Burst coherent detection with robust frequency and timing estimation for portable radio communications

The authors describe two approaches that make burst coherent demodulation robust against frequency offset between transmitter and receiver: using a second-order PLL (phase lock loop) to track frequency error, and performing transforms between phase and rectangular vector components to eliminate errors caused by wraparound discontinuities. It is found that with a small increase in circuit complexity (mostly additional read-only memory), the second method can estimate symbol timing and frequency offset very accurately, even for a phase bias close to 45 degrees per symbol the residual frequency error can easily be corrected by a second-order PLL. By using this implementation, a low-overhead TDMA (time division multiple access) burst can be coherently demodulated in a portable radio environment without requiring very stable frequency references