43,311 research outputs found
Delay Considerations for Opportunistic Scheduling in Broadcast Fading Channels
We consider a single-antenna broadcast block fading
channel with n users where the transmission is packetbased.
We define the (packet) delay as the minimum number of channel uses that guarantees all n users successfully receive m packets. This is a more stringent notion of delay than average delay and is the worst case (access) delay among the users. A delay optimal scheduling scheme, such as round-robin, achieves the delay of mn. For the opportunistic scheduling (which is throughput optimal) where the transmitter sends the packet to the user with the best channel conditions at each channel use, we derive the mean and variance of the delay for any m and n. For large n and in a homogeneous network, it is proved that the expected delay in receiving one packet by all the receivers scales as n log n, as opposed to n for the round-robin scheduling. We also show that when m grows faster than (log n)^r, for some r > 1, then the delay scales as mn. This roughly determines the timescale required for the system to behave fairly in a homogeneous network. We then propose a scheme to significantly reduce the delay at the expense of a small throughput hit. We further look into the advantage of multiple transmit antennas on the delay. For a system with M antennas in the transmitter where at each channel use packets are sent to M different users, we obtain the expected delay in receiving one packet by all the users
Secure Communications for the Two-user Broadcast Channel with Random Traffic
In this work, we study the stability region of the two-user broadcast channel
(BC) with bursty data arrivals and security constraints. We consider the
scenario, where one of the receivers has a secrecy constraint and its packets
need to be kept secret from the other receiver. This is achieved by employing
full-duplexing at the receiver with the secrecy constraint, so that it
transmits a jamming signal to impede the reception of the other receiver. In
this context, the stability region of the two-user BC is characterized for the
general decoding case. Then, assuming two different decoding schemes the
respective stability regions are derived. The effect of self-interference due
to the full-duplex operation on the stability region is also investigated. The
stability region of the BC with a secrecy constraint, where the receivers do
not have full duplex capability can be obtained as a special case of the
results derived in this paper. In addition, the paper considers the problem of
maximizing the saturated throughput of the queue, whose packets does not
require to be kept secret under minimum service guarantees for the other queue.
The results provide new insights on the effect of the secrecy constraint on the
stability region of the BC. In particular, it is shown that the stability
region with secrecy constraint is sensitive to the coefficient of
self-interference cancelation under certain cases.Comment: Submitted for journal publicatio
Wireless Network-Level Partial Relay Cooperation: A Stable Throughput Analysis
In this work, we study the benefit of partial relay cooperation. We consider
a two-node system consisting of one source and one relay node transmitting
information to a common destination. The source and the relay have external
traffic and in addition, the relay is equipped with a flow controller to
regulate the incoming traffic from the source node. The cooperation is
performed at the network level. A collision channel with erasures is
considered. We provide an exact characterization of the stability region of the
system and we also prove that the system with partial cooperation is always
better or at least equal to the system without the flow controller.Comment: Submitted for journal publication. arXiv admin note: text overlap
with arXiv:1502.0113
Interference-Based Optimal Power-Efficient Access Scheme for Cognitive Radio Networks
In this paper, we propose a new optimization-based access strategy of
multipacket reception (MPR) channel for multiple secondary users (SUs)
accessing the primary user (PU) spectrum opportunistically. We devise an
analytical model that realizes the multipacket access strategy of SUs that
maximizes the throughput of individual backlogged SUs subject to queue
stability of the PU. All the network receiving nodes have MPR capability. We
aim at maximizing the throughput of the individual SUs such that the PU's queue
is maintained stable. Moreover, we are interested in providing an
energy-efficient cognitive scheme. Therefore, we include energy constraints on
the PU and SU average transmitted energy to the optimization problem. Each SU
accesses the medium with certain probability that depends on the PU's activity,
i.e., active or inactive. The numerical results show the advantage in terms of
SU throughput of the proposed scheme over the conventional access scheme, where
the SUs access the channel randomly with fixed power when the PU is sensed to
be idle
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