On multimedia networks: self-similar traffic and networkperformance

The main objective in telecommunications network engineering is to have as many happy users as possible. In other words, the network engineer has to resolve the trade-off between capacity and QoS requirements. Accurate modeling of the offered traffic load is the first step in optimizing resource allocation algorithms such that provision of services complies with the QoS constraints while maintaining maximum capacity. As broadband multimedia services became popular, they necessitated new traffic models with self-similar characteristics. We present a survey of the self-similarity phenomenon observed in multimedia traffic and its implications on network performance. Our current research aims to fill the gap between this new traffic model and network engineering. An immediate consequence of this study is the demonstration of the limitations or validity of conventional resource allocation methods in the presence of self-similar traffic     

Reducing computation time of a wireless resource scheduler by exploiting temporal channel characteristics

Wireless Networks - The long term evolution downlink scheduler must attain a low computation time as it performs scheduling decisions every 1 ms. 5G New Radio introduced mini-slots for the...     

Selective Multiuser Detection for Cellular CDMA Systems

Multiuser detection-oriented CDMA systems have been anticipated to significantly improve system capacity in third-generation W-CDMA-based systems. However, they are greatly limited by the computational complexity of multiuser receivers. In this work, we propose a new, computationally efficient approach to multiuser detection (MUD), consisting in MUD of the subset of preselected users, and conventional detection of the rest of users, called selective multiuser detection (SMD). It allows for full exploitation of available processing power at the receiver by use of MUD and provides remedy for computational complexity of MUD techniques when the number of active users increases beyond the processing capability. We propose and examine three different criteria for selection of users to be processed by the multiuser receiver and analyze the capacity for the single-cell and the multicell CDMA cellular system. The capacity improvement with respect to the conventional CDMA detector combines the gain from MUD and reduction of other-cell interference. We apply the analysis to two SMD schemes using decorrelator and successive interference canceller (SIC) as the multiuser receiver. The results indicate that the SMD is a promising alternative for MUD-oriented CDMA systems with large numbers of active users.     

Performance benchmarking for wireless location systems

Accuracy criteria for wireless location systems have been the subject of much discussion due to the different interpretations and assumptions regarding the requirements that were stated in the FCC's wireless E-911 ruling. Indeed, these requirements cover only the expected accuracy/error percentage in location measurements, which is insufficient because it allows potentially misleading information from and about location systems. This article draws analogies with well-known performance criteria for wireless communications systems toward setting a comprehensive suite of benchmarks for wireless location systems     

Multiuser Detection Techniques for Hierarchical Cell Structures in CDMA Cellular Systems

CDMA-only microcell/macrocell cellular systems have traditionally suffered from the near-far problem in the microcells located near the macrocell boundary. Strong macrocell interference in these microcells disables conventional single-user detectors. The solutions currently adopted in the literature include bandwidth-consuming frequency separation between macrocell and microcell tiers and complex hybrid architectures. In this work we present the techniques for multiuser receiver design that address this problem. The preprocessing stage, called the projection stage, which projects the received signal onto the space orthogonal to the subspace spanned by macrocell users' signature sequences, is introduced. It is followed by the stage employing conventional multiuser detection (MUD) techniques. This class of detectors, called multiuser projection detectors (MPD), provides efficient protection against macrocell interference in all microcells, regardless of their location within the macrocell. The protection is optimal if the amplitudes of macrocell interferers are not known by the microcell BS. We analyze four MPDs using different MUD techniques in the detection stage, and perform performance comparison.     

Fatty acid composition of wild and cultivated gilthead seabream (Sparus aurata) and sea bass (Dicentrarchus labrax)

Total lipid content and fatty acid composition were determined for wild and cultivated gilthead seabream and sea bass. Fatty acid analyses were carried out by gas chromatography‐ mass spectrometry. Respective total lipid content of flesh in cultivated gilthead seabream and sea bass were 1.7‐5.0‐times those of wild samples. Palmitic acid (C16:0) and oleic acid (C18:1n‐9) were the major fatty acids respectively among the saturated fatty acids and monounsaturated fatty acids of each fish species. It is noteworthy that both linoleic acid (C18:2n‐6) and arachidonic acid (C20:4n‐6) were predominant in total n‐6 polyunsaturated fatty acids in the respective cultivated and wild types. Eicosapentaenoic acid (C20:5n‐3) and docosahexaenoic acid (C22:6n‐3) amounts were significantly higher in flesh of cultivated fish than in wild fish.     

Location-Based Service Provisioning for Next Generation Wireless Networks

We study how the wireless network infrastructure can support location-based services (LBSs). We assume that each mobile is equipped with self-geolocation capability. The wireless network can provide geolocation information of mobiles to an application services provider (ASP) so that the ASP can customize services based on the geolocation of the users. The main challenge in wireless networking is to keep track of the geolocation of mobile users such that the application service can maintain a certain quality of service (QoS). In general, the quality of service depends on how often mobiles update their geolocation. Because geolocation updates require battery power, radio resources, and signaling in the wired network, optimization of the geolocation update frequency is critical. In this paper, we present geolocation update schemes in which we can minimize the update frequency while satisfying the QoS of application service. For case study, we consider location-based traffic report service (LBS-TR) and location-based navigation service (LBS-NS). In LBS-TR, each mobile user about to enter a heavily jammed highway is informed in a timely manner so that the user can avoid traffic congestion. In LBS-NS, a mobile user is given navigation instructions custom-tailored to the geolocation of the user. The granularity of navigation instructions changes as the user moves from highway to local street and from local street to building complex.     

Mussel Inspired Dynamic Cross‐Linking of Self‐Healing Peptide Nanofiber Network

A general drawback of supramolecular peptide networks is their weak mechanical properties. In order to overcome a similar challenge, mussels have adapted to a pH‐dependent iron complexation strategy for adhesion and curing. This strategy also provides successful stiffening and self‐healing properties. The present study is inspired by the mussel curing strategy to establish iron cross‐link points in self‐assembled peptide networks. The impact of peptide‐iron complexation on the morphology and secondary structure of the supramolecular nanofibers is characterized by scanning electron microscopy, circular dichroism and Fourier transform infrared spectroscopy. Mechanical properties of the cross‐linked network are probed by small angle oscillatory rheology and nanoindentation by atomic force microscopy. It is shown that iron complexation has no influence on self‐assembly and β‐sheet‐driven elongation of the nanofibers. On the other hand, the organic‐inorganic hybrid network of iron cross‐linked nanofibers demonstrates strong mechanical properties comparable to that of covalently cross‐linked network. Strikingly, iron cross‐linking does not inhibit intrinsic reversibility of supramolecular peptide polymers into disassembled building blocks and the self‐healing ability upon high shear load. The strategy described here could be extended to improve mechanical properties of a wide range of supramolecular polymer networks.     

Nanomechanical characterization by double-pass force-distance mapping

We demonstrate high speed force-distance mapping using a double-pass scheme. The topography is measured in tapping mode in the first pass and this information is used in the second pass to move the tip over the sample. In the second pass, the cantilever dither signal is turned off and the sample is vibrated. Rapid (few kHz frequency) force-distance curves can be recorded with small peak interaction force, and can be processed into an image. Such a double-pass measurement eliminates the need for feedback during force-distance measurements. The method is demonstrated on self-assembled peptidic nanofibers.