Stopping Smuggling & Collusion: How Our Prison Signal Jammer Secured a Sichuan Correctional Facility

(I) Requirements for the Prison Mobile Phone Jamming System

1. Scope and Functional Requirements

The system shall provide effective jamming and control of all public mobile communication standards currently used in China, including CDMA, GSM, DCS, 3G (CDMA2000, TD-SCDMA, WCDMA), and 4G (TDD-LTE, FDD-LTE).
It must operate without interfering with the normal functionality of other mission-critical electronic systems inside the correctional facility.

The primary objective is to eliminate all unauthorized mobile communications within the prison—across China Mobile, China Unicom, and China Telecom networks—thereby enhancing operational security and preventing information leakage, collusion, smuggling, and other high-risk incidents.

2. Targeted Coverage Areas

The system shall provide full signal control inside the second security perimeter, covering key inmate activity zones such as:

• Housing units and dormitory blocks

• Workshops and production areas

• Isolation and disciplinary cells

• Visitation areas

• Hidden or enclosed spaces within or between standalone buildings

3. Performance Requirements

1. Housing units (including cells, corridors, stairwells, and window zones): ≥99.9% effective jamming rate

2. Production/workshop areas: ≥99% effective jamming rate

3. Confined or high-risk hidden spaces (e.g., interview rooms, storage rooms, restrooms): ≥99.9% effective jamming rate

4. Non-jamming areas such as administrative buildings, armed police buildings, and surrounding civilian areas shall remain fully operational and unaffected.

5. Electromagnetic emissions must comply with all applicable national standards.

6. Power distribution shall be centralized or regionally centralized, with lockable breaker boxes to prevent unauthorized shutdown.

7. The system shall demonstrate high operational reliability, anti-tampering capability, and support for continuous long-term operation.

8. Adequate output redundancy must be reserved to ensure extended service life and accommodate future system upgrades.

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(II) Proposed Solution for the Prison Mobile Phone Jamming and Control System

1. System Architecture – Hybrid IMSI-Catcher + RF Jamming Platform

This solution adopts a combined approach using 4G (FDD-LTE 1800 MHz public network or 400 MHz private network) pseudo-base station technology integrated with RF jamming modules.

A total of three pseudo-base station signal sources are installed in the main equipment room. Signals are distributed via three 1-to-8 optical transceivers to twenty remote optical units deployed across multiple buildings. These signals are then merged with the existing jamming system using combiners and duplexers before being transmitted through the antenna network.

The IMSI-catcher subsystem performs IMEI/IMSI identification, enabling:

• Blacklist control: unauthorized mobile devices are forced to remain registered within the virtual base station and cannot access the public network.

• Whitelist pass-through: authorized police terminals can return to the public network and retain access to 4G push-to-talk, police apps, and other mission-critical services.

2. System Topology

Prison Mobile Signal Control System – Topology Overview

3. Implementation Methodology

A professional RF spectrum survey shall be conducted using a spectrum analyzer to assess actual frequency bands, signal levels, and coverage distribution throughout the facility. All system configurations and equipment models shall be determined based on the measured onsite data.

The design principles are as follows:

1. Accurate Handling of Strong-Signal Environments and Minimizing External Interference

Using multi-band hybrid distribution with appropriately placed antennas ensures effective jamming inside inmate areas while preventing interference with external residential or administrative zones.

2. TD-SCDMA Time-Slot Synchronized Jamming

Since TD-SCDMA uses TDD (same uplink/downlink frequency), improper interference may disrupt operator base stations.
The system uses synchronized tracking to avoid uplink time-slot interference, ensuring regulatory compliance and operational safety.

3. Combined Point-Frequency and Sweeping Jamming Strategy

For ultra-strong signals from nearby base stations, point-frequency hopping precisely locks onto pilot and control channels, ensuring high blocking efficiency with minimal electromagnetic output.
For weaker signals from distant base stations, frequency sweeping provides broadband coverage.

4. Outdoor Coverage as the Primary Layer, Indoor Coverage for Reinforcement Only

Outdoor jamming aligns with signal entry paths, ensuring balanced indoor attenuation and significantly reducing indoor electromagnetic exposure. Wall attenuation (10–15 dB per wall, >20 dB for concrete) further enhances safety.

5. Precision Antenna Engineering

Antenna models, gain, direction, tilt angle, and installation height must be engineered based on actual building layouts. Reflectors or shielding plates may be added to meet national electromagnetic environmental standards.

6. Power Supply

Centralized or region-based centralized power supply is required, utilizing lockable electrical enclosures to prevent operational tampering.

7. Optional: Network-Based Fault Monitoring

Main units may include integrated alarm modules, enabling facility-wide real-time monitoring from the central control room.