Energy-Efficient Operation through Interference Avoidance for Interconnected Bluetooth WPANs

A Wireless Personal Area Network (WPAN) provides wireless networking among proximate devices, usually carried by an individual. Bluetooth is a first instance of the WPAN technology. The basic networking entity in Bluetooth is a piconet. Several piconets (WPANs) can be interconnected into a scatternet, which can be considered as an extendable multi-hop ad hoc networking structure. Since Bluetooth operates in the unlicensed ISM band, each piconet uses pseudorandom frequency hopping. If collocated piconets use the same channel simultaneously, the piconets interfere with each other and the transmitted packets are lost in collisions. This interference is termed self-interference. The piconets that are networked into scatternet exhibit spatial overlapping and naturally produce multi-piconet self-interference. The collisions cause retransmissions and increase the energy spent per data portion, which results in energy-inefficient operation. To tackle this problem, in our previous work we have proposed a self-interference avoidance (SIA) mechanism. However, this basic SIA mechanism is oblivious with respect to the physical topology and does not account for the mitigation of self-interference due to the propagation effects. Furthermore, the basic SIA mechanism relies on the assumption that all piconets are using packets of identical and fixed length. In this paper we will generalize the SIA mechanism to overcome the stated restrictions. We propose the adaptive SIA (A-SIA) algorithm, which adapts the SIA algorithm to the actual interference. The simulation results show that A-SIA largely retains the energy gain offered by the SIA algorithm, while significantly improving the goodput. We also design an instance of the SIA mechanism that operates with variable-length packets, referred as generalized SIA (G-SIA) algorithm. Our simulation results show that the G-SIA algorithm offers good performance in terms of goodput and energy efficiency, but the goodput is degraded if inappropriate segmentation/reassembly policy is used. Petar Popovski received the Dipl.-Ing. in electrical engineering and M.Sc. in communication engineering from the Faculty of Electrical Engineering, Sts. Cyril and Methodius University, Skopje, Macedonia, in 1997 and 2000, respectively and a Ph.D. degree from Aalborg University, Denmark, in 2004. He is currently Assistant Research Professor at the Department of Communication Technology at the Aalborg University. His research interests are focused on wireless ad hoc networks, wireless sensor networks, and high-speed wireless multi-carrier communications. Hiroyuki Yomo received B.S. degree in communication engineering from Department of Communication Engineering, Osaka University, Osaka, Japan, in 1997, and M.S. and Ph.D. degrees in communication engineering from Department of Electronic, Information, and Energy Engineering, Graduate School of Engineering, Osaka University, Osaka Japan, in 1999 and 2002, respectively. From April 2002 to March 2004, he was a Post-doctoral Fellow in Department of Communication Technology, Aalborg University, Denmark. From April 2004 to September 2004, he was working at NEC Corporation, Japan. Since October 2004, he has been an Assistant Research Professor in Center for TeleInfrastructure (CTIF), Aalborg University, Denmark. His research interests include medium access protocols, link-layer techniques, routing protocols, and their interactions in wireless networks. Liljana Gavrilovska received her B.Sc., M.Sc. and Ph.D. from University of Skopje (76), University of Belgrade (85) and University of Skopje (95) respectively. She joined the Faculty of Electrical Engineering, University of Skopje, Republic of Macedonia, where she currently holds positions of Professor at the Institute for Telecommunications, chief of Telecommunications Laboratory and head of CWMC (Center for Wireless and Mobile Communications), working in the area of networking and mobile communications. During 2001–2002 she joined the Centre for PersonKommunikation, Aalborg University, Denmark, where she was holding a position as Associate Research Professor and was involved in several EU (ASAP, PACWOMAN, MAGNET) and national/international projects. She is still working part-time for CTiF, Aalborg University, Denmark. Her major research is concentrated on ad hoc networking, wireless and personal area networks, cross layer optimizations, future mobile systems, traffic analysis and admission techniques. She is a senior member of IEEE and serves as a Chair of the Macedonian Communications Chapter. Ramjee Prasad is a distinguished educator and researcher in the field of wireless information and multimedia communications. During February 1988–May 1999 he has been with the Telecommunications and Traffic-Control Systems Group of Delft University of Technology (DUT), The Netherlands, where he was actively involved in the area of wireless personal and multimedia communications (WPMC). He was head of the Transmission Research Section of International research Centre for Telecommunications Transmission and Radar (IRCTR) and also Founding Program Director of the Centre for Wireless Personal Communications (CWPC). As from June 1999 Ramjee Prasad joined as the Wireless Information Multimedia Communications chair and co-director of Centre for PersonKommunikation at Aalborg University, Denmark. From January 2004 he is Founding Director of the “Centre for Teleinfrastruktur (CTIF)”. He has published over 500 technical papers, and authored and co-edited 15 books about Wireless Multimedia Communications (Artech House). His research interest lies in wireless networks, packet communications, multiple access protocols, adaptive equalisers, spread-spectrum CDMA systems and multimedia communications. Prof. Prasad is the founding chairperson of the European centre of Excellence in Telecommunications known as HERMES Partnership. He is the General Chairman of International Wireless Summit (IWS 2005) to be held in Aalborg, Denmark in September 17–22, 2005. He is a fellow of the IEE, a fellow of IETE, a senior member of IEEE, a member of NERG, and a member of the Danish Engineering Society (IDA). He is advisor to several multinational companies.     

Potentials for Application of Millimeter Wave Communications in Cellular Networks

Future 5G cellular networks will need to deliver significantly increased system capacity and user data rates. This expected growth along with today’s shortage of spectrum raises the need for new frequency allocations. Millimeter wave spectrum is emerging as a suitable candidate with a vast amount of available bandwidth (around 60 GHz). Extending cellular networks communications on millimeter wave frequencies requires extensive measurement campaigns and analysis of signals propagation characteristics. This paper gives an overview of recent measurement studies and results used for modeling millimeter wave channel behavior in different propagation environments. Also , the paper provides a preliminary simulation analysis of a hybrid LTE-millimeter wave heterogeneous network, which suggests that Gbps user data rates are achievable with sufficient beamforming gains. However, the millimeter wave cellular extensions will require architectural changes to address the technical issues spanning from the transceivers design to the operational procedures in both access and backhaul network parts.     

Visions Towards 5G: Technical Requirements and Potential Enablers

Compared to the previous generations of mobile networks, 5G will provide a significant paradigm shift by including beyond state of the art technical solutions, like very high carrier frequencies with massive bandwidths, extreme base station and device densities, and very high number of transceiver antennas. However, unlike the previous generations, it will also be highly integrative and backward compatible: combining the novel 5G air interface and spectrum together with legacy wireless systems like LTE/LTE-A and WiFi, in order to facilitate an umbrella of high-rate coverage and a seamless user experience. In order to support this advances in the radio interface, the core network will also have to reach unprecedented levels of elasticity and intelligence. Spectrum regulation will need to be rethought and significantly improved, whereas energy and cost efficiencies will become one of the key parameters that will steer the 5G design and development. This paper elaborates on the 5G related topics, identifying the key challenges for future research and preliminary 5G standardization activities, as well as providing a comprehensive survey of the current literature.     

Matrix metalloproteinase-7 facilitates immune access to the CNS in experimental autoimmune encephalomyelitis

Background  

Metalloproteinase inhibitors can protect mice against experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). Matrix metalloproteinase-9 (MMP-9) has been implicated, but it is not clear if other MMPs are also involved, including matrilysin/MMP-7 – an enzyme capable of cleaving proteins that are essential for blood brain barrier integrity and immune suppression.     

On some questions about selective separability

CH implies that selective separability is not preserved by finite powers (solving [3, Problems 3.7 and 3.9]). In ZFC, selective separability does not imply H‐separability (solving [4, Problem 34]) (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)