Digital Signal Processing Reference
In-Depth Information
metric, e.g. the number of hops or the required energy to forward a packet to the
sink. The benefit of the cost-based routing is that the knowledge of forwarding path
states is not required: a node forwards its data by sending it to any neighbor that
has lower cost. The drawback is that the routes must be created proactively. Also,
although data to the sink is forwarded efficiently, another routing mechanism, such
as flooding, must be used for data traveling in the other direction. However, the
trade-off can be acceptable since most of the traffic is usually toward the sink.
6.3
Hybrid Transport and Routing Protocols
and routing layers to achieve a low communication cost. Data is transmitted with
relatively slow speed by delaying forwarding with two configured time values
T
min
and
T
max
. In broadcast networks, the
T
min
parameter allows a node to receive a frame
multiple times. A node then evaluates the necessity to forward the frame based on
how many times it was received. If a sequence number gap in a received frame
is detected, PSFQ uses a negative acknowledgment to request all missed frames.
The frame is requested in less than
T
min
, which allows reducing latency on error
situations.
forwarding with inbuilt congestion control mechanism and soft latency guarantees.
The protocol does not guarantee strict limit for latency, but defines an end-to-end
delay that is proportional to the distance between source and destination nodes.
Thus, it maintains a certain delivery speed. In SPEED, the next hop is selected
randomly among the neighbors with the probability that is proportional to the link
speed. Only the nodes that advance towards the target and meet the delivery time
can be selected. The link speed is calculated by dividing the distance between nodes
(obtained with the geographic location information) by measured link delay. The
next hop selection is combined with feedback received from neighbors. If a node
cannot forward a packet due to congestion or a hole in the network, it sends a
backpressure beacon, which reduces the forwarding probability to that node.
7
Embedded WSN Services
This section describes localization and synchronization in WSNs. On one hand,
these can be seen as services that enable building various WSN applications, such
as surveillance or tracking system. On the other hand, signal processing is used
in various localization and synchronization algorithms that might benefit from an
implementation with an embedded processing chip.
