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Pushing Wi-Fi's Limits: Problems and Solutions

Posted by CmdrTaco on from the bits-and-bytes-wizzing-around-your-noggin dept.

securitas writes "Forbes technology columnist Arik Hesseldahl discusses the problems with 802.11x Wi-Fi - speed and range - and how to push its limits in a pair of his Ten O'Clock Tech columns. He discusses the alphabet soup of Wi-Fi standards, so-called 'Super G' dual channel bonding that allows two of 11 channels to act as one (and the interference problems that ensue), and the multiple input/multiple output (MIMO) method 'using multiple antennas to break a single, high-rate signal into several lower-rate signals' that could be a solution. Pushing Wi-Fi's Limits, Part Two focuses on repeaters, Wi-Fi mesh networks, WiMax and a company called BelAir Networks that has deployed several Wi-Fi mesh networks."

11 of 80 comments (clear)

  1. Real issue by kneecarrot · · Score: 5, Informative

    While standards and spectrum sharing are definitely factors, hardware must move quite a bit forward if it is going to become more useful than small home networks and looking cool at a Starbucks. The real problem right now is the quality of the radio chips coming out of Taiwan. They are typically way under specified range and allow for alot of bleeding between channels. The average home user won't notice it, but when you are rigging up multi-antenna setups or relying on precise timing for a repeater, it matters to a HUGE extent.

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    1. Re:Real issue by Jeff+DeMaagd · · Score: 4, Insightful

      One thing that scares me is the multi-channel radios. There are effectively only three non-overlapping channels, and some APs are starting to take up two of them? I know the spectrum is unlicenced for low power, but I think that's usually just rude and mean for one person to just take two channels. Right now, I experiment with three APs being on, all three channels, but being in a rural area and having checked with all the neighbors, no one else is using the spectrum near me.

  2. I wonder how healthy it is by 2057 · · Score: 3, Interesting

    I wonder how healthy it is to be surrounded day in and day out by all these microwaves and such....

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    1. Re:I wonder how healthy it is by MikeXpop · · Score: 3, Insightful

      How would we know?

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    2. Re:I wonder how healthy it is by mOoZik · · Score: 5, Interesting

      All the popular notions of microwaves being harmful are pretty unfounded. You must remember, they're like other waves, like radio, UV, IR, radar, and so forth. It seems to me most misconception arises from the fact that we use microwaves to cook food and that stray waves from cell phones and other such things could be harmful to us, but again, this is untrue for most purposes.

      You see, microwaves excite water molecules - they make them move back and forth really fast - thus heating them and increasing their temperature; this is how a microwave oven works. The fear with cell phones (which have a very weak transmitter) is that they may increase the temperature of brain cells or other, critical cells above a normal temperature, thus cause an unfavorable outcome. However, studies have shown that the increase of temperature from a cell phone antenna - when put against one's ear - is less than 1/10th of a degree Centigrade. As you can imagine, this is insignificant; our bodies are able to remain undamaged at temperatures MUCH higher than this.

      The point is that cellphones, while not the topic of this article, transmit much more powerful microwaves, much closer to the head. This means most WiFi waves are not at all powerful enough to have an impact.

      Of course, I do not suggest you stick your head near a multi-megawatt microwave transmitter.

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    3. Re:I wonder how healthy it is by jdhutchins · · Score: 3, Insightful

      The rate of cancer that we found went up 64% between 1970 and 1997. That doens't necessarily mean there was 64% more cancer, it just means we know how to find cancer better. I'm not saying that cancer hasn't gone up any, but it's probably not that dramatic.

  3. A clever concession to state of the market. by ofdm · · Score: 5, Interesting
    This solution seems to be quite a clever approach. A fundamental problem with 802.11b is the lack of spectrum. Although the channels are labelled 1 to 11 (in the USA), the numbers refer to a spacing of 5MHz chunks over 50MHz in the 2.4GHz ISM band. The problem is that the 802.11b signal uses almost 4 of those channels to actually transmit data. As a result, in order to have systems on different frequencies which are not interfering with each other, you end up with three effective channels - 1, 6, and 11. (If you have a WiFi AP accessible, check what channel it's on - most likely it will be one of those). Due to the low number of channels, it's impossible to do much in the way of channel planning. The result is that adjacent APs have to share the spectrum. The net outcome is that the data rate that users get between their client and the AP is reduced.

    802.11a at 5GHz was supposed to solve this. The 5GHz band is notable because of the extra spectrum it has. Compared to the 3 effective channels at 2.4GHz, the 5GHz UNII band has (again, it depends on your country) at least 8 usable channels of 20MHz. Additionally, the link rate is between 6 and 54 Mbps (as compared to 1 to 11Mbps for 11b, although this is somewhat moot given the growing preponderance of 11g solutions at 2.4Ghz). However, the 802.11a market never really took off and killed the 11b market the way we (engineers) expected it to. Mostly due to good (if slippery) marketing of 11g. As a result, there's a lot of unused 11a spectrum begging to be used. There are a lot of people with 2.4GHz equipment who want more range without losing data throughput. Using the 11a spectrum to extend the 11b/g range is what these guys have done. Neat - they get to use a superior technology with cheap chips available, to leverage a large market (albeit of dullards wed to an inferior solution).

  4. Problems on a more fundamental level by BelugaParty · · Score: 5, Insightful

    I can sit in a college library and browse people's laptops as if they are on a trusted network. People don't realize how public WiFi is in these environments. I think the main cause for this is the connection wizard (microsoft specifically). When you first connect the computer for wireless access it automagically, without a lot of warning, shares folders, printers ... etc, because it is assuming you are at your house with your linksys router; not at the library, coffee shop, or hijacking i-net from an apartment complex across the street.

  5. Pushing Wi Fi Limits by fegriffin · · Score: 3, Insightful

    Although there is never enough bandwidth, until we can solve the last mile bottleneck, 11Mbs 802.11b networks will be sufficient. With ADSL and cablemodem rates at less than 1Mbs that is where the problem needs to be solved.

  6. Re:use more power by ofdm · · Score: 3, Informative
    This is, unfortunately, a common misconception. Increasing the range of 11b means that the available bandwidth has to be shared more widely - meaning that each user gets less bandwidth, which is to say data throughput.

    Imagine if you will, a world where you could hear everyone talking within a block of you. Sounds great - you can hear your stereo from a mile away (well, this already happens). Unfortunately you can also hear everyone elses stereo, and everyone else talking, and their refrigerators humming, and their dogs barking. The net result is that you can't hear anything clearly. It's very much the same as being in a very full pub towards the end of a horse race - everyone's making a tonne of noise, and you can't understand much of it at all.

    The solution is to have smaller cells, in the limit pico-cells, where an individual user gets the full channel to herself, and 10m away another user gets their own full channel. An alternative is to have large cells, but with APs having different non-overlapping frequencies - so that the cells are isolated in the same manner as for the pico-cells. Sadly, the lack of spectrum for 11b at 2.4Ghz makes this second solution unrealistic.

  7. Re:use more power by ofdm · · Score: 3, Interesting
    I ... never experience any symptoms of interference
    That's most likely because, as you said, your traffic requirements are low, and possibly the traffic on the newtworks you can see isn't particularly heavy. If you have access to the PHY layer, you will see that collisions are in fact very common. The standard provides a couple of ways for dealing with this. (I'm sorry if I'm teaching you how to suck eggs here - I don't know what you know, so I'm aiming low).

    At the base level, each data packet is acknowledged by the recipient. If it isn't acknowledged (an ACK) then the packet is re-sent. Depending on the particular manufacturers implementation, the retries continue, and if still unsuccessful, at some point the rate is dropped (the lower rates are more robust). Eventually, if there's no acknowledgement, the packet is dropped.

    At the higher level the MAC can take advantage of RTS/CTS. In this mode, before sending a data packet, a small "Request to Send" packet is transmitted - telling all the radios in range that it is about to send a packet and it will take such and such a length of time to do it - so please stay off the air. The recipient (the STA to whom the eventual data packet is addressed) responds with CTS - Clear-to-Send. Then the data transfer goes ahead. The RTS/CTS mechanism is designed to reduce collisions in heavily loaded networks. Unfortunately, it relies on all the radios which can make noise being able to hear and succesfully demod the RTS/CTS. Adjacent channels have the annoying property that they are load and interfere with you, but they are also incomprehensible. As a result RTS/CTS doesn't help with one of the more common mechanisms for collisions.

    In summary, collisions do happen, and adjacent cells/frequencies do lower throughput. Many users never notice this because of their low data requirements. As many posters have noted, even 1Mbps is more than most people need at present. However, as requirements go up (streaming video etc), this will become a much more visible problem.