Comparison of OQPSK and CPM for Communications at 60 GHz with a Nonideal Front End

Short-range digital communications at 60GHz have recently received a lot of interest because of the huge bandwidth available at those frequencies. The capacity offered to the users could finally reach 2Gbps, enabling the deployment of new multimedia applications. However, the design of analog components is critical, leading to a possible high nonideality of the front end (FE). The goal of this paper is to compare the suitability of two different air interfaces characterized by a low peak-to-average power ratio (PAPR) to support communications at 60GHz. On one hand, we study the offset-QPSK (OQPSK) modulation combined with a channel frequency-domain equalization (FDE). On the other hand, we study the class of continuous phase modulations (CPM) combined with a channel time-domain equalizer (TDE). We evaluate their performance in terms of bit error rate (BER) considering a typical indoor propagation environment at 60GHz. For both air interfaces, we analyze the degradation caused by the phase noise (PN) coming from the local oscillators; and by the clipping and quantization errors caused by the analog-to-digital converter (ADC); and finally by the nonlinearity in the PA.