Information Technology Reference
In-Depth Information
2
⎛
π
⎞
p
(
γ
)
≈
Q
6
(
γ
−
3
sin
⎝
⎠
3
8
A
DAPTIVE
E
RROR
C
ONTROL FOR
B
LUETOOTH
M
ULTI
-H
OP
N
ETWORKS
Using the same error control scheme for the whole network could be a good choice in
some cases, but not always. Sometimes it is needed to apply the best error control available,
while in other cases less error control should be used. To use an adaptive error control
scheme, a mechanism has to be designed to judge the importance of a packet and then
choosing the most efficient error control scheme for that particular packet. In Bluetooth case,
to change the error correction scheme means to change the packet type to be transmitted. In
order to apply an adaptive scheme in a multi-hop network, where the most important factor is
to reduce the energy consumption, an approach presented in [7] was used.
The importance of a packet is evaluated using the multi-hop principle, as shown in Figure
3. The choice of the packet type and the respective error control technique shall be based on
the number of hops the packet traveled within the ad hoc network. For instance, a node sends
a data packet containing the information of the temperature of a region to the sink node,
which collects the data of all the sensors of the network.
However, before the packet reaches the sink node, it may travel through some other
nodes of the network with routing capacity. If the packet gets lost at the first hop, only the
energy to send the packet from a node to other specific node is lost. If the packet is corrupted
after few more hops, much more energy will be spent to transmit the packet through the
network. In this sense, a packet is more important if it travels through more nodes in the
network, and consequently, more energy is being consumed. An adaptive scheme might use
stronger error control techniques for packets that travel more hops and weaker error control
for packets with fewer hops.
In the adaptive error control scheme, each packet must have a counter with the number of
hops the packet had in the network. This can be implemented as a field in the payload of the
packet. Two different adaptive schemes were used: ADP1 and ADP2 [7]. A packet with
weaker error control is used for the initial hops and a packet with more powerful coding for
the remaining hops throughout the sensor network. Table 3 shows the packet types proposed
in these schemes. Although only two schemes are being presented here, other adaptive
strategies with different packet types might also be proposed.
Table 3. Adaptive schemes
1
st
and 2
nd
Hops
3
rd
, 4
th
and 5
th
Hops
Scheme
Other Hops
ADP1
AUX2
HAM2
DH1
ADP2
AUX2
BCH2
DH1
