Uplink Power-Domain Non-Orthogonal Multiple Access (NOMA)

2020 ◽  
Vol 12 (4) ◽  
pp. 65-73
Author(s):  
Faeik T. Al Rabee ◽  
Richard D. Gitlin
Keyword(s):  
Channel Estimation ◽  
Interference Cancellation ◽  
Multiple Access ◽  
Signal To Noise Ratio ◽  
Estimation Error ◽  
Channel Estimation Error ◽  
Estimation Errors ◽  
Channel Estimation Errors ◽  
Fifth Generation ◽  
Power Domain

Non-orthogonal multiple access (NOMA) has been proposed as a promising multiple access (MA) technique in order to meet the requirements for fifth generation (5G) communications and to enhance the performance in internet of things (IoT) networks by enabling massive connectivity, high throughput, and low latency. This paper investigates the bit error rate (BER) performance of two-user uplink power-domain NOMA with a successive interference cancellation (SIC) receiver and taking into account channel estimation errors. The analysis considers two scenarios: perfect (ideal) channel estimation and a channel with estimation errors for various modulations schemes, BPSK, QPSK, and 16-QAM. The simulation results show that, as expected, increasing of the modulation level increases the SIC receiver BER. For example, at a signal-to-noise ratio (SNR) of 5 dB for perfect channel estimation and QPSK modulation, the user that is detected first has a BER of 0.005 compared to 0.14 for the user that is detected with the aid of the SIC receiver. Similarly, the BER of QPSK, assuming 0.25 channel estimation error of user 1, is equal to 0.06 at SNR = 15 dB compared to 0.017 for perfect estimation.

scholarly journals ENERGY-EFFICIENT POWER ALLOCATION FOR IMPERFECT CSI DOWNLINK NOMA SYSTEM

2021 ◽  
Vol 11 (2) ◽  
pp. 118-129
Author(s):  
Reem Aldebes ◽  
Kaharudin Dimyati ◽  
Effariza Hanafi
Keyword(s):  
Energy Efficiency ◽  
Channel Estimation ◽  
Outage Probability ◽  
Power Allocation ◽  
Multiple Access ◽  
Estimation Error ◽  
Base Station ◽  
Channel Estimation Error ◽  
Imperfect Csi ◽  
Fifth Generation

The fifth generation (5G) networks must provide the massively increased number of users by thousand times higher data rate at lower power consumption. Thus, optimizing the energy efficiency (EE) becomes an essential issue that has to be researched from the green communication perspective. Non-orthogonal multiple access (NOMA) is considered one of the high potential techniques in fifth-generation systems. This technology is favorable to maximize the energy efficiency and the spectrum efficiency by composing different signals at the same time on the same carrier at different power levels. In this paper, a low complexity power allocation algorithm is proposed in imperfect channel state information (CSI) downlink NOMA cellular system, where obtaining full CSI at the base station is considered a challenge. The proposed algorithm relies on the fact that the allocated power is inversely proportional to the channel strength of the user to implement the successive interference cancellation (SIC) technique at the user terminal to reconstruct the desired signal. The performance of the system is analyzed in terms of energy efficiency and outage probability and compared to the conventional orthogonal multiple access (OMA) system. Results show that the proposed algorithm increases the energy efficiency by about 50% compared to the conventional OMA technology, and an improvement in the outage probability has been achieved. Furthermore, the effect of the error in the channel estimation on the energy efficiency in imperfect CSI NOMA system is evaluated. The simulation shows that the energy efficiency reduces when the channel estimation error increases; and the best performance is achieved in the perfect CSI case where the channel estimation error is zero.

scholarly journals On the Performance of Cognitive Satellite-Terrestrial Relay Networks with Channel Estimation Error and Hardware Impairments

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3292 ◽  
Author(s):  
Kefeng Guo ◽  
Kang An ◽  
Bangning Zhang ◽  
Yuzhen Huang ◽  
Daoxing Guo
Keyword(s):  
Channel Estimation ◽  
Signal To Noise Ratio ◽  
Estimation Error ◽  
Relay Network ◽  
Channel Estimation Error ◽  
High Signal ◽  
Signal To Noise ◽  
Decode And Forward ◽  
Estimation Errors ◽  
Hardware Impairments

This paper investigates the joint impact of channel estimation errors (CEEs) and hardware impairments (HIs) on the performance of a cognitive satellite-terrestrial relay network (CSTRN), where the terrestrial and satellite links are considered following Rayleigh fading and shadowed Rician (SR) fading distributions, respectively. Besides, the terrestrial relay is working in half-duplex decode-and-forward (DF) mode. By employing a general and practical model to account for both the CEEs and HIs at each link, the end-to-end signal-to-noise-plus-distortion-and-error ratio (SNDER) is first obtained for the CSTRN. Then, closed-form expressions for the outage probability (OP) and throughput of the CSTRN are obtained, which allows us to demonstrate the aggregate impact of CEEs and HIs. In order to gain insightful findings, we further elaborate on the asymptotic OP and throughput at the high signal-to-noise-ratio (SNR) condition and quantitatively determine the fundamental performance ceiling. Finally, Monte Carlo (MC) computer simulations are provided to verify the correctness of the analytical results. Besides, with representative numerical analysis’s help, interesting findings are presented.

scholarly journals Uplink Non-Orthogonal Multiple Access with Channel Estimation Errors for Internet of Things Applications

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 912
Author(s):  
Minjoong Rim ◽  
Chung Kang
Keyword(s):  
Internet Of Things ◽  
Channel Estimation ◽  
Communication Systems ◽  
Multiple Access ◽  
Base Station ◽  
Shared Resources ◽  
Estimation Errors ◽  
Channel Estimation Errors ◽  
Pilot Symbols ◽  
Shift Keying

One of the key requirements for next generation wireless or cellular communication systems is to efficiently support a large number of connections for Internet of Things (IoT) applications, and uplink non-orthogonal multiple access (NOMA) schemes can be used for this purpose. In uplink NOMA systems, pilot symbols, as well as data symbols can be superimposed onto shared resources. The error rate performance can be severely degraded due to channel estimation errors, especially when the number of superimposed packets is large. In this paper, we discuss uplink NOMA schemes with channel estimation errors, assuming that quadrature phase shift keying (QPSK) modulation is used. When pilot signals are superimposed onto the shared resources and a large number of devices perform random accesses concurrently to a single resource of the base station, the channels might not be accurately estimated even in high SNR environments. In this paper, we propose an uplink NOMA scheme, which can alleviate the performance degradation due to channel estimation errors.

scholarly journals Robustness of Time Reversal versus All-Rake Transceivers in Multiple Access Channels

2018 ◽  
Vol 2018 ◽  
pp. 1-16
Author(s):  
Luca De Nardis ◽  
Jocelyn Fiorina ◽  
Guido Carlo Ferrante ◽  
Maria-Gabriella Di Benedetto
Keyword(s):  
Channel Estimation ◽  
Time Reversal ◽  
Multiple Access ◽  
Estimation Errors ◽  
Channel Estimation Errors ◽  
Multiple Access Channels ◽  
Large Channel ◽  
Multiple Access Communications ◽  
Analytic Expressions ◽  
Non Gaussian

Time reversal (TR) is an effective solution in both single user and multiuser communications for moving complexity from the receiver to the transmitter, in comparison to traditional postfiltering based on Rake receivers. Imperfect channel estimation may, however, affect pre- versus postfiltering schemes in a different way; this paper analyzes the robustness of time reversal versus All-Rake (AR) transceivers, in multiple access communications, with respect to channel estimation errors. Two performance indicators are adopted in the analysis: symbol error probability and spectral efficiency. Analytic expressions for both indicators are derived and used as the basis for simulation-based performance evaluation. Results show that while TR leads to slight performance advantage over AR when channel estimation is accurate, its performance is severely degraded by large channel estimation errors, indicating a clear advantage for AR receivers in this case, in particular when extremely short impulsive waveforms are adopted. Results however also show a stronger non-Gaussianity of interference in the TR case suggesting that the adoption of a receiver structure adapted to non-Gaussian interference might tilt the balance towards TR.

Non-Orthogonal Multiple Access

2019 ◽  
Author(s):  
Sanjeev Gurugopinath
Keyword(s):  
Interference Cancellation ◽  
Communication Systems ◽  
Multiple Access ◽  
Future Research ◽  
Superposition Coding ◽  
Fifth Generation ◽  
Power Domain ◽  
Code Domain ◽  
5G Communication ◽  
Code Division Multiple

Non-orthogonal multiple access (NOMA) has been recently proposed as a technique to increase the network throughput and to support massive connectivity, which are major requirements in the fifth generation (5G) communication systems. The NOMA can be realized through two different approaches, namely, in (a) power-domain, and (b) code-domain. In the power-domain NOMA (PD-NOMA), multiple users are assigned different power levels – based on their individual channel quality information – over the same orthogonal resources. The functionality of PD-NOMA comprises of two main techniques, namely, superposition coding at the transmitter and successive interference cancellation (SIC) at the receiver. An efficient implementation of SIC would facilitate to remove interference across the users. The SIC is carried out at users with the best channel conditions and is performed in descending order of the channel. On the other hand, in the code-domain NOMA (CD-NOMA), multiplexing is carried out using low-density spreading sequences for each user, similar to the code division multiple access (CDMA) technology. In this article, we provide an introduction to NOMA and present the details on the working principle of NOMA systems. Later, we discuss the different types of NOMA schemes under PD- and CD-domains, and investigate the related applications in the context of 5G communication systems. Additionally, we discuss the integration of NOMA with other technologies related to 5G such as cognitive radio and massive MIMO, and discuss some future research challenges.

Performance Analysis of OFDM Channel System

2011 ◽  
Vol 268-270 ◽  
pp. 1438-1446
Author(s):  
Zhang Lei ◽  
Cong Feng Liu ◽  
Wei Jiang ◽  
Gui Zhou Xu ◽  
Ning Dai
Keyword(s):  
Channel Estimation ◽  
Correlation Coefficient ◽  
Signal To Noise Ratio ◽  
Estimation Error ◽  
Error Model ◽  
Channel Estimation Error ◽  
Ofdm Systems ◽  
Signal To Noise ◽  
Estimation Scheme ◽  
Complex Correlation

OFDM is a promising digital communications technique for high data rate transmissions. In this paper, we have analyzed the performance of mobile OFDM systems in the presence of channel estimation error. A new channel estimation error model is presented. Based on the estimation error model, new and simple expressions for the average bit error probability of M-QAM OFDM systems are derived for zero-forcing, minimum mean square error and maximum likelihood receivers. A complex correlation coefficient is used to quantify the quality of the channel estimation scheme. We have shown that if the complex correlation coefficient is a function of the signal to noise ratio, then the inter-carrier interference caused by channel variations is the dominant source of performance degradation. On the other hand, if the channel estimation scheme produces a constant value for the complex correlation coefficient (estimation quality is not a function of the signal to noise ratio), then the channel estimation error will cause an error floor that is larger than the one caused by the inter-carrier interference, and is considered as one of the dominant causes of degradation. And channel estimation using pilot symbols are discussed in terms of different pilot symbol placement schemes.

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