RFID Technology Development

Radio Frequency Identification (RFID) is a technical evolution of the bar code system. The goals are similar, i.e., to identify goods, items, and objects in general, using labels and dedicated label readers. Both bar code systems and RFID employ wireless technologies [73]. Despite these similarities, there are some differences. This is shown in Table 14.1.

The differences are in the areas of convenience (line-of-sight), environmental requirements, and, above all, in their capacity to identify individual objects. Bar coding is capable of identifying classes of similar objects but not individual items. And, here is the major advantage of RFID; it is an excellent candidate to provide tracking systems for individual items throughout the supply chain.

In this context, the supply chain is a staged suite of processes. It starts with the procurement of raw materials or basic components, followed by manufacturing or assembling goods, quality control, distribution, and, finally, the retail processes. The needs and the advantages of labeling have been known since the time of assembly lines, and systems resembling wireless identification were applied decades ago. But only in the current stage of mobile communications do we have a technology capable of identifying and tracking items in real-time.

At the heart of RFID technology labeling systems is the Electronic Product Code (EPC). It resembles the Universal Product Code (UPC) used in bar code systems.

WLAN Convergent Network Architecture

In the previous chapter, we defined and described Fixed-Mobile Convergence (FMC) as a multidimensional concept that implies convergence of terminals (cellular handsets and computing devices), networks (NFSN, WPAN, WLAN, WMAN, and cellular mobile WWAN), and applications (data, voice, video, and multimedia). The primary focus of this book is on network convergence. A simplified high-level depiction of FMC at the network level is shown in Figure 11.1.

In this diagram we see that the most compelling convergence/integration cases are between cellular mobile networks and any of the wireless contained networks. The prevalent case, which introduced the notion of FMC to the market, is between WLAN (Wi-Fi) networks and cellular mobile networks. This convergence is attractive because WLANs are included within the wide area coverage of mobile networks but provide higher throughput. Another convergence case is between WPANs and WLANs, where the higher data rate and larger area coverage of WLANs can extend the functionality of WPAN technology such as Bluetooth and Near-Field Sensor Networks such as NFC and RFID. This chapter will focus on convergence between cellular mobile and WLANs.

WLAN Convergent Applications

In Chapter 6 we listed the functionality built into WLAN networks without indicating those applications that are facilitated by convergence of WLAN with other fixed or mobile wired and wireless networks. A short list of WLAN convergent applications follows. Some of these applications will be detailed when we analyze WLAN convergent case studies in subsequent sections of this chapter.

• WLAN and cellular mobile convergence (dual-mode handsets and connectivity across cellular mobile networks);

• […]

Having worked on the development of the 802.11n standard for some time, we presented a full day tutorial on the 802.11n physical layer (PHY) and medium access control (MAC) layer at the IEEE Globecom conference held in San Francisco in December 2006. Our objective was to provide a high level overview of the draft standard since, at the time, there was very little information on the details of the 802.11n standard available to those not intimately involved in its development. After the tutorial, we were approached by Phil Meyler of Cambridge University Press and asked to consider expanding the tutorial into a book.

Writing a book describing the standard was an intriguing prospect. We felt that a book would provide more opportunity to present the technical details in the standard than was possible with the tutorial. It would fill the gap we saw in the market for a detailed description of what is destined to be one of the most widely implemented wireless technologies. While the standard itself conveys details on what is needed for interoperability, it lacks the background on why particular options should be implemented, where particular aspects came from, the constraints under which they were designed, or the benefit they provide. All this we hoped to capture in the book. The benefits various features provide, particularly in the physical layer, are quantified by simulation results. We wanted to provide enough information to enable the reader to model the physical layer and benchmark their simulation against our results.

Wireless local area networking has experienced tremendous growth in the last ten years with the proliferation of IEEE 802.11 devices. Its beginnings date back to Hertz's discovery of radio waves in 1888, followed by Marconi's initial experimentation with transmission and reception of radio waves over long distances in 1894. In the following century, radio communication and radar proved to be invaluable to the military, which included the development of spread spectrum technology. The first packet-based wireless network, ALOHANET, was created by researchers at the University of Hawaii in 1971. Seven computers were deployed over four islands communicating with a central computer in a bi-directional star topology.

A milestone event for commercial wireless local area networks (WLANs) came about in 1985 when the United States Federal Communications Commission (FCC) allowed the use of the experimental industrial, scientific, and medical (ISM) radio bands for the commercial application of spread spectrum technology. Several generations of proprietary WLAN devices were developed to use these bands, including WaveLAN by Bell Labs. These initial systems were expensive and deployment was only feasible when running cable was difficult.

Advances in semiconductor technology and WLAN standardization with IEEE 802.11 led to a dramatic reduction in cost and the increased adoption of WLAN technology. With the increasing commercial interest, the Wi-Fi Alliance (WFA) was formed in 1999 to certify interoperability between IEEE 802.11 devices from different manufacturers through rigorous testing. Since 2000, shipments of Wi-Fi certified integrated circuits (IC) reached 200 million per year in 2006 (ABIresearch, 2007).

Wireless LAN Architecture

Traditional Local Area Networks (LANs) use wired cables (copper-based coaxial or twisted pairs and fiber optic) as the communications media. Extending on the success and resilience of LAN technologies, Wireless LANs (WLANs) use short-range Radio Frequency (RF) communications to connect the WLAN components. Although communication within a WLAN can be done using wireless infrared links, our focus will be on WLANs that are based on radio links. WLAN technologies bring the users one step closer to the technical ideal of communications “anywhere, anytime, any technology”.

A typical WLAN configuration consists of Wireless Terminals (WT), standard laptops, desktops, PCs, and PDA clients equipped with RF transceivers (PC wireless cards). These units communicate with a WLAN Access Point (AP), a device that communicates with WTs across radio links. The WLAN infrastructures of single or multiple APs connect WLANs to a wired network that may consist of wired LANs, switches, and routers. The WLAN architecture is depicted in Figure 6.1.

A wireless Fire Wall security gateway may separate the WLAN from the rest of the network. A dedicated Remote Access Dial-In User Service (RADIUS) server provides Authentication, Authorization, Access (AAA) security services.

Working in the low microwave frequency range, below 10 GHz, the coverage area is limited by the allowable power radiation, interference from other radio frequency sources, physical obstacles such as metal walls, and multi-path propagation effects due to reflections.

The past two decades have marked an unprecedented growth in size and sophistication of almost every aspect of telecommunications. Two major achievements stand out in this development. First, the Internet network, the quintessence of data communications and public/private access to information. Second, Cellular Mobile Radio wireless communication, the untethered jewel of voice communication beyond borders that opened another door to worldwide conversation. As a result, today, there are hundreds of millions of users with continuous access to the Internet and over three billion users of cell phones.

Cellular mobile communications has moved in a decade through three generations. The first generation was marked by the need to build a large physical/geographical presence. The second generation has moved from analog formats to digital communications and added features that allow decent data services running along with voice communications. More recent advancements have led to the third generation of cellular mobile transmission with a focus on providing data services in the class of broadband communications.

In the same span of time, a similar growth has taken place in the wireless expansion of well-established networking technologies, commonly known as “fixed wireless”. The most popular customer premises technology, the Local Area Network, has become Wireless LAN, matching its data rate with wired frontrunners. This metamorphosis has continued by adopting voice communication over a traditional data dedicated technology. Identical phenomena took place in the Wireless Personal Area Network thanks to the Bluetooth, ZigBee, and other technologies.

802.11n is the high throughput amendment to the 802.11 standard. This section describes all the aspects of the physical layer which increase the data rate. MIMO/SDM is a key feature of 802.11n, which is discussed in Chapters 3 and 4. The other significant increase in data rate is derived from the new 40 MHz channel width. This section also discusses short guard interval, Greenfield preamble, and other modifications to the 20 MHz waveform.

40 MHz channel

In the last several years, regulatory domains have made much more spectrum available for unlicensed operation in the 5.47–5.725 GHz band for wireless local area networking. The addition of the new spectrum has more than doubled the number of available 20 MHz channels in the USA and Europe. Table 5.9 and Table 5.10 in Appendix 5.1 describe the current allocation in the USA and Europe, and the corresponding 802.11 channel number. Even with doubling the channel width to create 40 MHz channels, there are still more channels available for frequency re-use than in the early days of 802.11a. Furthermore, products currently in the market with proprietary 40 MHz modes have demonstrated that the cost for 40 MHz products is roughly the same as for 20 MHz products. Therefore, with free spectrum and relatively no increase in hardware cost, doubling the channel bandwidth is the simplest and most cost effective way to increase data rate.

Introduction

The wireless arena has been experiencing exponential growth in the past decade. We have seen great advances in network infrastructures, rapid growth of cellular network users, the growing availability of wireless applications, and the emergence of omnipresent wireless devices such as portable or handheld computers, personal digital assistants (PDAs), and cellular phones, all becoming more powerful in their applications. The mobile devices are becoming smaller, cheaper, more convenient, and more powerful. They can also run more applications on the network services. For example, mobile users can rely on their cellular phones to check e-mail and browse the Internet. They can do so from airports, railway stations, cafes, and other public locations. Tourists can use the global positioning system (GPS) terminals installed in cars to view driving maps and locate attractions. All these factors are fueling the explosive growth of the cellular communication market. As of 2006, the number of cellular network users approached two billion worldwide. Market reports from independent sources show that worldwide cellular users have been doubling every 1.5 years.

In addition to that of the traditional cellular networks, an exponential growth of the wireless access point (AP), which is a device that connects wireless communication devices together to create a wireless network, is also being experienced. The AP is usually connected to a wired network and can relay data between devices on each side. Many APs can be connected together to create a larger network, which is a so-called ad hoc network.

Introduction

Ensuring the security of both the collected data and the process of data collection is vital for the success of WSNs. Because of the constraints of the particular applications and the resource limitations, the security of WSNs is vastly different from that of conventional wired networks. For the example of military applications, wireless sensor nodes usually are sent to an unattended environment (e.g., the battlefield). In these scenarios, wireless sensor nodes are easier to capture or destroy. Thus, the foremost important thing for WSNs is that they can tolerate the dysfunction of a certain number of nodes; e.g., the network formed by nondestroyed nodes should be always connected. The second possible attack for WSNs is that the enemy could distribute a certain number of faked sensor nodes to disturb or even disrupt the communications of legitimate sensors. It is important for a sensor network to design a security mechanism to protect the sensor nodes from malicious attack or to ensure that the sensor network can “tolerate” the malicious attack to some extent. The second challenge for the design of security mechanisms for WSNs is that sensor nodes are always equipped with limited battery and memory. Thus, the traditional public-key–based schemes, such as the Rivest–Shamir–Adleman (RSA) and Diffie–Hellman (D-H) protocols, are not suitable for WSNs. For example, Mica Mote, produced by UC Berkeley, has 128 kb Flash and 4 kb RAM.

Introduction

Multihop structures in wireless networks provide enhanced capacity and fault tolerance. This capacity allows the use of wireless nodes as repeaters, and thus not only enhances the range of communication at low power levels but at the same time short-hop communication causes less spatial interference and allows reuse of the bandwidth available on the frequency channels. The ability for nodes to act as intermediate routers builds into the communication system a natural resilience to node and link failures because alternative paths become available for routing of communications. An important requirement of these networks is that they be self-organizing; i.e., data paths or routes are dynamically restructured with changing topology.

One of the critical issues in the implementation of wireless networks is the design of routing structures and routing protocols. Of considerable importance in this context is the design of distributed efficient algorithms that dynamically update the routing structures. Because the geometric location information regarding the nodes is more readily available, routing algorithms that incorporate this information for effective routing form an increasingly important subject of study.

In this chapter and Chapter 14, we study a number of energy-efficient routing protocols for wireless ad hoc networks. Routing protocols can be categorized as proactive protocols or reactive protocols, depending on when the routing structure is constructed when a routing request is issued from a source node. Routing protocols can also be categorized as flat routing protocols and hierarchical routing protocols.

In this chapter, some simple but also widely accepted models of wireless ad hoc networks are introduced. Notice that WSNs comprise a special subclass of wireless ad hoc networks; thus, when we use the term “wireless ad hoc networks,” we also include WSNs if not specifically clarified. In this chapter, the main focus is on the wireless channel model, the interference model, the energy-consumption model, and the mobility model.

Wireless Channels

The main difference between wireless networks and traditional wired networks is that the wireless devices in a network communicate over wireless channels via wireless transceivers. Thus, to understand wireless ad hoc networks and design efficient protocols and algorithms for wireless networks, we need to understand the characteristics of wireless communications. An important building block of wireless ad hoc network studies is thus the wireless channel model. In the literature, there are a number of wireless channel models proposed and the model presented in this chapter is based on the material contained in Rappaport (1996) and Santi (2005b).

It is widely assumed that a radio channel from a transmitting wireless device u to a receiving wireless device v is established if and only if the received power of the radio signal at node v is above a certain threshold. Let p(u, v) denote the power assigned to node1u to transmit a signal from u to v. We always assume that this power can maintain a reasonably good communication link quality2 from node u to node v.