184 research outputs found
Grant-free Radio Access IoT Networks: Scalability Analysis in Coexistence Scenarios
IoT networks with grant-free radio access, like SigFox and LoRa, offer
low-cost durable communications over unlicensed band. These networks are
becoming more and more popular due to the ever-increasing need for ultra
durable, in terms of battery lifetime, IoT networks. Most studies evaluate the
system performance assuming single radio access technology deployment. In this
paper, we study the impact of coexisting competing radio access technologies on
the system performance. Considering \mathpzc K technologies, defined by time
and frequency activity factors, bandwidth, and power, which share a set of
radio resources, we derive closed-form expressions for the successful
transmission probability, expected battery lifetime, and experienced delay as a
function of distance to the serving access point. Our analytical model, which
is validated by simulation results, provides a tool to evaluate the coexistence
scenarios and analyze how introduction of a new coexisting technology may
degrade the system performance in terms of success probability and battery
lifetime. We further investigate solutions in which this destructive effect
could be compensated, e.g., by densifying the network to a certain extent and
utilizing joint reception
Enabling Ultra-Reliable and Low-Latency Communications through Unlicensed Spectrum
© 2018 IEEE. In this article, we aim to address the question of how to exploit the unlicensed spectrum to achieve URLLC. Potential URLLC PHY mechanisms are reviewed and then compared via simulations to demonstrate their potential benefits to URLLC. Although a number of important PHY techniques help with URLLC, the PHY layer exhibits an intrinsic trade-off between latency and reliability, posed by limited and unstable wireless channels. We then explore MAC mechanisms and discuss multi-channel strategies for achieving low-latency LTE unlicensed band access. We demonstrate, via simulations, that the periods without access to the unlicensed band can be substantially reduced by maintaining channel access processes on multiple unlicensed channels, choosing the channels intelligently, and implementing RTS/CTS
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