RF Performance
A Shared Medium
A wireless communication medium is a shared medium, and this is especially true of the unlicensed spectrum. In this spectrum, devices such as wireless LAN equipment, Bluetooth headsets, microwave ovens, and cordless phones all compete for the available spectrum. In order to get the best performance for wireless networking equipment, it is important to understand the frequency spectrum in use, the device’s ability to transmit a signal with adequate power, the device’s ability to receive and process a signal at a certain signal power, and the environment in which the device is operating. In the United States, the Federal Communications Commission regulates the usage of the radio frequency spectrum. FCC 47 CFR Part 15 
The Institute of Electrical and Electronics Engineers (IEEE) defines and maintains the standards for WLAN under the title 802.11. The standards for WLAN have evolved over the years to support higher data rates and increased coverage. The earliest version 802.11b used the 2.4 GHz frequency band, which was closely followed by the 802.11a standard operating in the 5.8 GHz frequency band. While both 802.11a and 802.11b were important efforts, neither could handle the demands of multimedia applications, such as streaming audio and video. The 802.11g version brought higher data rates and lowered the latencies but continued to use the 2.4 GHz band. The 2.4 GHz band provides only three non-overlapping channels, hence the latest version 802.11n standard, which uses both the 2.4 GHz and 5.8 GHz spectrums simultaneously. This boosts bandwidth and throughput and takes advantage of the larger number of channels as well as enables more efficient radio transmissions at the higher frequency range. Since wireless network devices share the medium with other technologies and are more likely to face interference, a site survey is highly recommended to better understand the environment and ensure success. Device density is also a factor when assessing wireless network performance. Successful wireless communication relies on collision avoidance in the air. As the number of devices competing for the use of a particular frequency spectrum increases, a single device gets less chance to transmit to full capacity. This reduces its performance significantly. Transmit PowerA wireless medium is inherently noisy. A transmitting device in a wireless LAN must be able to transmit the signal at sufficient power (above the noise level) to allow the receiver to interpret the signal accurately. Transmitter power is measured in milliwatts. However, for the ease of calculation, the power of a signal is measured as a logarithmic ratio of power called dB. A dB is defined as follows:  If the ratio of power is with reference to 1 mW, then it is referred to as dBm. The signal-to-noise ratio of a signal determines how good the signal is at a given point in time. The signal-to-noise ratio is the highest at the transmitter and diminishes as it travels toward the receiver. The signal strength diminishes due to several factors, including propagation loss (through both free space and in cables), obstacles, reflections and interference from other signals. Propagation loss through free space depends primarily on frequency and distance. Propagation loss indoors is very hard to determine due to the different types of obstacles, such as walls, furniture, and other household or office items. Propagation loss outdoors is partially estimated based on expected propagation loss in free space; however, obstructions and reflections significantly impact actual loss. In general, the higher the transmit power, the better the chance the signal will arrive at the receiver with a good signal-to-noise ratio. However, it is not always a good idea to transmit at the highest power because of the potential interference to other wireless devices and non-wireless equipment. It may be better to deploy multiple devices operating at moderate power, instead of a single device operating at maximum power. In addition, multiple wireless devices may provide better throughput by sharing the traffic load and providing better geographic coverage. Antennas and Power Amplifiers
An antenna plays a critical role in an RF system. It transmits and receives the radio (electromagnetic) waves and can significantly enhance the range of a wireless system. The basic physical properties of an antenna are shape, size or height, and weight. There are three common antenna types that are used for wireless applications: the panel antenna, the dish or parabolic antenna, and the omnidirectional antenna. Panel and dish (or parabolic) antennas are directional antennas, so beamwidth is focused in a narrower area. Omni-directional antennas send the signals in a 360◦ cylindrical Reflections
Receive Sensitivity
Fortress ValueFortress products offer the highest RF performance in a very compact and low power wireless device. The reasons why Fortress products outperform the competition are as follows:
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envelope all around the antenna. Dish (or parabolic) antennas are highly directional and typically used for satellites or long distance links. An antenna can also be used in combination with a power amplifier (which is then called an active antenna) to further boost the signal. Although using an amplifier significantly enhances the signal strength, the FCC regulates the maximum signal strength that any wireless device is permitted to use. Power amplifiers also distort the signal, which could degrade the signal quality. Using a power amplifier requires an additional DC or AC supply, which makes deployment more difficult. Radios with an inherent capability to transmit at high power eliminate the need for a power amplifier and work well using passive antennas. 
Radio waves emitted by a directional antenna dissipate in several directions.
However, most of the energy is contained within what is called the first Fresnel zone or ellipsoid. Obstructions in the first zone are highly detrimental to the signal strength and at least 60% of this zone must be clear of obstacles. Signals in other Fresnel zones (for example, the second, third, fourth and so on) are not directed toward the receiver unless they get reflected off another surface. The reflected signal could arrive either in phase or out of phase. In-phase signals are beneficial as they enhance the signal strength, but out-of-phase signals end up canceling the signal as it arrives at the receiver. The earth’s surface itself acts as a significant obstruction when a signal is propagated over a long distance. This distortion can be mitigated by raising the height of the antenna. The earth’s surface also reflects radio waves creating in-phase or out-of-phase signals. Other obstacles such as buildings, trees, and hills also diminish the signal strength through obstruction or reflection (diffraction). Installers must carefully consider all of these effects when preparing for outdoor wireless deployments.
The receiver can also assist in interpreting the received signal correctly. The receiving antenna can amplify the signal, but the biggest challenge is the ability of the receiver to extract a weak signal accurately. An antenna with very good receive sensitivity is able to successfully process a low signal-to-noise ratio. The receive sensitivity is a good measure of the quality of a receiver. In a wireless network receive sensitivity is specified in terms of the lowest signal strength that a receiver can process at a given network speed. For example, a receiver could have a receive sensitivity of -95 dBm at 6 Mbps but only -80 dBm at 24 Mbps. Since a wireless medium is very likely to be subject to signal loss due to various factors discussed earlier, having a receiver with high receive sensitivity is critical to the performance of a wireless network.