7.3 Wireless Systems

Satellites provide an important link in the Internet, and wireless transmission enables phones and similar mobile devices.

Transmission Protocols

Mobile phones are full-duplex, i.e. users can talk and listen at the same time because two transmission channels are employed. Each transmission is over a few miles only, but contact is maintained by a regular deployment of transmission towers that divide the intervening area into hexagonal cells measuring some 10 square miles each (in densely inhabited areas: size depends on the number of mobile phones and signal frequencies: low frequencies travel further). Each cell site has a base station with a computerized 800 or 1900 megahertz transceiver and an antenna. Once switched on, the mobile estimates the signal strength to find which cell should carry the call, and then assigns a vacant radio channel within that cell to take the conversation. Hand-offs ( moving from cell to cell) are managed in the same way, the mobile automatically switching when the signal drops below a threshold level.

American cell phone frequencies make use of several thousand channels in a 50 MHz chunk of the 824 MHz - 894 MHz frequency interval, (the remainder being taken up by Airphone, Nextel, SMR, and public safety services). Cell phones and base stations communicate with each other through two duplex channels. The first constitutes the control channel and sets up the communication. Once the mobile telephone switch (MTSO) assigns a voice channel to the mobile, that mobile uses its second duplex channel to carry the traffic.

Digital phones convert the voice into binary information (a sequence of 1s and 0s), and then compress that information, indeed so effectively that 3 to 10 digital cell-phone calls occupy no more space than would a single analog call. As on the Internet, information is sent in packages, but these are here called time slots. Several slots make up a frame. The frame, and often the slot itself, carries three types of information. The first is control information, which specifies the frame's length, destination, and origin. The second is the actual traffic or data (speech, images, Internet information). The third is an error checking routine, often known as 'error detection and correction bits.'

Though transmission is by radio signal, mobiles also require their network protocols, though these differ from those of the Internet (and indeed from country to country, unfortunately, making many American mobile phones nonfunctional in Europe). Second generation phones (2G) employ one of three protocols. Frequency division multiple access (FDMA) puts each call on a separate frequency. Time division multiple access (TDMA) assigns each call a certain portion of time on a designated frequency. Code division multiple access (CDMA) gives a unique code to each call and spreads it over the available frequencies. To overcome some of these incompatibilities, phones are generally offered with multiple bands (switch between frequencies), multiple modes (switch between protocols) or both facilities.

Third generation (3G) employ increased bandwidth and transfer rates to accommodate web-based applications and phone-based audio and video files. Different protocols apply: CDMA2000 ( based on 2G Code Division Multiple Access), WCDMA (Wideband Code Division Multiple Access) and TD-SCDMA (Time-division Synchronous Code-division Multiple).

Technology

The Mobile Web introduces new components into the web ecosystem, including:

1. Markup languages and styles optimized for mobile devices
2. MIME types (see webpages) that differentiate mobile markup from desktop HTML
3. Browser clients (i.e. mobile devices) with a wide variety of capabilities
4. Network proxies (radio transmissions) that further adapt content to potential clients

Some popular mobile groups {3}

Mobile	% Market and Date	Note
Internet Explorer Mobile	considerable	launched 1996: default mobile browser on all Windows Mobile, Windows CE, and many Palm devices.
Openwave	29% in 2008	launched 1997 with WAP, but now supports modern markup languages
Nokia	34% in 2008	launched 1999 with WAP, but now supports XHTML
Opera Mobile and Opera Mini	-	launched 2000: operating system independent
Blazer	-	launched 200 with WAP, HTML and iMode for Palm OS Palm and Treo machines.
Blackberry Internet Browser	considerable	originally supported only WAP, but HTML capability was added with the launch of Symbian 4.0 in 2005
Mobile Safari	considerable	primary browser that runs the Apple operating system on the iPhone.
Mobile Chrome	growing	primary browser for phones running Android operating system developed by Google.
SkyFire	still in beta	true Web browser running QuickTime, SilverLight and Flash.

Mobile platforms also vary in the markup languages employed:

Device	Screen Size	Usable Display Area	Operating System	Markup Languages Supported	Multimedia Supported
Apple iPhone	320 x 480 px	320 x 480 px	Proprietary iOS	XHTML-MP, CSS2 and most of HTML5 & CSS3	GIF87, GIF89a, JPEG, PNG, MIDI, MP3, 3GPP, & MP4
Google Android	480 x 854 px (rotates auto.)	320 x 240 px	Google Android	XHTML-MP, CSS2, and most of HTML5 and CSS3	GIF87, GIF89a, JPEG, PNG, MIDI, MP3, 3GPP, & MP4
RIM Blackberry (87 models) Model Bold 9700	480 x 360 px (rotates auto.)	460 x 348 px	Proprietary OS RIM	XHTML-MP & CSS2	GIF87, GIF89a, JPEG, PNG, MIDI, MP3, 3GPP & MP4
Palm (many models) Model Palm Pre	320 x 480 px	316 x 480 px	Palm OS	XHTML, XHTML-MP, and CSS2, limited for HTML5 & CSS3	GIF87, JPEG, PNG, MP3, 3GPP & MP4
Windows Mobile	320 x 480 px	320 x 480 px	Windows	XHTML-MP, CSS2, JS & Microsoft programs	GIF87, JPEG, PNG, MP3, 3GPP & MP4
Motorola (533 models) Model RZR V3m	167 x 220 px	-	OS Symbian	XHTML, XHTML-MP	Midi, MP3, MP4, 3GPP

The wireless Internet access systems vary considerably in transmission speeds and ranges:

Technology	Transmission Speed	Range	Leading Companies
Bluetooth	1-3 Mbps	1-30 meters	Apple, Ericsson, HP, Nokia and device manufacturers
Ultra Wideband	10 Mbps	10 meters	Intel, Freescale, etc.
Wi-Fi	11-70 Mbps	100 meters	Cisco, Linksys and other manufacturers
WiMax	50-70 Mbps	50 km	Alcatel, Clearwire, Intel, Fujitsu, Sprint, etc.
Zigbee	250 Kbps	10 meters	Chipcon, Freescale, Mitsubishi, Motorola, etc.

Second-generation iPhones are equipped with GPS features, which advertising companies track with commercial services like Admob, Bango and Mobilytics.

Applications

There are literally thousands of applications for the Palm, iPhone, iPad, and the more popular mobile phones, all of which have to be approved by (and sold through) the mobile device manufacturer. Some applications are free, being used in viral advertising, but most are charged at $1 to $15.

A further development is that of SPRXmobile. Available in Amsterdam, the service employs the smartphone camera and embedded GPS to automatically provide the mobile user with information on surrounding shops, restaurants, theaters, etc. as the smartphone is pointed. Maps can also be displayed, and the businesses pay a fee to SPRXmobile to be so listed. Wikitude is similar, but provides tourist information on scenes, buildings and other places of interest. Slifter is a location-based best-price-finder that can be used on the web, or downloaded to the Blackberry or iPhone. Very similar are NearbyNow, Krillion, ShopSavy and Quattro Wireless. Revenues from such location-based services are growing rapidly, and could total more than $12.7 billion by 2014. {18}

Trends

1. Mobiles are becoming increasing popular: over 35% of Americans don't now use a landline phone.
2. Mobiles are part a worldwide trend towards portable and easy-to-use devices, leaving conventional computers for more particular and demanding tasks.

Questions

1. Describe the transmission protocols operating in US wireless systems.
2. Describe the frames that make up a wireless transmission.
3. What new components have been added to the web ecosystem by mobile phones, and illustrate them by reference to some popular mobile phone groups.
4. Compare six wireless Internet access systems, their transmission speeds, ranges and implementations.

Sources and Further Reading

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