Interference management in cooperative multi-cell networks

Student thesis: Doctoral ThesisDoctor of Philosophy


In multi-cell networks where resources are aggressively reused, eliminating
interference is the key factor to reduce the system energy consumption.
This thesis proposes interference management techniques based on beamforming
with different levels of cooperation amongst base stations (BSs).
First, a multi-cell beamforming (MBF) technique is introduced to design
beamformers as if geographically distributed BSs were a single BS. The
aim is to minimise the total transmit power across the network while maintaining
the required signal-to-interference-plus-noise ratio (SINR) for every
user. An iterative algorithm is proposed to solve the optimisation problem
of MBF. Since the MBF scheme requires the circulation of all users’ data
amongst coordinating BSs, a user position aware (UPA) algorithm is developed
for MBF to reduce the backhaul overhead by allocating each user
to nearby BSs only. To completely avoid user data circulation, a semi definite
programming (SDP) algorithm, named as coordinated beamforming
(CBF), is introduced to jointly calculate beamformers for all coordinating
BSs in a manner that each BS transmits to its local users only. Taking
into account errors in channel estimations, robust beamforming designs are
developed for CBF. Next, fast wireless backhaul protocols, i.e., Star and
Ring, are proposed using network coding to enable links amongst coordinating
BSs. The maximum achievable throughput of each protocol is
analysed. The power consumption of the Ring protocol is characterised
and used to compare and evaluate the performance of the proposed beamforming
schemes. The deployments of MBF, UPA-MBF and CBF schemes
require a central unit for a group of coordinating BSs as well as backhaul
links amongst them. In fact, a central unit may not always be available,
e.g., in femtocell and self-organising networks, while backhaul links may
be limited. Hence, distributed beamforming (DBF) is proposed to independently
design beamformers for the local users of each BS. In DBF, the
combination of each BS’s total transmit power and its resulting interference
power toward other BSs’ users is minimised while the required SINRs for
its local users are maintained. SDP and iterative algorithms are introduced
to solve the optimisation problem of DBF.
Date of Award1 Nov 2012
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorMohammad Nakhai (Supervisor) & Vasilis Friderikos (Supervisor)

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