Jongbu Lim

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.

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.

Reflected Self-Interference Channel Measurement for mmWave Beamformed Full-Duplex System

In this paper, we present the results and analyses of the reflected self-interference channel measurement in the beamformed full-duplex system. To measure the reflected self-interference channel in mmWave band, we transmit 18-bit PN sequence signal with more than 100 dB SNR using a transceiver with 27.925GHz center frequency. In the measurement results, we found the self-interference channel with long propagation delay caused by the reflection due to various nearby objects. This self-interference channel cannot be removed using conventional analog cancellation circuit which has limited analog delay. To overcome this limitation, it seems to be a good solution to apply opportunistic full-duplex scheme and a beam selection approach taking into account the residual self-interference.

MIMO Spatial Multiplexing Technique With Transmit Diversity

This letter proposes a multiple-input multiple-output (MIMO) technique for single carrier frequency-domain equalization (SC-FDE). The proposed system achieves spatial multiplexing and transmit diversity gains altogether, thus improving error performance and increasing spectral efficiency compared to conventional spatial multiplexing and transmit diversity techniques, respectively. In order to achieve both of the gains, independent data streams are transmitted simultaneously through all transmit antennas with different cyclic delay patterns for each data stream. Corresponding receiver structure is also presented, where a successive interference cancellation (SIC) algorithm without ordering process is introduced. Simulation results show that the proposed system with iterative receiver structure provides considerable performance gains over conventional MIMO techniques.

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.