Performance Analysis of QPSK-OFDM in the Presence of Multiple Narrowband Interferers

Analytical expressions for the symbol (SER) and bit error (BER) rates are presented for quadrature phase shift keying (QPSK) modulated orthogonal frequency division multiplexing (OFDM) systems in the presence of multiple narrowband interferers (NBIs). The analytical expressions can be used for additive white Gaussian noise (AWGN) channels, and flat& frequencyselective fading channels. These analytical expressions have been validated via a Monte Carlo based numerical model. Unlike the interference-free case, results show that the error rates for QPSKOFDM are different from those obtained previously for BPSKOFDM. Results also show that, unlike code division multiple access (CDMA) systems, when analysing multiple NBIs it is not sufficient to take the total signal-to-interference ratio (SIR) and perform the analysis for a single equivalent NBI, since the error rates are sensitive to the NBI’s frequency. An investigation of the performance of BPSK-, and QPSK-OFDM systems in a real, measured environment with 6 NBIs based on 3 floors is presented as an example of the practicality of the analytical models.