back to article ZTE in 4G boost after 'world-first' VoTD-LTE call

Chinese telecoms kit maker ZTE has moved to cement its place at the forefront of next-generation LTE services and fly the flag for the TDD variant by completing what it claims to be the world’s first voice-over TD-LTE (VoTD-LTE) call. The Shenzhen-based firm’s TD-LTE equipment powers a China Mobile network in the nearby city of …

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Boffin

Not simple. Conclusions wrong

TDD can be LESS efficient. It just can work (more slowly) in less spectrum. Also FDD can be cheaper to implement.

Uplink needs lower symbol rate as client power is more limited than Base Station. Thus even at a 8:1 ratio of download vs upload (a reasonable factor) the uplink needs about the same spectrum.

This means if you use a single unpaired channel your receiver is potentially de-sensed by other nearby modems and the available download speed on average less than 1/2 the FDD paired spectrum. You need guard time between the half duplex Transmit and Receive, reducing efficiency.

TDD will always have higher latency too.

FDD is the more efficient cheaper solution. TDD is only of value to use up odd chunks of spectrum. WiMax had it as it was Intel's concept of outdoor WiFi, hence they stuck it in the LTE spec later to satisfy the small number of operators that would want it.

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Re: Not simple. Conclusions wrong

Interesting. Thanks for info.

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Anonymous Coward

"Unlike FDD, which requires a paired spectrum that has been criticised for being inefficient, TD-LTE transmits the up- and downlink traffic in the same unpaired frequency band, maximising available bandwidth and incurring lower power costs."

But of course,

" FDD-LTE, is favoured in Europe, the US and elsewhere"

Why do we always seem to get it wrong?

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Simple, we didn't

Even assuming the myth is true that there is less need for uplink FDD makes a lot of sense, since you can move to lower modulation schemes and better error correction which allow you to use a lot less transmission power. With TDD you need to transmit for short times at high power, which is hard from an engineering perspective.

Plus with FDD you can use your downlink all the time so you get 100% of your downlink capacity. With TDD you need to pause for the mobile station to respond. During that time you cannot do anything with your channels, and if you want to have low latency network, you need to wait a lot.

There may be situations where TDD is certainly better, but usually FDD makes more sense.

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