ISSN : 1796-2021
Volume : 4    Issue : 3    Date : April 2009

Special Issue: Wireless Gigabit Technologies
Guest Editors: Simone Frattasi, Nicola Marchetti, Muhammad Imadur Rahman, Ernestina Cianca

Simone Frattasi, Nicola Marchetti, Muhammad Imadur Rahman, Ernestina Cianca
Page(s): 143-145
Full Text:
PDF (197 KB)

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.  

Index Terms
Special Issue, Wireless Gigabit Technologies