Muhammad Basit Shahab

Exploiting Non-Orthogonal Multiple Access in Cooperative Relay Sharing

We propose and investigate a dual-hop cooperative relaying scheme using non-orthogonal multiple access (NOMA) (termed NOMA-RS), where two sources communicate with their corresponding destinations in parallel over the same frequency band via a common relay. In this scheme, after receiving symbols transmitted in parallel by both sources with different allocated powers, the relay forwards a super-position coded composite signal using NOMA to the destinations. One of the main benefits of NOMA-RS is that multiple (two) sources can share the same relay, unlike the previous works. Through the simulations and mathematical analysis, we demonstrate the effectiveness of the proposed protocol in terms of ergodic sum capacity by considering perfect and imperfect successive interference cancellation.

A Virtual User Pairing Scheme to Optimally Utilize the Spectrum of Unpaired Users in Non-orthogonal Multiple Access

This letter proposes a strategy to efficiently utilize the spectrum of unpaired users in non-orthogonal multiple access (NOMA) systems. This is done by pairing multiple similar gain users to a single distant user in a nonoverlapping frequency band pairing fashion. We consider a case where the number of far users in a cell is larger than the number of near users. Thus, some far users cannot be paired and should get data using conventional multiple access (OMA). In such case, we propose a strategy where a near user can be paired with multiple (two) far users to optimally utilize the spectrum of unpaired users in the NOMA system. Performance of the proposed pairing scheme is evaluated in terms of ergodic sum capacity over independent Rayleigh flat fading channel. Analytical and simulation results show that significant increase in the capacity gain of the system is achieved by using the proposed strategy compared to OMA and conventional NOMA.

User pairing schemes for capacity maximization in non-orthogonal multiple access systems

This paper addresses the issues related with conventional near–far user pairing in non-orthogonal multiple access. Performance effects of near–far pairing on regions with negligible channel gain differences between users are investigated. These regions occur when pairing is performed between cell center and cell edge users, thus leaving the cell mid users to be either paired with each other or kept unpaired. Pairing these mid users with each other causes successive interference cancelation (SIC) performance degradation resulting in capacity reduction for these users. On the other hand, leaving these mid users unpaired perfectly avoids the SIC issue but makes these users unable to benefit from the capacity gains provided by non-orthogonal multiple access. Therefore, two user pairing strategies have been proposed that can provide capacity gains to almost all the users by accommodating them in pairs, while avoiding or minimizing the mid users pairing problem. A generalized M-users pairing scheme is also proposed. Simulations have been performed to investigate the performance of proposed schemes for both perfect and imperfect SIC receiver scenarios in comparison with conventional pairing where the mid users are kept paired with each other. Simulation results show that proposed schemes achieve high capacity gains, especially when imperfect SIC is considered. Copyright

On the power allocation of non-orthogonal multiple access for 5G wireless networks

This paper addresses the power allocation issue in non-orthogonal multiple access (NOMA) systems. In NOMA, multiple paired users can simultaneously utilize the frequency bands of each other such that the message signals of all these users are superimposed by the transmitter by allocating different powers to all users. As the paired users communicate over the same frequency band, high amount of interference is faced by them. Thus, some paired users perform successive interference cancellation to decode and cancel the signals of other users while some users recover their signals by simply treating signals of other users as noise. Inefficient power allocation may increase the interference significantly, which causes degradation in data recovery at the user ends. We propose a novel power allocation strategy that can optimize the system ergodic sum capacity while minimizing the mutual interference between the paired users. It is shown through simulations that the proposed scheme outperforms conventional power allocation in terms of bit error rates at the user ends with negligible effect on the system ergodic sum capacity.

On the performance of a virtual user pairing scheme to efficiently utilize the spectrum of unpaired users in NOMA

This paper evaluates the performance of a virtual user pairing scheme that efficiently utilizes the spectrum of unpaired users in non-orthogonal multiple access (NOMA), termed as VP-NOMA. The scheme aims at utilizing the frequency bands of those users which remain unpaired due to the non-uniform distribution of users in a cellular area. We consider a case where the cell edge users are more than the cell center users, so that complete one-to-one correspondence does not exist between all cell center and cell edge users to be accommodated/paired using conventional NOMA (C-NOMA) user pairing. Thus, some cell edge users remain unpaired, and are served using conventional multiple access (OMA) schemes. In such scenario, VP-NOMA pairs a single cell center user with two or more clustered (closely located) cell edge users over non-overlapping frequency bands, thus enabling the cell center user to efficiently use the frequency bands of these previously unpaired cell edge users. Performance of VP-NOMA in terms of ergodic sum capacity (ESC), outage probability (OP), and outage sum capacity (OSC), is analyzed through comprehensive mathematical derivations and simulations for a generalized system model. Moreover, the mathematical analysis is validated through close concordance between analytical and simulation results of ESC, OP, and OSC.

Cooperative spectrum sharing with energy harvesting best secondary user selection and non-orthogonal multiple access

We propose two novel cooperative spectrum sharing (CSS) protocols by using time-switching and power-splitting based energy harvesting (EH), namely CSS-TSP and CSS-PSP, respectively. The considered system consists of a set of energy constrained secondary transmitters (STs) that cooperate with the primary user to forward its symbol. All STs rely on the harvested energy from the source signal to forward the primary symbol. In exchange of cooperation, one of the STs behaving as the best EH decode-and-forward relay (STbr) gets channel access simultaneously with the primary user according to the non-orthogonal multiple access. Two STbr selection strategies, namely STbr selection based on harvested energy in current block of time and STbr selection based on harvested energy from current plus previous blocks of time, have been proposed. The distributed nature of the STbr selection in the proposed schemes to forward the primary symbol increases the network lifetime. We have investigated the achievable sum data rate/throughput of both CSS-TSP and CSS-PSP. Moreover, the optimal EH ratio that maximizes the sum data rate of both protocols is also investigated numerically.

Bandwidth Adaptation by Squeezing Idle Traffic in Browsers: An Active Window Detection Based Approach for Next Generation Networks

This letter proposes a novel algorithm named bandwidth adaptation by squeezing idle traffic (BASIT), which aims at reducing the video traffic in idle tabs/windows of browsers. The algorithm is based on detecting active tabs/windows in the browsers at client end. Video data on idle tabs are intelligently compressed by the server to save network bandwidth. Bandwidth wasted on idle video traffic is reduced by either sending the lowest quality of the video or only audio throughout the idle duration of the tabs/windows. It is understandable that substantial amount of bandwidth can be saved by applying BASIT algorithm on browsers.

Simulink implementation of non-orthogonal multiple access over AWGN and Rayleigh fading channels

Non-orthogonal multiple access (NOMA) is considered as a promising candidate for future radio access. This paper presents the Simulink implementation of NOMA over additive white Gaussian noise (AWGN) and Rayleigh fading channel. The presented model also forms strong basis for the software defined radio based platform for hardware implementation of NOMA. Performance of the provided model has been carried out by comparing the bit error rate of the implemented model with the theoretical results. It has been shown that the model proposed in this paper provides results in close concurrence with the theoretical reference.

User pairing and power allocation for non-orthogonal multiple access: Capacity maximization under data reliability constraints

Abstract This paper comprehensively investigates the dynamics of user pairing and power allocation (UPPA) in non-orthogonal multiple access (NOMA). The focal point of this work is to explore the effects of UPPA on capacity and bit error rate (BER) of NOMA users, thereby understanding the tradeoffs involved when UPPA is performed. These tradeoffs facilitate the design of UPPA strategies to maximize system capacity and satisfy individual target data rates of users without exceeding their allowed BER upper bounds to meet the strict data reliability constraints. Data reliability is critical in NOMA and serves as bottleneck to its manifold capacity gains, as NOMA users are prone to significant interference. The existing UPPA strategies focusing on capacity maximization or user fairness completely neglect this extremely critical tradeoff. This paper provides extensive analysis and results of UPPA considering individual/sum capacity and BER of users. Results are summarized in the form of look-up tables, which facilitate swift selection of user pairs and power allocation factors. The process of performing UPPA by using the developed look up tables, such that both capacity and data reliability goals can be simultaneously achieved, is comprehensively explained in the end.

Non-orthogonal multiple access for a full-duplex cooperative network with virtually paired users

Abstract Non-orthogonal multiple access (NOMA) is recognized as a promising radio access technology for next generation wireless networks. In this paper, a novel full-duplex (FD) cooperative relaying scheme for a NOMA based system (termed FD-NOMA-VP) is proposed, where K similar gain near users and relay-aided N similar gain far users are distributed into different NOMA cluster. In each cluster, one near user is virtually paired (VP) with multiple far users over non-overlapping frequency bands. In FD-NOMA-VP, the near user directly communicates with the base station, whereas far users communicate via a dedicated FD relay, in each cluster. The performance of FD-NOMA-VP is studied comprehensively in terms of the ergodic sum capacity, outage probability, and outage sum capacity along with analytical derivations under both perfect and imperfect interference cancellation (IC) scenarios. The results demonstrate that FD-NOMA-VP shows significant performance gains compared to the conventional multiple access scheme under perfect IC, while the residual interference has a substantial impact on the performance gain under imperfect IC. In addition, a strong agreement between analytical and simulation results affirms the correctness of our analysis.