Signal Processing - November 2016 - 119

The ith SP firms its demand set. The demand set for SPi is
equal to the index of the FAPs that provides the maximum
utility. If the demand set is not empty, the SP will bid for the
FAP in its demand set; otherwise, the SP will not bid and
remains unmatched.
Then, each FAP will decide if it wants to match with
the SPs. There are three possibilities. The first possibility
is if some FAPs have bids from multiple SPs. The FAP will
increase its price-allocation number by e for the next iteration, that is, the (t + 1)l st iteration. Note that here also e ! R +
represents the price-step number, which indicates the increment of the price-allocation number offer. The second possibility is if a group of the FAPs has a bid from only one SP. In
this case, this group of the FAPs will be matched with this SP.
The third possibility is that some of the FAPs do not receive
any bid from the SPs. In this case they do not change their
price-step number and wait for the next round. The algorithm
ends when there is no new offer.

Cellular machine-to-machine communications network

of this mechanism on the CUs and the CUs' performance
degradation have not been discussed. All these works
are centralized approaches. For the M2M networks with a
large number of MTDs, the centralized schemes will be highly
complex and introduce excessive overhead. In [59], a distributed
resource allocation algorithm for cellular M2M communication
networks is proposed, where all MTD traffic is sent through the
channels allocated to some CUs. They assumed that different MTDs have different requirements. Then they developed
a distributed matching algorithm based on matching theory,
which negotiates between CUs and MTDs and determines
matching from MTDs to CUs. The MTDs will provide monetary compensation to the CUs in exchange for the subchannel
access. Under this framework, the CUs and MTDs are assumed
to be selfish and rational entities, as they are in practical scenarios, and their negotiation results in a stable equilibrium point
such that the sum weighted data rate of all the MTDs is maximized. In the sum weighted data rate, the data rate of an MTD is
weighted according to its priority, and more urgent MTDs will
be given a higher weight.
They considered an OFDMA uplink single-cell scenario
with multiple CUs and one eNB located at the center of the cell
as depicted in Figure 7. All the CUs, MTDs, and the eNB are
equipped with a single omnidirectional antenna. It is assumed
that each MTD has a minimum required data rate and a maximum tolerable delay. A set of orthogonal subchannels are

Machine-to-machine (M2M) communications is a new type
of communications that enables pervasive connectivity
between one or more autonomous machine-type devices
(MTD) without or with minimal human intervention [54].
M2M communication is the key technology to facilitate the
new paradigm of applications, such as smart city, intelligent
transportation, building automation,
eHealth, security, and surveillance.
Cellular networks are currently one
of the most widely deployed wireless
networks with wide coverage, and
they have played an important role in
M2M communications development.
Machine
Surveillance
To fully use the widely deployed comMTD2
Users
MTD1
munications infrastructure, it is beneSatellite
MTD8
ficial and economical to support M2M
CU5
communications by using the existing
cellular networks. In M2M networks,
eNB
there is a massive number of MTD
eHealth
devices, significantly higher than the
number of users in existing cellular netMachine-Type
Machine
CU1
Server
Users
works, each has only a small amount of
MTD7
Smart
traffic, and they are mostly distributed
Security
in the uplink [55].
MTD3
Although some existing cellular
CU4
CU2
Smart
MTD4
MTD6
technologies such as LTE-Advanced
Meters
incorporated some limited M2M feaCU3
tures in their design, there is little
MTD5
progress in addressing these challengAppliances
Appliances
es [56], such as excessive overhead,
delays, and control channel congestion.
To guarantee a minimum required
Smoke
QoS for a large number of MTDs with
Alarm
diverse QoS characteristics in congested areas, [57], [58] developed a 3GPP
access mechanism. However, the effects FIGURE 7. An M2M wireless network configuration [59].
IEEE Signal Processing Magazine

November 2016

119

Table of Contents for the Digital Edition of Signal Processing - November 2016