Contraband cell phones are sometimes used by prisoners to talk to a child after school, for Facebook updates, or to post videos to YouTube. Other times they’re used to plan strikes, organize escapes, and order executions. Prisoner-directed crimes will occur with or without wireless, but cell phone access reduces barriers to them, and it’s a growing problem.

Why not work harder to keep cell phones out? Corrections officials say they try, but can’t get them all. For one thing, prison staff is sometimes a source. If that or other smuggling don’t get them in, suppliers can try throwing them over a fence; almost 30 phones and chargers have been stuffed into a football. And so on. With untraceable prepaid phones available for $20 at discount stores, and with the phones valued at $1000 in prison, the incentive and creativity to get them inside is high. Lose a few and you still make money.

With physical boundaries inadequate, electronic countermeasures are getting more attention. In December NTIA released a report discussing these. The report is based on responses to a Notice of Inquiry begun by NTIA in May 2010 at the direction of Congress. It’s also based on NTIA’s own laboratory and field tests. In the report, three technologies get the most attention: jamming, managed access, and detection.

Jamming is straightforward; signals are transmitted that interfere with cell phone use on prison grounds. The main problem is keeping those signals from interfering with legitimate users outside the grounds, while keeping them strong enough inside to be effective. This requires a significant engineering and testing effort up front. As cellular frequencies are changed, the jamming system has to be updated. Moreover, NTIA and some others say that jammer operation by non-Federal entities violates the Communications Act of 1934, as amended. Consultant Michael Marcus, who does some work in this area and participated in the NOI, has an alternative view of the Act based on its legislative history and makes the case that the FCC is authorized to make rules that would allow such jamming. (He assisted the South Carolina Department of Corrections and 30 other state correctional agencies in petitioning the FCC in the summer of 2009 to make rules permitting jamming within correctional institutions; they’re still waiting for a response.)

With the managed-access technique, a small cellular base station intercepts call attempts from the prison. Legitimate callers, identified by a list in the station, are connected to the outside cellular infrastructure. Illegitimate callers are blocked. All calls to 911 can be put through. The hardware to do this is generally more expensive compared to jamming; in one case, a prison pay phone provider paid for the system, a point NTIA reminds us of several times. With such subsidization schemes, however, can come calling costs that are unaffordably high for some. Managed access also requires an ongoing relationship with local cellular providers. When cellular frequencies or air-interfaces change, the managed access system has to be changed. Depending on how it’s implemented, it might violate certain wiretap statutes. As with jamming, there is up-front engineering required to provide good coverage in the prison and minimize interference with legitimate users outside. An advantage of managed access is that, unlike jamming and detection, all equipment can be kept outside the prison grounds; this can make installation and maintenance easier and eliminate tampering by prisoners.

In the detection method, receiving equipment with multiple antennas in the prison detects unauthorized cell phone transmissions; the location of the phone can be estimated to within about 3 meters with the most sophisticated (and costly) detection systems being proposed. After detection comes the human process of retrieving the phone, something not necessary with jamming or managed access. Unlike jamming and managed access, there are no interference issues.

Three other technologies were brought to the attention of NTIA by their proponents. In one scheme, Bluetooth devices throughout a prison send instructions to unauthorized cell phones to lock themselves; this would require a firmware change in phones, and thus changes to standards in relevant wireless standards bodies. Another method, a hybrid managed access scheme, would not only intercept the call, but also force the phone to send location information. Lastly, non-linear junction detectors could be used to detect semiconductor devices in the phone whether the phone is on or off; the detector must be close to the phone for this to work, so it is a a manual process involving prison staff.

NTIA concludes that one technology does not fit all; there are tradeoffs of effectiveness and cost. Each prison is unique in infrastructure and security requirements. For some, a combination of technologies may be best. Cost and time may drive the preferred solution. There are a couple of tables in the report that provide handy comparisons of these techniques, but realize they’re slanted a bit against jamming. The tone of the report suggests a preference by NTIA for managed access.

The report doesn’t address evaluating the performance of these systems once they’re installed and on an ongoing basis. How does one establish how effective the system is at installation and at later dates? Jamming and managed access can be made to work, mostly; due to variations in propagation, however, it will be hard to assure there won’t locations in the prison at which a cell phone will work. Access to these spots may become a new prison currency.

No solution is perfect. The corrections agencies realize this. Once the FCC acts on their petition, which would be even more timely with the release of NTIA’s report, they’ll know what options they have.

[cross-posted from Steve Crowley’s blog]