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 A two-way radio is a radio that can both transmit and receive radio waves (a transceiver), unlike a radio broadcasting, broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and radio receiver, receive ...

s (

transceiver In radio communication, a transceiver is an electronic device which is a combination of a radio ''trans''mitter and a re''ceiver'', hence the name. It can both transmit and receive radio waves using an antenna, for communication purposes. Thes ...

s) for bidirectional person-to-person voice communication. It was developed jointly by

Icom Incorporated is a Japanese manufacturer of radio transmitting and receiving equipment, founded in 1954 by Tokuzo Inoue with the company's original name being "Inoue". Its products now include equipment for radio amateurs, pilots, maritime applications, land ...

and

Kenwood Corporation is a Japanese brand of consumer electronics. It has been owned by JVCKenwood ever since October 2011, when Kenwood Corporation merged with JVC. Kenwood manufactures audio equipment such as cassette tape decks/recorders, amateur radio (ham) e ...

as an advanced

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...

system using FSK modulation that supports

encrypted In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can deci ...

transmission and data as well as voice transmission. Like other land mobile systems, NXDN systems use the

VHF Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF ...

and

UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (on ...

frequency bands. It is also used as a niche mode in

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency commu ...

. NXDN is implemented by Icom in their IDAS system and by Kenwood as NEXEDGE; both Kenwood and Icom now offer dual-standard equipment which supports the European dPMR standard. NEXEDGE NXDN

History

Icom and Kenwood began their collaboration in 2003. The NXDN protocol was announced in 2005, and NXDN-compatible products first appeared in 2006. 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 a
an international digital land mobile system

Applications

The NXDN protocol and the communications products in which it is used are intended for commercial Private Land Mobile Radio (PLMR) and public safety communications systems. The technology satisfies the U.S.

Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdicti ...

(FCC) mandate requiring all communications systems covered by Part 90 regulations to use

narrowband Narrowband signals are signals that occupy a narrow range of frequencies or that have a small fractional bandwidth. In the audio spectrum, narrowband sounds are sounds that occupy a narrow range of frequencies. In telephony, narrowband is usua ...

technology by January 1, 2013. Part 90 regulations specify a bandwidth of 12.5 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.”

Technical characteristics

NXDN uses

Frequency-Division Multiple Access Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing ...

(FDMA) technology in which different communication streams are separated by frequency and run concurrently.

Time-Division Multiple Access Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession ...

(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) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...

(CDMA) systems allow many users to share a common spectrum allocation by using

spread-spectrum In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (e.g., an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency do ...

techniques. The basic NXDN channel is digital and can be either 12.5 kHz or 6.25 kHz wide. 6.25 kHz 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. The architecture of NXDN is such that two NXDN channels, within a 12.5 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

(137-174 MHz) and

(406-512 MHz) bands. Data is transmitted using 4-level

frequency-shift keying Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather bal ...

(FSK) modulation. NXDN uses the AMBE+2 vocoder (

codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...

) 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 and slightly better multi-path characteristics than analog FM in typical RF environments, specifically at the 12 dB

SINAD Signal-to-noise and distortion ratio (SINAD) is a measure of the quality of a signal from a communications device, often defined as : \mathrm = \frac, where P is the average power of the signal, noise and distortion components. SINAD is usually ex ...

threshold. The transmission bit rate is 4,800 bit/s. 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

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 In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can d ...

: **"Scramble encryption": A

pseudorandom binary sequence A pseudorandom binary sequence (PRBS), pseudorandom binary code or pseudorandom bitstream is a binary sequence that, while generated with a deterministic algorithm, is difficult to predict and exhibits statistical behavior similar to a truly rand ...

created by combining an exclusive-or bitwise operation on the audio or data stream and a

linear-feedback shift register In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state. The most commonly used linear function of single bits is exclusive-or (XOR). Thus, an LFSR is most often a ...

with a feedback polynomial of

x^ + x + 1

, which has a 32,767-bit repeat period, yielding 32,767 possible encryption keys except all zero. ** DES Encryption: 64-bit block encryption cipher operating in OFB mode using a 56-bit key expressed in 64 bits with parity bits. **

AES Encryption The Advanced Encryption Standard (AES), also known by its original name Rijndael (), is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES is a variant ...

: 128-bit block encryption cipher operating in OFB mode using a 256-bit key. *

Paging In computer operating systems, memory paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storage ...

& status reporting: radio-to-radio and dispatch-to-radio *User aliases: 65,545 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 compression In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data si ...

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 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 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 Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent public companies, Motorola ...

MOTOTRBO radio family as well as Hytera's DMR systems, and the

Project 25 Project 25 (P25 or APCO-25) is a suite of standards for interoperable digital two-way radio products. P25 was developed by public safety professionals in North America and has gained acceptance for public safety, security, public service, and ...

(P25) mobile radio system. The following reports and papers are descriptions of laboratory-environment evaluations of AMBE+2 and other speech vocoders. Compromises in audio quality are inherent in the use of any

codebook A codebook is a type of document used for gathering and storing cryptography codes. Originally codebooks were often literally , but today codebook is a byword for the complete record of a series of codes, regardless of physical format. Cryptog ...

-based 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 The United States Department of Commerce is an executive department of the U.S. federal government concerned with creating the conditions for economic growth and opportunity. Among its tasks are gathering economic and demographic data for busi ...

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.

NXDN Forum

The NXDN Forum was formed in order to promote the NXDN protocol in North and South America. The forum's members are: *CML Microcircuits * Freedom Communication Technology * Hytera Communications *

InterTalk Critical Information Systems
*

Ritron, Inc.
* Trident Micro Systems which was bought by Motorola Solutions in December 2014.
Remota Tecnologia em Comunicação

References

External links

Comparison of FDMA and TDMA SystemsNDXN Standard
{{DEFAULTSORT:Nxdn Wireless Mobile telecommunications standards Telecommunications-related introductions in 2005