A spread spectrum modem for 2.4GHz ISM(Industrial Scientific and Medical) band is designed in this thesis work. Direct sequence spread spectrum modem is implemented using Direct Sequence Spread Spectrum Burst Processor(STEL 2000A) and an embedded microprocessor, 80C186EC which controls the entire modem system.
The modulation method used in this work is DBPSK and DQPSK for noncoherent demodulation at the receiver. For the fast code acquisition required in time division duplex mode, a pseudo noise matched filter is used. Processing gain of the modem is programmable up to 64. The frequency offset is detected symbol-by-symbol by a frequency discriminator.
An asynchronous data terminal equipment(DTE) can be attached to this modem. All data is synchronously transferred through a channel in a high level data link control(HDLC) frame. The HDLC frame is placed in an assigned time slot for the TDD.
As a result, the modem receiver implemented in this work can detect the data well at 38.4kbps or above with the matched filtering and frequency drift compensation in the laboratory test.
