41 research outputs found
Relay Switching Aided Turbo Coded Hybrid-ARQ for Correlated Fading Channel
Hybrid-Automatic-Repeat-reQuest (HARQ) has become an indispensable technique in reliable communications systems. However, its performance is inevitably affected by the channel’s fading correlation. In this paper, we proposed a novel relay-switching aided HARQ scheme in order to mitigate the detrimental effects of correlated fading without unduly increasing the system’s complexity and delay. Our results show that the proposed relay-switching regime operates efficiently in correlated channels, hence significantly reduces the error floor of turbo-coded HARQ. Additionally, a HARQ scheme using Segment Selective Repeat (SSR) is incorporated in the relay-switching scheme for achieving further improvements. Quantitatively, the proposed relay-switching aided turbo-coded HARQ scheme using SSR may achieve an approximately 2 dB gain, compared to the conventional amplify-and-forward aided turbo coded HARQ arrangement using Chase Combining. Index Terms - Relay switching, correlated fading channel, Hybrid-ARQ, turbo codes, chase combining, incremental redundancy, selective segment repeat
Achievable Diversity Order of HARQ-Aided Downlink NOMA Systems
The combination between non-orthogonal multiple access (NOMA) and hybrid
automatic repeat request (HARQ) is capable of realizing ultra-reliability, high
throughput and many concurrent connections particularly for emerging
communication systems. This paper focuses on characterizing the asymptotic
scaling law of the outage probability of HARQ-aided NOMA systems with respect
to the transmit power, i.e., diversity order. The analysis of diversity order
is carried out for three basic types of HARQ-aided downlink NOMA systems,
including Type I HARQ, HARQ with chase combining (HARQ-CC) and HARQ with
incremental redundancy (HARQ-IR). The diversity orders of three HARQ-aided
downlink NOMA systems are derived in closed-form, where an integration domain
partition trick is developed to obtain the bounds of the outage probability
specially for HARQ-CC and HARQ-IR-aided NOMA systems. The analytical results
show that the diversity order is a decreasing step function of transmission
rate, and full time diversity can only be achieved under a sufficiently low
transmission rate. It is also revealed that HARQ-IR-aided NOMA systems have the
largest diversity order, followed by HARQ-CC-aided and then Type I HARQ-aided
NOMA systems. Additionally, the users' diversity orders follow a descending
order according to their respective average channel gains. Furthermore, we
expand discussions on the cases of power-efficient transmissions and imperfect
channel state information (CSI). Monte Carlo simulations finally confirm our
analysis
On the Performance of the Relay-ARQ Networks
This paper investigates the performance of relay networks in the presence of
hybrid automatic repeat request (ARQ) feedback and adaptive power allocation.
The throughput and the outage probability of different hybrid ARQ protocols are
studied for independent and spatially-correlated fading channels. The results
are obtained for the cases where there is a sum power constraint on the source
and the relay or when each of the source and the relay are power-limited
individually. With adaptive power allocation, the results demonstrate the
efficiency of relay-ARQ techniques in different conditions.Comment: Accepted for publication in IEEE Trans. Veh. Technol. 201
Effective Capacity Analysis of H-ARQ Assisted Cooperative Communication Systems
In this paper, the effective capacity of cooperative communication (CC)
systems with hybrid Automatic repeat request (HARQ) is derived. The derived
expressions are valid for any channel distribution and with any arbitrary
number of retransmissions by the source and relay for both HARQ-repetition
redundancy (RR) and HARQ-incremental redundancy (IR) over asymmetric channels.
As an example, we use the derived EC expression over Rayleigh fading channels.
Several results are obtained for a low rate and signal-to-noise ratio (SNR). We
can see that the EC attends its maximum value with a small number of
retransmissions. As expected when the relay-destination channel has low SNR, it
is better than the relay does not participate especially when we assign a large
number of transitions at the relay. For high data rates and strict quality of
service (QoS) constraints, it is better to increase the number of relay
transmissions. Finally, when we increase the number of source retransmissions,
the effective capacity improves even for low values.Comment: 30 pages, 6 figure