Simone Frattasi

Channel-aware scheduling algorithms for SC-FDMA in LTE uplink

Single-carrier frequency division multiple access (SC-FDMA) has been selected as the uplink access scheme in the UTRA Long Term Evolution (LTE) due to its low peak-to-average power ratio properties compared to orthogonal frequency division multiple access. Nevertheless, in order to achieve such a benefit, it requires a localized allocation of the resource blocks, which naturally imposes a severe constraint on the scheduler design. In this paper, three new channel-aware scheduling algorithms for SC-FDMA are proposed and evaluated in both local and wide area scenarios. Whereas the first maximum expansion (FME) and the recursive maximum expansion (RME) are relative simple solutions to the above-mentioned problem, the minimum area-difference to the envelope (MADE) is a more computational expensive approach, which, on the other hand, performs closer to the optimal combinatorial solution. Simulation results show that adopting a proportional fair metric all the proposed algorithms quickly reach a high level of data-rate fairness. At the same time, they definitely outperform the round-robin scheduling in terms of cell spectral efficiency with gains up to 68.8% in wide area environments.

OFDMA vs. SC-FDMA: performance comparison in local area imt-a scenarios

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 multiuser 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 blocks chemes.

Mobile Positioning and Tracking: From Conventional to Cooperative Techniques

This book presents the most recent state of the art in mobile positioning and tracking techniques. This book discusses mobile positioning solutions applied on top of current wireless communication networks. In addition, the authors introduce advanced and novel topics such as localization in heterogeneous and cooperative networks, providing a unified treatment of the topic for researchers and industry professionals alike. Furthermore, the book focuses on application areas of positioning, basics of wireless communications for positioning, data fusion and filtering techniques, fundamentals of tracking, error mitigation techniques, positioning systems and technologies, and cooperative mobile positioning systems. Key Features: Covers the state of the art of satellite- and terrestrial-based positioning systems, spanning from outdoor to indoor environments and from wide area networks to short-range networks Discusses a whole range of topics related to mobile positioning: from fundamentals of positioning to the description of a wide spectrum of mobility models for tracking, from details on data fusion and filtering techniques to error mitigation techniques (including aspects of signal processing) Provides a solid bridge between research and industry envisaging a potential implementation of the presented solutions Fills the gap between positioning and communication systems, showing how features of communication systems can be used for positioning purposes and how the retrieved location information can be used to enhance the performance of wireless networks. Includes an accompanying website This book will be a valuable guide for advanced students studying related courses. Professionals and practitioners in the field of positioning and mobile technologies, and software and service developers will also find this book of interest.

Cooperative Positioning Techniques for Mobile Localization in 4G Cellular Networks

In this paper, we exploit the concept of cooperative localization by utilizing the additional information obtained from short-range links to enhance the location estimation accuracy in forthcoming cellular systems. Simulations for a hybrid WiMAX/Wi-Fi system are carried out considering an outdoor environment, where time difference of arrival (TDOA) and received signal strength (RSS) measurements are combined thanks to advanced data fusion techniques. Results show that the proposed system allows to meet the federal Communications Commission (FCC) requirements and overcome the ever changing channel conditions.

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.

Fixed Frequency Reuse for LTE-Advanced Systems in Local Area Scenarios

LTE-Advanced systems, which aim to provide high data rate wireless services, have received world-wide researching interests nowadays. In this paper, the performance of fixed frequency reuse with different reuse factors is studied in LTE-Advanced systems. Performance is measured in terms of both average cell throughput and cell edge user throughput. It is found that a properly chosen reuse factor with respect to cell size (which leads to different level of inter-cell interference), can offer up to 30% gain in average cell throughput and much higher gain for cell-edge user throughput in Local Area (LA). This high gain from frequency reuse makes it attractive for future LTE-Advanced systems.

Heterogeneous services and architectures for next-generation wireless networks

Even though it is named as the successor of the previous cellular generations, the fourth generation of wireless mobile communication systems (4G) is predominantly presented as a convergence platform that provides clear advantages in terms of coverage, bandwidth, energy consumption and a variety of heterogeneous services, ranging from pop-up advertisements to location-based and interactive or on-demand ones (so called IP datacasting). Based on the above vision of 4G, in this paper we propose innovative services and architectures that may achieve enhanced security, energy efficiency, and just-for-you and just-in-time content delivery. Furthermore, since the state-of-the-art technologies do not appropriately cover the needs required for 4G, a context sensitive service discovery that can operate in a wireless as well as in a wired network environment, ranging from local to global distances, is described and applied to the case of the proposed services.

Cooperative Mobile User Location for Next-Generation Wireless Cellular Networks

Along with a vision that foresees the fourth generation (4G) as based on a cellular system that will also support short-range communications among its terminals, in this paper we propose an innovative geolocation scheme that exploits such an architecture and combines long- and short-range location information in a novel location algorithm. The simulation results presented in the paper show that our proposed scheme permits to enhance the location estimation accuracy with respect to the actual stand-alone hybrid cellular solutions.

Designing socially robust 4G wireless services

The difficulties and technical limitations of the third generation (3G) of wireless mobile communication systems as well as the emergence of new mobile broadband technologies on the market have prompted university and industry researchers to thoroughly reflect on the fourth generation (4G) of these technologies. In this article, we outline the interaction between technology and society that shall help to develop 4G in a way that maximize its acceptance and penetration in the market, while minimizing the downside risk of its failure. This presupposes that the user is considered as the cornerstone in the design of 4G. As a consequence, we sum up the relevant service design rules derived from such a user-centric model and propose innovative 4G services

A pragmatic methodology to design 4g: from the user to the technology

The ever-increasing growth of user demands, the limitations of the Third Generation of Mobile Communication Systems (3G) and the emergence of new mobile broadband technologies on the market have brought researchers and industries to a throughout reflection on the Fourth Generation (4G). Many prophetic visions have appeared in literature presenting the future generation as the ultimate boundary of the wireless mobile communication without any limit in its potential, but practically not giving any designing rules and thus any definition of it. In this paper we hence propose a new user-oriented methodology that considers the user as “the angular stone in the design of 4G” and identifies his functional needs and expectations, reflecting and illustrating them in everyday life situations. In this way, we devise fundamental user scenarios where new services are significant assets for the user. The latter implicitly reveal the key features of 4G, which are then explicated in a new framework – the “user-centric” system – that, through a satellite hierarchical vision, describes the various level of interdependency among them. This approach consequently brings to the identification of the designing rules and therefore to a more pragmatic definition of 4G. Finally, an example of a new 4G application is also given in order to demonstrate the validity of the overall methodology.