Advances in single carrier block modulation with frequency domain processing

International audienceThis special issue focuses on single carrier block modulation (SC-BM) with frequency domain processing. This class of modulation and multiple access schemes complements the orthogonal frequency division multiple access (OFDMA) and its variations. For example, LTE (the long term evolution of the 3GPP standard), and LTE-Advanced, employ OFDMA in the downlink (base stations to mobiles) and SC-FDMA, a version of SC-BM in the uplink (mobiles to base stations). The main reason for adapting the technology of SC-FDMA for uplink LTE is the fact that OFDMA has high "peak-to-average power ratio" (PAPR), which is a disadvantage for mobile devices that are limited by power availability. Besides its advantage of low PAPR, SC-BM technology has a similar performance/complexity to that of OFDMA, and simple frequency domain equalization methods for combating dispersive channels. There were 17 papers submitted to this special issue. All had merits, but the review process reduced the number of accepted papers to 9. The accepted papers cover a number of novel and advanced aspects of single carrier block modulation with frequency domain processing: near-optimal nonlinear and iterative equalization techniques; applications to CDMA, MIMO and ARQ; channel estimation; and application to free-space optical transmission. Following is a summary of the papers. In the paper "Iterative Successive Interference Cancellation for Quasi-Synchronous Block Spread CDMA Based on the Orders of the Times of Arrival", Wang, Bocus, and Coon [1] describe an interference cancellation scheme based on the times of arrival of the signals from different users, and they show that for practical channels this ordering criterion is equivalent to ordering with respect to decreasing average SINR. In "Complexity Reduced MLD Based on QR Decomposition in OFDM MIMO Multiplexing with Frequency Domain Spreading and Code Multiplexing", Nagatomi, Kawai, and Higuchi [2] propose a reduced-complexity maximum likelihood signal detection method for MIMO-OFDM systems with frequency-domain spreading and code multiplexing. They show how to exploit signal orthogonalization based on QR decomposition of the product of the channel and spreading code matrices in the frequency domain to obtain significant complexity reductions. In "Frequency-domain Block Signal detection with QRM-MLD for Training Sequence-aided Single-carrier Transmission", Yamamoto, Takeda and Adachi [3] propose replacement of the cyclic prefix with a known training sequence. The object is to improve BER performance of an equalization scheme which uses QR decomposition with M-algorithm detection, while keeping the number of surviving paths low for reduced complexity. The scheme is especially effective for 16QAM and 64QAM modulation. The paper "Joint Iterative Tx/Rx MMSE-FDE and ISI Cancellation for Single-carrier Hybrid ARQ with Chase Combining" by Takeda and Adachi [4] applies transmitter and receiver equalization and iterative intersymbol interference cancellation to a system with hybrid ARQ transmission, Chase combining and antenna diversity. The equalizer parameters at both transmitter and receiver are optimized for each retransmission. The paper "Novel Techniques of Single Carrier Frequency Domain Equalization for Optical Wireless Communications" by Acolaste, Bar-Ness, and Wilson [5] investigates the application of single-carrier frequency-domain equalization to diffuse optical wireless communications and demonstrates its advantages over OFDM in terms of reduced PAPR and improved error rate in the presence of LED nonlinearity. In the paper "Semi-Blind Channel Estimation for IFDMA in Case of Channels with Large Delay Spreads", Sohl and Klein [6] propose a subspace-based channel estimation algorithm which can cope with large delay spreads. In previous work on IFDMA, the number of channel taps that can be estimated was limited to the number of subcarriers per user. The subspace analysis in this paper relaxes this constraint and increases the number of taps that can be estimated. The paper "Channel Frequency response Estimation for MIMO with Systems with Frequency-Domain Equalization " by Yang, Shi, Chew, and Tjhung [7] suggests a training-based channel frequency response (CFR) estimation scheme which is hardware efficient when integrated with and SC-FDE and space time coding (STC) in MIMO Systems. An MSE analysis of this CFR estimation scheme is provided, which considered linear estimators based on both LS and minimum MSE criteria. Also with a given constraint which effectively limits the transmit power of the training signals, the paper investigates the optimal design of training signals under different a priori knowledge of the channel statistics. For the special case of 2 transmit antennas, it was demonstrated that CFR estimation could be implemented in adaptive manner. The paper by Dang, Ruder, Schober and Gerstacker [8], "MMSE Beamforming for SC-FDMA Transmission over MIMO ISI Channels", derives minimum mean squared error beamforming strategies for multi-antenna reception, as well as further modifications to reduce the transmitted peak to average power ratios. The paper by Nishino, Tanahashi, and Ochiai [9], "A Bit Labeling Design for Trellis-Shaped Single-Carrier PSK with PAPR Reduction", investigates application of trellis shaping to reduce the PAPR of band-limited single-carrier PSK signals. The authors demonstrate that the uncoded bit error rate and PAPR reduction capability of trellis shaping is highly dependent on bit labeling. They propose a bit labeling scheme for high-order PSK constellation that can efficiently reduce PAPR while achieving BER performance comparable to that of Gray labeling

Analysis of a Gradient Algorithm for Simultaneous Passband Equalization and Carrier Phase Recovery

A two‐dimensional receiver structure has been proposed, incorporating two innovations: passband equalization, which mitigates intersymbol interference, and data‐directed carrier recovery and demodulation following equalization, which enables compensation of carrier frequency offset and phase jitter, but does not require transmission of a separate pilot tone with the data signal. The receiver is fully adaptive; the adjustment of the equalizer tap coefficients and of the estimate of the current channel phase shift is based on a gradient algorithm for jointly minimizing the mean squared error with respect to those parameters. In this paper, we analyze the dynamic behavior of the deterministic gradient algorithm (where channel parameters entering into the gradient expression are assumed known in advance). The corresponding estimated gradient algorithm (where these parameters are initially unknown) has previously been studied experimentally, but is not treated here. The first part of the present study concerns system start‐up (or transient) response when the channel's phase shift is fixed. Examination of the analytical solution leads to the qualitative conclusion that, if the equalizer tap adaptation coefficient β it small relative to the phase‐tracking coefficient a, the added phase estimation feature does not strongly affect the start‐up behavior of the passband equalizer under typical operating conditions. Indeed, if the equalizer tap coefficients all start at zero, their evolution in the deterministic gradient algorithm is completely unaffected by the phase‐tracking loop. The second situation analyzed is the steady‐state response of the system to a constant carrier frequency offset. In this case, the phase‐tracking loop is found to reduce the resulting rate of rotation of the equalizer taps to about β/(α + β) of the original frequency offset. As a result, the degradation in system mean squared error due to frequency offset is typically quite small. The final analysis is of the response of a linearized version of the receiver structure to sinusoidal phase jitter. When the channel's linear distortion is not too severe and the coefficient β is small, the system mean squared error owing to phase tracking error is found to approximate that of a simple, first‐order, phase‐locked loop

Adaptive Reference Echo Cancellation

The AREC (adaptive reference echo cancellation) algorithm is presented for an echo canceler used in full-duplex two-wire digital transmission on digital subscriber loops. The AREC algorithm incorporates a decision-directed estimation of and compensation for the far-end signal which is a source of interference to the conventional echo canceler adaptation algorithm. The AREC algorithm thus offers much faster convergence and shorter coefficient Wordlengths than the conventional algorithm. Analysis and simulation of the performance and convergence of both AREC and conventional echo canceler adaptation algorithms are carried out. Included in the analysis is the effect of receiver delay and coefficient wordlength requirements. A simple and robust startup procedure is proposed and investigated by simulation. Copyrigh

A system architecture for broadband millimeter-wave access to an ATM LAN

We present a system architecture for a broadband indoor wireless digital communications system, capable of supporting ATM at transport bit rates up to about 160 Mb/s for broadband LANs. Access is via a radio system with carrier frequencies within the 20 to 60 GHz range, because of the relative abundance of available bandwidth in this range. The system design is shaped by a set of service requirements, by the characteristics of indoor millimeter wave radio channels, and by the constraints and opportunities of the relevant device technologies. The design includes a multi-access microcellular architecture accommodating ATM traffic with a wide range of broadband and narrowband bit rates and services in an office environment. A modem configuration incorporating bandwidth spreading, signal processing, and coding measures to provide immunity to the effects of radio channel fa