With 3G having seen lack luster performance in mobilizing the Internet, the media and communications industries are migrating to more advanced technologies with the intention of improving the underlying performance and economics for delivering broadband services. Advanced technologies such as 3G-LTE, UMB, mobile WiMAX, are being touted as the migratory technologies towards 4G, with the support of technologies like 802.11n, and WiFi-mesh. As these technologies come to market it remains to be seen how well they perform relative to service demands. The open mobile Internet environment created with 4G will challenge the traditional service provider business models and dramatically lower the barriers for new entrants to penetrate the market with a variety of innovative solutions. It is competition derived from these innovative solutions that will drive the 4G market.

Introduction

As the media and communications industries grapple with 3G, and the mobilization of the Internet, 4G is emerging on the horizon with the promise of enabling the economic delivery of high bandwidth services to a plethora of cellphone, consumer electronic and computing devices. Traditionally 4G has been considered the realm of the mobile service providers, with the notion that they would migrate their legacy 3G networks to 4G once the technology was available and market demand evident. However advanced technologies like WiFi-mesh, 802.11n and WiMAX provide opportunities for fixed and broadband service providers and new entrants to offer portable and mobile Internet solutions that challenge the traditional position of mobile operators.

Introduction

There are a variety of unlicensed wireless networks that operate in shared frequency bands. Many of these networks are installed in portable and hand-held devices. Given that these devices are portable it is not uncommon for devices using one unlicensed network to be in close proximity to another device using another unlicensed wireless network. These unlicensed wireless networks may operate in the same frequency band and may even operate in the same channel within the band. This raises the issue of whether these two networks can coexist in the same location. This chapter describes this coexistence issue.

Section 20.2 gives an overview of the various unlicensed frequency bands in the United States. Many of these bands are also unlicensed bands in other countries. Section 20.3 is a short survey of some of the unlicensed wireless networks that share these frequency bands. Section 20.4 gives a short history of coexistence of unlicensed wireless networks. Section 20.5 illustrates how to evaluate coexistence of two unlicensed wireless networks. Section 20.6 describes several methods of improving coexistence. Sections 20.7 and 20.8 give example of evaluating coexistence of wireless networks, using two IEEE 802 standards as case studies. And finally Section 20.9 discusses the issue of dynamic spectrum access in which unlicensed wireless networks identify and use unused portions of licensed frequency bands.

Overview of Unlicensed Frequency Bands

Unlicensed wireless networks can operate in a variety of frequency bands.

Introduction

If you are reading this book, I probably do not have to convince you that wireless LANs (WLANs) are experiencing dramatic growth and are rapidly becoming an entrenched technology in every day life. Today, we see that WLANs have become a competitive differentiator for hotels, multi-tenant dwellings, coffee shops and other establishments where customers are expected and encouraged to stay for more than a few quick moments. Conversely, it is quickly becoming a negative distinction to not have WLAN services in those circumstances.

Like the personal computer revolution before it, as WLAN products permeate applications from the least significant to the mission critical, product lines are stratifying to serve those new and different market segments. However, with this increased popularity and diversity, comes increased deployment at the hands of those that do not understand, and should not need to, the intricacies of RF propagation and network management, often resulting in poor performance and disillusionment with the technology.

To date, two architectures have emerged as the leading approaches to WLAN implementation: independent and dependent. The independent architecture was first to arrive and is a logical extension of standard bridging practices followed in the wired LAN (Ethernet) world. With this approach, access points (APs) are treated as individually managed edge devices. Each AP is configured and managed independently from other peer APs irrespective of whether or not the APs belong to a specific administrative domain.

Introduction

A Wi-Fi “Hot Spot” is the common term used to describe locations that provide public Internet access using IEEE 802.11a,b or g wireless Ethernet, otherwise known as “Wi-Fi” (Wireless Fidelity). Wi-Fi uses a wireless Ethernet protocol that comes in various flavors including the most popular 802.11b/g, both of which operate in the 2.4 GHz frequency band of unlicensed spectrum. 802.11b can transmit/receive up to 11 megabits/second and 802.11g can transmit/receive up to 54 megabits/second. The new proposed 802.11n standard uses multi-path capabilities to transmit/receive at up to 155 megabits/second. 802.11a is a close cousin to 802.11g, with transmit/receive speeds of up to 54 megabits/second, but 802.11a runs in the 5 GHz unlicensed band. Most hotspots provide 802.11b and 802.11b/g (dual-mode capable) access – that is, the access points have radios that are able to function with either 802.11b or 802.11g connections. Some access points have tri-mode radios that run in 802.11a/b/g modes.

Wi-Fi has become extremely popular. Whereas 8 years ago, 802.11b was on the fringe edge of techno-geek toys with only a few thousands of devices sold, now more than 90% of the mobile computers shipped by Dell, HP and IBM (Lenovo) come with 802.11b/g built in (many also with 802.11a forming tri-mode radios). Hence, there are hundreds of millions of laptop computers with Wi-Fi built in. Those that do not have it built in can add it on with a PCMCIA card or USB drive device for less than $30.00.

In this chapter we present the requirements, architecture and design challenges for municipal wireless broadband access networks. We first provide an overview of the requirements and services anticipated for municipal Wi-Fi networks based on five recent municipal RFPs. Next, we present design guidelines for a layered network using access, mesh, injection and backhaul tiers to create a cost-effective municipal broadband network utilizing equipment conforming to the 802.11 family of standards in the mesh and access tiers. To illustrate the challenges involved in creating mesh networks we explore the costs and benefits of building single versus multi-radio mesh networks and of creating a network capable of supporting session-persistence roaming across a municipality. We provide design equations supported by measured data for multi-hop mesh networks using a single mesh radio configuration. Our roaming solution is designed to operate in the context of a routed mesh network and offers seamless integration with network access controllers, and in conjunction with dedicated network branch routers, session-persistent roaming within metro-scale Wi-Fi networks.

Introduction

Envisioned as a replacement for traditional Ethernet Local Area Networks in home and office environments, 802.11-based broadband access networks have seen an explosive growth in the public space over the last five years. Beginning with small scale hotspot deployments in high use public areas such as airports, cafes and businesses, cities have begun to embrace Wi-Fi technology as a catalyst for attracting customers and revitalizing downtown areas.

With all the ongoing commotion about Wi-Fi access gravitating towards free since the inception of the hotspot industry, it might come as a surprise that most networks in high profile locations remain for-fee, commercial hotspots. Among the top airports, fewer than 10% have chosen to deploy free Wi-Fi. Even within the airline club rooms, most of the clubs charge for service – or outsource the service to an operator who charges for service.

Similarly, outside of the business economy hotels (think about the second and third tier offerings from the prominent hotel brands), Wi-Fi access in major hotels remains feebased, with some frequent traveler programs subsidizing this service for their members. Some hotels are returning to fee-based access after enduring what they consider a failed experiment in providing free access.

While there will always be a place in the market for free Wi-Fi, the explosive growth and exponentially increasing usage of fee-based Wi-Fi demonstrates the viability of a market that was projected to be on its last legs in 2003.

In order to capitalize on this opportunity, it is best to assess the factors that will maximize the chances of success, which generally means generating meaningful revenue. Fee-based Wi-Fi depends heavily on business travelers – users with a real need for Internet access – who are willing to pay for service.

In this regard, the first rule of real estate applies to commercial hotspots as well, “Location, Location, Location.”

Introduction

One of the key factors for the wide acceptance and deployment of IEEE 802.11 Wireless Local Area Networks (WLANs) is the simplicity and robustness of the Medium Access Control (MAC) protocol. Based on the well-known carrier sense paradigm, with an exponential backoff mechanism devised to minimize the probability of simultaneous transmission attempts by multiple stations, the protocol is able to work in presence of interference, which is very critical for networks operating in unlicensed spectrum. In fact, interfering sources are simply revealed by the carrier sense mechanism in terms of channel occupancy times, or by the acknowledgement mechanism in terms of collisions. However, the simplicity and the robustness have often been traded off with the efficiency of the access protocol, in terms of radio resources which are wasted or underutilized.

In this chapter, we provide a detailed analysis of the 802.11 distributed access protocol, by examining the protocol parameters which most critically affect the protocol efficiency. We quantify the protocol overheads due to control information (i.e., physical headers, frame headers, acknowledgement and other control frames) and to the distributed management of the channel grants (i.e., collisions and idle backoff slots). Then, we consider the distributed channel access extensions, defined in the recently-ratified 802.11e standard in order to support service differentiation among stations with different Quality-of-Service (QoS) requirements. Finally, we attempt to show how these parameters affect the resource repartitioning among the stations and how they can coexist with legacy DCF stations.

Much of the impetus for the free and open software movement arose as a reaction to legal issues related to software licensing. Consequently, questions concerning what is commonly called intellectual property have been a habitual feature of the open source landscape. Intellectual property includes creations like copyrighted works, patented inventions, and proprietary software. The purpose of this chapter is to survey some of the relevant legal issues in this domain in an accessible manner informative for understanding their relevance to free and open development. The legal and business mechanisms that have been developed to protect intellectual property are intended to address the core objective of protecting creations in order to provide appropriate incentives for innovators. Traditionally, such protection has been accomplished through exclusion. For example, under copyright law, one is not allowed to distribute a copyrighted work without the authorization of the owner of the copyright. The General Public License (GPL) that lies at the heart of the free software movement takes an unconventional perspective on the use of copyright. It focuses not on how to exclude others from using your work, but on how to preserve the free and open distribution of your work when you do allow others to modify and redistribute it (Weber, 2004). We will consider the basic legal concepts associated with intellectual property and how they have been brought to bear in the open source movement.

With both the enterprise and residential sectors embracing voice over IP (VoIP) at an accelerating pace, and the pervasive use of wireless local area networks (WLANs), the natural requirement emerged for a technology to support VoIP over WLANs without degradation of its quality of service (QoS). QoS requirements for WLANs are imposed also by video and multimedia applications tailored for use with WLANs. A QoS-focused MAC Layer standard, IEEE 802.11e, was developed to meet the QoS requirements of a range of applications. In addition to VoIP/ multimedia QoS, the new standard serves mission-critical functions by reducing latency across a WLAN. This chapter discusses the enhancements the new standard adds to WLAN technology with respect to QoS performance, channel use efficiency, and power management of battery-based wireless devices.

Introduction

Since the initial emergence of the 802.11 network interface card for laptop computers and access points, the appeal of 802.11 technology has been so strong worldwide that it is now appearing in a wide range of devices, including consumer electronics devices and VoIP phones. Enterprises wish to extend VoIP over wireless LANs for the convenience wireless service brings to the mobile user throughout the building, campus, quad and warehouse, as well as anywhere a WLAN is accessible. Residential users purchasing VoIP service for cost savings, look to the WLAN to enable them to make their telephones cordless. The installation of WLANs in public spaces, backed up by a ubiquitous Internet, makes the case of VoIP over WLANs even more compelling.

This chapter looks at open source development from an economic and business point of view. We have two objectives. One is to understand the economic matrix in which open source development operates, what characteristic economic factors affect its viability, and what proven business models have been established. The other objective is to consider some of the classic motivational questions about why people do open development from an economic perspective. Some standard economic factors we consider are the influence of vendor lock-in, network effects (or network externalities), the total cost of use of software, the impact of licensing on business models, the potential for customizability for open source versus proprietary products, implications of complementary products, and the effect of commoditization. We also examine some of the successful open source business models that have evolved over time. The longstanding question about open business models is basically how can people make money off a product that is given away for free? Who pays for the cost of developing this software? We consider various approaches that have proved successful, including dual licensing, consultation on open source products, provision of open source software (OSS) distributions and related services, and hybrid business models like the use of open source for in-house development or horizontally in a strategic synergistic combination with proprietary products such as in the case of IBM's involvement with the Apache Foundation and Linux.

Open source development is a form of distributed, collaborative, asynchronous, partly volunteer, software development. A new paradigm for cooperation like this invariably introduces new questions about its social characteristics and its affects on human behavior. Matters of interest range from the characteristics of the participants (demographic, motivational, etc.), the social psychology of their interactions, and the effectiveness of their cooperative processes, to the cognitive and problem-solving side effects of this kind of development. The purpose of this chapter is to survey these issues and identify some of the scientific and social concepts that can help in understanding them. We believe these social science perspectives can help provide a conceptual framework for better understanding open development. We will begin by considering the basic demographics of the phenomenon: the characteristics of the developer population, the motivations of developers and community participants, how participants interact, the diversity of projects, and so on. The survey by Kim (2003) is one of a number of useful surveys that have been done on these issues. We also examine relevant concepts from the field of social psychology, including the classic notions of norms and roles, factors that affect group interactions like compliance, internalization, identification and normative influence, the impact of power relationships and group cohesion, and the application of these concepts to open development. There are other useful abstractions available from cognitive science, such as the cognitive biases that affect group interactions and problem solving.

We use the term open source platform to refer to the combination of open operating systems and desktops, support environments like GNU, and underlying frameworks like the X Window System, which together provide a matrix for user interaction with a computer system. The provision of such an open infrastructure for computing has been one of the hallmark objectives of the free software movement. The GNU project sponsored by the Free Software Foundation (FSF) had as its ultimate objective the creation of a self-contained free software platform that would allow computer scientists to accomplish all their software development in a free environment uninhibited by proprietary restrictions. This chapter describes these epic achievements in the history of computing, including the people involved and technical and legal issues that affected the development. We shall also examine the important free desktop application GIMP which is intended as a free replacement for Adobe Photoshop. We shall reserve the discussion of the GNU project itself to a later chapter.

The root system that serves as the reference model for open source operating systems is Unix whose creation and evolution we shall briefly describe. Over time, legal and proprietary issues associated with Unix opened the door to Linux as the signature open source operating system, though major free versions of Unix continued under the BSD (Berkeley Software Distributions) aegis.

The public sector is uniquely important to the success of open source for a number of reasons. It offers well-suited opportunities for open development, in domains ranging from technological infrastructure, science, and innovation to national security and education. Furthermore, not only do public agencies and society benefit from the use of open products, the public sector, through its role in policy formulation, also provides a vehicle for advocating the expanded use of open software in society. To appreciate the opportunities, consider some of the roles the public sector plays. It has a central position in supporting the maintenance and evolution of technological infrastructure for society, an area where open software has proven extremely successful. It has also historically played an extensive role in promoting innovation in science and technology. For example, the government was the leader in funding the development of the Internet with its myriad of underlying open software components. Thus, clearly, public investment in open development has paid dramatic dividends in the past and can be expected to continue to do so in the future. The public sector is also where decisions on national economic objectives and strategy are made. These decisions, whether of a legal, legislative, or policy-driven character, can significantly affect the expansion of open source use within the government or by the public at large. The public sector is broadly charged with responsibilities from education to national security, domains that are particularly compatible with the characteristics of open source.

Small unmanned aircraft (UA) are an ideal addition to mobile ad hoc networking. An ad hoc network allows any two nodes to communicate either directly or through an arbitrary number of other nodes that act as relays. Ad hoc networks that include UA improve traditional ground-based networking through the added connectivity provided by the more prominent UA. The networking also extends the operational scope of the overall Unmanned Aircraft System (UAS) beyond the limits of point-to-point and centralized communication architectures. As well, the ad hoc network increases the UAS operational range as communication can be extended across the set of networked UA and ground nodes. While these capabilities support a wide variety of applications, little prior work has fielded and tested the capabilities of such a system in practice. This chapter describes the implementation of a wireless mobile ad hoc network with radio nodes mounted at fixed sites, on ground vehicles, and in UA. The radio is an IEEE 802.11b/g (WiFi) wireless interface and is controlled by an embedded computer. The ad hoc routing protocol is an implementation of the Dynamic Source Routing (DSR) protocol. A network monitoring architecture is embedded into the nodes for detailed performance analysis and characterization. The following sections describe the network components in detail and provide performance data measured at a large-scale outdoor test bed.

Introduction

Communication networks between and through aerial vehicles are a mainstay of current battlefield communication.