HSOPA: The Next Step For GSM?

By Sue Marek
May 15, 2005
Wireless Week

http://www.wirelessweek.com/article/CA601562.html?spacedesc=Departments

Cingular Wireless made high-speed downlink packet access, or HSDPA, a familiar industry term last year when the carrier announced its intention to deploy the packet data technology throughout its network at the same time that it's upgrading to UMTS. HSDPA technology has been demonstrated and tested but is still months away from commercial reality. Cingular is expected to have some commercial HSDPA markets deployed later this year and in early 2006.

Of course, working hand-in-hand with HSDPA, which increases downlink speeds, is HSUPA, or high-speed uplink packet access the comparable uplink technology that is currently being standardized by the 3GPP. When deployed together, the two technologies promise as much as 14.4 Mbps downlink speeds and 5.8 Mbps uplink, enabling operators to offer applications that require more symmetric data speeds such as real-time person-to-person mobile gaming.

While the data speeds that HSDPA and HSUPA provide may seem like more than enough for the anticipated data applications, vendors already are looking at the next phase in the race for faster network data speeds. Behind this push to look beyond HSDPA and HSUPA is the impending competition from other technologies such as 802.16e.

One possibility is HSOPA, or high-speed OFDM packet access technology. Nortel Networks is behind this concept, which incorporates orthogonal frequency division multiplexing and multiple-input multiple-output (MIMO) technologies.

For the past few years, the company has been encouraging the 3GPP to support OFDM. According to Nortel executives, the company made 70 contributions on OFDM to the 3GPP from June 2002 through June 2004 in hopes of convincing the standards body that OFDM is a suitable technology for 3GPP-standardized evolution based on the HSDPA architecture. In April, Nortel submitted its OFDM/MIMO proposal at the 3GPP meeting in Beijing.

Analysts say Nortel is pushing the technology as part of its strategy to position itself as a technology leader. "Nortel is trying to prove it's a strong vendor. They want to show that they are in a position to set standards," says Peter Jarich, principal wireless analyst with Current Analysis.

Nortel insists that HSOPA is just a concept that will require collaboration from the rest of the 3GPP. Alan Pritchard, marketing vice president for GSM and UMTS at Nortel, says the company is trying to build a consensus around this concept. "MIMO and OFDM will have a role in CDMA and UMTS," Pritchard says. "That's our view. You have these technologies available and there's no reason why these approaches can't be applied in the 3GPP environment."

Nortel has some intellectual property rights that are part of its proposed HSOPA solution. However, Pritchard says that while the company would like for the HSOPA technology to include its IPR, it doesn't want its IPR to delay or stop this concept from moving forward. "We do have IPRs, but we are not vested in using them," Pritchard says.

OFDM Advantage What OFDM and MIMO can bring to the GSM world is a higher speed downlink connection. By combining OFDM air interface with MIMO at the physical layer, Nortel believes it can support peak rates of as much as 37 Mbps. The prototype architecture used to evaluate the system concept is based on a UMTS frequency-division duplex framework with 5 MHz bandwidth and UMTS signal timing. The downlink is based on a MIMO-OFDM air interface with two transmit antennas and up to four receive antennas. The OFDM subcarrier spacing is 6.2 kHz. The uplink is based on an enhanced W-CDMA uplink supporting peak data rates of 2 Mbps.

Besides faster speeds, HSOPA is expected to dramatically reduce costs because OFDM allows more capacity with a given amount of spectrum. That efficiency will be important, says Pritchard, when operators deploy services such as VoIP. Plus, Nortel estimates a round trip latency delay of 20 to 40 milliseconds vs. 65 milliseconds with HSDPA. "OFDM is not just a downlink improvement, but also a quantum improvement in latency," Pritchard says.

Of course, OFDM proponents are thrilled about the possibility of OFDM being incorporated into the GSM migration path. "Look at what has taken place during the last five years," says Ronny Haraldsvik, vice president of global communications and marketing at Flarion Technologies. "It's becoming more apparent that all roads lead to OFDM."

Analysts agree that incorporating OFDM into the 3GPP standard is a good idea. "Nortel isn't really proposing a product as much as they are announcing a strategy to migrate toward OFDM," says Phil Marshall, director, wireless/mobile technologies at the Yankee Group. However, Marshall believes carriers ultimately will need more than 5 MHz of spectrum to make the most of OFDM's technology advantage. "OFDM is more appropriately positioned with more than 5 MHz of spectrum. I think carriers will need 20 MHz of spectrum so they may implement it in a different frequency band as an overlay service."

Nortel Not Alone Texas Instruments is working with Nortel on HSOPA, but the company says the work is still at the theoretical level. "We are doing modeling studies and analysis," says Bill Krenik, wireless advanced architectures manager at Texas Instruments.

Krenik warns that HSOPA is just one of many concepts that are being submitted to the 3GPP. "At this phase in the 3GPP standards process, there are a lot of ideas being considered," he says. "The standards body is hearing from a lot of people about what the technology should be and what the long-term evolution of 3GPP is." Krenik adds that many of those proposed technologies include OFDM.

Of course, one key issue is whatever standard the 3GPP approves, it must be backward compliant to the rest of the 3GPP standard technologies.

If HSOPA should move forward in the standards procedure, Nortel estimates the technology will make its commercial debut sometime around late 2007 or early 2008.





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