Enabling high-quality, low power mobile broadband services
Submitting InstitutionUniversity of Bedfordshire
Unit of AssessmentComputer Science and Informatics
Summary Impact TypeTechnological
Research Subject Area(s)
Information and Computing Sciences: Computation Theory and Mathematics, Information Systems
Technology: Communications Technologies
Summary of the impact
Femtocells provide short-range (e.g. 10m) wireless coverage which enables
a conventional cellular communication system to be accessed indoors. Their
widespread and growing use has been aided by the work in UoA11 by the
University of Bedfordshire (UoB).
In 2008, while the femtocell concept was still in its infancy,
researchers at UoB with expertise in wireless networks recognised that
coverage prediction and interference reduction techniques would be
essential if the benefits of that concept were to be realised.
Collaboration with two industrial partners (an international organisation
and a regional SME) resulted in tools that enable operators to simulate
typical femtocell deployment scenarios, such as urban, dense apartments,
terraced house and small offices, before femtocells can be reliably
deployed by users without affecting the rest of the network (a benefit of
the technology). These tools have been deployed by those partners to
support their businesses. A widely-cited textbook, written for network
engineers, researchers and final year students, has brought knowledge of
femtocell operation to a wider audience.
The research team
(Where a researcher has left the University of Bedfordshire, the leaving
date is shown.)
Group Leader: Prof. Jie Zhang (Jan 2011)
Lecturer (now Reader): Dr Enjie Liu
Senior Research Fellow: Dr Guillaume de la Roche (May 2011)
Research Fellow: Dr Zhu Xiao UoB (March 2012)
Marie Curie Research Fellow: Dr David Lopez-Perez (July 2010)
Research student: Dr Alvaro Valcarce (July 2010)
The research was carried out between 2008 and 2010.
Background and problem to be solved
The femtocell concept had been under discussion among wireless network
experts since 2006, but its realisation was impeded by a lack of suitable
communication protocols and an understanding of the nature of the radio
channel in the confined space in which a femtocell operates, together with
the associated sources of interference and ways of combatting their
effects. The Centre for Wireless Networks at UoB (CWiND) had built up
extensive expertise and knowledge in network management and protocols, and
in 2008 was one of the first research groups to propose the possibility of
using WiMAX technology and protocols for building and deploying
femtocells. The research began in UoB in 2008 under an EPSRC-funded
project in the `Digital Economy' theme. The fact that CWiND had already
been actively involved in wireless network planning and optimisation meant
that the relevant expertise was available to make a rapid and effective
start to the initial project.
The research started by identifying some key technical challenges in
WiMAX-based femtocells, namely Interference, mobility management and
auto-configuration. The challenges of using WiMAX technology in building
and deploying femtocells identified by our research have been recognised
by other researchers as well, as noted in Section 3.
Research was carried out to investigate these challenges. This was
initially under an EPSRC-funded project, then in cooperation with, and
funding from, T-mobile (a telecoms operator) and RANPLAN (an SME). The
elements of the research and the resulting transferable knowledge and
experience may be summarised as follows.
- An experimental evaluation of the effect of interference caused by
femtocells on the associated macrocell, [3.1], [3.6]
- Characterisation of the indoor-to-outdoor propagation channel through
an extensive channel measurement campaign in a residential area. The
collected data was used to calibrate a Finite-Difference Time Domain
(FDTD) propagation model, which is now a reference tool for the accurate
prediction of signal coverage [3.7].
- Prediction of channel fading distributions in a femtocell scenario.
The developed model can be used in the femtocell deployment tool in
modelling channel fading [3.3].
- Development of an indoor radio propagation model, which can be used by
network planners to aid effective femtocell installations
- Characterisation of an indoor-outdoor-indoor propagation channel, as a
result of a measurement campaign, which produced a new path loss model
applicable to femtocell deployment.
- An effective approach to mobility management, especially on cell
identification, which is particularly useful for inbound handover in
multilayer networks. The solution was based on cell activity level
prediction to allocate PCIs, and the results outperformed the existing
approach in term of achieved less handover failure [3.8].
- Enhanced interference management techniques applicable to small cells,
as a result of measurement campaigns for UMTS/HSPAL/LTE networks at 0.8,
2 and 2.6 GHz in typical residential and business environments [3.7].
(This work was funded by T-mobile.)
- System level simulation (SLS) for WiMAX and UMTS/HSPA/LTE (3G/4G)
femtocells [3.1], [3.3], [3.5].
- Interference avoidance algorithms between indoor femtocells and
outdoor macrocells [3.4].
- Performance analysis and evaluation (throughput, handover, outage,
quality of service) of both femto and macrocell layers based on SLS
[3.1], [3.4], [3.5].
- Indoor and indoor-to-outdoor radio propagation models based on FDTD
(Finite Difference Time Domain), and 3D ray tracing/launching [.33],
The project results were disseminated through a series of femtocell
workshops. For example, there were 56 participants from both industry (11
companies including T-Mobile, Vodafone, Alcatel-Lucent), and academia (10
universities) who attended the first workshop in 2009. The 5th
workshop was held in Feb 2012. The research was also disseminated through
EPSRC's Digital Economy impact review.
References to the research
A list of the main publications is given below. To date,  has been
cited 124 times,  has been cited 63 times and  has been cited 357
times since their publication.
3.1 J. Zhang, G. de la Roche, A. Valcarce, D. López, E. Liu, H. Song,
"Femtocells — Technologies and Deployment," Wiley, Jan. 2010, (ISBN:
(Note: A new book on small cells, a new name for femtocell and its like,
was invited by Wiley and the draft is now ready to be submitted.)
3.2 D. Lopez-Perez, A. Valcarce, G. De La Roche, E. Liu and J. Zhang,
`Access methods to WiMAX femtocells: A downlink system-level case study',
in Proc. 11th IEEE Int. Conf. on Communication Systems, 2008, Nov. 2008,
pp.1657-1662. (Note: Although this is a conference paper, it was one of
the first papers on femtocells.)
3.3 G. De La Roche, A. Valcarce, D. Lopez-Perez, E. Liu and J. Zhang,
`Coverage Prediction and System Level Simulation of WiMAX Femtocells',
COST 2100 6th Meeting, Lille (France), October 2008. (Note: The COST
project itself is Influential, and models presented at COST are generally
accepted as bench marks.)
3.4 D. López-Pérez, A. Valcarce, G. De La Roche and J. Zhang, `OFDMA
femtocells: A roadmap on interference avoidance', IEEE Communications
Magazine, September, 2009.
3.5 G. De La Roche, A. Valcarce, D. López-Pérez and J. Zhang, "Access
Control Mechanisms for Femtocells," IEEE Communications Magazine,
Jan. 2010. (IF 2012: 3.66).
3.6 A. Valcarce, H. Song and J. Zhang, `Characterization of the Numerical
Group Velocity in Yee's FDTD Grid, IEEE Transactions on Antennas and
Propagation, Vol 58, Issue 12, 2010, pp.3974-3982
3.7 A. Valcarce; J. Zhang, `Empirical Indoor-to-Outdoor Propagation Model
for Residential Areas at 0.9-3.5GHz', IEEE Antennas and Wireless
Propagation Letters, Vol 9, pp.682-685, 2010
3.8 Zhu Xiao, Peng Wang, Xu Zhang, Shyam Mahato, Lei Chen and Jie Zhang,
`Incentive mechanism for uplink interference avoidance in two-tier
macro-femto networks', Proc. IEEE 75th VTC, May 2012.
Details of the impact
Context to the impact
About 10 years ago, there was interest among telecoms experts in extending
cellular coverage so that users could access a network from inside a
building without loss of service quality. Several technical approaches to
achieve this were considered, and the `femtocell' name was coined in 2005
for a standalone, self-configuring home base station which did not require
a dedicated handset. The in-building wireless access point was intended to
communicate with approximately 10 handsets within a distance of up to
(typically) 10m. The Femto Forum was set up in 2007 so that manufacturers
and operators could obtain and exchange information relevant to
small-scale cellular communications.
Impact achieved by the CWiND/CWR team at the University of
For the femtocell concept to be effective, a range of technical challenges
would have to be overcome, mainly those associated with interference,
mobility management and auto-configuration (as noted in Section 2 above).
Researchers in CWiND (now Centre for Wireless Research, CWR) at the
University of Bedfordshire recognised that these problems existed, and
with their expertise in wireless networks were in a position to address
them through a research programme. Funds were obtained in 2008 from EPSRC
to start the first research supported by EPSRC on femtocells; this showed
forward thinking at the time, as there were no femtocell deployments when
the project started.
The benefits of using WiMAX (as compared with other candidate
technologies) were also appreciated by the CWiND team, and the results of
the initial research were recognised by the telecoms company T-mobile, and
by RANPLAN (www.ranplan.co.uk), a small company located in Luton near to
the University who specialise in radio network planning and optimisation.
T-mobile already knew of the work of the team, as a result of a
presentation given by Prof. Jie Zhang at a meeting of the Femto Forum in
2008, T-mobile proposed a cooperative programme to extend the research
findings to cover their specific interests. One of the researchers in
CWiND was a was a technical adviser to RANPLAN, and had recommended to
that company that the tools developed by the CWiND team (as described in
section 3) should be taken up to enhance RANPLAN's ability to offer
planning services to their customers. He is now (since January 2011)
R&D Manager at RANPLAN Wireless Network Design Ltd.
In the next phase of the work, in 2009, cooperation with and funding from
T-mobile resulted in enhanced interference management techniques
applicable to small cells, encapsulated in an model provided by the CWiND
team to T-mobile applicable to the effect of femtocell/macrocell
interactions [5.1]. Consultations with RANPLAN led to investment by that
company to incorporate the CWiND team's research results into an existing
cutting-edge indoor planning tool which RANPLAN uses extensively in its
commercial offering to customers [5.2].
Following the generation of specialised knowledge and experience of
femtocells, the team wrote a book [3.1] which covers the principles and
practical aspects of femtocell technology and deployment, and which has
been widely cited. It has been published internationally, and has been
translated into Chinese. The book has been written for researchers,
practitioners and installers of femtocells, as well as final year
undergraduates. At the invitation of the publishers, which confirms the
good impact of the book (at November 2013, more than 700 copies of the
English edition had been sold), a second book has been prepared by the
same authors to provide an update and expansion of the material in the
The impacts of the work of UoA11 on femtocells (now also known as small
cells) can be described under various headings.
The research has economic impact in terms of enabling a new alternative
cellular communications technology which can improve data access (speed
and capacity) and communications convenience, and thus improve efficiency
of working for customers and business reach for operators. The femtocells
were deployed after this project started. Effective network planning
initially benefits the operators, but it consequently affects the service
tariff, and thus benefits the user business or household.
A knock-on benefit is an ecological one. According to ABI research, by 2014
energy savings from femtocells for operators will be equivalent to planting
12,000 acres of forest. As most major operators have deployed femtocells in
their network (this link shows a full list: www.smallcellforum.org/aboutsmallcells-small-cells-consumer-faqs
the CWiND work has contributed to this benefit.
The work in UoA11 on femtocells is timely. According to the Femto-Forum:
the number of small cells is growing from 3.2 million in 2012 to 62.4
million by 2016 - a 20-fold increase, constituting 88% of all base
stations globally. It aligns with the Government's mission of `Digital
Britain' to increase the quality of life for the general public in terms
of research on an alternative wireless broadband access technology.
The research has an impact on society, culture and creativity. The
initial results were disseminated through EPSRC's Digital Economy impact
review, whose readers include policy makers, researchers and the general
public. A full report of the work done by UoA11 with EPSRC funding can be
found at: www.rcuk.ac.uk/documents/documents/DEIREvidencePart3-EvidencefromthePortfolioSurvey.pdf
We attended several conferences which were strongly influenced by
industry, such as the Femto Forum conferences in London and Dallas in
2008, while a member of the UoA11 team was the chairman of a femtocell
panel entitled "Femtocells: Deployment and Applications" at the IEEE
International Conference on Communications (ICC) in 2009.
Sources to corroborate the impact
5.1. Senior Head of Research Trials at T-mobile
5.2. R&D Manager at RANPLAN Wireless Network Design Ltd.