Wireless Infrastructure 101

November 23, 2017 at 8:00 AM

 

You would be hard pressed to find a business, industry or home that doesn’t use wireless communication in some way. We depend on wireless networks used by our mobile devices, laptops, tablets and gaming systems to keep us connected, entertained and informed every day. Here, we’ll look at indoor and outdoor wireless infrastructure design considerations.

 

Frequencies

 

For wireless communication to work, radio frequency (RF) and microwaves are used to transmit voice, video and data. Radio frequencies are usually used in wireless networks, they range from 3 kHz to 300 GHz and are also used for AM broadcasting, navigational beacons and shortwave radio. Microwaves range from 300 MHz to 300 GHz and are typically used for television, FM broadcasting, aviation communications, and radar and satellite links. Most home, business and government networks operate on the Industrial, Scientific and Medical (ISM) frequency bands that range from 900 MHz to 5 GHz. The ISM band frequencies incorporate many of the IEEE 802.11wireless standards.

 


Design Considerations

 

When designing a wireless network, you must always take into consideration the environmental variables in the installation area that will or could affect network performance.

 


Indoor RF Wireless Networks

 

During installation or expansion, indoor networks present a special set of factors to consider. Most wireless access points and routers have a typical range capability specified by the manufacturer. But these ranges are based on having clear line of sight, which requires an unobstructed view of the antenna from the remote point in the link. Unfortunately, this is not the case in most indoor installations, there is usually some type of obstacle present. For example, signals typically will not penetrate concrete walls and the other building materials such as metal studs, aluminum siding, foil-backed insulation, pipes, electrical wiring and furniture. All of these common obstacles can reduce signal range and affect the coverage area. Plus, other wireless equipment such as cordless phones, microwave ovens, radio transmitters and electrical equipment can cause interference and decrease the signal range.

 


Outdoor RF Wireless Networks

 

Outdoor wireless networks face many of the same challenges as indoor networks, such as reflections and multipath. Having a clear line of sight is also critical for an outdoor network, trees and leaves can obstruct 802.11 frequencies and block the signal completely. A site survey is recommended before an outdoor wireless network is deployed, it might also be necessary to clear obstacles.

 

To help you plan and design your wireless network, we offer a series of wireless calculators to get you started.

What You Need to Know about Line of Sight

August 25, 2016 at 8:00 AM


When designing a wireless network, one of the most significant factors to consider is Line of Sight (LOS) - the path between two antennas. Obstructions in the LOS path can wreak havoc on a Wi-Fi signal so determining what, if anything, is between the antennas is crucial to your network working properly. Here, we’ll examine the main concepts you need to know in order to clear the path for Line of Sight and make sure your wireless network is a success.

 

The first step in navigating Line of Sight is to determine the LOS conditions. Once the conditions are defined, the correct type of wireless system can be chosen for the network area. There are three main Line of Sight conditions:

 

1.       Full Line of Sight (LOS) – no obstacles between the two antennas

2.       Near Line of Sight (nLOS) – partial obstructions between the two antennas, such as tree tops

3.       Non Line of Sight (NLOS) – full obstructions between the two antennas, such as an entire tree  

 

Outdoor networks may encounter the largest obstacles, but Line of Sight is also important for indoor wireless networks. Obstacles like walls, ceilings and furniture have to be considered because they will also affect the wireless signal reception.                                                                                                                         

In addition to obstructions, there are three other factors to consider that can affect Line of Sight:

 

1.       Multipath and Reflections

2.       Fresnel Zone

3.       Path Loss

 

In wireless transmissions, multipath and reflections are as important as signal strength because they too can degrade the performance of the network. Multipath is when wireless signals travel in multiple paths and arrive at the receiver at different times. Reflections occur when wireless signals "bounce" off of objects. When signals are transmitted through walls and ceilings and are reflected off of metallic objects, they will also have peaks and nulls in amplitude and changes in polarization (vertical or horizontal).

 

Fresnel Zone is an electromagnetic phenomenon where light waves or radio signals get diffracted or bent by solid objects near their path. The reflected waves/signals become out-of-sync with those that traveled directly to the receiving antenna, this delay reduces the power of the received signal.

 

Path Loss is another area of concern when determining Line of Sight. Some radio frequencies travel well through certain objects while other frequencies are not able to pass through, resulting in path loss. For example, 2.4 GHz radio waves easily pass through walls but experience path loss when going through trees and leaves. This is because walls are very dry, trees contain high levels of moisture and 2.4 GHz radio waves are easily absorbed into water. On the other hand, 900 MHz radio waves are not as easily absorbed by water. In cases like this, when trees cause nLOS or NLOS conditions, 900 MHz is a better frequency to use than 2.4 GHz to avoid path loss.

 

There are many factors to consider when designing a wireless network, but with proper site evaluation and planning you can correctly navigate Line of Sight obstacles to achieve peak performance.

 

 Comments on this post? Other topics you’d like us to cover? Email us at engineeringhub@l-com.com

 

900 MHz Is Your NLOS Friend

November 12, 2015 at 8:00 AM

 

Non-Line-of-Sight (NLOS) applications can be difficult to overcome when designing a wireless network. Trees, buildings and other obstructions can be formidable foes when trying to establish a point-to-point or point-to-multipoint wireless link. Able to break through most obstacles, 900MHz is the ideal ally when dealing with NLOS situations.


Of the unlicensed ISM frequencies used in the United States, 900 MHz is the perfect choice for NLOS wireless networks. Unlike the very popular 2.4 GHz frequency band, 900 MHz wireless transmissions are not absorbed by leaves and trees that contain water. This makes 900 MHz the ideal solution for dealing with trees and other foliage in the line of site.

 

900MHz signals can travel up to 1,500 feet through obstructions such as trees and buildings.  For indoor wireless NLOS applications, some higher powered 900 MHz radios can penetrate up to 10 walls!

 

Despite all of its benefits, the 900 MHz frequency does have some drawbacks and limitations including:

 

- A limited amount of unlicensed bandwidth in the 900 MHz spectrum (only 26 MHz). If there are a lot of other devices in close range, using the same spectrum range, excessive "noise" from nearby devices could adversely affect signal quality

 

- 900 MHz supports lower data rates than the 2.4 and 5 GHz ISM frequency bands, in most cases only 1 to 1.5 Mbps maximum

- In most countries outside of the United States, 900MHz is not open for unlicensed use

 

When planning a wireless network without clear line-of-sight, for any application that involves NLOS conditions and lower data rates, 900 MHz may be your best bet.

  

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How Line of Sight (LoS) Can Affect Your Wireless Installation

September 18, 2014 at 10:00 AM

 

Though the term Line of Sight seems self explanatory, there’s actually more than meets the eye when it comes to LoS and installing a wireless network.

 

As you might already know, Line of Sight is the path between two antennas. One of the first questions you’ll want to ask yourself when designing an outdoor wireless network is what is between point A (antenna 1) and point B (antenna 2)?

 

These details are important since Line of Sight does not only apply to a straight line. Wireless signals being sent from point A to point B can and will, most likely, run into to some obstacles that will alter the path they take.

 

When light waves or radio signals get diffracted or bent due to solid objects near their path, it’s an electromagnetic phenomenon referred to as The Fresnel Zone (referenced in the diagram below). The radio waves reflecting off the objects may arrive out of phase with the signals that traveled directly to the receiving antenna, thus reducing the power of the received signal.

 

It is important to also note that the line of site broadens with wavelength, which means that for low frequency, high wavelength signals, you need to have a larger Fresnel radius free of obstructions.  

 

 

 

 

As you can see, there are three main categories of Line of Sight to use as guidelines:

1.       Full Line of Sight (LOS), where no obstacles reside between the two antennas.

2.       Near Line of Sight (nLOS) which includes partial obstructions, such as tree tops between the two antennas.

3.        Non Line of Sight (NLOS), where full obstructions exist between the two antennas.

 

By determining the specific line of sight conditions in the WiFi network area, you can then determine the correct type of wireless system to install.

 

For example, most WiFi systems typically run on the 2.4 GHz and 5.8 GHz frequencies. Both of these frequencies are very dependent on a clear line of sight to obtain good performance, so clear LoS is very important.

 

View L-com’s comprehensive WiFi antenna offering

 

 

The ISM Band Frequency Dilemma: Which One is Right for You?

January 23, 2014 at 10:00 AM

 

The FCC allocates different frequencies for different purposes, and each has its own advantages. In the US, 900, 2400 and 5000 MHz frequency bands are set aside by the FCC for unlicensed Industrial, Scientific and Medical (ISM) applications. The lack of licensing requirements has greatly encouraged the growth of the wireless industry. These bands are used for consumer and commercial WiFi and WLAN applications as well as for commercial Radio Frequency Identification (RFID) and Supervisory Control and Data Acquisition (SCADA) applications. Here are some highlights of each ISM band frequency for you to consider:


900 MHz

900 MHz 9 dBi Yagi Antenna

The 900 MHz ISM band is known to be very narrow, thus limiting the maximum data rates. Typically applications such as SCADA and RFID use the 900 MHz ISM band since their data rate requirements are lower than applications found in the 2.4-5 GHz frequency bands. Many times the type of data packets being sent in these types of applications is a simple on /off command to something like a motor or value.

 

When obstructions such as trees and leaves are in the Line of Sight (LOS), the 900 MHz frequency will fare better than 2.4 GHz. The 2.4 GHz frequency is absorbed by water found in trees and leaves, which then causes path loss of the 2.4 GHz transmission. 900 MHz is often used in Non-Line-Of-Sight (NLOS) applications.

 

 

2.4 GHz

WiFi Grid Antenna

For the home user and commercial businesses, 2.4 GHz ISM Band is the primary band used for WiFi, Bluetooth, cordless phone, printer, keyboard, mouse and gaming controller applications. Voice, video and data communications are also typically used in 2.4 GHz systems where higher data rates are required (up to 300 Mbps for 802.11n applications).

 

2.4 GHz is the most widely used frequency (especially since it includes devices like microwave ovens, baby monitors, cordless phones etc.) and in some cases may even be overcrowded. When too much overcrowding occurs, your WiFi network signal may be weak or not work at all. In some cases it's best to use 5 GHz backhaul links to connect 2.4 GHz WiFi networks as 5 GHz is a less crowded frequency.

 

 

5 GHz

5.8 GHz Sectorized Antenna Array with four 90°  Sectorial Antennas

The 5 GHz frequency is often used in commercial WiFi applications. As mentioned above, it is often used as a backhaul link connecting two 2.4 GHz systems over some distance. 5 GHz is also the frequency used for the emerging standard 802.11ac which will provide up to 1.3 Gbps of wireless data throughput. Additionally, 802.11n can also use the 5 GHz frequency.

 

 

 

 

For more information about US Frequency Allocations, click here.

 

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