PhD Thesis Proposal Defence
Title: "Optimization of User Association for MIMO Wireless Local Area Networks"
Mr. Wang Kit WONG
The ever-growing wireless bandwidth requirement has spurred recent development
of Multiple-Input-Multiple-Output (MIMO) based physical-layer technologies,
such as transmit beamforming, interference cancellation, and interference
alignment. Such technologies substantially improve the performance of MIMO
WLANs over single-antenna WLANs.
Users are often covered by multiple access points (APs) in today’s WLAN
deployment. User association control is to assign or associate users in the
overlapping regions to one of the APs for service. The default implementation
always associates a user to the best signal AP. This leads to unsatisfactory
throughput performance at congested APs and channel under-utilization at
others. The performance of MIMO WLANs are highly related to user association.
In this thesis, we study three challenging optimization problems in WLANs: 1)
user association; 2) joint user association and random access control and 3)
joint user association and AP grouping.
We first study the user association problem for MIMO WLANs. We formulate user
association as an integer programming problem, which considers user migration
cost. Then, we propose a factor-4 approximation algorithm to tackle the
problem, which achieves similar performance as previous schemes but incurs much
less user migration cost.
Secondly, we study the joint user association and random access control
optimization problem. Random access control determines APs’ transmit
probabilities, which is another factor affecting the performances of WLANs. APs
associated with more users require higher channel access opportunities. On the
other hand, APs with higher transmit probabilities should serve more users.
Therefore, they are coupled. We propose a distributed algorithm termed CARA
(Joint Client Association and Random Access Control) to tackle the joint
optimization problem, which achieves higher throughput than sequential
Finally, we study the joint user association and AP grouping optimization
problem. Coordinated beamforming (CB) has emerged as a promising interference
coordination approach for cooperative MIMO systems. CB allows interfering APs
to transmit as a group. Due to heavy channel state information (CSI) feedback
overhead, APs need to be partitioned into cooperation groups no larger than a
certain size where only APs in the same group are able to cooperate with CB. We
study the novel optimization problem of minimizing AP load by joint AP grouping
and user association as they are coupled. Based on alternating direction
optimization, we propose DAGA (Distributed Joint AP Grouping and User
Association) to tackle the optimization problem. DAGA produces an approximated
user association solution which is at most elogm (m is the number of APs) times
of the optimum.
Date: Friday, 21 December 2018
Time: 4:00pm - 6:00pm
Venue: Room 3494
Committee Members: Prof. Gary Chan (Supervisor)
Prof. Cunsheng Ding (Chairperson)
Dr. Pan Hui
Prof. James Kwok
**** ALL are Welcome ****