Digital Signal Processing Reference
In-Depth Information
Fig. 7.2
. When the interferer
is assumed to be closest to the transmitter, an aggressive strategy can be used (
k
The network operator can select its
k
value from the interval
[−
1
,
1
]
1). When the
interferer is assumed to be closest to the receiver, a defensive strategy needs to be employed. This
defines the selection of the carrier sense threshold according to (
7.2
)
=−
point,
k
=
1, assumes that the interference power, when measured at the transmitter,
suffers an extra path loss from receiver to transmitter (see Fig.
7.2
). Throughout the
remainder of this chapter, we will use a neutral setting (
k
=
0).
This CS setting implies that the transmitter needs to know the value of
P
r
. A com-
monly accepted way is to piggyback the received power estimated at the receiver in
the acknowledgment. As mentioned in [126], this has already been integrated in cur-
rent IEEE 802.11 commercial products (e.g., the Lucent ORiNOCO AP-1000 card).
Even when it would be difficult to estimate the received power, SL will compensate
by selecting appropriate states within the state space.
We denote this improved state space as
P
r
-
space
. The state space described in
Sect.
7.2.2.1
, will be referred to as
T
Rx
-
space
.
7.3.3 System Scenarios
In order to design the DT procedures (i.e., heuristic recommendations), we must first
find out which is the current scenario. We use scenario identification techniques,
quite similar to those presented in [92]. The scenarios we can identify are the hid-
den terminal starvation, asymmetric starvation and neighborhood starvation and the
starvation-free scenario. Below, we describe how we can identify these different
scenarios.
•
Hidden terminal starvation is the easiest to detect, as only an inspection of
p
c
is
needed. Indeed, it is signaled through a high collision probability.
•
Asymmetric starvation is detected as follows. We keep a timer from the begin-
ning of transmission until we can decrement our backoff timer. If a successful
transmission lasts longer than expected (the expected duration of a collision or
a successful transmission can be easily calculated), a neighboring node started
