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Irish Shark
Play Like A Champion Today
MVM
join:2000-07-29
Las Vegas, NV

2 edits

Irish Shark

MVM

[iPhone] -114 dBm RSSI - How can it even work?

My iPhone 5 reports the above signal strength. Translated into bars it varies from 1/2 - 1 1/2. According to the specs, the phone should not connect to any signal source.

I have AT&T and all the grid maps show that I am in a solid green area (excellent). The "G" indicator will come on as well as the "LTE" (makes no sense to me).

The signal is the same outside as inside the house. If I drive around and take some signal samples, they get better in some spots, but not so good in other areas.

I am about 1 1/2 miles from the tower and a 1/2 mile from a repeater.

Talking to AT&T, they said the grid maps are wrong and I am in a small "fringe" area with low signals. They also said that I am connecting to a tower that is 3 miles away.

Phone calls seem OK with neither me or the other party having static, fade, or garbled sound.

Is this phone just not reporting the correct signal level or am I missing something and should just go back to sleep?

EDIT: Sorry, but RSSI does have units.

squircle
join:2009-06-23
OTWAON10

1 edit

squircle

Member

Re: [iPhone] -114 db RSSI - How can it even work?

Just FYI, RSSI is not measured in decibels. Your RSSI is -114 dBm, not -114 dB.

Edit: noticed my HTML entities were mangled by DSLr.

Irish Shark
Play Like A Champion Today
MVM
join:2000-07-29
Las Vegas, NV

Irish Shark

MVM

said by squircle:

Just FYI, RSSI is not measured in decibels. Your RSSI is -114, not -114 dB.

Sorry, wrong answer.

The signal bar on top left of your iPhone screen will be replaced by number, indicating the actual signal strength of your device. The reading is in dBm and the higher the number is, the lower its signal strength and anything below -110dBm may experience call failure or drop.

»opengear.org.uk/faq386-C ··· gth.html

»www.maximintegrated.com/ ··· /gpk/252

»www.developer.nokia.com/ ··· 8RSSI%29

squircle
join:2009-06-23
OTWAON10

3 edits

squircle

Member

Sorry, wrong answer.

The signal bar on the top left of your iPhone screen will be replaced by a number, indicating the actual relative signal strength of your device the cellular signal.

You have to understand that dB and dBm are only somewhat related. Yes, RSSI does have units, and yes I did typo my last post, but they're certainly not dB. Quick explanation: it's not an arbitrary ratio (like dB) but a ratio relative to 1 mW. The ISA has a nice explanation.

You also have to consider that signal strength is not the only factor; there's also the signal quality. You can be receiving a very, very weak signal, but as long as it is relatively clean (i.e. free of noise and other interference), you can still have a perfect phone call. On the iPhone's hardware specifically, the minimum value is -121; -110 is not the "minimum". You can make a perfect phone call at -120 (and I personally have).

Think of it like a DSL line. If your line is clean, has minimal interference and crosstalk, as long as your SNR is above 6 dB (yes, this is actually decibels and not dBm), your attenuation won't matter as much.

TL;DR: RSSI is not measured in dB, is relative (not absolute) and signal quality matters more than signal strength

Edit: To answer your original question, your phone is reporting the correct signal level and you should not worry about it.

Edit 2: I remembered the name of the app I used to use from Cydia, it's called "Signal". It costs a few dollars but it's interesting to see how the signal quality compares to signal strength for any given tower.
Kearnstd
Space Elf
Premium Member
join:2002-01-22
Mullica Hill, NJ

Kearnstd to Irish Shark

Premium Member

to Irish Shark

Re: [iPhone] -114 dBm RSSI - How can it even work?

silly question, How can db be negative? I had a stereo once that listed the volume as negative db too which made no sense to my mind the numbers should be positive. But the dial was basically full loud if it was 0db and pretty much muted at -99.

Stefania
Jezu Chryste, Kubi
Premium Member
join:2003-03-17
Chicago, IL

Stefania

Premium Member

Because you're modulating the attenuator on your pre-amplifier. At -99dB the signal was fully attenuated or 'restricted' if you will. At 0dB the pre-amp is no longer attenuated and is feeding your power amplifier the full signal. The final volume output is going to be based on the impedance load on your power amplifier and the sensitivity of your transducers or "speakers" if you will.

Irish Shark
Play Like A Champion Today
MVM
join:2000-07-29
Las Vegas, NV

Irish Shark to squircle

MVM

to squircle

Re: [iPhone] -114 db RSSI - How can it even work?

We all make typos. That's what I did. I missed the "m" after the "dB" and that is what caused all the hoopla.

The -110dBm was referenced for a 4 and 4s. I also seen that referenced for the 5. Top of my head, I don't remember where I read that. I'll see if I can find it.

Sorry for all the confusion.