Abstract
This paper proposes a novel design of cooperative non-orthogonal layered multicast multiple access in a heterogeneous network, where the information is encoded into the messages of high priority (HP) and low priority (LP). Two types of multicast users coexist in the network: 1) regular users (RUs), which are located far away from the base station (BS) and expect to decode only the HP message (due to the weak channels), and 2) advanced users (AUs), which are located close to the BS and expect to decode both HP and LP messages. To improve the reliability of layered multicast, we consider that the successful AUs (those AUs who successfully decode the HP and LP messages) serve as potential relays to assist other AUs/RUs. Based on this idea, two novel cooperation strategies are proposed for different cases of channel information availability. For each proposed strategy, we derive closed-form exact outage probabilities of AUs and RUs and then further analyze their diversity orders. Moreover, considering that the layered multicast is outage-constrained, we theoretically evaluate the energy consumption of both strategies and demonstrate their energy saving gains over the direct non-orthogonal multiple access for layered multicast. Finally, our theoretical analysis is verified by numerical results, and the advantages of the proposed strategies are also demonstrated.
Highlights
The application of non-orthogonal multiple access (NOMA) to the future wireless networks has drawn increased attention from both industrial and academic communities [2]–[6]
To improve the reliability/capacity of NOMA systems, cooperative relaying technique has been incorporated into NOMA, termed as cooperative NOMA, in which the information is forwarded by a successful user [12]–[14] or by a dedicated relay [15]– [19]
To enhance reliability of layered multicast in a downlink NOMA network, we propose two user-assisted cooperative NOMA multicast strategies, namely, the distributed cooperative NOMA (DC-NOMA) multicast and the opportunistic cooperative NOMA (OC-NOMA) multicast, for different cases of channel state information (CSI) availability
Summary
The application of non-orthogonal multiple access (NOMA) to the future wireless networks has drawn increased attention from both industrial and academic communities [2]–[6]. As multicast users own heterogeneous and time-varying channel conditions, the non-layered multicast which employs fixed data-rate and coding scheme cannot best serve all multicast users simultaneously, especially in video multicast that requires seamless connectivity and low latency [25]. Compared to the cooperative NOMA strategies for non-layered multicast in [23] and [24], the design of cooperative NOMA strategy for layered multicast is a more challenging and practically useful issue for video multicast in 5G systems In this novel design, the video information is encoded into data streams of highpriority (HP) and low-priority (LP), corresponding to the base-layer and enhancement-layer streams in the digital video broadcasting (DVB) [29].
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