331 research outputs found
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
On the Performance Gain of NOMA over OMA in Uplink Single-cell Systems
In this paper, we investigate the performance gain of non-orthogonal multiple
access (NOMA) over orthogonal multiple access (OMA) in uplink single-cell
systems. In both single-antenna and multi-antenna scenarios, the performance
gain of NOMA over OMA in terms of asymptotic ergodic sum-rate is analyzed for a
sufficiently large number of users. In particular, in single-antenna systems,
we identify two types of near-far gains brought by NOMA: 1) the large-scale
near-far gain via exploiting the large-scale fading increases with the cell
size; 2) the small-scale near-far gain via exploiting the small-scale fading is
a constant given by nat/s/Hz in Rayleigh fading channels.
Furthermore, we have analyzed that the performance gain achieved by
single-antenna NOMA can be amplified via increasing the number of antennas
equipped at the base station due to the extra spatial degrees of freedom. The
numerical results confirm the accuracy of the derived analyses and unveil the
performance gains of NOMA over OMA in different scenarios.Comment: 7 pages, 5 figure
On the Performance of Network NOMA in Uplink CoMP Systems: A Stochastic Geometry Approach
To improve the system throughput, this paper proposes a network
non-orthogonal multiple access (N-NOMA) technique for the uplink coordinated
multi-point transmission (CoMP). In the considered scenario, multiple base
stations collaborate with each other to serve a single user, referred to as the
CoMP user, which is the same as for conventional CoMP. However, unlike
conventional CoMP, each base station in N-NOMA opportunistically serves an
extra user, referred to as the NOMA user, while serving the CoMP user at the
same bandwidth. The CoMP user is typically located at the cell-edge, whereas
users close to the base stations are scheduled as NOMA users. Hence, the
channel conditions of the two kind of users are very distinctive, which
facilitates the implementation of NOMA. Compared to the conventional orthogonal
multiple access based CoMP scheme, where multiple base stations serve a single
CoMP user only, the proposed N-NOMA scheme can support larger connectivity by
serving the extra NOMA users, and improve the spectral efficiency by avoiding
the CoMP user solely occupying the spectrum. A stochastic geometry approach is
applied to model the considered N-NOMA scenario as a Poisson cluster process,
based on which closed-form analytical expressions for outage probabilities and
ergodic rates are obtained. Numerical results are presented to show the
accuracy of the analytical results and also demonstrate the superior
performance of the proposed N-NOMA scheme
Uplink Cooperative NOMA for Cellular-Connected UAV
Aerial-ground interference mitigation is a challenging issue in the
cellular-connected unmanned aerial vehicle (UAV) communications. Due to the
strong line-of-sight (LoS) air-to-ground (A2G) channels, the UAV may
impose/suffer more severe uplink/downlink interference to/from the cellular
base stations (BSs) than the ground users. To tackle this challenge, we propose
to apply the non-orthogonal multiple access (NOMA) technique to the uplink
communication from a UAV to cellular BSs, under spectrum sharing with the
existing ground users. However, for our considered system, traditional NOMA
with local interference cancellation (IC), termed non-cooperative NOMA, may
provide very limited gain compared to the OMA. This is because there are many
co-channel BSs due to the LoS A2G channels and thus the UAV's rate performance
is severely limited by the BS with the worst channel condition with the UAV. To
improve the UAV's achievable rate, a new cooperative NOMA scheme is proposed by
exploiting the backhaul links among BSs. Specifically, some BSs with better
channel conditions are selected to decode the UAV's signals first, and then
forward the decoded signals to their backhaul-connected BSs for IC. To
investigate the optimal design of cooperative NOMA, we maximize the weighted
sum-rate of the UAV and ground users by jointly optimizing the UAV's rate and
power allocations over multiple resource blocks. However, this problem is hard
to be solved optimally. To obtain useful insights, we first consider two
special cases with egoistic and altruistic transmission strategies of the UAV,
respectively, and solve their corresponding problems optimally. Next, we
consider the general case and propose an efficient suboptimal solution via the
alternating optimization. Numerical results show that the proposed cooperative
NOMA yields significant throughput gains than the OMA and the non-cooperative
NOMA benchmark.Comment: 13 pages, 6 figures. Accepted for publication in IEEE JSTSP. arXiv
admin note: text overlap with arXiv:1807.0821
Full-Duplex Non-Orthogonal Multiple Access for Modern Wireless Networks
Non-orthogonal multiple access (NOMA) is an interesting concept to provide
higher capacity for future wireless communications. In this article, we
consider the feasibility and benefits of combining full-duplex operation with
NOMA for modern communication systems. Specifically, we provide a comprehensive
overview on application of full-duplex NOMA in cellular networks, cooperative
and cognitive radio networks, and characterize gains possible due to
full-duplex operation. Accordingly, we discuss challenges, particularly the
self-interference and inter-user interference and provide potential solutions
to interference mitigation and quality-of-service provision based on
beamforming, power control, and link scheduling. We further discuss future
research challenges and interesting directions to pursue to bring full-duplex
NOMA into maturity and use in practice.Comment: Revised, IEEE Wireless Communication Magazin
On User Pairing in NOMA Uplink
User pairing in Non-Orthogonal Multiple-Access (NOMA) uplink based on channel
state information is investigated considering some predefined power allocation
schemes. The base station divides the set of users into disjunct pairs and
assigns the available resources to these pairs. The combinatorial problem of
user pairing to achieve the maximum sum rate is analyzed in the large system
limit for various scenarios, and some optimum and sub-optimum algorithms with a
polynomial-time complexity are proposed. In the first scenario, users and
the base station have a single-antenna and communicate over subcarriers.
The performance of optimum pairing is derived for and
shown to be superior to random pairing and orthogonal multiple access
techniques. In the second setting, a novel NOMA scheme for a multi-antenna base
station and single carrier communication is proposed. In this case, the users
need not be aware of the pairing strategy. Furthermore, the proposed NOMA
scheme is generalized to multi-antenna users. It is shown that random and
optimum user pairing perform similarly in the large system limit, but optimum
pairing is significantly better in finite dimensions. It is shown that the
proposed NOMA scheme outperforms a previously proposed NOMA scheme with signal
alignment.Comment: Submitted to Transaction on Wireless Communication
Energy-Efficient Joint User-RB Association and Power Allocation for Uplink Hybrid NOMA-OMA
In this paper, energy efficient resource allocation is considered for an
uplink hybrid system, where non-orthogonal multiple access (NOMA) is integrated
into orthogonal multiple access (OMA). To ensure the quality of service for the
users, a minimum rate requirement is pre-defined for each user. We formulate an
energy efficiency (EE) maximization problem by jointly optimizing 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 resource blocks (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, we first derive the feasibility
condition. If feasible, a low-complexity algorithm is proposed, which obtains
optimal EE under any successive interference cancellation (SIC) order and an
arbitrary number of users. In addition, for the special case of two users per
cluster, analytical solutions are provided for the two SIC orders,
respectively. These solutions shed light on how the power is allocated for each
user to maximize the EE. Numerical results are presented, which show that the
proposed joint user-RB association and power allocation algorithm outperforms
other hybrid multiple access based and OMA-based schemes.Comment: Non-orthogonal multiple access (NOMA), energy efficiency (EE), power
allocation (PA), uplink transmissio
Energy-efficient techniques for combating the influence of reactive jamming using Non-Orthogonal Multiple Access and Distributed Antenna Systems
The aim of this work is to propose new approaches for maximizing the energy
efficiency of downlink 5G mobile communication systems, in the presence of a
reactive jammer. The concepts of non-orthogonal multiple access (NOMA) and
distributed antenna systems (DAS) are exploited to devise joint subband, power
and antenna assignment techniques, so as to guarantee a certain quality of
service (QoS) to users. Also, the scheduler relies on jamming statistics,
observed at the end of each timeslot, to perform resource allocation based on
the prediction of the jammer behavior over the next timeslot. A particular care
is given, in the proposed techniques, to maintain a moderate complexity at the
receiver level, and to limit the number of active RRHs (remote radio heads) in
the cell. Simulation results show that a proper combination of NOMA with DAS
can allow a significant enhancement of the system robustness to jamming, with
respect to centralized antenna systems and orthogonal multiple access.Comment: Accepted conference pape
Uplink Non-Orthogonal Multiple Access for 5G Wireless Networks
Orthogonal Frequency Division Multiple Access (OFDMA) as well as other
orthogonal multiple access techniques fail to achieve the system capacity limit
in the uplink due to the exclusivity in resource allocation. This issue is more
prominent when fairness among the users is considered in the system. Current
Non-Orthogonal Multiple Access (NOMA) techniques introduce redundancy by
coding/spreading to facilitate the users' signals separation at the receiver,
which degrade the system spectral efficiency. Hence, in order to achieve higher
capacity, more efficient NOMA schemes need to be developed. In this paper, we
propose a NOMA scheme for uplink that removes the resource allocation
exclusivity and allows more than one user to share the same subcarrier without
any coding/spreading redundancy. Joint processing is implemented at the
receiver to detect the users' signals. However, to control the receiver
complexity, an upper limit on the number of users per subcarrier needs to be
imposed. In addition, a novel subcarrier and power allocation algorithm is
proposed for the new NOMA scheme that maximizes the users' sum-rate. The
link-level performance evaluation has shown that the proposed scheme achieves
bit error rate close to the single-user case. Numerical results show that the
proposed NOMA scheme can significantly improve the system performance in terms
of spectral efficiency and fairness comparing to OFDMA.Comment: Presented in the International Symposium on Wireless Communications
Systems (ISWCS), 201
A Fair Power Allocation Approach to NOMA in Multi-user SISO Systems
A non-orthogonal multiple access (NOMA) approach that always outperforms
orthogonal multiple access (OMA) called Fair-NOMA is introduced. In Fair-NOMA,
each mobile user is allocated its share of the transmit power such that its
capacity is always greater than or equal to the capacity that can be achieved
using OMA. For any slow-fading channel gains of the two users, the set of
possible power allocation coefficients are derived. For the infimum and
supremum of this set, the individual capacity gains and the sum-rate capacity
gain are derived. It is shown that the ergodic sum-rate capacity gain
approaches 1 b/s/Hz when the transmit power increases for the case when pairing
two random users with i.i.d. channel gains. The outage probability of this
approach is derived and shown to be better than OMA.
The Fair-NOMA approach is applied to the case of pairing a near base-station
user and a cell-edge user and the ergodic capacity gap is derived as a function
of total number of users in the cell at high SNR. This is then compared to the
conventional case of fixed-power NOMA with user-pairing. Finally, Fair-NOMA is
extended to users and prove that the capacity can always be improved for
each user, while using less than the total transmit power required to achieve
OMA capacities per user.Comment: This paper has been accepted for publication in the IEEE Transactions
of Vehicular Technology; 12 pages, 6 figure
- …