Energy-Efficient Power Allocation for Cooperative NOMA Systems with IBFD-Enabled Two-Way Cognitive Transmission
Abstract: To compensate for the transmission efficiency in a cooperative non-orthogonal multiple access (NOMA) system, we enable in-band full-duplex (IBFD) and twoway cognitive transmission at the mobile relay, which assists the NOMA user in weak channel condition while transmitting and receiving its own data by means of spectral sharing. To strike a balance between spectral efficiency and energy conservation, we consider the power allocation problem to maximize the energy efficiency of the hybrid system while maintaining the bit rate requirements of NOMA users. To overcome the non-convexity of the original problem, we apply the successive inner approximation technique and propose an efficient iterative scheme to obtain a Karush- Kuhn-Tucker point in polynomial time. The gain of IBFD-enabled two-way cognitive transmission and the efficiency of the proposed power allocation scheme are validated via simulation results. Existing system: Based on the above observations, the contributions of this paper are threefold: We will integrate cooperative NOMA with IBFD-enabled two-way cognitive
transmission, where an MR assists the NOMA user in weak channel condition while simultaneously transmitting and receiving its own data on the same spectrum; To control the co-channel interference, including the self-interference (SI), and strike a balance between SE and energy conservation, we will apply power allocation and maximize the energy efficiency (EE) of the hybrid system while satisfying the bit rate requirements of (primary) NOMA users; To overcome the intractability of the above problem, we will propose an efficient iterative scheme to obtain a near-optimal solution in polynomial time. Proposed system: The above issue, an incentive mechanism was proposed in to reward MRs with certain spectrum for their own transmission. Nevertheless, the spectrum rewarded to MRs is different from the one used for the cooperation. In this regard, cooperative NOMA with cognitive transmission (overlay mode) was investigated. Particularly, an MR adopted NOMA to simultaneously transmit the data of NOMA users and that of its own on the same spectrum. However, the cooperative process is half duplex (HD), the cognitive transmission is one-way, and the transmission policy is hold fixed. Besides, in an interference-limited scenario, the maximization of spectral efficiency (SE) consumes excessive transmit power. Advantages: We will integrate cooperative NOMA with IBFD-enabled two-way cognitive transmission, where an MR assists the NOMA user in weak channel condition while simultaneously transmitting and receiving its own data on the same spectrum. To control the co-channel interference, including the self-interference (SI), and strike a balance between SE and energy conservation, we will apply power allocation and maximize the energy efficiency (EE) of the hybrid system while satisfying the bit rate requirements of (primary) NOMA users. Disadvantages: We consider a primary NOMA system with one primary transmitter (PT) and two primary receivers (PRs), i.e., PR1 and PR2. In particular, the direct link between PT and PR2 is unavailable due to strong obstruction. Meanwhile, a decode-and-
forward based secondary relay (SR) directly communicates with a secondary companion (SC) in its proximity at the expense of providing the cooperation for PR2. Due to the spectrum scarcity, NOMA is implemented at SR for the simultaneous transmission to SC and PR2 on the same spectrum together with IBFD and twoway cognitive transmission. The entire communication process is made up of two parts. Modules: Non-orthogonal multiple access: COOPERATIVE non-orthogonal multiple access (NOMA) has recently received much attention and mobile relays (MRs) are used to assist the transmission between the base station and NOMA users. In, the prior information at the NOMA user with better channel condition (near user) was utilized to improve the outage performance of the other (far user). To create more cooperative opportunities, dedicated MRs were introduced to both one-way and two-way cooperative NOMA, and in-band full-duplex (IBFD)- enabled cognitive relaying (underlay mode) was also studied. But, the works in fail to incentivize MRs to participate in the cooperation. To address the above issue, an incentive mechanism was proposed in to reward MRs with certain spectrum for their own transmission. Nevertheless, the spectrum rewarded to MRs is different from the one used for the cooperation. In this regard, cooperative NOMA with cognitive transmission (overlay mode) was investigated. Particularly, an MR adopted NOMA to simultaneously transmit the data of NOMA users and that of its own on the same spectrum. However, the cooperative process is half duplex (HD), the cognitive transmission is one-way, and the transmission policy is hold fixed. Besides, in an interference-limited scenario, the maximization of spectral efficiency (SE) consumes excessive transmit power. Self-interference: Based on the above observations, the contributions of this paper are threefold: We will integrate cooperative NOMA with IBFD-enabled two-way cognitive transmission, where an MR assists the NOMA user in weak channel condition
while simultaneously transmitting and receiving its own data on the same spectrum; To control the co-channel interference, including the self-interference (SI), and strike a balance between SE and energy conservation, we will apply power allocation and maximize the energy efficiency (EE) of the hybrid system while satisfying the bit rate requirements of (primary) NOMA users; To overcome the intractability of the above problem, we will propose an efficient iterative scheme to obtain a near-optimal solution in polynomial time. Primary transmitter: We consider a primary NOMA system with one primary transmitter (PT) and two primary receivers (PRs), i.e., PR1 and PR2. In particular the direct link between PT and PR2 is unavailable due to strong obstruction. Meanwhile, a decode-andforward based secondary relay (SR) directly communicates with a secondary companion (SC) in its proximity at the expense of providing the cooperation for PR2. Due to the spectrum scarcity, NOMA is implemented at SR for the simultaneous transmission to SC and PR2 on the same spectrum together with IBFD and two-way cognitive transmission. The entire communication process is made up of two parts: SR performs IBFD-enabled relaying and simultaneously receives and transmits the message of PR2; While providing the above cooperation, SR is rewarded to conduct the IBFD-enabled two-way cognitive transmission with SC by means of spectral sharing. Specifically, the transmission between SR and SC can be viewed as an incentive mechanism that inspires SR to participate in the cooperation. For simplicity, all the network nodes are assumed to be stationary during each time slot and are equipped with one transmit antenna. For efficient interference mitigation, PR1, PR2, SR, and SC are all equipped with Nr receive antennas.