Abstract
The success of fifth generation (5G) mobile network and its long-term evolution (LTE) relies on enabling demanding services with massive connectivity requirements, including Internet of Things (IoT) nodes, mobile devices, or unmanned aerial vehicles (UAVs). Towards this end, non-orthogonal multiple access (NOMA) schemes allow multiple users and devices to communicate using the same temporal and spectral resources. In this context, buffer-aided (BA) relay selection can significantly enhance the quality and reliability of communication, through increased diversity. So, in this paper, we employ BA relay selection in the uplink of the NOMA networks where users and devices coexist and demand access to the wireless resources. The presented relay selection policy, namely flex - NOMA, facilitates simultaneous transmissions from multiple sources to multiple relays, exploiting channel state information at the reception, and dynamic decoding ordering by the relays performing successive interference cancellation (SIC). The theoretical analysis and performance evaluation results are provided and comparisons, in terms of outage probability, average sum-rate and average delay show that flex - NOMA offers improved performance without incurring high complexity and coordination overheads.
Highlights
Fifth generation (5G) networks introduce new services, based on Internet of Things (IoT) devices and unmanned aerial vehicles (UAVs), that current networks are struggling to support due to limited spectrum resources
The theoretical analysis and performance evaluation results are provided and comparisons, in terms of outage probability, average sum-rate and average delay show that flex − non-orthogonal multiple access (NOMA) offers improved performance without incurring high complexity and coordination overheads
This can be justified by the {R→D} proritization that is targeted in flex − NOMA and its equivalent orthogonal multiple access (OMA) scheme, in order to
Summary
Fifth generation (5G) networks introduce new services, based on Internet of Things (IoT) devices and unmanned aerial vehicles (UAVs), that current networks are struggling to support due to limited spectrum resources. The NOMA transmission might not be successful, i.e., due to low available transmit SNR, negligible channel asymmetry between the destinations or high rate requirements In these cases, the network can avoid a complete outage, if at least, one destination Dj is able to receive a packet from the relays belonging in FRDj , j ∈ {1, 2}, i.e., the set of links that can support an OMA transmission towards Dj. 2. 4) ILLUSTRATIVE EXAMPLE (N = 3, K = 1, L = 6) In order to better show the operation of flex − NOMA, an illustrative example is presented, focusing on the transition probabilities of state S111, i.e., the state where one packet from each source resides in the relay’s buffer In this example, S1 and S2 require rates rmin = rS1 = rS2 = 1 bps/Hz, while S3 demands rS3 = 3 bps/Hz. the success probabilities of transmitting in the {S→R} and {R→D} links with the required rates are clearly depicted in the transition probabilities of Fig. 2. By expanding the state transition diagram to include all the possible states, the state transition matrix A and the network outage probability can be calculated
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