• KIPS Transactions on Computer and Communication Systems
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• v.4 no.1
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• pp.5-10
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• 2015

D2D (Device-to-Device) communication underlaying LTE-advanced networks is a promising technology to improve the system capacity and spectral efficiency. By sharing the same radio resources with cellular user equipments, D2D communications can significantly enhance the overall spectral efficiency. However, it may cause interference between D2D link and cellular link. Careful resource allocation and interference coordination between cellular and D2D communications are very important and need to be properly handled. This paper proposes a radio resource allocation scheme based on FFFR (Flexible Fractional Frequency Reuse) for D2D communication underlaying cellular networks. The base station selects randomly resource blocks assigned to cellular users, and reuses them for a D2D pair. Through simulations, we have confirmed that the proposed scheme improves the system throughput, reduces the computational complexity, and mitigates the interference of D2D link and cellular link.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5209-5228
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• 2016

Device-to-device (D2D) communication underlaying cellular networks can bring significate benefits for improving the performance of mobile services. However, it hinges on elaborate resource sharing scheme to coordinate interference between cellular users and D2D pairs. We formulate a joint mode selection, link allocation and power control optimization problem for D2D communication sharing uplink resources in a multi-user cellular network and consider the efficiency and the fairness simultaneously. Due to the non-convex difficulty, we propose a three-step scheme: firstly, we conduct mode selection for D2D pairs based on a minimum distance metric after an admission control and obtain some cellular candidates for them. And then, a cellular candidate will be paired to each D2D pair based on fairness. Finally, we use Lagrangian Algorithm to formulate a joint power control strategy for D2D pairs and their reused cellular users and a closed-form of solution is derived. Simulation results demonstrate that our proposed algorithms converge in a short time. Moreover, both the sum rate of D2D pairs and the energy efficiency of cellular users are improved.

• Journal of Communications and Networks
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• v.18 no.3
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• pp.429-438
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• 2016

In this paper, we investigate an interference mitigation scheme by antenna selection in device-to-device (D2D) communication underlaying downlink cellular networks. We first present the closed-form expression of the system achievable rate and its asymptotic behaviors at high signal-to-noise ratio (SNR) and the large antenna number scenarios. It is shown that the high SNR approximation increases with more antennas and higher ratio between the transmit SNR at the base station (BS) and the D2D transmitter. In addition, a tight approximation is derived for the rate and we reveal two thresholds for both the distance of the D2D link and the transmit SNR at the BS above which the underlaid D2D communication will degrade the system rate. We then particularize on the small cell setting where all users are closely located. In the small cell scenario, we show that the relationship between the distance of the D2D transmitting link and that of the D2D interfering link to the cellular user determines whether the D2D communication can enhance the system achievable rate. Numerical results are provided to verify these results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.4
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• pp.325-336
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• 2013

FlashLinQ, one of the typical D2D communication systems developed by Qualcomm, considers a single-tone communication based distributed channel-aware link scheduling method to realize the link scheduling process with low control overheads. However, considering the frequency selective fading effect of practical multi-path channel, the single-tone based SIR estimation causes a critical scheduling error problem because the received single-tone signal has quite different channel gain at each sub-carrier location. In order to overcome this problem, we propose a novel link scheduling method based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence for D2D communication system. In the proposed method, each link has a unique offset value set for the generation of CAZAC sequences. CAZAC sequences with the cyclic offsets are transmitted using multiple sub-blocks in the entire bandwidth, and then each device can obtain nearly full-band SIR using a good cyclic cross-correlation property of CAZAC sequence.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.10
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• pp.1986-1993
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• 2015

We investigate the optimal resource and power allocation for device-to-device (D2D) communications in a multicell environment. When D2D links reuse the cellular radio resources, each D2D user will interfere with a cellular link and other D2D links, in its own cell as well as in adjacent cells. Under such situation, we propose a coordinated resource allocation scheme that can handle the intercell interferences as well as the intracell interference. For a given resource allocation, we also formulate a power optimization problem and present an algorithm for finding the optimal solution. The resource and power allocation algorithms are designed to maximize the achievable rate of the D2D link, while limiting the generated interference to the cellular link. The performance of the proposed algorithms is evaluated through simulations in a multicell environment. Numerical results are presented to verify the coordination gain in the resource and power allocation.

• Journal of the Korea Society of Computer and Information
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• v.24 no.3
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• pp.57-64
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• 2019

We consider the D2D sum utility maximization in the cellular system. D2D links reuse the uplink resource of cellular system. This reuse may cause severe interference to cellular users. To protect the cellular users, interference limit from the D2D links is required. In this setting, D2D sum utility maximization problem is investigated. Each D2D link has limited transmit power budget. Because optimum solution may require global information between links and computational complexity, we propose the distributed algorithm which only require the local information from each D2D link and simple broadcasting. Simulation results are provided to verify the performance of the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.885-894
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• 2012

Currently, Demand of data traffic has rapidly increased by popular of smart device. It is very difficult to accommodate demand of data traffic by limited resource of base station (BS). To solve this problem, method has proposed that the Device-to-Device (D2D) reduce frequency overload of the BS and all of the user equipment (UE) inside the BS and neighbor BS don't allow communicating directly to BS. However, in LTE-Advance system cellular link and sharing radio resources of D2D link, the strong interference of the cellular network is still high. So we need to eliminate or mitigate the interference. In this paper, we use the transmission power control method and Soft Frequency Reuse (SFR) resource allocation method to mitigate the interference of the cellular link and D2D link. Simulation results show that the proposed scheme has high performance in terms of Signal to Noise Ratio (SINR) and system average throughput.

• Journal of Digital Convergence
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• v.18 no.10
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• pp.225-232
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• 2020

The underlaying communication scheme in 5G cellular network is a very promising resource sharing scheme, and it is an effective scheme for improving service performance of 5G and reducing communication load between a cellular link and a device to device (D2D) link. This paper proposes the algorithm to minimize the resource interference that occurs when performing 5G-based multi-class service on gNB(gNodeB) and the cooperative priority-based resource allocation scheduling scheme (CPRAS) to maximize 5G communication service according to the analyzed control conditions of interference. The proposed CPRAS optimizes communication resources for each device, and it optimizes resource allocation according to the service request required for 5G communication and the current state of the network. In addition, the proposed scheme provides a function to guarantee giga-class service by minimizing resource interference between a cellular link and a D2D link in gNB. The simulation results show that the proposed scheme is better system performance than the Pure cellular and Force cellular schemes. In particular, the higher the priority and the higher the cooperative relationship between UE(User Equipment), the proposed scheme shows the more effective control of the resource interference.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.11
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• pp.112-122
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• 2014

This paper proposes a PMSM torque control method considering DC-link voltage variation and friction torque. In general EV/HEV application, two dimensions look-up table(2D-LUT) is used for reference current generation due to its stable and robust torque control performance. Conventionally, this 2D-LUT is established by flux-torque table to overcome the DC-link voltage variation. However, the flux table establishment is more complex than the speed table establishment. Moreover, one flux data reflects several speed conditions in variable DC-link voltage, friction torque cannot be considered by using the flux table. In this paper, speed-torque 2D-LUT is used for current reference generation. With this table, PMSM torque control is well achieved regardless of DC-link voltage variation by the proposed control method. Simulation and experimental results validate improvement of torque control error through friction torque compensation.

• Journal of the Korea Society of Computer and Information
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• v.24 no.5
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• pp.19-26
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• 2019

In this paper, we consider the D2D Transmitter(Tx) and Receiver(Rx) pair assignment problem in the cellular system. Sharing the resource of the cellular system, D2D users may cause interference to the cellular system, though it is beneficial to improve the D2D user Capacity. Therefore, to protect the cellular users, D2D transmit power should be carefully controlled. Previously, optimal Tx-Rx assignment to minimize the total transmit power of users was investigated. Accordingly, the iterative algorithm to find the optimum Tx-Rx asignment was obtained. In this work, we consider the case where Tx group users becomes Rx group users, and Rx group users become Tx group users. We prove that the Tx-Rx assignment problem has the duality property. We present the numerical examples that show the duality between U-link and D-link.