science

NXDN

NXDN is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand NXDN rather than just read about it. In short: NXDN stands for Next Generation Digital Narrowband, and is an open standard for public land mobile radio systems; that is, systems of two-way radios (transceivers) for bidirectional person-to-person voice communication. It was developed jointly by Icom Incorporated and Kenwood Corporation as an advanced digital system using FSK modulation that supports encrypted transmission and data as well as voice transmission.

Key takeaways

NXDN belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NXDN to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NXDN from memory before moving on to harder problems.

Reference excerpt

NXDN stands for Next Generation Digital Narrowband, and is an open standard for public land mobile radio systems; that is, systems of two-way radios (transceivers) for bidirectional person-to-person voice communication. It was developed jointly by Icom Incorporated and Kenwood Corporation as an advanced digital system using FSK modulation that supports encrypted transmission and data as well as voice transmission. Like other land mobile systems, NXDN systems use the VHF and UHF frequency bands. It is also used as a niche mode in amateur radio. 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.

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 as 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 (FCC) mandate requiring all communications systems covered by Part 90 regulations to use narrowband 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 (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 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 VHF (137-174 MHz) and UHF (406-512 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 and slightly better multi-path characteristics than analog FM in typical RF environments, specifically at the 12 dB SINAD 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: "Scramble encryption": A pseudorandom binary sequence created by combining an exclusive-or bitwise operation on the audio or data stream and a linear-feedback shift register with a feedback polynomial of x 15 + x + 1 {\displaystyle x^{15}+x+1} , which has a 32,767-bit repeat period, yielding 32,767 possible encryption keys except all zero. This level of encryption offers absolutely no protection and there is software that allows you to find the key instantly. DES Encryption: 64-bit block encryption cipher operating in OFB mode using a 56-bit key expressed in 64 bits with parity bits. This level of encryption helps protect against casual attackers but not against a company. AES Encryption: 128-bit block encryption cipher operating in OFB mode using a 256-bit key. This last level of encryption provides complete security. 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

… excerpt ends here. Continue reading the full article.

Illustrations

NXDN: IDAS Radio IC-F3162DT — IDAS Radio IC-F3162DT

Worked examples

Example 1 — a first encounter with NXDN

Start with the simplest possible case. Write down what NXDN claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to NXDN before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about NXDN ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of NXDN

In research: NXDN appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses NXDN in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: NXDN is common in secondary-school and first-year university syllabi. It links to neighbouring topics Mobile telecommunications standards, Telecommunications-related introductions in 2005, Wireless, so understanding it makes those chapters shorter.
In everyday life: Look for NXDN outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study NXDN in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NXDN means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain NXDN out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NXDN in simple terms?

Why does NXDN matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study NXDN?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on NXDN.