2 research outputs found
Location-Quality-aware Policy Optimisation for Relay Selection in Mobile Networks
Relaying can improve the coverage and performance of wireless access
networks. In presence of a localisation system at the mobile nodes, the use of
such location estimates for relay node selection can be advantageous as such
information can be collected by access points in linear effort with respect to
number of mobile nodes (while the number of links grows quadratically).
However, the localisation error and the chosen update rate of location
information in conjunction with the mobility model affect the performance of
such location-based relay schemes; these parameters also need to be taken into
account in the design of optimal policies. This paper develops a Markov model
that can capture the joint impact of localisation errors and inaccuracies of
location information due to forwarding delays and mobility; the Markov model is
used to develop algorithms to determine optimal location-based relay policies
that take the aforementioned factors into account. The model is subsequently
used to analyse the impact of deployment parameter choices on the performance
of location-based relaying in WLAN scenarios with free-space propagation
conditions and in an measurement-based indoor office scenario.Comment: Accepted for publication in ACM/Springer Wireless Network
Cooperative communication in wireless local area networks
The concept of cooperative communication has been proposed to improve link capacity, transmission reliability and network coverage in multiuser
wireless communication networks. Different from conventional point-to-point and point-to-multipoint communications, cooperative communication
allows multiple users or stations in a wireless network to coordinate
their packet transmissions and share each other’s resources, thus achieving
high performance gain and better service coverage.
According to the IEEE 802.11 standards, Wireless Local Area Networks
(WLANs) can support multiple transmission data rates, depending
on the instantaneous channel condition between a source station and
an Access Point (AP). In such a multi-rate WLAN, those low data-rate stations
will occupy the shared communication channel for a longer period
for transmitting a fixed-size packet to the AP, thus reducing the channel
efficiency and overall system performance.
This thesis addresses this challenging problem in multi-rate WLANs
by proposing two cooperative Medium Access Control (MAC) protocols,
namely Busy Tone based Cooperative MAC (BTAC) protocol and Cooperative
Access with Relay’s Data (CARD) protocol. Under BTAC, a low
data-rate sending station tries to identify and use a close-by intermediate
station as its relay to forward its data packets at higher data-rate to the AP through a two-hop path. In this way, BTAC can achieve cooperative
diversity gain in multi-rate WLANs. Furthermore, the proposed CARD
protocol enables a relay station to transmit its own data packets to the AP
immediately after forwarding its neighbour’s packets, thus minimising the
handshake procedure and overheads for sensing and reserving the common
channel. In doing so, CARD can achieve both cooperative diversity
gain and cooperative multiplexing gain. Both BTAC and CARD protocols
are backward compatible with the existing IEEE 802.11 standards.
New cross-layer mathematical models have been developed in this
thesis to study the performance of BTAC and CARD under different channel
conditions and for saturated and unsaturated traffic loads. Detailed simulation
platforms were developed and are discussed in this thesis. Extensive
simulation results validate the mathematical models developed and show
that BTAC and CARD protocols can significantly improve system throughput,
service delay, and energy efficiency for WLANs operating under realistic
communication scenarios