multiframe is dedicated to control channel signaling.
Summary of Contents for ESG series
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