EditorialAdvanced MIMO Techniques in the Heterogeneous Networks

Xiang Zhang,1 Lin Zhang,2 Guangyue Lu,3 Xiaoli Chu,4 and Yulong Zou5

1 Beijing Key Lab of New Generation Broadband Wireless Mobile Communication Technology, Standard andVerification, China Academy of Telecommunication Research of MIIT (CATR), Beijing 100191, China

2 Faculty Development Center, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, China3 School of Telecommunications and Information Engineering, Xi’an University of Posts and Telecommunications, Xi’an 710121, China4The Communications Group, Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street,Sheffield S1 3JD, UK

5McGill University, 3480 Rue University, Montreal, Canada H3A 0E9

Correspondence should be addressed to Xiang Zhang; zhangxiang2468@gmail.com

Received 3 August 2014; Accepted 3 August 2014; Published 12 August 2014

Copyright © 2014 Xiang Zhang et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Since the first commercial long term evolution (LTE) wasdeployed in South Korea, 300 operators have commerciallylaunched LTE networks in 107 countries reported by theglobal mobile suppliers association. At least 20% of networkoperators are investing to deploy LTE-Advanced techniques.The downlink throughput for LTE-Advanced category 6(CAT6) user equipment (UE) is 300Mbps. However, with thedevelopment of mobile internet service, the peak rate andspectrum efficiency of the cellular network need to be furtherenhanced. Multiple input multiple output (MIMO) andheterogeneous network (HetNets) are adopted in LTE and thefifth generation (5G) system to improve user experience. Byemploying multiple antennas in both base station (BS) andUE, a new space domain is introduced inMIMOarchitecture.Multiantenna precoding and receiving can achieve array gainand diversity gain. As the spectral efficiency in a singlelink between the BS and UE approaches theoretical limits,the demand of mobile traffic data requires increasing thenode density to further improve cell capacity. Therefore,heterogeneous network performance optimization is of greatimportance in the wireless network, especially for scenario ofMIMO technique in the heterogeneous network.

To fully realize the potential of advanced antenna tech-nologies and to solve the problems of heterogeneous net-work performance optimization, this special issue aims toattract the attention of investigators to contribute original

research articles. We have received a total of 11 submissions,out of which 9 papers were accepted for publication afterpeer reviewing. The accepted papers cover a broad area ofadvanced MIMO topics.

Different from the traditional wireless network, whichonly uses macrocell to provide outdoor coverage, plentyof small cells are adopted in the LTE-A and 5G stage toenhance the data rate in the hot spot area. Therefore manualoptimization is not very efficient. One potential solution toaddress these issues is to introduce the extensively attractedself-organizing network (SON).There are three papers in thisspecial issue focusing on SON technology.The paper entitled“Capacity analysis and optimization in heterogeneous networkwith adaptive cell range control” by X. Gu et al. proposedan adaptive cell specific offset updating algorithm. System-level simulations results indicate that the proposed algorithmcan ensure a nearly optimal performance in all tested trafficload situations. The paper entitled “Cell outage detection andcompensation in two-tier heterogeneous networks” by W. Xueet al. developed a cell outage detection and compensationmethods in two-tier HetNets where macrocell and picocellscoexisted. In the paper “Advanced load balancing based onnetwork flow approach in LTE-A heterogeneous network,” Dr.S. Jia et al. first evaluated the negative impact of unbalancedload among cells through the Markova model. Then, theyproposed a novel algorithm named optimal solution-based

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2014, Article ID 193954, 2 pageshttp://dx.doi.org/10.1155/2014/193954

2 International Journal of Antennas and Propagation

load balancing. System-level simulation shows that the pro-posed scheme can provide up to 20% gain in load distributionindex.

Due to deployment of small cell in HetNets, macro celland small cell may be overlapped in some scenario. There-fore, interference cancellation needs to be well investigated.The paper entitled “High energy efficient heterogeneous net-works: cooperative and cognitive techniques” by H. Wanget al. introduced both the cooperative communication andcognitive radio techniques to mitigate the interference inHetNet, while the authors of the paper entitled “Coordinatedbeamforming with altruistic precoding and user selection forMU-MIMO system” proposed an altruistic precodingmethodto minimize the sum of interference. Furthermore, the lowerbound of the capacity and local optimal solution for multicelluser selection problem were also discussed.

In the paper entitled “Performance analysis of jointbase-station multiantenna multibeam and channel assignmentscheme for hierarchical cellular system,” P. Yang et al. intro-duced a joint base-station multiantenna multibeam andchannel assignment scheme for hierarchical cellular. Multi-beam base-station antenna splitting and dynamic channelallocation scheme are studied.

Full duplexing mode is a hot topic recently because ofits potential use in 5G. The paper entitled “Full-duplex modein amplify-and-forward relay channels: outage probability andergodic capacity” by R. Hu et al. investigated the outageprobability and ergodic capacity performances for full-duplexmode in two-way amplify-and-forward relay channel scenar-ios.

In the paper entitled “Model of handover and trafficbased on cellular geometry with smart antenna,” the authorsdiscussed the impact of the width of the smart antenna beamsin terms of dwell time and traffic performance.

The paper entitled “Miniaturization design for 8 × 8 Butlermatrix based on back-to-back bilayer microstrip” by Y. Zhai etal. presented a low-cost compact 8 × 8 Butler matrix basedon a novel bilayer microstrip configuration. Some measuredresults were also shown in this paper.

Acknowledgment

Before the end of this editorial, we would like to thank theanonymous reviewers for their great efforts in reviewing thesubmitted papers, without which this special issue would nothave been published as scheduled.

Xiang ZhangLin Zhang

Guangyue LuXiaoli ChuYulong Zou

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