Mobile Data Networks for Small Agencies

Mobile data applications are commonplace in the more populous areas of the country, where law enforcement agencies have found them to be within their economic grasp. In the smaller communities where private industry has not built out the necessary communications infrastructure, and for highway patrols, sheriff’s offices and conservation agencies that work in isolated areas, mobile data capability is rare. Some recent developments in technology and in the communications industry have now brought mobile data within the reach of most any public safety operation.

Historically, any public safety entity that wanted a mobile data capability had to build the infrastructure necessary to support the network. Large urban agencies could afford (though just barely) to construct enough repeater towers and access points within their relatively small area of operations, because the network would serve so many users.

The return on investment was a public safety force that was better informed and more efficient than one that used voice radio. As the cellular telephone industry built out their networks, the channels that carried cell phone conversations could also support data communications. Wireless service providers were (and are) anxious to sell as much ofthat bandwidth as possible to defray their considerable investment in radio spectrum rights, antenna towers, fiber optic cable, and the other bits and pieces necessary to create and maintain a wireless system.

Smaller local governments that were fortunate enough to be located in a market where the network was extensive enough to support data could purchase airtime and build their mobile data networks on the backbone already created by the private sector.

This solution doesn’t work in less populous areas, because the cellular companies haven’t found it to be cost effective to provision data capacity when there are relatively few subscribers. Although the development of the cellular networks have made it possible to make or receive a wireless voice call in all but the most remote areas, the additional carrying capacity necessary for data hasn’t been available over the cellular system, and isn’t likely to be available anytime soon.

Some of the public safety agencies that bought into the private sector/public sector model for their data networks have to reevaluate their strategies. Much of the shared mobile data bandwidth runs on the Cellular Digital Packet Data (CDPD) system, which is provisioned (mostly) by AT&T Wireless where it is available at all. AT&T has the most extensive wireless network in the United States, but its capacity is limited by the Time Division Multiple Access (TDMA) technology that it uses to make a single radio channel carry multiple data streams.

Other wireless providers use Code Division Multiple Access (CDMA), which allows for more data streams per bandwidth unit than TDMA, and the newest networks use GSM/GPRS (Global System for Mobile Communications/GSM Radio Packet Service). GSM is the standard overseas, and promises “3G” (third generation) carrying capacity that far exceeds the ability of TDMA and CDMA to cany data. Unfortunately, equipment configured for CDPD isn’t compatible with GSM, and AT&T is gradually abandoning its CDPD networks in favor of GSM.

Customers using CDPD have to decide whether to buy the new hardware that will allow them to continue their relationship with AT&T, or look for another technology altogether. Other data carriers have coverage in communities where they have made a market and built their infrastructure, but no cellular carrier can promise blanket coverage from sea to shining sea.

MeshNetworks

An alternative for agencies operating in all but the most remote environments is the system available through MeshNetworks, which made its first appearance at an APCO show in August 2003. MeshNetworks is the result of privatization of technology developed for the military by DARPA, the Defense Advanced Research Projects Agency (which, some years back, created a system known today as the Internet). MeshNetworks functions on a model similar to Wi-Fi, otherwise known as 802.1 Ix (the “x” denoting which of several standards are in effect for that network).

Wi-Fi networks unleash computer users from their Ethernet network cables and make it possible to use network resources anywhere within range of a wireless access point. Access points, which are hardwired to the network, have a typical wireless range of a few hundred feet, and can be purchased for less than $100. Sales of these devices exceed a million per month, as home, office and school computer users provision their networks without having to string ugly, cumbersome and expensive Cat-5 Ethernet cable. Multiple wireless devices operating on the same network can communicate with one another on a peer-to-peer basis, just as if they were hardwired to a common network.

MeshNetworks takes advantage of the same principle, operating on the 2.4 GHz 2nd ISM band. A Mesh-Enabled Architecture (MEA) device functions both as an access point and as a repeater. If one device on the network has connectivity to the Internet or an internal network, then every other device having connectivity to that station, directly or indirectly, also has connectivity. In situations where network clients are isolated from the network, they still have interoperability with one another for mutual support.

In a typical MEA public safety system, a local government would install MeshNetworks Wireless Intelligent Access Points (IAPs) at fixed locations within their area of operations, such as light poles, water towers, public buildings, and other sites where the agency had rights and access. The IAPs would have access to a reliable hardwired power supply (with a battery backup) and would supply network coverage over a mapped area.

The carrying capacity of the network is expanded by the use of wireless routers that are also installed at fixed locations and assist in managing the flow of data. Without these, the network would be subject to bottlenecks where data throughput could be reduced. Wireless routers are used to expand the geographic footprint of the network at less cost than would be incurred with IAPs alone, since they do not require a hardwired backhaul connection.

The fixed IAPs and wireless routers serve a dual function- besides serving as relay stations for network data, they also serve as reference points to triangulate the precise locations of wireless clients on the network. This is a significant distinction between MEA and other wireless networks, and one that provides a critical capability for public safety employees. More conventional locating methods, such as GPS, don’t work well when the overhead view is blocked.

MeshNetworks uses a system independent of GPS to locate clients in three dimensions. Rescue workers and others working inside a building can be located continuously not only in terms of longitude and latitude (or other convenient coordinates), but also in elevation, making it possible to determine which floor of a high- rise structure contained officers or firefighters.

Wireless clients on the network, usually patrol vehicles and fire trucks, are not passive users with MeshNetworks. Each wireless client serves as a relay station, extending the scope and connectivity of the network to the limit of its access point. This feature has a twofold benefit. If an agency needs to operate in an area outside of the range of its hardwired IAPs or routers, but still relatively close to the established network footprint, one or more mobile units can be positioned as relay stations between the central network and the outlying area of operations to keep the most remote units connected to the network.

Used in this way, the remote units would still have access to all network resources, sueh as criminal justice databases and agency files. When operations are taking place in areas separated from the home network by a distance that makes it impractical to deploy relay stations, every MeshNetworks-equipped unit acts as a node for all the others within range. Used this way, units conducting a search or fighting a fire in a remote location would be able to network with each other, sharing data, photos and other digital information between mobile units, even though there might not be any connectivity to the hardwired network.

MeshNetworks has a demonstration network established in the Orlando metropolitan area. They often provide exhibitions of the technology to visitors, driving down Florida freeways at 65 miles per hour while sending and receiving text and photo data, streaming video, and voice traffic over the MeshNetwork with throughput that rivals a hardwired network.

MEA networks involve a one-time investment in hardware for the fixed and mobile access points, but no recurring costs for airtime or network access fees since it operates on license-free frequencies. This compares favorably with the cost of buying into a commercial network where the network provider supports the hardware and network, but charges the subscriber a fee (based on airtime, amount of data transmitted, or a flat periodic access fee) for use of the network facilities. This is a consideration when agencies have a one-time grant or budget opportunity for the purchase of data or communications facilities, such as a federal grant or spec\ial capital property allocation.

MeshNetworks is a good solution for agencies that need to build out a network over a relatively small area, such as a city, but organizations that have operational areas of hundreds or thousands of square miles aren’t going to have utility poles at convenient locations on which to mount their access points, and the closest mobile unit might be a hundred miles away. These operators need a communications system that will work just about anywhere, regardless of the immediate environment or locale. The solution is the same one that people in remote areas have used for some years to get television, and more recently, commercial radio service- satellite.

Mobile Satellite Ventures

In 1995, Mobile Satellite Ventures (MSV) placed two geosynchronous communications satellites in orbit (MSAT-1 and MSAT- 2), covering North America from the East and West. So long as one has a clear overhead view of the sky, one of the satellites can “see” you in the United States, Canada, Central America, northern portions of South America and the Caribbean. Two-way communication with the satellites can be facilitated by a Packet Data Terminal (PDT) that looks a little like an oversized bike helmet. The PDT is mounted on the roof or trunk lid of a vehicle for line-of-sight communications with one of the satellites.

Mobile Satellites Ventures’ system can be integrated to work with most any mobile data software. The New Mexico State Police, one of those agencies with a lot of open ground to cover, uses the network to run its Motorola Printrak mobile data system. When troopers are in more developed areas and in range of conventional networks, the system switches seamlessly to the local network to take advantage of least-cost routing. The systern can also defer high-bandwidth transactions, such as transmission of picture or video data, to times when the unit is in range of the conventional wireless network. Recurring access fees are determined by the amount of data transmitted or received through the satellite link.

Because of the distance that signals have to travel between Earth and satellite, there is a bit more of a lag or delay than is the case with voice conversations on conventional wireless networks. The signal requires 375 milliseconds to travel between Earth and the satellite, and another 375 milliseconds back to Earth. The net effect is a delay of about of a second between transmission and reception. MSV says that this delay is barely noticeable once the user becomes accustomed to the system.

The cost of implementing an MSV-based system varies with the installation. When the New Mexico State Police installed its MSV hardware, it already had a mobile data system in place, albeit one that wasn’t functional in remote locations. This reduced its startup cost to around $2,000 per mobile unit. A portable system contained in a large Pelican “suitcase” available from Liberty Communications System runs from $2,500-$4,000, but can function completely independent of a vehicle or other base station.

A recent add-on to the MSV system is the LifeGuard, a belt-worn personal safety device. Workers operating alone in remote locations within a mile of their PDT-equipped vehicle can send a distress signal over the network by either pushing a button or remaining immobile for a preset period. The LifeGuard sends a signal to the PDT on the vehicle, which is relayed over the satellite network.

MSV has plans for its next generation network that will extend the reach of the network through the use of “ancillary terrestrial components,” in essence repeater stations that receive and transmit signals without going over the satellite link. These land-based access points serve to effectively re-use the satellite L-band spectrum, thereby increasing the capacity of the network and making it available everywhere in North America.

MSV has joined the Public Safety Integration Center (PSlC) in McLean, VA, a venture operated by Science Applications International Corporation (SAIC). PSIC is intended as a demonstration center and incubator for clients seeking to develop solutions to the challenges of providing homeland security. Visitors to PSIC can see products and services from MSV and other vendors in action, and often integrated with other related services. MSV is working closely with Intergraph Public Safety to facilitate the use of Intergraph’s computer-aided dispatch product over MSVs satellite network.

The MSV network can cany voice, data, fax or virtually any other information that can be transmitted over a wireless network. Mobile Satellite Ventures has offices in Ottawa, ON and Reston, VA.

www.meshnetworks.com

www.msvlp.com

Tim Dees is a former officer who writes and consults about applications of technology in law enforcement. He can be reached at (509) 585-6704 or by e-mail at tim@timdees.com.

Copyright Hendon, Inc. Aug 2004