Device-to-device (D2D) communication is one of the key enabling technologies for 5G to support many connections efficiently. In a cooperative out-band D2D communication network, relay nodes have an essential role in receiving and forwarding information signals from source (S) to destination (D), making the system more reliable and with higher energy efficiency. Therefore, the relay selection method is very important in determining the best relay among existing relays to achieve maximum performance. This paper proposes a new Adaptive Relay Selection (ARS) scheme for cooperative out-band D2D networks based on channel gain value and transmission link distance. Firstly, the best relay is adaptively selected among N available relays (R) based on the maximum channel gain values between S to R if the channel gain-based signal-to-noise ratio (SNR) is greater than the distance-based SNR. Otherwise, the best relay is selected based on the minimum distance between S to R. We also analyzed an exact closed-form throughput and the total energy consumption required for a cooperative out-band D2D communication system using the Quantization-and-Forward (QF) protocol. The numerical results show that the proposed ARS scheme has a higher throughput than the two previous schemes: maximum channel gain and minimum distance. Furthermore, the proposed ARS can reduce the total energy consumption, which indirectly impacts the resulting energy efficiency level. The proposed ARS scheme achieves higher energy efficiency than the previous schemes, either by link distance or power allocation. So, the proposed ARS scheme for an out-band D2D communication network is an appropriate solution for the next generation of cellular communications.
The cooperative device-to-device (D2D) system is becoming one of the most popular communication models in wireless 5G technology that combines the D2D system with cooperative communication to extend coverage and increase system performance. However, interference is one of the factors of decreasing service quality in cooperative D2D systems because of adjacent users/clusters and excessive power usage, which also causes interference to the receiver. Interference management, such as power control, can overcome interference problems in the cooperative D2D communication system. Therefore, this paper proposes a new form of adaptive power control (APC) based on the low-energy adaptive clustering hierarchy (LEACH) protocol for interference management systems in cooperative D2D systems that other studies have not considered. For a fair comparison, this paper also modifies the conventional fixed power control (FPC) method using the LEACH protocol and the modified fixed power control (MFPC) used in the previous study and then considers the system without power control. The simulation results show that the proposed APC can significantly reduce interference in cooperative D2D communication compared to the MFPC and without power control. Moreover, the simulation results also show that concerning the signal-to-interference and noise ratio (SINR) to the outage probability and throughput, the proposed APC performs better than the MFPC and without power control. Thus, the proposed APC can effectively reduce interference in cooperative D2D systems.
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