  The explosive growth in data traffic is resulting in a spectrum crunch
forcing many wireless network operators to look towards refarming their 2G
spectrum and deploy more spectrally efficient Long Term Evolution (LTE)
technology. However, mobile network operators face a challenge when it comes to
spectrum refarming because 2G technologies such as Global System for Mobile
(GSM) is still widely used for low bandwidth machine-to-machine (M2M) devices.
M2M devices typically have long life cycles, e.g. smart meters, and it is
expensive to migrate these devices to newer technology since a truck roll will
typically be required to the site where a device is deployed. Furthermore, with
cost of 2G modules several times less than that of LTE, even newly deployed M2M
devices tend to adopt 2G technology. Nevertheless, operators are keen to either
force their 2G M2M customers to migrate so that they can refarm the spectrum or
set aside a portion of the 2G spectrum for continuing operating 2G and only
refarm the rest for LTE. In this paper we propose a novel solution to provide
GSM connectivity within an LTE carrier through an efficient overlay by
reserving a few physical resource blocks for GSM. With this approach, operators
can refarm their 2G spectrum to LTE efficiently while still providing some GSM
connectivity to their low data rate M2M customers. Furthermore, spectrum can be
dynamically shared between LTE and GSM. An approach similar to that proposed in
this paper can also be applied for other narrow band technology overlays over
LTE.
