Implications of I/Q Imbalance, Phase Noise and Noise Figure for SNR and BER of FSK Receivers

In energy-constrained applications like Body Area Networks (BAN) receiver performance is traded for lower power consumption. The limited receiver performance will deteriorate the output signal-to-noise-ratio (SNR) and bit-error-rate (BER) of the receiver. In this paper we present closed-form output SNR and BER models of a non-ideal receiver front-end with limiter-discriminator demodulator for binary FSK. The presented model is very useful in defining the minimally required receiver specifications. Moreover, the models are useful for gaining insight into the influences of the receiver impairments on its performance. In the models, the gain and phase imbalances between the in-phase and quadrature-phase paths as well as the receiver generated noise and the phase noise produced by the local frequency reference are taken into account. This paper shows that the gain and phase imbalances shift the FM threshold to higher carrier-to-noise-ratios (CNR) and only have small influence on the SNR above threshold. On the other hand, receiver generated noise reduces the output SNR both below and above the FM threshold, and phase noise limits the maximum output SNR. Additionally, a trade-off between the FSK frequency deviation and phase noise robustness is derived.