  The growing popularity of Machine-to-Machine (M2M) communications in cellular
networks is driving the need to optimize networks based on the characteristics
of M2M, which are significantly different from the requirements that current
networks are designed to meet. First, M2M requires large number of short
sessions as opposed to small number of long lived sessions required by the
human generated traffic. Second, M2M constitutes a number of battery operated
devices that are static in locations such as basements and tunnels, and need to
transmit at elevated powers compared to the traditional devices. Third,
replacing or recharging batteries of such devices may not be feasible. All
these differences highlight the importance of a systematic framework to study
the power and energy optimal system design in the regime of interest for M2M,
which is the main focus of this paper. For a variety of coordinated and
uncoordinated transmission strategies, we derive results for the optimal
transmit power, energy per bit, and the maximum load supported by the base
station, leading to the following design guidelines: (i) frequency division
multiple access (FDMA), including equal bandwidth allocation, is sum-power
optimal in the asymptotically low spectral efficiency regime, (ii) while FDMA
is the best practical strategy overall, uncoordinated code division multiple
access (CDMA) is almost as good when the base station is lightly loaded, (iii)
the value of optimization within FDMA is in general not significant in the
regime of interest for M2M.
