Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide a better bit error rate (BER) performance than rake combining. To further improve the BER performance, cyclic delay transmit diversity (CDTD) can be used. CDTD simultaneously transmits the same signal from different antennas after adding different cyclic delays to increase the number of equivalent propagation paths. Although a joint use of CDTD and MMSE-FDE for direct sequence code division multiple access (DS-CDMA) achieves larger frequency diversity gain, the BER performance improvement is limited by the residual inter-chip interference (ICI) after FDE. In this paper, we propose joint FDE and despreading for DS-CDMA using CDTD. Equalization and despreading are simultaneously performed in the frequency-domain to suppress the residual ICI after FDE. A theoretical conditional BER analysis is presented for the given channel condition. The BER analysis is confirmed by computer simulation.

In this paper, we propose a novel iterative transmit/receive equalization technique for single-carrier (SC) block transmission in a severe frequency-selective fading channel. Iterative frequency-domain inter-symbol interference (ISI) cancellation (FDIC) is introduced to the previously proposed joint iterative transmit/receive frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion. 1-tap FDE is employed at the transmitter. At the receiver, a 1-tap FDE and FDIC are jointly used and they are updated in an iterative manner. The transmit FDE weight is derived based on the MMSE criterion by taking into account the reduction of residual ISI in the receiver. To derive the weight, the transmitter assumes that the receiver can partially reduce the residual ISI after the FDIC. We conduct a computer simulation to investigate the achievable bit error rate (BER) performance to confirm the effectiveness of our proposed technique.

One-tap frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can significantly improve the bit error rate (BER) performance of single-carrier (SC) transmission in a frequency-selective fading channel. However, a big performance gap from the theoretical lower bound still exists due to the presence of residual inter-symbol interference (ISI) after MMSE-FDE. In this paper, we point out that the frequency-domain received SC signal can be expressed using the matrix representation similar to the multiple-input multiple-output (MIMO) multiplexing and therefore, signal detection schemes developed for MIMO multiplexing, other than simple one-tap MMSE-FDE, can be applied to SC transmission. Then, for the reception of SC signals, we propose a new signal detection scheme, which combines FDE with MIMO signal detection, such as MMSE detection and Vertical-Bell Laboratories layered space-time architecture (V-BLAST) detection (we call this frequency-domain block signal detection). The achievable average BER performance using the proposed frequency-domain block signal detection is evaluated by computer simulation.

Single-carrier (SC) multiple access is a promising uplink multiple access technique because of its low peak-to-average power ratio (PAPR) property and high frequency diversity gain that is achievable through simple one-tap frequency-domain equalization (FDE) in a strong frequency-selective channel. The multiple access capability can be obtained by combining either frequency division multiple access (FDMA) or code division multiple access (CDMA) with SC transmission. In this article, we review the recent research on the SC multiple access techniques with one-tap FDE. After introducing the principle of joint FDE/antenna diversity combining, we review various SC multiple access techniques with one-tap FDE, i.e., SC-FDMA, SC-CDMA, block spread CDMA, and delay-time/CDMA.

Frequency-domain equalization (FDE) based on minimum mean square error (MMSE) is considered as a promising equalization technique for a broadband single-carrier (SC) transmission. When a square-root Nyquist filter is used at a transmitter and receiver to limit the signal bandwidth, the presence of timing offset produces the inter-symbol interference (ISI) and degrades the bit error rate (BER) performance using MMSE-FDE. In this paper, we discuss the mechanism of the BER performance degradation in the presence of timing offset. Then, we propose joint MMSE-FDE & spectrum combining which can make use the excess bandwidth introduced by transmit filter to achieve larger frequency diversity gain while suppressing the negative effect of the timing offset.

The performance of single-carrier (SC) transmission in a frequency-selective fading channel degrades due to a severe inter-symbol interference (ISI). Using frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can improve the bit error rate (BER) performance of SC transmission. However, the residual ISI after FDE limits the performance improvement. In this paper, we propose a joint use of Tomlinson-Harashima precoding (THP) and FDE to remove the residual ISI. An approximate conditional BER analysis is presented for the given channel condition. The achievable average BER performance is evaluated by Monte-Carlo numerical computation method using the derived conditional BER. The BER analysis is confirmed by computer simulation of the signal transmission.

Broadband single-carrier frequency division multiple access (SC-FDMA) uplink using frequency-domain square-root Nyquist filtering is considered. The peak-to-average power ratio (PAPR) of filtered SC signals can be reduced by increasing the filter roll-off factor α. Furthermore, an additional frequency diversity gain can be obtained by making use of the excess bandwidth introduced by the transmit root Nyquist filtering. However, if the carrier-frequency separation is kept the same as in the case of α=0, the adjacent users' signal spectra overlap with the desired users' spectrum and the multiuser interference (MUI) is produced. In this paper, we propose two frequency-domain iterative MUI cancellation schemes which can achieve the frequency diversity gain through spectrum combining. The achievable bit error rate (BER) and throughput performances are evaluated by computer simulation.

Broadband wireless technology that enables a variety of gigabit-per-second class data services is a requirement in future wireless communication systems. Broadband wireless channels become extremely frequency-selective and cause severe inter-symbol interference (ISI). Furthermore, the average received signal power changes in a random manner because of the shadowing and distance-dependant path losses resulted from the movement of a mobile terminal (MT). Accordingly, the transmission performance severely degrades. To overcome the performance degradation, two most promising approaches are the frequency-domain equalization (FDE) and distributed antenna network (DAN). The former takes advantage of channel frequency-selectivity to obtain the frequency-diversity gain. In DAN, a group of distributed antennas serve each user to mitigate the negative impact of shadowing and path losses. This article will introduce the recent advances in FDE and DAN for the broadband single-carrier (SC) transmissions.

In the next generation mobile communication systems, multiple-input multiple-output (MIMO) multiplexing is an indispensable technique to achieve very high-speed data transmission with a limited bandwidth. In MIMO multiplexing, it is necessary to estimate the channels between transmit and receive antennas for signal detection. In this paper, we propose a minimum mean square error (MMSE) channel estimation using cyclic delay pilot for single-carrier (SC)-MIMO multiplexing. In the proposed channel estimation, the same pilot block is altered through the addition of different cyclic delays and transmitted from different antennas at the same time for simultaneous estimation of all channels between transmit and receive antennas. We evaluate by computer simulation the bit error rate (BER) performance of MIMO multiplexing using the proposed channel estimation and compare it to those using time-multiplexed pilot based channel estimation (TMP-CE) and code-multiplexed pilot based channel estimation (CMP-CE).

In this paper, joint water filling and maximal ratio transmission (joint WF-MRT) downlink transmit diversity for a single-carrier distributed antenna network (SC DAN) is proposed. The joint WF-MRT transmit weight allocates the transmit power in both transmit antenna dimension and frequency dimension, i.e., the power allocation is done both across frequencies based on WF theorem and across transmit antennas based on MRT strategy. The cumulative distribution function (CDF) of the channel capacity achievable by joint WF-MRT transmit diversity is evaluated by Monte-Carlo numerical computation method. The channel capacities achievable with joint WF-MRT, MRT, and WF transmit weight (WF transmit weight is done across transmit antennas and frequencies based on WF theorem) are compared. It is shown that the joint WF-MRT transmit weight provides the highest channel capacity among three transmit weights.

In this paper, we propose an iterative minimum mean square error detection with interference cancellation (MMSED-IC) for frequency-domain filtered single carrier (SC)-frequency-division multiple-access (FDMA) uplink transmission. The use of a square-root Nyquist transmit filter reduces the peak-to-average power ratio (PAPR) while increases the frequency-diversity gain. However, if carrier-frequency separation among multiple-access users is kept the same as the one used for the case of roll-off factor α=0 (i.e., brick-wall filter), then the adjacent users' spectra will overlap and multi-user interference (MUI) occurs. The proposed MMSED-IC can sufficiently suppress the MUI from adjacent users while achieving the maximum frequency-diversity gain. We apply the proposed MMSED-IC to a packet access using filtered SC-FDMA, multi-input multi-output (MIMO) multiplexing, and hybrid automatic repeat request (HARQ). It is shown by computer simulation that filtered SC-FDMA with α=1 can achieve higher throughput than orthogonal frequency division multiple access (OFDMA).

Multi-user multi-input multi-output (MIMO) system has been attracting much attention due to its high spectrum efficiency. Non-linear MIMO signal detection methods with less computational complexity have been widely studied for single-user MIMO systems. In this paper, we investigate how a lattice reduction (LR)-aided detection and a maximum likelihood detection (MLD) employing the QR decomposition and M-algorithm (QRM-MLD), which are commonly known as non-linear MIMO signal detection methods, improve the uplink capacity of a multi-user MIMO-OFDM cellular system, compared to simple linear detection methods such as zero-forcing detection (ZFD) and minimum mean square error detection (MMSED). We show that both LR-aided linear detection and QRM-MLD can achieve higher uplink capacity than simple linear detection at the cost of moderate increase of computational complexity. Furthermore, QRM-MLD can obtain the same uplink capacity as MLD.

Recently, assuming ideal brick-wall transmit filtering, we proposed a frequency-domain block signal detection (FDBD) with maximum likelihood detection employing QR decomposition and M-algorithm (called QRM-MLD) for the reception of single-carrier (SC) signals transmitted over a frequency-selective fading channel. QR decomposition (QRD) is applied to a concatenation of the propagation channel and discrete Fourier transform (DFT). However, a large number of surviving paths is required in the M-algorithm to achieve sufficiently improved bit error rate (BER) performance. The introduction of filtering can achieve improved BER performance due to larger frequency diversity gain while keeping a lower peak-to-average power ratio (PAPR) than orthogonal frequency division multiplexing (OFDM). In this paper, we develop FDBD with QRM-MLD for filtered SC signal reception. QRD is applied to a concatenation of transmit filter, propagation channel, and DFT. We evaluate BER and throughput performances by computer simulation. From performance evaluation, we discuss how the filter roll-off factor affects the achievable BER and throughput performances and show that as the filter roll-off factor increases, the required number of surviving paths in the M-algorithm can be reduced.

In the conventional iterative superimposed pilot-assisted channel estimation (SI-PACE), simple averaging of the instantaneous channel estimates obtained by using the pilot over several single-carrier (SC) blocks (called the frame in this paper) is taken in order to reduce the interference from data symbols. Therefore, the conventional SI-PACE has low tracking ability against fading time variations. To solve the tracking problem, Wiener filtering (WF)-based averaging can be used instead of simple averaging. However, WF incurs high computational complexity. Furthermore, the estimation error of the fading autocorrelation function significantly degrades the channel estimation accuracy. In order to improve the channel estimation accuracy while keeping the computational complexity low, a new iterative SI-PACE using sliding WF (called iterative SWFSI-PACE) is proposed. The channel estimation is done by sliding a WF having a shorter filter size than the measurement interval. The bit error rate (BER) and throughput performances of SC-FDE using iterative SWFSI-PACE are investigated by computer simulation to show that the proposed scheme achieves good BER and throughput performances while keeping the computational complexity low irrespective of the fading rate (or maximum Doppler frequency).

Recently, overlap frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion which requires no guard interval (GI) insertion was proposed for signal transmission using multi-code direct sequence code division multiple access (DS-CDMA) in a frequency-selective fading channel. Another promising equalization technique is time-domain sliding-window chip equalization (SWCE). In this paper, the bit error rate (BER) performances achievable with overlap FDE and SWCE are compared. It is shown that, by extending the fast Fourier transform (FFT) block size, overlap FDE can achieve almost the same BER performance as SWCE with much less computational complexity than SWCE.

Recently, frequency-domain equalization (FDE) has been attracting much attention as a way to improve single-carrier (SC) signal transmission in a frequency-selective wireless channel. Since the SC signal spectrum is spread over the entire signal bandwidth, FDE can take advantage of channel frequency-selectivity and achieve the frequency diversity gain. SC with FDE is a promising wireless signal transmission technique. In this article, we review the pioneering research done on SC with FDE. The principles of simple one-tap FDE, channel estimation, and residual inter-symbol interference (ISI) cancellation are presented. Multi-input/multi-output (MIMO) is an important technique to improve the transmission performance. Some of the studies on MIMO/SC with FDE are introduced.

Turbo coded hybrid ARQ (HARQ) is known as one of the promising error control techniques for high speed wireless packet access. However, in a severe frequency-selective fading channel, the HARQ throughput performance significantly degrades for direct sequence code division multiple access (DS-CDMA) system using rake combining. This problem can be overcome by replacing the rake combining by the frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion. In a system with the conventional FDE, the guard interval (GI) is inserted to avoid the inter-block interference (IBI). The insertion of GI reduces the throughput. Recently, overlap FDE that requires no GI insertion was proposed. In this paper, we apply overlap FDE to HARQ and derive the MMSE-FDE weight for packet combining. Then, we evaluate the throughput performance of DS-CDMA HARQ with overlap FDE. We show that overlap FDE provides better throughput performance than both the rake combining and conventional FDE regardless of the degree of the channel frequency-selectivity.