  Machine-to-Machine (M2M) communications have been introduced to improve the
communication capacity in dense wireless networks. One of the most important
concerns for network designers is maintaining the high performance of the
network when the quality of connections between sources and their destinations
is poor. Thus the careful selection of relays between data sources and their
destinations is a very important issue. The possibility of simultaneous use of
different Radio Frequency (RF) interfaces for transmitting data, which
communication devices are equipped with them, can increase the capacity of data
transmission over the network. In this paper, two novel M2M relay selection
algorithms are proposed, named as Optimal Relay Selection Algorithm (ORSA) and
Matching based Relay Selection Algorithm (MRSA). ORSA is a centralized
algorithm for the optimal selection of relays by transforming the main problem
to a k-cardinality assignment problem that can be solved using the Hungarian
algorithm. MRSA is a distributed algorithm that leverages concepts from
matching theory to provide a stable solution for the relay selection problem.
In both proposed algorithms static RF interfaces usage is applied to enable
simultaneous use of different interfaces for data transmission. The simulations
show that ORSA is optimally solving the relay selection problem. MRSA has an
optimal stable result, that when there is no restriction on the number of
channels, is only about 1% lower than ORSA. Besides, MRSA provides better
results than direct transmission Without any Relay Selection Algorithm (WRSA)
and Random Relay Selection Algorithm (RRSA), about 15% and 98%, respectively.
