Will WiMAX, LTE coexist in multimode?

For many players, there are compelling reasons for peace. Saving money tops the list. A head-to-head battle over the next few years would require an outlay of multiple billions of dollars in equipment deployment. It would also be confusing for end users, and might even determine a winner and loser in a very high-stakes game.

Until recently, much has been made of the differences between the two 4G wireless-communications candidates, usually by comparing performance characteristics and ignoring architectural similarities.

But from a technology perspective, how different are the WiMAX standard and the Third-Generation Partnership Project’s Long Term Evolution specifications? More important, what multimode technologies are beginning to surface that make a standards-oriented battle for market supremacy pointless in the long run?

’80% similar’
Earlier this month, Sean Maloney, executive VP at WiMAX champion Intel Corp., hinted that the two standards should be harmonized because they are "about 80 percent similar." Maloney added that the chip giant is looking into ways to integrate the technologies. It is technically possible to create a chipset that could be used for both, he said.

Maloney’s comments might be interpreted as a response to speculation at February’s Mobile World Congress that WiMAX could find a place within the LTE standard. Vodafone Group CEO Arun Sarin tossed out that suggestion during his keynote in Barcelona, Spain. Intel, of course, considers WiMAX the more mature standard.

While the feelers may not qualify as a love fest, they come at a time when emerging semiconductor technologies promise to make LTE-WiMAX multimode operation a reality in the not-too-distant future. In that context, spending billions to deploy standard-specific networks becomes unattractive.

"The differences are more political than anything else," said Nadine Manjaro, senior analyst for wireless infrastructure at ABI Research. Although Manjaro predicted the standards would merge, she also said LTE will not be a formal standard until 2009 or 2010. Thus, she said, it would be 2015 before any merger takes place.

Peas in the pod
The single most important similarity between LTE and WiMAX is OFDM signaling. Both technologies also employ Viterbi and turbo accelerators for FEC.

From a chip designer’s perspective, that makes the extensive reuse of gates highly likely if one had to support both schemes in the same chip or chip et. From a software-defined radio (SDR) perspective, the opportunity is even more enticing. Flexibility, gate reuse and programmability seem to be the answers to the WiMAX-LTE multimode challenge—and that might spell SDR.

LTE and WiMAX may be two peas in an OFDM pod, but they are not twins. Here are three significant differences:

1. 1. Both use OFDMA in the downlink. But WiMAX optimizes for maximum channel usage by processing all the information in a wide channel. LTE, on the other hand, organizes the available spectrum into smaller chunks.

   WiMAX pays a price for high channel utilization, however, because processing that much information might require a 1,000-point fast Fourier transform. LTE can get by with a 16-point FFT. This translates into higher power consumption, because it’s difficult to design fixed-function WiMAX hardware that is also efficient in LTE designs. An architecture that exploits the principles of SDR, however, could reconfigure its FFT function for better power efficiency.

2. LTE uses single-carrier frequency division multiple access (SC-FDMA) for uplink signaling, while WiMAX sticks with OFDM access (OFDMA). A major problem with OFDM-based systems is their high peak-to-average power ratios. The average power spec cited in marketing present(52RD.com)