Implementation Issues for OFDM-Based Multihop Cellular Networks

In this article we present various issues that need careful design for the successful implementation of OFDMA-based multihop cellular networks which need incorporation of relay terminals. The first issue we present is synchronization. We show that it is not a problematic issue for infrastructure-based relaying, where the relay is deployed by a system operator at strategic points in the cell. Second, we focus on the advantage of adaptive relaying and provide a frame structure to enable adaptive relaying in a cellular network operating according to the IEEE 802.16e standard. The third issue we present is related to hardware implementation aspects. Hardware performance and resource usage analysis will show that cooperative diversity schemes increase hardware resource usage and power/energy consumption at mobile terminals. The last issue we present is within the context of link layer ARQ, where we propose a novel retransmission method, named local retransmission-ARQ (LR-ARQ), which is designed to take advantage of the multihop nature of the cellular network. Practically, we show that LR-ARQ improves performance with respect to its single-hop counterpart in terms of cell latency, goodput, and throughput.     

OFDMA vs. SC-FDMA: performance comparison in local area imt-a scenarios [recent advances and evolution of WLAN and WMAN standards]

The system requirements for IMT-A are currently being specified by the ITU. Target peak data rates of 1 Gb/s in local areas and 100 Mb/s in wide areas are expected to be provided by means of advanced MIMO antenna configurations and very high spectrum allocations (on the order of 100 MHz). For the downlink, OFDMA is unanimously considered the most appropriate technique for achieving high spectral efficiency. For the uplink, the LTE of the 3GPP, for example, employs SCFDMA due to its low PAPR properties compared to OFDMA. For future IMT-A systems, the decision on the most appropriate uplink access scheme is still an open issue, as many benefits can be obtained by exploiting the flexible frequency granularity of OFDMA. In this article we discuss the suitability of using OFDMA or SC-FDMA in the uplink for local area high-data-rate scenarios by considering as target performance metrics the PAPR and multi-user diversity gain. Also, new bandwidth configurations have been proposed to cope with the 100 MHz spectrum allocation. In particular, the PAPR analysis shows that a localized (not distributed) allocation of the resource blocks (RBs) in the frequency domain shall be employed for SC-FDMA in order to keep its advantages over OFDMA in terms of PAPR reduction. Furthermore, from the multiuser diversity gain evaluation emerges the fact that the impact of different RB sizes and bandwidth configurations is low, given the propagation characteristics of the assumed local area environment. For full bandwidth usage, OFDMA only outperforms SC-FDMA when the number of frequency multiplexed users is low. As the spectrum load decreases, instead, OFDMA outperforms SC-FDMA also for a high number of frequency multiplexed users, due to its more flexible resource allocation. In this contex different channel-aware scheduling algorithms have been proposed due to the resource allocation differences between the two schemes.     

Defining 4G technology from the users perspective

The ever-increasing growth of user demand, the limitations of the third generation of wireless mobile communication systems, and the emergence of new mobile broadband technologies on the market have brought researchers and industries to a thorough reflection on the fourth generation. Many prophetic visions have appeared in the literature presenting 4G as the ultimate boundary of wireless mobile communication without any limit to its potential, but in practical terms not giving any design rules and thus any definition of it. In this article we give a pragmatic definition of 4G derived from a new user-centric methodology that considers the user as the "cornerstone" of the design. In this way, we devise fundamental user scenarios that implicitly reveal the key features of 4G, which are then expressed explicitly in a new framework - the "user-centric" system - that describes the various level of interdependency among them. This approach consequently contributes to the identification of the real technical step-up of 4G with respect to 3G. Finally, an example of a potential 4G application is also given in order to demonstrate the validity of the overall methodology.     

An Integrated AP for Seamless Interworking of Existing WMAN and WLAN Standards

Broadband Fixed Wireless Access (BFWA) systems represent a potential technological foundation for the Fourth Generation of Wireless Mobile Communication Systems (4G) as they can replace wired broadband and, with sufficient widespreading deployment, can significantly cut into the usage of cellular networks in many areas. In this context, the seamless interworking of Wireless Metropolitan Area Network (WMAN) and Wireless Local Area Network (WLAN) technologies is an efficient solution to provide the indoor extension of BFWA systems coverage, which would largely contribute to their success and penetration in the market. In this paper, we introduce a novel Access Point (AP), called WMAN/WLAN AP (WWAP), which essentially integrates in a compact device a WMAN Subscriber Station (SS) and a WLAN AP in order to extend the WMAN coverage in-house and to guarantee the end-to-end Quality of Service (QoS). Besides the technical features, the market trends and the usage scenarios where the WWAP might be a cost-effective and a very efficient solution are outlined. Finally, simulation results are carried out in order to demonstrate the effectiveness of the proposed AP. Simone Frattasi was born in Rome, Italy, on December 13, 1977. He received his B.Sc. and M.Sc. degrees from the University of Rome Tor Vergata, Italy, in 2001 and 2002, respectively. He has been employed by the University of Aalborg, Denmark, in the Wireless Networking Group (WING) as Research engineer (2002–2004), working on the IST-STRIKE (Spectrally Efficient Fixed Wireless Network based on Dual Standards) and VeRT (Vehicular Remote Tolling) projects. He is currently a Ph.D. student in the Center for TeleInFrastruktur (CTIF), Aalborg University, working on the JADE (Joint Advanced Development Enabling 4G) project, a joint cooperation of CTIF and SAMSUNG. His research interests mainly concern the Fourth Generation of Wireless Mobile Communication Systems (4G), in particular, heterogeneous services and architectures, clustering algorithms and MAC protocols related to the issues of cooperation and relaying in cellular extended short-range communication systems, hybrid and cooperative location techniques, QoS and ARQ/HARQ. Ernestina Cianca graduated cum laude in Electronics Engineering in 1997 at the University of L'Aquila. She was Italtel/Siemens (L'Aquila) from 1997 to 1998. She got her Ph.D. degree from the University of Rome Tor Vergata (URTV). The thesis work was on power management in CDMA-based satellite systems. She has been employed by the University of Aalborg, Denmark, in the Wireless Networking Group (WING), as Research engineer (2000–2001) and as Assistant Professor (2001–2003). She is currently Assistant Professor in Telecommunications at the URTV (Department of Electronics Engineering), teaching DSP, Information and Coding. Her research mainly concerns wireless access technologies (CDMA and MIMO-OFDM-based systems), in particular, Radio Resource Management at PHY/MAC layer, ARQ/HARQ, TCP-IP issues over wireless links, integration of terrestrial and satellite systems. She has been the vice-coordinator of the following national research programs: CABIS, on CDMA integrated mobile systems (2000–2002) and SHINES, on satellite-HAP integrated networks for multimedia applications co-financed by MIUR (2002–2004). She is currently working on various European Projects. She is author of about 40 papers, on international journals/transactions and proceedings of international conferences. Ramjee Prasad was born in Babhnaur (Gaya), Bihar, India, on July 1, 1946. He is now a Dutch Citizen. He received his B.Sc. (Eng) degree from Bihar Institute of Technology, Sindri, India, and his M.Sc. (Eng) and Ph.D. degrees from Birla Institute of Technology (BIT), Ranchi, India, in 1968, 1970 and 1979, respectively. Since June 1999, Dr. Prasad has been with Aalborg University, where currently he is Director of the Center for TeleInFrastruktur (CTIF), and holds the chair of wireless information and multimedia communications. He is the coordinator of the European Commission Sixth Framework Integrated Project MAGNET (My personal Adaptive Global NET). He was involved in the European ACTS project FRAMES (Future Radio Wideband Multiple Access Systems) as a DUT project leader. He is a project leader of several international, industrially funded projects. He has published over 500 technical papers, contributed to several books, and has authored, coauthored, and edited eleven books. He has served as a member of advisory and program committees of several IEEE international conferences. In addition, Dr. Prasad is the coordinating editor and editor-in-chief of the Kluwer International Journal on Wireless Personal Communications and a member of the editorial board of other international journals, including the IEEE Communications Magazine and IEE Electronics Communication Engineering Journal. Dr. Prasad is also the founding chairman of the European Center of Excellence in Telecommunications, known as HERMES. He is a fellow of IEE, a fellow of IETE, a senior member of IEEE, a member of The Netherlands Electronics and Radio Society (NERG), and a member of IDA (Engineering Society in Denmark). Dr. Prasad is the advisor of several multinational companies.