Cell Phone Jamming

The illicit introduction of cell phones into correctional facilities began to emerge as a serious problem with dangerous public-safety ramifications just a few short years ago. Today, as predicted and feared by many, the proliferation of cell phones in prisons has reached epidemic proportions.
While many of us have confronted this security threat firsthand, we have all seen the headlines detailing how inmates have used cellular technology to orchestrate criminal activities from credit card fraud to murder from behind the walls of an ostensibly secure correctional facility. It is a risk that must be neutralized and a threat that must be defeated.
Although the problem may be quite obvious, and its existence and potential consequences commonly understood in the hyper-security-conscious field of corrections, implementing an effective, efficient solution presents a far more complex and challenging proposition that requires deliberate consideration. Knowledge, expertise and a combination of technological, operational and legislative strategies will be required to combat this problem.
In terms of technological solutions, detection and defeat are the most prevalent methodologies. The latter strategy — specifically the use of jamming technologies to interfere with cellular transmission signals to disrupt cell phone calls — resonates from the prison walls to the halls of government.

Jamming 101
Cell phones work by communicating with a cellular service network through a cell tower. Jamming devices and cell phones transmit on the same radio frequencies, causing the two signals to collide, with the higher power from the jamming device disrupting the signal between the phone and cell tower. Cell phones are full-duplex devices that use two separate frequencies simultaneously for talking and listening.
Some jammers block only one frequency. The phone can receive only one of the frequencies and is effectively fooled into perceiving that there is no service.
Different cellular systems process signals differently, but all cell phone networks use radio signals. Jammers can broadcast on any frequency and can interrupt most systems, including AMPS, CDMA, TDMA, GSM, PCS, DCS and iDEN.
The Communications Act of 1934 and the Telecommunications Act of 1996 strictly prohibit all entities other than agencies of the federal government from the operation of devices deliberately designed to disrupt radio or wireless communications.
Last year Sen. Kay Hutchison ® Texas) introduced the Safe Prisons Communications Act of 2009, which would allow correctional facilities to petition the Federal Communications Commission for waivers permitting the jamming of cell phone communications. The Senate approved the bill in October and referred it to the Subcommittee on Crime, Terrorism and Homeland Security.
There is wide support for the bill from correctional agencies throughout the country. However, while many believe the problem will be solved with the flip of a switch, even if the bill were enacted into law tomorrow, it would not be possible to effectively and efficiently deploy jamming technology in prison settings without compromising public safety.
Correct Settings
Cellular communications jamming technology, in principle and practice, has been proven to work. Indeed, it is currently sold by several companies and is being used successfully by the military and other federal government entities in unique venues.
The correctional setting, however, is not that simple or straightforward. There are significant technological barriers that need to be overcome before jamming can be considered a viable option.
Jamming technology is effective in settings without defined structural borders, but its effectiveness can be compromised by a number of factors. Building design, structural elements, construction materials and the location and positioning of jamming system components, particularly antennas, can present impediments to the effective jamming of illicit cell phone transmissions.
Each correctional facility has a unique combination of perimeter protection, architecture, construction and engineering, site and location characteristics and population density. The actual range and effectiveness of the jamming device or system depends on its power and the proximate environment, which may include walls of a building or elevated areas of the surrounding facility site that block the jamming signal.
The phenomenon of multipathing represents a significant technical complexity that can impair the functionality of jamming equipment. Multipathing occurs when radio signals are reflected off one or more nearby physical barriers.
In an open setting, the stronger signal of the jamming device travels on a direct path and hits the weaker cell phone signal, causing disruption of the transmission. When large objects such as buildings or walls are in the area, they block the direct path and cause the jamming signals to bounce off the object. This collision prevents the jamming signal from making a direct hit on the cell signal to jam the call. In order to compensate for the multipathing effect and maintain a jamming signal within the perimeter, numerous strategically placed antennas within each discrete room, area or building are needed.
Another potential impediment relates to signal power. In order to jam the call, the device must emit a stronger signal than the cell phone transmission.
Cell phone carriers continuously change power levels throughout the day. The proposed legislation would require that jamming devices use the minimum power possible.
The jamming system would require active feedback throughout the day regarding what power various carriers are operating on in order to determine the appropriate jamming power level at any given time there. Additionally, jamming at higher signal power levels is more susceptible to multipathing and more difficult to contain within a defined perimeter. Given these constraints, setting the optimal signal power presents a significant technical challenge.
It is not yet known if the technology can disrupt all illicit transmissions with a high degree of accuracy while still being contained within a tightly defined perimeter.
Interference with legitimate cell phone transmissions by the general population, commercial entities, public agencies and emergency services within or in close proximity to the prison could jeopardize public safety — a concern that forms the basis of much of the opposition to the proposed jamming waiver legislation.
Many professionals in the field of corrections believe that selective jamming may be another option. Selective jamming allows predetermined cell phone numbers to make and receive calls within the perimeter. Such a strategy, however, does not solve the threat posed to emergency services operating in close proximity to the facility.
Additionally, given that a significant portion of contraband cell phones are smuggled into facilities by staff, selective jamming does not prevent them from bringing in approved cell phones. Selective jamming may have the same legal ramifications.
To date, cell phone jamming in the correctional setting has not been fully evaluated; therefore, the efficacy in this context is unknown. Significant engineering and rigorous testing need to be carried out before a definitive answer can be rendered. Although passage of the bill would be a promising start, a fully funded government-sponsored test of jamming technology is needed, sooner rather than later, to determine whether it offers a viable solution. If successful, jamming could prove to be the most valuable tool yet in the effort to eliminate the rampant epidemic of illicit cell phone use in correctional facilities.
In our next article, we will highlight cell phone detection technology, together with alternative strategies and operational issues. We will also explore the other side of the coin — the recovery of intelligence information using widely available cell phone forensics tools.
After 29 years with the Massachusetts Department of Correction, Alex Fox retired from his position as director of security technology to launch a private consulting venture.

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E-mail your security and technology questions, comments, insights, experiences and topic suggestions for the Fox TechWatch column to cn@emlenmedia.com