Uplink Coordinated Multi-Point ARQ in MIMO Cellular Systems

QUEK, Tony Q. S.,WORADIT, Kampol,SHIN, Hyundong,LEI, Zander 'Institute of Electronics, Information and Communi 2011 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.eb94 No.12

Multiple Finger Expansion for Blind Interference Canceller in the Presence of Subchip-Spaced Multipath Components

Quek, Tony Q. S.,Suzuki, Hiroshi,Fukawa, Kazuhiko The Korea Institute of Information and Commucation 2004 Journal of communications and networks Vol.6 No.1

A blind interference canceller in the presence of subchipspaced multipath channels for direct-sequence code division multiple access (DS-CDMA) down-link system is considered. This technique is based on combining the existing blind interference canceller with a technique that involves assigning subchip-tap spacing to the Rake receiver. The proposed receiver minimizes the receiver’s output energy subject to a constraint in order to mitigate the multiple access interference (MAI) along each multipath component, and then suboptimally combining all the multipath components. Moreover, it is able to mitigate the mismatch problem when subchip-spaced multipath components arrive at the blind interference canceller. It is known that optimal combining techniques perform a decorrelation operation before combining, which requires both knowledge and computational complexity. In the following, we have adopted a simpler but suboptimum approach in the combining of the suppressed signals at the output of our proposed receiver. Computer simulation results verify the effectiveness of the proposed receiver to handle subchip-spaced multipath components and still suppresses MAI significantly.

Beamforming Optimization for Multiuser Two-Tier Networks

정영민,Tony Q. S. Quek,신현동 한국통신학회 2011 Journal of communications and networks Vol.13 No.4

With the incitation to reduce power consumption and the aggressive reuse of spectral resources, there is an inevitable trend towards the deployment of small-cell networks by decomposing a traditional single-tier network into a multi-tier network with very high throughput per network area. However, this cell size reduction increases the complexity of network operation and the severity of cross-tier interference. In this paper, we consider a downlink two-tier network comprising of a multiple-antenna macrocell base station and a single femtocell access point, each serving multiples users with a single antenna. In this scenario, we treat the following beamforming optimization problems: i) Total transmit power minimization problem; ii) mean-square error balancing problem; and iii) interference power minimization problem. In the presence of perfect channel state information (CSI),we formulate the optimization algorithms in a centralized manner and determine the optimal beamformers using standard convex optimization techniques. In addition, we propose semi-decentralized algorithms to overcome the drawback of centralized design by introducing the signal-toleakage plus noise ratio criteria. Taking into account imperfect CSI for both centralized and semi-decentralized approaches, we also propose robust algorithms tailored by the worst-case design to mitigate the effect of channel uncertainty. Finally, numerical results are presented to validate our proposed algorithms.

Multicasting in Stochastic MIMO Networks

Youngmin Jeong,Quek, Tony Q. S.,Jin Sam Kwak,Hyundong Shin IEEE 2014 IEEE Transactions on Wireless Communications Vol.13 No.4

<P>Physical-layer multicast transmission, which seeks to deliver information messages to all users simultaneously, is becoming more important in wireless systems with demand for various multimedia mobile applications such as Multimedia Broadcast Multicast Services. The spatial randomness of communicating nodes in a wireless network is one of inevitable uncertainties in the design and analysis of network information flow and connectivity. The use of multiple antennas at both transmitting and receiving nodes is the most promising strategy to increase spectral efficiency and communication reliability as well as to enhance physical-layer confidentiality of wireless systems. In this paper, we characterize multicasting in such a stochastic multiple-input multiple-output (MIMO) network where a probe transmitter broadcasts confidential data with sectorized transmission to legitimate receivers sitting in a region R. We first put forth a measure of the total amount of information flow, called the space-time capacity, into R in a spatial random field of legitimate receivers without accounting for intrinsic confidentiality at the physical layer. We then derive the space-time capacity into the sectoral region R and the nth nearest ergodic capacity in a Poisson field to characterize the spatial average and ordering of MIMO ergodic capacity achieved by legitimate receivers in R. Using the Mar\u{c}enko-Pastur law, we further assess the asymptotic space-time capacity and the nth nearest ergodic capacity per receive antenna as the antenna numbers tend to infinity. In the presence of eavesdropping, we determine a total amount of confidential information flow per receive antenna, called the space-time secrecy rate, into R in Poisson fields of receiving equivalents-with asymptotic arguments. Using an asymptotic secrecy graph on R, we also characterize local confidential connectivity such as the secrecy range, out-degree, and out-isolation probability of the probe transmitter. The framework developed in this work enables us to quantify the local information flow in random MIMO wireless networks by averaging first small-scale fading processes over time and then large-scale path losses over space.</P>

Cooperative Caching and Transmission Design in Cluster-Centric Small Cell Networks

Chen, Zheng,Lee, Jemin,Quek, Tony Q. S.,Kountouris, Marios INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS 2017 IEEE Transactions on Wireless Communications Vol. No.

<P>Wireless content caching in small cell networks (SCNs) has recently been considered as an efficient way to reduce the data traffic and the energy consumption of the backhaul in emerging heterogeneous cellular networks. In this paper, we consider a cluster-centric SCN with combined design of cooperative caching and transmission policy. Small base stations (SBSs) are grouped into disjoint clusters, in which in-cluster cache space is utilized as an entity. We propose a combined caching scheme, where part of the cache space in each cluster is reserved for caching the most popular content in every SBS, while the remaining is used for cooperatively caching different partitions of the less popular content in different SBSs, as a means to increase local content diversity. Depending on the availability and placement of the requested content, coordinated multi-point technique with either joint transmission or parallel transmission is used to deliver content to the served user. Using Poisson point process for the SBS location distribution and a hexagonal grid model for the clusters, we provide analytical results on the successful content delivery probability of both transmission schemes for a user located at the cluster center. Our analysis shows an inherent tradeoff between transmission diversity and content diversity in our cooperation design. We also study the optimal cache space assignment for two objective functions: maximization of the cache service performance and the energy efficiency. Simulation results show that the proposed scheme achieves performance gain by leveraging cache-level and signal-level cooperation and adapting to the network environment and user quality-of-service requirements.</P>

Beamforming Optimization for Multiuser Two-Tier Networks

Jeong, Young-Min,Quek, Tony Q.S.,Shin, Hyun-Dong The Korea Institute of Information and Commucation 2011 Journal of communications and networks Vol.13 No.4

With the incitation to reduce power consumption and the aggressive reuse of spectral resources, there is an inevitable trend towards the deployment of small-cell networks by decomposing a traditional single-tier network into a multi-tier network with very high throughput per network area. However, this cell size reduction increases the complexity of network operation and the severity of cross-tier interference. In this paper, we consider a downlink two-tier network comprising of a multiple-antenna macrocell base station and a single femtocell access point, each serving multiples users with a single antenna. In this scenario, we treat the following beamforming optimization problems: i) Total transmit power minimization problem; ii) mean-square error balancing problem; and iii) interference power minimization problem. In the presence of perfect channel state information (CSI), we formulate the optimization algorithms in a centralized manner and determine the optimal beamformers using standard convex optimization techniques. In addition, we propose semi-decentralized algorithms to overcome the drawback of centralized design by introducing the signal-to-leakage plus noise ratio criteria. Taking into account imperfect CSI for both centralized and semi-decentralized approaches, we also propose robust algorithms tailored by the worst-case design to mitigate the effect of channel uncertainty. Finally, numerical results are presented to validate our proposed algorithms.

Binary signaling design for visible light communication: a deep learning framework

Lee, Hoon,Lee, Inkyu,Quek, Tony Q. S.,Lee, Sang Hyun The Optical Society 2018 Optics express Vol.26 No.14

Dynamic Network Formation Game With Social Awareness in D2D Communications

La, Quang Duy,Quek, Tony Q. S.,Shin, Hyundong IEEE 2018 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.17 No.10

<P>The benefit of having a complementary network such as device-to-device (D2D) communications underlaying cellular systems lies in alleviating the traffic overloading burdens at base stations (BSs). This is critical in modern-day scenarios, e.g., in offloading and caching of mobile data traffic, and delivery of popular Internet contents to users. In this paper, we are chiefly interested in the establishment of D2D networks and how such a network evolves dynamically over time as D2D links are continuously formed and broken. Another important yet challenging research opportunity, i.e., the leverage of human users’ social ties for D2D communications, will also be addressed in this paper. To investigate the D2D network formation problem, we look at a game-theoretic framework where the utility function is designed to balance the physical and social domains—where we systematically extract social tie strengths from a real-world data set. To study the evolution of such D2D networks through time in a dynamic stochastic context, we propose a dynamic potential game and show that its equilibrium behaviors can be achieved through some strategy and payoff learning mechanisms. Simulation results verify our analysis. Using a content delivery application to assess the performance of our proposed scheme, it can be shown that major improvements can be obtained in terms of network delay, content accessibility, and BS load reduction.</P>

Joint Channel Identification and Estimation in Wireless Network: Sparsity and Optimization

Nguyen, Thang Van,Quek, Tony Q. S.,Shin, Hyundong IEEE 2018 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.17 No.5

<P>In this paper, we study channel identification for a wireless network with the aid of compressed sensing (CS) in both cases of known and unknown sparsity levels of clusters. For the unknown case, we propose using <I>blind</I> CS signal recovery algorithm to sequentially estimate both sparsity level and channel gains. The <I>refined</I> version of blind CS technique is also provided to improve the <I>consistency</I> of channel identification process. The <I>convergence</I> of two algorithms is guaranteed by ensuring that the cost functions decrease after each update. We then investigate the cluster sparsity of users in the case of known sparsity levels of all clusters. By exploiting the alternating direction method of multipliers algorithm through distributed optimization, we can identify channels in sparse clusters parallelly and efficiently compared with conventional convex techniques. In summary, this paper provides some insight into employing sparse and distributed algorithms to efficiently solve the problem of fast channel identification and estimation of users in future network.</P>

Content Placement for Wireless Cooperative Caching Helpers: A Tradeoff Between Cooperative Gain and Content Diversity Gain

Chae, Seong Ho,Quek, Tony Q. S.,Choi, Wan IEEE 2017 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.16 No.10

<P>Depending on what and how caching helpers cache content in their finite storage, the caching helpers can offer either a content diversity gain by serving diverse content or a cooperative gain by jointly transmitting the same content. This paper identifies a tradeoff between the content diversity gain and the cooperative gain according to content placements and proposes a probabilistic content placement to optimally balance the tradeoff. Using stochastic geometry, we quantify this tradeoff by deriving the cache hit rate and the rate coverage probability. To efficiently control the tradeoff, we determine the near-optimal caching probabilities that maximize the average content delivery success probability with the cooperative caching helpers. Our analysis and numerical results reveal that our proposed content placement outperforms the conventional caching schemes, such as caching with uniform probabilities, caching the most popular contents, and caching the content maximizing the cache hit, in terms of the average content delivery success probability.</P>