Motorola Pro FLX Manuel d'utilisateur télécharger pdf (Page 13)

Design and Implementation of a Practical FLEX Paging Decoder

Grayson Wireless 5

transmitting a preamble in an asynchronous protocol can be time used to transmit revenue

generating data. The FLEX pager uses its low power CMOS circuit to keep time and only during

its time slot does it power on the receiver for a short time to search for a synchronization word.

The synchronous FLEX paging data is organized so that GPS clock accuracy can be used at the

transmitter. [Wal 94]

2.2 FLEX Data Rate and Modulation

FLEX can operate at three data rates: 1600 bits per second (bps), 3200 bps, and 6400 bps. The

modulation used is both two level frequency shift keying (2-FSK) and four level frequency shift

keying (4-FSK). The 6400 bps FLEX is sent with 4-FSK, the 3200 bps can be sent either 2-FSK

or 4-FSK, and the 1600 bps is always sent using 2-FSK. Thus there are only two baud rates in

FLEX: 1600 baud and 3200 baud, where the number of bits in a symbol can be one or two. [Wal

94]

The frequency deviation for FLEX is 4.8 kHz for 2-FSK and 1.6 kHz and 4.8 kHz deviation for

4-FSK. Figure 2-1 shows a sample bit waveform and associated deviation for FLEX 2-FSK. A

frequency above the center frequency (at +4.8 kHz) is a symbol 1 and below center frequency (at

-4.8 kHz) is a symbol 0. For 2-FSK, there is one bit per symbol, so the symbol is the bit.

+4.8 kHz

-4.8 kHz

Frequency

Deviation

Bit Pattern

000 00011111

Bit Values

Figure 2-1

FLEX 2-FSK bit pattern with frequency deviation

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 73 74

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Motorola Pro FLX Manuel d'utilisateur Page 13