3G Takes Charge but 4G Looms Large

Sure, almost everyone is inextricably tied to a cell phone these days. But how much do we know about these phones? What technology drives them? And what can we expect in the future? Once you get past the alphabet soup of acronyms, the landscape gets intriguing.

Most people own 2.5G phones, which still get the job done (see “Perspective From The Past”). Voice calls remain their primary application, but data services like instant messaging, SMS, and e-mail are growing in popularity. Current data rates can easily handle these functions.

Apple’s iPhone uses EDGE. So do some of the BlackBerry phones. Others employ cdma2000 EV-DO. And while Internet access has been around for years using 2G and 2.5G, it never caught on in the cellphone arena mainly due to browser, screen, and keyboard limitations. However, that’s changing.

The main justification for 3G is mobile Internet access and faster e-mail. Multimedia transmissions from digital cameras, video, and audio also drive the networks to 3G. Video and audio downloads will continue to grow, as will gaming and location-based services thanks to improved GPS navigation (see “Surging Markets Drive New Wireless Technologies”).

One marked change in these phones is the presence of Wi-Fi, much like Apple’s iPhone. EDGE is fine for phone calls and slowspeed data. But if you need higher speeds, go to Wi-Fi. Since hotspots are everywhere these days, they are a good alternative to 3G data services. And as screens expand and browsers improve, Internet access gets more practical. AT&T, Sprint Nextel, and Verizon already offer 3G data services. TMobile doesn’t, but it does take the dual-mode phone route with built-in Wi-Fi. TMobile has a huge hotspot network, so this strategy works well. The company’s [email protected] service is an affordable option available right now.

Most 3G services are tied to the Card bus or USB modems for laptops (Fig. 1). These high-performance 3G modems give laptop road warriors fast Internet access, even in the absence of a decent Wi-Fi hotspot. Most carriers offer 3G phones, but the number of choices is small.

There are three 3G technologies: UMTS, cdma2000, and TDSCDMA (Fig. 2). The European Telecommunications Standards Institute (ETSI) defined the orginal 3G back in 2000, but now the Third Generation Partnership Project (3GPP) manages the standard. It became an ITU standard, with first implementations in Europe and Japan, in 2001.

The Universal Mobile Telecommunications System (UMTS) also is known as International Mobile Telecommunications 2000 (IMT- 2000). Defined as the upgrade path for GSM, it’s system-compatible with GSM. However, there’s a different radio technology. Specifically, UMTS 3G uses wideband CDMA (WCDMA) with direct-sequence spreadspectrum (DSSS) in 5-MHz channels with frequency-division duplexing (FDD).

With such an arrangement, it’s possible to get downlink data rates up to 2 Mbits/s when fixed, up to 384 kbits/s while moving slowly, and up to 144 kbits/s when moving rapidly. In the U.S., the UMTS 3G spectrum sits in the 806- to 890-MHz band, with potential for the 1.710- to 1.755- GHz and 2.1-GHz bands. In Europe, 3G uses 1900 to 2025 MHz and 2110 to 2200 MHz. Built by Qualcomm, cdma2000 with EV-DO is a fully recognized 3G standard. The 3GPP2 organization, like 3GPP, develops the cdma2000 standard.

The cdma2000 standard began its life as a 2.5G standard, yet it is continuously spilling into 3G’s domain as a result of various upgrades. The 1xRTT version supported data rates to 144 kbits/s, while the first EV-DO versions (Rev. 0) crossed into 3G territory with a maximum downlink speed of 2.45 Mbits/s under ideal conditions. Later versions, known as Rev. A and Rev. B, have leaped well ahead of UMTS in a number of ways.

China developed Time Division-Synchronous Code Division Multiple Access (TDSCDMA) to fulfill its 3G needs. Instead of the spectrum-eating FDD methods that use paired chunks of spectrum with UMTS and cdma2000, its time-synchronized time-division duplex (TDD) modem only employs a single 1.6-MHz band. It also demonstrated a 384-kbit/s data rate using Analog Devices’ Othello chip set, lagging behind the other 3G technologies, but future advances are expected.

While the rest of the world is well on its way to expanding UMTS and cdma2000, China seems content with its own standard. With hundreds of millions of potential customers, it will be a success and could exceed the other 3G standards in overall volume. China also expects to build some conventional 3G systems to support the crowd at the Beijing Olympics in 2008.

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Yes, 3G already is getting upgrades, sometimes known as IMT-2000 Enhanced. The first, High Speed Downlink Packet Access (HSDPA), is an extension to the UMTS WCDMA systems. Different modulation options provide peak downlink speeds up to 14.4 Mbits/s. It also uses adaptive coding and modulation.

HSDPA has 12 different categories. Some use quadrature phase-shift keying (QPSK), and others use 16QAM (quadrature amplitude modulation). Data rates run from 1.2 to 3.6 to 7.3 to 10.2 to 14.4 Mbits/s. Actual speeds are far slower but still exceed 1 Mbit/s, which is higher than typical standard UMTS 3G.

The companion High Speed Uplink Packet Access (HSUPA) standard provides higher uplink rates to a maximum of 5.76 Mbits/s using QPSK. Combined, these standards are called High Speed Packet Access (HSPA). Enhanced versions (HSPA+) have already been defined but have yet to be implemented. Some UMTS 3G sites offer these 3.5G services with higher data rates, for a price.

In the cdma2000 camp, the Rev. A and Rev. B versions of EVDO offer much higher data rates, too. Rev. A uses the standard 1.25-MHz channel, but it’s separate from the voice channel. With QPSK, it can achieve a peak download data rate of 3.1 Mbits/s and a peak uplink rate of 1.8 Mbits/s.

Rev. B technology uses two or three 1.25-MHz channels and QAM16 or QAM64 modulation. Its download rate can soar to 9.3 Mbits/s and the uplink to 5.4 Mbits/s. By aggregating channels up to 20 MHz wide and using 64QAM, a maximum rate of 75 Mbits/s is possible with 27 Mbits/s on the uplink. Most Rev. B adoptions won’t be that aggressive, but will certainly give users greater speed.

As you can probably tell from the 3G standards, these technologies evolve over a multiyear period. Adoption occurs as applications emerge and as carriers upgrade and offer services.

Yet as we all know, the future is always at the forefront of discussion. That said, the fourth generation is already in development. Like 3G, it will evolve and be adopted over time. So far, though, 4G hasn’t been formally defined. The ITU and 3GPP/3GPP2 groups are working on the definition, which should be published soon.

In general, 4G is expected to be an all-IP (Internet Protocol) network using IPv6. All apps, including voice, will be built on top of it. It will offer rates to 100 Mbits/s in mobile situations, with potentially 1 Gbit/s in a fixed mode. Uplink speed will approach 50 Mbits/s.

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