One of the functional requirements in the development of the 802.11n standard was that some modes of operation must be backward compatible with 802.11a (and 802.11g if 2.4 GHz was supported) as described in Stephens (2005). Furthermore, the 802.11n standard development group also decided that interoperability should occur at the physical layer. This led to the definition of a mandatory mixed format (MF) preamble in 802.11n. In this chapter, we first review the 802.11a packet structure, transmit procedures, and receive procedures to fully understand the issues in creating a preamble that is interoperable between 802.11a and 802.11n devices. For further details regarding 802.11a beyond this review, refer to clause 17 in IEEE (2007a). Following this overview, the mixed format preamble, which is part of 802.11n, is discussed.

11a packet structure review

The 802.11a packet structure is illustrated in Figure 4.1.

The Short Training field (STF) is used for start-of-packet detection and automatic gain control (AGC) setting. In addition, the STF is also used for initial frequency offset estimation and initial time synchronization. This is followed by the Long Training field (LTF), which is used for channel estimation and for more accurate frequency offset estimation and time synchronization. Following the LTF is the Signal field (SIG), which contains the rate and length information for the packet. Example rates are BPSK, rate ½ encoding and 64-QAM, rate ¾ encoding. Following this is the Data field. The first 16 bits of the Data field contain the Service field. An example of an 802.11a transmit waveform is given in Figure 4.2.

WiMAX Mobile Convergent Applications

In Chapter 8 we listed the applications carried over WiMAX networks but didn't separate out those that are facilitated by convergence of WiMAX with other fixed or mobile wired and wireless networks. A short list of WiMAX convergent applications follows. Some of these applications will be detailed when we analyze WiMAX convergent case studies in subsequent sections of this chapter.

• WiMAX and cellular mobile convergence (extension of reach and connectivity of cellular mobile networks to remote, rural areas);

• WiMAX and WLAN networks convergence;

• WiMAX and WLAN metro mesh networks convergence;

• WiMAX, WLAN, and WPAN networks convergence;

• Backhaul connectivity for cellular mobile networks and traffic;

• Backhaul channel for wired Internet Service Providers;

• Disaster recovery using WiMAX links as wireless channel alternatives;

• WiMAX and EPON (as a backhaul link) networks convergence;

• WiMAX-based broadband location/navigation and customer search; and

• Internet Protocol Television (IPTV) and High Definition Television (HDTV).

WiMAX and Internet Protocol Television

IPTV, one of the applications listed above, is considered the killer application in both the fixed wired public Internet and cellular mobile networks. WiMAX, as a broadband wireless access network in metropolitan areas, is a good candidate to support IPTV. This support will include video on demand, live content, and multicast video communications, either as managed (paid TV) or unmanaged service (You Tube, for example).

WiMAX technology is strengthened by the degree of mobility conferred by the newly adopted IEEE 802.16e standard.

What is the Session Initiation Protocol-SIP?

The Session Initiation Protocol (SIP) is an Internet application layer protocol designed to control voice calls or multimedia session setups. SIP is a family of IETF-recommendations and draft standards that provide signaling specifications for Internet conferencing, VoIP, event notifications, and instant messaging over IP-based networks.

SIP-based signaling serves as multimedia call control between calling parties, and is used to set up calling sessions such as audio/video conferences, peer-to-peer communications, or to just indicate the caller's presence. SIP works in tandem with another application layer protocol, Session Description Protocol (SDP), hence the tandem abbreviation of SIP/SDP.

As indicated in Figure 16.1, there are three major components that make up a SIP network/system: Endpoints SIP User Agents (SIP-UA), the callers and beneficiaries of services; SIP Proxies (SIP-P), acting as relays of SIP messages; and SIP Registrars (SIP-R), acting as SIP directories.

As indicated with broken lines, communications between SIP UA and SIP Proxies as well as between SIP Proxies is limited to signaling. The actual transport service is delivered by specialized Applications Servers (AS) such as VoIP Servers, Presence Servers or Push-to-Talk over Cellular (PoC) Servers. The user information, data or digitized voice/video multimedia, is carried in separate frames and packets, using different transport protocols.

SIP System Architecture

A high-level SIP-based functional model is indicated in Figure 16.2.

Communications between SIP User Agents may use a series of SIP proxies that relay SIP/SDP call setup messages.

Economic Drivers of Fixed-Mobile Convergence

Although the title of this section includes the word “economics”, it is not the intent here to provide an economic analysis of fixed-mobile convergence implementations beyond some general considerations. It is not a secret that cost considerations can make or break any technical solution. The convenience of having one mobile phone that works transparently across all wireless networks is very appealing. However there are cost considerations that make such services economically justifiable. Three economics terms are used that need short explanation: Return on Investment (ROI), Compound Annual Growth Rate (CAGR), and Average Return Per Unit (ARPU).

Return on Investment (ROI), or rate of return, is the ratio of money gained relative to the money invested. It is usually calculated on an annual basis. ROI is also used to give a general qualification for a sound investment that brings profit as opposed to losing money. Compound Annual Growth Rate (CAGR) is the cumulative annualized growth rate that takes into account the cumulative effect of investment or growth over a period of time; five years for example. Average Return Per Unit (ARPU), as used in mobile telephony, indicates the revenue generated per unit, on a monthly basis, as the result of subscription and usage of services. Addition of a new service increases the ARPU.

If we consider a working network infrastructure, the cost of building a Fixed-Mobile Convergent network can be quantified by calculating the value of the following main components:

• Cost of the initial design of the FMC network;

• […]

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.