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NXDN

Overview

NXDN™ is an Common Air Interface (CAI) technical standard for mobile communications. It was developed jointly by Icom, Incorporated and Kenwood Corporation. The NXDN Forum was formed in order to promote the NXDN protocol in North and South America. The forum's members are:

Aeroflex Wichita Inc.

Daniels Electronics Ltd.

Icom Incorporated and Icom America Incorporated

Kenwood Corporation and Kenwood USA Corporation

Ritron Inc.

Trident Datacom Technologies (Trident Micro Systems)

NXDN is implemented by Icom in their IDAS™ system and by Kenwood as NEXEDGE™.

Applications

The NXDN standard and the communications products in which it is used are intended for commercial Private Land Mobile Radio (PLMR) and low-end public safety communications systems. The technology satisfies the FCC mandate requiring all communications systems covered by Part 90 regulations to use narrowband technology by 1 Jan 2013. 

NXDN Technical Characteristics

The NXDN standard is based on the European Telecommunications Standards Institute (ETSI) Technical Standard 102 490, "Peer-to-Peer Digital Private Mobile Radio using FDMA with a channel spacing of 6,25 kHz with e.r.p. of up to 500 mW".

NXDN uses Frequency-Division, Multiple-Access (FDMA) technology in which different communication streams are separated by frequency and run concurrently. (Time-Division, Multiple-Access (TDMA) systems combine the communications streams into a single stream in which information from the different streams is transmitted in interleaved time allocations or "slots." Code-Division, Multiple-Access (CDMA) systems  allow many users to share a common spectrum allocation by using spread-spectrum techniques.)

The basic NXDN channel is 6.25 kHz wide. Dual-channel systems can be configured to fit within a 12.5 kHz channel. This effectively doubles the spectrum efficiency compared to an analog FM system occupying a 12.5 kHz channel. Two NXDN signals can occupy a 12.5 kHz channel allocation as voice/voice, voice/data, or data/data.

Systems that use NXDN also support mixed analog FM and digital NXDN equipment, including direct radio-to-radio communications. This allows system owners to migrate to a narrowband, digital system without replacing the entire system at once. NXDN equipment is currently FCC type-accepted for use on VHF (136-174 MHz) and UHF (400-520 MHz) bands.

Data is transmitted using 4-level frequency-shift keying (FSK) modulation. NXDN uses the AMBE+2™ vocoder (codec) for digital audio. This combination provides better weak-signal voice quality than for analog FM. For an equivalent transmitter power, NXDN is represented as having a wider range than analog FM at the 12 dB SINAD   threshold. The transmission bit rate is 4800 bps.

Within the NXDN protocol data structure the codec bit rate is 3600 bps. Of the codec bit rate, 2450 bps are allocated to voice data and the remaining 1150 bps consist of error correction data. Digital data can be included in the data stream with a net data rate of 800 to 950 bps. If the equipment is configured such that only digital data is transmitted, the net data rate is 4400 to 4550 bps. The NXDN frame transmission length is 80 msec.

The following FCC emission designators apply to NXDN transmissions:

8K30F1E 12.5 kHz single channel digital voice

8K30F1D 12.5 kHz single channel digital data

8K30F1W 12.5 kHz single channel digital voice and data

4K00F1E 6.25 kHz single channel digital voice

4K00F1D 6.25 kHz single channel digital data

4K00F1W 6.25 kHz single channel digital voice and data

4K00F2D 6.25 kHz single channel analog CW ID

Application Functions Supported by NXDN

The NXDN protocol provides support for the following functions. Implementation of the functions and the user-level interfaces by which they are accessed and used may vary by manufacturer.

Encryption – Spectrum-inversion digital voice scrambling, 15-bit key (32,768 different codes)

Paging & Status Reporting – Radio-to-Radio and Dispatch-to-Radio

User Aliases – 65,545 different Group ID's and User ID's

Man-down and Emergency call

Remote radio management functions - Stun/Kill/Revive and Monitor

Current Implementations of NXDN

Icom IDAS

Kenwood NEXEDGE

See Also:

ETSI Technical Standard 102 490, "Peer-to-Peer Digital Private Mobile Radio using FDMA with a channel spacing of 6,25 kHz with e.r.p. of up to 500 mW".

Comparison of FDMA and TDMA Systems