Delay Optimal State Dissemination
with Piggybacking
We design Geo-MAC, a MAC
protocol that exploits
spatial diversity in highly
mobile wireless networks. It
aims to achieve low latency
and high reliability, goals
that are intrinsic to the
success of many envisioned
vehicular safety
applications. Conventional
MAC layers address
reliability through ARQ
mechanisms that re-transmit
messages from the source, if
earlier transmissions were
not acknowledged. Unlike
GeoMAC, these schemes
essentially exploit temporal
diversity since
retransmissions are only
likely to succeed if the
channel has improved.[
pdf]
In very dense networks,
safety messaging can lead to
offered traffic loads that
saturate the shared wireless
medium. One approach to
address this problem is to
reduce the frequency of
location update messages
when the movements of a
vehicle can be predicted by
nearby vehicles. We study
the predictability and
compressibility of location
traces under different
driving conditions.
[pdf]
Even in congested networks,
when applications may not be
able to achieve very high
messaging rates, on-road
vehicles must be able to
converge to the best
possible messaging rate, a
rate that minimizes the
average age (delay) of
vehicles’ information at any
vehicle in the network. We
design a rate control
algorithm that achieves the
best rate. The algorithm is
distributed in nature and
adapts to varying number of
cars in the network.
We consider the problem of
periodic dissemination of
time-varying state among
nodes in a wireless network,
with minimum average delay.
We assume packets have large
overheads such that node
transmissions can piggyback
other nodes’ state
information with negligible
increase in their packet
transmission times. Each
node will track the state
information of any other
node with some delay. The
optimization problem is to
find round robin schedules
that minimize the system
delay, which is the state
information delay averaged
over all pairs of nodes in
the network.