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.

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.

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.

Every now and then, a technology comes along which changes everything. Wi-Fi is one of those technologies.

Although wireless LAN technology has been around for close to 20 years, what we think of today as Wi-Fi has really existed for less than a decade. The IEEE 802.11b standard was ratified in 1999, enabling the then unheard of speed of 11Mbps. Shortly thereafter, the Wi-Fi Alliance was formed to focus on product interoperability certification and the development of the ecosystem and market. The combination of the right industry standard, unprecedented industry cooperation, and the novel utilization of unlicensed spectrum, created a new paradigm in terms of how people could connect to the Internet without wires.

Today, with the advent of draft 802.11n technology, we are able to deliver data rates in the multi-hundred Mbps range. We can now reliably cover most homes with a single access point using sophisticated MIMO techniques. We can connect large cities using advanced mesh architectures. With these developments, Wi-Fi is no longer confined to just the PC and networking application segments. Rather, Wi-Fi is now becoming a must-have feature in the latest consumer electronics products and handsets, ushering in new applications like voice and video. In a short period of time, Wi-Fi has moved from a cool, niche technology to one that is a mainstream, global phenomena.

I hope this book gives you a better appreciation for the power of Wi-Fi and stimulates your thoughts on where it can go in the future. Enjoy!

The specification and broad adoption of strong AES-based encryption and data authentication and strong end user authentication in IEEE 802.11 Wireless Local Area Network (WLAN) systems provide strong link layer security. Since the wireless link for data traffic is secure, standards work now turns to the protection of management frames and implementers look to deploy intrusion detection tools, while attackers look for implementation-flaw based attacks, such as “fuzzing”. This chapter discusses the topics of WLAN link security, key management, end user authentication, standards, wireless driver vulnerability attacks and wireless intrusion detection techniques.

Introduction

The level of required security in a system changes over time, as technology and export regulations change and as the processing capabilities of both valid users and potential attackers increase. One static aspect, however, is the need for end users to adhere to recommended security practices, such as keeping up-to-date virus software and intrusion detection software on their laptops or client devices. There are conflicting requirements of security and convenience. End users desire a simple, quick logon using stored passwords on client devices; however, for stronger authentication, particularly in enterprise networks, two separate credentials from the user, a password and a time-changing code are typically required. This is similar to the credentials required to withdraw cash from an ATM, you must present both a password (something you know) and the appropriate ATM card (something you have).

This chapter presents an overview of design challenges involved in mobile mesh networks that support multimedia applications. First, various types wireless mesh networks are enumerated and the historical developments in the area of mobile mesh networks are briefly reviewed. The need for and value of autonomous mobile mesh networks for broadband applications is described later. This is followed by an overview of technical challenges that need to be addressed in designing autonomous mobile mesh networks and for providing useful multimedia peer-to-peer services over such networks. Emphasis is placed on describing generic system level challenges rather than on specific solutions for component subsystems, some of which are only beginning to evolve.

Introduction

Ad hoc wireless networks are interconnected sets of mobile nodes that are self-organizing, self-healing, survivable, and instantaneously available, without any need for prior infrastructure. Since Internet Protocol (IP) suite is now recognized as the universal interface or “glue” for interconnecting dissimilar networks, an IP-based ad hoc network has the potential to solve the interoperability problems faced by various conventional stovepipe networks that are designed for specific usage cases.

A multi-hop mesh network can be defined as a communications network that has two or more paths to any node, providing multiple ways to route data and control information between nodes by “hopping” from node to node until a connection can be established. Mobile mesh networks enable continuous efficient updates of connections to reconfigure around blocked or changed paths.

Evolving from ad hoc 802.11 networking, earlier generations of wireless mesh provided basic networking over extended outdoor areas. With the emergence of demanding data applications along with video and voice, single-radio “First Generation” single-radio wireless mesh solutions are proving unsatisfactory in many of these demanding environments. Third Generation wireless mesh solutions are based on multi-radio backhauls and deliver 50-1000 times better performance, but some custom hardware-oriented approaches limit flexibility and create deployment challenges. Software-oriented Third Generation wireless mesh based on distributed dynamic radio intelligence delivers the same high performance but with the additional benefits of easier installation, better avoidance of interference, and the added flexibility of easy mobility. These new capabilities are enabling many new types of applications beyond the traditional wireless mesh metro/muni environment.

Introduction

Mesh network requirements have evolved from their military origins as requirements have moved from the battlefield to the service provider, and residential networking environments. Today, to cover large areas with a single wired Internet link, more cost effective and efficient means of bandwidth distribution are needed. This implies more relay nodes (hops) than were needed before. Further, growing demands for Video and Voice-over-IP require packets to be moved over the mesh at high speeds with both low latency and low jitter. These new mesh requirements (more hops to cover large areas, more efficient bandwidth distribution and better latency and jitter for Video and VoIP) has given rise to the third-generation of mesh architectures.

The IEEE 802.11 effort (11k) to provide measurements has resulted in a request/response mechanism so end user devices and Access Points can obtain information from each other. In addition, the Management Information Base (MIB) serves as the repository of the information for use by upper layers. The mechanism for accessing the information in the MIB is by Object Identification (OID) addressing. This chapter provides an overview of the mechanisms and the use of the MIB to deliver more accurate and useful information for a more precise wireless environment. At publishing time, 11k had passed from Working Group Letter Ballot to Sponsor Ballot and therefore was still be subject to change until the specification is approved as a standard.

Introduction

One of the major difficulties with radio and wireless environments is the propensity for interference and radio physics to cause issues for the applications and users of these wireless systems. This propensity is what makes national regulatory control necessary, but there is much more to the issues than just regulatory control. In order to manage and control wireless, standards are needed and information is required to assess what to do about frequency allocations, radio physics problems, interference, and protocols needed to manage the exchange of data wirelessly. Measured wireless systems are the first step to managing the interference and radio physics issues in all wireless systems. In the case of the IEEE 802.11 Wireless Local Area Networks (WLAN), the measured WLAN is specified in the “k” amendment to 802.11.

Introduction

In the wired Ethernet environment, distance limitations and data rates are fully defined. This is a result of specific transmitter and receiver standards and a controlled media, i.e. the wire. A controlled media (such as wired Ethernet) is the key point here because a defined data rate can be maintained over a specified distance.

Things change significantly with wireless communications and once again the key is a controlled media, or lack there of. Physical media will always return fixed results; distances and data rates can vary greatly when using Radio Frequency (RF) as the transmission medium. It is because of this “fluid” nature of RF that deploying a Wi-Fi network can be fraught with issues, miss met expectations and a generally unhappy group of users.

It is also important to note the range, or the coverage area of a Wi-Fi Access Point is impacted by several items including data rate, capacity, interference and other variables so there are many things to contend with when going wireless.

However, with an understanding of a few basic principles such as antenna design and gain along with some information on items that impact a Wi-Fi network, you will be in a position to better create a higher performing, longer range wireless network.

Defining Range and Coverage

Before the RF signal leaves the antenna, a digital signal processor will convert the data stream into complex symbols that carry it over the air as it is transmitted.

Wi-Fi Hotspots Introduction

Wi-Fi hotspots are wireless Local Area Network (LAN) locations that provide broadband Internet access and Virtual Private Network (VPN) access from a location. One or more access points can cover a single hotspot location. It enables customers at a hotspot to use their wireless-enabled laptop, PDA (personal digital assistant) or cell phones to access the Internet with a secure connection. While the costs of portable devices continue to decline, the popularity of Wi-Fi technology and the acceptance of Wi-Fi in the marketplace continue to increase.

The size of hotspots can range from a single room to many square miles of overlapping hotspots. Hotspots are often located at restaurants, train stations, airports, libraries, coffee shops, bookstores, and other public places. Today, many universities and schools have wireless networks deployed on their campus.

Brief History of Hotspots

The concept of Wi-Fi hotspots was first proposed by Brett Stewart at the Net World/InterOp conference in the San Francisco Moscone Center in August 1993. Stewart, instead of using the term ‘hotspot’, referred to them as public accessible wireless LANs. The term “Hotspot” was first introduced by Nokia in 1998.

Overview of Commercial Hotspots

Commercial hotspots are now deployed in places such as Internet cafes, coffee houses (commonly called Wi-Fi-cafés), hotels, and airports around the world. These business establishments may charge the customers for the service, but some hotels provide the service for free to guests as an added amenity.

A whole new thinking is needed for mobile computing. We call this the Mobile Computing Environment. This encompasses a deep understanding of requirements for the mobile user and the specific mechanisms required to effectively supply services (a combination of applications and resources pertaining to those applications) to a broad variety of mobile devices. This chapter provides an overview of this emerging field, together with an outline of Appear's solution for this new environment.

Introduction

As high-performance computing in small form factor devices arrives, a shift from traditional browser-based interfaces to a combination with full self-contained services has become increasingly evident. These same mobile devices are standardized and inexpensive, creating whole new opportunities to cost-effectively computerize groups of mobile workers.

These services offer superior interactivity, work both online and offline and utilize the onboard processing power to execute locally, saving both bandwidth and precious battery life. To support these services, new powerful distribution mechanisms are needed to allow for automatic installation, filtering and execution over wireless networks - a service profiling and provisioning scheme that makes discovery, download and installation as natural as sending an email. These distribution mechanisms need to take into account several dimensions of the user's context (i.e., the information that describes the situation of a person or entity such as its location, time, profile, available bandwidth, language, and device type), when determining which services, data or content a user requires.

Wireless Fidelity (Wi-Fi) networks have become mainstream over the last few years. What started out as cable replacement for static desktops in indoor networks has been extended to fully mobile broadband applications involving moving vehicles, high-speed trains, and even airplanes. Perhaps lesser known is the proliferation of unique Wi-Fi applications, from Wi-Fi mosquito nets (for controlling malaria outbreaks) to Wi-Fi electric utility and parking meters to Wi-Fi control of garden hose sprinklers. The global revenue for Wi-Fi was nearly $3 billion at the end of 2006 and will continue its upward trend in the coming years.

When Wi-Fi wireless LANs were first deployed, they give laptop and PDA users the same freedom with data that cellphones provide for voice. However, such networks need not transfer purely data traffic. It can also support packetized voice and video transmission. People today are spending huge amounts of money, even from office to office, calling by cellphones. With a Wi-Fi infrastructure, it costs them a fraction of what it will cost them using cellphones or any other equipment. Thus, voice telephony products based on 802.11 have recently emerged. A more compelling use of Wi-Fi is in overcoming the inherent limitations of wireless WANs. An increasing number of municipal governments around the world and virtually every major city in the U.S. are financing the deployment of Wi-Fi mesh networks with the overall aim of providing ubiquitous Internet access and enhanced public services.

Ultra-Wideband (UWB) signaling technology is a modern wireless technique crafted to comply with recent regulations permitting UWB technology. Historically UWB, once called impulse radio, was defined by very short baseband signals that are transmitted and received without a radio frequency (RF) carrier in the usual sense. The technique reuses previously allocated RF bands by spreading the energy thinly in a wide spectrum, thus having a minimal impact on incumbent spectrum users. Regulations and Recommendations have been written in a way that restricted the permitted operating frequency ranges along with the emission levels, but remained silent on the modulation and signal characteristics. Hence in addition to pulse-based UWB technology, conventional technologies such as OFDM have been exploited under the rules. This chapter will expand on pulse-UWB, particularly at very high data rates, wherein the bandwidth of the signal is directly related to the inverse of the emitted pulse duration. Applications of UWB devices are presented, and potential use cases are described. It is shown that short-pulse low-power techniques have enabled practical through-wall radars, centimeter-precision 3-D positioning, and communications capabilities at the high data rates and with exceptional spatial capacities.

Introduction

Ultra-Wideband (UWB) wireless signaling is essentially the art of generating, modulating, emitting and detecting signals that inherently occupy large bandwidths. Wide band transmissions date back to the infancy of wireless technology. They include the wireless experiments of Heinrich Hertz in the 1880s, Alexander Popov in the 1890s, and later the 100 year old trans-Atlantic spark gap “impulse” transmissions of Guglielmo Marconi.