What's up with FDD WiMAX?

There seems to be some confusion brewing in the WiMAX camp, after revelations that the WiMAX Forum has been working on an FDD profile for the technology and is aiming to implement it within six months.

The assertion came from Paul Senior, CTO of Airspan and founding member of the WiMAX Forum, who recently told telecoms.com sister publication MCI, “The WiMAX forum will have an FDD profile for Mobile WiMAX inside six months. We’ve been working on it for the last 12 months.”

Senior made a similar comment to another of Informa Telecoms & Media’s titles, Global Mobile, back in November too. But Ron Resnick, president and chairman of the WiMAX Forum, has since moved to counter the claim.

Resnick told another publication, WiMAX Day, that the six month timeline for FDD was “unofficial”, and that no decision has yet been made when to propose an FDD WiMAX air interface to the ITU.

Understandably, the WiMAX Forum had to tiptoe around the FDD subject when putting the technology forward for approval as part of the IMT 2000 family. As Senior told MCI, “We’ve been a bit quiet about it because we wanted to get the IMT 2000 decision. And if we had gone to IMT with an FDD profile, we probably couldn’t have got it through. We decided to go for something that was a little less threatening, which was a TDD profile.”

Under 3GPP standardisation the 2.5GHz spectrum band is typically split into paired spectrum, known as Frequency Division Duplex (FDD), which has separate channels for uplink and downlink, and unpaired spectrum, known as Time Duplex Division (TDD), which has a single channel but up- and down-link timeslots.

The creation of an FDD profile for WiMAX would remove the last impediment on using WiMAX as a voice centric technology and would also pitch it head to head against HSPA, LTE and EV-DO in the 2.5GHz band.

As Senior told Global Mobile, “the importance of the TDD vs. FDD issue is really all about whether you believe the future of services is going to be data – and not simply pushing data services to smartphones – or voice-centric. The business today remains very voice-centric, and to a certain extent there is no need for significant data infrastructure.”

Dean Bubley, industry analyst with Disruptive Analysis, also notes that some regulators, especially Ofcom, have been keen to see WiMAX evolve as a competitor to established UMTS FDD. Over the last year, the UK regulator has been working very hard on a controversial structure for the upcoming 2.5GHz auction.

This itself has cause lots of debate in terms of auction design and assessments over interference and the need for guard bands, but now with the FDD profile for WiMAX in the pipeline, Bubley says, “I wonder if that means that Ofcom and other regulators need to go back to the drawing boards and re-work their interference assumptions for a possible cellular/WiMAX mix across the whole band.”