SS1102C datasheet(44/129 Pages) ETC1

44 / 129 page

Direct Sequence Spread Spectrum Baseband Modem (SSTM)

PRELIMINARY V1.8

(EQ 1)

In (EQ 1), fburst is the burst rate and fmosc is the master oscillator frequency. As the

transmitter uses a quadrature modulation scheme, the chip rate is 16 times the burst rate

(EQ 2)

where fchip is the chip rate and fmosc is the master oscillator frequency. Effectively, the

spread spectrum transceiver operates at 16 chips/bit or 32 bits/symbol where each

symbol is composed of 2 bits.

The total number of bits per burst is fixed and equal for both the Master and the Slave.

The Slave derives its burst timing from the Master by detecting the UW pulse

transmitted by the Master.

12.7.

TDD Protocol

Initially, the two communicating devices need to establish “sync”. The TDD protocol

achieves this by using a special handshaking protocol. The Master first transmits an

“acquisition burst”. The acquisition burst consists of 32 bits of preamble (binary 0’s),

followed by 230 bits of “zero stuffing”, and four 22-bit unique words (UW). When the

Slave receives the acquisition burst from the Master correctly (by decoding the 4

consecutive UWs), it sends an acquisition burst in response. When the Master receives

the acquisition burst, it sends an “empty burst”. An empty burst contains a 32-bit

preamble followed by a single 22-bit unique word, and 296-bit of “1” (One stuffing). In

response to the master’s empty burst, the Slave also sends an empty burst back to the

Master. When the Master receives the empty burst from the Slave, the communication

link is considered to have been established and “sync” condition achieved. On the

following burst, both the Master and the Slave start genuine data transmission by

sending out “data bursts”. Each of the data bursts contain a 32-bit preamble, followed

by a 22-bit UW, a 8-bit Signaling Word (SW), and 288 bits of user data. The three

different types of burst frame structures are shown in Figure 13.

burst

mosc

192

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chip

mosc

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burs t

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