The Long Term Evolution (LTE) standard has been declared the victor over WiMAX in the war between radio technologies vying to dominate fourth-generation wireless networks. But the battlefield isn’t quiet yet, and a variation on the LTE standard known as TD-LTE is the latest frontline in the 4G network rollout.
As I wrote back in 2008, the competing 4G technologies aren’t that far apart, especially compared to the rival GSM vs. CMDA technologies of the 3G network wars. Those relatively small differences are paving the way for LTE to gain even more adoption, even among the 600 operators already deploying WiMAX networks. This article looks at which operators can make the switch, and why they will or won’t.
The Two Flavors of LTE
There are two versions of LTE. The difference between them is how an operator can use the spectrum allocated to it for delivering wireless broadband.
- FDD-LTE requires paired spectrum channels: one for the uplink and one for the downlink. This is the most widely used flavor today, in part because the larger operators are used to dealing with FDD paired spectrum, which was perfect for voice because the uplink and the downlink were symmetrical.
- TD-LTE uses unpaired spectrum channels — instead of the uplink and the downlink being in separate bands of spectrum, they’re both on the same band. This gives more flexibility to operators for services like data, where the downlink capacity needs are generally higher than uplink needs. Operators can also reallocate spectrum as needed in real-time, based on demand. Another benefit of unpaired spectrum is that it’s cheaper to buy because the incumbents have been interested in deploying FDD services only and therefore viewed unpaired spectrum as fairly worthless.
TD-LTE Comes Out of the Shadows
But unpaired spectrum isn’t, in fact, worthless. There are 600 carriers using it to deliver WiMAX services, after all, and operators, such as Clearwire in the U.S., bought unpaired spectrum for less than one-fifth the cost of the paired 4G spectrum.
Lately, many operators have expressed interest in using that spectrum for delivering TD-LTE. Reliance said earlier this month that it would build a TD-LTE network in India, and Japan’s KDDI has tested equipment to transition its WiMAX network to LTE, although it is unclear what version of LTE it is using. Just last month, Russian WiMAX operator Yota said it would deploy LTE in its future network rollouts. Thus, TD-LTE will be a bridge for many operators to move from WiMAX to an LTE network, which will also reduce the number of pure-play WiMAX operators.
The sudden interest in TD-LTE isn’t just a matter of using unpaired spectrum, it’s also a story of vendor support. China Mobile, which has more than half a billion subscribers, has committed to the technology as the follow-up to TD-SCDMA, the Chinese homegrown cellular tech. Having such a large operator commit to the technology gets everyone from chipmakers to equipment companies and handset makers interested in building gear for the technology. Already, Huawei, ZTE and Motorola have touted their TD-LTE gear, and other big vendors, including Ericsson, who told me back in 2008 that it wasn’t doing TD-LTE equipment, have decided to jump on the TD-LTE bandwagon.
But not every operator will ditch WiMAX for TD-LTE.
Will WiMAX Survive LTE-TD?
Essentially there are four hurdles an operator has to jump in order to make the shift from WiMAX to TD-LTE: new end-user devices, enough spectrum, network equipment and cash.
End-user devices: In smaller markets, where the average revenue per user is less than $10-15 per month, Fred Gabbard, VP of product management for Motorola, told me WiMAX deployments will persist, primarily because the cost of upgrading the consumer devices would be prohibitive. However, TD-LTE will cannibalize WiMAX business in markets where the end consumers will pay to replace their WiMAX-only devices with those that have dual-mode or TD-LTE chips inside.
Network Equipment: Because LTE and WiMAX are both OFDM technologies, the underlying equipment shares about 75 to 80 percent of the same technology, which means the equipment can be updated gradually and more cheaply than replacing everything all at once. It also makes it easier to build dual-mode chips that will work with both technologies. Beceem, a chip company, in February announced a dual-mode radio for handsets that will allow operators to issue phones next year that are capable of operating on both LTE and WIMAX networks. Qualcomm is also making such chips. Motorola last week introduced a software-defined radio that will allow operators to upgrade a WiMAX network to an TD-LTE network with a software upgrade, rather than a full on replacement of radios in the base stations.
The other two hurdles are figuring out the business model and spectrum resources. The two are somewhat intertwined. A company with lots of spectrum can afford to operate the networks side by side, but one with limited spectrum holdings, Gabbard guesstimates about 30 MHz or less, would have to build out the network and seed the market with dual-mode devices, then abruptly switch at some point in time.
In the U.S., Clearwire owns up to 100 MHz of spectrum in the 2.5 GHz band in many U.S. cities. With plentiful spectrum holdings and a relatively well-off subscriber base that is likely to upgrade to dual-mode gear when it becomes available, the decision about when to make a switch is purely about the business model. Clearwire is going all out right now, adding cities and subscribers in an attempt to cover 120 million people by the end of the year, so refocusing its executive talent on a network switchover may not make much sense.
The spectrum operators own could make a difference too. Clearwire’s spectrum holdings are in the 2.5 GHz band, which is also the band that parts of China, perhaps Softbank in Japan, and even Yota is using for its WiMAX and possibly TD-LTE launch. That means it won’t have a problem getting chipmakers and handset makers to create devices that work in its frequency band. The same goes for WiMAX providers who hold TD spectrum in the 2.3 GHz band, which is what India’s Reliance owns.
Therefore, operators like Clearwire — with a relatively wealthy customer base and the right spectrum bands — could easily make the transition from WiMAX to TD-LTE. Which means the goal of a universal wireless technology and phones that would work around the world are becoming more feasible.