Electronic Design

3G Takes Charge But 4G Looms Large

3G finally percolates the cell-phone arena with UMTS, cdma2000, and TD-SCDMA, but companies gear up for 4G products.

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.

3G IS HERE • 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 cell-phone 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 slow-speed 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. T-Mobile 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 original 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 spread-spectrum (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 is the organization, like 3GPP, that develops the cdma2000 standard.

The cdma2000 standard began as a 2.5G standard, yet it's 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 some ways.

China developed Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) 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.

3.5G EXPANDS THE OPTIONS
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 prevailing 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 certainly 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 EV-DO 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.

Many HSDPA and Rev. A sites are working. The cdma2000 movement seems to be slightly ahead of the UMTS WCDMA/HSDPA movement in total subscribers, basestations, and products, but that will continue to change. HSUPA hasn't been widely adopted, and Rev. B remains on the sidelines. Look for them in 2008 and beyond.

All told, less than half of all cell phones use 3G. It's had a slow roll-out, despite the fact that it's been available for years. Europe and Japan are ahead of the U.S. in 3G adoption. Infrastructure build-out costs and the availability of spectrum remain as the major issues of contention, but the lack of services to justify the extra expense for carriers and subscribers also is to blame. Still, we're well on the path to greater usage of 3G in the coming years.

4G TECHNOLOGIES
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. For the time being, 3G technologies will continue to change and carriers will continue to upgrade.

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 in the near future.

In general, 4G is expected to be an all-IP (Internet Protocol) network using IPv6. All applications, including voice, will be built on top of it. It will offer data rates to 100 Mbits/s in mobile situations, with potentially 1 Gbit/s in a fixed mode. Uplink speed will approach 50 Mbits/s. The spectrum needed will depend on the service offered, but peak rates will require up to 20 MHz.

The 3GPP group has toiled away on a 4G technology called Long Term Evolution (LTE). Like a "super" version of 3G, some call it IMT-2000 Advanced, but most refer to it as the 4G upgrade from GSM-UMTSHSPA. The system uses orthogonal frequency-division multiple access (OFDMA) with up to 2048 carriers and options for QPSK, 16QAM, and 64QAM.

A key part of the LTE definition is MIMO, or multiple-input multiple-output. This spatial-division multiple-access (SDMA) technique uses two or more antennas at the transmitter and the receiver to achieve higher data rates as well as greater link reliability in the presence of multipath conditions.

The LTE definition is in the final stages, with testing and evaluation now taking place. Look for a final ratification around 2010, and actual implementation in the 2011-2012 time frame.

A version of cdma2000 originally called Rev. C now is known as Ultra Mobile Broadband (UMB). The 3GPP2 group is developing this Qualcomm technology. It also uses OFDMA and can potentially deliver 280 Mbits/s downlink and up to 68 Mbits/s uplink in a mobile environment. Channel bandwidths will vary from 5 to 20 MHz, and both FDD and TDD modes will be available. Up to 4x4 MIMO and SDMA will be part of the definition.

UMB could show up before LTE, but instead look for it in 2010 and beyond. At that point, we'll wonder what we will do with all that speed.

COMPETING TECHNOLOGIES
Existing 3G and future 4G technologies are moving forward at a pace set by the standards development effort and the financial wherewithal of potential adopting carriers. As the need grows and carriers identify the services that can pay the bills to upgrade technologies, we'll see adoptions over an extended period.

In the meantime, other technologies are moving ahead. Some of them even overlap into the advanced 3G and 4G space. These include Wi-Fi and dualmode phones, WiMAX, the enigmatic 802.20 standard, and mobile TV.

• Wi-Fi and dual-mode phones: 3G and 4G are being developed specifically for higher-speed access to the Internet, email, video, and other services requiring fast IP delivery. Some alternative services already deliver that. Wi-Fi provides great access via hotspots for laptops. In addition, you're going to see Wi-Fi in more cell phones, despite their high power consumption.

One good example is Wi-Fi in the iPhone. Other phones have it, too, with more on the way. On top of that, some of these phones offer VoIP over Wi-Fi or VoWLAN. Known as dual-mode phones, these hybrids provide regular cellular service, but offer voice over any access point or hotspot. These phones are growing in popularity and will certainly turn into one of 3G's and 4G's strongest competitors.

• WiMAX: IEEE's WiMAX 802.16-2004 wireless broadband access standard was initially developed to compete with cable and DSL broadband services to the home, especially in small towns and rural areas that are under-served by traditional broadband access services. It's also used for backhaul for Wi-Fi and other services.

One potential application is Voice over IP (VoIP) over WiMAX, providing VoIP to consumers who select WiMAX as their broadband service. And with WiMAX potentially landing in many laptops along with Wi-Fi, VoIP becomes another option via laptop.

Some parties even believe that a newer mobile version of WiMAX (IEEE 802.16e) could emerge as a third 4G technology. It uses OFDMA like LTE and UMB, plus it accommodates moving nodes and handoffs. By using VoIP, 802.16e could be competitive. With Clearwire and Sprint Nextel building out a nationwide WiMAX network, you could see this even earlier than either LTE or UMB.

Potential hurdles include the power consumption of WiMAX chips for use in handsets and the widespread availability of service. Initially, mobile WiMAX may show up as an alternate to cellular service in a dual-mode cellular-WiMAX phone. But it won't be real 4G, as it will never hit 4G's 100Mbit/s target.

• 802.20: This IEEE standard is still in the works. It was established in 2002 as a spinoff from the 802.16 (WiMAX) group—802.16 was a fixed broadband wireless standard, while 802.20 was to be the mobile version. Its goals then and today were to establish an IPbased transport service with speeds in excess of 1 Mbit/s in the bands below 3.5 GHz, with a vehicular mobility capability up to 250 km/s or about 155 mph with full handoff.

The project got started okay, but two things happened. First, the 802.16 group decided to do its own mobile version, given its success in building the fixed version of WiMAX. And, it did establish and ratify that mobile standard in 2005. Second, the 802.20 group got bogged down with internal politics, company battles, irregularities, and a whole host of other problems. In 2006, the IEEE shut the group down and re-established it with new leadership. It's back on track now, but far from delivering a finished standard.

When it does become available, will it be too little too late? Mobile WiMAX delivers those basic goals now, as do 3G services. So while 802.20 is back on track, it doesn't appear to be in this competitive mix unless it delivers some feature or benefit that the other services can't. It may become a niche player in that case, for example, supplying broadband wireless to high-speed trains.

• Mobile TV: Mobile IPTV represents some indirect competition. Most TV that will appear on cell phones won't come via the cell-phone network, but rather from separate TV stations set up to serve this market. Handset manufacturers are building a separate TV receiver chip into the phone. AT&T and Verizon have already adopted Qualcomm's MediaFLO here in the U.S., and stations are being constructed. The DVB-H standard was adopted in Europe, with stations also coming online.

Taking the video away from the carriers means just one more service that won't require 3G or 4G speeds. But carriers aren't up in arms over this, given that any heavy video usage over the network will overwhelm it and potentially destroy the reliability of the lucrative voice service.

Should you get a 3G phone now? If you want the latest speed and features, by all means, get one. Don't wait for 4G, which is a long way off. Besides, when the two-year plan on your 3G phone runs out, it should be just in time for a new 4G phone.

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