The need for speed

It may not have involved a desolate strip in the desert. There were no ambulances standing by. No one was wearing a crash helmet. But Beceem Communications is breaking speed barriers nonetheless.

Specifically, Beceem claims to have over-clocked the speed measured over a WiMAX transmission, performing the feat in a field trial over one of its partner's trial networks (although it won't reveal the specific vendor). The BSC200 chipset using 2×2 multiple input/multiple output (MIMO) antennas was able to maintain data rates in excess of 33 Mb/s over a 10 MHz channel in the 2.5 GHz band using both FTP and videoconferencing. And that measurement was real-time speed over the application layer, accounting for encoding and IP framing, said Lars Johnsson, vice president of business development for Beceem. At the physical layer, the transmission exceeded 40 Mb/s of raw capacity, he said. To put it in context, high speed packet access (HSPA) theoretically tops out at 14.4 Mb/s over the same amount of spectrum. On the physical layer, the Beceem WiMAX chip far more than doubles 3G's capacity, Johnsson said.

To be fair, wideband CDMA HSPA is a frequency division duplexing technology that allocates half of its 10 MHz for the uplink and half for the downlink, whereas WiMAX in its time division duplexing configuration is free to spread its downlink capacity across all 10 MHz of spectrum as uplink demands decrease. But Johnsson said Beceem factored real-time usage into its test case, allocating specific amounts of capacity for the upstream in both the FTP and videoconferencing trials. In most cases, 6 Mb/s to 7 Mb/s were allotted to uplink transmission and 25 Mb/s to the downlink, he said.

Of course, no individual user will see speeds like that. With handoff, users moving toward and away from the cell edge, scheduling, and multiple users on each cell, subscribers likely will see multiple Mb/s of downlink capacity and a single Mb/s on the uplink. But while these speed tests may be purely academic, the resulting technology will have some very real consequences on the network, Johnsson said. A big honking pipe allows scheduled tasks to be performed faster, which in turn opens up the network for more tasks and more users over any given time frame. “I serve you and get rid of you so I can serve more people,” Johnsson said.

And there's still plenty of room to make that pipe bigger. Johnsson said that, using current modulation techniques, the upper theoretical physical layer limit for the technology is 70 Mb/s. There's still 30 Mb/s of physical capacity that Beceem can strive for.

“We'll never reach that physical limit,” Johnsson said. “There's too much overhead in the data transmission. Part of it's encoding, but mainly it's the framing of the IP packets.”

Beceem does have competition. Sequans just announced field trials with low-power WiMAX chipsets that exceeded 30 Mb/s using the same spectrum and configuration, and other chipset makers are hot on Beceem's heels. But for now Beceem has bragging rights.