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What is TD-LTE?

9/26/2011 10:47 PM EDT
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tb1
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re: What is TD-LTE?
tb1   10/4/2011 9:52:23 PM
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Well Marvell recently announced a chip that can do both FDD and TD LTE (as well as HSPA+, and lots of other standards).

Bert22306
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re: What is TD-LTE?
Bert22306   10/4/2011 7:32:35 PM
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I'm not familiar with the details of LTE options, but is it necessary to assign the same amount of bandwidth to UL as to DL? I know LTE channels can be cobbled up from a number of separate RF slices, starting with as narrow as 1.25 MHz (just like cdma2000). So, why is it not possible to assign , say, a 5 MHz UL channel, and a 15 MHz DL channel? Or if this isn't possible, why not? I mean, why not make it possible, since it seems like it should be straightforward, and it can certainly make better use of spectrum.

Zouhayr
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re: What is TD-LTE?
Zouhayr   10/4/2011 12:03:01 PM
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If you have 20 MHz of spectrum and you deploy FDD flavor, than you have to use 10 MHz in DL and 10 MHz in UL which make no sense. We know that in average the DL represents 75% of the total usage. Now if you go with TDD flavor, you can take the 20 MHz and assign 75% to downlink (that is 15 MHz) and gives the remaining 5 MHz to uplink, which is more efficient. This ratio can be changed anytime based on real usage ratio. One important thing here, is you can not have the DL/UL ratio adjust dynamically otherwise you will run into self-interference.

green_is_now
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re: What is TD-LTE?
green_is_now   9/28/2011 6:07:44 PM
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Can this be used in conjunction with FDD, switched on, on the fly? Can this be a software radio function or must this be seperate dedicated hardware?

green_is_now
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re: What is TD-LTE?
green_is_now   9/28/2011 6:05:49 PM
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Perhaps dedicated, interleaved time slices would preclude interference between xsmt & rcvr. What is the interference comparison on both a nearby user at the next frequency slice, when non-linearities are considered from the handsets? Can the uplink windows be kept close to the center frequency to mitigate and allow the cell tower use the outer edges? perhaps this will not help on average if static. But may be advantaguos if done as needed on the ocasional (4 now) high data throughput uplink. Perhaps this can be figured out in advance and switched on when needed for high data rate uplinks.

green_is_now
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re: What is TD-LTE?
green_is_now   9/28/2011 5:56:27 PM
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I think this may hold true at the base station where cost is not at the same constraints as a handset. But the handset RF section must be relativlly cheap. So this may cause problems when being "pulled" from the ideal case.However in most cases, for cell users you either are downloading or uploading in terms of data, so recieve and transmit may not interfere. This thought does not hold when thinking of new breakout applications such as video conferencing.

Mulder
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re: What is TD-LTE?
Mulder   9/28/2011 5:51:07 PM
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I think of how much I download and how little I upload from my cell phone. If that upload could be mixed in the same carrier as the download while allowing for flexibility in the rate to alow for full speed downloads, it would effectively free up half the carriers out there which would be a big benefit in a high density urban market. At least that's my two cents.

sivan_ramachandran
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re: What is TD-LTE?
sivan_ramachandran   9/28/2011 5:47:19 AM
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TDD-LTE is attractive mainly because of the fact that there is no need for paired spectrum (which is required for LTE). There are fragmented spectrum available in different countries which can readily be assigned for TDD-LTE if required. I do not see an immediate implementation of the dynamically changing uplink to downlink ratio, since it brings other complexities like radio receiver saturation due to eNodeB receiving at the same time the adjacent eNodeB is transmitting (in effect blocking the receiver and rendering it ineffective). I think there are research efforts underway to make the TDD configurations more dynamic, but for now, this is not advantage.

Bert22306
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re: What is TD-LTE?
Bert22306   9/27/2011 10:04:58 PM
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I'm not sure I can see a big difference in these two techniques, in terms of bandwidth usage. LTE can use channel widths from 1.25 MHz all the way up to 20 MHz, and soon (or maybe already now) 100 MHz. Seems to me that if you use FDD, and size the uplinks and downlinks appropriately, you should be able to obtain very similar spectyrum usage, whether you're TD or FDD. Perhaps the TD method can adjust itself more dynamically over time, e.g. if the ratio of downstream to upstream traffic changes rapidly?

tb1
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re: What is TD-LTE?
tb1   9/27/2011 4:37:47 PM
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I've heard that Sprint's (Clearwire's?) eventual conversion from WiMax to LTE will use TD-LTE, because WiMax uses similar technology, making the conversion easier. I've heard arguments that TD-LTE is lower power and uses bandwidth more efficiently (when upload/download is unbalanced) than FD-LTE. I would be great if anyone with technical knowledge on thiscould chime in.

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