Alpha Omega Wireless Blog

The wireless backhaul industry is booming and not just because of the build out of 4G, like WiMax backhaul and LTE. Government agencies, utilities, and private industry are all realizing the benefit of point to point wireless backhaul, point to multipoint wireless bridges, and wireless mesh. Microwave communication, also known as fixed wireless backhaul, is a great network solution because of its quick ROI, high throughput speeds, quick deployments, extreme reliability, and as a wireless last mile solution the ability to get bandwidth where traditional cable and fiber infrastructure is not available.

So how does someone that is not a wireless backhaul expert decide what the right wireless backhaul solution is and what wireless equipment to use? There are so many outdoor wireless vendors that claim their wireless hardware is the best. Who do you believe and how do you know you are getting the best solution? Whether a licensed microwave link or an unlicensed wireless Ethernet bridge, here are a few things that someone looking into a microwave communication solution should consider:

Hire a Good Outdoor Wireless Integrator
People that have deployed indoor Wi-Fi sometimes think that doing a wireless installation of an outdoor wireless backhaul is something they can do themselves. Understand that Wi-Fi is pretty easy to deploy indoors and is very forgiving. Outdoor wireless bridges are a whole other story. Outdoor wireless backhaul needs to be properly engineered. There are considerations about frequency coordination, spectrum analysis, Fresnel Zone criteria, multipath issue, signal propagation, EIRP regulations by the FCC, security, and so on. Hiring a good outdoor wireless integrator or wireless installer will ensure a successful wireless deployment. An outdoor wireless integrator can provide a proper wireless network design, perform a wireless sight survey, and help pick the right wireless hardware solution.

Understand the Solution Before Choosing the System
So many times an end user finds out that wireless backhaul might be a good solution to a networking need by a case study or white paper from a wireless manufacture. Naturally they may call the manufacture to get more information. That's where the issue starts. It becomes the particular wireless manufacture sales rep's job to fit their wireless radio system into the end user's solution, whether they are a good fit or not. The best approach it to fully understand what the wireless backhaul solution is first. Is it a point to point licensed microwave link or an unlicensed non line of sight wireless bridge that is right for the application? Once you understand what the right wireless solution is then you can look for various manufactures of that type of hardware.

Wireless Hardware Marketing Material Is Just Marketing
Marketing material is great to get an overview of a solution or piece of hardware. But understand that it's the job of a wireless manufacture to position their equipment as the best solution and sometimes the only solution. It most cases the toted performance of a wireless radio is based on optimum conditions and sometimes only achievable in a lab environment. Be sure before choosing a particular wireless backhaul platform to consult a good outdoor wireless installation VAR that works with multiple wireless manufactures and has personally installed the wireless hardware that can help decipher hype from reality.

Choose Proven and Field Tested Wireless Backhaul Systems
There is nothing better than getting positive feedback from a peer or other organization similar to yours on what type of outdoor wireless they have experienced and finding out what works and what doesn't. When you have done thousands of wireless installations you learn real quick what wireless equipment is good and what wireless systems are junk.

Know the Wireless Equipment You are Buying
There are so many outdoor wireless companies that come and go. Many wireless hardware platforms are not actually made by the so called wireless vendor. There are a handful of manufactures that OEM their wireless bridge equipment to other companies that put their label on it, change the graphics on the software and call it their own. The problem is who really knows the engineering behind the microwave radios and who can provide quality support for it. A lot of the wireless bridge equipment is cheaply made but allows for a so called wireless manufacture to make good profit margins without having any of their own R&D and testing costs.

Have a Professional Wireless Installer to Do It Right
Again, there are a lot of factors that go into a good reliable outdoor wireless backhaul system. A good wireless installer is worth their weight in gold. No matter how good the wireless hardware is, if it isn't installed properly you'll have issues (see "Outdoor Wireless Installation Done Properly").

Service providers have adopted WiMax backhaul as a technology that they could readily deploy cost effectively to provide the last mile fixed wireless connectivity with greater bandwidth. It wasn't until later that WiMax backhaul evolved to the mobile carrier space. WiMax currently is a competing 4G technology to LTE (note: see article "WiMax Outdoor Wireless Bridges versus LTE Wireless Networks" for more detial). There are a lot of articles on whether WiMax and LTE truly compete or will end up being complimentary technologies providing different service benefits. The one issue with WiMax is because of the higher frequency bands it does not do well with penetrating obstructions like passing through walls of a building providing coverage indoors. The use of OFDM and MIMO do allow for (NLOS) non-line-of-sight wireless connectivity outdoors.

WiMax backhaul does not compete with the Wi-Fi standards, nor does it replace it. There will continue to be the need for Wi-Fi indoors and around campus environments to provide network connectivity to the LAN. WiMax backhaul will allow mobile device to get high speed internet from the carrier service provider companies that the devices are associated with (such as AT&T, Verizon, T-Mobile, Sprint, etc.).

The bottom line is WiMax backhaul is truly for service providers and mobile carriers. WiMax is not a solution for an end-user. The technologies used by WiMax have already been used for years now (e.g. OFDM and MIMO). WiMax is not a licensed microwave wireless solution that will completely avoid wireless interference. Nor will WiMax backhaul replace point to point wireless backhaul, licensed microwave links or unlicensed wireless Ethernet bridges. Because of the small channel width available currently, WiMax doesn't bring any higher bandwidth for an end user application. The WiMax 2 initiative takes more advantage of the use of MIMO and will provide more bandwidth, like wireless Ethernet bridges that use 802.11n chipsets today.

Today there are many systems that can produce higher wireless backhaul bandwidth by using standard unlicensed wireless Ethernet bridges compared to using WiMax as a wireless backhaul solution. Many manufactures have cashed in on the WiMax standard and have over sold its capabilities and what it's for to the end user market place.

If you are not a mobile carrier or a service provider (WISP), WiMax backhaul does not provide you any advantages over other outdoor wireless Ethernet bridge systems that have been deployed for many years now. To register WiMax is pretty difficult in many areas because many WISP and mobile carriers already have taken the spectrum. Note: see image below showing the areas already registered by service providers and mobile carriers in the Sacramento and San Francisco, CA area.

Is WiMax good for you? As a mobile user it will provide us great wireless backhaul throughput to our mobile devices. For end users that need another internet provider solution, especially in areas where they can't get DSL, WiMax will allow service providers to provide a high quality wireless Ethernet bridge to areas that were either technically difficult or too costly to provide connectivity to. But for Government, Enterprise, or Private networks it does nothing!

Many customers come to us and say that they need a wireless backhaul solution, but say they are waiting for WiMax. We ask, "Why?"

Many people that are not part of (or don't closely follow) the wireless backhaul, point to point wireless bridges or point to multipoint wireless backhaul, industry or the 4G mobile (LTE and WiMax) carrier industry really don't understand what WiMax is all about. Some think it's a Wi-Fi replacement. Others think it's a new technology that is going to replace all outdoor wireless backhaul, like licensed microwave links or wireless mesh networks. There is a lot of talk about the standards-based technology of WiMax backhaul. Many people do not know what WiMax is or what WiMax is not.

The term WiMax has become a marketing machine and has pushed the outdoor wireless backhaul industry into one the fastest growing technology industries. Just as the term Wi-Fi has been trademarked to the indoor wireless LAN market, WiMax is a trademarked term for a standards-based point to multipoint technology for the outdoor wireless backhaul market. WiMax in itself is not encompassing of all outdoor wireless backhaul. Note: image below is reported by the WiMax Forum as of Feb, 2010.

A General Background:
WiMax backhaul was originally designed to be a point to multipoint wireless backhaul solution for providing last mile wireless Ethernet bridges, as alternative to DSL to the home and T1 replacement to businesses. A point to multipoint wireless system consists of a base station unit ("BSU") or sometimes called an Access Point ("AP"), as a standalone or part of a cluster to provide multiple sectors of wireless backhaul coverage that provides wireless backhaul to multiple Subscriber Units ("SU"). SU's are sometimes called CPE's (customer premise equipment). This was for the WISP and telecommunication provider markets.

Part of the equation was also to make mobile devices (like laptops and mobile phones) equipped with WiMax 802.16 chipsets so they could become an actual subscriber unit, creating direct internet access through the service provider (like a giant outdoor hot spot). This would basically provide a direct wireless Ethernet bridge connection directly to a WiMax point to multipoint wireless base station array. Like a mobile phone connecting to a cellular tower.

Manufactures of outdoor wireless bridges and the WISP market realized that wireless interference is a huge issue with outdoor Ethernet wireless bridges. When you start using unlicensed wireless bridges to be a point to point wireless backhaul to unlicensed point to multipoint wireless bridges, which then provide backhaul for Wi-Fi access, in unlicensed 2.4GHz (802.11b/g/n) and 5.8GHz (802.11a/n), there is a large risk of wireless interference. At the same time many people have tried to extend Wi-Fi to outdoor environments to provide greater wireless connectivity to mobile devices, but this still needs a backhaul at some point.

WiMax backhaul was originally going to be in a frequency band away from the popular 5GHz band (5.3GHz, 5.4GHz, and 5.8GHz) used for most unlicensed wireless bridges. Unfortunately, the FCC did not allow for this. Later the FCC did open up a small piece of spectrum, 50MHz wide, of the 3.65GHz band to be used by WiMax backhaul radios. The 3.65GHz band is non-exclusive, meaning it's not a licensed microwave bridge requirement, but just a lightly regulated space that requires service providers to register the microwave wireless broadcast. The 3.5GHz band is used for WiMax backhaul wireless radios in other countries. Some mobile carriers have manufactured their own radios to operate in their licensed 2.5GHz frequencies.

For a piece of wireless backhaul equipment to be considered WiMax Certified (by the WiMax Forum^TM) it must comply with the 802.16 IEEE standards and be completely interoperable with other manufactures WiMax equipment. The problem is that there are not many devices that are truly interoperable or have been fully tested to work with one another. It's funny how many of the WiMax 802.16 standards, like OFDM, were already found in the existing product lines or outdoor wireless Ethernet bridge manufactures like Proxim, Alvarion, Motorola, and others. Most WiMax equipment is almost no different than current point to multipoint wireless systems operating in the 2.4GHz or 5.8GHz unlicensed wireless bridge frequency bands. Most use OFDM and MIMO technologies. WiMax backhaul just operates in a different 3.65GHz wireless band, which provides a smaller channel width and less data throughput.

More to come in Part 2...

An experienced IT Director once told me, "The question is not if your fiber backhaul will go down, but when will it go down." This was on a day where he experienced his fiber being cut due to some construction workers trenching up the conduit that his fiber was in during a road repair project. This happens more often than you think. Why do you think most SLA'a by a telecommunications companies are only 99.9% uptime.  

Ever question how long it takes for a telecommunications company to do a truck roll to repair a cut fiber? If it's a clean break fiber can sometimes be fusion spliced back together. In most cases where a fiber pole goes down or gets ripped out by a backhoe, the fiber gets stretch and has to be replace but cutting it at two ends and a new piece fusion spliced back in. This can take hours if not days to accomplish. What would be the cost to your business if that occurred?

This picture shows a local telecommunications companies main fiber line providing the main backhaul for a city government laying on the ground after a pole fell over. It has been like this for weeks. 

Most people don't think about the fiber once it leaves their building or know the path it takes. Most long haul fiber in established urban areas runs inside sewer lines. In rural areas fiber mostly runs along telephone poles. Ever drive down a road and see a bunch of wood telephone poles leaning from side to side? Well that might just be the fiber your network is running on.

Now let's talk about microwave communication using a point to point wireless bridge. A fixed wireless microwave link can go distances up to 50+ miles and provide data rates of 10Mbps full duplex to GigE Full Duplex (gigabit wireless). If proper wireless system design is done, a fixed wireless Ethernet bridge can provide a predictable reliability of 99.999% uptime. That's less than 5 minutes of predictable outage a year.

Microwave communication can be in the form of a point to point wireless backhaul, a point to multipoint wireless bridge system, or a mesh wireless Ethernet bridge. If a microwave radio fails it can be swapped out in the matter of minutes (provided a spare is maintained). After an earthquake or other natural disaster, a wireless system can be realigned immediately getting communications back up and running. Wireless backhaul was used after Hurricane Katrina for months before the telecommunication companies could get their fiber repaired. The biggest concern with wireless backhaul is the potential for wireless interference. Using a licensed microwave link can solve any interference concerns.

Customers that have experienced a good wireless installation typically use their point to point wireless backhaul as their primary connection and downgrade their leased telco circuit (saving them reoccurring costs) as a secondary. A wireless link also puts control back into the hands of the owner rather than relying on a telco. You can't fixed a down telephone pole because a tree branch fell on it, but you can swap out a wireless Ethernet bridge radio easily.

Does an outdoor wireless point to point bridge require Line-of-Sight ("LOS") or can a quality wireless Ethernet bridge perform under Non-line-of-Sight ("NLOS") conditions? LOS is when both antennas in a outdoor wireless bridge system must have clear visibility with one another and have no encroachments to the first Fresnel Zone. In a NLOS situation there is either limited visibility from one wireless antenna to the other (near-line-of-sight or" nLOS") caused by a Fresnel Zone encroachment or complete obstruction blocking the visibility between the two wireless antennas.

When evaluating wireless backhaul technology, whether point to point wireless, point to multipoint wireless, or wireless mesh, the possibility of radio frequency interference disrupting a wireless link poses a concern. Interference can degrade a radio system's performance and in some cases even prevent the system from functioning at all.

For the purpose of this article "Wireless Interference" is defined as a wireless signal that alters, modifies, or disrupts the desired wireless signal as it travels from the transmitting source antenna to the receiving antenna.

Typical wireless interference is a result caused by the introduction of two or more radio waves being received into the receiving antenna from unwanted radio frequency (RF) signals disrupting the system's communication. Typically these signals are at or near the same frequency as the receive frequency of an established wireless backhaul system. The source of interference is usually from other transmitters operating very close in frequency to the impacted system or caused by "multipath" which is a result of a wireless signal reaching the receiving antenna from two or more paths.

Wireless interference can cause fading or noise on the receiving wireless antenna lowering the quality of signal. Noise is often measured by SNR ("signal to noise ratio") or a relationship of the desired signal quality to the level of undesired or corrupting signal (background noise). This can make it difficult for a wireless system to clearly understand the signal (communications) from the desired transmitting wireless radio. Interference can come into the receiving antenna either in or out of phase. The wireless backhaul system has to differentiate from the signal it should be receiving from its partnered outdoor wireless bridge from the wireless signal it is hearing from the wireless interference source.

This can be thought of in terms much like that of listening to music. Even if the music you are trying to listen to is at a desired volume but there is a lot of background noise, it can be difficult to listen to the music. The background noise can drown out the signal of the desired source causing missed bits of information. In an outdoor wireless backhaul system we see this as errors caused by dropped packets and/or multiple resends having to occur. A wireless link will have a certain threshold of wireless interference it can overcome before experiencing issues. This is often referred to a wireless system's CIR or carrier to interference ratio.

For a wireless backhaul system to operate properly it must maintain a quality receive signal level ("RSL"). Wireless bridges are designed to operate with a certain level of "Fade Margin" that allows the system to operate at a predictable reliability (for most point to point wireless systems 20 to 25dB of Fade Margin is recommended, but many point to multipoint wireless and wireless mesh systems can meet the manufactures requirements at a lower amount of Fade Margin). 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.

Even if a wireless backhaul radio receiver has a good RSL the quality of the signal can be distorted by interference. A wireless bridge must have enough Fade Margin to overcome the interfering signal or have good enough CIR to function properly.

Wireless interference in regards to outdoor wireless backhaul often occurs with unlicensed wireless bridges ("license-exempt") operating in the 902-928MHz (spread spectrum), 2.4GHz, 5.3GHz, 5.4GHz, and 5.8GHz frequency bands. Note: 60GHz millimeter wave, often used in gigabit wireless backhaul, is unlicensed but is extremely immune to interference due to its inherent features of narrow beam widths and the occurrence of oxygen absorption over fairly short relative distance.

With unlicensed wireless bridges it can never be guaranteed that the wireless link will operate interference free and with any predictable reliability. Many manufactured wireless backhaul systems can help overcome interference by having a good carrier to interference ratio inherent with the hardware and by proper RF path design and wireless installation. Prior to deploying an outdoor unlicensed wireless backhaul a wireless spectrum analysis should be performed. A wireless installation company should use a proper Spectrum Analyzer to evaluate the amount of potential interfering signals in the desired frequency that is to be used (e.g. if you are deploying a 5.8GHz wireless backhaul system, as defined by the U-NII radio band of 5.725 to 5.825GHz, you would want to capture the amount of potential interference and the source of any particular wireless interference on any given channel in the 5.8GHz spectrum that will be used). A spectrum analysis will only show the amount of potential interference on the date it was taken. Other unlicensed wireless systems may be deployed at a later date that can introduce newer wireless interference.

The term "Microwave" is a broad term that covers the UHF (Ultra High Frequency with frequencies between 300MHz and 3GHz) to the EHF (Extremely High Frequency with frequencies between 30GHz to 300GHz). Licensed microwave wireless Ethernet bridge systems operate in the SHF (Super High Frequency with frequencies between 3GHz to 30GHz) and the EHF bands. Typical licensed microwave link frequencies used for wireless backhaul operate within 3.65GHz WiMax (as a point to multipoint wireless backhaul), 4.9GHz public Safety, 6GHz, 11GHz, 18GHz, 23GHz bands and the 80GHz millimeter wave E-band. 

For example: a licensed microwave point to point wireless Ethernet bridge that operates in 23GHz band will have a licensed frequency channel to transmit on and a channel to receive on. One end of the wireless link being channelized on the low end of the 23GHz band and the other end of the wireless link channelized on the high end of the 23GHz band.

A fixed wireless microwave link can go distances up to 50+ miles and provide data rates of 10Mbps full duplex to GigE Full Duplex (gigabit wireless). Licensed microwave backhaul radios provide security from the risk of interference from other RF systems. Interference can degrade a radio system's performance and in some cases even prevent the system from functioning at all. Licensed microwave wireless systems can be engineered to provide predictable reliability of 99.999% uptime.

Licensed microwave wireless radio systems are typically built and designed for long term solutions. The wireless bridge hardware is designed to provide carrier grade performance (high bandwidth and low latency). Unlike many of the Atheros (Wi-Fi) chipset based wireless Ethernet bridge systems many use, licensed microwave link systems use actual transceivers and receivers hardware that do not have high IP packet overhead. Because a microwave link is licensed and is not to inject and interference on other licensed microwave backhaul operators in the area they must have LOS (line of sight) and not cause heavy multipath. This is a common question of why licensed microwave radios don't use OFDM or MIMO and why they can't be used in NLOS (non line of sight) applications. In a NLOS wireless link application radios that use OFDM or MIMO take advantage of multipath for their connectivity.

Prior to considering a licensed microwave backhaul a wireless site survey and a proper wireless path calculation should be performed. As with any point to point wireless backhaul system a certified expert should perform the wireless installation. When an organization needs a carrier grade network connection where fiber is not an option or is too expensive, a point to point wireless licensed microwave link is a cost effective solution.

Outdoor point to multipoint wireless Ethernet bridge systems are flexible, economical, and easily deployed wireless backhaul solutions for connecting multiple remote sites to a network. Point to multipoint wireless backhaul is an ideal wireless last mile solution for interconnecting campus buildings, remote facilities, security systems, access control systems, IP video surveillance cameras, SCADA PLC's, or WISP applications as a DSL replacement. Point to multipoint wireless can also be used to backhaul wireless mesh networks. Theycan also be used to eliminate telco dependancy or to provide wireless network redundancy.

Point to multipoint wireless Ethernet bridge systems are made up of a Base Station Unit (BSU or AP) that can communicate with multiple Subscriber Units (SU's). Many systems can handle over 100 plus SU's per BSU. In most cases the BSU's provide a sector antenna beam pattern (typical is 60 degree, with some systems allowing external antenna configurations for expanding to 90 and 120 degree sector antennas). Multiple BSU's can be installed to create a 360 degree sector (like a typical cell site configuration). 

Point to multipoint wireless Ethernet bridge systems can operate in the unlicensed wireless spectrum (900MHz, 2.4Ghz, 5.3GHz, 5.4GHz, or 5.8GHz), the 3.65GHz WiMax spectrum,  or in the 4.9GHz public safety band. There are propriatery point to multipoint wireless backhaul systems operated by various telecommunication providers that operate in the lincensed microwave wireless spectrums.

Point to multipoint wireless backhauls is generally used where bandwidth requirements are generally low, such as a DSL or T1 repalcement. Recently though  many point to multipoint wireless systems have taken advantage of the Wi-Fi 802.11n chip sets and can now provide wireless bandwidth up to 300Mbps aggregate throughput. Note: the actual throughput at any given SU is determined by the number of SU's connected in the system and the network configuration.

Some of the better point to multipoint wireless systems use OFDM (Orthogonal Frequency Division Multiplexing) to provide better near and non line of sight ("NLOS") connectivity. The newer 802.11n chip set systems also take advantage of multipathing by incorporating MIMO (2x2 or 3x3) to give even better NLOS capability and higher bandwidth. The range of a point to multipoint wireless backhaul can extend as far as 10 miles with clear line of sight ("LOS"), by using high gain directional antennas connected to the SU's. The optimum performance though of most point to multipoint wireless is in the 1 to 2 mile max range. NLOS applications need to be closer to the BSU / AP in order to have adequate system gain. 

There are a lot of manufactures that offer point to multipoint wireless Ethernet bridges. Some manufactures have been in the point to multipoint wireless arena for many years. Proxim with their Tsunami MP.11 series (5054-R which is a tri-band 5.3GHz, 5.4GHz, or 5.8GHz system, MP.16  that is a 3.3GHz, 3.5GHz, or 3.65GHz licensed WiMax system, and their newer high bandwidth MP8100 series), Motorola with their Canopy wireless (their newest is their Canopy 400 series that operates in the 5.4Ghz and the PtMP320 WiMax), and others such as: Alvarion, Firetide, Trango, Solectek and BelAir. Some of the newer players include FluidMesh (which specializes in wireless video backhaul and wireless mesh), Ubiquiti,and InscapeData.

When designing a point to multipoint wireless Ethernet bridge system it is highly recommended to perform a wireless site survey and a spectrum analysis. All systems regardless of how good they are have their limitations. The biggest source of failure we come across is unrealistic expectations of performance. Any organization thinking of deploying a point to multipoint wireless system should consult a professional wireless integration company that has a lot of experience designing and performing outdoor wireless installation. 

Point to point wireless Ethernet bridges, also known as fixed wireless backhaul, are becoming extremely popular among organizations across all vertical markets. Once used only by the large telecommunication companies, wireless Ethernet bridges are being implemented by everyone, from federal, state, county, and local governments, utilities, health care organizations, agricultural industries, and even the private commercial sectors. 

Wireless backhaul is an ideal complement or complete replacement to leased lines and fiber. Whether the requirement is to link the data and voice networks between individual buildings or link networks across large distances, organizations are increasingly turning to point to point wireless networks, both licensed microwave links and unlicensed wireless backhaul, as the preferred solution. Point to point wireless backhaul provides several advantages over leased lines:

• Increased Bandwidth - With all the applications that are now driven across the network, IT departments are requiring more bandwidth across their network infrastructure. An outdoor wireless Ethernet bridge can provide true Ethernet throughput up to GigE Full Duplex (using gigabit wireless links).
• Lower cost of installation and no recurring costs - Probably the number one driver for turning to outdoor wireless backhaul is the tremendous ROI point to point wireless bridges provide. On a 100Mbps Full Duplex wireless backhaul link the typical ROI is about 3 months. This is compared to a leased  DS3 at 45Mbps. So you can get over double the throughput and eliminate any reoccuring operational costs almost immediately. The wireless cost reduction savings can be even greater when compared o the cost of installing fiber networks.
• Last mile connections - In many cases, organizations such as government or utilities who maintain multiple sites, just can't get their required bandwidth out to remote locations. Sometimes the best a local telco can provide is a T1. Point to point wireless can reach up to 50+ miles (if designed and installed properly). Where once you could only get a T1 circuit, you can now get 100Mbps Full Duplex up to GigE  (gigabit wireless) throughput, better known as wireless last mile.
• Quick installation- A typical point to point wireless backhaul can be installed in a couple days. I always recommend using industry professionals that have a lot of experience (see my article "Wireless Installtion Done Properly").We've talked to a lot of clients that have waited over 6 months to have their telco provision a simple circuit. This is especially true when compared to fiber installations that can takes years to gain right away access and time it takes to trench conduit paths.
  
• Reliability - Wireless backhauls designed and installed properly can provide 99.999% predictable reliability (see my article "Is Wireless Reliable"). Most telco's only provide a SLA of 99.9% uptime. In many cases where a client has installed wireless backhaul, like licensed microwave or millimeter wave gigabit wireless, for fiber redundancy we have seen the client actually convert over to using the wireless point to point backhaul as their primary and down grade their fiber connection as their redundancy. This is because the wireless backhaul typically provides a more direct path (less routing in the case of leased circuits) and is cheaper to maintain.
  

Point to point wireless Ethernet bridges can be used by any organization that has more than one facility that they need to connect to. There is a multitude of products in the market, both licensed microwave links and unlicensed wireless Ethernet bridges, that can solve many connectivity issues. Th price of wireless backhaul has come way down in price and is more affordable than ever. The quality of outdoor wireless backhaul is better than most other methods of connectivity.

The main reason more organizations haven't turned to outdoor wireless backhaul is either it is just not feasible do to their locations or a lack of education on what can be done with today's technology. The first step is to get a Feasibility Study by a qualified outdoor wireless vendor. A good wireless integrator can outline the best solution and the cost benefits.

Proper outdoor wireless installation is the most important element of a wireless backhaul system. Over the past decade I have troubleshot hundred's of wireless backhaul networks and 95% of the issues I have seen are due to improper wireless installation.

Many would argue that choosing the right outdoor wireless bridge equipment is the most important. I would agree that there are both good and bad outdoor wireless backhaul equipment on the market, but for the most part the majority of wireless backhaul manufactures build pretty reliable radio hardware. The biggest difference comes between Carrier/Enterprise grade (higher end, low latency, microwave equipment that typically have a 20+ year shelf life) and Value Line equipment (typically under $5K and using 802.11b/g/a/n chip sets). 

Others would say that proper wireless network design and choosing the right technology, e.g. licensed microwave links or unlicensed wireless backhaul systems, is the most important. There are pluses and minuses with both systems, such as: potential wireless interference on unlicensed wireless backhaul systems or the need for clear line-of-sight with a licensed microwave link. Both systems if installed properly can provide reliable networks. Proper wireless engineering will produce the optimum  wireless network design using the appropriate equipment.

Even with the best wireless network design and best outdoor wireless backhaul equipment on the market, improper wireless installation will prevent a wireless backhual network from truly working to its potential. Many times we hear clients say the system worked fine when it was first installed but it has degraded over time. This can be caused by many issue. There was no interference when the system was first installed. Trees or other obstructions are now in the path, either creating a complete Fresnel Zone blockage or partial encroachment on the first Fresnel Zone. Antennas could have come out of alignment. Cabling and connectors could be weathered or damaged. The list goes on. Just like a race car, it must be built properly and maintenanced to work optimally. 

Many outdoor wireless bridge systems we troubleshoot lack proper materials for cabling, mounting, and weather proofing. Over time these systems get effected by the weather and slowly degrade. Systems that are not weather proofed correctly can get damaged over time by water getting into the connections or cabling. Improper mounting can cause antenna systems to come out of alignment. Systems installed with out the proper amount of fade margin can also have periodic issues with weather (see my article "Does Weather Effect Wireless").

Wireless backhaul, whether you are talking about wireless mesh, WiMax, point to multipont wireless, or point to point wireless backhaul, systems can function with extreme reliability and predictability if installed correctly. The mobile wireless carriers take this matter critically and waste no expenses on ensuring their systems are installed properly. Any down time can cost them tens of thousands of dollars. The craziest thing we see is organizations that are willing to rely on wireless technology for their primary connectivity but pinch pennies by choosing the cheapest and many times least experienced installation companies. Worst is when a manufacture convinces and end user with little to no experience installing an outdoor wireless bridge that they can do it themselves.

The best wireless installers are those that have a lot of tower installation experience. They typically install systems to last for many years. They also don't want to lose revenue having to come back and climb a tower again to repair a bad installation. Even though many of the outdoor wireless systems seem straight forward or easy to install based on the manufactures operation manual, the fact remains that outdoor wireless installation is a skilled trade and best performed by professionals with years of experience. You can change the oil in your high end sports car but that doesn't mean you should!