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Exec stresses need for antenna, backhaul upgrades in cellular nets

Posted: 12 Aug 2008 ?? ?Print Version ?Bookmark and Share

Keywords:cellular network? smart antenna? backhaul upgrade? WiMAX?

Cellular networks need better antennas and backhaul upgrades if they are going to optimize the performance of next-generation technologies, according to an engineering manager who has helped build many such nets.

Early versions of smart antennas for tomorrow's cellular nets based on OFDM still need some improvement and the T1 links used for most of today's antenna sites are inadequate, said Jake MacLeod, chief technology officer at Bechtel Communications.

MacLeod recently evaluated prototype cellular antenna designs from two manufacturers. After the reviews, he introduced top engineers from the companies to a nanomaterials expert at Los Alamos National Labs, seeding innovations that may not emerge for more than two years.

The new multiple-input, multiple-output (MIMO) antennas for future cellular base stations "look really good, but these antennas are using the same materials as antennas I saw when I was a junior engineer 30 years ago," said MacLeod. "The new nanotechnology materials are awesome and the performance boost you can get is incredible," he said.

"I'm trying to get people to think outside the box in antenna design," he added.

Links from the antennas to the core carrier network also need work because only about 16 percent of them have re optic connections today, MacLeod said.

Wasting the benefits
"You won't get the benefits of OFDM if you don't have adequate backhaul," MacLeod said. "All the carriers are struggling with how to deal with this by increasing fibre or using microwave," he added.

"Next-generation LTE [Long Term Evolution] and WiMAX networks are high-throughput links that can send 100Mbit/s or more," he said. "You can't transmit that if you only have a backhaul of 4- to 5Mbit/s of the T1 lines typically going to these cell sites."

Ultimately, carriers may be forced in some situations to bring active elements such as optical to RF converters directly to the antenna. In the past, operators avoided putting any active elements on antennas because they were hard to service and could be damaged by lightning.

But that is changing. More antennas are being placed on rooftops where the electronics can be more readily accessed. In addition, many tower-based antenna sites are getting crowded leaving no room for more electronics on the ground.

LTE vs. WiMAX
MacLeod and other industry observers said LTE likely will become the dominant flavor of OFDM in tomorrow's wide-area cellular nets with WiMAX taking a smaller piece of the pie.

"Two years ago, I said LTE will dominate, through WiMAX could be big and convergence of the two technologies is a possibilitythat's still the case," said Macleod.

The Next Generation Mobile Networks Alliance recently gave LTE the nod as its preferred direction.

"That blessing really established LTE as the default network of choice, and Verizon's planned move from CDMA to LTE was significant also," said Peter Rysavy, principal of Rysavy Research, a cellular technology consulting firm. "It will be LTE and WiMAX and LTE will be dominant," he added.

Given the two specs are well defined, any convergence between the two should come at the next turn of the screw between the IEEE 802.16m standard and the LTE Advanced spec, he said. But the road to OFDM cellular is a long one.

"These are multi-decade long transitions and deployments," said Rysavy. "It costs many billions of dollars to make these upgrades so carriers need to balance the return on their investments against their competitive pressures," he added.

He noted that as many as 90 percent of worldwide subscribers are still on so-called 2G nets and 3G nets are just ramping up today. In this scenario, significant deployments of OFDM nets will probably not be broadly underway until 2015 with carriers such as Verizon likely to be among the first with plans to start LTE deployments in 2010.

- Rick Merritt
EE Times





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