LTE delivers on the promise of 4G, but no panacea for fragmentation

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LTE delivers on the promise of 4G, but no panacea for fragmentation

A few years ago, while 3rd Generation (3G) wireless technology was still not widely available, arguments were already raging among industry pundits over which contender, Worldwide Interoperability for Microwave Access (WiMAX) or Long Term Evolution (LTE), would become the dominant technology for 4G. WiMAX (officially Wireless Metropolitan Area Network or WirelessMAN) advocates would point to the endorsement of the Institute of Electrical and Electronics Engineers (IEEE), embodied in the IEEE 802.16 technical standard. LTE advocates, backed by organizations such as the 3rd Generation Partnership Project (3GPP) and Groupe Speciale Mobile Association (GSMA), would cite the advantage of their technology as a de facto industry standard, since LTE had been adopted by a majority of the world’s largest wireless operators. In the end, the organization that actually has the authority to set standards that are backed by governments – the International Telecommunication Union (ITU), an agency of the United Nations – accorded both LTE-Advanced and WirelessMAN-Advanced the official designation of International Mobile Telecommunications-Advanced (IMT-Advanced), “qualifying them as true 4G technologies.” The advanced versions will be the next generation (5G?) for mobile broadband, building on the WiMAX and LTE technologies that industry is calling 4G today.

Whether “true 4G” or not, both WiMAX and LTE can deliver a mobile broadband experience that equals that of Digital Subscriber Line (DSL) or cable broadband services. I have personally used the Clearwire/Sprint WiMAX service, and currently use Verizon’s LTE, and have experienced connectivity speeds ranging from a few Megabits per second (Mbps) to 20 Mbps (on my LTE-based HTC Thunderbolt). But as far as standards go, the difficulty of roaming off each carrier’s 4G network is even greater than it ever was with 3G; in fact, it’s not currently possible.

The cracks are spreading

Although the 3GPP states that one of the motivations for their Release 8 standard, “The LTE Release,” is to “avoid unnecessary fragmentation of technologies,” practical and political realities prevent that ideal from being achieved. Both LTE and WiMAX standards support multiple frequency bands and channel widths, since spectrum availability differs greatly in the various countries where 4G will be deployed. Both also support Frequency Division Duplex (FDD) modes with separate paired spectrums for download and upload, as well as Time Division Duplexing (TDD), where channels are dynamically allocated to upload/download. The push for TD-LTE began with China Mobile, but has now been adopted by Clearwire in the U.S. as their migration path from WiMAX.

The U.S. is currently leading the world in deployment of LTE, but the amount of fragmentation here is increasing. Verizon Wireless is currently using the 700 MHz spectrum for their FDD-LTE, from 746-787 MHz, but AT&T will be primarily using 704-746 MHz and the carriers are not planning to make their 4G phones interoperable. Sprint, previously the greatest advocate of WiMAX through their Clearwire relationship, has announced that they will begin deploying LTE on their 1.9 GHz spectrum in 2012, while also entering into a relationship with LightSquared to host LTE on 1.6 GHz. To further complicate matters, Sprint has just recently resolved their differences with Clearwire, and the two now plan to “work collaboratively to support the ecosystem for TDD-LTE in Band Class 41” (2.5-2.7 GHz). And on December 2, Verizon announced their intention to purchase 122 Advanced Wireless Services (AWS) licenses for $3.6 billion, consisting of 1.7 GHz/2.1 GHz paired spectrum, saying this “will enable us to bring even better 4G LTE products and services to our customers.”

Patching up

With all this fragmentation, delivering better services for customers will require establishing seamless interoperability across the multiple LTE bands and modes, at least within a single operator’s network. Solutions will be required both on the base station infrastructure end of the network, and in the handsets and other mobile devices used by consumers. Sprint CEO Dan Hesse says he expects chipsets will be developed for multimode devices that will deliver a seamless handoff, with different frequency bands carrying different parts of the load for mobile data consumption. On the infrastructure side, Sprint has laid out their “Network Vision” strategy to provide multimode flexibility for their network of networks. Alcatel-Lucent, Ericsson, and Samsung will be installing new network equipment and software that brings together Sprint’s 800 MHz, 1.9 GHz, and Clearwire’s 2.5 GHz spectrum in a single, multimode base station.

Chip vendors are also rising to the challenge, creating more flexible baseband processors that incorporate Software Defined Radios (SDRs) that can be tuned for FDD, TDD, and even LTE or WiMAX. Altair Semiconductor has worked with AsiaTelco to build a mobile hotspot for China Mobile’s future TD-LTE network, but the company says that the chipset can also support both FDD and TD-LTE in any band from 700 MHz to 2.7 GHz. Also, 4G modem chip designer Sequans is collaborating with Malaysia-based WiMAX solutions provider Greenpacket on the development of dual-mode WiMAX/LTE devices that will facilitate migration to LTE on their subsidiary Packet One Networks. Beceem, now owned by Broadcom, announced that they too had developed a chip that they claim can provide real-time band/channel reconfiguration for FDD/TDD as well as WiMAX or LTE.

The future is low power

Now that chipsets have been demonstrated with SDR architectures that can overcome LTE fragmentation, designers need to work to reduce the power required to support multiple, high-bandwidth radios. The connectivity speeds on 4G networks are impressive, but battery lifetime is now a limiting factor that will inhibit adoption if devices can’t match users’ experiences with 3G devices.

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