Digital Cordless Phones
Digital cordless phones (DECT) operate in the 1.88–1.90 GHz band (Europe) or 1.92–1.93 GHz (US) with 120-channel TDMA, 32 kbps ADPCM voice.
DECT: Digital Enhanced Cordless Telecommunications
DECT is the dominant standard for digital cordless phones worldwide. It operates in different frequency bands depending on region, but all use the same fundamental TDMA-based air interface:
| Region | Frequency Band | Channels |
|---|---|---|
| Europe | 1880–1900 MHz (1.88–1.90 GHz) | 120 channels (10 carrier × 12 time slots) |
| North America (DECT 6.0) | 1920–1930 MHz (1.92–1.93 GHz) | 5 channels |
| Japan | 1895–1918 MHz | PACS variant |
Technical Specifications
- Access method: TDMA (Time Division Multiple Access) — 12 time slots per frame
- Voice codec: 32 kbps ADPCM (G.726); Cat-iq supports wideband (7 kHz audio)
- Range: 50–300 m outdoors (line of sight); 30–50 m indoors typical
- Power: 250 mW peak transmit; TDMA burst mode
- DECT NR (New Radio): 5G voice integration for DECT spectrum; extended range and data rates
DECT vs Analog Cordless
Early cordless phones (900 MHz) used analog FM transmission — trivially intercepted by any scanner. DECT introduced digital encryption:
- Analog: Anyone with a scanner can listen to 900 MHz analog cordless calls
- DECT: Uses 64-bit A5-like cipher (brittle by modern standards); encryption is present but weaker than cellular
Security Considerations
DECT encryption has known vulnerabilities:
- DECT Standard Cipher: 64-bit key with 35-bit initialization vector; considered weak by modern standards due to short IV, not true 64-bit encryption strength
- NG-DECT/CAT-iq: AES-128 encryption (DSC2 algorithm, when supported by device)
- Known attacks:intercept and decrypt DECT traffic with software-defined radio and open-source tools (e.g., gr-dect)
- Recommendation: Use VPN or end-to-end encryption for sensitive calls
DECT Devices and Ecosystem
- Home cordless phones: Panasonic, Siemens Gigaset, VTech, AT&T
- Business DECT: Spectralink, Ascom, Alcatel-Lucent Enterprise
- Baby monitors: Many use DECT 6.0; range ~300 m
- Smart home: DECT-based home automation (ENERGYlet, etc.)
DECT NR (New Radio) — 5G Voice
DECT NR (New Radio) is being standardized for 5G voice over the DECT spectrum band (1.9 GHz). It provides a path for voice services in the DECT band while maintaining backward compatibility with existing DECT devices.
Other Digital Cordless Standards
- PACS (Personal Access Communications System): US/Japan variant at 1.9 GHz; similar to DECT but with different channelization
- CT2 (Cordless Telephone 2): UK standard from 1980s; basic digital cordless
- WDECT (Wideband DECT): Wideband audio extension for DECT
Range and Propagation
DECT at 1.9 GHz provides moderate penetration through walls. Range depends on:
- Transmit power: 250 mW peak (TDMA burst); average much lower
- Antenna: Handset and base both use compact antennas
- Environment: Indoor range 30–50 m; line-of-sight outdoors 100–300 m
- Building materials: Metal studs, concrete reduce range significantly