21 research outputs found
Random Access Schemes in Wireless Systems With Correlated User Activity
Traditional random access schemes are designed based on the aggregate process
of user activation, which is created on the basis of independent activations of
the users. However, in Machine-Type Communications (MTC), some users are likely
to exhibit a high degree of correlation, e.g. because they observe the same
physical phenomenon. This paves the way to devise access schemes that combine
scheduling and random access, which is the topic of this work. The underlying
idea is to schedule highly correlated users in such a way that their
transmissions are less likely to result in a collision. To this end, we propose
two greedy allocation algorithms. Both attempt to maximize the throughput using
only pairwise correlations, but they rely on different assumptions about the
higher-order dependencies. We show that both algorithms achieve higher
throughput compared to the traditional random access schemes, suggesting that
user correlation can be utilized effectively in access protocols for MTC.Comment: Submitted to SPAWC 201
Analysis of the Communication Traffic for Blockchain Synchronization of IoT Devices
Blockchain is a technology uniquely suited to support massive number of
transactions and smart contracts within the Internet of Things (IoT) ecosystem,
thanks to the decentralized accounting mechanism. In a blockchain network, the
states of the accounts are stored and updated by the validator nodes,
interconnected in a peer-to-peer fashion. IoT devices are characterized by
relatively low computing capabilities and low power consumption, as well as
sporadic and low-bandwidth wireless connectivity. An IoT device connects to one
or more validator nodes to observe or modify the state of the accounts. In
order to interact with the most recent state of accounts, a device needs to be
synchronized with the blockchain copy stored by the validator nodes. In this
work, we describe general architectures and synchronization protocols that
enable synchronization of the IoT endpoints to the blockchain, with different
communication costs and security levels. We model and analytically characterize
the traffic generated by the synchronization protocols, and also investigate
the power consumption and synchronization trade-off via numerical simulations.
To the best of our knowledge, this is the first study that rigorously models
the role of wireless connectivity in blockchain-powered IoT systems.Comment: Paper accepted at IEEE International Conference on Communications
(ICC) 201
Traffic Prediction Based Fast Uplink Grant for Massive IoT
This paper presents a novel framework for traffic prediction of IoT devices
activated by binary Markovian events. First, we consider a massive set of IoT
devices whose activation events are modeled by an On-Off Markov process with
known transition probabilities. Next, we exploit the temporal correlation of
the traffic events and apply the forward algorithm in the context of hidden
Markov models (HMM) in order to predict the activation likelihood of each IoT
device. Finally, we apply the fast uplink grant scheme in order to allocate
resources to the IoT devices that have the maximal likelihood for transmission.
In order to evaluate the performance of the proposed scheme, we define the
regret metric as the number of missed resource allocation opportunities. The
proposed fast uplink scheme based on traffic prediction outperforms both
conventional random access and time division duplex in terms of regret and
efficiency of system usage, while it maintains its superiority over random
access in terms of average age of information for massive deployments.Comment: Accepted to IEEE International Symposium on Personal, Indoor and
Mobile Radio Communications (PIMRC) 202
Statistical Multiplexing of Computations in C-RAN with Tradeoffs in Latency and Energy
In the Cloud Radio Access Network (C-RAN) architecture, the baseband signals
from multiple remote radio heads are processed in a centralized baseband unit
(BBU) pool. This architecture allows network operators to adapt the BBU's
computational resources to the aggregate access load experienced at the BBU,
which can change in every air-interface access frame. The degree of savings
that can be achieved by adapting the resources is a tradeoff between savings,
adaptation frequency, and increased queuing time. If the time scale for
adaptation of the resource multiplexing is greater than the access frame
duration, then this may result in additional access latency and limit the
energy savings. In this paper we investigate the tradeoff by considering two
extreme time-scales for the resource multiplexing: (i) long-term, where the
computational resources are adapted over periods much larger than the access
frame durations; (ii) short-term, where the adaption is below the access frame
duration. We develop a general C-RAN queuing model that describes the access
latency and show, for Poisson arrivals, that long-term multiplexing achieves
savings comparable to short-term multiplexing, while offering low
implementation complexity.Comment: Accepted for presentation at the 3rd International Workshop on 5G RAN
Design (ICC 2017
How to Identify and Authenticate Users in Massive Unsourced Random Access
Identification and authentication are two basic functionalities of
traditional random access protocols. In ALOHA-based random access, the packets
usually include a field with a unique user address. However, when the number of
users is massive and relatively small packets are transmitted, the overhead of
including such field becomes restrictive. In unsourced random access (U-RA),
the packets do not include any address field for the user, which maximizes the
number of useful bits that are transmitted. However, by definition an U-RA
protocol does not provide user identification. This paper presents a scheme
that builds upon an underlying U-RA protocol and solves the problem of user
identification and authentication. In our scheme, the users generate a message
authentication code (MAC) that provides these functionalities without violating
the main principle of unsourced random access: the selection of codewords from
a common codebook is i.i.d. among all users