Real time implementation of a symbol timing recovery algorithm for a narrowband wireless modem

ALGORITHM FOR A NARROWBAND WIRELESS MODEM J. H. Grimm, R. N. Kumar, J. Kusuma, and J. V. Krogmeier School of Electrical and Computer Engineering Purdue University West Lafayette, IN 47907-1285 http://yake.ecn.purdue.edu/ cominfo/ ABSTRACT This paper examines some of the complexity issues arising in the real time implementation of the symbol timing subsystem of a narrowband wireless modem. The modem prototype has been designed for 4 kHz channels in the 220-222 MHz land mobile band. In an e ort to achieve high bandwidth e ciency, the modem architecture employs transmitter diversity, pilot symbol assisted modulation, and trellis coded modulations. An experimental, non-real time system has been implemented and extensively eld tested demonstrating bandwidth e ciencies in excess of 3 bits per second per Hz. The work on this project is currently focused on the real-time implementation of the baseband receiver functions using the Texas Instruments C54x xed point digital signal processor. Here we report on some of the performance/complexity tradeo s present in the design of a DSP implementation of the digital lter and square symbol timing recovery algorithm.