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Physical-Layer Research


This research theme develops and analyses the latest communications approaches in the physical layer (PHY). Current research lines include:

1. Massive MIMO

A great deal of research has been to investigating the maximum achievable rates for various single-user and multiuser MIMO channels, in particular the large-system MIMO or recently known as massive MIMO where there are a large number of antennas at the transmitter and/or receiver. Members of the group and collaborators have contributed to revealing the fundamental performance limits of a wide class of MIMO fading channels in the very low SNR regime under interference-limited environments [Zhong 2010; Jin 2010; Li 2010; Wen 2010]. Another important direction is to understand the performance of MIMO under practical settings in the presence of such as rank deficiency due to the phenomenon of keyholes. Several major contributions have been made in this regard [Zhong-Wong 2010; Zhong-Jin 2010; Jin 2008]. Finally, recent work has been looking at the performance impacts of deploying high numbers of antennas in fixed physical dimensions [Masouros 2013], along with practical linear and non-linear precoding schemes for large MIMO systems [Masouros-Sellathurai 2013],[Masouros-Sellathurai 2012], [Masouros 2011].

Increasingly, relaying has emerged as a revolutionary technique for cellular networks, particularly for improving the performance of users at the cell edges. Several significant contributions have been made in this area, not only for understanding the capacity of MIMO relaying channels but also the sum-rate of a multiuser MIMO channel [Jin-McKay 2010; Zhong-Jin-Wong 2010; Wen 2011; Wen-Wong 2010].

2. Cognitive Cooperative Communications

Future spectrum allocation as proposed by Ofcom and FCC is required to be dynamic, adaptive and self-organised, with a strong need for interference control and management within and across networks. This breaks the rigid boundaries across networks and demands network coordination, giving rise to several fundamental challenges. In the context of primary-secondary link co-existence for cognitive radio, a number of interference-constrained transmission schemes have been introduced [Khan 2012], [Masouros-Ratnarajah 2012], [Ratnarajah 2013], [Masouros-Ratnarajah-Sellathurai 2013] for the cognitive downlink channel. In addition, several significant contributions in the optimisation of using cooperative relays for beamforming and some in the context of cognitive radio technologies have been made [Huang 2012; Huang 2011; Zheng 2009; Zheng-Wong 2009; Zheng-Wong-Paulraj 2009].

3. Wireless Interference as Useful Signal Power

While interference has always been regarded as the main obstacle in wireless systems, recent work has revealed that, on an instantaneous basis, it can contribute constructively to the useful signal energy gleaned at the wireless receiver [Masouros-2011],[Masouros-Ratnarajah-Sellathurai 2013], ( This important source of useful energy, is currently ignored by the techniques adopted in the communication standards. The existing work of Green Communications focuses on energy-efficient network planning, smart duty-cycled BSs, heterogeneous cell deployment, integration with renewable energy sources and use of ICT for energy saving, amongst others. The radical approach of exploiting interference power promises a vast reduction in the power consumption of the network, without the cost of redesigning and redeploying network components as per the solutions above. While the signal processing work on wireless communications to date has focused on cancelling or minimizing interference, this work focuses on allowing the utilization of signal power from constructive interference to achieve the required link performance with a much reduced actual transmit power.

4. Integrated Optical/Wireless Networks

Recent technological advances and deployments are creating a new landscape in the access networks, with an integration of wireless and fiber technologies a key supporting technology. Our research work considers how the optical fibre access network can be best used to support the next generation of radio access networks. It considers front and back-haul networks, including how mm-wave wireless technologies can support 5G wireless (see IPHOBAC-NG). The group have been involved in system demonstrations for mm-wave back-haul [Omomukuyo 2013] as well as architectures to support dynamic allocations of bandwidth [Milosaclievic 2012], [Attard 2006].

5. Optical Access Networks

Research in collaboration with BT investigated the deployment of long reach (100km), high aggregate bit rate (10Gbit/s) and high customer number (1024) optical access networks. These use advanced optical components currently only feasible in core networks to provide highly efficient optical access networks [Shea 2007]. The area of long-reach optical access networks is now gaining a great deal of attention [Shea & Mitchell 2007]. We have now extended this idea to consider how multiple short-reach PONs could be consolidated into a multi-wavelength long reach architecture. This was first demonstrated for 2.5Gbit/s PONs using Semiconductor Optical Amplifiers (SOAs) and cross-gain modulation(XGM) [Shea 2009] and has since been expended to 10Gbit/s PONs using an interferometric structure of SOAs and cross-phase modulation (XPM) in [Cao 2013]. As part of this work, collaborations with the UCL optical networks group considered the impact on the burst mode receiver requirement of such technologies [Mendinueta 2011a] and [Mendinueta 2011b].

Academics involved in the theme:

Representative projects:

  • “RC3: Robust cognitive cooperative communications”, Standard Grant, awarded £315,750, 06/2013-05/2016, EPSRC
  • “Cognitive communications: Self-optimising interference alignment for opportunistic spectrum access”, EPSRC Industrial CASE Doctoral Research Studentship, awarded £67,443 from EPSRC and £30,000 from BT, 2012-, EPSRC-BT (The PI in BT is Dr Maziar Nekovee)
  • Interference as a Source of Green Signal Energy in Wireless Communications”, Royal Academy of Engineering Research Fellowship, awarded £550,000, 09/2011-08/2016
  • “High-performance MIMO transceiver design for single and multiuser wireless communications”, Standard Grant, awarded £589,081, 09/2007-08/2010, EPSRC
  • “Adaptive space and frequency modulations for high-quality high-speed wireless LANs”, Standard Grant, awarded £217,967, 09/2006-08/2009, EPSRC
  • "Integrated Photonic Broadband Radio Access Unitsfor Next Generation Optical Access Networks - IPHOBAC-NG", European Union, Framework 7. €3M, 11/2013-10/2016

Representative publications:

[Zhong 2010] C. Zhong, S. Jin, K. K. Wong, M.-S. Alouini, and T. Ratnarajah, “Low SNR capacity for MIMO Rician and Rayleigh-product fading channels with single co-channel interferer and noise,” IEEE Transactions on Communications, Vol. 58, No. 9, pp. 2549-2560, September 2010.

[Jin 2010] S. Jin, M. R. McKay, K. K. Wong, and X. Li, “Low SNR analysis of multiple-antenna systems with statistical channel state information,” IEEE Transactions on Vehicular Technology, Vol. 59, No. 6, pp. 2874-2884, July 2010.

[Li 2010] X. Li, S. Jin, M. R. McKay, X. Gao, and K. K. Wong, “Low SNR capacity of MIMO-MAC with transmit channel knowledge,” IEEE Transactions on Wireless Communications, Vol. 9, No. 3, pp. 926-931, March 2010.

[Wen 2010] C. K. Wen, K. K. Wong, and J. C. Chen, “Asymptotic mutual information for Rician MIMO-MA channels with arbitrary inputs: A replica analysis,” IEEE Transactions on Communications, Vol. 58, No. 10, pp. 2782-2788, October 2010.

[Zhong-Wong 2010] C. Zhong, S. Jin, K. K. Wong, and M. R. McKay, “Outage analysis for optimal beamforming MIMO systems in multi-keyhole channels,” IEEE Transactions on Signal Processing, Vol. 58, No. 3, pp. 1451-1456, March 2010.

[Zhong-Jin 2010] C. Zhong, S. Jin, and K. K. Wong, “MIMO Rayleigh-product channels with co-channel interference,” IEEE Transactions on Communications, Vol. 57, No. 6, pp. 1824-1835, June 2009.

[Jin 2008] S. Jin, M. R. McKay, K. K. Wong, and X. Gao, “Transmit beamforming in Rayleigh product MIMO channels: Capacity and performance analysis,” IEEE Transactions on Signal Processing, Vol. 56, No. 10, pp. 5204-5221, October 2008.

[Jin-McKay 2010] S. Jin, M. R. McKay, C. Zhong, and K. K. Wong, “Ergodic capacity analysis of amplify-and-forward MIMO dual-hop systems,” IEEE Transactions on Information Theory, Vol. 56, No. 5, pp. 2204-2224, May 2010.

[Zhong-Jin-Wong 2010] C. Zhong, S. Jin, and K. K. Wong, “Dual-hop systems with noisy relay and interference-limited destination,” IEEE Transactions on Communications, Vol. 58, no. 3, pp. 764-768, March 2010.

[Wen 2011] C. K. Wen, K. K. Wong, and C. T. K. Ng, “On the asymptotic properties of amplify-and-forward MIMO relay channels,” IEEE Transactions on Communications, Vol. 59, No. 2, pp. 590-602, February 2011.

[Wen-Wong 2010] C. K. Wen, and K. K. Wong, “On the sum-rate of uplink MIMO cellular systems with amplify-and-forward relaying and collaborative base stations,” IEEE Journal on Selected Areas in Communications Special Issue on Cooperative Communications in MIMO Cellular Networks, Vol. 28, No. 9, pp. 1409-1424, December 2010.

[Huang 2012] Y. Huang, G. Zheng, M. Bengtsson, K. K. Wong, L. Yang, and B. Ottersten, “Distributed multicell beamforming design approaching Pareto boundary with max-min fairness,” IEEE Transactions on Wireless Communications, Vol. 11, No. 8, pp. 2921-2933, August 2012.

[Huang 2011] Y. Huang, G. Zheng, M. Bengtsson, K. K. Wong, B. Ottersten, and L. Yang, “Distributed multicell beamforming design with limited intercell coordination,” IEEE Transactions on Signal Processing, Vol. 59, No. 2, pp. 728-738, February 2011.

[Zheng 2009] G. Zheng, K. K. Wong, and B. Ottersten, “Robust cognitive beamforming with bounded channel uncertainties,” IEEE Transactions on Signal Processing, Vol. 57, No. 12, pp. 4871-4881, December 2009.

[Zheng-Wong 2009] G. Zheng, K. K. Wong, A. Paulraj, and B. Ottersten, “Robust collaborative-relay beamforming,” IEEE Transactions on Signal Processing, Vol. 57, No. 8, pp. 3130-3143, August 2009.

[Zheng-Wong-Paulraj 2009] G. Zheng, K. K. Wong, A. Paulraj, and B. Ottersten, “Collaborative-relay beamforming with perfect CSI: Optimum and distributed implementation,” IEEE Signal Processing Letters, Vol. 16, No. 4, pp. 257-260, April 2009.

[Masouros 2013] C. Masouros, M. Sellathurai, T. Ratnarajah, “Large-Scale MIMO Transmitters in Fixed Physical Spaces: The Effect of Transmit Correlation and Mutual Coupling”, IEEE Trans. Comms., early access online,

[Masouros-Sellathurai 2013] C. Masouros, M. Sellathurai, T. Ratnarajah, “Computationally Efficient Vector Perturbation Using Thresholded Optimization”, IEEE Trans. Comms., vol.61, no.5, pp.1880,1890, May 2013

[Masouros-Sellathurai 2012] C. Masouros, M. Sellathurai, T. Ratnarajah, “Interference Optimization for Transmit Power Reduction in Tomlinson-Harashima Precoded MIMO Downlinks”, IEEE Trans. Sig. Proc., vol.60, no.5, pp.2470-2481, May 2012

[Masouros 2011] C. Masouros, “Correlation Rotation Linear Precoding for MIMO Broadcast Communications", IEEE Trans. on Sig. Proc., vol 59, issue 1, pp. 252-262, Jan 2011

[Khan 2012] F. Khan, C. Masouros, T. Ratnarajah, “Interference Driven Linear Precoding in Multiuser MISO Downlink Cognitive Radio Network”, IEEE Trans. Veh. Tech.,  vol.61, no.6, pp.2531-2543, July 2012

[Masouros-Ratnarajah 2012] C. Masouros & T. Ratnarajah, “Interference as a Source of Green Signal Power in Cognitive Relay Assisted Co-Existing MIMO Wireless Transmissions”, IEEE Trans. Comms, vol 60, issue 2, pp. 525-536, Feb 2012

[Ratnarajah 2013] T. Ratnarajah, C. Masouros, F. Khan, M. Sellathurai, “On the Multiuser Diversity Gains of Opportunistic Spectrum Sharing in Cognitive Radio Systems”, IEEE Trans. Comms, early access online

[Masouros-Ratnarajah-Sellathurai 2013] C. Masouros, T. Ratnarajah, M. Sellathurai, C. Papadias, A. Shukla, “Known Interference in Wireless Communications: A Limiting factor or a Potential Source of Green Signal Power?", IEEE Comms. Mag.,  in press.

[Omomukuyo 2013] Omomukuyo, OThakur, MPMitchell, JE; (2013) Simple 60-GHz MB-OFDM ultrawideband RoF system based on remote heterodyning. IEEE Photonics Technology Letters , 25 (3) 268 - 271.

[Milosacljevic 2012] Milosavljevic, M and Thakur, MP and Kourtessis, P and Mitchell, JE and Senior, JM (2012) Demonstration of wireless backhauling over long-reach PONs. Journal of Lightwave Technology , 30 (5) 811 - 817

[Attard 2006] Attard, JC and Mitchell, JE (2006) Optical network architectures for dynamic reconfiguration of full duplex, multiwavelength, radio over fiber. OSA Journal of Optical Networking , 5 (6) 435 - 444

[Shea 2007] Shea, DP and Mitchell, JE (2007) A 10-Gb/s 1024-way-split 100-km long-reach optical-access network. J LIGHTWAVE TECHNOL , 25 (3) 685 - 693

[Shea & Mitchell 2007] Shea, DP and Mitchell, JE (2007) Long-reach optical access technologies. IEEE NETWORK , 21 (5) 5 - 11.

[Shea 2009] Shea, D.P. and Mitchell, J.E. (2009) Architecture to integrate multiple PONs with long reach DWDM backhaul. IEEE Journal on Selected Areas in Communications , 27 (2) pp. 126-133

[Coa 2013] Cao, BMendinueta, JMDThomsen, BCMitchell, JE; (2013) Demonstration of a 10 Gbit/s Long Reach Wavelength Converting Optical Access Network. IEEE/OSA Journal of Lightwave Technology , 31 (2) 328 - 333.

[Mendinueta 2011a] Mendinueta, JMD and Mitchell, JE and Bayvel, P and Thomsen, BC (2011) Digital dual-rate burst-mode receiver for 10G and 1G coexistence in optical access networks. Optics Express , 19 (15) 14060 - 14066

[Mendinueta 2011b] Mendinueta, JMD and Cao, B and Thomsen, BC and Mitchell, JE (2011) Performance of an optical equalizer in a 10 G wavelength converting optical access network. OPTICS EXPRESS , 19 (26) 229 - 234