Towards Efficient Communication in WLANs Based on Cross-Layer Design

The Hong Kong University of Science and Technology
Department of Computer Science and Engineering


PhD Thesis Defence


Title: "Towards Efficient Communication in WLANs Based on Cross-Layer 
Design"

By

Mr. Haochao LI


Abstract

Wireless communication is becoming an indispensable part of people’s daily 
life. Over the last decade, the widespread adoption of Wireless Local Area 
Networks (WLAN) has triggered the proliferation of mobile devices, 
resulting in a dramatic growth in the amount of the mobile data traffic. 
To complement this growth in demand, there has been a steadily advancement 
of the data rate in recent years. However, the high theoretical data rate 
often sustains a low actual throughput in the real world transmissions, 
referred as a low efficiency problem in wireless communication. Therefore, 
it is essential to achieve efficient communication in the wireless design.

In traditional WLANs with point-to-point communication, the low efficiency 
problem is mainly induced by the coordination overhead. To avoid radio 
interference and packet collisions, coordination is required to allow 
multiple access in the multi-station WLANs. But the existing coordination 
schemes themselves account for too much of the transmission air time by 
exchanging control messages, resulting in a significant control overhead. 
This motivates us to provide a cost-effective coordination scheme in the 
wireless transmission. To achieve this, we propose a cross layer design, 
named hJam, for OFDM-based WLANs. Rather than interleaving or separating 
the control messages and data traffic as the traditional communication 
paradigms, hJam serves them together at the same time. By exploiting the 
redundancy in the preamble, the control messages are able to be 
transmitted in an attached manner with the data traffic. Therefore, hJam 
eliminates the control overhead by enabling the concurrent transmission of 
coordination message and traffic data to improve the coordination 
efficiency. Through extensive experiments, we have demonstrated the 
significant improvement of channel efficiency based on the design of hJam.

In recent years, the emerging Multi-user Multiple-Input-Multiple-Output 
(MU-MIMO) has also attracted attention in wireless communication by 
allowing the concurrent transmissions among multiple transmitters to the 
same receiver. The traditional approaches only focus on the efficiency in 
the time domain by reducing the control overhead. Differently, the channel 
efficiency problem becomes even more challenging in MU-MIMO networks by 
introducing an extra dimension, i.e., spatial domain, for the concurrent 
transmission for multiple nodes. Through analysis, we investigate that it 
is crucial to utilize the antenna usage by ensuring as many as possible 
simultaneous streams sent to the AP in MU-MIMO networks. Therefore, 
channel utilization in MU-MIMO networks should consider both the time and 
spatial domain, i.e., the efficient channel time and antenna usage at AP. 
To achieve this, we propose a new MAC-PHY design, named CUTS, by using 
interference nulling for attaching the antenna information in frequency 
domain channel contention, combined with the technique ACK in the 
frequency domain using self-jamming. We have validated and prove the 
effectiveness on channel efficiency by using the CUTS design through 
extensive experiments. We also discuss the potential research issues of 
efficiency in wireless communications.


Date:			Thursday, 22 May 2014

Time:			2:00pm – 4:00pm

Venue:			Room 4480
 			Lifts 25/26

Chairman:		Prof. Kai Tang (MAE)

Committee Members:	Prof. Lionel Ni (Supervisor)
 			Prof. Shing-Chi Cheung
 			Prof. Qiong Luo
 			Prof. Zongjin Li (CIVL)
                         Prof. Jiannong Cao (Computing, PolyU)


**** ALL are Welcome ****