678 research outputs found
HARQ Feedback in Spectrum Sharing Networks
This letter studies the throughput and the outage probability of spectrum
sharing networks utilizing hybrid automatic repeat request (HARQ) feedback. We
focus on the repetition time diversity and the incremental redundancy HARQ
protocols where the results are obtained for both continuous and bursting
communication models. The channel data transmission efficiency is investigated
in the presence of both secondary user peak transmission power and primary user
received interference power constraints. Finally, we evaluate the effect of
secondary-primary channel state information imperfection on the performance of
the secondary channel. Simulation results show that, while the throughput is
not necessarily increased by HARQ, substantial outage probability reduction is
achieved in all conditions.Comment: Published in IEEE Communications Letter
On the Average Rate of HARQ-Based Quasi-Static Spectrum Sharing Networks
Spectrum sharing networks are communication setups in which unlicensed secondary users are permitted to work within the spectrum resources of primary licensees. Considering quasi-static fading environments, this paper studies the effect of hybrid automatic repeat request (HARQ) feedback on the average rate of unlicensed spectrum sharing channels. The results are obtained for different scenarios; Under both peak and average secondary user transmission power constraints, the channel average rate is determined under primary user limited received interference power conditions when there is perfect information about the interference available at the secondary user transmitter. An approximate solution for power allocation between incremental redundancy (INR) HARQ-based data retransmissions is proposed which can be applied in single-user networks as well. Then, we investigate the effect of imperfect secondary-primary channel state information on the interference-limited average rate of the secondary channel. Finally, we restudy all mentioned scenarios in the case where the data transmission is constrained to have limited outage probability. Substantial performance improvement is observed with even a single HARQ-based retransmission in all simulations
On the Performance of Millimeter Wave-based RF-FSO Links with HARQ Feedback
This paper studies the performance of hybrid radio-frequency (RF) and
free-space optical (FSO) links in the cases with and without hybrid automatic
repeat request (HARQ). Considering millimeter wave (mmwave) characteristics in
the RF link and pointing errors in the FSO link, we derive closed-form
expressions for the message decoding probabilities as well as the throughput
and the outage probability of the RF-FSO setups. We also evaluate the effect of
various parameters such as power amplifiers efficiency, different transmission
techniques in the FSO link, pointing errors in the FSO link as well as
different coherence times/symbol rates of the RF and the FSO links on the
throughput and outage probability. The results show the efficiency of the
RF-FSO links in different conditions. Moreover, the HARQ can effectively
improve the outage probability/energy efficiency, and compensate the effect of
hardware impairments in RF-FSO links.Comment: Under review in PIMRC'201
Spectrum sharing via HARQ feedback and adaptive power allocation
Recently, substantial attention has been paid to improve the spectral efficiency of communication setups using different spectrum sharing techniques. This paper studies the throughput of spectrum sharing channels utilizing hybrid automatic repeat request (HARQ) protocols. Considering different HARQ schemes, the unlicensed user throughput is obtained under an outage probability constraint for the licensed user. The outage-limited throughput is obtained for both independent and spatially-correlated fading conditions, where there is spatial dependency between the fading coefficients. The results show that, using HARQ and adaptive power allocation, the maximum throughput is achieved by combination of simultaneous transmission and interference-avoiding spectrum sharing paradigms. The performance of the spectrum sharing networks is not sensitive to spatial correlation, within the practical range, and the throughput
changes are negligible at low/moderate correlations. Finally, there is considerable potential for data transmission of the unlicensed user with limited performance degradation of the licensed user
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
Performance of cognitive stop-and-wait hybrid automatic repeat request in the face of imperfect sensing
The cognitive radio (CR) paradigm has the potential of improving the exploitation of the electromagnetic spectrum by detecting instantaneously unoccupied spectrum slots allocated to primary users (PUs). In order to support the process of spectrum reuse, we consider a CR scheme, which senses and opportunistically accesses a PU's spectrum for communication between a pair of nodes relying on the stop-and-wait hybrid automatic repeat request (SW-HARQ) protocol. This arrangement is represented by the cognitive SW-HARQ (CSW-HARQ), where the availability/unavailability of the PU's channel is modeled as a two-state Markov chain having OFF and ON states, respectively. Once the cognitive user (CU) finds that the PU's channel is available (i.e., in the OFF state), the CU transmits data over the PU channel's spectrum, while relying on the principles of SW-HARQ. We investigate both the throughput and the delay of CSW-HARQ, with a special emphasis on the impact of the various system parameters involved in the scenarios of both perfect and imperfect spectrum sensing. Furthermore, we analyze both the throughput as well as the average packet delay and end-to-end packet delay of the CSW-HARQ system. We propose a pair of analytical approaches: 1) the probability-based and 2) the discrete time Markov chain-based. Closed-form expressions are derived for both the throughput and the delay under the perfect and imperfect sensing environments that are validated by simulation. We demonstrate that the activity of PUs, the transmission reliability of the CU, and the sensing environment have a significant impact on both the throughput and the delay of the CR system
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