Can I Get A Witness?

Hav­ing trou­ble under­stand­ing why your hotspot isn’t get­ting a Wit­ness? Are you see­ing mes­sages about being above or below the bounds of an RSSI met­ric? Let’s dig in!

We’ll start with this, the infa­mous PoC V10 SNR lim­its graphic:

I’ll explain the X and Y axis in a bit, but at first glace it’s pret­ty basic. 

Green = Good, Red (pink?) = Bad. Find the num­bers report­ed for your spe­cif­ic Wit­ness event, see where they inter­sect, and you’ll know why you have an Invalid wit­ness. Yes, yes, yes, if you’re a “radio head” you instant­ly see some­thing wrong, but for now let’s keep it simple.

We’ll go through two exam­ples; 1 invalid, and 1 valid. Here’s an invalid witness.

Three things are listed: 

  • The dis­tance in meters. This is used to cal­cu­late FSPL, or Free Space Path Loss. More on that in a sec.
  • The sig­nal strength in dBm (RSSI)
  • The lev­el of sig­nal above the noise floor, in dB. (SNR)

Here’s how that wit­ness charts out:

With a high SNR (any­thing above 0 is high for Heli­um), at only 914 meters this sig­nal is basi­cal­ly too good for the distance.

Ok, so what does it look like if the wit­ness is valid?

We’re look­ing at the same three things, but now we’re at about twice the dis­tance, and if you remem­ber your dB strength rules (every 3 dou­bles or halves), about a quar­ter of the SNR.

Easy enough to read a chart, right? But what does it mean, and how can you get more valid witnesses?

We’ll start by defin­ing two things first: RSSI and SNR.

RSSI = Received Sig­nal Strength Indi­ca­tor. In very sim­ple terms, RSSI mea­sures the strength of the radio sig­nal you’re receiving. 

In RSSI mea­sure­ments, the larg­er the neg­a­tive num­ber, the weak­er the sig­nal. ‑130 is weak­er than ‑100. In gen­er­al, in the land of Heli­um, you want your RSSI to be between ‑82 and ‑134.

SNR = Sig­nal to Noise Ratio. This is a mea­sure of the qual­i­ty of a sig­nal com­pared to the back­ground radio “noise”. It’s expressed in terms of dB (deci­bels), and the big­ger the num­ber, the bet­ter. Except when it’s not.

Wait, a sig­nal can be too good? Yep. 

When Heli­um start­ed (and basi­cal­ly, up until the present, August 2021), Heli­um had a prob­lem: They were sell­ing radio devices. Why is that a prob­lem? This’ll get more com­pli­cat­ed before it gets sim­ple, so buck­le up and pay attention.

Every­one (in the US, and in most coun­tries) sell­ing a radio device has to have it cer­ti­fied by some nation­al body. In the US, that body is the FCC. One of the things they check dur­ing cer­ti­fi­ca­tion is that your device does­n’t break any emis­sion-strength rules (tech­ni­cal­ly EIRP, more on that here.)

Heli­um is required to stay with­in the lim­its of the rules. To do that, they used a low gain anten­na (1.8 dBi gain) and a rea­son­able amount of ener­gy out­put (-27 dBm). That put them at ‑28.8 dBi for max EIRP, well with­in the lim­its for the US, which is a max EIRP of ‑36 dBi. 

The FCC also requires a man­u­fac­tur­er to build units that “pre­vent” the con­sumer from chang­ing the anten­na. Heli­um accom­plished this by using RP-SMA con­nec­tions. Yep, that counts as pre­ven­tion. It’s an out­dat­ed sys­tem, for sure.

An addi­tion­al mea­sure tak­en to ensure there was no encour­age­ment to “improve” your anten­na (and even they acknowl­edge it isn’t a great one) is to set fair­ly strict and some­times unrea­son­able rules regard­ing what a received radio sig­nal should be in terms of the sig­nal strength and quality.

This is accom­plished in part by mea­sur­ing ALL anten­nas (even your high gain fan­cy wazoo anten­nas) AS IF THEY WERE THE HELIUM STOCK ANTENNA.

No, that does­n’t make sense. Yes, it was rea­son­able at the time. Yes, it will be changed. 

How did Heli­um come up with those rules, and why? I’ll start with the Why: To stop cheaters, also known as “gamers” because they game the sys­tem with­out pro­vid­ing any actu­al benefit.

Cheaters used to be able to just plug in a bunch of hotspots stacked on top of each oth­er. Those hotspots would wit­ness each oth­er from inch­es away while report­ing false­ly assert­ed loca­tions that made them seem to be much fur­ther apart. It appeared they were pro­vid­ing great cov­er­age. So they earned. Mas­sive­ly earned. 

One of the most egre­gious exam­ples hap­pened in a lit­tle town called Modesto, in Cal­i­for­nia. At the peak of the cheat­ing, in late sum­mer 2020, a group of hotspots (prob­a­bly in a clos­et, and not even in Modesto) were earn­ing thou­sands of HNT per day. Yes, per day. 

Heli­um has since worked to com­bat gam­ing in more and more nuanced ways, but the way they approached Modesto was with a giant radio-sig­nal mea­sur­ing ham­mer: The RSSI/SNR chart. This was cre­at­ed by a Heli­um employ­ee who ana­lyzed almost half a mil­lion PoC receipts and looked for out­lier results. 

He was approach­ing this in clas­sic Sil­i­con Val­ley fash­ion: Look at the actu­al dataset, don’t rely on “old” thought, and fig­ure out a new way to do a bet­ter job. Admirable, but it turned out to penal­ize not only egre­gious gamers, but many of the rest of us who just want­ed to do an above aver­age job.

The Modesto clus­ter was gut­ted, but the RSSI/SNR chart stayed in place. Oth­er changes (HIP 15 & 17) entered into the sys­tem and incen­tivized spread­ing out and being reward­ed for pro­vid­ing bet­ter and bet­ter cov­er­age, but the RSSI/SNR chart stayed.

It was­n’t because the Heli­um team was ignor­ing it. They had much a big­ger chal­lenge to sur­mount: Get­ting Val­ida­tors online so the blockchain could stop suf­fo­cat­ing itself. With that mis­sion-crit­i­cal task accom­plished, they can now (summer/late sum­mer 2021) turn to mak­ing sure the blockchain improves in accu­rate­ly reward­ing superb coverage.

Which brings us, almost, to today, some­time in August of 2021. With PoCv11 (Proof of Cov­er­age Ver­sion 11) on the hori­zon, we’re about to take a strong step in the direc­tion of reward­ing strong & clear sig­nal cov­er­age over short and long distances. 

As you’re see­ing in the app, Heli­um is offer­ing you the chance to enter your anten­na gain and ele­va­tion. This will help them more accu­rate­ly assess whether or not your wit­ness­es are valid. As of today (Aug 4th, 2021), those two met­rics don’t actu­al­ly make a dif­fer­ence for you, the hotspot own­er, but…they will.

In the future, when PoCv11 comes online, the details you enter will be applied to your wit­ness receipts. In order to com­bat gam­ing (essen­tial­ly to stop every­one from just say­ing they have a 50 dBi gain anten­na so all of their wit­ness­es are good), Heli­um will simul­ta­ne­ous­ly apply your gain AND decrease your trans­mit strength. That’s fair, by the way, and you should want that to happen. 

I know, I know. Nobody likes decreased strength. Trust me on this one: LoRa already gives you TONS of range. Your goal is not long range, it’s increased earn­ings, and earn­ings come from valid wit­ness receipts. 

What will that look like? Full details over here, but for those of you who aren’t deep into radio geek­ery, the big pic­ture is that Heli­um will drop SNR and just use RSSI and dis­tance. Here’s a pro­posed chart. Meters on the Y axis, RSSI on the X axis.

Ok, so you’ve got three lines on there: Red, Yel­low, Green. The lines rep­re­sent the cur­rent cut­off (Red) for a valid wit­ness as well as pro­posed future cut­offs (Yel­low and Green). 

You’re also see­ing a bunch of blue dots. Those blue dots rep­re­sent report­ed wit­ness met­rics of RSSI at some dis­tance. The green line is the most restric­tive, but is based on actu­al val­ues of RSSI at some giv­en dis­tance, which is far more accu­rate than the cur­rent RSSI/SNR curve.

To keep it sim­ple, this means that in the future, when PoCv11 replaces the cur­rent ver­sion, a hotspot using a non-stock anten­na will not be penal­ized for it. Whether the yel­low, or green, or some oth­er line is used is still up for debate. 

We’ll wrap this up with one of the most impor­tant take­aways: What anten­na will help you stay with­in the pro­posed lim­its? Easy: It’s the LOWEST gain anten­na you can use. See how the curves all shoot up at a fair­ly defined RSSI? That’s the key. If your RSSI is even a few points “to the left”, you can be on the wrong side of the line. 

This helps explain why in many cas­es, when you get that fan­cy super high gain anten­na, your valid wit­ness­es dis­ap­pear. So what anten­na should you buy?

My rec­om­men­da­tion is still the HNTen­na, but any of the low gain (4 or less) anten­nas in your coun­tries fre­quen­cy, from a wide vari­ety of sources like McGill, Par­ley Labs, L‑com, or Laird will be fine.

If you’re will­ing to explore your inner geek and you like to tin­ker, take a look at atten­u­a­tors. They’ll atten­u­ate (or weak­en) the sig­nal (both tx & rx), but they’ll also increase the SNR, so exper­i­ment cau­tious­ly. Here are a few options:

Expen­sive (~$400) and unnec­es­sary, but hey, if you want a great unit — Fairview 0–11 dB Step Attenuator

Cheap­er ($25), less pre­cise with­out extra mea­sur­ing equip­ment — ATM RF Vari­able Atten­u­a­tor AF033-10 DC-1000 MHz 50 Ohm

An atten­u­a­tor decreas­es your sig­nal strength both ways. They’re not a great long term option. The best option is to use a low gain anten­na and get it up high in the right loca­tion. If you see that the Near­son 9 or RAK 8 that you bought when you were in “Big­ger is bet­ter” mode gets more valid wit­ness­es once you’ve tak­en a lit­tle sauce out of it, well, you’ll have some use­ful data points (that I’d love to hear about.)

Want to go deep­er? Con­sid­er hir­ing me to help you out; I love help­ing peo­ple crush with Helium.

Hap­py Witnessing!

**This post was writ­ten with tech­ni­cal over­sight from @jerm on Dis­cord. He is an absolute wiz­ard with this. All right­eous accu­ra­cy is his, any errors are mine. ‑Nik@GKI

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