By BP Tiwari
The industry around 4G FDD is clearly evolving towards LTE as major operators committed their plans or intentions to move into LTE. However, the 4G TDD path for LTE is not going to be an easy ride owing to the competition from WiMAX. Most of the current WiMAX deployments are in TDD and operators would certainly like to recover their investments before migrating to any other evolving technologies in near future.
Operators have also realized that the investments made in building network based on WiMAX TDD cannot be turned in to LTE-TDD overnight even if they like to. Clearwire for instance acquired more than 300k subscriber last quarter marking its entry to 1 Million mobile broadband clubs. If they choose to migrate to LTE, what will happen to those 1M wimax devices? By the time TDD LTE matures clearwire will acquire anywhere between 3 to 5 Million subscribers and upgrading a 5 Million serving WiMAX network to a new TDD LTE RAN might just not be a practical case. I am sure Yota , UQ, Atheeb, Taiwanese WiMAX operators and new WiMAX deployments expected in India would also face with similar dilemma.
It appears like operators too has recognized the fact and asked leading 16e suppliers to take 16m research and development in priority and show them a working 16m system quickly. The ecosystem of 16m could be as large as TDD-LTE or better since all WiMAX TDD operators will naturally migrate to 16m, while the only operator who is behind TDD-LTE is China Mobile. If Indian BWA operators choose WiMAX path than odds are quite high that 16m TDD ecosystem may supersede TDD-LTE.
Samsung, Motorola and Huawei may demonstrate a working 16m trail systems to their operators by end of this year. IEEE standardization is on track and it is expected to release final 16m draft by Q1 2011. Sequans and Beceem plans to release 16e/16m based engineering samples in early 2011. The development effort for migrating core network elements like ASN-GW, AAA and others to 16m is estimated minimal and hence early readiness can be expected.
The whole battle of LTE vs WiMAX is basically turning around two facades. First, It is highly publicized that Performance of LTE –TD based system will be superior to 16e. Second, TD-LTE ecosystem will bring vast economy of scale to operators. I spent some time to figure out the performance of TD-LTE and WiMAX 16e. Since WiMAX 16e doesn’t support 20 Mhz channels, on a 10 MHz of channel bandwith following observations were noted.
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Most of the current WiMAX deployments are on a reuse 3 network. If WiMAX is deployed in reuse 3 network and LTE is deployed in Reuse 1 network, than performance of WiMAX systems is better than LTE Rel 8. Data presented below is measured in different commercial wimax networks and LTE is based in NGMN simulations.
- LTE Rel 8 was ratified recently (2009), and in LTE release 8 special attentions were given to introduce methods to circumvent interference and improve overall network efficiency. 16e if deployed in reuse 1 scenario will perform inferior as compared to LTE Rel8. This is one of the major rationales behind most of the 16e deployments in 30MHz of spectrum.
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16m is expected to be deployed in reuse 1 networks and has more advanced interference mitigation techniques and supports even higher spectral efficiency than LTE Rel 8.
WiMAX Forum recognized these aspects and in the last general meeting at Taiwan, they have included features like interference mitigation, frequency reuse 1 support, downlink beamforming and 4X2 Mimo in their technology roadmap for 2010. Roadmap features will be further enhanced to support IMT-A requirement by 2012 with introduction to 4×4 Mimo, self organizing networks, multicarrier and enhanced locations services.
It would be interesting to see how the 4G TDD ecosystem shapes but definitely 16m has a important role to play.
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