Strong foundations

US carrier Sprint officially announced plans to begin offering LTE services to more than 250 million potential customers in early October. As the industry’s worst kept secret the move came as no surprise, but what did raise eyebrows was the firm’s target launch date of mid-2012 with a view to full network build out by 2013. A full two years sooner than anticipated.

We caught up with Stephen Bye, chief technology officer of Sprint, just a few days after the announcement, and spoke to him about the challenges ahead and the groundwork that has already gone into the programme.

Bye moved to Sprint from US cable carrier Cox Communications, which had been dabbling with LTE as a platform for rolling out services over wireless. But Sprint represented a whole new set of challenges. As well as the WiMAX network at 2.5GHz, it also runs a CDMA EVDO 3G network at 1900MHz as well as Nextel’s legacy iDen network, operating at 800MHz. Operating all these technologies together makes for a large, bulky and relatively inefficient macro base station set-up, a challenge that has already been addressed by the firm’s Network Vision initiative, which is a universal rebuild of the network on a next generation multi mode cabinet architecture.

While the announcement on October 7 was the news everyone had been waiting for, Sprint’s CTO is eager to highlight the importance of the Network Vision project, unveiled in December 2010, as the foundation stone for the network upgrade.

“October 7 wasn’t the ‘now let’s begin’ point of our network upgrade. A lot had already happened by then, work had been going on for months, to develop the roadmap for the technology and make sure there was a device ecosystem,” Bye says. “In fact, a much bigger announcement was the Network Vision initiative that came out almost a year ago.

“This is the real network modernisation plan. We’re rebuilding the network with multimode base station capabilities. This is what really laid the foundation for us, so the LTE announcement is really just the next chapter of that, the next step along that continuum.”

An overhaul of the operator’s basestations packs more equipment into a smaller space and replaces ageing, signal degrading coax with fibre. Multimode cabinets allow Sprint to use different RF technologies on different frequency bands, so the firm can have a combination of CDMA, LTE or WiMAX across different radio bearers, be it 800MHz or 1.9MHz. The idea is to make the addition of new technologies much smoother, but Bye is careful to avoid the term “rip and replace” for the network upgrade.

“No, it’s not a rip and replace strategy. We already have over 50 million customers on our network and a sustainable and solid business with infrastructure in place today. But we recognise the move forward will need us to modernise that network, so Network Vision enables us to deploy a next generation platform in parallel with our existing business and then as that platform turns up we migrate those customers over and at a future point in time we will take down the legacy iDen network,” Bye says. “The key here is that we can manage that transition very gracefully. It’s not like we have to rip and replace, we complete the migration then take down the other network and reduce a lot of costs we’ve had to bear with that previous network. It alters our cost structure fundamentally, but allows us to migrate and upgrade going forward.”

The legacy iDen network, Sprint inherited as part of its merger with Nextel has been both a boon and a burden. It’s been a success with many vertical customers, but is now outdated and adds further complexity to the multi-0technology network. Hence it’s eventual decommissioning.

“We still have vertical segments that like the Push To Talk (PTT) functionality of iDen and we need to preserve that relationship by giving them something better than they have today. But this upgrade also allows us to take down the iDen network and the costs associated with it. It’s been a burden but as we turn up the new network we are recreating the PTT experience on CDMA with better performance and coverage. In fact, we launched our first CDMA PTT phone on October 2, which is just the start of a portfolio we will use to migrate users over to CDMA,” says Bye.

The device ecosystem is something Bye considers as of the utmost importance. The operator plans to launch dual mode CDMA/LTE devices by mid-2012, with approximately 15 devices—including handsets, tablets and data cards—set to hit shelves throughout the year. The CDMA/WiMAX devices that Sprint currently offers, such as the Nexus S 4G, will continue to be sold throughout 2012.

According to Bye, the biggest challenge in the industry right now is how many spectrum frequencies you can squeeze into a device, in order to ensure global roaming, capacity and keep the device cost effective. A tall order in a world that is moving from being one dominated by voice to one dominated by data.

“It’s a moving target that presents a technology challenge for all of us in the industry,” says Bye. “Not long ago people were struggling to put dual band radios together, now we’re talking about hexaband. “But it’s a good thing that devices are getting bigger,” he says referring to the tablet trend. “It was more challenging when devices were getting smaller but now we have more real estate to play with. These devices are more of a mobile computing device than a cellphone.”

As an industry we will continue to be challenged by the data demands on the network and will continually be looking for ways to improve spectral capability and network performance. In the past when voice was king, it was these demands that drove the network model. “Voice is deterministic. People would talk in minutes and it was easier to plan for capacity. Networks were semi static,” Bye says. “But with data, we are moving to a supply constrained model. If you put in capacity, users will take advantage of it. We have moved from feature phones to mobile computing devices and usage on those devices is taking advantage of the capacity available. This makes life very challenging as a network planner as you have a more dynamic load,” he says.

“To build and manage a network today is now an order of magnitude more complex than it was for voice. So in order to deliver a satisfactory experience we’ve got to make sure the network can support that data but we cannot forget about voice as this is still the biggest indicator to the customer of the quality of the network.”

An oft quoted phrase in this industry is that the customer experience counts more than anything. So as an engineer, Bye’s task is to deliver the experience the customer expects but to do it cost effectively. “It’s easy for us to get to enamoured by technology,” he says, “But customers don’t care. Our job is to hide that complexity and give customers what service they expect regardless of what the pipe is.

“If you peel apart the acronyms: LTE; WiMAX; whatever, you’re fundamentally talking about an OFDM technology. So that’s what you’re putting on chipset. While the acronym has shifted from WiMAX to LTE, we already have a lot of learning on the OFDM front as the first carrier to launch WiMAX,” he says.

“So last year, Network Vision, was the beginning of that journey. Our next generation, multi mode basestation technology. Adding LTE is a much smoother migration than it would have been otherwise. Other carriers are essentially building out a new network, but we’ve said no, lets go back and rebuild and re-engineer our CDMA network onto a new platform that now makes it easier for us to upgrade to LTE or whatever might come next in terms of LTE Advanced or future releases. We now have a much more future proof platform that we had before.”


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