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Author(s): Simone Frattasi | Nicola Marchetti | Muhammad Imadur Rahman | Ernestina Cianca

Journal: Journal of Communications
ISSN 1796-2021

Volume: 4;
Issue: 3;
Start page: 143;
Date: 2009;
Original page

Keywords: Special Issue | Wireless Gigabit Technologies

The use of the Internet for more entertainment-like services, which is a major component in the dramatic change of broadband services and expectations, is leading to a continued growth in the demand for higher capacity in wireless systems. This is one of the reasons that are driving the wireless industry to strive harder for designing more bandwidth efficient system. As an example; music file swaps and downloads are growing at an annual rate of 50% to 60%, and video downloading and streaming are so bandwidth intensive that they may already account for 50 to 60% of all wireless traffic at this moment. This fast-rising demand for bandwidth will reach the limits in terms of data rates not only for currently available technologies such as Wi-Fi and 3G, but even for upcoming high data rate systems, such as UTRA-LTE and WiMAX systems, which can achieve much higher bandwidth efficiencies compared to previous systems, such as GSM, WCDMA, etc. Moreover, the growth in capabilities of consumer devices (e.g., 60 frames/s Ultra-HDTV targeted for a mass market 10 years from now) and futuristic applications such as 3D Internet, virtual and augmented reality and telepresence will lead in the forthcoming years to capacity needs of the order or multi-gigabits per second. These data rates are today only achievable with optical fibers. Within the realm of wireless communication, a first step towards this goal is represented by IMT-Advanced (IMT-A) systems, currently specified by the International Telecommunications Union (ITU). IMT-A systems are expected to provide peak data-rates in the order of 1Gbit/s in local area and 100Mbit/s in wide area scenarios. The deployment of these kinds of systems at mass market level is believed to take place around year 2015 and these systems will facilitate what has already been a buzzword for the last decade, namely “4G”. The ability to offer such high data rates in 100MHz bandwidth requires overall a very high spectral efficiency, and hence the need for multi-antenna techniques (MIMO) with spatial multiplexing, fast dynamic link adaptation and packet scheduling, wideband access techniques, and most likely non-contention based spectrum sharing among multiple operators. Moreover, to achieve this performance level, major advancements in the state-of-the-art are required in several key technologies, spanning all the layers. Flexible spectrum usage through carrier aggregation and cognitive radio solutions, and cooperative relaying are some of the most promising solutions. Many of these required technology components and techniques are well researched and established. What we now need to consider is how we can integrate and optimize their use in providing the target cell data rates with high availability, thus, new research on multifaceted system level design is very important for realizing the dreams of ‘4G’. As presented in Paper 1, “The Evolution of LTE towards IMT-Advanced”, by S. Parkvall and D. Astely, some of the above-mentioned technologies are included in the Long Term Evolution-Advanced (LTE-A) air interface as defined by the Third Generation Partnership Project (3GPP).  LTE-Advanced systems have a target peak data rate which satisfies the requirement as specified for IMT-A. Some key technology components for future LTE-A systems are presented in this tutorial paper. While Paper 1 gives an overview of the advanced techniques that are foreseen in LTE-A systems,, Paper 2, “On the Feasibility of Precoded Single User MIMO for LTE-A Uplink”, by G. Berardinelli et al., focuses on one specific feature that is expected to be included in LTE-A: the use of uplink single-user MIMO (SU-MIMO). In particular, the paper discusses several channel-aware precoding techniques applied to both orthogonal frequency division multiplexing (OFDM) and single-carrier frequency division multiplexing (SC-FDM), covering both spatial multiplexing and transmit diversity. SU-MIMO only considers access to the multiple antennas that are physically connected to each individual terminal. In a multi-user scenario, it might be interesting to exploit the availability of multiple independent radio terminals in order to enhance the communication capabilities of each individual terminal (e.g., to get some diversity gain). The so-called multi-user MIMO (MU-MIMO) technique is considered in Paper 3, “Distributed Scheduling Algorithm for Multiuser MIMO Downlink with Adaptive Feedback”, by L. Zhao et al.. The distributed scheduling algorithm with adaptive feedback proposed for the downlink is shown to achieve higher system capacity than existing schemes. Finally, it is well known that the performance of MIMO techniques is strongly related to the physical channel properties experienced at the both of ends of transmissions. One such issue is the spatial correlation between the channels seen at different antenna terminals. Paper 4, “Performance of Spatial Modulation in Correlated and Uncorrelated Nakagami Fading Channels”, by A. Alshamali and B. Quza, in fact derives the exact integral expressions for calculating the symbol error rate of M-QAM modulations of spatial multiplexing schemes in correlated and uncorrelated Nakagami fading channels. Targeting gigabit per second communications requires very high spectrum allocation, in the range of 100MHz. Therefore, techniques that allow an efficient and flexible use of the spectrum are of paramount importance. Cognitive radio (CR) networks, which are able to sense the environment and adapt their communication to it, can be used to exploit unused licensed spectrum without interfering with incumbent users. Papers 5, “Accumulative Interference Modeling for Cognitive Radios with Distributed Channel Access”, by M. Timmers et al., deals with the modeling of the accumulated interference generated from a large scale CR network. This accurate modeling evaluates how the density of the network affects the sensing requirements of the CRs in meeting a certain interference constraint. Cooperative relaying is another important enabling technology for gigabit per second communications. On the one hand, when the terminal is a small node of a sensor network, and it is impractical to equip it with multiple antennas due to size and power limitations, cooperative relaying represents an interesting alternative to achieve high data rates. In cooperative relay networks, a diversity gain is achieved from virtual antenna arrays consisting of a collection of distributed antennas belonging to different relays. Paper 6, “A Hybrid Cooperative Relay Selection Algorithms for Fixed Relay Based Cellular Networks”, by J. Fan et al., presents a hybrid cooperative relay selection algorithm for fixed relay-based cellular networks that can dynamically choose different cooperative strategies according to current user conditions in the cell. On the other hand, cooperative communications can help in enhancing the efficient wireless bandwidth utilization, meant as a reduction of overheads and data retransmissions. Paper 7, “Exploiting Cooperation for Performance Enhancement and High Data Rates”, by T.K. Madsen et al., discusses an approach to increase the bandwidth utilization based on a cooperative network architecture, referred to as cellular controlled peer-to-peer (CCP2P). In CCP2P networks, a group of terminals in close proximity form a cooperative cluster; those terminals are connected with the “outside world” using cellular links. Performance gain can be achieved by exploiting the cooperative behavior of the terminals in the cluster. Finally, Paper 8, “Turning the Cellphone into an Antipoverty Vaccine, by D. Raha and S. Cohn-Sfetcu, includes a review of the social impact that cell phone has represented and can represent in the near future. In particular, it focuses on the issues facing the application of wireless technologies on the huge scale and at the costs required for access by the poor and illiterate masses of the world. As such, the article poses the challenges faced by the technology world in achieving the success of the Mobile Revolution. The editors would like to thank reviewers and authors, who, in different ways, have contributed to this Special Issue. We would like to acknowledge all the other authors who have submitted their contributions for this issue.  
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