SC-FDE Systems Research Articles

Fine time synchronization and residual ISI influence in SC-FDE systems

Abstract We show a novel method for a fine time synchronization in a presence of residual intersymbol interferences (ISIs). The proposed method is compared with a (1) Cramer-Rao lower bound (CRLB) for data-aided timing estimators and with a (2) maximum likelihood (ML) estimator both in (a) ISI-free additive white Gaussian noise (AWGN) channel and (b) in a residual ISI channel. The effect of the residual ISI is introduced via a power-delay profile (PDP) with a delay spread spanning over several samples. We consider a single-carrier system with a frequency domain channel estimation. The proposed method almost reaches the performance of the ML estimator in AWGN, while in the presence of the residual ISI, the proposed method shows superior performance evaluated in terms of error vector magnitude improvement of up to 10%.

Novel Pilot Position Detection for SC-FDE Systems With Frequency Domain Pilot Multiplexing Technique

Frequency domain pilot multiplexing technique (FDPMT) has recently emerged as an appealing technique for channel estimation in single-carrier frequency domain equalization systems as it achieves high spectral efficiency at the expense of tiny signal distortion. In FDPMT, pilot positions are dynamically selected to achieve a relatively low level of signal distortion, rendering pilot position detection (PPD) indispensable at the receiver. In this letter, by exploiting both the prior known pilots and the statistical information of the data tones, we propose a novel PPD scheme based on the maximum-likelihood criterion. Simulation results show that our proposed PPD scheme significantly improves the PPD accuracy and outperforms the existing counterparts in terms of bit error rate.

Novel Pilot Design and Signal Detection for SC-FDE Systems With Frequency-Domain Pilot Multiplexing Technique

The performance of single-carrier frequency-domain equalization systems with the frequency-domain pilot multiplexing technique is affected by the level of signal distortion, which highly depends on the pilot position selection (PPS) scheme at the transmitter and the signal detection (SD) scheme at the receiver. In this letter, by exploring the relationship between distorted symbols and decision boundaries, we propose a novel PPS scheme to confine the distorted symbols within their designated decision regions, which dispenses with a priori knowledge of the channel. Based on the maximum-likelihood criterion, we also propose a novel SD scheme to avoid error propagation, which operates on a symbol-by-symbol basis. Simulation results on bit error rate show that our proposed PPS scheme achieves almost the same performance as the optimal one and our proposed SD scheme outperforms the existing one in additive white Gaussian noise channels; in addition, both proposed schemes outperform their existing counterparts in frequency-selective Rayleigh fading channels.

Single-carrier Transmission Frequency-domain Equalization Based on a Wiener Filter for Broadband Wireless Communications

Recently, frequency-domain equalization for single-carrier transmission (SC-FDE) has been given much attention. For example, the enhanced mobile phone system, a SC-FDMA (Single-carrier frequency division multiple access) method using SC-FDE and multiple access will be adopted. However in previous research, there are many papers describing the features and advantages of SC-FDE based on a comparison of SC-FDE and orthogonal frequency-division multiplexing (OFDM) systems. In this technical note, we discuss single-carrier transmission equalization in the time-domain (SC-TDE) and SC-FDE in a unified way centered on the Wiener filter based on the minimum mean square error (MMSE) criterion. The reason to take up a Wiener Filter is that it is a basic filter based on the MMSE criterion. Also, we explain the basic principle of the SC-FDE and SC-FDMA in an organized and systematic way. Moreover, we point out the physical meaning of the Wiener solution in SC-FDE and relationship between SC-TDE and SC-FDE Wiener solutions. As a result, we show useful information and pointers, especially for when we want to replace existing SC-TDE technology with SC-FDE technology.

Bandwidth-efficient frequency-domain equalization for single carrier multiple-input multiple-output underwater acoustic communications

This paper proposes a single carrier (SC) receiver scheme with bandwidth-efficient frequency-domain equalization (FDE) for underwater acoustic (UWA) communications employing multiple transducers and multiple hydrophones. Different from the FDE methods that perform FDE on a whole data block, the proposed algorithm implements an overlapped-window FDE by partitioning a large block into small subblocks. A decision-directed channel estimation scheme is incorporated with the overlapped-window FDE to track channel variations and improve the error performance. The proposed algorithm significantly increases the length of each block and keeps the same number of training symbols per block, hence achieving better data efficiency without performance degradation. The proposed scheme is tested by the undersea data collected in the Rescheduled Acoustic Communications Experiment (RACE) in March 2008. Without coding, the 2-by-12 MIMO overlapped-window FDE reduces the average bit error rate (BER) over traditional SC-FDE schemes by 74.4% and 84.6% for the 400 m and 1000 m range systems, respectively, at the same data efficiency. If the same BER performance is required, the proposed algorithm has only 8.4% transmission overhead, comparing to over 20% overhead in other existing UWA OFDM and SC-FDE systems. The improved data efficiency and/or error performance of the proposed FDE scheme is achieved by slightly increased computational complexity over traditional SC-FDE schemes.

Frequency-domain multipacket detection: a high throughput technique for SC-FDE systems

The traditional approach to cope with collisions is to discard the packets involved in it and to ask for their retransmission. However, since the signal associated to a collision has important information concerning the packets involved, we can efficiently resolve collisions with proper retransmissions. In this paper we consider severely time-dispersive channels and we propose a technique that allows efficient packet separation. We employ SC-FDE schemes (single-carrier with frequency-domain equalization) and we propose an iterative frequency-domain multi-packet detection. Since our technique requires uncorrelated channels for different retransmissions, we also propose an SP technique (Shifted Packets) for retransmissions in fixed channels. Since the total number of transmissions is equal to the number of packets involved in the collision (even when the channel remains fixed for the retransmissions), our technique allows high throughputs. The analysis of our detection technique combined with the NMDA (network-assisted diversity multiple access) MAC (medium access control) protocol shows significant throughput and delay improvements for low E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> values compared to a TDMA (time division multiple access) approach, where collisions are avoided. This technique is particularly appealing for the uplink of broadband wireless systems, since we consider SC-FDE schemes and the complexity is concentrated in the receiver. By employing the SP scheme we can use the same channel for the retransmissions, with only a small performance degradation.

Iterative Interference Cancellation and Channel Estimation for Mobile SC-FDE Systems

This letter presents a combination of iterative channel equalization and estimation algorithms for mobile users in an interference-prone single carrier (SC) space division multiple access (SDMA) uplink system. It is shown that the soft decision based iterative block decision feedback equalization (SD-IBDFE) with parallel interference cancellation (PIC) and a least squares (LS) adaptation algorithm give significant improvement in estimating the SDMA users' channels in an iterative manner. Also, iterative channel estimation over multiple frames to estimate the desired user's channels provides additional gain. Simulation results show that the combination of these low complexity algorithms gives reasonably good results in interference-dominated doubly selective channels.