737 research outputs found
Resource allocation for NOMA wireless systems
Power-domain non-orthogonal multiple access (NOMA) has been widely recognized as
a promising candidate for the next generation of wireless communication systems. By
applying superposition coding at the transmitter and successive interference cancellation
at the receiver, NOMA allows multiple users to access the same time-frequency resource
in power domain. This way, NOMA not only increases the system’s spectral and energy
efficiencies, but also supports more users when compared with the conventional orthogonal
multiple access (OMA). Meanwhile, improved user fairness can be achieved by NOMA.
Nonetheless, the promised advantages of NOMA cannot be realized without proper
resource allocation. The main resources in wireless communication systems include time,
frequency, space, code and power. In NOMA systems, multiple users are accommodated
in each time/frequency/code resource block (RB), forming a NOMA cluster. As a result,
how to group the users into NOMA clusters and allocate the power is of significance. A
large number of studies have been carried out for developing efficient power allocation
(PA) algorithms in single-input single-output (SISO) scenarios with fixed user clustering.
To fully reap the gain of NOMA, the design of joint PA and user clustering is required.
Moreover, the study of PA under multiple-input multiple-output (MIMO) systems still
remains at an incipient stage. In this dissertation, we develop novel algorithms to allocate
resource for both SISO-NOMA and MIMO-NOMA systems.
More specifically, Chapter 2 compares the system capacity of MIMO-NOMA with
MIMO-OMA. It is proved analytically that MIMO-NOMA outperforms MIMO-OMA in terms of both sum channel capacity and ergodic sum capacity when there are multiple
users in a cluster. Furthermore, it is demonstrated that the more users are admitted to
a cluster, the lower is the achieved sum rate, which illustrates the tradeoff between the
sum rate and maximum number of admitted users.
Chapter 3 addresses the PA problem for a general multi-cluster multi-user MIMONOMA
system to maximize the system energy efficiency (EE). First, a closed-form solution
is derived for the corresponding sum rate (SE) maximization problem. Then, the EE
maximization problem is solved by applying non-convex fractional programming.
Chapter 4 investigates the energy-efficient joint user-RB association and PA problem
for an uplink hybrid NOMA-OMA system. The considered problem requires to jointly
optimize the user clustering, channel assignment and power allocation. To address this
hard problem, a many-to-one bipartite graph is first constructed considering the users
and RBs as the two sets of nodes. Based on swap matching, a joint user-RB association
and power allocation scheme is proposed, which converges within a limited number of
iterations. Moreover, for the power allocation under a given user-RB association, a low complexity
optimal PA algorithm is proposed.
Furthermore, Chapter 5 focuses on securing the confidential information of massive
MIMO-NOMA networks by exploiting artificial noise (AN). An uplink training scheme is
first proposed, and on this basis, the base station precodes the confidential information
and injects the AN. Following this, the ergodic secrecy rate is derived for downlink transmission.
Additionally, PA algorithms are proposed to maximize the SE and EE of the
system.
Finally, conclusions are drawn and possible extensions to resource allocation in NOMA
systems are discussed in Chapter 6
Short-Packet Communications for MIMO NOMA Systems over Nakagami-m Fading: BLER and Minimum Blocklength Analysis
Recently, ultra-reliable and low-latency communications (URLLC) using
short-packets has been proposed to fulfill the stringent requirements regarding
reliability and latency of emerging applications in 5G and beyond networks. In
addition, multiple-input multiple-output non-orthogonal multiple access (MIMO
NOMA) is a potential candidate to improve the spectral efficiency, reliability,
latency, and connectivity of wireless systems. In this paper, we investigate
short-packet communications (SPC) in a multiuser downlink MIMO NOMA system over
Nakagami-m fading, and propose two antenna-user selection methods considering
two clusters of users having different priority levels. In contrast to the
widely-used long data-packet assumption, the SPC analysis requires the redesign
of the communication protocols and novel performance metrics. Given this
context, we analyze the SPC performance of MIMO NOMA systems using the average
block error rate (BLER) and minimum blocklength, instead of the conventional
metrics such as ergodic capacity and outage capacity. More specifically, to
characterize the system performance regarding SPC, asymptotic (in the high
signal-to-noise ratio regime) and approximate closed-form expressions of the
average BLER at the users are derived. Based on the asymptotic behavior of the
average BLER, an analysis of the diversity order, minimum blocklength, and
optimal power allocation is carried out. The achieved results show that MIMO
NOMA can serve multiple users simultaneously using a smaller blocklength
compared with MIMO OMA, thus demonstrating the benefits of MIMO NOMA for SPC in
minimizing the transmission latency. Furthermore, our results indicate that the
proposed methods not only improve the BLER performance but also guarantee full
diversity gains for the respective users.Comment: 12 pages, 8 figures. This paper has been submitted to an IEEE journal
for possible publicatio
Capacity Comparison between MIMO-NOMA and MIMO-OMA with Multiple Users in a Cluster
In this paper, the performance of multiple-input multiple-output
non-orthogonal multiple access (MIMO-NOMA) is investigated when multiple users
are grouped into a cluster. The superiority of MIMO-NOMA over MIMO orthogonal
multiple access (MIMO-OMA) in terms of both sum channel capacity and ergodic
sum capacity is proved analytically. Furthermore, it is demonstrated that the
more users are admitted to a cluster, the lower is the achieved sum rate, which
illustrates the tradeoff between the sum rate and maximum number of admitted
users. On this basis, a user admission scheme is proposed, which is optimal in
terms of both sum rate and number of admitted users when the
signal-to-interference-plus-noise ratio thresholds of the users are equal. When
these thresholds are different, the proposed scheme still achieves good
performance in balancing both criteria. Moreover, under certain conditions,it
maximizes the number of admitted users. In addition, the complexity of the
proposed scheme is linear to the number of users per cluster. Simulation
results verify the superiority of MIMO-NOMA over MIMO-OMA in terms of both sum
rate and user fairness, as well as the effectiveness of the proposed user
admission scheme.Comment: accepted IEEE Journal on Selected Topics in Communications, June
2017, Keywords: Non-orthogonal multiple access (NOMA), multiple-input
multiple-output (MIMO), channel capacity, sum rate, fairness, user admission,
power allocatio
On the Performance Gain of NOMA over OMA in Uplink Communication Systems
In this paper, we investigate and reveal the ergodic sum-rate gain (ESG) of
non-orthogonal multiple access (NOMA) over orthogonal multiple access (OMA) in
uplink cellular communication systems. A base station equipped with a
single-antenna, with multiple antennas, and with massive antenna arrays is
considered both in single-cell and multi-cell deployments. In particular, in
single-antenna systems, we identify two types of gains brought about by NOMA:
1) a large-scale near-far gain arising from the distance discrepancy between
the base station and users; 2) a small-scale fading gain originating from the
multipath channel fading. Furthermore, we reveal that the large-scale near-far
gain increases with the normalized cell size, while the small-scale fading gain
is a constant, given by = 0.57721 nat/s/Hz, in Rayleigh fading
channels. When extending single-antenna NOMA to -antenna NOMA, we prove that
both the large-scale near-far gain and small-scale fading gain achieved by
single-antenna NOMA can be increased by a factor of for a large number of
users. Moreover, given a massive antenna array at the base station and
considering a fixed ratio between the number of antennas, , and the number
of users, , the ESG of NOMA over OMA increases linearly with both and
. We then further extend the analysis to a multi-cell scenario. Compared to
the single-cell case, the ESG in multi-cell systems degrades as NOMA faces more
severe inter-cell interference due to the non-orthogonal transmissions.
Besides, we unveil that a large cell size is always beneficial to the ergodic
sum-rate performance of NOMA in both single-cell and multi-cell systems.
Numerical results verify the accuracy of the analytical results derived and
confirm the insights revealed about the ESG of NOMA over OMA in different
scenarios.Comment: 51 pages, 7 figures, invited paper, submitted to IEEE Transactions on
Communication
Performance analysis of spatial modulation aided NOMA with full-duplex relay
A spatial modulation aided non-orthogonal multiple access with full-duplex relay (SM-NOMA-FDR) scheme is proposed for the coordinated direct and relay transmission in this paper. Specifically, the signal of the near user is mapped to an M-ary modulated symbol and the signal of the far user is mapped to an SM symbol. The base station first transmits signals to the near user and relay via SM-NOMA, and then the relay decodes and retransmits the signal of the far user. An SM-assisted FDR is used in this scheme to improve the spectral efficiency while reducing energy consumption and making full use of the antenna resources at the relay, since SM only activates one antenna in each transmission. We derive the ergodic capacity and bit error rate of the proposed scheme over independent Rayleigh fading channels. Numerical results validate the accuracy of the theoretical analysis and show the superior performance of the proposed SM-NOMA-FDR scheme
Performance Analysis of SSK-NOMA
In this paper, we consider the combination between two promising techniques:
space-shift keying (SSK) and non-orthogonal multiple access (NOMA) for future
radio access networks. We analyze the performance of SSK-NOMA networks and
provide a comprehensive analytical framework of SSK-NOMA regarding bit error
probability (BEP), ergodic capacity and outage probability. It is worth
pointing out all analysis also stand for conventional SIMO-NOMA networks. We
derive closed-form exact average BEP (ABEP) expressions when the number of
users in a resource block is equal to i.e., . Nevertheless, we analyze the
ABEP of users when the number of users is more than i.e., , and derive
bit-error-rate (BER) union bound since the error propagation due to iterative
successive interference canceler (SIC) makes the exact analysis intractable.
Then, we analyze the achievable rate of users and derive exact ergodic capacity
of the users so the ergodic sum rate of the system in closed-forms. Moreover,
we provide the average outage probability of the users exactly in the
closed-form. All derived expressions are validated via Monte Carlo simulations
and it is proved that SSK-NOMA outperforms conventional NOMA networks in terms
of all performance metrics (i.e., BER, sum rate, outage). Finally, the effect
of the power allocation (PA) on the performance of SSK-NOMA networks is
investigated and the optimum PA is discussed under BER and outage constraints
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