38 research outputs found
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 NOMA with Hybrid ARQ
In this paper, we investigate the outage performance of hybrid automatic
repeat request with chase combining (HARQ-CC) assisted downlink non-orthogonal
multiple access (NOMA) systems. A closed-form expression of the individual
outage probability and the diversity gain are obtained firstly. Based on the
developed analytical outage probability, a tradeoff between the minimum number
of retransmissions and the transmit power allocation coefficient is then
provided for a given target rate. The provided simulation results demonstrate
the accuracy of the developed analytical results. Moreover, it is shown that
NOMA combined with the HARQ-CC can achieve a significant advantage when only
average channel state information is known at the transmitter. Particularly,
the performance of the user with less transmit power in NOMA systems can be
efficiently improved by utilizing HARQ-CC
Hybrid Automatic Repeat Request for Downlink Rate-Splitting Multiple Access
This work investigates the design of Hybrid Automatic Repeat Request (HARQ)
strategies for downlink Rate-Splitting Multiple Access (RSMA). The existence of
private and common stream as well as their conditioning for Successive
Interference Cancellation (SIC), gives rise to an expanded set of opportunities
for retransmission of failed packets. Specifically, we devise a scheme in which
the retransmissions are scheduled through the common stream, which offers a
higher success probability. With this, the common stream needs to carry both
new and retransmitted bits, which leads to a layered HARQ (L-HARQ) strategy
which is capable of trading off throughput and reliability. Simulation results
demonstrate that the devised HARQ scheme outperforms RSMA with conventional
HARQ, where each retransmission is handled independently through its own
stream. It also helps in closing the throughput gap between HARQ and Adaptive
Modulation and Coding (AMC) in the high Signal-to-Noise Ratio (SNR) regime
while also achieving a decreased Packet Error Rate (PER) and a lower latency
Performance Analysis of Uplink Rate-Splitting Multiple Access with Hybrid ARQ
Rate-splitting multiple access (RSMA) has attracted a lot of attention as a
general and powerful multiple access scheme. In the uplink, instead of encoding
the whole message into one stream, a user can split its message into two parts
and encode them into two streams before transmitting a superposition of these
two streams. The base station (BS) uses successive interference cancellation
(SIC) to decode the streams and reconstruct the original messages. Focusing on
the packet transmission reliability, we investigate the features of RSMA in the
context of hybrid automatic repeat request (HARQ), a well-established mechanism
for enhancing reliability. This work proposes a HARQ scheme for uplink RSMA
with different retransmission times for a two-user scenario and introduces a
power allocation strategy for the two split streams. The results show that
compared with non-orthogonal multiple access (NOMA) and frequency division
multiple access (FDMA), RSMA outperforms them in terms of error probability and
power consumption. The results show that RSMA with HARQ has the potential to
improve the reliability and efficiency of wireless communication systems
Heterogeneous network optimization using robust power-and-resource based algorithm
In order to meet the increasing mobile data-traffic, spatial densification of network with several low-power nodes, the high-power macro BS and HetNet are the major key enabling solution. However, the HetNet is unplanned in nature, causes irregularities and interferences that without any user association rules. The appropriate deployment of the femto-cell in HetNet can provide effective traffic offloading, where the alleviate mobbing in the macro-cells can decrease the power consumption therefore it optimizes the user experience. Moreover, the protection is also important for the macro and femto cell users in a network through maintaining the min-max level of interferences. In this paper, we proposed RPRA that comprises two robust approach such as robust power-controller and the robust channel-allocation approach, which can improve the spectral efficiency and user experiences at lower network coverage areas via eliminating the week coverage zones. Also provide high user rate connection by effective interference in an efficient spectrum, lowering in transmission power and cost-effectiveness via less time delay. To show the effectiveness of our proposed model we have compared with several existing techniques and we got significant improvement in throughput, also reduction in time delay and transmission power