In this thesis work, a baseband π/4-DQPSK wireless modem is implemented in real time using a T.I. TMS320C50 fixed point DSP chip and the performance of the system is obtained. The modem is capable of transmitting digital data 38.4kbps or above.
In the transmitter, the roll-off factor of the square root raised cosine shaping filter is set to 0.35. The modulated output signal is over-sampled by four times the symbol rate. This signal is fed to a radio frequency(RF) module of 219MHz. At the receiver side, the baseband signal at the RF module output is sampled at four times the symbol rate. After matched filtering the sampled receiver input signal, the DSP processes the signal to recover the transmitted information data sequence.
The baseband modem receiver implemented in this thesis includes the functional blocks of timing recovery, synchronization, frequency drift compensation, and decoding. We implement the timing recovery block to have fast convergence suitable for burst mode transmission. The frequency drift is compensated in a decision-directed fashion.
As a result, the implemented modem converges well within 15 symbol period with the timing recovery and frequency drift compensation algorithm for TDD mode in laboratory test.
