Digital Signal Processing Reference
In-Depth Information
[
]
Only when the SINR at the receiver exceeds SINR
, packets can be received. It
is assumed that when using a
T
CS
equal or lower than
T
CS
[
i
]
i
to transmit at rate
i
,
it is unlikely that the transmitter will overestimate the interference tolerance at the
receiver. Hence, we are looking for a
T
CS
≤
T
CS
[
i
]
.
. When a cer-
tain number
S
of consecutive transmissions succeed, the rate is increased to
R
[
i
+
Transmitters start at the lowest rate,
R
[
0
]
and its associated
T
CS
[
0
]
,
unless it's already transmitting at the highest rate. Likewise, when a certain number
F
of consecutive failures is seen, transmitters try to compensate by first lowering
their
T
CS
. This is done as long as the
T
CS
is higher than
T
CS
[
1
]
i
]
. When the current
T
CS
of the transmitter is equal to
T
CS
[
i
]
and transmissions continue to fail, the rate
is decreased to
R
[
i
−
. When decreasing to a lower rate,
T
CS
is reset to its last
known successful value for
R
[
i
−
1
]
.
In order to stabilize on a certain point the number of consecutive transmissions
needed to increase rate is increased
S
1
]
, increases each time the transmitter falls
back to rate
i
. A similar procedure is used for failures.
[
i
]
7.2.2.2 Opportunities
In this section, we shortly describe opportunities that exist to improve SB. In the
next sections, we address these opportunities in the design of our control algorithm.
•
Improve monitors
SB uses a starvation detection mechanism to avoid a complete loss of transmis-
sion opportunities. This mechanism (no transmission during a certain period of
time) is quite slow and only detects the most severe cases of starvation, when a
transmitter is deprived of all access to the medium.
•
Increase the number of scenarios
SB only considers collisions. Collisions, however, are not always a good indica-
tor for throughput as a node may increase its throughput by using decreasing its
transmission rate, while increasing its carrier sense threshold. This can signifi-
cantly increase the successful transmission opportunities.
•
Improve DT policy
The selection of
T
CS
[
i
]
in SB is also quite defensive. Indeed, when the received
power is high, the transmitter doesn't need to be as protective as when the received
power is equal to
T
Rx
.
•
Improve RT policy
The proposed converging method can be quite slow, when the transmitter has a lot
of neighbors and occasionally a packet fails through a coordinated collision [92].
7.2.3 Multi-Agent Learning
In this section we give a short overview of the current research on multi-agent and
heuristic learning. Thorough reviews of the current state of research in these fields
can be found in [119-122].
