Understanding wireless communications in public safety
Concluding excerpts from a guidebook to technology, issues, planning and management for public safety communications professionals. This month: Wireless communications options.
Editor’s note: Through the National Law Enforcement and Corrections Technology Center – Rocky Mountain Region (NLECTC – RM), a program of the National Institute of Justice, authors Imel and Hart have prepared a guidebook to help both new and experienced public safety communications managers over the hurdles of system procurement and operations.
The September issue of MRT presented excerpts from Part 1 of that 135-page book concerning “Planning and managing a communications project.” Parts 2 and 3 discuss “Wireless communications technology” and “Wireless communications issues,” respectively. This month we conclude our excerpts with a look at Part 4 – “Wireless communications options,” which discusses voice system options, data system options and the latest developments in communications technology.
The target audience for this guidebook consists of those middle and upper managers who are responsible for funding and/or managing communications at their agencies, but who have little or no technical background in wireless technology. Information on obtaining a copy of the complete work appears in the auth-ors’ credit.
Weighing your options This section looks at the options public safety agencies have for wireless communications, including the purchase of their own radio components and systems. The authors also have included examples in which local governments have used commercial services.
One special case is described in which a tower and radio supplier provided radio communications to a town by entering into an agreement to use some of the town’s high-elevation real estate for commercial radio development in return for dedicated government radio systems. Examined are the many commercial voice and data services available to law enforcement, including cellular and PCS, CDPD, SMR/ESMR and data networks.
Networks are complicated. They consist of three generic components: hardware, software and middleware. Hardware consists of radios, modems and laptop computers; software is the programming that runs the radio controllers, modems, and laptop computers; and middleware is the (software) glue that interconnects all the components. Middleware must be selected that supports the required hardware and software protocols.
(c) A reminder – All radio systems should be carefully checked to make sure they have the coverage you need. If you are purchasing a new system, make sure that the supplier gives you written assurances that the system meets your needs. If you need to communicate with hand-held radios in reinforced concrete buildings, make sure the supplier knows and makes calculations taking that into account. There are independent consultants who also can perform these calculations if you need a verification check. If the radio network is already constructed, borrow or rent equipment from the supplier and make sure the coverage satisfies your requirements.
Dedicated radio systems Dedicated public safety radio systems include all radio technologies, ranging from conventional FM simplex and repeater systems to complex and expensive trunked wide-area analog and digital radio systems at all of the two-way frequencies.
There are many suppliers for public safety radio systems. Three companies, however, have supplied and continue to supply the majority of public safety radio systems: Motorola, Com-Net Ericsson, and the E.F. Johnson division of Transcrypt.
The three major companies had representatives on the Project 25 committee, which selected the first-phase digital trunked system technology standard to carry public safety communications into the next century. The Motorola protocol was selected for the first phase, and Motorola has offered its intellectual properties, royalty free, to other suppliers to allow competition. A large number of suppliers are developing systems using the new standard.
There are many other smaller suppliers of FM equipment, and some are supplying narrowband systems for the 220 MHz frequency band.
Sample vendors (c) Motorola – Motorola offers some sophisticated digital radio networks, as evidenced by its Smartzone system, which can be configured for conventional repeaters, single or multiple site trunked repeaters, and/or simulcast trunked repeaters. The company is currently upgrading the radio and dispatch systems for the city of Los Angeles.
(c) Com-Net Ericsson Critical Radio Systems – In January 2000, Ericsson announced it was selling its private radio systems operations to Com-Net Critical Communications, with the company renamed Com-Net Ericsson Critical Radio Systems. Com-Net Ericsson’s main line of equipment for public safety is its enhanced digital access communications system (EDACS). EDACSs are used in trunked repeater systems including wide-area simulcast coverage. Com-Net Ericsson has stated recently that it will begin to address and manufacture more conventional radio system products tailored toward the small law enforcement agencies around the world.
(c) E.F. Johnson Division of Transcrypt – Transcrypt offers both conventional and trunked analog and digital radio systems on all the two-way frequency bands through its LTR product line. It also offers Project 25-compliant radios for public safety requirements.
Advantages of dedicated systems – Public safety entities may generate specifications to meet their exact sys-tem needs. They have complete control of the design and operations.
– As part of the tailoring, the priority of use may be established within the entity.
– Combined dedicated radio systems (i.e., shared with other communities) may save considerable investment and still preserve the tailoring at a more reasonable cost per agency.
Disadvantages of dedicated systems – The capital outlay may be quite high and prohibitive for a small- to medium-size community.
– The owner of the system must pay for all maintenance and improvements.
Cellular and PCS radio Many law enforcement agencies are already using cellular radio systems in addition to their dedicated radio systems for the transmission of voice messages. Almost all urban and suburban areas in the United States are covered by one or more cellular providers, although in sparsely populated areas, coverage may not be available.
In addition, the construction of personal communications systems (PCS), most of which are cellular systems in the 2GHz band, has proliferated in higher-density areas, and these systems are competing directly with 800MHz cellular communications systems. There are as many as nine different technologies being used by different suppliers of cellular and PCS radio. So, once a user has chosen a company and handsets, it may be stuck with that supplier until the end of the contract.
System coverage System coverage is a major consideration in selecting a cellular system or PCS. The first thing to do when you think you want cellular or PCS service is to identify the suppliers in your area. Contact them or go to the Internet and obtain a coverage map for your area for each supplier, as well as its prices and terms. Borrow phones from suppliers and test different systems, where available, to determine which one covers your needs best.
Pricing With the advent of increasing competition in many areas of the United States, the pricing packages are changing rapidly, so you will need to get the latest information at the time of purchase. Law enforcement may have an advantage in negotiating with suppliers because it is a highly visible public agency.
Sample vendors (c) AT&T Wireless Services – AT&T has cellular and PCS licenses for most of the states in the country. However, it is not licensed in Montana, North Dakota, parts of Minnesota, Wyoming or Texas. To determine if AT&T does provide coverage in your area, it is best to get the actual current coverage maps showing the specific area of interest. (Most can be obtained from the AT&T Web site, www.att.com.)
(c) Sprint – Similarly, Sprint has almost all of the nation licensed for PCS coverage, but it is building its network in the highest-density areas first, where it can most easily attract a large number of subscribers.
Advantages of cellular/PCS Radio – Where there is coverage, subscribers should be able to contact any field or fixed personnel, regardless of agency or jurisdiction (i.e., it supports a high level of interoperability).
– Pricing is competitive in most areas.
– Service can supplement dedicated radio communications.
– With digital protocols used by many cellular/PCS radios, listening by unauthorized scanners is limited or eliminated.
– Under certain emergency conditions, some vendors can supply portable cell sites to the scene to provide for increased cellular radio traffic.
Disadvantages of cellular/PCS radio – Coverage is limited or non-existent in sparsely populated areas.
– Most systems competing in local areas use different modulation techniques, so a particular hand-held phone may not work with any other system.
– In some locations, cellular radio sys-tems are prone to overload in emergency situations.
Voice – SMR/ESMR When the FCC wrote the trunked radio rules, it provided for licensing specialized mobile (trunked) radio service companies (SMRs) to provide leased two-way mobile radio service. As time passed, with the development of digital radio trunking systems called “enhanced specialized mobile radio” (ESMR), greater spectrum efficiency was achieved. These systems use the 800MHz and 900MHz portions of the radio spectrum.
Many SMR/ESMR systems are extremely reliable and are well suited for use by public safety agencies. SMR/ESMR systems work well for radio dispatch and for interconnection to the public telephone system. Offerings are usually competitive with other available mobile radio services.
Sample vendors (c) Nextel – One ESMR provider with national coverage is Nextel (although, like the cellular/PCS providers, its presence is spotty in small-population areas). Nextel’s system uses Motorola’s IDEN equipment. The system is quite similar to that of cellular radio; however, in addition to making phone calls, Nextel offers paging and dispatching services whereby a subscriber may call another mobile station or a group of stations on company-owned repeaters. The service allows for full-duplex communications. Thus, one device gives you the capabilities of both a cellular phone and a hand-held radio.
(c) Lower Colorado River Authority – The Lower Colorado River Authority (LCRA) is a conservation and reclamation district in Texas that monitors and controls portions of the Colorado River. LCRA has an extensive Com-Net Ericsson EDACS digital radio system with extra capacity available for leasing to other utilities and, most recently, to public safety organizations.
SMR/ESMR advantages – Capital expenses are amortized in monthly invoices and spread over the total customer base of the company.
– Many modes of operation are available by using this service, as discussed above.
SMR/ESMR disadvantages – The agency must purchase special telephone/radio units.
– Prioritizing transmissions for public safety agencies is generally not provided at this time. In case of an emergency, public safety agencies may not be preferred customers.
– Flat-rate billing may not be provided. Rates are commonly based on a fixed fee plus usage.
– The service may not be available in your area.
Wireless data systems Regardless of the type of radio system used for data transmission, software also is required for these systems to work properly. Software on the laptop (usually licensed on a per-PC basis) and software back at the main computer site must both be present and be able to talk to each other over whatever backbone you select. The effective speed of your data network will depend heavily on the efficiency of the software used to pass the data back and forth.
Cellular digital packet data (CDPD) If you are planning on transmitting data for dispatching, for license and criminal record information, or for writing accident reports, CDPD may be the technology to use. CDPD uses packet radio hardware and software and is regularly used with laptop computers or mobile data terminals. CDPD may be available from a cellular supplier in your area. Some CDPD suppliers with interesting offerings are described in the following section.
Sample vendors (c) AT&T Wireless – AT&T Wireless Services developed a white paper in 1997 titled “CDPD for Public Safety,” outlining the use of CDPD by law enforcement agencies. The document includes information on the wireless environment applicable to public safety dispatch users and the economics for CDPD usage. It compares CDPD with the other options available to public safety organizations for the transmission of wireless mobile data, including government-owned, voice- and data-dedicated private mobile radio systems, SMR trunked radio systems, and public networks.
(c) Bell Atlantic Mobile – Bell Atlantic Mobile offers its Airbridge service using CDPD to access the Internet as well as corporate or local government internal computers for database inquiries. The Metropolitan Police Department of Washington uses Airbridge, and patrol car personnel regularly access criminal databases and motor vehicle records using laptop computers.
(c) GTE Wireless – GTE offers an “Intelligent Patrol” turnkey package that bundles together hardware (including a ruggedized laptop computer and modem), software and service, training, installation, integration and maintenance with a leasing option. The laptop computer can handle inquiries to criminal databases, warrants, and mug shots. Besides retrieving information, laptops can also dispatch using CDPD. GTE offers usage-based pricing on its service.
Advantages of CDPD – The service is available in many areas in the United States and is ideal for applications involving short, rapid data exchange. Police officers can readily access local, state, and national databases from their patrol cars.
– The capital expenses are only for computers, modems and software. The communications network is provided by the cellular service provider, so entry costs for agencies are quite low.
– Information may be obtained quickly from database resources, including NCIC, without the need to extend time to go through a dispatcher.
– The accuracy of the information may be better if it is directly obtained from a law enforcement database without any voice involved.
– Industry standard TCP/IP protocols make the connection with standard databases.
– Some service providers are willing to prioritize traffic on their CDPD networks so that law enforcement may be able to displace non-critical traffic during emergencies.
– Hardware and software are available from multiple sources, allowing for competitive bids in a community where there is more than one source.
– CDPD can act as a backup communications network if the primary law enforcement radio communications network goes down.
Disadvantages of CDPD – CDPD cell coverage may be limited or not available in sparsely populated communities or rural areas.
– There may not be enough capacity to handle law enforcement requirements during a heavy rush for information.
– The maximum data rate is 19,200bps, which may not be satisfactory for obtaining high-quality fingerprints or complex mug shots quickly.
– In large agencies with a large number of vehicles, the cumulative cost of CDPD service could exceed the cost of a dedicated radio infrastructure.
– Some service providers will not prioritize traffic for public safety users.
Private national data networks At this time, there are two private national data networks: ARDIS and RAM. Both networks offer data communications services within urban areas and between many cities across the continental United States, Alaska, and Hawaii.
Sample vendors (c) American Mobile Satellite Corporation (ARDIS Mobile Data) – Motorola recently sold its ARDIS data and messaging network to American Mobile Satellite Corporation (AMSC), making AMSC the owner of the largest two-way wireless data communications network in the United States. The network covers 427 urban areas (10,700 cities and towns) in the continental United States, Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands.
Packet data network technology is employed by the system. According to the company, the combined satellite/terrestrial network allows the company to optimize the transmission of data by using both terrestrial and satellite paths, thus minimizing their costs.
(c) BellSouth Mobile Data (RAM Network) – BellSouth Mobile Data Corporation took over RAM Mobile Data in early 1998 and is expanding the number of base stations in metropolitan areas across the United States. According to BellSouth, “The primary objective of the RAM network is to send and receive messages and data from anywhere at anytime.” The system is a data-only, packet-switched network and uses packets of 512 bytes transmitted at an 8kbps rate. The service is based on Ericsson’s Mobitex standard used throughout Europe. The network supports many data communications protocols including UDP/IP, TCP/IP, SNA/3270, X.25, asynchronous, and MPT/1 transport protocol.
To operate on the RAM network, an agency needs laptop or palmtop computers, application software supported by appropriate middleware, a wireless modem and BellSouth’s RAM wireless two-way data transmission service. BellSouth provides open interfaces that enable many vendors to supply hardware, software and system integration services. Coverage information may be obtained from the company’s Web site. As said previously, an agency is encouraged to perform its own coverage testing before making a commitment for the use of the network.
Information on the system may be obtained by calling BellSouth or by visiting its Web site.
Advantages of private data networks – Network store and forward. Packets may be stored for sending at a later time.
– Companies guarantee fast network response and delivery of data, within seconds of being transmitted.
– Both companies provide encrypted service, if desired.
– Costs are proportional to usage.
Disadvantages of private data networks – The two national data networks do not yet support data rates in excess of 8kbps.
– Because these are packet networks, with 200 to 1,000 bits per packet, they are not very efficient for long messages. They need to be used for files of less than 10,000 bits.
Regional voice and data systems A number of ESMRs provide digital radio systems for both voice and data traffic. One is discussed below. Other communications and utility companies across the country have offerings for the provision of regional communications.
Sample vendor (c) Racom Corporation – This company, headquartered in Marshalltown, IA (See “It Is Heaven – and It Is Iowa,” MRT, May 2000), operates a large 800MHz trunked digital wireless network and boasts of some 6,000 customers in Iowa, Minnesota, Nebraska, South Dakota, Wisconsin and Illinois with some 4,000 contiguous channels (see Figure 1 on page PS4). The company’s core business consists of wireless voice and data services for public safety, utility, and industrial customers. By combining the needs of many entities on a common network and providing a high level of network maintenance, Racom claims that users can avoid substantial cash outlays while experiencing a high degree of system reliability and flexibility.
Advantages of regional voice and data – Lower capital outlay by sharing existing system.
– Maintenance is taken care of by the system supplier.
– Capital expenses are amortized in monthly invoices and spread over the total customer base of the company.
– Many modes of operation are available by using this service, as discussed previously.
Disadvantages of regional voice and data – Law enforcement agency does not have complete control over the system.
– The agency must purchase special telephone/radio units.
– Prioritizing transmissions for public safety is often not provided. In case of an emergency, public safety agencies may not be preferred customers.
– Flat rate billing may not be provided by companies. Rates are commonly based upon a fixed fee plus usage.
– The service may not be available in your area.
Mobile satellites (c) Voice communications satellites – Besides GEOs, medium-earth-orbit (MEO) and low-earth-orbit (LEO) satellites have been proposed for relaying radio transmissions. MEO and LEO satellites require less output power from phones and have less time delay than GEO systems. The relationship of GEO, MEO and LEO satellites is shown in Figure 2 on page PS6.
(c) Other voice satellite systems – Four other PCS satellite systems are being installed. Two similar systems, Globalstar (being implemented by Loral and Qualcomm) and Constellation Communications’s ECCO, are LEO systems with 48 and 46 satellites, respectively. As of February 2000, it appears that these companies are proceeding with their plans even though another provider, Iridium, has filed for bankruptcy.
Mobile Communications Holdings’ Ellipso and ICO Global Communications’ ICO satellites are in MEOs, spaced at about 6,000 to 10,000 miles above the earth’s surface.
There are tradeoffs between the LEOs and MEOs. Far fewer satellites are required in the MEO system than in the LEO system, but higher effective power is required for transmissions by the subscriber units, and time delays are greater.
Pricing of services has not yet been finalized, but it is estimated that prices will be in the range of $3 to $5 per minute. Almost all of these companies have Web sites. Visit those sites as the technologies develop to evaluate the use of satellite services as they become operational. Because of the large number of commercial providers for both voice and data systems, there will most likely be considerable competition when all of the systems are turned up.
(c) Data communications satellites – Since 1992, American Mobile Satellite has offered Skycell service employing geosynchronous satellites for communication of data up to 4,800bps. Both voice and data may be handled on the same system.
One type of use of the Skycell system includes mobile messaging services for large fleets that can be used virtually anywhere in North America. The system uses L-band technology with antennas mounted in small domes on the roofs of vehicles to allow for two-way data transmission and position tracking. Interfaces use standard dispatch application software. The service may be used to send data reports, email, and faxes, as well as to connect to the Internet.
(c) High-altitude long-endurance (HALE) platforms – In this proposed network, relay of signals would be accomplished using large blimp-like repeaters at several miles (20,000m) above the earth. The devices would cost less than the big satellite systems and could be recalled to earth for maintenance. Multibeam, phased-array antennas would support both mobile two-way communications and broadband video.
Four types of HALE platforms have been proposed, which include:
– helium-filled, robotically controlled dirigibles stabilized by ion engines.
– units powered by solar or fuel cells.
– piston-driven platforms.
– jet engine-driven platforms.
The biggest challenge faced by all of them will be power requirements versus refueling requirements. The first two types need little or no refueling but may not produce the transmit power needed, whereas the latter two types will have plenty of power but will need to be refueled every few days.
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Summary At no time in the history of public safety communications have so many options been available. Technological advances and regulatory changes have combined to make selecting a communications system very complex.
As we move into the future, it is unlikely to get any better. NLECTC-Rocky Mountain and other groups [such as the Federal Public Safety Wireless Network program (PSWN)] are dedicated to helping you through the maze of technology jargon and bureaucratic rules as you proceed on your communications project.