More WiFi Bandwidth? Not This Year

If you have a network of computers, you're probably connected by Ethernet in some portion of the network, so you're used to the Ethernet 100M (or newer 1G) bandwidth. You like the freedom of WiFi, but freedom comes at a cost - loss of bandwidth. The current WiFi standard 802.11g has a maximum bandwidth of 54M (and I should emphasise maximum, here).

So the WiFi manufacturers are trying to satisfy your need for high bandwidth, and they came up with a couple solutions, which will have a maximum bandwidth of 108M. The new standard includes 2 features (using names which vary by vendor):

• MIMO.
  
• Super-G.
  

MIMO, or Multiple-input Multiple-output, uses multiple radios and antennas. MIMO has two components.

• Antenna diversity. If you're familiar with FM radio in your car, and multi-path interference, you'll know the value of antenna diversity. The idea behind antenna diversity is that, if the signal from a radio transmitter is weak on one antenna, because of MPI, it will, hopefully, be stronger on another antenna some distance away from the first. A special processor does nothing but compare the signal being received by two different antennas, and select the stronger.
  
• Beamforming. Antenna diversity counter acts multi-path interference. Beamforming uses the principle of multi-path interference, at the transmitter, to focus the strength of the transmitted signal in one direction. Using the diversity antennas on a MIMO component, it's possible to identify the relative location of the other device in communication; using beamforming, the transmitted signal is focused in that direction.
  
• By combining antenna diversity and beamforming, it's possible to extend the effective range of a WiFi conversation. You can locate the router / access point, and the client computer(s), at a greater distance from each other, and yet get acceptable performance.
  

With 108M, aka Super-G, there is one channel - "6".


Are you curious about how many WiFi channels actually exist?



Both MIMO and Super-G will give you more bandwidth, and more effective range, assuming that you have no neighbours with WiFi. If you have neighbours (and who doesn't), only one of you can use a channel at any given time. Your equipment will have to decide how to share the channel. But, there are additional issues here.

• MIMO will increase the effective size (area) of your WiFi neighbourhood, by increasing the effective distance between WiFi components that can detect each others signals. This increases the number of devices that have to share the channel, at any time.
  
• Super-G will increase the size (volume) of your WiFi neighbourhood, by using more of the frequency spectrum to create more bandwidth. More channels used by your WiFi router increases the number of devices that have to share the channel, at any time.
  
• More devices that have to share the channel means less time each device can transmit, and less bandwidth available to each client device. More devices that have to share the channel means more possibility of collisions, at any time, and again, less bandwidth available to each client device.
  
• Neither MIMO nor Super-G are part of any ratified standards. You can't predict, with any reliability, how well equipment from different vendors will interact with each other. This will affect performance on your LAN, and between your LAN and your neighbours LAN. Check out ExtremeTech: Real-World Interoperability Tests of Five 802.11n Routers for a good discussion of this issue, with actual hardware testing results.
  

The dynamic effect of MIMO beamforming may have another effect. When you setup a WiFi LAN, you're advised to try different channels (most objectively, using NetStumbler or a similar site survey tool). Over some period of time, you should be able to identify the majority of your WiFi neighbours, and pick a less congested channel.

With a WiFi router that uses beamforming, you'll have a dynamic signal pattern, which will change as a WiFi client is moved around the house. There will be a constantly changing visibility of WiFi neighbours, on any given channel (or group of channels). This will cause problems similar to the WiFi hidden node problem. Some victims of a neighbour using beamforming may see this as "channel hopping", as a neighbouring network will come and go, repeatedly, on the channel.

In short, neither MIMO nor Super-G are products which will be useful in neighborhoods of any density.

For more information, and discussions pro and con, see

• 54g.org White Papers Index
• Atheros White Papers Index
• Texas Instruments: WLAN Channel Bonding: Causing Greater Problems Than It Solves

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Your Neighbour's WiFi

One of the limitations of WiFi is that it's not scalable, and it has a finite capacity. You cannot get more than (currently) 108M bandwidth. You simply won't be able to stream the latest movie in 3D multi-colour to every media computer in your house without seeing some performance limitations. And that is your own performance limitation. If your neighbour has a WiFi LAN, you will also have to share the bandwidth with him (her). WiFi simply does not have unlimited bandwidth, new technology or not.

In any domestic situation with neighbours, for a problem like a loud stereo, the tendency is to turn your own stereo up. Crank that sucker. This is, however, not a good, long term solution.

• You possibly have up to 8 immediate neighbours, and more beyond them. Some of those neighbours, also currently suffering from your neighbour stereo, now have to suffer from yours too.
• Your neighbour will probably turn his volume up yet again, to overcome the new "noise" from your system.

Like every analogy, this one suffers from a major problem. With loud stereos, it's easy to find where the noise is. Just follow your ears. Then call the police, and have them deal with the problem.

If your neighbour has a "loud" WiFi LAN (ie SuperG or MIMO), you won't be able to follow your ears. Nor will, I suspect, the police be interested in becoming involved. You're going to have to find your neighbour, and you're going to have to convince him to turn his stereo (WiFi) down. Or suffer in silence.

You can start with NetStumbler, and triangulate the problem. Then, you'll have to use diplomacy, not technology. You'll not solve the problem by getting a high power AP.

I, and others like me, have seen this situation coming for some time. Here is one possible real life example, and here is a second possible real life example. And even if neither discussion is diagnosed with this cause, this scenario is coming. Channel saturation, and unexplainable intermittent bandwidth variation, will become the norm, not the exception.

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You Have To Share The WiFi Bandwidth

The most common networking medium today is Ethernet. The most popular Ethernet uses 4 wires, 2 for sending and 2 for receiving, to provide 100M full duplex bandwidth. The equivalent to 100M Ethernet is 802.11g WiFi, which provides 54M half duplex bandwidth.

If you have just 2 computers with Ethernet adapters, the simplest thing to do is to connect both with a cross-over cable. If you have 3 or more computers, you'll likely get a switch or router, and connect each computer to that, one Ethernet cable / computer. With full duplex switched Ethernet, you'll get a total of 200M bandwidth in each conversation between a pair of computers - 100M sending, and 100M receiving. As you add computers and Ethernet cables, the total bandwidth provided by your network grows. This is why we say that an Ethernet network is scalable.

Wifi, on the other hand, is not scalable. With your computers connected thru WiFi adapters, whether directly to each other (ad-hoc mode), or to a WiFi router (infrastructure mode), all computers must use the channel together. No matter how many computers you have - 2, 3, or more, your computers will have to share the channel. And if your neighbour has a WiFi LAN on that channel, your computers will have to share the channel with your neighbours WiFi LAN.

By saying "share the channel", I am saying that, when your WiFi router is transmitting, no other computer or router within range of your router can transmit. Only one device - computer or router - can transmit over any channel at any time.

To share the channel, a WiFi device uses a strategy called Carrier Sense Multiple Access/Collision Aviodance (CSMA/CA). CSMA/CA, which is similar to a strategy previously used by classical (pre-switched) Ethernet, is not an efficient strategy.

• Each WiFi component has to listen to the channel for some amount of time, before transmitting, to ensure that nothing else is currently transmitting. Precious portions of your 11M (54M, 128M) bandwidth are wasted, when listening.
• Even with each WiFi component listening to the channel before transmitting, it's always possible to have a collision, when two or more components pick the same time to start transmitting. When there's a collision, both components will have to retransmit; more of your bandwidth is wasted, when retransmitting.

With Ethernet, if you use the proper equipment and design your network within limits (mainly, with each computer connected, by no more than 100 metres of Cat-5 or better cable, to the router or switch), you're pretty much guaranteed 100M bandwidth. With WiFi and CSMA/CA, the general estimate is that you will get 1/3 - 1/2 of the stated bandwidth. And that only involves your computers and router, with your router managing the relationship. When your neighbour's WiFi LAN becomes involved (and both routers have to manage a peer-peer relationship), your channel availability, and bandwidth, drops further.

There are 11 802.11 channels, but only 3 do not overlap. To minimise interference with other WiFi networks, everybody should use only channels 1, 6, or 11.



Non Overlapping Channels
Bottom ("1")
Middle ("6")
Top ("11")


Now, 802.11b and 802.11g are mature, ratified standards. Each manufacturer of standard equipment designs it to perform in a predictable way, so if your WiFi router has to share the channel with a router made by another manufacturer, it will perform properly. But 802.11g doesn't provide enough bandwidth, so the manufacturers have developed a new standard, 802.11n. The new standard was only recently ratified by the various WiFi vendors, and this will limit its effectiveness.

As you increase the effective size (area / volume) of your WiFi neighbourhood, your WiFi components will be able to detect ("see") more WiFi networks using any channel. Since only one WiFi device can transmit at any time, your WiFi network will spend more time waiting to use the channel. When simply waiting becomes unsuccessful, it will spend additional time recovering from collisions. More waiting / collisions = less effective bandwidth = slower file transfers. Pure and simple.

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WiFi Will Never Be As Fast As Ethernet

With "Fast" Ethernet, you expect (and generally get) 100Mbps performance from the network. With Gigabit Ethernet, you expect (and possibly get) 1000Mbps. With 802.11g WiFi, you expect 54Mbps, but you seldom get that. Why is WiFi less reliable?

Ethernet (IEEE 802.3), and WiFi (IEEE 802.11) are Layer 2 specifications of the OSI Network Model. Physical Ethernet also occupies Layer 1 of the model.

If you observe the limitations imposed by IEEE specifications, you get predictable results - those limitations should exceed your operating requirements. For instance, 100M Ethernet is provided for cable runs of up to 100 Metres (300 feet) between the computer, and the other network device (generally a hub / router / switch, or another computer).

With Ethernet, you control the environment completely. That is, you own the physical network, and you control what you own. With WiFi, you use the radio frequency spectrum included in IEEE 802.11, but share that spectrum with other electronic devices. Some devices may be non compliant with 802.11 (baby monitors, portable phones, and microwave ovens may transmit on that frequency band), and may be treated as analogue interference. Other devices may be 802.11 compliant, but owned by your neighbours, may also operate in the same frequency spectrum, and may be treated as digital interference.

The bottom line - with WiFi, there are things you can't control easily, and others that you can't control at all.

• Ethernet is a full duplex, dedicated medium. WiFi is half duplex, and shared - it has one media, the WiFi channel, which has to be shared for both sending and receiving the packets. And it's shared with your neighbours.
  
  
• Ethernet is a mature technology - it's been around for much longer than WiFi. WiFi components have frequently upgraded firmware. Any time you ask the vendor for help, their first question will be "What version firmware are you running?". This is not a delaying tactic, or needless protocol - it's an attempt to ensure that your drivers are up to date, so they can help you effectively.
  
  Any time you get new hardware, you should always consider the possibility that the firmware was upgraded after your unit was packaged. Always get up to date firmware - and get it from the vendor.
  
  
• Ethernet is a scalable medium. With Ethernet, each computer has its own cable connecting it to the network. With "n" number of computers in an Ethernet network, you can theoretically have "n/2" simultaneous conversations between computers. As you add computers, and cables (and higher rate cables), the total amount of bits being passed in any network, simultaneously, increases constantly. With WiFi, there is a ceiling. At any location in a WiFi neighbourhood, you can have a maximum number of bits being passed, "simultaneously", shared among all WiFi devices near that location. WiFi is not scalable.
  
  
• Ethernet is a much more stable medium. With switched Ethernet, you have two hosts, for instance a router / switch, and a client computer. The two hosts are connected by a physical cable. The firmware and hardware on each host has to manage the conversation only with the other host.
  
  With WiFi, each host is managing / blocking conversations with dozens of other hosts (multiple channels, locations, and networks) constantly, and no two hosts are seeing the same complement of other hosts at any time or in any place. Managing relationships in the constantly changing WiFi population takes resources - and can make the WiFi device slower than it should be.
  
  Besides the constantly changing and differing population issue, there's the security needs. WEP, WPA, WPA2, AES, CCMP, TKIP... The list of security protocols and standards is endless, and changes frequently. Managing security in any WiFi conversation takes resources - and can make the WiFi device slower than it should be.
  
  
• Can you actually see a computer from the Access Point? With WiFi, if you don't have a clear line of sight visibility between the network devices, you'll not get a full strength signal. Distance is another factor. Signal strength falls off as distance increases. Put the computer in one room, and the AP in another (a normal use for WiFi), and see what signal strength you get. Walls and floors are a major signal problem. Signal loss will be higher if the signal has to travel diagonally thru the wall or floor, rather than at a right angle.
  
  
• Look at the antennas on the AP and the computer, and see how much they are parallel - you will get maximum signal strength only when the 2 are perfectly parallel. Draw an imaginary line, extending at a right angle, from one antenna towards the other. Does it intersect the other? Try and make a line between the two intersect at a right angle. Signal loss will be higher if one network device is located directly above the other, and on another floor, if both antennas are pointed vertically.
  
  To make this simplest to understand, look at some examples.
  
  
  
  • If the AP and a computer are in the same room, locate both devices so both antennas are the same height off the floor. Point both antennas vertically.
    
  • If the AP and a computer are on different floors, locate both devices so the antennas are immediately above and below each other. Point both antennas horizontally.
    
  • If the AP and a computer are in different rooms, position both so a line from one to the other goes at a right angle thru the wall. Locate both devices so both antennas are the same height off the floor. Point both antennas vertically.
    
  • When you can't be so precise in physical placement, point both antennas parallel to each other, per the above strategies.
    
  
  
• An Ethernet cable is a media that YOU own, and physically control. With WiFi, you have to share the channel with all of your neighbours. And, with CSMA/CA, the sum of your usable bandwidth plus your neighbours usable bandwidth will never add up to 54M (for 802.11g) or 108M (or whatever is promised, for 802.11n). Relying upon Collision Avoidance will always require wait time, where neither of you is transmitting. And the more neighbours that you have, the more time that your equipment will be waiting to use the channel.
  
  
  
  • If your equipment is compatible, you may benefit from using NetStumbler, or a similar product. Find out how many of your neighbours are also using WiFi, and how close each is.
    
  • Try using a channel that isn't being used by a neighbour close to you. With 802.11G 54M, only channels 1, 6, and 11 don't overlap in frequency. If you have 2 neighbours - one on channel 1, and the other on channel 6, your best choice (avoiding digital interference) is channel 11. Analogue interference, or noise, may make this conclusion less certain.
    
  • Remember that wireless networks may come and go, so watch over a period of hours, if not days. NetStumbler is great for this - leave it running, and it will make a running list, showing each observed access point, and graphing its signal strength by time.
    
  
  
• Your wireless neighbours are interference sources outside your home. You probably also have interference sources inside your home.
  
  
  
  • Baby monitors.
    
  • Computers.
    
  • Cordless phones.
    
  • Microwave ovens.
    
  • Wireless stereo speakers.
    
  
  If you install a WiFi device on your desktop computer, try and get one with an antenna that you can move above, and away from, the computer. Signal loss will be higher with a PCI WiFi card, with the antenna stuck at the back of the computer. This is particularly the case if your computer is a tower, sitting on the floor. The higher the antenna from the floor, the better the signal level.
  
  
• You will only get maximum performance from similar equipment, and with no WiFi neighbours. You will have to share the channels with your neighbours. In any WiFi neighbourhood, no two WiFi devices will be within range of the same complement of other WiFi devices. The hidden node problem, where it is recognised that no two networks have to share the spectrum with the identical complement of other networks, is a well known WiFi issue.
  
  
• Maybe the router configuration has a setting that's causing your problem. Start by checking your Transmission Rate setting.
  
  
  
  • If it's on Auto, try setting it to a realistic rate. Start by setting it at the rate you think you're getting, and see if your bandwidth improves even slightly. If there is any problem with your signal, auto may make the router spend more time recovering from problems, and less time actually sending and receiving.
    
  • If it's on a low rate, try setting it at a higher rate. See if your bandwidth improves.
    
  • When tuning your Transmission Rate, using NetStumbler to analyse performance would be a very good idea.
    
  
  
• For more thoughts on this subject, see BBR Forums How Can I Boost My Range? (#10944).
  
  
• And consider that, even though WiFi doesn't use wires as heavily, general physical networking principles may still apply.
  

And however you set up your WiFi in the end, please secure your LAN. The performance hit you get, when your neighbours WiFi LAN comes on, pales in comparison to what happens if your computer is hacked, and joins a botnet.

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