Quantization Effects in OFDM Systems

The advantage of using orthogonal frequency division multiplexing (OFDM) over the single-carrier modulation is its ability to mitigate interference and fading without complex equalization filters in the receiver. OFDM systems have a high peak-to-average ratio (PAPR) which results in a high requirement for the resolution of AD converters. High-resolution AD converters are therefore widely used in OFDM receivers. However, the power consumption is proportional to the resolution of the AD converters. In this paper we investigate the quantization effects in OFDM systems. Quantization is a nonlinear function which happens in the time domain, so the quantization effect in the frequency domain (important for OFDM) is not simple. Here, we derive a model for the quantization effect in the frequency domain. Further, we investigate whether it is possible to apply low-resolution AD converters in reliable communications based on OFDM. Simulations with an AWGN channel reveal that the proposed model predicts the quantization noise in the frequency domain very well. Difference in $\sigma_\mathrm{q}^2$ between simulation outcomes and our model is less than 0.6\%. Also, simulations show that 5-bits AD resolution is required for OFDM communication over an AWGN channel.