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Making Sense of Wireless Broadband — Part I




With all the MegaHertzes and 802.whatevers being bandied about, you might be confused as to what the difference is between WiMAX and pre-WiMAX, licensed and unlicensed, GSM and CDMA. But categorizing wireless broadband is essential to knowing what to pitch to your customers. In Part I of a two-part series, we discuss cellular broadband technologies.

At the most basic level, there are wireless technologies for voice (mobile phones and cellular), and wireless data technologies (Wi-Fi, WiMAX and proprietary broadband wireless access BWA solutions). Within each category there are nuances.

In the cellular world, mobile networks were created with the idea of carrying voice, first and foremost. A patchwork of mobile networks has emerged in the United States and abroad since the 1980s, as operators built their networks using different types of technology. Generally, those different kinds of networks have shaken out into two camps: Global System for Mobile communications (GSM) and Code Division Multiple Access (CDMA). In the United States, GSM network owners include Cingular Wireless and T-Mobile USA. CDMA network owners include Cricket Communications, Sprint PCS and Verizon Wireless.

Background

GSM, a non-proprietary open standard, originally was developed for Europe but now has in excess of 71 percent of the world market according to GSM World. GSMs chief differentiators are its capability for international, single-number roaming, and its use of Time Division Multiple Access (TDMA), defined by the International Engineering Consortium as digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel.

The TDMA digital transmission scheme multiplexes three signals over a single channel. The current TDMA standard for cellular divides a single channel into six time slots, with each signal using two slots, providing a three-to-one gain in capacity over first-generation cellular technology. Each caller is assigned a specific time slot for transmission.

Developed originally by Qualcomm and enhanced by Ericsson, CDMA is characterized by high capacity and small cell radius, employing spread-spectrum technology, which means it does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a random digital sequence. It is governed by Qualcomm patents.

According to Webopedia, CDMA is a military technology first used during World War II by the English allies to foil German attempts at jamming transmissions. The allies decided to transmit over several frequencies, instead of one, making it difficult for the Germans to pick up the complete signal.

Evolution to Data

As good at carrying voice as these technologies are, the usefulness of supporting mobile data applications on a cellular network has become obvious in the last few years, leading to a plethora of PDAs, BlackBerries, and phone/Internet hybrid handsets like the Motorola Kyocera to provide mobile Internet access, e-mail and applications, such as gaming. However, to truly ignite the market for revenue-generating advanced applications, the industry realized it needed to offer broadband.

Cellular voice requires only a narrowband connection, but to roll out true mobile multimedia applications requires more throughput than what the networks originally were built for. Enter 3G, the third-generation technology.

The first hurdle was spectrum allocation. In wireless, creating a bigger pipe means squeezing more capacity out of a finite radio band, or adding more bands. Cellular traffic is carried in licensed spectrum, which means operators pay a fee to the government to send traffic in that frequency. To help the launch of 3G, governments made additional license bands available, and operators the world over have bid on and won this 3G spectrum at high cost.

The industry supports worldwide harmonization of spectrum to facilitate global roaming. Harmonization of frequency bands also will provide economies of scale that lower the cost of equipment and services, allowing more consumers to benefit from a wide range of voice, data and multimedia services. While a single band to support 3G and other advanced mobile services is not likely, the identification of a few bands will maximize the chances that global harmonization can be achieved. CDMA systems operate largely in the 800/1900MHz bands, while GSM initially was developed for operation in the 900MHz band and was subsequently modified for the 850, 1800 and 1900MHz bands.

Types of 3G

3G rollouts that is, cellular wireless broadband are underway. The 3G versions of CDMA include Wideband CDMA (WCDMA) and Evolution Data-Only (EV-DO), a data-only 3G specification used by Verizon Wireless and Sprint PCS to launch 3G services in the United States.

The GSM family of wireless technology platforms includes General Packet Radio Services (GPRS), Enhanced Data for GSM Evolution (EDGE) and 3GSM. In the United States, Cingular owns a 3G-like EDGE network courtesy of its 2004 merger with AT&T Wireless. 3GSM also is deployed by AT&T Wireless/Cingular in the United States.

GPRS is an interim 2.5G technology that enables networks to offer always-on, higher capacity, Internet-based content and packet-based data services like Internet browsing, e-mail on the move, multimedia messages and location-based services.

EDGE is a technology that provides a way of supporting many of the 3G-type services using upgrades and additions to existing GSM systems. EDGE technology also enables each base station transceiver to carry more voice and/or data traffic, an advantage for those with limited spectrum or without 3G licenses. It allows consumers to connect to the Internet and send and receive data, including digital images, Web pages and photographs, three times faster than possible with a GPRS network.

True GSM 3G is referred to as 3GSM. According to GSM World, there are 20-plus 3GSM networks live around the world, with another 40 to 50 expected to be launched in the next year. 3GSM services are delivered at a technical level using WCDMA and, in some markets, EDGE air interfaces. It is also known as the Universal Mobile Telecommunications System (UMTS). Because UMTS uses air interfaces from the other camp, and offers backward compatibility to GPRS and EDGE but not GSM, many are confused as to where UMTS belongs.

UMTS was developed mainly for countries with GSM networks, because these countries have agreed to free new frequency ranges for UMTS networks. Standards developers have kept the core network as close to the GSM core network as possible. While UMTS phones are not backward compatible with earlier GSM systems, it is considered a GSM system. Dual-mode phones are expected to solve the issue. In the ideal world, some in the industry would like to see the open-standards integration of UMTS with WCDMA, which would enable operators to leverage and maximize all existing spectrum and assets.

Worldwide, more than 60 UMTS networks are operating commercially in 25 countries.

Speeds

UMTS in its initial phase offers theoretical bit rates of up to 384kbps in high-mobility situations, says the UMTS Forum. That can rise as high as 2mbps in stationary or nomadic (where the phone is moved from one location to another, but not mobile) user environments. Symmetry between uplink and downlink data rates when using paired spectrum also means that UMTS can support real-time video telephony.

In actual deployment, AT&T Wireless says its UMTS service provides average wireless data speeds between 220 and 320kbps, with bursts up to 384kbps. Verizon Wireless, meanwhile, says its CDMA-based EV-DO service delivers 300 to 500kbps, with burst rates up to 2mbps.

AT&T Wireless notes that UMTS can be upgraded to High Speed Downlink Packet Access (HSDPA), a mobile network of the future that will provide efficient IP support enabling provision of services through an all-IP core network. HSDPA is meant to be a rival to EV-DO. HSDPA will offer initial throughput rates of between 400kbps and 600kbps, with a peak rate of 14.4mbps.

As a side note, vendors have developed 3G laptop cards to enable PCs to take advantage of 3G broadband. This potentially positions the technology as a competitor to BWA technologies like WiMAX, which will be the topic of discussion next month.


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