Mobile Clouds

1

Motivation

Inventions have long since reached their limit, and I see no hope for further development.

Julius Sextus Frontinus, highly regarded Roman engineer, 1st century A.D.

1.1 Introduction

Untethered communications, omnipresent and fundamental in today’s hyper-connected world, evolved rapidly in the last decades. The impact on our lives is so deep that it is hard to imagine how difficult it would be living now without the informational and social connectivity, freedom as well as flexibility brought by wireless communications technology. In this introduction we briefly discuss the evolutionary development of wireless communications until the present, from networks and mobile devices points of view. This overview will provide some useful and motivating background information before focusing on mobile clouds. Two evolutionary paths characterize untethered communications, the developments in wide–area communications on one hand, and the developments in short–range communications on the other hand. The former can be denominated the mobile path, while the latter is the wireless path, due to the fact that typically mobile communications, and wireless communications are the terms used for wide–area and short–range technologies, respectively. Radio broadcasting, the very first example of wide–area communications, started to be developed at the turn of the 20th century. WWI and WWII provided an immense thrust to the development of radar and communications technology. The further developments in solid–state components resulted in miniaturization, made possible implementation of complex systems and gave birth to the era of truly portable communications equipment. The first urban mobile communications systems were deployed as early as in the latest 1940’s. Single powerful base stations with high–rise antennas were initially used to provide access to areas with radius of up to some 50km. Already at that time scarcity in the available spectrum was identified as an issue and Bell Labs proposed the idea of covering large geographical regions by using a number of smaller service areas. Further developments in the upcoming decades led to the introduction of basic cellular systems for public and private use in the 1970’s. Most of this pioneering work took place in the US but in the next decades Europe and Japan developed also their own commercial cellular systems. The cellular concept, based on frequency reuse in smaller coverage areas, or cells, allowed city–wide support of a large number of users. Through the 1980’s until the present day four generations of cellular systems were developed, such that 2G, 3G and the rather recently introduced 4G coexist today. Requirements for higher supported data rates and network capacity led to a gradual reduction of cell sizes, typically up to few tens of kilometers in macro–cells, few hundred meters to few kilometers in micro–cells and from meters to a few hundred meters in the case of pico–cells. Certainly cell size is also related to mobility, large cells support higher degrees of mobility with the need for frequent handovers to adjacent cells. Providing untethered connectivity over short distances has also proved to be highly important, if not absolutely necessary, to a great deal of applications and in many practical scenarios. Over the last two decades a large number of communication technologies for short–range communications were developed fulfilling the demands for local wireless connectivity to computers, home and office appliances and other portable, movable or fixed equipment. This parallel development, the aforementioned wireless path, produced a very eclectic range of communications technologies covering from millimeters to a few hundred meters. Examples of short–range communications include wireless local area networks, (WLAN), wireless personal area network (WPAN), wireless body area network (WBAN), wireless sensor networks (WSN), radio frequency identification (RFID) and near field communications (NFC). Besides radio communication there is also optical communication, especially visible light communication (VLC). As compared to the developments in wide–area communications, focused mostly on overlay cellular networks operating on a centralized manner, short–range communications is a highly fragmented development arena, technology–, applications– and architecture–wise. The industry behind wide–area cellular and short–range communication fields are typically different. Large telecom manufactures back the former, whereas a diverse array of technology industry, with computer industry having the largest share, being behind the eclectic solutions existing for short–range communications. As we are moving towards a highly integrated mobile and communications era, the division between industry supporting cellular and short–range communications becomes blurred. Stretching from millimeters ranges of to hundreds of kilometers, wireless communications today consists of a large collection of different technologies omnipresent in our life. Figure 1.1 illustrates current representative mobile and communications approaches as a function of their typical ranges. Broadly speaking short–range and wide–area cellular communications remain today the main two approaches to untethered communications.

Figure 1.1 The realm of wireless and mobile communications today: from millimeters to hundreds of kilometers.

1.2 From Brick Phones to Smart Phones

Personal computers, Internet and mobile communications are among the most rapidly adopted technologies in history. In particular, the emergence and further popularization of mobile communication technologies are truly remarkable and unique achievements. Today, after a quarter of a century since the inception of mobile communications, the worldwide penetration of mobile and wireless communication devices exceeds 86% as given in [1]. Connectivity is seen today as an indispensable commodity, or even more, as a basic right of each individual. Mobile devices provide wireless access, making possible portable connectivity in most of the scenarios where people live, work and spend their free time. The outstanding development of mobile communications can be seen as the result of huge global research and development efforts by related industry, academia and regulators. Envisaging this rapid development in this area has always been a real challenge. Even the most optimistic forecasts were short to predict the colossal growth of mobile communications. In 1997 it was estimated that by 2010 there would be from one to two billion mobile subscribers [2, 3], whereas in 2006 such figure was estimated to be three billion [4]. The actual figure in 2010 well exceeded the five billions. In a few years from now (2014) the worldwide penetration is expected to reach or even exceed 100%.

These impressive figures are just one part of the story. Mobile and wireless communications have changed radically the way people communicate with each other and access information. And more changes will certainly follow. The impact of mobile communications on how people socialize, work, retrieve information, do business and entertain themselves is really enormous. The global process of adopting mobile communications technology has been quick and its impact on individuals and the society as a whole has been profound, far beyond the initial expectations. The so far two–and–a–half decades of mobile communications development has basically spanned four mobile technology generations, known as 1G, 2G, 3G and 4G. These generations, encompassing several technologies, have coexisted and continue to coexist on a global scale. Today, 2G and 3G are the most widely used mobile technologies while 4G, being at this time rapidly deployed, will be the mainstream mobile technology in the near future. Moreover, 5G, aiming at a time-frame beyond 2020, is currently being developed. While mobile communications continues to shape the way that people live, such deep impact would have not been possible without the outstanding technical achievements that took place in the rather short mobile communications era. Among the most representative developments that occurred in the past 25 years mobile users witnessed the following technological enhancements: data rate support increased from some 100bps to 1Mbps and higher; memory onboard devices was boosted from some 1MB to 32GB and higher; weight of terminals reduced from about 5kg down to 100g and below; device size (volume) decreased from 5000cm3 to 50cm3; prices dropped from 5000Euro down to the range 50Euro to 500Euro; operating time saw a ten–fold decrease (1h–10h) whereas the total number of devices on a worldwide scale jumped from a few millions to nearly six billion units today.

Figure 1.2 summarizes these accomplishments by showing the approximate enhancing factors of key capabilities of mobile communications devices. Another major development...