Low-complexity linear frequency domain equalization for continuous phase modulation

In this paper, we develop a new low-complexity linear frequency domain equalization (FDE) approach for continuous phase modulated (CPM) signals. As a CPM signal is highly correlated, calculating a linear minimum mean square error (MMSE) channel equalizer requires the inversion of a nondiagonal matrix, even in the frequency domain. In order to regain the FDE advantage of reduced computational complexity, we show that this matrix can be approximated by a block-diagonal matrix without performance loss. Moreover, our MMSE equalizer can be simplified to a low-complexity zero-forcing equalizer. The proposed techniques can be applied to any CPM scheme. To support this theory we present a new polyphase matrix model, valid for any block-based CPM system. Simulation results in a 60 GHz environment show that our reduced-complexity MMSE equalizer significantly outperforms the state of the art linear MMSE receiver for large modulation indices, while it performs only slightly worse for small ones.

I. Introduction

WE are witnessing an explosive growth in the demand for wireless connectivity. Short range wireless links will soon be expected to deliver bit rates of over 2 Gbits/s. Worldwide, recent regulation assigned a 3 GHz or wider frequency band at 60 GHz to this kind of applications [1]. Continuous phase modulation (CPM) has been proposed as an attractive modulation technique for 60 GHz communications in [2], [3] and [4] and in the IEEE 802.15.3c standardization committee.