Sprint's magic box | Hacker News Reader

Sprint's magic box

newsroom.sprint.com

26 pointsasimpletune18 comments

T-Mobile has a similar box. But it comes as two units. One unit connects to the cellular network. The other is a microcell. The two communicate wirelessly. You put one where it can see a tower, and the other where you have a dead spot. I have one of these because there is a hill between me and the nearest T-Mobile cell site.

What is the t-mobile unit called? i have a similar issue in a basement workshop

The "4G LTE signal booster".[1]

T-Mobile also has the "4G LTE CellSpot", which needs an Internet connection like the Sprint AIRAVE.

T-Mobile has better device names. "Magic Box" tells you nothing. Does it make popcorn, or what?

[1] https://support.t-mobile.com/docs/DOC-14947

T-Mobile has something even better, you can use WiFi instead of cellular connection on compatible phones: https://support.t-mobile.com/docs/DOC-1680

Yeah -- "wifi calling" (running LTE signalling/data over an IPSec tunnel over wifi) is frankly superb -- I use it all the time, it seems to reduce battery drain (I imagine there's somewhat less use of the LTE modem), it even works on my phone (iphone 6 on t-mobile in US) when it's in airplane mode with wifi enabled.

I've been using a Sprint AIRAVE*[1] in my home for almost three years. This product seems to do something similar but without the requirement of your home network

It's been a must have for my in now both a low-income city and rural New Jersey. Without the extra signal support I am constantly dropping calls and having the audio cut out.

https://www.sprint.com/landings/airave/

I was a long-time Airave user. I always had problems with the device not getting a GPS lock and thus refusing to work. When I got a Galaxy S5 with WiFi calling I stopped relying on the Airave. I've since moved to Project Fi and haven't looked back.

This new device looks like it receives service from a nearby Sprint tower and uses it to serve your home/office. That wouldn't have worked at my home where it was nigh impossible to get Sprint service even when outdoors.

I had a Sprint AIRAVE. It needs GPS to tell it where it is. Not just at setup, but constantly. That's strange. It also has the serious defect that it publishes itself as a strong cell site even if it loses its Internet connection. So if your Internet connection goes down, so does your cell service, until you unplug the thing.

TDMA needs accurate clocks to work. All cell sites have GPS receivers in them for time signal reception.

People with a better understanding of the LTE protocols than I do -- is it possible to make an LTE relay (like this "magic box") but without any cooperation from the network operator (so no access to any cryptographic keys/secrets and no special/internal access to the operator's network)?

I know that to avoid self-interference, the relay needs to either implement frequency separation between its link to the real eNB and its link to the UEs it serves, or implement time separation. AIUI, time separation gets done by (for DL) not transmitting to real eNB when needing to listen to UE and (for UL) by not transmitting to UE when needing to listen to eNB. I think this gets more complicated when DL and UL are in the same band (TDD LTE).

Since I have no access to any key material, I cannot read anything that's encrypted and I cannot modify anything that'll get verified cryptographically or gets used as an input to a KDF (changes in KDF inputs will lead to different keys on the UE than the network expects). Given this limitation, is it possible to either:

1. Demodulate signals from the real eNB (on its DL band), replace any reference to the real DL band (in the master/system information blocks) with our DL band, and radiate that on a different DL band to the UE -- and do the same transform with the UL bands. Is it possible to fool the UE this way? Is the UARFCN used as a KDF input or talked about over some signalling radio bearer in RRC / NAS messages (which afaict, is encrypted and thus inaccessible)?

2. Is it possible to intercept/consistently modify/pass-on scheduling requests / resource grants for both UL and DL without breaking anything? Are scheduling requests / resource grants ever encrypted or otherwise protected by cryptography? Does anything above that layer actually know/care about the precise scheduling? Would this be a feasible method to ensure that there's no self-interference at the relay (by telling the UE to radiate on UL at a different time than the relay will radiate on UL to the eNB, and similarly for DL)?

It's been a while since I have been out of the wireless telco. world, but is this really new tech, the notion of having small cell sites for businesses ? I think it happens all the time, just maybe not with LTE Plus per say.

It's quite common, even in the home. The ones I've seen all need an Ethernet link however--maybe that's the innovation?

Not really. See T-Mobile's 4G LTE signal booster [1]

[1]: https://support.t-mobile.com/docs/DOC-14947

Those are probably proper femtocells, that broadcast a new cellular signal. These are repeaters or dumb signal boosters, that rely on a cellular connection back to the actual network.

The Press release implies that what they have done is use their newly acquired low frequency spectrum to create a carrier signal that only those boxes can pick up on then the boxes rebroadcast at frequencies existing smartphones can interact with.

The lower frequencies will in theory have better range than the higher frequencies they use for typical LTE

Isn't this just a souped up femtocell?

femtocells require a local broadband connection to create the connection to the cellular network. This is just a repeater for towers within a certain distance. Requires no connection to broadband for the customer.

Which is to say if there is no sprint tower near you this is a useless product.

In technical terms it's a femtocell, yes. But if they're handing out femtocells that themselves connect over the cellular network that users can just dump on a windowsill to improve their signal with no configuration, that's somewhat interesting, and different than how carriers have been deploying femtocells until now.

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