Radio Freqency settings

[momalley1]

Hi All,

Im currently doing a school project on cisco wireless equiptment and having trouble finding some info.

Im trying to find some simple to understand information about the differnet power and frequency settings which you find on the Cisco Aironet 1200 e.g. mW and dBm settings.

Ive looked at all the user guides and still found nothing which is really understandable - more mathematical.

Any help greatly appreciated

Michael

[Rob Huffman]

Hi Michael,

Here are some docs for you to have a look at:

Cisco Aironet 1200 Series

Cisco Aironet Access Point FAQ

http://www.cisco.com/en/US/products/hw/wireless/ps430/products_qanda_item09186a008009483e.shtml

Configuring Radio Settings

http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_configuration_guide_chapter09186a00802085c3.html#wp1034946

Channels and Antenna Settings

http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_configuration_guide_chapter09186a0080209251.html

Cisco Aironet 1200 Series

Guide to Configuring 5-Ghz Radios in EU and Other CEPT Countries

http://www.cisco.com/en/US/products/hw/wireless/ps430/products_usage_guidelines09186a00800fa79f.html

Let me know if any of these answered the questions you had.

Hope this helps!

Rob

Please remember to rate helpful posts.......

[momalley1]

Hi Rob,

Thanks for the links, but ive read most of that information.

Im just trying to find out the connection between the two and how adjusting them will change the coverage area.

The answer may be obvious to put up the maximum power level, but what does adjusting this value or the antenna do? I am using standard areals for the 1200.

Thanks a lot

Michae;

[Rob Huffman · Accepted solution]

Hi Michael,

Sorry about that! Here are 2 more docs which might give you what you are looking for;

Cisco Aironet 1200 Series

Cisco Aironet Antenna Reference Guide

http://www.cisco.com/en/US/products/hw/wireless/ps430/products_data_sheet09186a008008883b.html

Cisco Aironet 1200 Series

Capacity Coverage & Deployment Considerations for IEEE 802.11g

http://www.cisco.com/en/US/products/hw/wireless/ps430/products_white_paper09186a00801d61a3.shtml

Here is an excerpt:

"As a matter of physics, there is an inverse relationship between wavelength and range. All other things being held equal, a signal transmitted in a lower portion of the frequency spectrum will carry further than a signal transmitted in a higher band. Additionally, a longer waveform (from lower in the spectrum) will tend to propagate better through solids (like walls and trees) than a shorter waveform. Because 802.11g operates in the same 2.4 GHz portion of the radio frequency spectrum as does 802.11b, it will share its fundamental advantage over the 5 GHz-based 802.11a. With 802.11b and 802.11g all things are not, however, held equal. Another fundamental rule is that as data rates increase, range decreases. 802.11b uses DSSS to support data rates of 11, 5.5, 2, and 1 Mbps each, with correspondingly longer ranges as the data rates decrease. 802.11g uses OFDM to support data rates of 54, 48, 36, 24, 18, 12, 9, and 6 Mbps each, with correspondingly longer ranges as the data rates decrease. The higher data rates supported by 802.11g result in shorter range than the range supported by the maximum 802.11b data rate. Still, OFDM is a more efficient means of transmission than is DSSS, meaning that at a given range, higher OFDM-based data rates will be supported than DSSS-based data rates (all other things being held constant).

Other factors to consider are transmit power and receive sensitivity. The selection of either DSSS or OFDM transmission type has an effect on the maximum power the transmitter can use, as well as the capability of the receiver, particularly at higher data rates. The reason for this is that higher-order modulation schemes such as the 64 quadrature amplitude modulation (QAM) used to support 54 and 48 Mbps data rates requires a high degree of acuity on the part of the receiver. High power coming from the radio's transmitter tends to desensitize the receiver, a phenomenon known as Error Vector Magnitude (EVM). This leads to a counterintuitive effect, whereby increasing transmit power tends to decrease the range of the device at these higher data rates. Radios operating in 802.11g mode therefore use lower transmit power than when operating in 802.11b mode."

Hope this helps!

Rob

Please remember to rate helpful posts......

[momalley1]

Hi Rob,

Thanks for the posts, very helpful indeed.

UNDERSTANDING RF POWER VALUES

Radio frequency (RF) signals are subject to various losses and gains as they pass from transmitter through cable to antenna, through air (or solid obstruction), to receiving antenna, cable, and receiving radio. With the exception of solid obstructions, most of these figures and factors are known and can be used in the design process to determine whether an RF system such as a WLAN will work.

Decibels

The decibel (dB) scale is a logarithmic scale used to denote the ratio of one power value to another-for example:

dB = 10 log10 (Power A/Power B)

An increase of 3 dB indicates a doubling (2x) of power. An increase of 6 dB indicates a quadrupling (4x) of power. Conversely, a decrease of 3 dB is a halving (1/2) of power, and a decrease of 6 dB is a quarter (1/4) the power.

POWER RATINGS

WLAN equipment is usually specified in decibels compared to known values. Transmit Power and Receive Sensitivity are specified in "dBm," where "m" means 1 milliWatt (mW). So, 0 dBm is equal to 1 mW; 3 dBm is equal to 2 mW; 6 dBm is equal to 4 mW, and so on.

It was exaclty what i was looking for!

Thanks again

Michael

[Rob Huffman]

Hi Michael,

Glad to help! Good luck on your project!!

Take care.

Rob