Digital Signal Processing Reference
In-Depth Information
7.2.1.4 Hybrid Control
Many algorithms exploit more than one parameter. Here, we present some of these
hybrid control algorithms.
In [117] the authors present a power/rate adaptation algorithm that relies on the
RTS/CTS exchange. They propose to extend the range of RTS and CTS packets to
protect the CTS, DATA and ACK packets. This way, they try to remove all hidden
terminals.
In [97] and [96], it is recommended to keep the product of transmit power and
CS threshold constant in the network. In [97] this constant is found through Gibbs
sampling, while in [96] the optimal constant is experimentally established when the
network-wide PER is near-zero, which is optimal from a throughput perspective.
In [118], the authors investigate the effects of the 3 parameters on spatial reuse.
They show that spatial reuse only depends on the ratio of transmit power to car-
rier sense threshold in the case that the achievable channel rate follows Shannon's
law. Furthermore, they claim that tuning transmission power should be preferred
over tuning the carrier sense threshold as terminals can then save energy addition-
ally. Based on this observation, the authors present a power and data rate adaptation
algorithm that uses the SINR as its input. Similar to [94], they suggest that termi-
nals should use the minimum transmission power needed to sustain high data rates.
Doing this, terminals achieve optimal throughput, while maximizing spatial reuse.
In [98] a spatial backoff contention resolution is presented. This is a heuristic al-
gorithm that tunes both carrier sense threshold and rate and we will use it to bench-
mark the performance of our hybrid DT/RT optimization algorithm.
7.2.2 Benchmark Solution: Spatial Backoff
In this section, we introduce Spatial Backoff (SB) as our main reference [98].
This algorithm tunes both rate and carrier sense threshold to optimize individual
throughput in IEEE 802.11 networks. We present an overview of the algorithm in
Sect.
7.2.2.1
and present opportunities for further improvements of the algorithm in
Sect.
7.2.2.2
.
7.2.2.1 Algorithm Overview
Spatial Backoff assumes that the IEEE 802.11 MAC protocol has a set of discrete
rates available. For each rate an associated carrier sense threshold,
T
CS
, is defined
as follows:
T
Rx
SINR
T
CS
[
i
]=
,
(7.1)
[
i
]
where
T
Rx
is the receiver sensitivity (no packets with a power below
T
Rx
can be
received) and SINR
[
i
]
is the signal-to-interference-noise threshold for rate
R
[
i
]
.
