Abstract-Device-to-Device (D2D) communications have been proposed as a means of realizing the potential advantage of the physical proximity of communicating devices, improving user experience and resource utilization. Discovery is one of the major design issues in the D2D communications, since they must discover each other and identify services provided by each other to directly communicate with one another. There are some requirements for discovery such as energy-efficiency (e.g. low duty cycle), scalability (e.g. support for high device density) and proximity-based autonomous detection in the D2D communications. In this paper, we propose a discovery scheme for D2D communications in synchronous distributed networks. In particular, we present a discovery scheme that each device advertises its presence and service and discovers other nearby devices autonomously and continuously, along with resource allocation in distributed manner. Using simulation, we evaluate the performances of our proposed scheme in terms of discovery latency and the number of discovered devices.
To enable the coexistence of Licensed Assisted Access (LAA) and Wi‐Fi in 5 GHz unlicensed bands, a new channel access mechanism is proposed. Accounting for the fairness between LAA and Wi‐Fi, the proposed mechanism finds the optimal transmission time ratio by adaptively adjusting the transmission durations for LAA and Wi‐Fi. In addition, we propose a new analytical model for the distributed coordination function of IEEE 802.11 through some modifications of conventional analytical models for saturation and non‐saturation loads. By computing the activity ratio of Wi‐Fi, the proposed analytical model is able to control the time ratio between LAA and Wi‐Fi, which is required for practical implementation of the proposed access mechanism. Through numerical simulations, the proposed channel access mechanism is compared with conventional methods in terms of throughput and utility.
Recently, device-to-device (D2D) communications have been highlighted to improve the spectral efficiency and offer various user experiences in cellular networks. In this paper, we survey standards and literatures related to the D2D technology and address various advantages of D2D technology, and the problems to be resolved before practically implemented. Especially, by considering an important interference issue between cellular and D2D links, five resource allocation and interference management scenarios are provided and their performances are evaluated through the system level simulations. The simulation results show that the use of D2D significantly improve the cell capacity and the D2D user rate due to the effects of frequency reuse and data off-loading. Notably, it is also shown that an optimal D2D communication range exists to maximize the system performance.
Ⅰ. 서 론최근 스마트폰과 스마트패드 사용자들의 급증으로 인해 멀티미디어 및 소셜네트워크 서비스에 대한 수 요가 폭발적으로 증가하고 있다 [1,2] . 그 결과, 모바일 트래픽이 엄청난 속도로 늘어나고 있으며, 이를 위해 보다 빠른 속도의 차세대 무선통신 서비스에 대한 필 요성이 증대되고 있다 [3] . 전 세계적으로 다양한 모바
In this paper, we propose a new estimation method of time offset, frequency offset, and signal to interference plus noise ratio (SINR) using the synchronization channel preamble to provide IEEE 802.16.1a based talk-around direct communications (TDC). The proposed scheme estimates the time offset and frequency offset both in the time domain and in the frequency domain considering the preamble structure. In addition, it improves the estimation accuracy by combining the estimated values in two domains taking into account TDC synchronization scenarios. Through numerical simulations in the TDC channel environments, the performance of the proposed algorithm is compared with those of existing techniques such as the time domain estimation and the frequency domain estimation.
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