Research

Current research topics include heterogeneous networks, green communications, interference networks, cognitive radio, cooperative networks, smart grid, and wireless security.

Heterogeneous Networks


The ever-increasing need for higher data rates and multimedia services leads to stringent requirements on the area spectral efficiency that next-generation cellular wireless networks are expected to deliver. A promising approach to solving this problem is through the deployment of heterogeneous networks, which represent a novel networking paradigm based on the idea of deploying short-range, low-power, and low-cost base stations operating in conjunction with the main macro-cellular network infrastructure. Some contributions include:


  • Y. Yang, T. Q. S. Quek, and L. Duan, “Backhaul-Constrained Small Cell Networks: Optimization with Refunding,IEEE Trans. Wireless Commun., submitted.
  • L. Z. Wong, T. Q. S. Quek, M. Pidila, and H. P. Tan, “A potential game framework for approximate optimal pricing and algorithms in heterogeneous networks,” ACM SIGCOMM, Hong Kong, CHINA, Aug. 2013, submitted.
  • Y. S. Soh, T. Q. S. Quek, M. Kountouris, and G. Caire, “Cognitive Hybrid Division Duplex for Two-Tier Femtocell Networks,” IEEE Trans. Wireless Commun., revised.
  • T. M. Nguyen, Y. Jeong, T. Q. S. Quek, W. P. Tay, and H. Shin, “Interference Alignment in a Poisson Field of MIMO Femtocells,” IEEE Trans. Wireless Commun., vol. 12, no. , pp. -, 2013.
  • W. C. Cheung, T. Q. S. Quek, and M. Kountouris, “Throughput Optimization, Spectrum Allocation, and Access Control in Two-Tier Femtocell Networks,” IEEE J. Select. Areas Commun., vol. 30, no. 3, pp. 561–574, Apr. 2012.
  • D. Lopez-Perez, I. Guvenc, G. de la Roche, M. Kountouris, T. Q. S. Quek, and J. Zhang, “Enhanced Inter-Cell Interference Coordination Challenges in Heterogeneous Networks,” IEEE Wireless Commun. Mag., vol. 18, no. 3, pp. 22–30, Jun. 2011.

Green Communications


Future-generation wireless systems promise to provide high-rate and high-capacity multimedia services for residential as well as enterprise applications. However, the demands on multimedia services and broad radio coverage result in significantly increasing power consumption in devices, networks and also systems. For instance, larger service range requires higher power in radio transmitter. Multimedia services are resource-intensive, demanding high bandwidth, transmission delay, and energy consumption. This will eventually lead to radio pollution, global carbon dioxide emission, and greenhouse effects. With such environmental awareness, system designers have started to explore how to design and deploy more energy efficient wireless networks.
Some contributions include:


  • M. Wildemeersch, T. Q. S. Quek, A. Rabbachin, and C. H. Slump, “Cognitive Small Cell Networks: Energy Efficiency and Trade-Offs,” IEEE Trans. Commun., revised.
    Y. S. Soh, T. Q. S. Quek, M. Kountouris, and H. Shin, “Energy Efficient Heterogeneous Cellular Networks,” IEEE J. Select. Areas Commun., vol. 31, no. , pp. –, Jul. 2013.
  • T. Q. S. Quek, D. Dardari, and M. Z. Win, "Energy Efficiency of Dense Wireless Sensor Networks: To Cooperate or Not to Cooperate," IEEE J. Select. Areas Commun., vol. 25, no. 2, 459–470, Feb. 2007.

Interference Networks


Interference is an inherent feature of wireless communication when multiple users share the communication medium.
Proliferation of wireless applications creates an increased density of wireless devices as well as an increased level of network interference due to the broadcast property of wireless transmissions. Fundamental understanding of how to optimally manage interference will allow us to achieve better overall network spectral efficiency and performance. Some contributions include:




  • J. Zhao, T. Q. S. Quek, and Z. Lei, “User Admission, Clustering, and Partitioning for Uplink Multiuser Wireless Systems,” IEEE Trans. Commun., submitted.
  • D. W. H. Cai, T. Q. S. Quek, and C. W. Tan, “A Unified Analysis of Max-Min Weighted SIR for MIMO Downlink System,” IEEE Trans. Signal Processing, vol. 59, no. 8, pp. 3850–3862, Aug. 2011.
  • W. W. L. Ho, T. Q. S. Quek, S. Sun, and R. W. Heath Jr., “Decentralized Precoding for Multicell MIMO Downlink,” IEEE Trans. Wireless Commun., vol. 10, no. 6, pp. 1798–1809, Jun. 2011.
  • A. Rabbachin, T. Q. S. Quek, P. Pinto, I. Oppermann, and M. Z. Win, “Non-Coherent UWB Communications in the Presence of Multiple Narrowband Interferers,” IEEE Trans. Wireless Commun., vol. 9, no. 11, pp. 3365–3379, Nov. 2010.
  • T. Q. S. Quek, M. Z. Win, and D. Dardari, “Unified Analysis of UWB Transmitted-Reference Schemes in the Presence of Narrowband Interference,” IEEE Trans. Wireless Commun., vol. 6, no. 6, pp. 2126– 2139, Jun. 2007.

Cognitive Radio


With the proliferation of radio devices and communication services, multiple systems sharing a common spectrum must coexist. Conventional static spectrum management may not be suitable for such dynamic systems and may not lead to efficient system utilization.
This imbalance between the spectrum scarcity and low utilization motivates the concept of cognitive radio networks. A cognitive radio is designed to utilize the wireless spectrum efficiently while maximizing its own spectral efficiency under interference-limited regime. Some contributions include:





  • J. Wang, A. Huang, W. Wang, and T. Q. S. Quek, “Admission Control in Cognitive Radio Networks with Finite Queue and User Impatience,” IEEE Wireless Commun. Letters, vol. 2, no. , pp. -. 2013.
  • T. V. Nguyen, H. Shin, T. Q. S. Quek, and M. Z. Win, “Sensing and Probing Cardinalities for Active Cognitive Radios,” IEEE Trans. Signal Processing, vol. 60, no. 4, pp. 1833–1848, Apr. 2012.
  • A. Rabbachin, T. Q. S. Quek, H. Shin, and M. Z. Win, “Cognitive Network Interference,” IEEE J. Select. Areas Commun., vol. 29, no. 2, pp. 480–493, Feb. 2011.

Cooperative Networks

Cooperative wireless networking has recently emerged as one of the most promising enabling technologies, as it is able to address a wide range of application scenarios to enhance connectivity, extend coverage, and improve energy efficiency, and communication reliability. In these cooperative networks, the main feature is that relay nodes pool their resources in a distributed manner to enhance the reliability of wireless transmission links. Some contributions include:



  • J. Zhao, T. Q. S. Quek, and Z. Lei, “Coordinated Multipoint Transmission with Limited Backhaul Data Transfer Constraints,” IEEE Trans. Wireless Commun., vol. 13, no. -, pp. , 2013.
  • D. W. H. Cai, T. Q. S. Quek, C. W. Tan, and S. Low, “Max-Min SINR Optimization in Coordinated Multicell Downlink - Duality and Algorithms,” IEEE Trans. Signal Processing, vol.60, no. 10, pp. 5384-5395, Oct. 2012.
  • D. W. Soh, W. P. Tay, and T. Q. S. Quek, "Randomized Information Dissemination in Dynamic Environments,'' ACM/IEEE Trans. Networking., vol. , no. , pp. –, 2013.
  • H. Q. Ngo, T. Q. S. Quek, and H. Shin, “Amplify-and-Forward Two-Way Relay Networks: Error Exponents and Resource Allocation,” IEEE Trans. Commun., vol. 58, no. 9, pp. 2653–2666, Sep. 2010.
  • T. Q. S. Quek, M. Z. Win, and M. Chiani, “Robust Power Allocation Algorithms for Wireless Relay Networks,” IEEE Trans. Commun., vol. 58, no. 7, pp. 1931–1938, Jul. 2010.
  • K. Woradit, T. Q. S. Quek, W. Suwansantisuk, H. A. Wymeersch, L. Wuttisittikulkij, and M. Z. Win, “Outage Behavior of Selective Relaying Schemes,” IEEE Trans. Wireless Commun., vol. 8, no. 8, pp. 3890–3895, Aug. 2009.
  • T. Q. S. Quek, H. Shin, and M. Z. Win, “Robust Wireless Relay Networks: Slow Power Allocation with Guaranteed QoS,” IEEE J. Select. Topics Signal Processing, vol. 1, no. 4, pp. 700–713, Dec. 2007.

Smart Grid


In order to cope with future demand increases as well as to provide a more robust and efficient way of delivering and distributing electricity, developing smart grid has become an urgent global priority. With the growth of alternative energy generation and storage, the smart grid system will have to be able to intelligently integrate and control the different elements of the grid so as to realize the full potential of the system. Some contributions include:





  • TBA.

Wireless Security


Broadcast nature of wireless medium makes wireless networks susceptible to eavesdropping, and hence secure transmission is a fundamental issue in such networks. Traditionally, this has been addressed by employing cryptographic protocols that are believed to be computationally hard for the adversary to decipher.
For instance, eavesdropping is extremely easy since anyone within communication range can listen to the traffic in the air, and possibly extract information. Unlike conventional cryptographic security mechanisms, the main idea of the physical-layer security is to exploit the unique properties of wireless medium to provide ways of combating security threats. Some contributions include:






  • Y. Jeong, T. Q. S. Quek, and H. Shin, "Multicasting in Stochastic MIMO Network," IEEE Trans. Wireless Commun., revised.
  • T. V. Nguyen, Y. Jeong, T. Q. S. Quek, and H. Shin, “Secure MISO Communication: Switched Power Allocation and Secrecy Diversity,” IEEE Trans. Signal Processing, revised.