Fazlul Kader

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.

Cooperative Hybrid Spectrum Sharing: A NOMA-based Approach

AbstractNon-orthogonal multiple (NOMA) access using successive interference cancellation and cognitive radio are two promising techniques for enhancing the spectrum efficiency and utilization for future wireless communication systems. This paper presents a NOMA-based cooperative hybrid spectrum sharing protocol for cognitive radio networks. A two phase decode-and- forward (DF) relaying scheme in a multi-relay scenario is considered. Each secondary transmitter is grouped into one of the two clusters: a non-cooperative cluster (NCC) and a cooperative cluster (CC). The cluster head (CH) of the CC working as the best DF relay for the primary system is permitted to transmit its own signal superimposed on the primary signal using a NOMA approach in exchange for cooperation. On the other hand, the CH of the NCC transmits in parallel with the primary system satisfying a predefined peak transmit power and peak interference power constraints that guarantee a given primary quality of the service requirement. It is demonstrated that the performances of both the primary and secondary systems increase with the increasing number of secondary nodes. The simulation and theoretical results affirm the efficacy of the proposed protocol compared to the traditional overlay and underlay models in terms of the outage probability and the ergodic capacity.

Exploiting cooperative diversity with non-orthogonal multiple access over slow fading channel

ABSTRACT Non-orthogonal multiple access (NOMA) has attracted a significant attention to the research community as a potential candidate for 5G or future radio access. This article presents a NOMA-based cooperative network where a transmitter considered as a base station communicates simultaneously with two users treating as a far user and a near user via the help of a half-duplex decode-and-forward relay. We investigate the outage probability and the outage capacity of the proposed network over independent Rayleigh slow fading channels. Closed-form expressions of the outage probabilities are derived for both users. Approximate outage capacity of the users are also investigated at high signal to noise ratio regime. It has been shown that the proposed cooperative NOMA can achieve superior performance compared to the non-cooperative NOMA in terms of outage probability. The tightness between the simulation and theoretical results confirms the efficiency of the proposed protocol.

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.

Cooperative spectrum sharing with space time block coding and non-orthogonal multiple access

In this paper, we have proposed a novel two-phase cooperative spectrum sharing protocol on the basis of Alamouti space time block coded (STBC) non-orthogonal multiple access. The network scenario comprising of a primary transmitter-receiver pair and a secondary transmitter-receiver pair. During the first two time slots, the primary transmitter transmits two STBC primary symbols to the cooperative secondary transmitter. The secondary transmitter acting as a decode-and-forward relay for the primary system is allowed to transmit its own secondary signal superposed on the STBC coded primary signal in exchange of cooperation during the next two time slots. Simulation and theoretical results demonstrate the efficacy of the proposed protocol compared to the conventional super positing coding based overlay scheme in terms of the outage probability and the ergodic capacity.

Interference free cooperative spectrum sharing in cognitive radio networks using spatial modulation

Cognitive radio (CR) and spatial modulation (SM) are two exciting and emerging techniques to increase the spectrum efficiency for 5G. In this paper, we present a novel cooperative spectrum sharing protocol using SM. A two phases uncoded decode-and-forward (UDF) relaying scheme is considered. A secondary transmitter (ST) consisting of Mt transmit antennas act as UDF relay for the primary system (PS). In the first phase, a block of information bits of the primary transmitter (PT) is mapped into two information carrying units: a symbol which is chosen from a constellation diagram and a particular antenna number from a set of transmit antennas. The ST is then uses iterative-maximum ratio combining (i-MRC) to de-map the transmitted block of information bits. In the second phase, the ST forwards the estimated primary data by activating only one antenna based on the own secondary data. The primary receiver is then uses i-MRC to estimate the forwarded primary symbol and the secondary receiver uses i-MRC to estimate own secondary data by detecting only transmit antenna indices of the ST. As a result, mutual interference between the PS and secondary system (SS) is avoided. We investigate the bit error rate (BER) of the PS and SS. Simulation results show the efficacy of the proposed system.

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.

Cooperative spectrum sharing in cognitive radio networks: An interference free approach

Abstract We present a novel interference free dual-hop cooperative spectrum sharing protocol in cognitive radio networks exploiting spatial modulation (SM) at both primary transmitter (PT) and secondary transmitter (ST). A ST equipped with multi-antenna acts as a half-duplex decode-and-forward relay for the primary system. During phase-1, SM is invoked at PT, while ST keeps silent. The information bit stream of PT is mapped into two different sets: the M -ary phase shift keying ( M -PSK)/ M -ary quadrature amplitude modulation ( M -QAM) bits and the antenna index. The ST then exploits iterative-maximum ratio combining ( i -MRC) technique to de-map the block of information bits, transmitted by PT. During phase-2, ST forwards the primary data by activating only one antenna based on its own secondary data exploiting the concept of SM. The PT’s data is then retrieved at the primary receiver (PR) and the secondary receiver (SR) recover its own desired data by detecting only the transmit antenna indices of ST using i -MRC. As a result, mutual interference between primary and secondary systems is avoided and interference cancellation techniques at the PR and SR are no longer needed. In the proposed protocol, the primary user does not need to lease its spectrum or time slots to the secondary user in exchange for cooperation. Moreover, power of ST does not need to be distributed for primary and secondary transmission simultaneously during phase-2. The simulation and analytical results are presented to show effectiveness of the proposed protocol compared to conventional spectrum leasing and superposition coding based overlay protocols.