1.1).
2 CHAPTER ONE
Frame
Generation
Vocoder
Channel
Coding
Encryption
Bit
Interleaving
Burst/Frame Modulator
RF
Transmit
FIGURE 1.1 A typical transmit functional block diagram.
1.2.1 IS-136 North American TDMA
In this section, we will present the physical layer details for the North American Digital Cellular
(NADC) TDMA system [4]. This system uses Frequency Division Duplex (FDD) for uplink and
downlink communications. Below we list some high-level features of this digital cellular system:
Bit rate 48.6 kbps (aggregate channel bit rate)
Modulation /4-DQPSK w/SRC filtering with a roll-off of 0.35
VSELP 7.95-kbps voice coding
3 users per 30-kHz channel for full rate
6 users per 30-kHz channel for half rate
Beginning of Mobile Assisted Handoff (MAHO)
TDMA frame length 40 msec
Forward error correction (FEC) on voice
In-band signaling (FACCH)
Out-of-band signaling (SACCH)
The time-slot relationship between the downlink and uplink is given in Fig. 1.2, but first understand
that the downlink can be continuously transmitted while the uplink is only transmitted in bursts.
The users will share the channel frequency bandwidth by being time division multiplexed onto the
frame structure. Auser will typically transmit twice (pair of time slots) per 40-msec frame, for example,
the user data bits could be transmitted in slots 1 and 4, or slots 2 and 5, or slots 3 and 6.
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