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Future 600 MHz band & OTHER discussion thread (was "Sprint + 600 MHz?")

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The problem is that -- without CoMP or maybe even with CoMP -- we have LTE networks that are not truly VoLTE ready. VoLTE will be a significant step back in voice coverage because the RF robustness just is not there. Places where users can currently make low RSSI but still reliable CDMA1X voice calls -- in part due to soft handoff -- will be without VoLTE service.

 

AJ

I realize you were already writing that so, enjoy that white paper I just posted while I go get some coffee :)

 

On a fully-deployed network built on even Rel 8 and only PCS, VoLTE would work better than even the equivalent on ever-faithful 1x, where the UE is responsible for the bulk of the handoff. In LTE rel 8, an X2 priority-2 (voice call would be pri-2, signaling is 1) the UE doesn't really have to do much of anything. The X2 handoff with multiple-candidate eNodeBs is significantly more resilient than a CDMA soft handoff.

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Avocados are still fruit. :P

 

As an aside, one big reason that CDMA NV sites are brought up in clusters is that (possibly for reasons related to what you said), in many markets, NV 3G sites do not hand off properly to legacy sites. Chicago was one, and West Michigan is another.

 

Haha. I know! That's why I chose avocados as the third thing to apples and oranges in our fruity analogy. They're lopsided but more nutritive. :)

 

Good point. Read the white paper in the section on handoff to non-LTE for why. That has been quite troublesome in the interim for rollout. The NV 3G sites are setup for this but legacy is not capable. (If you've ever had, say, a Skype video call successfully continue after dropping from LTE to 3G, and another time had it not: this is why. It should be possible with minimal failures with all-NV. But until then, it won't always work!)

Edited by Txmtx

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I realize you were already writing that so, enjoy that white paper I just posted while I go get some coffee :)

 

I have not had a chance to read the white paper, though I will try to do so today.  But I do think that the current state of LTE with present day UEs is not all that you make it cracked up to be.

 

Sprint's band 25 LTE 1900 airlink, for example, does not even remotely provide the same level of coverage that its CDMA1X 1900 and EV-DO 1900 airlinks do.  Even with the 1:1 LTE site overlay, LTE has both urban and rural coverage gaps that do not affect CDMA1X and EV-DO.  Only additional sites or band 26 LTE 800 will fill those holes.

 

That is the fault of the LTE airlink.  It may be fast because it crams in so many OFDMA subcarriers, approaching the Shannon bound for its bandwidth in each MIMO spatial channel, but it is certainly not resilient.  As the saying goes, there is no such thing as a free lunch.

 

AJ

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Only additional sites or band 25 LTE 800 will fill those holes.

 

AJ

For those that don't know AJ made a typo and meant band 26 LTE 800. Unless he meant band 25 LTE and CDMA 800 but that doesn't make much sense given the context.

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For those that don't know AJ made a typo and meant band 26 LTE 800. Unless he meant band 25 LTE and CDMA 800 but that doesn't make much sense given the context.

 

Either I did not make a typo, or a moderator fixed it because the original post reads band 26 LTE 800.

 

AJ

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Either I did not make a typo, or a moderator fixed it because the original post reads band 26 LTE 800.

 

AJ

That's really weird, all I did was delete the parts that weren't relevant to cut on on the amount of scrolling on the page for the quote. :wacko: 

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That's really weird, all I did was delete the parts that weren't relevant to cut on on the amount of scrolling on the page for the quote. :wacko:

 

Maybe a moderator fixed it, but...

 

 

AJ

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I have not had a chance to read the white paper, though I will try to do so today. But I do think that the current state of LTE with present day UEs is not all that you make it cracked up to be.

 

Sprint's band 25 LTE 1900 airlink, for example, does not even remotely provide the same level of coverage that its CDMA1X 1900 and EV-DO 1900 airlinks do. Even with the 1:1 LTE site overlay, LTE has both urban and rural coverage gaps that do not affect CDMA1X and EV-DO. Only additional sites or band 26 LTE 800 will fill those holes.

 

That is the fault of the LTE airlink. It may be fast because it crams in so many OFDMA subcarriers, approaching the Shannon bound for its bandwidth in each MIMO spatial channel, but it is certainly not resilient. As the saying goes, there is no such thing as a free lunch.

 

AJ

In my earliest writing I certainly agree with you here. The whole "all things being equal..." part. If it is truly a seam, and you have visible coverage from multiple cells, LTE wins. If the seams are such that for LTE it is an edge while for CDMA it was a seam with choices, maybe not.

 

But the network is being designed with all that in mind. The paper will probably help illuminate some of the features and tricks designed-in to help. But in any case we will not see VoLTE supplant 1x voice until they have managed the seam regions properly with LTE in mind, whether that means waiting for HetNet or whatever. Frankly, LTE already far outperforms EvDO for data even in any 1:1 overlay... Any Ev link at seams/edges has long had its breath sucked away and is unusably saturated at present, despite a seemingly-usable RSSI value. This will not change without drastic offloading to LTE. Then perhaps at seams data will revert to 3G for a few hundred square meters, inside buildings of that region.

 

The key to reconciling my statements with yours (beyond the white paper) is basically:

 

For a 1:1 overlay of identical bands and current UE, *If and only if* the cell edge is also a seam (meaning multiple edges are visible to the UE) LTE outperforms CDMA at a seam -- even a "5-bar" CDMA seam. If, however, for CDMA it is a seam from the UE's perspective but for LTE it is effectively an edge, it is likely you will run into dead zones for LTE where you wouldn't for CDMA. For relatively-unloaded 1x, this means you can place calls where LTE would fade into nothingness.

 

Luckily the network engineers understand all this and will use the full bag of engineer trickery to prevent it... ;) I will be quite surprised if (after perhaps a few weeks of growing pains) VoLTE is not equally or more resilient in respect to dropped/failed calls, with equal or better call quality, and with all the other advantages of LTE. They won't launch it until then.

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