Electronic Design

3G May Be Here, But 4G Is On Its Way

We've been waiting for 3G cell phones for so long, most of us have forgotten what we were waiting for. Now the wait is finally over, but we still aren't seeing many handsets. Many carriers don't refer to 3G cell phones as 3G. As a result, most subscribers don't even know what it is. Average cell-phone users couldn't tell if they have a 2G, 2.5G, or 3G phone. In fact, they probably don't even know if they're using GSM, cdma2000, WCDMA, or whatever.

But they do know who their carrier is. Cingular and T-Mobile use GSM while Verizon, Alltel, and Sprint Nextel use cdma2000. The usage is split rather equally in the U.S., but GSM dominates the rest of the globe. In either case, 3G generally can be defined as a cellular service that provides data transfers of up to 2 Mbits/s or more in a packet-based format with mobility.

While the market has been slow to adopt 3G, the cell-phone business is still prosperous and growing, with over 2.6 billion worldwide subscribers in 2006. Last year alone, an estimated 956 million handsets were sold, with over 1 billion projected for 2007. Research company iSuppli expects a total of 4 billion subscribers by 2010, or twothirds of the world's 6 billion population.

Where's It Headed?
We're in the early stages of 3G adoption today (Fig. 1). EV-DO cdma2000 phones are probably more prevalent right now, but the use of WCDMA phones is growing. WCDMA is heavily used in Japan and widely used in Europe. WCDMA adoption in the U.S., meanwhile, is increasing, albeit slowly.

The adoption of WCDMA is a major change. It requires all-new basestation equipment, a multibillion-dollar investment. There also has been a shortage of WDCMA handsets and a lack of suitable spectrum space, especially in the U.S.

WCDMA phones use 5-MHz channels, unlike the 1.25-MHz channels of cdma2000 and the 200-kHz channels of GSM/GPRS/EDGE. WCDMA has been assigned to the 2.1-GHz spectrum where such bandwidth is available. But at this higher frequency, range is more limited, meaning more basestations are needed to provide equivalent coverage.

Finally, customers aren't clamoring for 3G. Yet cell-phone video will make 3G data rates necessary. We have some video over the networks from Verizon, Cingular, and Sprint Nextel, but more is on the way. Broadcast video directly to separate receivers in the cell phone should begin later this year with technology and spectrum supplied by Qualcomm's MediaFLO system in the 750-MHz band and Crown Castle's Modeo in the 1.67-GHz band.

And we're going to get even faster data services in the future. Some GSM/GPRS/ EDGE carriers may even hold back on adding WCDMA and opt for a cheap and easy data rate upgrade to EDGE Evolution instead. According to Brent Wilkins, director of marketing for cellular chip sets at RF Micro Devices, this standard has been put forth in the Third Generation Partnership Project's (3GPP) GSM Radio Access Network (GRAN) Release 6.

The standard changes EDGE's 8PSK (phase-shift keying) modulation scheme to 16QAM (quadrature amplitude modulation). It also boosts the number of GSM time slots and uses improved coding methods to get data rates well beyond 200 kbits/s depending upon conditions. Inexpensive hardware and software changes like this will no doubt make it a tempting way to get increased throughput without a major commitment to WCDMA.

In cdma2000, some carriers already have adopted Qualcomm's EV-DO (socalled Rev. 0) for a downlink data rate up to 2.45 Mbits/s within the same 1.25-MHz channels. Rev. A (2006-07) promises even more capacity, up to 3.1 Mbits/s, with quality of service (QoS), push to talk, and Voice over Internet Protocol (VoIP). Rev. B (2008+) offers even more with a downlink speed of up to 4.9 Mbits/s. Rev. C (200910) promises 16 Mbits/s.

Also, the WCDMA standards for higher speeds have been enhanced with highspeed downlink packet access (HSDPA) and high-speed uplink packet access (HSUPA). HSDPA uses 16QAM to achieve a peak of 3.6 Mbits/s or up to 14.4 Mbits/s. HSUPA promises greater uplink speeds with a peak to 5.6 Mbits/s.

Both technologies have been implemented in the U.S., Europe, and Japan to make WCDMA a more attractive and viable 3G option. They also will protect the carriers' big 3G investment. Beyond HSDPA and HSUPA, 3GPP's Long Term Evolution project will achieve not only faster data rates but also greater robustness and reliability.

And let's not forget the third form of 3G, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). This technology, a more spectrum-efficient version developed by the Chinese, is an official 3GPP/ITU-blessed option. According to Doug Grant of Analog Devices, the Chinese are moving rapidly ahead with this unique form of CDMA.

Fully operational systems should be online by 2008, when China will host the Summer Olympics. The Chinese most likely will be the primary user of this unique system, but the volume could be very high. Only about 25% of the total Chinese market has been tapped for cell phones, with nearly 400 million current subscribers—the largest subscriber group in the world.

The Fourth Generation
Some people call 3G LTE (long-term evolution) Super 3G, but others call it 4G. As the carriers and manufacturers invent the next generation of cell phones, they're looking at ways to cut basestation costs by reducing the number of required basestations, boost reliability and quality of service (QoS), reduce latency, boost data speeds beyond even the advanced 3G rates, and increase subscriber capacity per basestation.

3G LTE promises these benefits. It uses orthogonal frequency-division multiplexing (OFDM) instead of CDMA with multicarrier adaptive modulation options of quadrature phase-shift keying (QPSK), 16QAM, and 64QAM for the downlink and singlecarrier frequency-division multiple access (SC-FDMA) for the uplink.

Combined with adaptive bandwidth capabilities of 1.25, 2.5, 5, 10, 15, and 20 MHz, the maximum data rate goal is 100 Mbits/s downlink and 50 Mbits/s uplink in mobile environments within a 20-MHz band. 3G LTE also supports multiple-input multiple-output (MIMO) antenna techniques with up to four antennas on the handset and basestation tower. 3G LTE is still a long way off, but some expect it to begin showing up by 2012 in some places.

Some sources also say the WiMAX broadband wireless access technology could be a huge competitor for 4G. By using OFDM and SIP (session initiation protocol) VoIP, WiMAX will be very similar to 3G LTE. In fact, some say that since WiMAX is here now, it will become the 4G system, leaving 3G LTE undeveloped. That remains to be seen, but it's certainly an option to watch. High capital expenditures will continue to slow 3G rollout and 4G development, leaving the opportunity for WiMAX to potentially snag the 4G gold.

See Figure 2

Blue Sky Predictions

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