5,967 research outputs found
Multi-Round Contention in Wireless LANs with Multipacket Reception
Multi-packet reception (MPR) has been recognized as a powerful
capacity-enhancement technique for random-access wireless local area networks
(WLANs). As is common with all random access protocols, the wireless channel is
often under-utilized in MPR WLANs. In this paper, we propose a novel
multi-round contention random-access protocol to address this problem. This
work complements the existing random-access methods that are based on
single-round contention. In the proposed scheme, stations are given multiple
chances to contend for the channel until there are a sufficient number of
``winning" stations that can share the MPR channel for data packet
transmission. The key issue here is the identification of the optimal time to
stop the contention process and start data transmission. The solution
corresponds to finding a desired tradeoff between channel utilization and
contention overhead. In this paper, we conduct a rigorous analysis to
characterize the optimal strategy using the theory of optimal stopping. An
interesting result is that the optimal stopping strategy is a simple
threshold-based rule, which stops the contention process as soon as the total
number of winning stations exceeds a certain threshold. Compared with the
conventional single-round contention protocol, the multi-round contention
scheme significantly enhances channel utilization when the MPR capability of
the channel is small to medium. Meanwhile, the scheme automatically falls back
to single-round contention when the MPR capability is very large, in which case
the throughput penalty due to random access is already small even with
single-round contention
Power-Optimal Feedback-Based Random Spectrum Access for an Energy Harvesting Cognitive User
In this paper, we study and analyze cognitive radio networks in which
secondary users (SUs) are equipped with Energy Harvesting (EH) capability. We
design a random spectrum sensing and access protocol for the SU that exploits
the primary link's feedback and requires less average sensing time. Unlike
previous works proposed earlier in literature, we do not assume perfect
feedback. Instead, we take into account the more practical possibilities of
overhearing unreliable feedback signals and accommodate spectrum sensing
errors. Moreover, we assume an interference-based channel model where the
receivers are equipped with multi-packet reception (MPR) capability.
Furthermore, we perform power allocation at the SU with the objective of
maximizing the secondary throughput under constraints that maintain certain
quality-of-service (QoS) measures for the primary user (PU)
Maximum Throughput of a Cooperative Energy Harvesting Cognitive Radio User
In this paper, we investigate the maximum throughput of a saturated
rechargeable secondary user (SU) sharing the spectrum with a primary user (PU).
The SU harvests energy packets (tokens) from the environment with a certain
harvesting rate. All transmitters are assumed to have data buffers to store the
incoming data packets. In addition to its own traffic buffer, the SU has a
buffer for storing the admitted primary packets for relaying; and a buffer for
storing the energy tokens harvested from the environment. We propose a new
cooperative cognitive relaying protocol that allows the SU to relay a fraction
of the undelivered primary packets. We consider an interference channel model
(or a multipacket reception (MPR) channel model), where concurrent
transmissions can survive from interference with certain probability
characterized by the complement of channel outages. The proposed protocol
exploits the primary queue burstiness and receivers' MPR capability. In
addition, it efficiently expends the secondary energy tokens under the
objective of secondary throughput maximization. Our numerical results show the
benefits of cooperation, receivers' MPR capability, and secondary energy queue
arrival rate on the system performance from a network layer standpoint.Comment: Part of this paper was accepted for publication in PIMRC 201
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
Throughput of a Cognitive Radio Network under Congestion Constraints: A Network-Level Study
In this paper we analyze a cognitive radio network with one primary and one
secondary transmitter, in which the primary transmitter has bursty arrivals
while the secondary node is assumed to be saturated (i.e. always has a packet
waiting to be transmitted). The secondary node transmits in a cognitive way
such that it does not impede the performance of the primary node. We assume
that the receivers have multipacket reception (MPR) capabilities and that the
secondary node can take advantage of the MPR capability by transmitting
simultaneously with the primary under certain conditions. We obtain analytical
expressions for the stationary distribution of the primary node queue and we
also provide conditions for its stability. Finally, we provide expressions for
the aggregate throughput of the network as well as for the throughput at the
secondary node.Comment: Presented at CROWNCOM 201
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