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Table 1 Non-machine learning-based user clustering schemes in NOMA

From: Towards intelligent user clustering techniques for non-orthogonal multiple access: a survey

Clustering scheme

Related work

Scenario

Assumptions

Objective functions

Application

Findings

Mathematical optimization

[6, 8, 18]

Downlink

CSI is known at base station

Sum rate maximization

MISO

(1) It performs better than random clustering

(2) Jointly user clustering and power allocation

Game-theoretic approach

[9]

Downlink

The channels assumed to be Rician fading

Maximize the energy efficiency

MIMO

Joint user clustering, passive beamforming and power allocation

Matching algorithm

[10]

Downlink

The channels assumed to be Rician fading

Maximize the energy efficiency

RIS assisted NOMA

Joint user clustering, passive beamforming and power allocation

Other user clustering techniques

[12]

Downlink

Users inside a cell are independent of path loss effect

Sum rate maximization

MU-MIMO

To suppress multi-user and inter-symbol interference

 

[13, 14]

Downlink

Assume no inter-cluster interference

Higher spectral efficiency

Massive MIMO

To improve performance by NOMA beamspace with efficient user clustering

 

[15]

Downlink

Location information

is assumed to be known by the UE

Sum rate maximization

5G mm-wave

Location aided clustering approach is used for cluster assignment and improves the performance as compared to other beamforming schemes

 

[16]

Uplink

BS knows perfectly all the channel gains

Reduce system latency

MISO

To solve the problem of user clustering by optimally

resource block allocation with time-based

proportional fairness

 

[17]

Downlink

CSI is known at the

base station, fixed user distances

Improves transmission power

MISO

Iterative power and joint user clustering algorithm reduces the system’s power consumption

 

[19]

Downlink

CSI is known at the base station

Sum rate maximization

SISO

This schemes used Brute Force Search method and improves system performance

 

[20]

Uplink

No intercell interference

from other neighbouring cells

Sum rate

maximization

Narrow band IoT

(1) Joint user clustering and resource allocation of MTC devices

(2) Satisfying the QoS requirements and transmission power in each cluster

 

[21]

Uplink

CSI is known at the base station

Higher spectral efficiency

MISO

Provides optimal solution for decoding order and

power control

 

[11]

Downlink

CSI is known at the base station

Minimize total power consumption

SISO

(1) Consider decoding power consumption

(2) Compressive sensing method is used to solve the convex problem