Emergency communications support
Communications departments internal to government structures are getting serious about their role of providing emergency communications to “customer departments.”
Many forward-thinking (and usually better-funded) communications departments have been slowly building their emergency resources for years.
Even the late entrants have begun to develop some kind of plan that meets customer expectations within financial and technical constraints.
Level of support — When developing an emergency response plan with the customer, the level of support the customer needs and can sustain must be clearly defined. It could differ greatly from agency to agency.
Counties with a large tax base will be able to provide more, compared to a small municipality. Support services may range from handing out fresh batteries for portables to offering wide-band public safety network access via microwave for voice, data and radio applications.
Final authority — You have to establish who within the customer department has the authority to call for deployment of the emergency equipment and support team. Because emergencies often occur at inconvenient times (such as after hours), false rollouts on overtime can be expensive and disheartening to the support team.
Command officers at the scene of the incident might have a different perspective than officers at headquarters. While HQ management calls for emergency support deployment, authorities on-scene may want to clear the area and keep things as uncomplicated as possible.
The last things they might want to deal with are those they feel they don’t understand or need (such as communications technicians with their vehicles, trailers and other equipment).
Specifying limitations — Be sure the customer understands the inherent limitations of the support equipment.
For example, if mobile microwave equipment is transported to a fire staging area, the fire department staff has to be made aware of the requirement for a line-of-sight path from that location to another microwave site within their network.
They need to know that placement of the support equipment is critical and, once established, it cannot be moved without disrupting communications.
Broadband: Microwave it
If a line-of-site path does exist between the incident location and a coordinate microwave site, mobile microwave equipment offers a highly useful resource.
Microwave radios, multiplex and two-way equipment can be housed inside a truck, van or trailer. Various configurations of microwave antenna masts can be attached to the side or roof of the vehicle to establish a temporary link to the coordinate site.
If the equipment is mounted permanently inside the vehicle, a trailer is often the best option.
Motored vehicles can be more expensive, and they require additional maintenance.
An on-board air-conditioner and standby generator allow the vehicle to be cool and self-contained.
As a practical matter, many small generators intended for motor homes or trailers aren’t designed to operate non-stop for days or a week at a time. Because an emergency may require communications support for an extended period, arrange access to a large, continuous-duty generator as soon as the deployment is ordered.
Many large customer departments such as fire department and law enforcement agencies have this type of heavy equipment on-scene or available.
The least expensive option for the microwave radios include unlicensed, spread-spectrum units for the 2.4 GHz or 5.8 GHz bands. Different manufacturers and models offer variations in system gain and bandwidth.
These compact, lightweight radios and antennas have no special reputation for providing long-term, reliable communications. But emergencies are not permanent; thus, many consider these units to be an acceptable, cost-effective option.
A more reliable but expensive alternative is a licensed, fixed-frequency microwave radio. If the budget allows, redundancy could be used for even greater reliability.
During an emergency deployment, the best position available for the microwave trailer and antennas may provide a less-than-optimal path. Loss caused by trees, terrain features or other obstructions, along with unwanted reflections, can reduce the signal at path endpoints.
Path length is also a limiting factor and an important consideration when evaluating the various types, makes and models of microwave radios referenced to support expectations.
Greater system gains are achieved with narrower bandwidths. A single T1 spread-spectrum radio may have an advertised path length of 60 miles, where the DS-3 version is limited to about 15 miles.
If the customer department requires only a single T1, there would be no good reason to go wild with bandwidth while imposing severe limitations on path length.
Figure 1 shows how the signal flows from a public safety headquarters to a remote incident location.
In this example, T1 and/or discrete two-wire (2W) and four-wire (4W) circuits dedicated for emergency use can be connected into the communications department central office (CO).
Once at the T1 transmission level, the emergency traffic is cross-connected through a DSX panel into the appropriate microwave link. The traffic must be routed to the remote microwave site that provides optimal line-of-sight communications to the incident location.
Sufficient bandwidth must be made available on the existing microwave network to allow for the additional emergency circuits. If not, it will be necessary to prioritize and “bump” existing traffic for the sake of the emergency.
When the deployment order is given, one mobile microwave vehicle is moved to the incident location, and the other is taken to the optimal remote microwave site. The mobile equipment at the microwave site is connected into the existing public safety network through a DSX panel.
The mobile equipment at the incident location connects to customer equipment that can be housed either within the mobile microwave vehicle or in additional mobile vehicles (such as planning and strategy trailers) provided by the customer.
If the emergency deployment configuration resembles that of Figure 1, the communications support staff is broken up into three groups:
- one at the public safety HQ/communications department CO location
- one at the optimal remote microwave site
- one at the incident location.
If emergency circuit connections between the HQ and the CO are accomplished in advance and left ready for use, human resource requirements are usually least at that location.
More than one individual should be assigned to the remote microwave site for safety reasons because this involves transport of heavy equipment in often less-than-optimal locations and environmental conditions.
For the same reason, more than one should be assigned to the incident location.
Additionally, since work at the incident location involves direct interaction with the customers, it is helpful to have one of the on-site support staff be either a working supervisor or senior technician. This provides the customer with a “representative” of the communications support team and their department.
Wise allocation of human resources in the initial deployment stage will help ensure adequate support later in the form of fresh replacements as the incident plays out.
Waiting in the wings
One challenge of retaining emergency resources is making sure they are working and ready to go when needed.
Periodically verifying the operational status of all support equipment can be an unwanted task, particularly if it involves a considerable amount of time to set up and tear down.
An alternative is to keep the equipment running while waiting for deployment.
Most microwave networks employ an alarm monitoring system that automatically polls each remote communications site one-at-a-time. Any facility or equipment alarms are registered at a centralized maintenance location.
When connected into this system, alarm points within the mobile microwave vehicles also can be monitored.
Figure 2 shows an example of two microwave trailers (one for each end of the emergency link) stored side-by-side and left powered-up. The radios in the trailers communicate with one another through a transmission line and an in-line RF attenuator. The level of attenuation is set so that the radios are within just a few dB of the receiver Bit-Error-Rate (BER) threshold.
If transmit power or receiver sensitivity degrades, a corresponding microwave radio alarm will be generated and registered at the centralized maintenance location. Facility alarm indications such as an indoor HIGH TEMP alarm can be used to monitor operation of the trailer air conditioner.
Continuous T1 performance testing is accomplished by leaving a T1 test set running in one of the trailers. The test set injects a primary rate bit pattern into the associated microwave radio. The T1 signal is looped back in the other trailer such that the test set can receive its own recovered pattern, less significant problems, such as dribbling bit errors, to be identified.
Public concern has become heightened regarding government agency preparedness for disaster or emergency response.
Feeling the pressure, many communications departments are beginning to discuss levels and methods of support more seriously with customer departments.
With available funding, customers can find a practical broadband solution to the challenge of providing emergency communications support through the use of mobile microwave equipment.
Jeff Ashley is a communications technician and writer based in Ventura, Calif.
