The Early Days Of WiMAX
This tower rises above the hills in Hillsboro, OR. High above the ground, Clearwire has multiple WiMAX and system relay antennas mounted on someone else’s cellular tower.
TH: But aren’t we looking at the same problem with WiMAX? If I have a sporting event covered by a couple of towers, there’s only so much bandwidth we can eke out of them. Everybody’s expecting broadband apps, not phone calls and IMs. Aren’t we facing the same bottleneck, just with bigger numbers?
JS: At some point there is a capacity limitation to everything, but voice networks have limitations not only at the air link but also in the network itself, the way that it’s handling traffic, how traffic piggybacks with the voice traffic, the capabilities and capacities to the site. Clearwire has actually built a 4G network from the ground up. It’s a completely IP network with very large pipes that run between all of our sites, so that traffic bottleneck is eliminated. There is very little data translation that occurs in our network. We don’t have to go from switch environments to packetized environments and back and forth. Congestions that can occur just from traffic manipulation don’t occur within our network. Looking at the air link, the competitors’ bandwidth channels are 200 KHz or a meg and a quarter, whereas Clearwire with WiMAX starts with a 10 MHz channel and has the capability of going to 20 MHz. Also, WiMAX has congestion mitigation built into the air link channel to help manage that traffic, so it’s much better at handling the experience than what youmight find in a Wi-Fi hotspot.
This is the exception to the Clearwire rule. Customers are supposed to receive 6 Mbps of download bandwidth. We must have caught a good breeze on this test.
TH: Clearwire has had its high-speed Expedience service running in dozens of markets for some time now. How was this a precursor to WiMAX?
JS: We started off with Expedience as a proprietary, high-speed, wireless data network, owned and developed by Clearwire and later sold to Motorola. We launched Expedience in over 50 markets in the US and in Europe. Expidence is a precursor to WiMAX technology. It’s an OFDM-based technology, although not as refined and obviously not standardized like WiMAX—802.16e. But we proved out the concept and got ahead of the marketplace, building out these Expidence networks and gathering a customer base. As WiMAX matured, we built the beta network in Hillsboro, Oregon in partnership with Intel and Motorola to test the technology. From there, we rolled out Clearwire’s first market there in Portland, Oregon.
You might assume that WiMAX coverage would blanket a city evenly. This map shows that emphasis tends to focus on key population lanes are areas of highest projected use.
TH: First? I thought Baltimore beat Portland to market. Walking inside of a Clear store you might think you’d stepped into a notebook retailer. There’s an obvious mobility message here...and a lot of “clear” store space.
JS: Well, Baltimore was first in the sense that prior to the bringing together of Sprint and Clearwire, Baltimore was managed by Sprint. Sprint had a similar path of WiMAX testing. I believe that their trial area was in Arlington, Virginia. Building out from there, they decided to go with Baltimore element as their first WiMAX market.
TH: What’s the difference between a WiMAX signal and a cellular signal?
JS: Cellular signals were designed around low bandwidth and low latency for voice calling. We as consumers are accepting of the fact that 8 kilobits, 6.5 kilobits, or whatever is good enough on cell phone. But when you go to your landline phone, you notice the audio difference. With WiMAX, the channel was designed around low latency again, so you could carry on voice conversations or have real-time interactions, but it was also designed for broad bandwidth. More specifically, if you look at the design of a cellular channel, it has equal sharing of both the uplink and the downlink, which is very inefficient for that limited spectrum resource.
Clearwire has gone with a TDD format, which allows the system to adapt to whichever half of the interaction is “speaking” more. If more bandwidth is needed on the uplink, it shifts to allow you to talk more, if you will. It’s asymmetrical in its proportioning and adaptive to the transaction that’s occurring.