Abstract
Ubiquitous wireless sensor networks (UWSNs) have become a critical technology for enabling smart cities and other ubiquitous monitoring applications. Their deployment, however, can be seriously hampered by the spectrum available to the sheer number of sensors for communication. To support the communication needs of UWSNs without requiring more spectrum resources, the power-domain non-orthogonal multiple access (NOMA) technique originally proposed for 5th Generation (5G) cellular networks is investigated for UWSNs for the first time in this paper. However, unlike 5G networks that operate in the licensed spectrum, UWSNs mostly operate in unlicensed spectrum where sensors also experience cross-technology interferences from other devices sharing the same spectrum. In this paper, we model the interferences from various sources at the sensors using stochastic geometry framework. To evaluate the performance, we derive a theorem and present new closed form expression for the outage probability of the sensors in a downlink scenario under interference limited environment. In addition, diversity analysis for the ordered NOMA users is performed. Based on the derived outage probability, we evaluate the average link throughput and energy consumption efficiency of NOMA against conventional orthogonal multiple access (OMA) technique in UWSNs. Further, the required computational complexity for the NOMA users is presented.
Highlights
IntroductionNon-orthogonal multiple access (NOMA) is emerging as a strong candidate for adoption as the multiple access technology to enhance system capacity for 5th Generation (5G) cellular systems [1,2]
Non-orthogonal multiple access (NOMA) is emerging as a strong candidate for adoption as the multiple access technology to enhance system capacity for 5th Generation (5G) cellular systems [1,2].In NOMA, the transmitted signals of multiple users are multiplexed in the power domain using same time, frequency or code resource, and demultiplexed by applying an interference cancellation technique at the receiver [3]. originally proposed for cellular systems, NOMA exhibits strengths that we consider as highly relevant to addressing the deployment challenges of ubiquitous wireless sensor networks (UWSNs), i.e., large-scale networks of wireless sensors densely deployed for ubiquitous monitoring of physical environments
The results show that the proposed framework can improve reception reliability of existing multi-input multi-output (MIMO) NOMA systems
Summary
Non-orthogonal multiple access (NOMA) is emerging as a strong candidate for adoption as the multiple access technology to enhance system capacity for 5th Generation (5G) cellular systems [1,2]. For a given spectrum bandwidth, NOMA can enable more simultaneous connections than existing approaches without the overheads of coding and spreading to facilitate the separation of users’ signals at the receiver [4] This is attractive for supporting massive connectivity without requiring more spectrum resources in UWSNs. NOMA can be applicable to both uplink (sensors-to-sink) and downlink (sink-to-sensors) communication where powerful sink nodes can perform the equivalent role of base stations (BSs) for Sensors 2018, 18, 516; doi:10.3390/s18020516 www.mdpi.com/journal/sensors. Unlike in uplink communication where the sink node is the main destination of all sensors’ outgoing traffic, the routing table size for DL communication can grow prohibitively with a massive number of sensors as destinations [6] In this case, NOMA can offer a practical solution by enabling direct DL transmissions from sink node to multiple sensors simultaneously.
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