295 research outputs found

    Adaptive Aggregate Transmission for Device-to-Multi-Device Aided Cooperative NOMA Networks

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    The integration of device-to-device (D2D) communications with cooperative non-orthogonal multiple access (NOMA) can achieve superior spectral efficiency. However, the mutual interference caused by D2D communications may prevent NOMA from divering its high spectral efficiency advantage. Meanwhile, the low adaptability of the fixed transmission strategy can decrease the reliability of the cell-edge user (CEU). To further improve the spectral efficiency, we investigate a device-to-multi-device (D2MD) assisted cooperative NOMA system, where two cell-center users (CCUs) and one CEU are paired as a D2MD cluster. Specifically, the base station directly serves the two CCUs while communicating with the CEU via one CCU. Moreover, we propose an adaptive aggregate transmission scheme using dynamic superposition coding, pre-designing the decoding orders and prior information cancellation for the D2MD assisted cooperative NOMA system to enhance the reliability of the CEU. We provide the closed-form expressions for the outage probability, diversity order, outage throughput, ergodic sum capacity, average spectral efficiency, and spectral efficiency scaling over Nakagami-m fading channels under perfect and imperfect successive interference cancellation. The numerical results validate the correctness of the analytical derivations and the effectiveness of the proposed scheme

    Relaying in the Internet of Things (IoT): A Survey

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    The deployment of relays between Internet of Things (IoT) end devices and gateways can improve link quality. In cellular-based IoT, relays have the potential to reduce base station overload. The energy expended in single-hop long-range communication can be reduced if relays listen to transmissions of end devices and forward these observations to gateways. However, incorporating relays into IoT networks faces some challenges. IoT end devices are designed primarily for uplink communication of small-sized observations toward the network; hence, opportunistically using end devices as relays needs a redesign of both the medium access control (MAC) layer protocol of such end devices and possible addition of new communication interfaces. Additionally, the wake-up time of IoT end devices needs to be synchronized with that of the relays. For cellular-based IoT, the possibility of using infrastructure relays exists, and noncellular IoT networks can leverage the presence of mobile devices for relaying, for example, in remote healthcare. However, the latter presents problems of incentivizing relay participation and managing the mobility of relays. Furthermore, although relays can increase the lifetime of IoT networks, deploying relays implies the need for additional batteries to power them. This can erode the energy efficiency gain that relays offer. Therefore, designing relay-assisted IoT networks that provide acceptable trade-offs is key, and this goes beyond adding an extra transmit RF chain to a relay-enabled IoT end device. There has been increasing research interest in IoT relaying, as demonstrated in the available literature. Works that consider these issues are surveyed in this paper to provide insight into the state of the art, provide design insights for network designers and motivate future research directions

    Performance Analysis of 5G Cooperative-NOMA for IoT-Intermittent Communication

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    Non-orthogonal multiple Access (NOMA) is a potential 5G era multiple-access scheme that is proposed for the future mobile Internet and IoT applications which will require enormous increase in data traffic, massive-number of devices connectivity, high spectral efficiency, low-overhead and low-latency. It utilizes the same time-slots, frequency and spreading-codes for all the users. It uses the power-domain and assign different power levels to users for multiple access. The uplink (UL) communication in the present 4G-Networks is performed by the base station (BS) that uses a request-grant mechanism in which a large-overhead and latency is produced. This issue will get more severe in upcoming 5G-Networks. For this purpose, a grant-free NOMA for UL communication, in which dynamic compressed-sensing (DCS) algorithm will perform multi-user detection (MUD) as well as data-detection is proposed. It deploys the temporal-correlation of active-user sets (AUS) in adjacent time-slots from which the estimated AUS is used as the prior-knowledge to estimate AUS in the next time-slot. For the downlink (DL) communication, the proposed system performance evaluation is performed using Rician fading-channels for Cooperative Relaying System (CRS) NOMA. The simulations results show that the proposed DCS-MUD and CRS NOMA over Rician fading-channels perform much better than the conventional CS-MUD and traditional-CRS

    Enabling relay selection in non-orthogonal multiple access networks: direct and relaying mode

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    In this paper, we consider downlink non-orthogonal multiple access (NOMA) in which the relay selection (RS) scheme is enabled for cooperative networks. In particular, we investigate impact of the number of relays on system performance in term of outage probability. The main factors affecting on cooperative NOMA performance are fixed power allocations coefficients and the number of relay. This paper also indicate performance gap of the outage probabilities among two users the context of NOMA. To exhibit the exactness of derived formula, we match related results between simulation and analytical methods. Numerical results confirms that cooperative NOMA networks benefit from increasing the number of relay
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