Alpha Omega Wireless Blog

Over the years manufactures in the outdoor wireless bridge industry have migrated their designs of radio systems. In the past, most radios used in Point to Point microwave wireless were comprised of radio units that were mounted indoors. These radios hardware platforms required radios that were rack mounted indoors and had to use large coax (1/2" to 2 1/4" Heliax or LMR) or Elliptical Waveguide (requiring dehydrators) running out from the indoor radio unit up the tower (or to the roof top), connecting the antenna.

Because of the large amount of line loss, large cable or waveguide had to be used to compensate for the amount of line loss between the radio and the antenna (typical 6.1dB per 100ft with standard LDF 4-50 1/2" Heliax). To compensate for the line loss larger antennas also needed to be used in conjunction of the larger cable.

The advantages of this type of wireless backhaul radio system is that a technician can walk into a data room/closet or outdoor radio shelter to service the radio or replace it in event of a radio failure. But there are a lot of disadvantages with this set up:

1. The larger the cable/waveguide and antennas, the greater the cost of the overall system.
2. Less over gain of the radio system due to the line loss.
3. Greater infrastructure needed to support the loading of the larger antennas and cabling on the tower and/or mounts.
4. Costs with maintaining an in facility.
5. These types of radio systems typically have greater power consumption.
6. More points of failure to troubleshoot (dehydrators, couplers, cable, etc.)
   

The industry later came out with a split mount design radio system consisting of an indoor modem unit ("IDU" - typically a 1U rack mounted piece of hardware) and an outdoor RF Unit ("ODU") that mounts the actual radio RF component hardware directly onto the back of the antenna. This system typically uses a smaller IF (intermediate feed) coax cable to pass DC power and the data between the ODU to the IDU. The IF cable can be 1/2" coax or less. The advantages of this type of system are greater system gain (with virtually no loss between the radio and the antenna) and lower costs of system components (less cabling and no need for expensive waveguide or dehydrators). Still many of the same disadvantages still apply with the need for indoor space requirements and costlier power consumption.

Today the industry has migrated to full outdoor radio unit systems (FODU") comprised of a single outdoor unit mounted to the back of the antenna. These FODU's contain the RF components, modems, and network interface. The connection between the FODU and the network switch is typically outdoor shielded twisted pair (CAT-5e) or fiber. The FODU design has far greater advantages over the indoor radio or IDU+ODU spit mount designs:

1. FODU's consume a minimum of 20% less energy (typically use 25W to 30W DC).
2. Systems can be powered by solar or battery.
   
3. No equipment room or rack space needed.
4. Lower over all OPEX (operational expenditure costs).
5. Higher gain to virtually no loss between radio and antenna.
   
6. No cost for expensive coax or waveguide.
7. Single component which makes for simple troubleshooting
8. Easy to spare equipment.
9. Quicker and easier install and maintenance.
10. Easy to daisy chain radios at repeater sites or for dual radio set ups (1+1)
    

The argument that comes up with individuals that are use to the older way systems were designed is the fear of everything being up on the tower and not being able to service it. Most end-users are not tower certified and can't do their own servicing. In roof top applications this is a non-issue but it is true in a tower situation. But even with all indoor radio systems there is still the need for tower services for troubleshooting because the large number of potential points of failure of the system components that reside on the tower (e.g. the coax/waveguide, couplers, connectors, weather proofing, surge protection, antenna, etc.).

Troubleshooting an all indoor system or split mount design can take a lot of labor and have great costs associated to it. For example:

• a bad coupler on waveguide or moisture getting into the waveguide is very difficult and time consuming to identify.
  
• The same holds true for damaged coax (coax that might have been crushed or dinged during tower work on other existing systems).
• Blown or faulty surge protection.
• Worn or improper weather proofing.

Question 5: Is Wireless True Ethernet Throughput?

Answer: Yes!

Wireless point to point bridge networks can provide true usable Ethernet throughput from T1 speeds to over GigE Full Duplex (gigabit wireless). Wireless Point to Multipoint networks can provide T1 speeds up to 170Mbps+ aggregate throughput. Wireless mesh Networks can provide up to 25Mbps+ aggregate throughput. These are true usable throughputs.

Note: When evaluating wireless backhaul systems it is important to cut through all the marketing and look at the actual specifications of a chosen system. Many times we see the product marketing rounding up actual values or using the data burst rates of a radio system, rather than the actual usable data throughput.

Outdoor wireless backhaul networks can provide true low latency, high speed native  Ethernet connectivity. Think of wireless connectivity just as invisible copper or fiber. The value of wireless networks is that they can provide a more direct path of connectivity. This is true when looking at point to point wireless bridges. In the case of leased line connectivity, a clients network path may go through multiple CO's (central offices) or multiple switching locations in order to create a land line point to point network. 

A great example of this happens when some one sets up a Spanning Tree Network using wireless backhaul as a redundancy solution. Many times in this environment the network wants to converge over the outdoor wireless brdige network because it provides a more direct path (hence a lower cost average). As they say the most direct path between two points is a straight line. Also, wireless backhaul networks can have <1ms of latency, even over long distances (up to 50 miles). In most STP networks the wireless bridge network needs to be given a higher cost value in order to keep the network from automatically converging over it. Another value is that wireless point to point and point to multipoint wireless networks can provide connectivity where traditional copper or fiber cannot be installed. 

Many of the "Value Line" outdoor wireless bridge systems (e.g. the lower cost unlicensed wireless systems that use Wi-Fi chip sets) do have a distinction between the radio's data rates and the usable throughput. These radios, common among wireless mesh and point to multipoint wireless backhaul systems, do add packet headers to the IP packets that get passed across the wireless link. Commonly we see manufactures state a radio is 54Mbps, when in reality the true usable throughput is typically under 27Mbps aggregate. This is for several reasons: the radios operate in TDD (Time Division Duplexing) and they are using Wi-Fi radios that add overhead to the packet stream by encapsulating the IP packets and by sending out beacon requests.

Traditional microwave outdoor wireless backhaul systems, such as licensed microwave links, can offer true carrier grade Full Duplex (simultaneous up-link and down-link) Ethernet connectivity and can even offer traditional wayside TDM circuits. Often referred to as Carrier Grade systems, these radio systems do not carry the same overhead as Wi-Fi based radios systems. So these radio systems provide true usable Ethernet and TDM throughput. These systems can provide traditional native 100Mbps Full Duplex Ethernet connectivity or even expand up to over true GigE (Gbps) Full Duplex just like fiber.

Outdoor wireless backhaul can also provide scalable throughputs in between 10Mbps and GigE (gigabit wireless). For example, 200Mbps Full Duplex on a particular network segment which can then be spit into two 100Mbps Full Duplex segments. Wireless backhaul systems can also provide inherent security and added encryption, Layer 2 connectivity, QOS, VLAN tagging, etc.

When evaluating wireless backhaul technology, the possibility of radio frequency interference disrupting a wireless network link poses a concern. Radio interference results from unwanted radio frequency (RF) signals disrupting system communications. Typically these signals are at or near the same frequency as the receive frequency of an established wireless system. Interference can degrade a radio system's performance and in some cases even prevent the system from functioning at all.

The source of interference is usually other transmitters that are very close in frequency to the impacted system. Interference can affect all types of radio frequencies, although the issue of interference in regards to outdoor wireless often occurs with license-exempt ("unlicensed wireless") systems operating in the 902-928MHz (spread spectrum), 2.4GHz, 5.3GHz, 5.4GHz, and 5.8GHz frequencies. Note: 60GHz millimeter wave, often used in gigabit wireles backhaul, is considered to be unlicensed but is extremely immune to interference due to its inherent features of having narrow beam widths and oxygen absorption over fairly short relative distance.

The terms "unlicensed wireless bridge" and "licensed microwave link" refer to the radio frequency spectrum characteristics set by the U.S. Federal Communications Commission ("FCC") or equivalent national government regulatory body. Licensed products require regulatory approval before deployment while license-exempt products can be deployed without any regulatory approval.

Point to point wireless links can be designed and deployed in either licensed microwave or un-licensed frequencies. Point to multipoint and mesh wireless systems typically operate in the un-licensed 2.4GHz, 5.3GHz, 5.4GHz, and 5.8GHz frequency bands. Some point to multipoint wireless systems can operate in licensed UHF/VHF, 900MHz, 3.65GHz (WiMax), and 4.9GHz (public safety) frequency bands.

Note: There are licensed 2GHz bands owned by various telecommunication carriers being used for WiMax applications. The 4.9GHz public safety band is not truly a licensed band. It's a license registration that gives permission for use of the frequency among agencies that can prove that it's being used for public safety. Multiple agencies can be approved in the same operating area. The FCC states that the various agencies must self coordinate. They must work together on their operating channels to avoid interference, with each other, but provides no guaranty.

Licensed RF transmitters communicate using a specific transmit and receive frequency combination that is selected and assigned to the user (licensee). Licensed microwave wireless systems operate within parts of the radio spectrum, such as: UHF/VHF, 900MHz, 2GHz, 3.65GHz (WiMax), 4.9GHz (public safety), 6GHz, 11GHz, 18GHz, 23GHz, and 80GHz (E-Band millimeter wave) as designated by the FCC.

Licensed microwave wireless systems are becoming more popular as a result of noise interference in unlicensed wireless spectrum. Licensed microwave radios provide security from the risk of interference from other RF systems. In a licensed system the channels that the radio system transmits and receives on are owned by the user and are registered with the FCC for frequency coordination. Getting a license is inexpensive and can be obtained in the matter of weeks.

Prior to deploying and operating a licensed frequency an end user is responsible for performing a frequency coordination, filing a public notice, and submitting an application (601 form) with the FCC to ensure that no one else is already operating on the same frequency or a frequency that will inject interference on existing systems. This process provides full disclosure of the frequency assignment and typically avoids interference from any existing licensee already assigned in the area. If licensed radios encounter interference, it is typically resolved with the assistance of the regulatory body.

With un-licensed systems it can never be guaranteed that a system will operate interference free and with any predictable reliability. Many manufactured systems can help overcome interference by having a good carrier to interference ratio inherent with the hardware and by proper design and installation.

With licensed microwave systems one can have a predictable reliability because of the lack of interference. Many licensed systems can be design and installed for 99.999% predictable reliability (meaning the system is predicted to have less than 5 min of outage time a year).

The major difference between licensed wireless and license-exempt systems is that licensed radio users have a regulatory body that will assist them in overcoming any interference issues that may arise, while license-exempt users must resolve interference issues without governmental assistance.

Question 4: Is wireless safe?

Answer: Absolutely yes!

For organizations that have not been exposed to using wireless systems for their communication needs, the question always comes up about the safety and health risks of having wireless systems (transmitters and receivers) on their premises. Mostly driven from non-technical individuals and from legal departments comes this concern and sometimes even objection from using wireless technology. Fear driven images of people being radiated or having long term effects, such as cancer come into question. This has been mostly prominent in discussions regarding the use of cellular phones.

Wireless RF signals (radio frequency)are all around us, both man made and naturally occurring from the Earth itself. We are constantly exposed to radio waves of various frequencies at all times. Most people don't understand that. When we talk about the man made RF signals, people are concerned when the term "Microwave" is heard. Understand the term Microwave is broad definition of radio frequencies ranging from 300MHz to 300GHz and at various power levels. We think of our "microwave ovens" zapping our food until flaming hot. Microwave ovens operate at 2.45GHz at a power transmission of roughly 700W output. Most Wi-Fi and outdoor point-to-point, point-to-multipoint, Wi-Max, etc. systems operate at less than 1 Watt!

The concern then becomes about he risk of long-term exposure of RF and at what levels. Organizations, such as the Federal Communications Commission ("FCC"), Environmental Protection Agency ("EPA"), National Institute for Occupational Safety and Health, Occupational Safety and Health Administration("OSHA"), National Telecommunications and Information Administration ("NTIA") and others have performed numerous studies and consistently re-studied the effects of RF exposure on humans to answer this question. These organizations have established and set guidelines for safe levels of operation and exposure for wireless transmission.

In broadband wireless people get concerned because we are dealing with higher frequencies (e.g. 5GHz, 11GHz, 18GHz, 23GHz, 60GHz, etc) and they see antennas ranging from 1ft to 8ft on a tower. People assume that higher the frequency and larger the antenna the greater the health risk. This is just not true. For example at 60GHz the signal at 1 Watt cannot even penetrate the human skin. Again, outdoor wireless, regulated by the FCC, typically operate at extremely low levels of output power (<1W). 

According to the WHO ("World Health Organization") "In fact, due to their lower frequency, at similar RF exposure levels, the body absorbs up to five times more of the signal from FM radio and television than from base stations. This is because the frequencies used in FM radio (around 100 MHz) and in TV broadcasting (around 300 to 400 MHz) are lower than those employed in mobile telephony (900 MHz and 1800 MHz) and because a person's height makes the body an efficient receiving antenna. Further, radio and television broadcast stations have been in operation for the past 50 or more years without any adverse health consequence being established." - Fact sheet N°304 May 2006 -Electromagnetic Fields and Public Health.

The greatest amount of exposure occurs in a relatively close distance to the transmitting antenna. The exposure levels drops quickly over distance. Most antenna systems are installed at higher elevation levels above where a human would normally be standing (e.g. roof tops and on towers). Installers should take precautions and limit their exposure from standing directly in front of an operating antenna. Otherwise, there has been no scientific evidence that the lower levels of RF exposure that fixed Wi-Fi and outdoor wireless emit have any effects on human health.

Question 3: Is it secure?

Probably the number one question we receive from those that have never truly used wireless for their back haul is if it's secure. The main driver for this is either because a person has had no experience using wireless backhaul, they have read some negative press online about Wi-Fi being hacked, or they have tried to install wireless using SOHO (small office - home office) grade equipment.

The answer is "Yes!" outdoor wireless backhaul is extremely secure. Provided that the equipment is designed for outdoor wireless backhaul, it is installed properly, and it is configured correctly. Most outdoor wireless bridge systems can meet DOD (Department of Defense) specifications for security and HIPPA compliance.

True outdoor wireless bridge systems (e.g. licensed microwave links, point to multipoint wireless, WiMax, wireless mesh, etc.) are designed for secure outdoor radio signal propagation. Most all systems, both Consumer grade and Carrier/Industrial grade, have multiple levels of internal and inherent security.

For instance, most systems allow for encryption to be set at 128-bit to 256-bit AES or equivalent, MAC address or serial number filtering, and/or network security naming conventions. Also, many times systems are paired and only allow communications with a known partnered radio. Many of the Carrier/Industrial grade wireless have their own proprietary encryption built in and use various protocols not found in consumer electronic components. Meaning someone can't just buy something off the shelf that can even receive the signal and/or frequency. As is the case with most licensed microwave systems.

Inherent with properly designed and installed outdoor microwave wireless systems is the fact they they are typically set up as a point to point wireless backhaul system. This means the radios use directional antennas utilizing extremely narrow beam widths (typical under 3 degrees). The radio signal is also transmitted in a particular polarization plane (e.g. vertically or horizontally) which provides around 25dBm of signal separation. For someone to intercept such a signal they would have to place a receiving antenna directly or extremely close to the path of the original signal. Hard to do if they don't have access to a tower or roof top where the signal has originated from or in the direct path.

Wi-Fi systems, because they are broadcasted in an omnidirectional fashion and are typically set up by non-industry professionals, have been victims of hacking attacks. Plus the fact that most all portable electronic computing devices and mobile phones have built in Wi-Fi makes it easy for one to have all the equipment they need to find and identify the wireless source (access point). Still if Wi-Fi is installed and configured properly, using best practices, it too can be fully secure. Also, encryption standards continue to increase.

Outdoor wireless bridge systems are completely different that their Wi-Fi partners (provided that one isn't using Wi-Fi radios for outdoor wireless bridging). Outdoor wireless backhaul has been used by the telecommunication companies and the military for decades. System continue to provide increased levels of security.

In comparison to traditional land line circuits, wireless backhaul systems can provide a higher level of security. It is not difficult to gain access to a buildings telecommunications MPOE (main point of entry) wiring closet or access to outdoor, ground level, telecommunication vaults. These locations can allow someone to easily tap onto an organizations internal network. I've had clients tell me how they are completely secure on their WAN/LAN networks and wouldn't trust anything but their copper and fiber connections. They often forget that someone can easily plug their laptop into a data jack in their lobby, gain access to their cable infrastructure from neighboring ceiling crawlspace, or jump on their WAN infrastructure from an outdoor telecommunication cabinet (which if locked at all can be easily broken into). Note: even with physical land line infrastructure one should use best practices for encryption and security. I'm not saying that WAN/LAN infrastructures are not secure, but in many cases people forget to completely secure their networks. What I am saying is that wireless systems can be just as, if not more, secure than traditional wire/fiber networks.

Question 2: Is it reliable?

Yes! Provided it is designed / engineered correctly, you use the right equipment & frequencies, and it is installed properly.

As with the prior blog on this series "Does weather effect wireless? The 5 Misconceptions - Part 1", I stressed the importance of properly designing and installing the right outdoor wireless bridge equipment. This will be a common theme throughout the series. Outdoor wireless backhaul is different than indoor 802.11 a/b/g/n Wi-Fi that many are accustomed too. Indoor wireless devices take advantage of multipath and are very forgiving due to its short range, high power transmission using typically omnidirectional antennas.

Outdoor wireless, especially when dealing with point to point wireless or point to multipoint wireless networks, relies on having a concentrated directional signal in order to create the best possible signal and interference negation. This means a specific antenna communicates (sends and receives) with another specified antenna(s).

From "Part 1:" All wireless signals that travel from one antenna system to another experiences some form of "Path Loss". Properly designed systems use the correct antennas, frequencies, and transmit power ("Tx") to overcome the Path Loss to get the desired Receive Signal Level ("RSL" measured in dBm). Radios are designed to operate with a certain level of "Fade Margin" that allows the system to operate at a predictable reliability (for most systems 20 to 25dB of Fade Margin is recommended). This means if a system has an RSL of -50dBm and it has a receiver threshold of -72dBm, you'll have 22dB of Fade Margin or the amount of dB signal strength a system can lose before you will experience errors (referred to as BER - Bite Error Ratio) or loss of connectivity.

Factors that can effect a RSL to fade can be either natural (e.g trees, heavy rain, or wind moving the antenna) or man made (e.g. building built in the path) causing the signal to be partially or fully blocked. Other environmental factors can be interference (an undesired signal in the same frequency from another system) or multipathing caused be reflection off a physical surface, either in the near field or along the path.

Knowing the radio system's designed threshold one can perform path calculations, combining path loss, predictive modeling (terrain and weather models), system components (antenna and radio gain), etc. Software tools are available to perform the path calculations like: Path Loss or MicroPath.

With path calculations we can determine the predictable reliability of most wireless backhaul systems. Important to note you get what you pay for. There are both good and bad manufactured outdoor wireless bridge equipment. A properly designed system can achieve 99.999% reliability (<5min of predictable outage a year). This is typically better than any leased Telco circuit's SLA.

It all comes down to proper planning (design / engineering), proper  outdoor wireless backhaul equipment, frequency choice, and proper installation. Note: Installation should be done by a licensed professional that understands the key elements of proper wireless installation. Trust me. After years of troubleshooting systems that were installed by other so called professionals, I have seen about 80% of system issues being due to improper wireless installation. So please do your homework on the vendor you use and get reference by both other clients and the outdoor wireless bridge manufacture.

Question 1: Does the weather (like rain) effect wireless?

Well the answer is Yes & No!
Technically "Yes" - different forms of weather do have effects on various frequencies. Reality "No" - if the right frequency and antenna system is properly engineered, designed, and installed a wireless backhaul system can provide 99.999% reliability.

The obvious one is wind. Wind in itself doesn't effect the RF signal but it does put an external force (wind loading) on the antenna system that can cause it to move or come out of alignment. This is pretty easy to understand. The clear answer is to properly install antenna systems to withstand local wind patterns. Most antenna systems are designed to withstand wind gusts up to 110mph (varies by manufacture).

The main question arises with precipitation (e.g. fog, rain, and snow). All wireless signals that travel from one antenna system to another experiences some form of "Path Loss". Properly designed systems use the correct antennas, frequencies, and transmit power ("Tx") to overcome the Path Loss to get the desired Receive Signal Level ("RSL" measured in dBm). Radios are designed to operate with a certain level of "Fade Margin" that allows the system to operate at a predictable reliability (for most systems 20 to 25dB of Fade Margin is recommended). This means if a system has an RSL of -50dBm and it has a receiver threshold of -72dBm, you'll have 22dB of Fade Margin or the amount of dB signal strength a system can loose before you will experience errors or loss of connectivity.

Moisture such as fog, rain, and snow (depending on its water content) adds attenuation to the signal's path. The amount of moisture is critical to understand here. Fog, although dense, has very low moisture when it comes to its effect on RF signal. With snow it all depends on its density. Snow typically has less moisture content than actual rain. Rain depends on the amount of rainfall (measured in mm/h) and the size of the raindrops. Heavier the raindrops and the higher velocity of rainfall the higher the attenuation. Typical rainfall produces roughly 5.5dB. Again it depends on the amount of rain coming down and the frequency being used.

Also, the amount of attenuation rain can cause depends on the frequency being used. The lower the frequency the less attenuation. The high the frequency the higher the attenuation. To design a outdoor wireless bridge system correctly rain modeling is used (along with other Path Loss factors) for calculating the RSL needed to provide adequate Fade Margin necessary for any given system.

So, if a system is designed and installed properly, a wireless backhaul system can still produce 99.999% (<5min predictable yearly outage) reliability. Note: amazingly good since most telco's only guarantee 99.9% reliability on their fiber infrastructure).