Abstract
Non-orthogonal multiple access (NOMA) has gained attention as a promising multiple access scheme for the Internet of Things (IoT). A typical setting of user ordering in NOMA networks with user priority difference allows a service priority for solely low-rate high-priority users. In contrast, the diverse quality of service (QoS) requirements and service priorities are prerequisite features of users in the IoT. In this paper, we consider a downlink transmission scenario for NOMA-IoT networks in which the base station (BS) simultaneously serves the two users with a priority difference. To tackle the requirements of the IoT, we consider two schemes: a service priority scheme for high-priority user (SP-HP), and a service priority scheme for low-priority user (SP-LP). Meanwhile, the BS adopts a power allocation strategy to realize the desirable QoS provision for high-priority user and optimize the outage experience of low-priority user in an opportunistic manner. It is novel and interesting to extend the NOMA-IoT framework for a malicious attempt of a passive eavesdropper. To investigate the efficiency and security performances of both schemes, the connection and secrecy outage probabilities of both users are characterized, and their closed-form expressions are derived over Rayleigh fading channels. An effective secrecy throughput (EST) is presented to holistically characterize the performance of the system. Numerical results validate the accuracy of the theoretical results. The results suggest that the transmit power of both users in each scheme can be optimized for the maximum EST, and a selection of an optimal scheme for the reliable and secure transmissions of both users is possible under certain channel conditions.
Highlights
INTRODUCTIONThe fixed power allocation (PA) strategy does not guarantee the quality of service (QoS) requirement of high-priority user because a wrong choice of PA coefficients always leads to an outage probability, and it fails to provide the best performance to low-priority user
The power allocation (PA) strategy was adopted to bring the desirable quality of service (QoS) provision for high-priority user and to maximize the achievable rate for low-priority user; further, a malicious attempt of an eavesdropper was considered for the security aspect
The connection and secrecy outage probabilities and the effective secrecy throughput were derived to estimate the performance of the system
Summary
The fixed PA strategy does not guarantee the QoS requirement of high-priority user because a wrong choice of PA coefficients always leads to an outage probability, and it fails to provide the best performance to low-priority user In the latter approach [22], a set of PA coefficients is not predetermined and is dynamically adjusted to satisfy the target problem. Novel system setting: We consider a downlink transmission scenario in the NOMA-IoT networks where the base station BS) simultaneously serve two users with a priority difference. We consider a two-user power-domain NOMA setting in the framework because it provides the best intuitive view of the reliability and security performances of the users with priority difference.. In the SP-HP scheme, the maximum SINRs decoding x1 and x2 at E can be respectively obtained as 1→E (b∗)
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