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Antenna diversity doubles CDMA net capacity

By Patrick Mannion
EE Times
May 12, 2003 (2:12 p.m. ET)

 

Manhasset, N.Y. - Magnolia Broadband Inc. says it has achieved what it calls a breakthrough in CDMA handset design, more than doubling network capacity for uplinks and downlinks through the use of antenna diversity. By leveraging existing hooks within CDMA standards and using patent-pending algorithms and techniques, the three-year-old fabless company claims to have achieved full, two-way antenna diversity without the need for network upgrades or protocol changes.

The doubling of capacity is a direct result of Magnolia's technology, and the increase can be traded off against improved coverage, higher data rates and lower power to allow an operator to dynamically optimize a user's connection, according to the company. "Capacity, coverage and battery life are the operators' chief concerns right now," said Haim Harel, president and chief executive officer of Magnolia (Clinton, N.J.).

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Operators have been interested in antenna diversity for some time, but "it has generally required costly network infrastructure upgrades or protocol changes and has only been performed on the downlink," Harel said. Handsets with antenna diversity announced by Qualcomm and Nokia over the past 18 months, for example, have been limited to downlink implementations, Harel said.

Separately, Tantivy Communications Inc. has proposed a diversity-enabling proprietary protocol upgrade to CDMA called I-CDMA. But "that's a small player pushing a proprietary protocol that needs a network upgrade," said John Moon, senior vice president of corporate development at Magnolia.

Harel said Magnolia's DiversityPlus technology requires no infrastructure or protocol upgrades and operates on both the uplink and downlink to achieve an improvement of between 4 and 5 dB in the signal-to-noise ratio (SNR). "It also reduces PA [power amplifier] power consumption by up to 20 percent to get a 30-minute increase in talk time," Harel said.

"Because CDMA is interference-limited, every decibel increase in signal strength is an improvement in capacity," said Harel; hence the targeting of CDMA rather than GSM handsets, despite the larger potential market for GSM. "With a 3-dB improvement," Harel said, "you can double network capacity."

For downlink diversity, Magnolia's implementation is not much different from current implementations in that it leverages the well-known signal-quality indicator that's part of the CDMA standard. It uses that per-symbol update to perform equal-gain combining to achieve the downlink diversity.

But differences are apparent in the uplink diversity portion of the implementation, around which most of Magnolia's intellectual property and six pending patents revolve. "While the downlink has the quality indicator, not many have noticed that the uplink has similar capability," said Harel. "We change nothing; it's all there."

Magnolia's hook is the power control bit that follows channel fading and tells a handset either to increase or decrease output power depending on the channel impairments. "While a small change takes you out of the null, this is a brute-force technique," said Harel. "Instead we take that [power control bit] signal and, rather than ramp the PA, we change the phase to get a 4- to 5-dB improvement in signal strength." Field tests show transmitter and receiver improvements of 5 and 2 dB, respectively.

Exactly what Magnolia does with the control bit is what Moon calls "our secret sauce"-and the chefs aren't talking. The end result is implemented on two silicon germanium chips that reside between the antennas and the downconverter/upconverter sections of the CDMA transceiver. The first chip contains the low-noise amplifier (LNA) with the receive-side diversity circuitry; the second chip comprises the power amplifier and the transmit-side diversity circuitry. Both are linked to the host processor, which performs the proprietary signal processing needed to form the complete diversity solution.

"We don't add chips; we just replace already established chips," said Harel, referring to the LNA and PA. "Also, while the algorithms run on an ARM [processor], they're processor-independent." The processing consumes less than 0.5 percent of an ARM7's or ARM9's processing ability, he said.

Three physical implementations are planned. The first, the MBC-1100 chip set, performs the baseband processing on a host such as an ARM processor. The MBJ-1100 will perform the diversity processing within the LNA and PA chips themselves, while the MBS-1100 will include the upconverters and downconverters to form a complete RFIC solution.

The company is using a 0.18-micron SiGe process from Jazz Semiconductor, with packaging from Amkor Technology. Samples are expected to be available early in the fourth quarter of this year, with production by the third quarter of next year.

The company said it has already completed field trials with Samsung, Sprint PCS and SK Telecom. It expects to begin second-phase trials by June or July.

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