Page 125 - From Smart Grid to Internet of Energy

Smart grid network architectures Chapter 3 109

The use of a hybrid routing rule and airtime cost metric for static WMNs in
the SG NANs are proposed by HWMP of IEEE 802.11s that is also a tree-based
routing protocol [17]. Routing trees of HWMP are constituted on the basis of
systematically broadcasting root announcements. Currently, there are two types
of research going on about the HWMP. First one is to develop a practical routing
link cost metrics, because SG features are not reflected by the default metric.
A very crucial problem in such a network is to understand how traffic can be
balanced among multiple GWs [20].
For route selection, air cost metric is used in the HWMP. Any node can
improve route selection process by relating air cost information of obtained
packets with calculated air cost information. The air cost problems shown in
SG applications are taken into account in [17]. Number of MAC retransmissions
of every packet was preferred to find out failure rate of every node (i.e., air time
cost). Since different sizes of data packets may require different MAC retrans-
mission levels, this situation will be not practical. For different packet sizes, use
of the same retransmission level may decrease throughput of the network. This
should be tackled in SG applications since size of data packets may be different
for different services. A different method for calculation of error ratio at every
node was also suggested in which retransmission of a large packet is considered
less significant than retransmission of a small packet since smaller packets
probably have lower bit errors in most of the scenarios. Designing of air cost
metric using this technique is more desirable for SG NANs.
Multi-GW routing for SG NANs is explored in [20] where every node (every
SM) has a tree-table to store tree information. It examines the tree-table to
observe if there exists identical data aggregation point (DAP) information,
when it gets a DAP GW notice. If it is available, then the node updates its
tree-table on the basis of the pre-specified methods. Otherwise, a novel tree
is generated on the basis of the obtained DAP information and included to
the tree-table. In addition, a reserve path multi-GW diversity routing method
is also developed to enhance reliability of routing scheme. Firstly, the optimal
route for packet transmission is selected by a source node. In the event of a link
is broken, the second route is exploited. However, if the both links are failed
then on-demand route of HWMP is initialized, but another backup HWMP
buffer is included at every node in order to record self-created and conveyed
packets. Hence, a timer is required to systematically cancel stored backup
packets. Network reliability can be advanced by using this routing algorithm
on the cost of additional delay. For its ability to stabilize traffic among multiple
GWs, a packet scheduling algorithm based on back pressure approach was also
proposed. In this method, a conveying node chooses its following hop node
depending on a novel principle that examines order size and optimal path metric
value of its adjacent nodes. This process of choosing next hope will come to an
end when one of GWs is designated as the optimal neighbor. This scheduling
scheme enhance throughput of the whole network by equalizing traffic among
GWs. However, the scheduling scheme may increase computation complexity.