Alpha Omega Wireless Blog

Wireless backhaul, also known as fixed wireless bridges, has become a standard means of creating a microwave communication between locations; whether building to building, last mile wireless to connect remote locations to a network presence, or for connecting devices like IP video cameras, access control, SCADA devices, client devices, or phones to networks. Wireless backhaul can be deployed in several network configurations.

A point to point wireless bridge is when only two microwave radio ends are bridged together to create a single wireless network path. Point to point wireless links are an ideal complement or replacement to leased lines and fiber. A point to point microwave link is used to create a wireless bridge network between two buildings to connect LAN connectivity or for creating a microwave link between two towers to join two WAN network segments together across large distances. Point to point wireless bridges can be licensed microwave links or unlicensed wireless Ethernet bridges and can provide throughput as low as 10Mbps up to GigE full duplex (with gigabit wireless).

Licensed microwave links used for point to point wireless backhaul operate in the 6GHz, 11GHz, 18GHz, and 23GHz frequencies and provide true full duplex wireless Ethernet and TDM communications. Licensed microwave links can provide up to 366Mbps full duplex or 732Mbps aggregate throughput using a single radio unit. Dual radio units can be combined on a single antenna to provide double the bandwidth and complete failover redundancy.

A few exceptions are the 24GHz microwave links that are unlicensed but work just like the licensed 23GHz microwave links and provide the full duplex connectivity and the 60GHz millimeter wave systems that provide up to full duplex gigabit wireless backhaul. There is also the 80GHz millimeter wave E-band that is a registered frequency that is used to provide gigabit wireless links. Unlicensed point to point wireless Ethernet bridges typically communicate in TDD because they use the same frequency channel to talk and listen. They can provide up to 300Mbps aggregate throughput.

Point to multipoint wireless Ethernet bridges use a hub spoke configuration using a Base Station Unit ("BSU" or "AP") that communicates with multiple Subscriber Units. This is similar to a cellular network where multiple mobile devices talk back to a cell tower location. Point to multipoint wireless backhaul systems are ideal for interconnecting campus buildings, security systems, control systems, IP video surveillance cameras, WISP applications, integrating remote business sites, or installing last mile connections. Point to multipoint wireless bridges operate in the unlicensed wireless frequency bands of 900MHz, 2.4GHz, 5.3GHz, 5.4GHz, or 5.8GHz. Point to multipoint wireless Ethernet bridges can provide up to 300Mbps aggregate throughput.

Wireless mesh configurations are used to create a wireless network where a radio node can communicate with two or more other wireless mesh nodes. Wireless mesh networks offer great redundancy. If one wireless mesh node can no longer operate, all the other wireless mesh nodes can still communicate with each other, directly or through one or more intermediate outdoor wireless bridge links. Each wireless Ethernet bridge link can send and receive messages in a wireless mesh network. Each link also functions as a router and can relay messages for its neighbors. Through the relaying process, a packet of wireless data will find its way to its destination, passing through intermediate links with reliable communication.

Mesh wireless backhaul networks are typically configured in a star topology or can be in a daisy chain configuration. They are used a lot in networks for wireless video backhaul and municipal wireless networks. Wireless mesh radios operate in unlicensed wireless backhaul frequencies like that of point to multipoint wireless bridges and can provide up to 300Mbps aggregate throughput.

Is there still value in deploying a city wide outdoor wireless Wi-Fi network? Every day there the number of people that use mobile devices that are Wi-Fi enabled continues to grow. The demand for high speed connectivity to the internet is in high demand. So there is definitely a business case for it.

Many cities have tried a wireless installation to provide complete city wide Wi-Fi connectivity and have failed. In many cases the city governments, that have no staff trained and experienced in outdoor wireless backhaul and outdoor Wi-Fi systems, that tried to deploy the outdoor Wi-Fi technology rather than an outdoor wireless backhaul or mobile carrier provider, that does have experience and knowledge in mass deployments of RF and microwave communications.

Three major reasons why many of the outdoor Wi-Fi attempts failed are because there was no clear business model, projects were attempted without using highly skilled outdoor wireless installation and wireless engineering integrators, and a complete lack of understanding in the costs associated with deploying and maintaining an outdoor Wi-Fi system. Technically, it is very difficult to deploy the amount of wireless access points needed to provide complete RF coverage without causing self wireless interference. It can be done but so often wireless engineering was an afterthought when it should have been the first step.

On the other hand, WiMax backhaul promises high speed wireless connectivity to mobile devices and has already been deployed around the world with great success. WiMax backhaul, as a standard, was originally designed for outdoor wireless connectivity where Wi-Fi is a standard for indoor wireless connectivity. WiMax can cover much farther distances, requires much less infrastructure, is cheaper to deploy, wireless installation is easier, and is more cost effective to maintain. The problem is that there are not a lot of devices that are equipped with WiMax chipsets yet.

Over the years, there have been a lot of quality wireless manufactures that have come to market with outdoor wireless communication products for either outdoor Wi-Fi or WiMax solutions. Companies like Xirrus (who probably has the strongest outdoor Wi-Fi solution) and BelAir Networks have great solutions for outdoor Wi-Fi deployments. There are many others like Proxim, Motorola, and Aruba to name a few that have outdoor Wi-Fi solutions too. Companies like Alvarion, Motorola, Proxim, and Solectek to name a few make WiMax backhaul base stations and subscribers.

For the 2012 Olympics, London has declared that they will have a city wide outdoor Wi-Fi network. The services will not be offered for free but will allow tourists to stay connected to the world during the games. It is unclear who will be responsible for deploying the Wi-Fi network and who will maintain it after the Olympics. Will the City of London sell the network to an internet provider or mobile carrier or will they become a large WISP themselves. The hopes is that they will have a solid business model and will have the network designed and the wireless installation done by a credible wireless integrator. The one thing for sure is that both WiMax backhaul and outdoor Wi-Fi technology will provide a lot of benefit to the users of mobile wireless connectivity.

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").

If you thought wireless interference among unlicensed wireless Ethernet bridge systems is bad now, just wait. What's going to cause this flood of wireless interference is the introduction of 802.11n based, OFDM and MIMO, outdoor wireless backhaul systems. Add to the mix the amount of wireless backhaul being deployed in the IP video surveillance industry.

Now with the acceptance of 802.11n chipsets there has been a mad rush by the outdoor wireless manufacturers to introduce higher bandwidth point to point wireless backhaul, point to multipoint wireless bridges, and wireless mesh systems. Why not? It's pretty amazing that you can now buy an unlicensed wireless Ethernet bridge system that can provide up to 300Mbps of aggregate throughput for under $5,000.00

So what's the issue? In my article "Wireless Interference - The Effect on Unlicensed Wireless Backhaul" we discussed how wireless interference on unlicensed wireless Ethernet bridge systems has continued to grow. The new 802.11n based wireless backhaul radios use OFDM and MIMO taking advantage of multipath, especially helpful in nlos (non line of sight) applications. They also produce a lot of multipath! They also need to use a wider channel width to obtain a higher data rate, up to 40MHz wide. Because these systems, according to manufacture specifications and marketing, can produce high aggregate throughput at an attractive price many people that didn't use outdoor wireless bridge systems are now starting to.

As more and more people get tempted with the thought of 100Mbps, up to 300Mbps providing an extremely fast ROI compared to a leased telco line, more and more unlicensed wireless backhaul will be deployed. The one thing that that people don't understand is that to get the full throughput the system must run at full modulation and channel width with limited wireless interference. This is something that the manufactures forget to mention. Because people are not controlling their RF signals by deploying so called plug and play outdoor wireless bridge systems and using wide beam antennas at full transmit power the amount of interference is going to explode.

Add into the mix the amount of wireless backhaul for video surveillance. Wireless video backhaul is a huge topic and growing industry. Each year at the popular industry trade event, CTIA, there is a growing number of manufactures displaying their unlicensed wireless video backhaul systems. Using wireless backhaul for video is a great application. But with the large number of unlicensed wireless Ethernet bridges being deployed and the amount that is done improperly the amount of wireless interference is bound to grow.

Should you consider an unlicensed wireless Ethernet bridge, using OFDM and MIMO? These types of outdoor wireless Ethernet bridges provide a great inexpensive solution. They work extremely well on challenging near-line-of-sight and non-line-of-sight applications. They also provide a great amount of throughput at a great price. If you need a true enterprise point to point wireless bridge and have line-of-sight (LOS) there is no substitution to a licensed microwave link, see "Licensed Microwave Wireless Backhaul."

The one thing to keep in mind is prior to considering an unlicensed wireless Ethernet bridge for microwave communication a wireless site survey, spectrum analysis, and a proper wireless path calculations should be performed. As with any point to point wireless backhaul, point to multipoint, or wireless mesh system a certified expert should perform the wireless installation.

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.

The one thing that most people don't understand is the industry background between WiMax backhaul and LTE wireless networks.

WiMax backhaul was originally developed by outdoor wireless backhaul manufactures as a way to provide fixed last mile outdoor wireless bridge connectivity. These were wireless Ethernet bridge players like Alvarion and Proxim (funny how many of the WiMax 802.16 standards, like OFDM, were already found in their existing product lines). Other players like Intel, who has a big stake in IP based technologies, joined the forum. The early intent, of those pushing the WiMax 802.16 standard, was to get the FCC to open up the 3.5GHz space for point to multipoint wireless backhaul. This was to serve the WISP (Wireless Internet Service Provider) market place. Part of the equation was to make mobile devices (like laptops and mobile phones) equipped with WiMax chipsets so they could become an actual subscriber unit (a CPE device) and connect directly to a WiMax point to multipoint wireless base station array.

The one major issue many manufactures of point to multipoint wireless bridges were facing was that they were also providing point to point wireless backhaul in the unlicensed wireless backhaul space and providing outdoor Wi-Fi solutions. Wireless interference is becoming a huge issue in the outdoor Ethernet wireless bridge space when you start using unlicensed wireless bridges (like 5.8GHz wireless backhaul) to serve unlicensed point to multipoint wireless bridges, which then provide Wi-Fi access in unlicensed 2.4GHz (802.11b/g/n) and 5.8GHz (802.11a/n). WiMax equipment if offered in a separate frequency band like 3.5GHz would open up a lot of outdoor wireless backhaul spectrum.

It wasn't until later that WiMax backhaul evolved to the mobile carrier space. Carriers, both fixed wireless and mobile, have adopted WiMax as a technology that they could readily deploy cost effectively to provide the last mile connectivity with greater bandwidth. The other advantage of WiMax backhaul is that IT people (that understand IP networking) can easily take part in outdoor wireless backhaul network deployments because they understand the IP networking background required for WiMax backhaul networks.

LTE was the evolution of the carrier's TDM transport to gain broadband to mobile devices. Many carriers like LTE because it's just an evolved technology of what they are already using. LTE is a natural progression from 2G / 3G and allows fall back. When a mobile device roams out of quality signal strength of an LTE (4G) network it can easily fall back to 3G or lower speed connectivity. Another advantage of LTE over WiMax is that LTE offers less wireless backhaul latency. WiMax backhaul uses a bigger overhead in packets. Many of its supporters are the manufactures that have been part of the mobile market all along.

WiMax backhaul has gained great ground recently worldwide because the equipment is very inexpensive and can be readily deployed for both fixed wireless backhaul and mobile broadband applications. WiMax backhaul equipment can literally be purchased any day of the week form a wireless installation company or wireless distributor. Most outdoor wireless installation companies have equipment on the shelf. Although LTE is a natural progression for carriers that have an existing 2G / 3G networks, countries that do not have a built out cellular network, WiMax backhaul is an easy choice to jump to.

One big difference is that LTE is solely a licensed microwave technology that carriers are utilizing their existing licensed spectrum, where WiMax backhaul is mostly unlicensed (at least in the USA with the exception of a small slice of spectrum in the 3.65GHz space). Many carriers are having the WiMax backhaul manufactures produce outdoor wireless point to multipoint radio equipment that will work in their licensed bands.