Turbo Code Codec Implementation and Performance in a Software Radio

A turbo code codec is implemented as a portion of a modem in a software radio. The performance of this software radio is tested in a Monte Carlo simulation and on a hardware testbed. The codec uses two punctured rate 1/2 constituent codes and a 16383-bit pseudo-random interleaver to produce a net rate ~1/2 turbo code. The modem generates a binary phaseshift keyed modulation on a 200 kHz carrier. Frame headers are inserted between interleaver blocks for synchronization of the receiver’s deinterleaver and to detect loss of carrier or symbol synchronization. Bit error rate performance curves are reported. The Monte Carlo simulation shows an implementation loss of about 0.5 dB at threshold (i.e., an Eb/No of about 1 dB). This implementation loss is attributed to carrier and bit synchronization errors. The hardware testbed displayed a total implementation loss of about 2.5 dB. The additional 2 dB loss over the Monte Carlo results can be attributed to detector mismatch and inter-symbol interference caused by unmodeled band-limiting filters of the hardware. Some of these filterinduced losses should be recoverable if an equalizer is added to the modem software.