2,806 research outputs found
On the Benefits of Partial Channel State Information for Repetition Protocols in Block Fading Channels
This paper studies the throughput performance of HARQ (hybrid automatic
repeat request) protocols over block fading Gaussian channels. It proposes new
protocols that use the available feedback bit(s) not only to request a
retransmission, but also to inform the transmitter about the instantaneous
channel quality. An explicit protocol construction is given for any number of
retransmissions and any number of feedback bits. The novel protocol is shown to
simultaneously realize the gains of HARQ and of power control with partial CSI
(channel state information). Remarkable throughput improvements are shown,
especially at low and moderate SNR (signal to noise ratio), with respect to
protocols that use the feedback bits for retransmission request only. In
particular, for the case of a single retransmission and a single feedback bit,
it is shown that the repetition is not needed at low \snr where the
throughput improvement is due to power control only. On the other hand, at high
SNR, the repetition is useful and the performance gain comes form a combination
of power control and ability of make up for deep fades.Comment: Accepted for publication on IEEE Transactions on Information Theory;
Presented in parts at ITW 2007 and ICC 200
Optimal Random Access and Random Spectrum Sensing for an Energy Harvesting Cognitive Radio
We consider a secondary user with energy harvesting capability. We design
access schemes for the secondary user which incorporate random spectrum sensing
and random access, and which make use of the primary automatic repeat request
(ARQ) feedback. 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 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. We consider spectrum sensing errors and assume
multipacket reception (MPR) capabilities. Numerical results are presented to
show the enhanced performance of our proposed system over a random access
system, and to demonstrate the benefit of leveraging the primary feedback.Comment: in WiMob 201
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
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
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)
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