View source for NXDN

{{Short description|Radio standard}}
[[File:ICOM IC-F3162dt.jpg|thumb|150px|IDAS Radio IC-F3162DT]]
'''NXDN''' stands for '''Next Generation Digital Narrowband''', and is an open standard for [[public land mobile radio]] systems; that is, systems of [[two-way radio]]s ([[transceiver]]s) for bidirectional person-to-person voice communication.  It was developed jointly by [[Icom Incorporated]] and [[Kenwood Corporation]]  as an advanced [[digital modulation|digital]] system using [[frequency-shift keying|FSK]] modulation that supports [[encryption|encrypted]] transmission and data as well as voice transmission.  Like other land mobile systems, NXDN systems use the [[very high frequency|VHF]] and [[ultrahigh frequency|UHF]] frequency bands. It is also used as a niche mode in [[amateur radio]].

NXDN is implemented by Icom in their IDAS system <ref>{{Cite web|url=http://www.icom.co.jp/world/idas/index.html|title=Icom Inc. Global|url-status=dead|access-date=2009-01-22|archive-date=2009-01-23|archive-url=https://web.archive.org/web/20090123235526/http://www.icom.co.jp/world/idas/index.html}}</ref> and by Kenwood as NEXEDGE;<ref>{{Cite web|url=http://www.kenwoodcommunications.co.uk/about-nxdn/|title = Walkie Talkies &#124; NEXEDGE &#124; PMR446 &#124; Ham Radio • Kenwood Comms}}</ref> both Kenwood and Icom now offer dual-standard equipment which supports the European [[dPMR]] standard.<ref>{{Cite web|url=http://www.icom.co.jp/world/idas/dpmr/|title=Icom Inc. Global|url-status=dead|access-date=2012-02-11|archive-date=2012-04-04|archive-url=https://web.archive.org/web/20120404103245/http://www.icom.co.jp/world/idas/dpmr/}}</ref><ref>{{Cite web|url=http://www.kenwoodcommunications.co.uk/nexedge-dpmr/|title = Walkie Talkies &#124; NEXEDGE &#124; PMR446 &#124; Ham Radio • Kenwood Comms}}</ref> 
[[File:NEXEDGE NXDN.jpg|thumb|NEXEDGE NXDN Hand Portable]]

==History==
Icom and Kenwood began their collaboration in 2003. The NXDN protocol was announced in 2005, and NXDN-compatible products first appeared in 2006.<ref name="history">{{cite web |url=http://www.nxdn-forum.com/what-is-nxdn/history/ |title=The history of NXDN™ |publisher=NXDN-Forum |access-date=May 21, 2016}}</ref>

The NXDN Common Air Interface (CAI) was accepted at the Study Group 5 (SG5) meeting of the International Telecommunication Union Radiocommunications Sector (ITU-R) held in November 2016 and in report M.2014-3 published in February 2017 as [http://www.mccmag.com/News/NewsDetails/NewsID/15362 an international digital land mobile system].

==Applications==
The NXDN protocol and the communications products in which it is used are intended for commercial [[Land mobile radio system|Private Land Mobile Radio]] (PLMR) <ref>{{Cite web|url=http://wireless.fcc.gov/services/index.htm?job=service_home&id=private_land_radio|title=Private Land Mobile Radio Services|date=17 May 2016|access-date=22 January 2009|archive-date=22 February 2009|archive-url=https://web.archive.org/web/20090222034741/http://wireless.fcc.gov/services/index.htm?job=service_home&id=private_land_radio|url-status=dead}}</ref> and public safety communications systems. The technology satisfies the U.S. [[Federal Communications Commission]] (FCC) mandate requiring all communications systems covered by [[Land mobile service|Part 90]] regulations to use [[narrowband]] technology by January 1, 2013. Part 90 regulations specify a bandwidth of 12.5&nbsp;kHz, but the FCC “strongly urges licensees to consider migrating directly to 6.25 kHz technology rather than first adopting 12.5 kHz technology and later migrating to 6.25 kHz technology.”  The FCC “will expeditiously establish a schedule for transition to 6.25 kHz narrowband technology.”  <ref>{{Cite web |url=http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.pdf |title=In the Matter of Implementation of Sections 309(j) and 337 of the Communications Act of 1934 as Amended: THIRD MEMORANDUM OPINION AND ORDER, THIRD FURTHER NOTICE OF PROPOSED RULE MAKING AND ORDER |access-date=2009-01-22 |archive-date=2013-07-24 |archive-url=https://web.archive.org/web/20130724045248/http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.pdf |url-status=dead }}</ref>

==Technical characteristics==
NXDN uses [[frequency-division multiple access|Frequency-Division Multiple Access]] (FDMA) technology in which different communication streams are separated by frequency and run concurrently. [[time-division multiple access|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|Code-Division Multiple Access]] (CDMA) systems allow many users to share a common spectrum allocation by using [[spread spectrum|spread-spectrum]] techniques.

The basic NXDN channel is digital and can be either 12.5&nbsp;kHz or 6.25&nbsp;kHz wide.  6.25&nbsp;kHz dual-channel systems can be configured to fit within a 12.5&nbsp;kHz channel.  This effectively doubles the spectrum efficiency compared to an analog [[frequency modulation|FM]] system occupying a 12.5&nbsp;kHz channel.  The architecture of NXDN is such that two NXDN channels, within a 12.5&nbsp;kHz channel for example, can be allocated as voice/voice, voice/data, or data/data.  As of 2012, this capability cannot be implemented in commercially available hardware on simplex or "talkaround" frequencies, but only through repeaters.

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]] (137-174&nbsp;MHz) and [[UHF]] (406-512&nbsp;MHz) bands.

Data is transmitted using 4-level [[frequency-shift keying]] (FSK) modulation.  NXDN uses the AMBE+2 vocoder ([[codec]]) for digital audio.<ref>{{Cite web |url=http://www.dvsinc.com/press/PR20012.htm |title=New Vocoder Delivers Highest-Quality Available at 2.0 – 9.6 kbps |access-date=2009-01-22 |archive-date=2009-02-07 |archive-url=https://web.archive.org/web/20090207100636/http://dvsinc.com/press/PR20012.htm |url-status=dead }}</ref>  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 and slightly better multi-path characteristics than analog FM in typical RF environments, specifically at the 12&nbsp;dB [[SINAD]] threshold. The transmission bit rate is 4,800 bit/s.

The following FCC [[Types of radio emissions|emission designators]] apply to NXDN transmissions:<ref>{{Cite web|url=http://wiki.radioreference.com/index.php/Emission_Designator|title=Emission Designator - the RadioReference Wiki}}</ref>

*8K30F1E 12.5&nbsp;kHz single channel digital voice
*8K30F1D 12.5&nbsp;kHz single channel digital data
*8K30F1W 12.5&nbsp;kHz single channel digital voice and data
*4K00F1E 6.25&nbsp;kHz single channel digital voice
*4K00F1D 6.25&nbsp;kHz single channel digital data
*4K00F1W 6.25&nbsp;kHz single channel digital voice and data
*4K00F2D 6.25&nbsp;kHz single channel analog CW ID

==Application functions==
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]]:
**"Scramble encryption": A [[Maximum length sequence|pseudorandom binary sequence]] created by combining an [[Bitwise operation#XOR|exclusive-or bitwise operation]] on the audio or data stream and a [[linear-feedback shift register]] with a [[Primitive polynomial (field theory)|feedback polynomial]] of <math>x^{15} + x + 1</math>, which has a 32,767-bit repeat period, yielding 32,767 possible encryption keys except all zero.<ref name=":0">{{Cite book|title=NXDN Technical Specifications, TS 1-D Version 1.3|publisher=JVC KENWOOD Corporation and Icom Incorporated|year=2007–2012|pages=6, 9}}</ref> This level of encryption offers absolutely no protection and there is software that allows you to find the key instantly.<ref>{{cite web|title=NXDN scrambler key finder|url=https://archive.org/details/nxdnkeyfinder}}</ref>
**[[Data Encryption Standard|DES Encryption]]: 64-bit block encryption cipher operating in [[Block cipher mode of operation#OFB|OFB mode]] using a 56-bit key expressed in 64 bits with parity bits.<ref name=":0" /> This level of encryption helps protect against casual attackers but not against a company.<ref>{{cite web|title=Why is the Data Encryption Standard (DES) considered vulnerable to brute-force attacks|url=https://eitca.org/cybersecurity/eitc-is-ccf-classical-cryptography-fundamentals/conclusions-for-private-key-cryptography/multiple-encryption-and-brute-force-attacks/examination-review-multiple-encryption-and-brute-force-attacks/why-is-the-data-encryption-standard-des-considered-vulnerable-to-brute-force-attacks-and-how-does-modern-computational-power-affect-its-security/}}</ref>
**[[Advanced Encryption Standard|AES Encryption]]: 128-bit block encryption cipher operating in [[Block cipher mode of operation#OFB|OFB mode]] using a 256-bit key.<ref name=":0" /> This last level of encryption provides complete security.
*[[Pager|Paging]] & status reporting: radio-to-radio and dispatch-to-radio
*User aliases: 65,535 different group IDs and user IDs
*Man-down and emergency call
*Remote radio management functions: stun/kill/revive and monitor
*Over-the-air programming
*Over-the-air alias
*Interface to third-party applications for: paging to radio, GPS location, taxi data terminals, in-building tracking

==Audio quality==
In all [[Lossy audio compression|lossy compression]] schemes, trade-offs are made in voice reproduction quality in return for minimizing the raw bit rate of the transmission. This leads to artifacts and compromises of frequency response in reproduced speech. Encoders and other compression schemes that are highly optimized for speech are often unsuitable for non-speech audio, such as music or [[Frequency-shift keying|frequency-shift keyed]] data. Using an inappropriate encoder usually results in the creation of distortion and artifacts in the reproduced audio.

The audio reproduction quality of IDAS and NEXEDGE communications systems is dependent on the performance of the [[Advanced Multi-Band Excitation|AMBE+2]] voice codec used by NXDN. The AMBE family of vocoders has been subjected to comparative testing and found to be adequate for its intended uses, primarily mobile and aeronautical radio. The AMBE+2 vocoder has also been selected for use in the [[Motorola]] MOTOTRBO radio family as well as [[Digital mobile radio|DMR]] systems, and [[Project 25]] (P25) mobile radio system.  The following reports and papers are descriptions of laboratory-environment evaluations of AMBE+2 and other speech vocoders.<ref>{{cite journal|title=Voice Quality Assessment of Vocoders in Tandem Configuration|journal=NTIA Report 01-386|date=May 2001|url=http://www.its.bldrdoc.gov/pub/ntia-rpt/01-386/01-386_ocr.pdf|last1=Redding|first1=Christopher}}</ref><ref>{{cite book|year=1996|volume=ICASSP-96 Vol 1. Conference Proceedings|pages=499–502|doi=10.1109/ICASSP.1996.541142|chapter-url=http://dl.acm.org/citation.cfm?id=1256441|first=S.F.|last=Campos Neto|title=1996 IEEE International Conference on Acoustics, Speech, and Signal Processing Conference Proceedings |chapter=Performance assessment of 4.8 kbit/S AMBE coding under aeronautical environmental conditions |isbn=0-7803-3192-3|s2cid=9223464}}</ref><ref>{{cite journal|title=Project 25 Vocoder Evaluation Mean Opinion Score Test|journal=Tia TSB-102.babe|url=http://global.ihs.com/doc_detail.cfm?item_s_key=00534861}}</ref>

Compromises in audio quality are inherent in the use of any [[codebook]]-based [[speech coding|speech coder]], particularly when used in conditions of high background noise. Incremental improvements are being made in the algorithms, which may lead to differences in performance even while the basic method remains unchanged. In the US, the [[Department of Commerce]] Public Safety Communications Research laboratory regularly reports on progress in this field. While their work specifically pertains to Project 25 radios, it is directly applicable to any system using similar multi-band excitation coders.<ref>{{cite journal|url=http://www.pscr.gov/projects/audio_quality/mrt/mrt1.php |title=Welcome to the PSCR Program|journal=NIST |date=3 March 2016}}</ref>{{failed verification|date=August 2022|reason=Not substantiated by any text at this URL}}

==NXDN Forum==
The NXDN Forum was formed in order to promote the NXDN protocol in North and South America. The forum's members are:<ref>{{cite web|url=http://www.nxdn-forum.com/our-members/who-are-members/ |title=Who are our members? |website=nxdn-forum.com |accessdate=2022-08-04}}</ref>
*CML Microcircuits
*[[Freedom Communication Technology]]
*[[Hytera Communications]]
*[[Icom Incorporated]]
*[https://www.intertalksystems.com/ InterTalk Critical Information Systems]
*[[Kenwood Corporation]]
*[https://www.ritron.com/ Ritron, Inc.]
*[[Trident Micro Systems]] which was bought by Motorola Solutions in December 2014.
*[http://www.remotatec.com.br/ Remota Tecnologia em Comunicação]

==See also==
* [[Digital private mobile radio]]
* [[Digital mobile radio]]
* [[Terrestrial Trunked Radio]]

==References==
{{reflist}}

==External links==
*[http://www.icom.co.jp/world/idas/system/Information_Paper_FDMA_TDMA_Rev.1.0.pdf Comparison of FDMA and TDMA Systems]
*[https://www.nxdn-forum.com/download_file/ NDXN Standard]

{{Digital PMR standards}}
{{Trunked radio systems}}

{{DEFAULTSORT:Nxdn}}
[[Category:Wireless]]
[[Category:Mobile telecommunications standards]]
[[Category:Telecommunications-related introductions in 2005]]