Rf Signal Obstacles To Critical Thinking

When designing a wireless network, there are quite a few factors that one must consider. For example, it’s extremely important to estimate the user density in order to lay out the proper number of access points (APs). Another important consideration is what materials go into the building: the walls, the floors, the doors.

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It’s understandable that each different type of material affects wireless signal differently. Here’s a breakdown of the five different phenomena that can impact a Wi-Fi signal:

1. Reflection

A wireless signal is just radio waves. Just like light, it can bounce off of certain surfaces. Metal, for one, is a highly reflective material. This is a common occurrence for offices since they are generally in complex and intricately designed structures. If a large amount of reflection occurs, signals can be weakened and also cause interference at the receiver.

2. Refraction

Refraction is the bending of a wave when it enters a medium where the speed is different. For example, glass or water can refract waves. This can play into consideration when you’re carefully placing APs. Different media have different refractive indexes. It’s important to track possible refraction when designing your wireless network because if a signal changes direction in traveling from sender to receiver, this can cause lower data rates, high retries and lead to an overall lessening of capacity.

3. Diffraction

This is when waves encounter an obstacle and travel around it — the wave’s direction and intensity both change. In fact, diffraction can even be more pronounced or introduce a shadow zone depending on the size and shape of the obstacle. Hills are known to cause diffraction to wireless signals.

4. Scattering

While this phenomena is similar to refraction, it’s more unpredictable. Dust, humidity, unevenness and other qualities in a material can cause a signal to scatter in all directions. This can have a significant impact on signal integrity and strength. Chain-link fences and even smog are notorious for scattering RF signals.

5. Absorption

This is one of the most common reactions we see wireless signal have to materials. Basically, a material is converting the signal’s energy into heat. This occurs largely due to the molecules in the medium being unable to move fast enough to “keep up” with the RF waves that are trying to pass through it.

Different materials naturally have different absorption rates. Wood and concrete, for example, can make a huge impact on signal strength because of how much they absorb the radio waves.

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It’s important to note that any given material can exert a combination of these impacts signal. Glass can both refract and absorb. That is in part why it is so essential to meticulously plan your wireless network, taking careful consideration of the different materials that your signal will encounter.

For more information on the areas on which wireless network engineers must pay close attention, see 7 Gotchas of Wi-Fi.

Are you interested in having a wireless survey done for your facility? Or are you looking to upgrade to a smarter Wi-Fi network? Email us or call us at 502-240-0404 to get started!

This chapter explores the many facets of wireless networking, starting with some of the concepts and technologies that make wireless networking possible.

This chapter is from the book 

What You Need To Know

  • Review the characteristics of the various network topologies, including their strengths and weaknesses.
  • Review the characteristics of 802.11 standards, including the information provided in all tables in this chapter.
  • Identify the components involved in wireless communications.
  • Review the factors that cause wireless interference.
  • Review the Notes, Tips, and Exam Alerts in this chapter. Be sure that you understand the information in the Exam Alerts. If you don’t understand the topic mentioned in an Exam Alert, reread that information in the chapter, and then reread the Exam Alert.


One of the bigger changes in the networking world since the release of the previous Network+ is in wireless networking. Networks of all shapes and sizes incorporate wireless segments into their networks. Home wireless networking has also grown significantly in the last few years.

Wireless networking enables users to connect to a network using radio waves instead of wires. Network users within range of a wireless access point (AP) can move around an office freely without needing to plug into a wired infrastructure. The benefits of wireless networking clearly have led to its growth.

Today, wireless local area networks (WLANs) provide a flexible and secure data communications system that augments an Ethernet LAN or, in some cases, replaces it. Wireless transmissions send and receive data using radio frequency (RF) signals, freeing us from wired solutions.

In a common wireless implementation, a wireless transceiver (transmitter/receiver), known as an access point, connects to the wired network from a fixed location using standard cabling. The wireless access point receives and then transmits data between the wireless LAN and the wired network infrastructure.

Client systems communicate with a wireless access point using wireless LAN adapters. Such adapters are built into or can be added to laptops, PDAs, or desktop computers. Wireless LAN adapters provide the communication point between the client system and the airwaves via an antenna.

This chapter explores the many facets of wireless networking, starting with some of the concepts and technologies that make wireless networking possible.

Wireless Access Points

As discussed in Chapter 3, “Networking Components and Devices,” a wireless access point (AP) is both a transmitter and receiver (transceiver) device used for wireless LAN (WLAN) radio signals. An AP typically is a separate network device with a built-in antenna, transmitter, and adapter. APs use the wireless infrastructure network mode to provide a connection point between WLANs and a wired Ethernet LAN. APs also typically have several ports, giving you a way to expand the network to support additional clients.

Depending on the size of the network, one or more APs might be required. Additional APs are used to allow access to more wireless clients and to expand the range of the wireless network. Each AP is limited by a transmission range—the distance a client can be from an AP and still get a usable signal. The actual distance depends on the wireless standard being used and the obstructions and environmental conditions between the client and the AP. Factors affecting wireless transmission ranges are covered later in this chapter.

As mentioned in Chapter 1, an AP can be used in an infrastructure wireless network design. Used in the infrastructure mode, the AP receives transmissions from wireless devices within a specific range and transmits those signals to the network beyond. This network might be a private Ethernet network or the Internet. In infrastructure wireless networking, there might be multiple access points to cover a large area or only a single access point for a small area, such as a single home or small building.

Working with APs

When working with wireless APs, you need to understand many terms and acronyms. This section defines some of the more common wireless acronyms you will see both on the exam and in wireless networking documentation.

  • Service Set Identifier (SSID)—A network name needed to connect to a wireless AP. It is like a workgroup name used with Windows networking. 802.11 wireless networks use the SSID to identify all systems belonging to the same network. Client stations must be configured with the SSID to be authenticated to the AP. The AP might broadcast the SSID, allowing all wireless clients in the area to see the AP’s SSID. For security reasons, APs can be configured not to broadcast the SSID or to cloak it. This means that an administrator needs to give client systems the SSID instead of allowing it to be discovered automatically.

  • Basic Service Set (BSS)—Refers to a wireless network that uses a single AP and one or more wireless clients connecting to the AP. Many home offices are an example of a BSS design. The BSS is an example of the infrastructure wireless topology. Wireless topologies and other network topologies are discussed in Chapter 1.
  • Extended Service Set (ESS)—Refers to two or more connected BSSs that use multiple APs. The ESS is used to create WLANs or larger wireless networks and is a collection of APs and clients. Connecting BSS systems allows clients to roam between areas and maintain the wireless connection without having to reconfigure between BSSs.
  • Extended Service Set Identifier (ESSID)—Although the terms ESSID and SSID are used interchangeably, there is a difference between the two. SSID is the name used with BSS networks. ESSID is the network name used with an ESS wireless network design. With an ESS, not all APs necessarily use the same name.
  • Basic Service Set Identifier (BSSID)—The MAC address of the BSS AP. The BSSID is not to be confused with the SSID, which is the name of the wireless network.
  • Basic Service Area (BSA)—When troubleshooting or designing wireless networks, the BSA is an important consideration. The BSA refers to the AP’s coverage area. The BSA for an AP depends on many factors, including the strength of the AP antenna, interference in the area, and whether an omnidirectional or directional antenna is being used.

Wireless Antennas

A wireless antenna is an integral part of overall wireless communication. Antennas come in many different shapes and sizes, with each one designed for a specific purpose. Selecting the right antenna for a particular network implementation is a critical consideration and one that could ultimately decide how successful a wireless network will be. In addition, using the right antenna can save you money on networking costs, because you need fewer antennas and access points.

Many small home network adapters and access points come with a nonupgradable antenna, but higher-grade wireless devices require you to choose an antenna. Determining which antenna to select takes careful planning and requires an understanding of what range and speed you need for a network. The antenna is designed to help wireless networks do the following:

  • Work around obstacles
  • Minimize the effects of interference
  • Increase signal strength
  • Focus the transmission, which can increase signal speed

The following sections explore some of the characteristics of wireless antennas.

Antenna Ratings

When a wireless signal is low and is being affected by heavy interference, it might be possible to upgrade the antenna to create a more solid wireless connection. To determine an antenna’s strength, we refer to its gain value. But how do we determine the gain value?

Suppose that a huge wireless tower is emanating circular waves in all directions. If we could see these waves, we would see them forming a sphere around the tower. The signals around the antenna flow equally in all directions, including up and down. An antenna that does this has a 0dBi gain value and is called an isotropic antenna. The isotropic antenna rating provides a base point for measuring actual antenna strength.

An antenna’s gain value represents the difference between the 0dBi isotropic and the antenna’s power. For example, a wireless antenna advertised as 15dBi is 15 times stronger than the hypothetical isotropic antenna. The higher the decibel figure, the higher the gain.

When looking at wireless antennas, remember that a higher gain value means stronger send and receive signals. In terms of performance, the rule of thumb is that every 3dB of gain added doubles an antenna’s effective power output.

Antenna Coverage

When selecting an antenna for a particular wireless implementation, it is necessary to determine the type of coverage the antenna uses. In a typical configuration, a wireless antenna can be either omnidirectional or directional. Which one you choose depends on the wireless environment.

An omnidirectional antenna is designed to provide a 360-degree dispersed wave pattern. This type of antenna is used when coverage in all directions from the antenna is required. Omnidirectional antennas are advantageous when a broad-based signal is required. For example, if you provide an even signal in all directions, clients can access the antenna and its associated access point from various locations. Because of the dispersed nature of omnidirectional antennas, the signal is weaker overall and therefore accommodates shorter signal distances. Omnidirectional antennas are great in an environment that has a clear line of sight between the senders and receivers. The power is evenly spread to all points, making omnidirectional antennas well suited for home and small office applications.

Directional antennas are designed to focus the signal in a particular direction. This focused signal allows for greater distances and a stronger signal between two points. The greater distances enabled by directional antennas give you a viable alternative for connecting locations, such as two offices, in a point-to-point configuration.

Directional antennas are also used when you need to tunnel or thread a signal through a series of obstacles. This concentrates the signal power in a specific direction and allows you to use less power for a greater distance than an omnidirectional antenna. Table 7.1 compares omnidirectional and directional wireless antennas.

Table 7.1. Comparing Omnidirectional and Directional Antennas





Wireless area coverage

General coverage area

Focused coverage area.

Omnidirectional allows 360-degree coverage, giving it a wide coverage area. Directional provides a targeted path for signals to travel.

Wireless transmission range


Long point-to-point range.

Omnidirectional antennas provide a 360-degree coverage pattern and, as a result, far less range. Directional antennas focus the wireless transmission; this focus allows for greater range.

Wireless coverage shaping


The directional wireless range can be increased and decreased.

Omnidirectional antennas are limited to their circular pattern range. Directional antennas can be adjusted to define a specific pattern, wider or more focused.

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