Taehoon Kwon

Optimal Duplex Mode for DF Relay in Terms of the Outage Probability

This paper deals with a full-duplex relay (FDR) system over Rayleigh fading channels. The exact outage probability of FDR is derived as a closed form to consider interferences from full duplex. Then, we obtain the conditions of the signal-to-noise ratio (SNR) and the signal to interface ratios (SIRs) for cases of FDR showing a lower outage probability than that of the half-duplex relay (HDR) system under the target outage probability. According to this condition, FDR is superior to HDR with lower SIRs in the low-SNR region rather than in the high-SNR region. In addition, the target outage probability is only satisfied when the SNR and SIRs are within the boundaries. These boundaries vary due to the target rate, the channel states of each link, and the target outage probability.

Area Spectral Efficiency of Shared Spectrum Hierarchical Cell Structure Networks

This paper investigates the hierarchical cell structure (HCS) network consisting of macrocell and local area cell layers with partial cochannel sharing. We derive the ergodic capacity for each layer under cross-layer interference considering network-unplanned local area cell distribution. Based on the ergodic capacities, we also derive the area spectral efficiency (ASE) of the HCS network and investigate the optimum partial cochannel sharing that maximizes the ASE. It is confirmed that the maximum ASE is unchanged for a variable number of local area cells. Moreover, the spatial reuse benefit from the partial cochannel sharing is shown to be significant.

LLR-based symbol selective transmission with a near-optimal threshold to minimize BEP for demodulation-forward relay systems

Error propagation in the source-relay link limits the performance of demodulation-forward (MF) relay systems. In order to solve this problem and efficiently exploit the relay, we propose log likelihood ratio (LLR)-based symbol selective transmission with a near-optimum threshold to minimize the bit error probability (BEP). In the proposed scheme, the source information is forwarded by the relay only if it is likely to be detected correctly, as determined by a comparison of the LLR with the near-optimum threshold. To derive the near-optimum threshold, the BEP of the proposed scheme is analyzed in the case of binary phase shift keying (BPSK) signals. Simulation results confirm the accuracy of the analysis and prove that the proposed scheme efficiently mitigates error propagation.

RF Lens-Embedded Massive MIMO Systems: Fabrication Issues and Codebook Design

In this paper, we investigate a radio frequency (RF) lens-embedded massive multiple-input multiple-output (MIMO) system and evaluate the system performance of limited feedback by utilizing a technique for generating a suitable codebook for the system. We fabricate an RF lens that operates on a 77-GHz (millimeter-wave) band. Experimental results show a proper value of amplitude gain and an appropriate focusing property. In addition, using a simple numerical technique-beam propagation method-we estimate the power profile of the RF lens and verify its accordance with experimental results. We also design a codebook-multivariance codebook quantization-for limited feedback by considering the characteristics of the RF lens antenna for massive MIMO systems. Numerical results confirm that the proposed system shows significant performance enhancement over a conventional massive MIMO system without an RF lens.

A Power Division Reuse Partitioning Scheme with Half Frequency Reuse Factor for OFDMA Downlink Systems

In multicell OFDMA systems, throughput is severely degraded by other cell interference (OCI), especially at cell edge. To satisfy the performance requirement, OCI must be mitigated effectively. Several schemes have been proposed to handle this problem by coordinating the way to allocate spectrum resource to each cell. Since the allocation of spectrum has effects on OCI mitigation and the spectral efficiency, an wise strategy to consider those two factors is required. In this paper, we propose a new scheme named as power division reuse partitioning scheme (PDRPS). PDRPS balances OCI mitigation and spectral efficiency by adopting interference cancellation (IC) scheme. The simulation results show that PDRPS has more throughput and lower outage probability than the conventional schemes.

Comparison of FDR and HDR Under Adaptive Modulation With Finite-Length Queues

To identify the optimal duplex mode and maximize the offered gain in the relay system, we compare the performances of half-duplex relay (HDR) and full-duplex relay (FDR). Finite-state Markov chain (FSMC) models are presented, showing the joint effects of finite-length queues and adaptive modulation (AM) under uncorrelated Rayleigh fading channels. Transmission efficiency, packet loss rate, and delay are derived and compared based on these models. According to our results, FDR is superior to HDR in the low-signal-to-noise ratio (SNR) region but loses its advantage as the SNR increases. When the size of the queue is large enough, FDR can be superior to HDR, even in the high-SNR region.

A New Grouping-ML Detector with Low Complexity for SC-FDMA Systems

In this paper, we propose a new grouping-maximum likelihood detector (GMLD) for single carrier-frequency division multiple access (SC-FDMA) systems. The proposed detector performs local maximum likelihood (ML) detection by grouping the received symbol block based on orthogonal projection to reduce the complexity of ML detector. As a result, the proposed detector offers lower complexity than the ML detector, while its performance approaches that of the ML detector. In addition, the efficient group size to guarantee the lowest complexity and the BER performance close to the ML is also presented.

Robust Channel Estimation in Multicell OFDM(A) Downlink Systems With Propagation Delay

On estimating channel information in multicell OFDM(A) system, the received pilot signal is interfered by other cells signals. In this paper, we propose a new channel estimation technique based on orthogonal pilot structures in multicell OFDM(A) system. The proposed pilot structure in time domain has zero padding of the channel length to minimize the noise enhancement and use orthogonal sequences to eliminate other cells interference. Especially, we design orthogonal sequences to give robustness to propagation delay. Simulation results confirm that mean square error (MSE) performance of the proposed channel estimation is better than that of the conventional methods in multicell environment.

Limited channel feedback for RF lens antenna based massive MIMO systems

In this paper, we propose a radio frequency (RF) lens-embedded massive multiple-input multiple-output (MIMO) system. To analyze the characteristics of RF lens antennas, we first introduce the beam propagation method (BPM) and use it to construct a new channel model. We next design a low complexity codebook reflecting the characteristics of the RF lens antennas for limited feedback. Numerical results confirm that, compared to conventional approaches such as random vector quantization (RVQ), the proposed system shows significant performance enhancements in terms of the achievable rate and computational complexity.

A new hybrid division duplex scheme: Orthogonal frequency division duplex (OFDD)

In this paper, we propose orthogonal frequency division duplex (OFDD) which combines orthogonal division duplex (ODD) [1] and frequency division duplex (FDD) as a new hybrid division duplex scheme. In the asymmetric traffic environment, the mismatch of uplink and downlink between adjacent cells results in co-channel interference (CCI) which degrades the system performance. The proposed scheme can remove CCI of users at cell boundary by cell-partitioning. Furthermore, it can additionally reduce CCI of users at cell center by random sub-carrier allocation in ODD mode. From simulation results, we show that OFDD enhances average cell capacity by reducing CCI in the asymmetric traffic environment, compared with conventional schemes.