Ad Hoc Networks : Technologies and Protocols - University of ...

Overview of the Chapters in this Book 19
immediately since in ATP both source and destination TCP stacks are modified.
The remaining schemes are feasible and should be carefully evaluated.
Chapter 6: Energy conservation
In ad hoc networks consisting of moving nodes (e.g. vehicles), energy conservation
is generally not a critical issue. However, it clearly becomes a concern
in sensor networks or in ad hoc networks where the time to discharge a
“powered-on” node is less than the time between battery recharging opportunities.
This chapter provides an excellent survey of the various techniques to
conserve power, namely: power/topology control, energy routing, coordinated
sleep and power save management. If we go back to our urban grid example,
we note that cars have a practically unlimited reserve of energy. However,
pedestrians do not, especially if they use 802.11 in their PDAs. If the PDA has
multiple interfaces, say 802.11, ZigBee, cellular and Bluetooth, all the latter
options are more attractive as “always - on” options instead of 802.11. In fact,
radio interface selection could be yet another energy conservation strategy to
add to the above list. Another important component in the urban grid is the
environment sensor fabric. These sensors must interact with pedestrians and
cars (for example, a sensor field comes alive if a police car approaches). Thus,
sensors (and pedestrians) must be scheduled in such a way that their interaction
is most effective for a given recharge cycle. The schemes described in this
chapter are an excellent start for the investigation of suitable sensor/pedestrian
energy strategies,
Chapter 7: Use of Smart Antennas in Ad Hoc Networks
Directive antennas are used for at least three reasons: extending range, folding
jamming attacks and reducing the probability of detection. Smart antennas
add another feature - the ability to transmit simultaneously on multiple beams.
This chapter gives a brief overview of directional antennas. It then provides
an exhaustive survey of the interaction between antenna beamforming, MAC
protocols and routing protocols. It is in fact clear that, to take advantage of
antenna directionality, MAC and routing protocol changes are required. Are
smart antennas going to have an impact on our urban grid network strategy. Absolutely!
One can take advantage of the extended range of directional antennas
to establish backbone links along the major boulevards, say. Also, if UAVs are
used to assist in urban disaster recovery, directional antennas will do very well
for ground to air and air to air links. One important issue indirectly addressed
by this chapter is the coexistence of different MAC and routing protocols in the
same network, since only part of the nodes will be capable of antenna beaming.
In all, this chapter is an excellent start for an investigation of mixed antenna
strategies in complex environments such as urban grids and battlefields.