Move the Antenna(s)
Remember the days before everyone had cable or satellite TV? There was
a reason people would fiddle with the rabbit ears on a TV set â€” they were
trying to get the antennas into the ideal position to receive signals. Whether
the antenna is on the client or on the access point, the same concept applies:
Moving the antenna can yield results. Because different antennas have differ-
ent signal coverage areas, reorienting it in a different declination (or angle rel-
ative to the horizon) will change the coverage pattern. And a strong signal
translates to better throughput and performance.
Look at it this way: The antenna creates a certain footprint of its signal. If
youâ€™re networking a multi-story home and youâ€™re not getting a great signal
upstairs, try shifting your antenna to a 45Â° angle to increase a more vertical
signal â€” that is, send more signal to the upstairs and downstairs, and less
Each AP broadcasts its signals over portions of the wireless frequencies
called channels. The 802.11b standard (the most common system as we
write) defines 11 channels in the United States that overlap considerably,
leaving only 3 channels that donâ€™t overlap with each other. The IEEE 802.11a
standard specifies 12 (although most of todayâ€™s products only support 8)
non-overlapping channels. The 802.11g standard calls for the same 11 chan-
nels in the United States as 802.11b, again with overlapping channels.
This affects your ability to have multiple access points in the same area,
whether your own or your neighborsâ€™. Because channels can overlap, you
can have the resulting interference. For 802.11b access points that are within
range of each other, set them to different channels, five apart from each other
(such as 1, 6, and 11), to avoid inter-access point interference.
We discuss the channel assignments for wireless LANs like 802.11b further in
Chapter 18: Ten Ways to Troubleshoot Wireless LAN Performance
Check for Dual-Band Interference
Despite the industryâ€™s mad rush to wirelessly enable every networkable
device that it makes, a whole lot hasnâ€™t been worked through yet, particularly
interoperability. Weâ€™re not talking about whether one vendorâ€™s 802.11b PC
Card will work with another vendorâ€™s 802.11b AP â€” the Wi-Fi interoperability
tests usually make sure thatâ€™s not a problem (unless one of your products isnâ€™t
Wi-Fi certified). Instead, weâ€™re talking about having Bluetooth (see Chapter 15
for more on this technology) working in the same area as 802.11b, or having
802.11a modems and 802.11b modems operating in the same area. In some
instances, like the former example, Bluetooth and 802.11b operate in the
same frequency range, and therefore do have some potential for interference.
Because 802.11a and 802.11b operate in separate frequency bands, theyâ€™re
less likely to be exposed to interference.
There are also issues with how the different standards are implemented in
different products. Some APs that support 802.11b and g, for instance, really
support one or the other â€” not both simultaneously. If you have all g in your
house, great. If you have all b, great. If you have some g and the AP detects
that b is in the house, it will downshift to b rates. You might be all set, but
then your neighbor upstairs buys a b modem (because youâ€™ve said, â€śSure, no
problem, you can share my Internet connection.â€ť). Not only is he freeloading,
but heâ€™s probably forcing your whole AP to shift down to the lower speeds.
To be fair, many of these very early implementation issues are rapidly going
away while vendors refine their solutions. Check out how any multi-mode AP
that you buy handles multiple forms of wireless connecting to the AP and
asking for service. Some of the newer APs compartmentalize their signal so
that they can handle two at once, which is very nice and almost necessary.
Check for New Obstacles
Wireless technologies are very susceptible to physical obstacles . . . some
more than others. In Chapter 4, we show a Relative Attenuation of RF Obstacles
table that tells you the relative attenuation of your wireless signals (radio fre-
quency; RF) as they move through your house. One person in our neighbor-
hood noticed a gradual degradation of his wireless signal outside his house,
where he regularly sits and surfs the Net (by his pool). The culprit turned out
to be a growing pile of newspapers for recycling. Wireless signals donâ€™t like
such masses of paper.
318 Part V: The Part of Tens
Move around your house and think about it from the eyes of Superman,
using his X-ray vision to see your access point. If you have a bad signal, think
about whatâ€™s in the way. If the obstacles are permanent, think about using a
HomePlug wireless access point (which we discuss in Chapter 3) to go around
the obstacle by putting an access point on either side of the obstacle.
Another way to get around problems with obstacles is to switch technolo-
gies. In some instances, 802.11g could provide better throughput and reach
than 802.11a when it comes to obstacles. 802.11g operates at a lower fre-
quency, which does better moving through and around things. If youâ€™re in a
dense environment with a lot of clutter and youâ€™re using 802.11a, switching to
g might provide some relief.
Install Another Antenna
In Chapter 5, we point out that a detachable antenna is a great idea because
you might want to add an antenna to achieve a different level of coverage in
your home. Different antennas yield different signal footprints. If your AP is
located at one end of the house, itâ€™s a waste to put an omnidirectional antenna
on that AP because more than half of the signal might prove to be unusable. A
directional antenna would better serve your home.
Antennas are inexpensive relative to their benefit and can also more easily
help you accommodate signal optimization because you can leave the AP in
the same place and just move the antenna around until the signal is the best.
Within a home, thereâ€™s not a huge distance limitation on how far the antenna
can be away from the AP.
For a more technical explanation of how antennas work, check out the techni-
cal white paper section on the Linksys site (www.linksys.com/products/
images/antennawhtpaper.pdf), which at the time of this writing, had a
good overview of antennas.
Add a Signal Booster
If you have a big house (or a lot of interference), you can add a signal booster,
which essentially turns up the volume on your wireless home network trans-
mitter. A stronger signal means that the receiving point gets a higher quality
transmission. This increases throughput by reducing retransmissions of data
that occurs when the signal strength is weak.
Chapter 18: Ten Ways to Troubleshoot Wireless LAN Performance
A signal booster can also improve the range of your access point (although this
is much harder to quantify). Todayâ€™s 802.11b and g products typically have a
range of 100â€“150 feet indoors mainly because 802.11b/g products operate at a
lower frequency. Although 802.11a products reach a shorter distance â€” up
to 75 feet indoors â€” these products are getting better, and their distance is
improving. A booster might add another 25â€“50 feet to this, but it wonâ€™t take
you to the Starbucks and back.
The signal range of the APs on the market today is steadily increasing
because manufacturers are creating more efficient transceiver chipsets. We
recommend reading the most recent reviews of products because products
truly are improving month over month.
Linksys, for instance, sells its WSB24 Wireless Signal Booster
(www.linksys.com; $90) that piggybacks onto a Linksys wireless access
point (or wireless access point router) to increase the throughput, effective
range, and coverage area of a resulting 802.11b network. (See Figure 18-1.)
This is really easy to install. Simply unscrew the antenna from the AP, con-
nect the two linking wires (an SMA-to-TNC connector, if youâ€™re curious), reat-
tach the antennas onto the booster, and then plug the electric cords in.
Signal boosters are mated devices, meaning that theyâ€™re engineered for spe-
cific products. Vendors have to walk a fine line when boosting signals in light
of federal limits on the aggregate signal that can be used in the unlicensed
frequencies. For example, the Linksys Wireless Signal Booster is certified by
the Federal Communication Commission (FCC) for use with the WAP11
Wireless Access Point and BEFW11S4 Wireless Access Point Router only.
Linksys says that using the WSB24 with any other product from either
Linksys or another vendor voids the userâ€™s authority to operate the device.
The main reason why companies like Linksys sell their signal boosters for use
with only their own products is because of certification issues. The FCC has
to approve any radio transmission equipment sold on the market. A lot of
testing must be done for a piece of gear to get certified, and the certification
testing must be done for the complete system â€” and the vendors will usually
only do this expensive testing with their own gear.
That having been said, as some reviews have pointed out, you can use the
WSB24 with any wireless LAN product that operates in the 2.4 GHz band â€”
notably, 802.11b and 802.11g products. You cannot use it with 802.11a or any
dual-band 2.4/5 GHz products; its design cannot deal with the higher frequency.
320 Part V: The Part of Tens
mated to a
Photo courtesy of Linksys
Add an AP
Adding another AP (or two) can greatly increase your signal coverage,
as shown in Figure 18-2. The great thing about wireless is that itâ€™s fairly
portable â€” you can literally plug it in anywhere. The main issues are getting
power to it and getting an Ethernet connection (which carries the data) to it.
Chapter 18: Ten Ways to Troubleshoot Wireless LAN Performance
Coverage by one Access Point â€“ Signal fades with distance
Coverage by three Access Points â€“ Strong combined signals
a single AP.
322 Part V: The Part of Tens
The first item is usually not a problem because many electrical codes require
that in a residence, a power outlet should be placed every eight feet. However,
if youâ€™re mounting an AP high up on a wall, you might not want an electrical
power jack running to the spot. In that case, you might consider getting an AP
that supports a power over Ethernet (Power Over Ethernet; POE) option,
which delivers power to run the unit over the same wiring as carries the data
signal, meaning that only one Cat 5e (standard Ethernet cabling) wire has to
be run to where you want your AP to be.
Leviton also has a neat product called the PowerJack (www.leviton.com/
sections/prodinfo/newprod/powerjack/powerjack.htm; $25) that allows
you to hide the power cable behind a four-conductor RJ-11 jack, avoiding that
AC adapter cable strung across the wall as well. However, Leviton doesnâ€™t yet
have a version for an eight-conductor RJ-45 jack, but we expect one soon.
Check the Leviton site to see whether one is available â€” and get one of these if
you have problems with an AC adapter cable with your cordless phone as well
because theyâ€™re great.
The second issue (getting the Ethernet connection to your access point) used
to be a matter of running all sorts of wiring around the house, but depending
on the actual throughput that youâ€™re looking to provide, you might be able to
set up another access point by using the HomePlug, Home Phone Networking
Alliance (HPNA), or even wireless repeater functionality that we mention in
Chapter 3 and elsewhere in this chapter. Weâ€™re not going to repeat those
options here, but know that you have those options when moving away
from your office or other place where a lot of your network connections are
After you get the connectivity and power to the place you want it, what do you
need to consider when installing a second access point? Choose the right chan-
nel: If you have auto channel selection in your AP, you donâ€™t need to worry
about this because your APâ€™s smarts will handle it for you. If youâ€™re setting this
manually, donâ€™t choose the same channel that your other AP is set to.
Be sure to heed the previous advice about multiple access points on the
same or nearby channels. Make sure that you have proper spacing of your
channels if you have 802.11b or 802.11g access points (which have overlap-
ping bands). Read â€śChange Channelsâ€ť earlier in this chapter for more infor-
mation on channels.
Add a Repeater or Bridge
Wireless repeaters are an alternative way to extend the range of an existing
wireless network instead of adding more access points. We talk earlier in the
book about the role of bridges and repeaters in a wireless network. The topic
of bridges can be pretty complex, and we donâ€™t want to rehash here â€” go
back and read Chapter 2 for all that juicy detail.