Single-Carrier Frequency Domain Equalization

Orthogonal frequency division multiplexing (OFDM) has been recently adopted by major manufacturers and by standardization bodies for a wide range of wireless and wireline applications ranging from digital video/audio broadcasting to power-line communications. The major virtues of OFDM are 1) its resilience to multipath propagation providing a viable low-complexity and optimal (in the maximum likelihood sense) solution for intersymbol interference (ISI) mitigation, 2) the possibility of achieving channel capacity if the transmitted signal is adapted to the state of the communication channel (i.e., if energy and it-loading procedures are adopted), and 3) the availability of strategies for frequency diversity scheduling in multiuser communication systems. Although OFDM has become the physical layer of choice for broadband communications standards, it suffers from several drawbacks including a large peak-to-averagepower ratio (PAPR), intolerance to amplifier nonlinearities, and high sensitivity to carrier frequency offsets (CFOs) [6]. An alternative promising approach to ISI mitigation is the use ofsingle-carrier (SC) modulation combined with frequencydomainequalization (FDE). On the one hand, the complexityand performance of SC-FDE systems is comparable to that of OFDM while avoiding the above mentioned drawbacks associatedwith multicarrier (MC) implementation. On the other hand,FDE does not represent an optimal solution to signal detectionover ISI channels and SC systems cannot certainly offer thesame flexibility as OFDM in the management of bandwidth andenergy resources, both in single user and in multiuser communications.All these considerations have made the choicebetween SC-FDE and OFDM a strongly debated issue in academicand industrial circles. For this reason, we believe that SC-FDEtechniques deserve a deeper analysis in view of the significantattention given to MC techniques. The first MC scheme was proposed in 1966 [1], whereas the first approach to SC-FDE in digital communication systems dates back to 1973 [2]. Despite thesmall time separation between their introductions, many effortshave been devoted by the scientific community to the study ofMC solutions, but little attention has been paid to SC-FDE formany years. In the last decade, there has been a renewed interest in this area. The theoretical and practical gap between thetwo solutions is tightening, but the technical literature on MCcommunication is by far larger than that on SC-FDE. In thisarticle, we intend to provide an overview of the principles of SCFDE with a particular focus on wireless applications and to present an up-to-date review including the latest and most relevant research results in the SC-FDE area. Our article is tutorial in nature and, therefore, our emphasis is not on detailed mathematical derivations but rather on describing the salient features of SC-FDE techniques and comparing it to its MC counterpart.