Abstract
This paper investigates the energy-efficient communications and user capacity in the cognitive multiple input multiple output (MIMO) symmetric system of underlay mode. The advantage of the improved energy efficiency provided by the orthogonal slot allocation for time division multiple access (TDMA) has a side effect of restricting the number of users accessing the system. To tackle the above problem, this paper proposes a nonorthogonal time resource allocation method with sparse code multiple access (SCMA), which allows one to convert the orthogonal slot units of TDMA into non-orthogonal shared slot units for multiple secondary users (SUs). The method of adding virtual users is adopted, wherein each SU is treated as multiple SUs who occupy a shared unit, to facilitate the packet access. Finally, the greedy algorithm is applied to optimize the time slot allocation of unoccupied shared slot units. The simulation results show that SCMA-based nonorthogonal slot allocation can reduce not only the energy consumption by nearly 40%, but also the average power interference from SUs to primary users by nearly 2 dB if their number is relatively high. Moreover, in the case of satisfying the rate requirement of the users, the system user capacity increased by more than 50%.
Highlights
The state-of-the-art wireless communication system should have adequate characteristics of continuous wide area coverage, hot spot area, high capacity, low energy consumption, and mass connection [1]
To verify the performance of the proposed method regarding energy consumption, interference caused by the secondary system to the primary authorized users (PUs) links system and its user capacity, the simulation system is set up
It is assumed that each node in the multiple input multiple output (MIMO)-cognitive radio (CR) network has four antennas
Summary
The state-of-the-art wireless communication system should have adequate characteristics of continuous wide area coverage, hot spot area, high capacity, low energy consumption, and mass connection [1]. The latter two issues, given the increased energy consumption and limited spectrum supply/demand, are quite urgent. Numerous studies have been performed with the aim of more comprehensive use of spectrum resources, improving the spectrum utilization efficiency, reducing power/energy consumption, and overall improvement of the energy efficiency (EE). Many research efforts are dedicated to the cognitive radio (CR), which is a new type of radio with adaptive spectrum awareness that is centered on spectrum sensing and intelligent learning capabilities. CR will be a brand-new field for the tactile Internet, Symmetry 2020, 12, 1136; doi:10.3390/sym12071136 www.mdpi.com/journal/symmetry
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