222 research outputs found
On Improving Throughput of Multichannel ALOHA using Preamble-based Exploration
Machine-type communication (MTC) has been extensively studied to provide
connectivity for devices and sensors in the Internet-of-Thing (IoT). Thanks to
the sparse activity, random access, e.g., ALOHA, is employed for MTC to lower
signaling overhead. In this paper, we propose to adopt exploration for
multichannel ALOHA by transmitting preambles before transmitting data packets
in MTC, and show that the maximum throughput can be improved by a factor of 2 -
exp(-1) = 1.632, In the proposed approach, a base station (BS) needs to send
the feedback information to active users to inform the numbers of transmitted
preambles in multiple channels, which can be reliably estimated as in
compressive random access. A steady-state analysis is also performed with fast
retrial, which shows that the probability of packet collision becomes lower
and, as a result, the delay outage probability is greatly reduced for a lightly
loaded system. Simulation results also confirm the results from analysis.Comment: 10 pages, 7 figures, to appear in the Journal of Communications and
Networks. arXiv admin note: substantial text overlap with arXiv:2001.1111
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Approaching Fair Collision-Free Channel Access with Slotted ALOHA Using Collaborative Policy-Based Reinforcement Learning
On Throughput Maximization of Grant-Free Access with Reliability-Latency Constraints
Enabling autonomous driving and industrial automation with wireless networks
poses many challenges, which are typically abstracted through reliability and
latency requirements. One of the main contributors to latency in cellular
networks is the reservation-based access, which involves lengthy and
resource-inefficient signaling exchanges. An alternative is to use grant-free
access, in which there is no resource reservation. A handful of recent works
investigated how to fulfill reliability and latency requirements with different
flavors of grant-free solutions. However, the resource efficiency, i.e., the
throughput, has been only the secondary focus. In this work, we formulate the
throughput of grant-free access under reliability-latency constraints, when the
actual number of arrived users or only the arrival distribution are known. We
investigate how these different levels of knowledge about the arrival process
influence throughput performance of framed slotted ALOHA with -multipacket
reception, for the Poisson and Beta arrivals. We show that the throughput under
reliability-latency requirements can be significantly improved for the higher
expected load of the access network, if the actual number of arrived users is
known. This insight motivates the use of techniques for the estimation of the
number of arrived users, as this knowledge is not readily available in
grant-free access. We also asses the impact of estimation error, showing that
for high reliability-latency requirements the gains in throughput are still
considerable.Comment: Accepted for publication in ICC'201
Non-Orthogonal Contention-Based Access for URLLC Devices with Frequency Diversity
We study coded multichannel random access schemes for ultra-reliable
low-latency uplink transmissions. We concentrate on non-orthogonal access in
the frequency domain, where users transmit over multiple orthogonal subchannels
and inter-user collisions limit the available diversity. Two different models
for contention-based random access over Rayleigh fading resources are
investigated. First, a collision model is considered, in which the packet is
replicated onto available resources, of which are received
without collision, and treated as diversity branches by a maximum-ratio
combining (MRC) receiver. The resulting diversity degree depends on the
arrival process and coding strategy. In the second model, the slots subject to
collisions are also used for MRC, such that the number of diversity branches
is constant, but the resulting combined signal is affected by multiple
access interference. In both models, the performance of random and
deterministic repetition coding is compared. The results show that the
deterministic coding approach can lead to a significantly superior performance
when the arrival rate of the intermittent URLLC transmissions is low.Comment: 2019 IEEE 20th International Workshop on Signal Processing Advances
in Wireless Communications (SPAWC) - Special Session on Signal Processing for
NOMA Communication System
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