Exploring Wi-Fi Functionality in Physical Layer

MPhil Thesis Defence


Title: "Exploring Wi-Fi Functionality in Physical Layer"

By

Mr. Guanhua WANG


Abstract

Nowadays wireless networking is becoming more and more popular in our daily 
life. Compared with wired counterpart, wireless communication suffers a lot 
from the problems like interference in surrounding environment, low 
transmission rate, etc. Research literature tries different ways of enhancing 
wireless network performance. Particularly in Physical layer (PHY), many novel 
technologies have been proposed, such as Multiple Input Multiple Output (MIMO), 
zigzag decoding, full duplex antenna, etc.

Pursuing the same goal of enhancing wireless networking performance, two of my 
research projects, namely SimCast and TiM, enhance the performance of wireless 
networking in PHY.

SimCast is a cross-layer design for achieving efficient concurrent video 
uploading/ downloading in MU-MIMO WLANs. Wireless video stream delivery is 
choppy. This problem becomes much severer in MU-MIMO's simultaneous video 
transmission within the same band. Conventional schemes achieve graceful video 
delivery by harnessing from high data redundancy. However, with concurrent 
transmission in the same band, the leverage of high data redundancy leads to 
high probability of collisions and packets loss, which limits the performance. 
In concurrent video transmission, achieving efficiency over varied link 
condition is the main issue. To address this issue, I propose SimCast
(Simultaneous). The key idea of SimCast is to harness frequency diversity of 
the channel and spatial similarity of users.

TiM is a novel 3D modulation scheme to achieve fine-grained rate adaptation in 
wireless networking. Channel condition varies frequently in wireless networks. 
To achieve good performance, devices need rate adaptation. In rate adaptation, 
choosing proper modulation schemes based on channel conditions is vital to the 
transmission performance. However, due to the natural character of discrete 
modulation types and continuous varied link conditions, we cannot make a 
one-to-one mapping from modulation schemes to channel conditions. This matching 
gap causes either over-select or underselect modulation schemes which limits 
throughput performance. To fill-in the gap, I propose TiM (Time-line 
Modulation), a novel 3-Dimensional modulation scheme by adding time dimension 
into current amplitude-phase domain schemes. With estimation of channel 
condition, TiM changes base-band data transmission time by artificially 
interpolating values between original data points without changing 
amplitude-phase domain modulation type.

Recent research has extended the functionality of wireless signals into a new 
realm. More precisely, they push the limit of ISM (Industrial Scientific and 
Medical) band from data delivery to radiometric detection, including motion 
detection, recognition, localization, and even classification. By detecting and 
analyzing signal reflection, these approaches enable Wi-Fi signals to "See" or 
"Sense" target objects. This kind of sensing works via wireless signals can be 
collectively referred to as "Wi-Fi Radar".

WiHear system follows the "Wi-Fi Radar" trend, which bridges communication 
between human speaking and wireless signals. My WiHear system enables Wi-Fi 
signals to "hear" our talks without deploying any devices. To achieve this, 
WiHear needs to detect and analyze fine-grained radio reflections from mouth 
movements. WiHear solves this micro-movement detection problem by introducing 
Mouth Motion Profile that leverages partial multipath effects and wavelet 
packet transformation. Since Wi-Fi signals do not require line-of-sight, WiHear 
can "hear" people talks within the radio range. Further, WiHear can 
simultaneously "hear" multiple people's talks leveraging MIMO technology.


Date:			Friday, 8 May 2015

Time:			10:30am - 12:30pm

Venue:			Room 5510
 			Lifts 25/26

Committee Members:	Prof. Lionel Ni (Supervisor)
 			Dr. Qiong Luo (Chairperson)
 			Dr. Lei Chen


**** ALL are Welcome ****