78 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
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
Dynamic Non-Orthogonal Multiple Access (NOMA) and Orthogonal Multiple Access (OMA) in 5G Wireless Networks
In this paper, facilitated via the flexible software defined structure of the
radio access units in 5G, we propose a novel dynamic multiple access technology
selection among orthogonal multiple access (OMA) and non-orthogonal multiple
access (NOMA) techniques for each subcarrier. For this setup, we formulate a
joint resource allocation problem where a new set of access technology
selection parameters along with power and subcarrier are allocated for each
user based on each user's channel state information. Here, we define a novel
utility function taking into account the rate and costs of access technologies.
This cost reflects both the complexity of performing successive interference
cancellation and the complexity incurred to guarantee a desired bit error rate.
This utility function can inherently demonstrate the trade-off between OMA and
NOMA. Due to non-convexity of our proposed resource allocation problem, we
resort to successive convex approximation where a two-step iterative algorithm
is applied in which a problem of the first step, called access technology
selection, is transformed into a linear integer programming problem, and the
nonconvex problem of the second step, referred to power allocation problem, is
solved via the difference-of-convex-functions (DC) programming. Moreover, the
closed-form solution for power allocation in the second step is derived. For
diverse network performance criteria such as rate, simulation results show that
the proposed new dynamic access technology selection outperforms
single-technology OMA or NOMA multiple access solutions.Comment: 28 pages, 6 figure
On the performance of multi-packet HARQ protocols in NOMA systems
In this paper, we investigate the throughput performance of single-packet and multi-packet hybrid-automatic repeat request (HARQ) with blanking for downlink non-orthogonal multiple access (NOMA) systems. While conventional single-packet HARQ achieves high throughput at the expense of high latency, multi-packet HARQ, where several data packets are sent in the same channel block, can achieve high throughput with low latency. Previous works have shown that multi-packet HARQ outperforms single-packet HARQ in orthogonal multiple access (OMA) systems, especially in the moderate to high signal-to-noise ratio regime. This work amalgamates multi-packet HARQ with NOMA to achieve higher throughput than the conventional single-packet HARQ and OMA, which has been adopted in the legacy mobile networks. We conduct theoretical analysis for the throughput per user and also investigate the optimization of the power and rate allocations of the packets, in order to maximize the weighted-sum throughput. It is demonstrated that the gain of multi-packet HARQ over the single-packet HARQ in NOMA systems is reduced compared to that obtained in OMA systems due to inter-user interference. It is also shown that NOMA-HARQ cannot achieve any throughput gain with respect to OMA-HARQ when the error propagation rate of the NOMA detector is above a certain threshold
Dynamic non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) in 5G wireless networks
In this paper, a novel dynamic multiple access
technology selection among orthogonal multiple access (OMA)
and non-orthogonal multiple access (NOMA) techniques is proposed. For this setup, a joint resource allocation problem is
formulated in which a new set of access technology selection
parameters along with power and subcarrier are allocated for
each user based on each user’s channel state information. Here,
a novel utility function is defined to take into account the
rate and costs of access technologies. This cost reflects both
the complexity of performing successive interference cancellation
and the complexity incurred to guarantee a desired bit error
rate. This utility function can inherently capture the tradeoff
between OMA and NOMA. Due to non-convexity of the proposed
resource allocation problem, a successive convex approximation
is developed in which a two-step iterative algorithm is applied. In
the first step, called access technology selection, the problem is
transformed into a linear integer programming problem, and
then, in the second step, a nonconvex problem, referred to
power allocation problem, is solved via the difference-of-convexfunctions (DC) programming. Moreover, the closed-form solution
for power allocation in the second step is derived. For diverse
network performance criteria such as rate, simulation results
show that the proposed new dynamic access technology selection
outperforms single-technology OMA or NOMA multiple access
solutions
Outage Performance and Optimal Design of MIMO-NOMA Enhanced Small Cell Networks With Imperfect Channel-State Information
This paper focuses on boosting the performance of small cell networks (SCNs)
by integrating multiple-input multiple-output (MIMO) and non-orthogonal
multiple access (NOMA) in consideration of imperfect channel-state information
(CSI). The estimation error and the spatial randomness of base stations (BSs)
are characterized by using Kronecker model and Poisson point process (PPP),
respectively. The outage probabilities of MIMO-NOMA enhanced SCNs are first
derived in closed-form by taking into account two grouping policies, including
random grouping and distance-based grouping. It is revealed that the average
outage probabilities are irrelevant to the intensity of BSs in the
interference-limited regime, while the outage performance deteriorates if the
intensity is sufficiently low. Besides, as the channel uncertainty lessens, the
asymptotic analyses manifest that the target rates must be restricted up to a
bound to achieve an arbitrarily low outage probability in the absence of the
inter-cell interference.Moreover, highly correlated estimation error
ameliorates the outage performance under a low quality of CSI, otherwise it
behaves oppositely. Afterwards, the goodput is maximized by choosing
appropriate precoding matrix, receiver filters and transmission rates. In the
end, the numerical results verify our analysis and corroborate the superiority
of our proposed algorithm
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