FAQ about NXDN™
Q01:Who are the target users of NXDN™?
The acceptance of NXDN™ has far exceeded the initial Business and Industry market tier it was originally aimed. A myriad of market categories like security, transportation, railways, construction, shopping malls, factories, taxi companies, hotels and more use NXDN™ worldwide. The fastest growing user segment is public safety, with agencies from police, fire, municipal services and miltary quickly embracing NXDN technology.
Q02:What are the features of NXDN™?
The NXDN™ standard provides for most of the features that analog systems have supported like various call types, data communication, GPS location services, messaging and test/status features etc. For information on the specific feature sets of current NXDN™ products, it is recommended to look at individual product literature of our members.
Q03:Is there a time delay in digital communication?
There is a minimal delay between the transmission and reception in digital mode due to the characteristics of encoding and decoding voice by the vocoder. This delay is not noticeable to the user unless the calling person is within hearing range. The same delay occurs with cellular phones and other digital technologies too.
Q04:Is there “signaling” in digital mode?
Because it is digital, there is no "signaling" like CTCSS as such. However, the equivalent Selcall type functions like Individual Call or Group Call that you would utilize with signaling in analog mode, are available in digital mode too. For example, in NXDN™, the RAN (Radio Access Number) feature acts like a CTCSS/DTCS code in analog mode.
Q05:How many RAN (Radio Access Number) codes are available?
Up to 63 RAN codes are available.
Q06:Is there a digital encryption feature in NXDN™?
A 15-bit digital voice scrambler is a standard feature in the NXDN™ protocol. It does provide superior communications security compared to most standard analog voice scramblers. The NXDN™ digital voice scrambler has over 32,000 codes.
Q07:Is it possible to have more than a 15-bit digital scrambler?
The NXDN™ specification has recently added DES and AES encryption options that allow for high-level communications security.
Q08:What are Type-C and Type-D NXDN™ trunking?
Type-C is Centralized (Control channel) type trunking and Type-D is Distributed logic trunking.
Q09:Why have Type-C and Type-D NXDN™ trunking been developed?
The goal to become a defacto standard requires NXDN™ to appeal to as many markets and their specific needs as possible.
As NXDN™ was developed to meet the FCC mandate for narrowbanding, in a major market such as North America, it was recognized that both control channel and distributed logic trunking architectures were equally predominant in this market based on the analog equivalents already in deployment.
Q10:What are the licensing issues associated with NXDN™ and 6.25 kHz?
Due to the spread of NXDN™ throughout the world and the recognition of its capabilities as a communications protocol, many national administrations have already implemented licensing rules or adopted the use of 6.25 kHz channels in their national band plans for professional radio.
For example, the United States already has over 3,000 channels dedicated as 6.25 kHz channels and the FCC has recently announced a ruling allowing licensing of 2 x 6.25 kHz channels in a 12.5 kHz channel. (For UHF only at this time) Frequency co-ordination entities have also proactively made recommendations for systems interference parameters and installation guidelines.
As with any radio licensing issue, enquiries to the respective administration should be made in advance if there are doubts on what can be installed etc.
Q11:What exactly are the requirements for using 2 x 6.25 kHz in a 12.5 kHz channel in the USA?
Again we recommend that consultation with frequency coordinators and/or licensing authorities is done in advance, but the basic guidelines are as follows.
On January 5, 2012, the FCC Wireless Telecommunications Bureau and Public Safety and Homeland Security Bureau approved licensing two channels of 4 kHz occupied bandwidth with their center frequencies offset by 3.125 kHz above and below the center frequency of a designated 12.5 kHz frequency.
Specific procedures and conditions apply:
- Emission designations 4K00F1E, 4K00F1D, 4K00F2D and 4K00F7W (NXDN™)
- 450-470 MHz band listed within FCC Rule Sections 90.20 and 90.35
- 12.5 kHz (FB8) exclusive use channels pursuant to FCC Rule Section 90.187
- Normal rules for a mobile “pair”; separated by 5 MHz pursuant to Section 90.173(i)
Note: for a copy of the FCC letter, please click here:http://www.fcc.gov/document/non-standard-frequency-pairs-450-470-mhz-band
Q12:What is the process to make these requirements work?
The following is a general description of the logic.
- The “authorized bandwidth” of a narrowband channel is 11.25 KHz
- The “authorized bandwidth” of a ultra narrowband signal is 6 kHz
- The “occupied bandwidth” of an NXDN™ 6.25 kHz signal is 4 kHz
- Two NXDN™ signals (4kHz each) meet the 12.5 kHz emission mask without interfering with a neighbor or each other
- A licensee is able to maintain its current bandwidth and not “bleed over” into adjacent spectrum
- A frequency coordinator will submit license applications listing both the 12.5 kHz and non-standard channel centers
Q13:What is the real story regarding potential interference at 6.25 KHz? Fact or myth?"
As with analog equipment to date, any NXDN™ radio product MUST comply with national type approval regulations or they cannot be legally sold. Considering the vast numbers of NXDN™ radios already in the market as stated in this document, the most honest answer would be that NXDN™ would cause no more interference than any other two way radio technology.