Broadband OFDM using 16-bit precision on a SDR platform

This paper discusses our development of a robust broadband model of OFDM using 16-bit fixed-point ANSI C code that can be easily ported to a variety of software defined radio (SDR) platforms. The fixed-point model allows fast runtime, low power consumption, and low cost implementation. The receiver analog to digital converter (ADC) resolution and 16-bit fixed-point issues are explored. The OFDM system consists of DQPSK encoded data symbols, pilot symbols and null symbols to minimize aliasing and reduce filter requirements. The total number of OFDM subchannels is set to 256. A cyclic extension scheme is used to reduce the intersymbol interference (ISI) caused by long multipath delay spreads. The channel model consists of additive white Gaussian noise (AWGN) and continuously variable channel delay. The fixed-point OFDM algorithm was optimized with a system that uses no compensation for peak to average ratio (PAR). The model supports post-detection spatial diversity, which can be easily implemented by the multi-channel architecture provided by many SDRs.