1,721,185 research outputs found
Overhead reduction in frequency division duplexing (FDD) multiple-input multiple-output (MIMO)
No full textNetwork Coding Schemes for Device-to-Device Communications Based Relaying for Cellular Coverage Extension
Full text linkAlthough network assisted device-to-device (D2D) communications is known to improve the spectraland energy efficiency of proximal communications, its performance is less understood when employedto extend the coverage of cellular networks.In this paper, we study the performance of D2D basedrange extension in terms of sum rate and power efficiency when a relaying user equipment (UE) helps to improvethe coverage for cell-edge UEs.In our design, the relaying UE has own traffic to transmit and receive to/from the cellular base station (BS) andcan operate either in amplify-and-forward (AF) or decode-and-forward (DF) modes and can make use of either digital oranalogue (PHY layer) network coding.In this rather general setting, we propose mode selection, resource allocation and power control schemesand study their performance by means of system simulations.We find that the performance of the DF scheme with network coding is superior both to the traditional cellularand the AF based relaying schemes, including AF with two-slot or three-slot PHY layer network coding.QC 20150316</p
Millimeter Wave Cellular Networks: A MAC Layer Perspective
No full textThe millimeter-wave (mmWave) frequency band is seen as a key enabler of multigigabit wireless access in future cellular networks. In order to overcome the propagation challenges, mmWave systems use a large number of antenna elements both at the base station and at the user equipment, which leads to high directivity gains, fully directional communications, and possible noise-limited operations. The fundamental differences between mmWave networks and traditional ones challenge the classical design constraints, objectives, and available degrees of freedom. This paper addresses the implications that highly directional communication has on the design of an efficient medium access control (MAC) layer. The paper discusses key MAC layer issues, such as synchronization, random access, handover, channelization, interference management, scheduling, and association. This paper provides an integrated view on MAC layer issues for cellular networks, identifies new challenges and tradeoffs, and provides novel insights and solution approaches
MMSE Receiver Design and SINR Calculation in MU-MIMO Systems with Imperfect CSI
Full text linkThe performance of the uplink of multiuser multiple input multiple output systems depends critically on the receiver architecture and on the quality of the acquired channel state information. A popular approach is to design linear receivers that minimize the mean squared error (MSE) of the received data symbols. Unfortunately, most of the literature does not take into account the presence of channel state information errors in the MSE minimization. In this letter we develop a linear minimum MSE (MMSE) receiver that employs the noisy instantaneous channel estimates to minimize the MSE, and highlight the dependence of the receiver performance on the pilot-to-data power ratio. By invoking the theory of random matrices, we calculate the users’ signal-to-interference-plus-noise ratio as a function of the number of antennas and the pilot-to-data power ratio of all users. Numerical results indicate that this new linear receiver outperforms the classical mismatched MMSE receiver
Benchmarking Practical RRM Algorithms for D2D Communications in LTE Advanced
No full textDevice-to-device (D2D) communication integrated into cellular networks is an advanced tool to take advantage of the proximity of devices and allow for reusing cellular resources and thereby to increase the user bitrates and the system capacity. However, the introduction of D2D in legacy long term evolution (LTE) cellular spectrum requires to revisit and modify the existing radio resource management and power control (PC) techniques in order to fully realize the potential of the proximity and reuse gains and to limit the interference to the cellular layer. In this paper, we examine the performance of the legacy LTE PC tool box and benchmark it against an utility optimal iterative scheme. We find that the open loop PC scheme of LTE performs well for cellular users both in terms of the used transmit power levels and the achieved signal-to-interference-and-noise-ratio distribution. However, the performance of the D2D users as well as the overall system throughput can be boosted by the utility optimal scheme, by taking better advantage of both the proximity and the reuse gains. Therefore, in this paper we propose a hybrid PC scheme, in which cellular users employ the legacy LTE open loop PC, while D2D users exploits the utility optimizing distributed PC scheme. We also recognize that the hybrid scheme is not only nearly optimal, and can balance between spectral and energy efficiency, but it also allows for a distributed implementation at the D2D users, while preserving the LTE PC scheme for the cellular users.QC 20150422</p
Low-Latency Networking: Where Latency Lurks and How to Tame It
No full textWhile the current generation of mobile and fixed communication networks has been standardized for mobile broadband services, the next generation is driven by the vision of the Internet of Things and mission-critical communication services requiring latency in the order of milliseconds or submilliseconds. However, these new stringent requirements have a large technical impact on the design of all layers of the communication protocol stack. The cross-layer interactions are complex due to the multiple design principles and technologies that contribute to the layers’ design and fundamental performance limitations. We will be able to develop low-latency networks only if we address the problem of these complex interactions from the new point of view of submilliseconds latency. In this paper, we propose a holistic analysis and classification of the main design principles and enabling technologies that will make it possible to deploy low-latency wireless communication networks. We argue that these design principles and enabling technologies must be carefully orchestrated to meet the stringent requirements and to manage the inherent tradeoffs between low latency and traditional performance metrics. We also review currently ongoing standardization activities in prominent standards associations, and discuss open problems for future research
A Comparative Study of Power Control Approaches for Device-to-Device Communications
No full textDevice-to-device (D2D) communications integrated into cellular networks is a means to take advantage of the proximity of devices and thereby to increase the user bitrates and system capacity. D2D communications has recently been proposed for the 3GPP Long Term Evolution (LTE) system as a method to increase the spectrum- and energy-efficiency. Such systems support a wide range of power control schemes based on a combination of open-loop and closed-loop components and there is a need to set the associated control parameters such that spectrum- and energy-efficiency targets are met. In this paper we study the performance of various power control strategies applicable to D2D communications in LTE networks and compare them with a utility function maximization approach that balances spectrum efficiency and the total transmission power. Our reference scheme is based on a fully distributed algorithm that iteratively sets the signal-to-interference-plus-noise (SINR) targets and corresponding transmit power levels. We find that the LTE-based power control approach performs close to the optimal scheme provided that the associated parameters are properly set. 1 © 2013 IEEE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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