Abstract
Both Device-to-device (D2D) and full-duplex (FD) have been widely recognized as spectral efficient techniques in the fifth-generation wireless communications systems. By enabling FD mode in D2D communications, the attainable spectrum efficiency can be (in theory) up to twice as high as that of conventional half-duplex (HD) mode D2D technology, provided that the self-interference signal in the former can be sufficiently suppressed. Considering the fact that FD technology does not always outperform the HD technology in arbitrary channel condition, we will delve into the FD gain as well as its preconditions for acquisition in this paper. In particular, the performance of D2D-aided underlaying cellular networks is investigated by assuming that the D2D users are capable of operating at both HD and FD modes. Under a given user workload, the sum throughput in each DU is shown to be always improved by activating D2D links despite an extra DU-induced interference could be imposed on its co-spectrum cellular users. Numerical results show that the FD-D2D mode exhibits its superiority in terms of sum throughput than the HD-D2D mode in a light-workload scenario even if a non-ideal SI cancellation has been implemented in the former, but the latter pulls back a game in a heavy-workload scenario. Furthermore, to maximize the sum throughput, an appropriate mode-selection scheme (i.e., by choosing either FD or HD mode in the current time-slot for each individual D2D user) should be implemented for sufficiently exploiting the FD gain according to the instantaneous radio frequency environment.
Highlights
W ITH the rapid development of new technologies such as the Internet of Things as well as the rapid popularization of new services such as high-definition video on demand, Manuscript received June 2, 2019; revised October 31, 2019 and December 25, 2019; accepted January 14, 2020
In [31], the closed-form expressions for both the average coverage probability (ACP) and the sum data rate of underlaying cellular networks (CNs) were derived by taking the impact of inter-user interference into account
1) CLs are Activated Alone: If no D2D users (DUs) is allowed to be activated during the period that its co-spectrum activated CUs (ACUs) are communicating, the interference contributed by only CLs should be considered in expressing the signal-to-interference-plus-noise ratio (SINR)
Summary
W ITH the rapid development of new technologies such as the Internet of Things as well as the rapid popularization of new services such as high-definition video on demand, Manuscript received June 2, 2019; revised October 31, 2019 and December 25, 2019; accepted January 14, 2020. To meet the growing communication demands of customers, the spectral efficiency of the existing wireless networks must be substantially improved [1]–[5]. Device-to-device (D2D) technology, which allows the geographically neighboring devices to communicate directly without relying on the involvement of BSs, has been regarded as one of the core techniques of the fifth-generation (5G) wireless communications systems that will provide an unprecedented quality of service to the customers [7]–[9]. Besides D2D, the full-duplex (FD) technology has been regarded as an appealing technology with a great potential for improving the spectrum efficiency in 5G systems [18]. The HD mode has already been widely adopted in the existing D2D communication networks [22], the spectral efficiency of the D2D-aided underlaying cellular networks (CNs) can definitely be further improved by employing FD technology
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