Tae-Won Yune

SC-FDMA with iterative multiuser detection: improvements on power/spectral efficiency

This article outlines the basic principles of single-carrier frequency division multiple access with iterative multiuser detection, called grouped frequency division multiple access. GFDMA allows multiple users to share a common set of subcarriers and separates the signals of users by employing distinct interleavers and frequency-domain multiuser detection. Some attractive features of GFDMA are explained, including low-cost iterative multiuser detection, multiuser and frequency diversity gains, and flexibility in resource allocation. We also discuss the applications of GFDMA to spatial diversity schemes and to intercell interference mitigation in the cell edge. It is shown that GFDMA offers advantages over SC-FDMA with respect to power/spectral efficiency. Such power/spectral efficiency can provide considerable performance improvements in future wireless communication networks.

Opportunistic Network-Coded Cooperative Transmission with Demodulate-and-Forward Protocol in Wireless Channels

In this letter, we consider a multiuser cooperative transmission scheme with network coding over wireless channels. Network coding based on decode-and-forward protocol is a promising technique to improve network throughput. However, decoding errors at the relay cause error propagation, which degrades the performance of network-coded cooperations. To mitigate the error propagation in the network-coded signal, we first express a single equivalent gain, and then the opportunistic relay selection and proportional combining schemes are performed with the equivalent channel and the relay-destination channel. Simulation results show that all cooperative users can obtain a diversity gain of order two by using single network-coded transmission, even when there are detection errors at the relay.

Iterative multiuser detection with spectral efficient relaying protocols for single-carrier transmission

In this paper, we present an iterative multiuser detection scheme using frequency-domain equalization (IMDFDE), which can be incorporated into a single carrier frequency division multiple access (SC-FDMA) framework. The IMD-FDE scheme employs a different interleaver for each user at the transmitter, and removes multiuser interference with an iterative detection method in the frequency domain at the receiver. The extrinsic information transfer (EXIT) charts and bit-error rate (BER) plots are presented to investigate the iterative behavior of the IMD-FDE over additive white Gaussian noise and multipath fading channels. In a conventional time-division multiple-access (TDMA)-based relay protocol, cooperative transmission over two time slots leads to a 50% loss in spectral efficiency. We propose two spectral efficient relay protocols, where multiple sources access a relay, destination, or both simultaneously. We also present a new iterative detection scheme that effectively removes multiuser interferences for the proposed relay protocols.With the proposed protocols and the aid of iterative multiuser detection scheme, the proposed relay-assisted SC-FDMA with IMD-FDE can obtain diversity gain without sacrificing spectral efficiency and approaches the single-user bound over time-varying and frequency-selective fading relay channels.

QoS-constrained opportunistic scheduling for sc-fdma with iterative multiuser detection

This letter proposes a quality-of-service (QoS) constrained opportunistic scheduling for a single-carrier frequency division multiple access (SC-FDMA) scheme. The SC-FDMA scheme considered in this letter employs an iterative multiuser detection using frequency-domain equalization (IMDFDE), which allows several users to share a common set of subcarriers. In order to improve spectral efficiency and guarantee QoS of assigned users, the proposed method chooses users by iteratively performing user selection. At each user selection for a set of subcarriers, the scheduler takes into account multiuser interference from previously assigned users of corresponding subcarriers and QoS constraint. Simulation results show that the proposed method provides higher spectral efficiency compared with round-robin and max-SNR.

Iterative Multiuser Detection for Single-Carrier Modulation with Frequency-Domain Equalization

In this letter, we propose a new multiuser detection scheme for single-carrier modulation with frequency-domain equalization (SC-FDE). We first present mathematical formulations of multiuser detection for the SC-FDE system with user- specific interleaving. The proposed structure employs spreader and different interleaver for each user at the transmitter, and re moves multiuser interference with an iterative detection method in the frequency domain at the receiver. Simulation results show that the proposed scheme outperforms the interleave- division multiple-access (IDMA) scheme in the block error rate even for severely frequency-selective channel, while providing considerably lower computational complexity.

Iterative detection for spectral efficient user cooperative transmissions over multipath fading channels

Cooperative communications can achieve spatial diversity gain and enhance coverage. However, conventional half-duplex relaying schemes suffer from the loss in spectral efficiency, because the two channel uses are required for transmission from the source to the destination. In this paper, we present spectral efficient transmissions for a user cooperative diversity system over multipath fading channels. To increase the spectral efficiency, a node, which acts as a relay, employs a superposition coding to transmit its own data block and the data block from the other node simultaneously. For superposition, we consider two different re-encoding schemes. One is based on complex field superposition coding and the other is based on Galois field superposition coding. In both re-encoding schemes, we introduce a user-specific interleaver to the data blocks for user separation. We also propose an iterative detection scheme to combat the effects of inter-symbol interference caused by multipath fading and to extract diversity gain from the superposed signals. For performance estimation, we develop a density evolution technique. It is shown that the proposed schemes can obtain diversity gain without sacrificing spectral efficiency and the predicted performances are consistent with simulated performances.

Iterative Multiuser Detection with Spectral Efficient Protocol for Relay-Assisted SC-FDE

This letter proposes an iterative multiuser detection scheme using spectral efficient protocol for relay-assisted single- carrier frequency-domain equalization (SC-FDE). The proposed system achieves spatial diversity over fading channels in a distributed fashion. In the proposed system, two sources with user-specific interleavers access a relay simultaneously, which increases spectral efficiency of time-division multiple-access (TDMA)-based relay protocol. Interference from the other source is removed by an iterative detection method in the frequency domain at the destination. Simulation results show that the proposed system can obtain diversity gain without sacrificing spectral efficiency and approaches the single-user bound.

Decision-directed channel estimation for SC-FDE in amplify-and-forward relaying networks

In this letter, we propose a decision-directed channel estimation scheme for single-carrier frequency-domain equalization in amplify-and-forward (AF) relaying networks. For coherent combining of the received signals in AF-based cooperation, conventional channel estimation schemes have focused on estimation of source-destination and source-relay-destination channels. However, if the individual channels in the source-relay-destination link are not considered, the relaying gain is limited because the noise propagation from the relay to the destination affects the effective signal-to-noise ratio at the destination. The proposed scheme estimates the effective channel parameters for maximal-ratio combining, in the absence of channel-state information (CSI) from the relay. Simulation results show that the proposed scheme outperforms the conventional scheme and approaches the performance with perfect CSI.

Primary network cognition with spatial diversity signature

The identification of primary networks improves efficiency in dynamic spectrum access. We propose a spatial diversity signature for the primary signal detection, which exploits the structure of space-time or space-frequency codeword based on Alamouti scheme. The signature pattern informs the secondary user which network transmits the primary signal and enables to maintain an experiential database for each primary network. The proposed scheme provides reliable detection and network identification performance over frequency-selective fading channels in low signal-to-noise ratio regimes, without sacrificing the data rate of primary system.

Low-Complexity Iterative Detection for Spectral Efficient Cooperative Transmission

This paper proposes a low-complexity iterative detection scheme with cooperative transmission for single-carrier frequency-domain equalization (SC-FDE). To increase the spectral efficiency, a node, which acts as a relay, simultaneously transmits its own data block and the data block from the other node. For user separation, each data block is interleaved by a user-specific interleaver. At the destination, linear combining is performed and then the interference from the other source is effectively removed by an iterative detection method in the frequency domain. Simulation results show that the proposed system can obtain diversity gain without sacrificing spectral efficiency and approaches the performance of iterative maximum a posteriori (MAP) equalization at low computational cost.