Linksys Wireless Signal Booster Review

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Tim Higgins

Introduction

Linksys Wireless Signal Booster

Linksys Wireless Signal Booster
Summary Discontinued Jan 2004

Signal amplifier for 2.4GHz wireless products. Handles two antennas.

FCC certified and compatible with the Linksys Wireless Access Point (WAP11) and Wireless Access Point Router (BEFW11S4) only.
Update 8 June 2004 – Discontinued January 2004

30 June 2003 – Once again available for sale.

17 June 2003 – Temporarily removed from market by Linksys due to FCC request.

21 Jan 2003 – Added official Linksys policy on use with non-Linksys gear.
Pros • Provides both Transmit and Receive signal boost

• Can be used with any 2.4GHz wireless product (with proper cabling)

• No software required

• Affordable
Cons • May not significantly improve range

The range of 802.11b wireless networks seems like the weather… everyone talks about it, but no one can do much about it. Well, Linksys may not be taking on the challenge of getting the skies to cooperate with your weekend plans, but they have set out to improve your wireless network’s performance!

Their WSB24 Wireless Signal Booster adds a new trick to the wireless network builder’s toolkit. But can it really help you drive out the demon dead spots and let you take your wireless notebook to your favorite chair and sit in a comfortable position?

How Does It Work?

The WSB24 is actually a pretty simple box as the block diagram in Figure 1 shows.

Linksys WSB24: Block diagram

Figure 1: WSB24 Block Diagram

This excerpt from the FCCID filing’s detail documents shows that the WSB24 contains a low-noise receive pre-amplifier, transmit power amplifier, Transmit / Receive switch, and signal combiner. That may be hard to follow if you’re a little low on the geekometer, so I’ll break it down a little bit:

  • The combiner takes the two signal inputs from the product that the WSB24 is used with and comes up with a single signal. This is necessary because there is only one transmit and one receive amplifier in the WSB24
  • The switch senses whether the product being boosted is transmitting or receiving and automatically switches in the appropriate amplifier.
  • And, of course, the amplifiers are what actually provide the signal “boost”

Note that this means that if the product that you’re using the WSB24 with has a diversity antenna feature, you lose that function when you add the WSB24. Although the WSB24 has two antennas, Figure 1 shows that one is dedicated to transmitting and the other to receive. I wouldn’t worry about the loss, however, since the increased signal strength from the WSB24 should more than make up for the loss of the diversity function.

So how much do those amplifiers actually boost the signal? The FCCID document says that the WSB24 provides a “maximum fixed gain of 10dBm” (although they probably meant 10dB). At any rate, this means the WSB24 should improve both transmit and receive signal power by 10X, which I did confirm as part of my performance measurements.

Note that this does not mean that the WSB24 will increase your Access Point or wireless Router’s range by 10X! You will get a performance boost from the WSB24, but what you actually get is definitely a “your mileage may vary” story, as we’ll see later in the Performance section.

A Peek Inside

What does it take to work this magic? Judging by the surprisingly heavy weight of the WSB24, you’d think there’s a lot of stuff inside. But as Figure 2 shows, you actually don’t need much.

Figure 2: WSB24 Internal view

The pictures, which were also taken from the FCCID filing’s detail documents, show that all the WSB24’s circuitry is located under the metal shields that you see at the center of the board in Figure 2. Figure 3 shows a closer view of the circuitry, with the shields removed.

Figure 3: WSB24 circuitry

As you can see, the circuitry doesn’t require very much space, due to both the integration of all the components, and the fact that smaller is better when dealing with gigahertz frequencies. The weight, by the way, is from the metal mounting plate at the right side of Figure 1, which gives the box some heft and resistance to being dragged around by the weight of its cables.

Setting It Up

Getting the WSB24 up and running is simplicity itself… if you have either a Linksys WAP11 Access Point or BEFW11S4 Wireless router. All you need to do is:

  • plug the 5V “wall wart” power supply into a wall outlet and jack on back of the WSB24,
  • move the antennas from the WAP11 or BEFW11S4 to the WSB24, and
  • connect the two supplied jumper cables from the RP-SMA connectors on the WSB24 to the antenna connectors on the AP or wireless router that you’re boosting.

That’s it… nothing to configure, and no software or drivers to install.

As I mentioned before, you can use the WSB24 with any wireless LAN product that operates in the 2.4GHz band. This would include 802.11b, “enhanced” 802.11b, and 802.11g (both draft and final) products. You can’t use it with 802.11a or any dual-band 2.4 / 5GHz products because the circuitry won’t handle the higher frequency.

All you need to do to use it with non-Linksys products is to get a jumper cable for each of the antennas that your AP / wireless router has. The cables should be no longer than you need since the longer the cable, the more signal you lose. The ones that come with the WSB24 are about 6.625 in. (17cm) from connector end to connector end.

Your special cables will need an RP-SMA Male connector on one end to mate with the connectors on the WSB24. The other cable end will need a connector to mate with the product that you’re connecting the WSB24 to.

You’ll also need to buy one or two antennas (depending on whether you can re-use any from your existing equipment) that connect via an RP-TNC female (sometimes called an RP-TNC plug) connector. The WSB24 doesn’t come with any of its own antennas, instead relying on reusing those of its companion WAP11 or BEFW11S4.

21 Jan 2003 Update – I asked Linksys for their official positon on using the WSB24 with products other than their WAP11 and BEFW11S4. Here’s their reply:

“The Linksys Wireless Signal Booster is FCC Class-B certified for use only with the Linksys Wi-Fi 802.11b 2.4GHz Access Point (WAP11) and Wireless Router (BEFW11S4). Using the WSB24 with any other product from either Linksys or another vendor voids the user’s authority to operate the device. Linksys users are also reminded that opening a Linksys product chassis, tampering with, or disassembling a Linksys product voids the Linksys warranty.”

Now that we’re set up, let’s see what the definition of “boost” is by running some Performance tests…

Performance

My test approach was to run my usual four-Condition tests, once without, then once with the WSB24 connected to a WAP11 (original model) “boostee”. I chose my trusty ORiNOCO Gold PC card as a test client, primarily because it works with NetStumbler, which I used for Signal-to-Noise measurements.

The first thing I did was to try to quantify the “boost”, or signal “gain” provided by the WSB24. Linksys lists a “Peak Gain” spec of +14dBm, and “Receiver Gain” of +20dBm (nominal) on the WSB24’s product package and brochure. But since dBm is a measurement of power level and not gain (which is the ratio of two power levels), I’m not quite sure what to do with those numbers. There’s also the “maximum fixed gain of 10dBm” spec that I found in the FCCID document, again with the wrong units used. Whatever…

To make my measurement, I fired up Netstumbler and went to each of my four test locations, first measuring the WAP11 alone, then repeating the measurement with the WAP11 + WSB24. The resulting composite Netstumbler plot is shown in Figure 4.

Linksys WSB24: SNR comparison

Figure 4: SNR comparison

(click on the image for a full-sized view)

You should read the plot as four pairs of bars, representing test Condition locations 1 through 4, from left to right. The first bar of each pair is the Netstumber Signal-to-Noise (SNR) measurement for the WAP11 alone; the second bar is with the WAP11+WSB24. Although it’s not a clean measurement in all cases, the Conditon 2 and 3 plots most clearly show about a 10dB (or 10X) gain when the WSB24 is used.

With that little exercise out of the way, I then ran “with” and “without” throughput tests at all four locations. Table 1 summarizes the results.

Test Description

Transfer Rate (Mbps)

[without boost]

Transfer Rate (Mbps)

[with boost]

Client to AP – Condition 1

5.1

5.1

Client to AP – Condition 2

5.1

5.1

Client to AP – Condition 3

4.7

5.1

Client to AP – Condition 4

2.9

5.0

Table 1 – Throughput comparison

NOTE!NOTES

• Testing was done with a WinXP Home Dell Inspiron 4100 laptop, using an ORiNOCO Gold PC card client and Linksys WAP11 (original version) Access Point

• Details of the four test Conditions can be found here.

More Performance

The table clearly shows that the WSB24 improves the throughput under the weaker-signal Conditions 3 and 4, but has no effect in the Condition 1 and 2 tests, which use locations that provide a stronger signal. I also ran with and without-boost NetIQ Chariot plots, which are shown in Figures 5 and 6.

Linksys WSB24: Throughput plot - no boost

Figure 5: Throughput – no boost

(click on the image for a full-sized view)

Linksys WSB24: Throughput plot - with boost

Figure 6: Throughput – with boost

(click on the image for a full-sized view)

The plots clearly show that the WSB24’s boost both raises the average throughput, but also reduces throughput variation in the weaker-signal Conditons 3 and 4… both nice results to have!

But Will it Go the Distance?

Although better and more consistent throughput is a nice thing to have in a WLAN’s existing footprint, many WSB24 customers will be buying it with hopes of expanding their wireless LAN’s coverage area. Can it deliver the goods in that department?

To find out, I braved the snow and cold and lugged my notebook outside to do a distance test. My starting point for each test was right in front of my home’s front door, which was about 50 ft and about one interior wall, one ceiling, and one exterior wall as the crow flies from the WSB24 and WAP11. I then started both Chariot (to plot throughput) and Netstumbler (to plot SNR), and trudged slowly up my driveway until I lost the signal. Figures 7 and 8 tell the tale.

Linksys WSB24: Distance test - without WSB24

Figure 7: Distance test – without WSB24

(click on the image for a full-sized view)

Linksys WSB24: Distance test - with WSB24

Figure 8: Distance test – with WSB24

(click on the image for a full-sized view)

Both Figures show composite screenshots of the Netstumbler and Chariot runs that I took during both my treks. If you look closely, you can see that the Netstumbler and Chariot timescales are approximately the same in each Figure, so you can relate throughput and Signal-to-Noise readings over time.

In both diagrams, the 30 second point represents a point approximately 50 feet (15M) away from my front door (or about 100ft from the WAP11 and WSB24). In the “without boost” case (Figure 7), throughput has slowed to a crawl (about 0.5Mbps) and is pretty erratic. But the “with boost” (Figure 8) plot shows still erratic, but useable throughput between 1.2 and 2.4Mbps. I also estimate that the WSB24’s boost bought me between 25 to 50 feet (8 to 15M) additional feet of wireless coverage, although at a pretty low throughput.

Closing Thoughts

Linksys is once again taking a product that normally sells for much more money (around $300), and driving it down to a price that pretty much anyone can afford. They’ve done a nice job with the packaging by making it stackable with their other products, and keeping the design simple and free of any controls.

The good news is that for around $80 (on-line price at time of review), the WSB24 can help improve the performance of your wireless LAN, with very little effort, and no pulling wires through walls. Since it’s so easy to set up – given that you are using either Linksys’ WAP11 or BEFW11S4 – you’ll quickly know whether it will do the job that you want it to.

My advice is to think of the WSB24 as more of a way to improve connection reliability and throughput inside your existing wireless LAN’s coverage vs. a way to expand your WLAN’s coverage, and you’ll be less likely to be disappointed. Pair it up with the hot 802.11b radio in an Atheros-based dual-band client card (such as Linksys’ WPC51AB) though, and hoo Mama, then you’ll be talkin’ range expansion!

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