889 research outputs found
Optimal Cooperative Cognitive Relaying and Spectrum Access for an Energy Harvesting Cognitive Radio: Reinforcement Learning Approach
In this paper, we consider a cognitive setting under the context of
cooperative communications, where the cognitive radio (CR) user is assumed to
be a self-organized relay for the network. The CR user and the PU are assumed
to be energy harvesters. The CR user cooperatively relays some of the
undelivered packets of the primary user (PU). Specifically, the CR user stores
a fraction of the undelivered primary packets in a relaying queue (buffer). It
manages the flow of the undelivered primary packets to its relaying queue using
the appropriate actions over time slots. Moreover, it has the decision of
choosing the used queue for channel accessing at idle time slots (slots where
the PU's queue is empty). It is assumed that one data packet transmission
dissipates one energy packet. The optimal policy changes according to the
primary and CR users arrival rates to the data and energy queues as well as the
channels connectivity. The CR user saves energy for the PU by taking the
responsibility of relaying the undelivered primary packets. It optimally
organizes its own energy packets to maximize its payoff as time progresses
Optimal Spectrum Access for Cognitive Radios
In this paper, we investigate a time-slotted cognitive setting with buffered
primary and secondary users. In order to alleviate the negative effects of
misdetection and false alarm probabilities, a novel design of spectrum access
mechanism is proposed. We propose two schemes. First, the SU senses primary
channel to exploit the periods of silence, if the PU is declared to be idle,
the SU randomly accesses the channel with some access probability .
Second, in addition to accessing the channel if the PU is idle, the SU possibly
accesses the channel if it is declared to be busy with some access probability
. The access probabilities as function of the misdetection, false alarm
and average primary arrival rate are obtained via solving an optimization
problem designed to maximize the secondary service rate given a constraint on
primary queue stability. In addition, we propose a variable sensing duration
schemes where the SU optimizes over the optimal sensing time to achieve the
maximum stable throughput of the network. The results reveal the performance
gains of the proposed schemes over the conventional sensing scheme. We propose
a method to estimate the mean arrival rate and the outage probability of the PU
based on the primary feedback channel, i.e., acknowledgments (ACKs) and
negative-acknowledgments (NACKs) messages.Comment: arXiv admin note: substantial text overlap with arXiv:1206.615
Energy-Efficient Cooperative Cognitive Relaying Schemes for Cognitive Radio Networks
We investigate a cognitive radio network in which a primary user (PU) may
cooperate with a cognitive radio user (i.e., a secondary user (SU)) for
transmissions of its data packets. The PU is assumed to be a buffered node
operating in a time-slotted fashion where the time is partitioned into
equal-length slots. We develop two schemes which involve cooperation between
primary and secondary users. To satisfy certain quality of service (QoS)
requirements, users share time slot duration and channel frequency bandwidth.
Moreover, the SU may leverage the primary feedback message to further increase
both its data rate and satisfy the PU QoS requirements. The proposed
cooperative schemes are designed such that the SU data rate is maximized under
the constraint that the PU average queueing delay is maintained less than the
average queueing delay in case of non-cooperative PU. In addition, the proposed
schemes guarantee the stability of the PU queue and maintain the average energy
emitted by the SU below a certain value. The proposed schemes also provide more
robust and potentially continuous service for SUs compared to the conventional
practice in cognitive networks where SUs transmit in the spectrum holes and
silence sessions of the PUs. We include primary source burstiness, sensing
errors, and feedback decoding errors to the analysis of our proposed
cooperative schemes. The optimization problems are solved offline and require a
simple 2-dimensional grid-based search over the optimization variables.
Numerical results show the beneficial gains of the cooperative schemes in terms
of SU data rate and PU throughput, average PU queueing delay, and average PU
energy savings
Energy-aware cooperative wireless networks with multiple cognitive users
In this paper, we study and analyze cooperative cognitive radio networks with arbitrary number of secondary users (SUs). Each SU is considered a prospective relay for the primary user (PU) besides having its own data transmission demand. We consider a multi-packet transmission framework that allows multiple SUs to transmit simultaneously because of dirty-paper coding. We propose power allocation and scheduling policies that optimize the throughput for both PU and SU with minimum energy expenditure. The performance of the system is evaluated in terms of throughput and delay under different opportunistic relay selection policies. Toward this objective, we present a mathematical framework for deriving stability conditions for all queues in the system. Consequently, the throughput of both primary and secondary links is quantified. Furthermore, a moment generating function approach is employed to derive a closed-form expression for the average delay encountered by the PU packets. Results reveal that we achieve better performance in terms of throughput and delay at lower energy cost as compared with equal power allocation schemes proposed earlier in the literature. Extensive simulations are conducted to validate our theoretical findings
Protocol Design and Stability Analysis of Cooperative Cognitive Radio Users
A single cognitive radio transmitter--receiver pair shares the spectrum with
two primary users communicating with their respective receivers. Each primary
user has a local traffic queue, whereas the cognitive user has three queues;
one storing its own traffic while the other two are relaying queues used to
store primary relayed packets admitted from the two primary users. A new
cooperative cognitive medium access control protocol for the described network
is proposed, where the cognitive user exploits the idle periods of the primary
spectrum bands. Traffic arrival to each relaying queue is controlled using a
tuneable admittance factor, while relaying queues service scheduling is
controlled via channel access probabilities assigned to each queue based on the
band of operation. The stability region of the proposed protocol is
characterized shedding light on its maximum expected throughput. Numerical
results demonstrate the performance gains of the proposed cooperative cognitive
protocol.Comment: Accepted in WCNC 201
Wireless Throughput and Energy Efficiency under QoS Constraints
Mobile data traffic has experienced unprecedented growth recently and is predicted to grow even further over the coming years. As one of the main driving forces behind this growth, wireless transmission of multimedia content has significantly increased in volume and is expected to be the dominant traffic in data communications. Such wireless multimedia traffic requires certain quality-of-service (QoS) guarantees.
With these motivations, in the first part of the thesis, throughput and energy efficiency in fading channels are studied in the presence of randomly arriving data and statistical queueing constraints. In particular, Markovian arrival models including discrete-time Markov, Markov fluid, and Markov-modulated Poisson sources are considered, and maximum average arrival rates in the presence of statistical queueing constraints are characterized. Furthermore, energy efficiency is analyzed by determining the minimum energy per bit and wideband slope in the low signal-to-noise ratio (SNR) regime.
Following this analysis, energy-efficient power adaptation policies in fading channels are studied when data arrivals are modeled as Markovian processes and statistical QoS constraints are imposed. After formulating energy efficiency (EE) as maximum throughput normalized by the total power consumption, optimal power control policies that maximize EE are obtained for different source models.
Next, throughput and energy efficiency of secure wireless transmission of delay sensitive data generated by random sources are investigated. A fading broadcast model in which the transmitter sends confidential and common messages to two receivers is considered. It is assumed that the common and confidential data, generated from Markovian sources, is stored in buffers prior to transmission, and the transmitter operates under constraints on buffer/delay violation probability. Under such statistical QoS constraints, the throughput is determined. In particular, secrecy capacity is used to describe the service rate of buffers containing confidential messages. Moreover, energy efficiency is studied in the low signal-to-noise (SNR) regime.
In the final part of the thesis, throughput and energy efficiency are addressed considering the multiuser channel models. Five different channel models, namely, multiple access, broadcast, interference, relay and cognitive radio channels, are considered. In particular, throughput regions of multiple-access fading channels are characterized when multiple users, experiencing random data arrivals, transmit to a common receiver under statistical QoS constraints. Throughput regions of fading broadcast channels with random data arrivals in the presence of QoS requirements are studied when power control is employed at the transmitter. It is assumed that superposition coding with power control is performed at the transmitter with interference cancellation at the receivers. Optimal power control policies that maximize the weighted combination of the average arrival rates are investigated in the two-user case. Energy efficiency in two-user fading interference channels is studied when the transmitters are operating subject to QoS constraints. Specifically, energy efficiency is characterized by determining the corresponding minimum energy per bit requirements and wideband slope regions. Furthermore, transmission over a half-duplex relay channel with secrecy and QoS constraints is studied. Secrecy throughput is derived for the half duplex two-hop fading relay system operating in the presence of an eavesdropper. Fundamental limits on the energy efficiency of cognitive radio transmissions are analyzed in the presence of statistical quality of service (QoS) constraints. Minimum energy per bit and wideband slope expressions are obtained in order to identify the performance limits in terms of energy efficiency
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
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