By Jed Rabe, Senior Wireless Engineer, CWNE#280, ACDX#925, ACMPV8 —
DEFINITION:
A band of spectrum which utilizes wavelengths from 30GHz to 300GHz. The wave lengths are between ten to one millimeter in length. The millimeter wave band is above the micro-wave band and is typically used for similar applications.
Background:
Recently I was involved in a project that required a network upgrade and expansion for a rail yard. The scope of the project was to provide network connectivity to several out-buildings to support the current network requirements but to also support security cameras later.
Railyards are a challenging environment as they have many buildings that support different functions. It is cost prohibitive to run fiber or ethernet to these locations as it would require permits, scheduled maintenance and other factors that would become very costly. It is also difficult to provide high throughput and reliable wireless point-to-point or point-to-multipoint connections using 802.11 due to the distances required. The railyard I worked at was a little more than a mile long! Not only that but 802.11 WLAN networks have become overcrowded, bringing channel interference issues which is not good for wireless backhaul links.
This provided me with the opportunity to implement a solution that I had not worked with before — millimeter wave in the 60, 70, and 80GHz bands. I had deployed a couple point-to-point links using the 60GHz band, thanks to Aruba Networks and their AP387, but this AP is limited to about a quarter of a mile (400 meters). I knew that this AP wasn’t the right fit for this environment. To provide the appropriate solution, I looked to Siklu who provides point-to-point and point-to-multipoint solutions within the millimeter wave bands.
Design Considerations:
Millimeter wave is a great technology for providing wireless point-to-point or point-to-multipoint communications. The millimeter wave spans across multiple bands which offers unlicensed and licensed spectrum. In the United States the FCC requires a license in 70, 80 and 90GHz bands. With a controlled medium the risk of interference is very low which makes millimeter wave very attractive for high-speed wireless communications.
Another aspect of the millimeter wave technology that is attractive is the fact that the beams are highly directional, and the beam widths are very narrow. Millimeter wave is sometimes characterized as “pencil beams” due to the small beam widths. This characteristic also helps with reducing interference for the wireless links. However, this also means that aligning the radios needs to be precise!
Millimeter wave can also provide 10Gbps link speeds for many miles! Millimeter wave may not be able provide as long of a link as micro-wave radios do, but for shorter distance and less cost, these links can provide a lot of throughput at greater distances than 802.11 WLAN links. The millimeter wave links can be described as wireless links at fiber speed.
Even with these great characteristics, there are some design considerations to keep in mind. For instance, millimeter wave must be line of sight. Due to the size of the waves, millimeter is unable to propagate through objects like 802.11 radio waves can in 2.4GHz or 5GHz bands. In fact, rain, snow, fog, and other weather conditions can degrade the RSSI enough to cause the radios to downshift their modulation to compensate for the added attenuation. This means that the throughput of the link will drop until the link is broken and communication stops.
Siklu provides a link budget calculator which helps to identify the type of weather conditions that will affect the radios in a geographical area. It will then export several calculations that displays the expected uptime of a link and what the expected RSSI of the link is under perfect circumstances. The calculator takes into consideration the radio that is selected (the band that the radio link is operating in), the distance between the radios and expected weather conditions for the area. This is a great tool to leverage when selecting the appropriate radios for the environment.
I want to reiterate the importance of line of sight. While installing the Siklu radios at this rail yard we began the fine alignment process to ensure that the radios were aligned and within +/- 4dBm of the calculated RSSI, calculated from the Link Budget Calculator. During this process we could see the RSSI drop significantly when a hand, arm, or torso was placed in front of the radio. The link would either drop so significantly that we could not maintain IP connectivity across the link, or the link would be completely down. When designing for a millimeter wave link you MUST have line of sight! There is no way around this.
One other tool that Siklu offers is a project planner that interfaces with Google Maps. This allows you to place radios at specific locations (providing you with longitude and latitude coordinates) and building your links. This provides you with a nice visual representation of the links to include with a proposal. This tool will also create a Bill of Materials used to order the equipment necessary for the design.
Siklu Radios:
Siklu offers many different radios to provide point-to-point or point-to-multipoint solutions at various distances and throughput. We will only mention a few of the radios here which were used in the deployment scenario at the railyard.
First, the long-range radio used for this deployment was the EtherHaul 1200FX series radios. This radio operates in the 70GHz band and provides up to 1Gbps (requires a capacity license). Since this radio operates in the 70GHz band, it requires an FCC registration to operate. The unique characteristic of this radio link is that it operates in FULL DUPLEX! It can accomplish this by transmitting data on one channel and receiving on another channel. The radio on the opposite end transmits and receives on the opposite channels of the first radio. In our railyard scenario, this radio link provided the primary backhaul for the network.
Second, the medium range radio used for this deployment was the EtherHaul Hundred Series (614TX). This radio operates in the 60GHz band and provides up to 1Gbps aggregated throughput over the link. This radio was used as a secondary link to provide redundancy for the wireless backhaul.
Third, the short distance Point-to-Multipoint radios used for this deployment was the MultiHaul B100 and T200 radios. Notice, the model’s name changed from Etherhaul to MultiHaul. This indicates that these radios can be used for a point-to-multipoint solution. The MultiHaul series radios also operate in the 60GHz band. These radios do not require any kind of fine alignment as they include a 90-degree horizontal and 20-degree vertical beam width. These radios provide up to 1Gbps throughput over the wireless link (requires a capacity license). The B100 unit is the base unit that provides network access upstream. The T200 units are the terminal units that connect back to the B100. Because the B100 unit can provide wireless connectivity to multiple terminal units, the B100 has a max throughput of 1800Mbps. Also note that the B100 unit can support up to 8 terminal units.
The MultiHaul devices were used to provide connectivity back to buildings with the EtherHaul radios in our railyard scenario.
Figure 3: MultiHaul B100-CCCS/T200-CCC
Using these radios, we were able to extend the network to the out-buildings which significantly reduced the cost by not requiring fiber optics being installed. We were also able to reduce the time for deployment as we were able to simply install the units, perform a firmware upgrade and quickly configure the units to provide network connectivity, all while not interrupting production at the railyard. This solution also provided resiliency for the network with a redundant path at a minimal cost increase. At the end of the project, we had a point-to-point/point-to-multipoint solution that resembled something close to the following:
The above is an oversimplification of the solution and does not include all the radio links but it is enough to provide some idea of how the links were installed and brought online. Also, keep in mind that the distance between the 1200FX radios was roughly 1 mile long!
Conclusion:
As network engineers we encounter many different challenges to provide network connectivity between buildings, floors, and sometimes a single floor! It is important to think outside the box to provide a reliable solution that overcomes these challenges. In this instance, the challenge was to provide network connectivity to multiple buildings separated by railroad tracks that would have been cost prohibitive to run fiber optic or even ethernet cables. The other challenge was the distance between buildings making it difficult to use standard WLAN point-to-point or point-to-multipoint links. Fortunately, millimeter wave was a valid solution, and we were able to leverage the distance, throughput, and minimal interference characteristics of this wireless medium. There are different vendors that provide products that operate in the millimeter band, but I was fortunate enough to work with Siklu which I found to be very reliable and easy to configure. At this point, I would consider millimeter wave for most of the point-to-point and point-to-multipoint needs I come across over standard WiFi.
Jed Rabe is a Certified Wireless Network Expert, a prestigious expert-level certification within the wireless networking professional community. In order to obtain this certification, Jed needed to first obtain the CWNA, CWSP, CWDP, and CWAP certifications; publish a number of articles; receive peer recognition and recommendation; and then be approved by the CWNE board. This certification recognizes that Jed is a wireless network professional that understands wireless administration, security, design, and analysis principles at an expert level.
