1
\$\begingroup\$

a couple of days ago I had a discussion with a colleague when he told us he purchased a "WiFi Booster Adapter+Antenna". It was claimed that by plugging it in his USB and using it instead of his built-in WiFi adapter, he'd be able to connect to those "far away wireless networks".


My assumption about WiFi (or any form of 2-way connection):

  • The two devices should be in each other’s range.
  • There's no such thing as "receiving range".
  • Even if you boost one device's transmission range while the other device is moving further, you should also do the same boosting (more power gain) for the moving device.

Based on those assumptions I have the following in my head: enter image description here
(Both devices in each other's range; A's signals are reaching B, B's signals are reaching A)


enter image description here
(B is going further and boosting its signal. While B's signals are reaching A, A’s signals aren't reaching B)


The question is: away from the discussion itself, the brand of the booster or where he's installing it (one might purchase a super duper WiFi AP for example). Am I making wrong assumptions here? either about how sending/receiving signals works or how the booster works, if so can you please correct me?

\$\endgroup\$
  • \$\begingroup\$ @stevenvh, according to RadioLabs there are directional antennas. So "B" can boost and focus its signal in the direction of "A", right? (I honestly don't know, this is just what I've read) \$\endgroup\$ – Adi Jul 7 '12 at 8:42
  • \$\begingroup\$ I am no HF expert, but AFAIK your assumption "there is no such thing as a receiving range" is false in the context of directional antenna's. \$\endgroup\$ – Wouter van Ooijen Jul 7 '12 at 8:58
  • 1
    \$\begingroup\$ One problem what wasn't taken into account in the B picture: Since we're assuming that same antennas are used for both transmission and reception (as can be determined from There's no such thing as "receiving range".), the B device may be able to detect A's signal at greater distance if it has more sensitive antenna \$\endgroup\$ – AndrejaKo Jul 7 '12 at 8:58
  • \$\begingroup\$ @WoutervanOoijen, I don't mean "receiving range" as in frequency range. I mean it as the actual distance. @ AndrejaKo, thank you very much. I guess now we're starting to get somewhere with this "more sensitive antenna", \$\endgroup\$ – Adi Jul 7 '12 at 9:03
  • 1
    \$\begingroup\$ @Adnan More advanced antenna on B will increase B's ability to detect transmissions and to emit at longer range. That's not directly related to A's ability to send signals at long range. You can even see that form your diagram. A is in B's range, and that's fine is we take that transmission range and reception range are the same. \$\endgroup\$ – AndrejaKo Jul 7 '12 at 9:45
4
\$\begingroup\$

WiFi Signal Boosting
- The two devices should be in each other’s range.
- There's no such thing as "receiving range".
- Even if you boost one device's transition range while the other device is moving further, you should also do the same boosting (more power gain) for the moving device.

Your premises are partially correct.

  • An aside - Antenna gain:

    The following is liable to confuse more than help. Just accepting "antenna gain" as a focusing of signals as wit a magnifying glass, will suffuce for this dicussion.

    When I say below "increase antenna gain" I mean as far as the transmission between the two stations is concerned. Antenna "gain" is always only achieved by dealing with signals from a relatively smaller area. You can get an inefficient antenna, which clouds the issue, and antennae may reflect a radiation image in the ground plane, but for practical purposes antenna "gain" is identical to what you get with a magnifying glass. On the receive side, signal from a wider area may be captured but what is effectively being done is to acquire signal from a larger solid angle.

If you increase antenna gain of B relative to A then you will increase apparent transmitter power of B. But, using the same antenna you will also increase the apparent transmitter power of A as B will have the signal from a wider area "focused" by the receiver. So, increasing antenna gain increases range due to apparent boosting of transmit power by both stations.

If you increase the transmit power of B you will increase the B to A transmit distance but the A to B distance will not be affected. To provide an equivalent receive boost you need to reduce the receiver noise level of B proportionately. This is usually best achieved by use of a lower noise device in the receiver front end. This area involves the blackest of magic. It is usually easier to increase transmit at power at both ends than to increase receive gain and transmit power at one end only.

In a typical WiFi scenario the central station / master / access point / whatever, is shared amongst multiple channels and is able to bear a greater capital cost. By adding a booster that both increases transmit power and also adds a low noise receive amplifier you benefit all channels and remote devices concerned.

At least potentially, a unit which does not improve receiver performance and which increases transmit-power-only at the access point could support a greater outgoing data rate and slower incoming rate at lower power / signal to noise / worse BER. This would be useful for download dominant data streams which are what is commonly encountered. Whether the system used supports such split data rate configurations is protocol dependent.

\$\endgroup\$
  • \$\begingroup\$ Very interesting, as a non-expert in this I found a couple of new terms, as I'm reading about them now I'm having a better understanding of the whole model. Thanks a lot! \$\endgroup\$ – Adi Jul 7 '12 at 9:47
0
\$\begingroup\$

In addition to what Mr. McMahon has to say (excellent explanation there):

I assume the WiFi "booster" is a USB WiFi dongle with a beefed-up front end. So it especially increases the TX power. Note that this may violate relevant national regulations (typically limited to 100 mW with an "omni" low-gain antenna) which may or may not be a practical problem to a particular human user ;-)

There's not much you can do about the RX side LNA. The LNA's in the MiniPCI-e WiFi cards are not so bad that they would use external improvement. The WiFi card consists of a NIC chip and a smaller "radio front end" chip. The front end chip does the RX/TX direction switching and contains the PA and LNA stages - and therefore determines both the output power and the input noise floor. Hint: Google SkyWorks SE2593A20.

The maximum output TX power is not exactly even across the frequency spectrum, it tends to roll off towards the upper end of the spectrum and towards higher data rates... but generally the WiFi card maker can affect the TX power by choice of the front end chip. Hardly anyone does seperate RX and TX connectors on a WiFi card, most cards have combined RX+TX coax ports (two or three of them, one port per RXTX "chain"). Also note that in WiFi, the RX and TX run in the same channel - thus, RX vs. TX cannot be separated by a highpass/lowpass frequency splitter + combiner (to be treated separately). As the card makers do not venture their own designs of the PA and LNA made of discrete components, they have to use what's available from the RF front end chip makers, optionally adding heatsinks to be able to overdrive the WiFi front end chips a little outside of spec.

Even if "more power" was easily available, adding more power is not such a brilliant solution in environments with lots of crosstalk between neighboring AP's (residential blocks etc). Increasing the collision-avoidance sensitivity threshold might bring some improvement in such "dense" areas, but that's typically not a tweakable parameter and if it was, it would have its clear limits. More power is really only any help for long-distance links, if all you need is the sheer reach (and even that has its limits).

Generally the best amplifier is a quality antenna :-) Improves range in both directions. And, as others have said, high antenna gain means high directionality, and large dimensions (directional antennas have large reflectors, in proportion to wavelength).

With respect to antenna quality, an external USB WiFi dongle with RSMA port(s) for an antenna of your choice has the inherent advantage over built-in WiFi PCI-e cards, that the internal card tends to be attached by a foot of ultra-thin coax cable pigtail to some space-optimized dual-band flipper antenna in the corner of your laptop's display... anything is better than this, even a lambda/4 naked wire attached to a straight-out SMA connector, millimeters away from the RF front end chip on the USB dongle's inner PCB.

BTW, there is a distance limit: the ACK timeout. Not sure how this parameter is handled in modern 802.11 incarnations and implementations. It seems to be somehow "dynamic" in modern Mikrotik firmware for instance. In the old days, this could be configured manually in the AP firmware, and the default was good enough to cover about 2 km of distance from AP to client.

Ultimately the best solution to the shitty nature of WiFi is a good quality cable ;-)

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.