Yun Kuei Hua

Bio: Yun Kuei Hua is an academic researcher from National Cheng Kung University. The author has contributed to research in topics: Telecommunications link & Diversity gain. The author has an hindex of 1, co-authored 1 publications receiving 7 citations.

Time Shifted Pilots Scheme for Full-Duplex Massive MIMO Systems

Abstract: In this paper, a cocktail approach is proposed to delicately integrate the two conventional countermeasures, i.e., the fractional pilot reuse and time-shifted pilots (TSP) schemes, for the pilot contamination problem in the full-duplex massive multiple-input multiple-output system. Specifically, the TSP scheme is applied to duplicate for the inner and edge regions of a cell such that the number of accommodated users can be doubled. To achieve this, the base station should operate in the full-duplex mode; also, the pilot symbols rather than the pilot sequences are used to attain the user diversity gain. The simulation results verify the accuracy of the numerical analysis and the remarkably boosted sum rate for both the downlink and uplink cases.

Massive MIMO for Maximal Spectral Efficiency: How Many Users and Pilots Should Be Allocated?

Abstract: Massive MIMO is a promising technique for increasing the spectral efficiency (SE) of cellular networks, by deploying antenna arrays with hundreds or thousands of active elements at the base stations and performing coherent transceiver processing. A common rule-of-thumb is that these systems should have an order of magnitude more antennas $M$ than scheduled users $K$ because the users’ channels are likely to be near-orthogonal when $M/K > 10$ . However, it has not been proved that this rule-of-thumb actually maximizes the SE. In this paper, we analyze how the optimal number of scheduled users $K^\star$ depends on $M$ and other system parameters. To this end, new SE expressions are derived to enable efficient system-level analysis with power control, arbitrary pilot reuse, and random user locations. The value of $K^\star$ in the large- $M$ regime is derived in closed form, while simulations are used to show what happens at finite $M$ , in different interference scenarios, with different pilot reuse factors, and for different processing schemes. Up to half the coherence block should be dedicated to pilots and the optimal $M/K$ is less than 10 in many cases of practical relevance. Interestingly, $K^\star$ depends strongly on the processing scheme and hence it is unfair to compare different schemes using the same $K$ .

Joint Antenna Selection and Power Allocation for Secure Co-Time Co-Frequency Full-Duplex Massive MIMO Systems

Abstract: In this paper, we design a co-time co-frequency full-duplex (CCFD) massive multiple-input multiple-output (MIMO) network to improve the utilization of time–frequency resources and physical layer security. Simultaneous information transmissions of the base station and the users are regarded as same-frequency interference against interception by eavesdroppers. To promote energy conservation and improve utilization of system resources, we propose a joint antenna selection and power allocation (JASPA) strategy for CCFD massive MIMO networks. Considering the trade-off between secrecy performance and system communications quality, we formulate optimization functions based on JASPA for two security concerns. We design a quantum-inspired backtracking search algorithm (QBSA) to obtain the optimal JASPA scheme. Simulation results show that the performance of the proposed QBSA is superior to previous intelligent algorithms in CCFD massive MIMO systems. The effectiveness of the proposed JASPA scheme is demonstrated under various communications scenarios, and can be considered a cornerstone for future research in wireless communications domain.

Arithmetic/Geometric Progression Based Pilot Allocation With Antenna Scheduling for Massive MIMO Cellular Systems

Abstract: Pilot contamination in massive MIMO cellular network is a major hindrance for achieving desired system throughput. To address this, an efficient algorithm is developed to assign each of the available pilot sequences to a user or multiple users, where the number of users assigned to different pilots follow arithmetic or geometric progression. The effects of intra-cell interference, small scale fading, and uncorrelated noise along with inter-cell interference are taken into analysis of proposed algorithm. With finite base station antennas and multiple antennas at user terminals, antenna scheduling is applied to allocate the best-suited antenna to each user and pilot.

Channel Estimators for Full-Duplex Communication using Orthogonal Pilot Sequences

Abstract: Full-duplex communication is desirable to maximize the spectral efficiency, despite the challenges it puts forth. The key challenge inhibiting the operation of radios in full-duplex mode is self-interference. In this paper, we propose a pilot-based channel estimation to estimate both self-interference and communication channels simultaneously at both ends of a full-duplex link using orthogonal sequences. The Cramer-Rao Lower Bound for estimators of both the channels was determined and compared with the half-duplex channel estimator. We performed simulations varying sequence length and channel taps and studied the performance of the estimators. We also studied the effect of synchronization between the sequences on the performance of the estimators. Thus, providing a solution to balance the trade-off between the accuracy of the channel estimation and the overhead added to the transmissions for full-duplex communication.

Pilot Decontamination with Pilot Scheduling for 5G Communications

Abstract: Massive multiple-input multiple-output (MIMO) is projected as the most favorable technology among the latest for quality cellular services in fifth-generation wireless networks. This technology has been extensively studied for analyzing its advantages and bottlenecks. One of the main bottlenecks of massive MIMO that has come forward is the pilot contamination that is caused by the interference of signals sent by the users using similar pilots. The studies done in this regard have considered the inter-cell interference occurring due to pilot reuse and have successfully eliminated the same. In this paper, the pilot contamination taking place due to pilot reuse within the same cell in the uplink direction is taken into consideration. An efficient greedy algorithm has been proposed in this regard which greedily finds the user combinations with less interference using their channel coefficients and assigns them the pilots efficiently. Numerical results prove the efficacy of the algorithm in the context of eliminating the restraining effects of pilot contamination on system throughput in intra-cellular environment. Moreover, the proposed scheme proves to be superior to some of the existing schemes in this domain.