644 research outputs found
Cognitive Interference Management in Retransmission-Based Wireless Networks
Cognitive radio methodologies have the potential to dramatically increase the
throughput of wireless systems. Herein, control strategies which enable the
superposition in time and frequency of primary and secondary user transmissions
are explored in contrast to more traditional sensing approaches which only
allow the secondary user to transmit when the primary user is idle. In this
work, the optimal transmission policy for the secondary user when the primary
user adopts a retransmission based error control scheme is investigated. The
policy aims to maximize the secondary users' throughput, with a constraint on
the throughput loss and failure probability of the primary user. Due to the
constraint, the optimal policy is randomized, and determines how often the
secondary user transmits according to the retransmission state of the packet
being served by the primary user. The resulting optimal strategy of the
secondary user is proven to have a unique structure. In particular, the optimal
throughput is achieved by the secondary user by concentrating its transmission,
and thus its interference to the primary user, in the first transmissions of a
primary user packet. The rather simple framework considered in this paper
highlights two fundamental aspects of cognitive networks that have not been
covered so far: (i) the networking mechanisms implemented by the primary users
(error control by means of retransmissions in the considered model) react to
secondary users' activity; (ii) if networking mechanisms are considered, then
their state must be taken into account when optimizing secondary users'
strategy, i.e., a strategy based on a binary active/idle perception of the
primary users' state is suboptimal.Comment: accepted for publication on Transactions on Information Theor
Maximum Throughput of a Secondary User Cooperating with an Energy-Aware Primary User
This paper proposes a cooperation protocol between a secondary user (SU) and
a primary user (PU) which dedicates a free frequency subband for the SU if
cooperation results in energy saving. Time is slotted and users are equipped
with buffers. Under the proposed protocol, the PU releases portion of its
bandwidth for secondary transmission. Moreover, it assigns a portion of the
time slot duration for the SU to relay primary packets and achieve a higher
successful packet reception probability at the primary receiver. We assume that
the PU has three states: idle, forward, and retransmission states. At each of
these states, the SU accesses the channel with adaptive transmission
parameters. The PU cooperates with the SU if and only if the achievable average
number of transmitted primary packets per joule is higher than the number of
transmitted packets per joule when it operates alone. The numerical results
show the beneficial gains of the proposed cooperative cognitive protocol.Comment: Accepted WiOpt 201
Cognitive Access Policies under a Primary ARQ process via Forward-Backward Interference Cancellation
This paper introduces a novel technique for access by a cognitive Secondary
User (SU) using best-effort transmission to a spectrum with an incumbent
Primary User (PU), which uses Type-I Hybrid ARQ. The technique leverages the
primary ARQ protocol to perform Interference Cancellation (IC) at the SU
receiver (SUrx). Two IC mechanisms that work in concert are introduced: Forward
IC, where SUrx, after decoding the PU message, cancels its interference in the
(possible) following PU retransmissions of the same message, to improve the SU
throughput; Backward IC, where SUrx performs IC on previous SU transmissions,
whose decoding failed due to severe PU interference. Secondary access policies
are designed that determine the secondary access probability in each state of
the network so as to maximize the average long-term SU throughput by
opportunistically leveraging IC, while causing bounded average long-term PU
throughput degradation and SU power expenditure. It is proved that the optimal
policy prescribes that the SU prioritizes its access in the states where SUrx
knows the PU message, thus enabling IC. An algorithm is provided to optimally
allocate additional secondary access opportunities in the states where the PU
message is unknown. Numerical results are shown to assess the throughput gain
provided by the proposed techniques.Comment: 16 pages, 11 figures, 2 table
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
Optimal Random Access and Random Spectrum Sensing for an Energy Harvesting Cognitive Radio with and without Primary Feedback Leveraging
We consider a secondary user (SU) with energy harvesting capability. We
design access schemes for the SU which incorporate random spectrum sensing and
random access, and which make use of the primary automatic repeat request (ARQ)
feedback. We study two problem-formulations. In the first problem-formulation,
we characterize the stability region of the proposed schemes. The sensing and
access probabilities are obtained such that the secondary throughput is
maximized under the constraints that both the primary and secondary queues are
stable. Whereas in the second problem-formulation, the sensing and access
probabilities are obtained such that the secondary throughput is maximized
under the stability of the primary queue and that the primary queueing delay is
kept lower than a specified value needed to guarantee a certain quality of
service (QoS) for the primary user (PU). We consider spectrum sensing errors
and assume multipacket reception (MPR) capabilities. Numerical results show the
enhanced performance of our proposed systems.Comment: ACCEPTED in EAI Endorsed Transactions on Cognitive Communications.
arXiv admin note: substantial text overlap with arXiv:1208.565
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)
Access Policy Design for Cognitive Secondary Users under a Primary Type-I HARQ Process
In this paper, an underlay cognitive radio network that consists of an
arbitrary number of secondary users (SU) is considered, in which the primary
user (PU) employs Type-I Hybrid Automatic Repeat Request (HARQ). Exploiting the
redundancy in PU retransmissions, each SU receiver applies forward interference
cancelation to remove a successfully decoded PU message in the subsequent PU
retransmissions. The knowledge of the PU message state at the SU receivers and
the ACK/NACK message from the PU receiver are sent back to the transmitters.
With this approach and using a Constrained Markov Decision Process (CMDP) model
and Constrained Multi-agent MDP (CMMDP), centralized and decentralized optimum
access policies for SUs are proposed to maximize their average sum throughput
under a PU throughput constraint. In the decentralized case, the channel access
decision of each SU is unknown to the other SU. Numerical results demonstrate
the benefits of the proposed policies in terms of sum throughput of SUs. The
results also reveal that the centralized access policy design outperforms the
decentralized design especially when the PU can tolerate a low average long
term throughput. Finally, the difficulties in decentralized access policy
design with partial state information are discussed
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