5,019 research outputs found
Power allocation in repetition time diversity hybrid automatic repeat request feedback
This paper addresses the problem of optimal power allocation for hybrid automatic repeat request (HARQ) feedback over slowly-fading channels. We mainly focus on the repetition time diversity HARQ scheme where the results are obtained for both continuous and bursting communication models. Moreover, the effect of an outage probability constraint on the system data transmission efficiency is studied under different transmission power constraints. Simulation results show that 1) for Nakagami fading channels, the optimal HARQ-based (re)transmission powers maximizing the system throughput should be decreasing in every (re)transmission round, 2) higher rates are achieved in the continuous communication, when compared with the bursting model, and 3) HARQ feedback leads to considerable performance improvement even in outage-limited conditions
Green Communication via Power-optimized HARQ Protocols
Recently, efficient use of energy has become an essential research topic for
green communication. This paper studies the effect of optimal power controllers
on the performance of delay-sensitive communication setups utilizing hybrid
automatic repeat request (HARQ). The results are obtained for repetition time
diversity (RTD) and incremental redundancy (INR) HARQ protocols. In all cases,
the optimal power allocation, minimizing the outage-limited average
transmission power, is obtained under both continuous and bursting
communication models. Also, we investigate the system throughput in different
conditions. The results indicate that the power efficiency is increased
substantially, if adaptive power allocation is utilized. For instance, assume
Rayleigh-fading channel, a maximum of two (re)transmission rounds with rates
nats-per-channel-use and an outage probability constraint
. Then, compared to uniform power allocation, optimal power
allocation in RTD reduces the average power by 9 and 11 dB in the bursting and
continuous communication models, respectively. In INR, these values are
obtained to be 8 and 9 dB, respectively.Comment: Accepted for publication on IEEE Transactions on Vehicular Technolog
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
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
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