As the nation braces itself for hurricane season, it’s hard to forget the devastation of recent years – Andrew, Dennis, Rita, Wilma and, of course, Katrina. These names are synonymous with images of disaster and devastation that are indelibly etched in our minds. The National Hurricane Preparedness Week last May culminated in the message to prepare ourselves for another summer and fall of unpredictable and, possibly, severe weather. During this next hurricane season, it is natural to ask, “Just how prepared are we this time around?”
Regardless of the answer to that question, we all know now that in the event of a major storm, communications networks in the affected areas will be under siege. What most people don’t know is that wireless microwave networks are inherently less vulnerable and more reliable than their landline network counterparts. Given that cable of any type is a solid medium, landline networks must be continuously connected between termination points; consequently, they are extraordinarily vulnerable to the extreme conditions of wind, rain, flooding, ground movement, and falling or flying debris that hurricanes bring in their path.
First responders often turn to microwave to restore communications because it can be installed within hours, fully restoring voice, video and data communications. This article will analyze the benefits of deploying microwave technology to restore communications capabilities in disaster recovery scenarios.
Restoring Communications Quickly
Disasters can wipe out most or all voice and data communications for citizens and government agencies alike. Wireless communications used by public safety agencies and mobile phone service providers can be restored fairly quickly — normally within hours after dispatching crews to the affected sites. Restoring landline communications, however, can take days due to the need to find and fix the damage. Often, such repairs require heavy construction equipment.
Following any disaster, a central command center is usually created as a first step in the recovery effort. The command center’s main purpose is to support emergency response personnel but it may also have a role to play in restoring communications for the public. Telephone and Internet services are critical for a population that is desperate for news or instructions and that may be struggling to reach or reunite with family members.
In these urgent situations there is only one technology capable of restoring communications quickly: microwave backhaul. Wireless networking technology is available in many forms but microwave backhaul is preferred for its extended range and high bandwidth, making it capable of supporting both voice and broadband data communications. Microwave backhaul equipment is straightforward to install and configure and, without dependencies on physical infrastructure, there are no obstacles to deployment.
In the central command center scenario, the initial topology of the network is hub and spoke, with the number of point-to-point or point-to-multipoint spokes growing steadily as more locations are brought on-line. Such a topology makes it important to place the command center at a location with good line-of-sight visibility across the entire affected area. Such a configuration, however, can incur a crippling problem: self-interference.
Interference, in radio frequency (RF) parlance, exists whenever one radio system receives a signal from another system operating in the vicinity on the same channel. There may be no intention to have these two (or more) systems communicate directly but each inevitably receives the other’s transmissions, which then corrupts desirable signals being received. Interference is typically managed through a combination of spectrum allocation, channel selection and transmit power management. Self-interference is a special case of interference that occurs when multiple systems that are intended to communicate with one another attempt to do so at the same time. Imagine a meeting where everyone is trying to talk at once; that’s self-interference.
There are several techniques used to mitigate or eliminate self-interference but one involves a combination of spectrum management and synchronization of all transmissions on a common channel. Consider the relatively simple case of a command center with 10 point-to-point links with remote sites that must operate on multiple channels to achieve the throughput required. Even with a judicious choice of channels, some will inevitably overlap. But by synchronizing the time during which each point-to-point pair communicates, there is no chance for any self-interference between or among pairs. Although synchronization may appear to degrade throughput, it actually achieves the opposite by eliminating the need to retransmit information corrupted by interference.
In addition to synchronization or some other effective means to mitigate or eliminate self-interference at the centralized command center hub, any microwave equipment used for disaster recovery should have the following capabilities:
- Operation in the license-exempt 2.4 GHz and 5 GHz bands to enable immediate deployment
- Spectrum management that is flexible/tunable enough to effectively mitigate external interference
- Support for both data (Ethernet) and voice (Time-Division Multiplexing or TDM), in their native modes, enabling agencies to share both data and video images, and ensure voice communications are fully restored
- Advanced modulation techniques that maximize the bandwidth available for voice, data and video surveillance traffic
- The ability to provision bandwidth asymmetrically to optimize traffic flows, especially for “lopsided” applications such as video surveillance (with most traffic travelling upstream) and Internet access (mostly downstream)
- A requirement for minimal technical expertise and a simple initial configuration process to facilitate becoming operational as quickly as possible with available staff
- And last but certainly not least: carrier-grade five-nines reliability for dependable operation
Being Fully Prepared
In anticipation of future disasters, there are three ways organizations can become better prepared. The first and most obvious preparatory step is to arrange for ready access to a sufficient inventory of equipment that will be required in the recovery effort, including microwave bridges, antennas, mounting hardware and generators. Such an inventory likely already exists on a regional and/or statewide basis but it is prudent to ensure at least a minimum supply at the local level, as well.
The next two steps provide benefit both in normal times and during disaster recovery efforts: deploy at least some permanent microwave links to replace or supplement landline communications; and equip mobile command centers with microwave capabilities. Both afford cost-justifiable benefits year-round, and each provides a head-start on the disaster recovery effort.
Permanent microwave installations have a major advantage over landline networks, whether copper- or fiber-based: better immunity to damage with faster recovery times. Sensitive electronic microwave equipment can be protected indoors, leaving only external antenna to be reoriented, repaired or replaced after a disaster. Nothing in between can be damaged or destroyed because, quite simply, there is no “in between” with wireless communications. Wired networks, by contrast, require full end-to-end continuity and can be quite complex with intermediate nodes, cross-connects, electronic switching or routing, and other functions all subject to damage or failure in adverse conditions.
Most public safety agencies report another major advantage of microwave communications: full control over the infrastructure. As indicated above, landline networks rarely consist of a “home run” point-to-point wire safely buried in underground conduit. Portions of the end-to-end wired network are often under someone else’s control, such as the local telephone company or an Information Technology department that serves multiple government agencies. A microwave system, by contrast, is fully self-contained and, therefore, fully self-controlled.
Mobile command centers are now routinely used for incident response and can also play a similar and vital role in disaster recovery efforts. Most existing mobile command centers are equipped with narrowband radio communications and some even have satellite links. Microwave systems supplement the former and can replace the latter with broadband communications delivering 50 to 200 megabits-per-second of bi-directional throughput – and can do so without the problematic delays associated with satellite links.
Broadband bandwidth has become a requirement for many of the new applications mobile command centers must support. For example, live video feeds are now used by officials at the headquarters to gain situational awareness of the events unfolding at a disaster scene. And videoconferencing with whiteboarding or other collaborative work applications are being used to coordinate multi-agency response plans. Narrowband communication systems simply don’t have the throughput necessary to support these and other bandwidth-intensive applications.
To implement mobile command, both the mobile vehicle(s) and the office(s) are equipped with a microwave bridge. Note that there can be as many vehicles and office sites as necessary to adequately cover the jurisdiction. The more office sites (police or fire stations, other government buildings, or special hill-top or high-rise towers), the better the coverage. Each mobile command center merely orients its directional antenna to the nearest site or, alternatively, uses an omni-directional antenna to automatically find a site within range. The multiple stationary sites likely all have a backhaul link to a centralized command center and, as explained above, there are advantages to making these links microwave links, as well.
For both permanent links and mobile command centers, consider obtaining a license from the Federal Communications Commission in the U.S. for operation in the 4.9 GHz spectrum specifically allocated for public safety. The application and approval process takes time and use must be coordinated with multiple agencies across adjacent jurisdictions. The process takes far too long to postpone until a disaster occurs but with a license already in effect, use can be expanded as needed. Note that certain restrictions may apply in some areas for permanent infrastructure and operation in airplanes or helicopters, so these applications may still need to utilize the unlicensed 2.4 GHz or 5 GHz spectrum bands.
Conclusion
When it comes to restoring critical communications, microwave systems simply can’t be beat because they have no strings attached — literally and figuratively. Literally, between antennas, there is nothing but air — and potentially lots of it with some microwave systems able to operate at up to 30 miles or more. Figuratively, there is virtually no limit to the deployment possibilities. Full communications with mobile command centers and first responders can be re-established almost immediately. Special response centers can be erected quickly in areas where the recovery needs are greatest. Mobile service providers can rapidly restore critical cell sites and backhaul traffic from these sites to the nearest surviving link in the Public Switched Telephone Network. An ad-hoc Wi-Fi network can be set up to give everyone in the vicinity temporary Internet access.
Without wires, it is possible to begin restoring communications without delay. Yes, some preparation and a minimal amount of training on RF technology and the specific equipment being used are required but the advantages are compelling, especially with a system capable of concentrated, high-speed and long-range backhaul of both voice and data traffic. It is equally important to note that these advantages are now available at a remarkably low cost. Compared to leased lines with their recurring monthly fees or trenching to lay fiber optic cable, microwave communications delivers the lowest cost per megabit-mile available in the industry today. Fast (both to install and during operation) and affordable. What could possibly be better in any disaster recovery situation?
Mark Davis is the senior director of product marketing at Exalt Communications. Davis has more than 14 years of wireless and telecommunications industry experience in a wide range of marketing, business development and sales roles.
"Appeared in DRJ's Winter 2009 Issue"
