Specialized Mobile Radio

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Specialized Mobile Radio (SMR) may be an analog or digital trunked two-way radio system, operated by a service in the VHF, 220, UHF, 700, 800 or 900 MHz bands. Some systems with advanced features are referred to as an Enhanced Specialized Mobile Radio (ESMR).[1] Specialized Mobile Radio is a term defined in US Federal Communications Commission (FCC) regulations. The term is of US regulatory origin but may be used in other regions to describe similar commercial systems which offer a radio communications service to businesses.

## History[edit]

SMRs were created when the Federal Communications Commission began to license business and commercial 800 MHz two-way radio systems in the late 1970s.[2]

## Compatibility and purpose[edit]

Any company, such as a taxi service, towing service, or construction company, may use an SMR service. These concerns may rent radios from the SMR operator or may buy compatible radios. SMR systems use differing protocols, frequency ranges, and modulation schemes: not every radio is compatible with every SMR system.

These systems generally consist of one or more repeaters used to maintain communications between a dispatch fleet of mobile or hand-held walkie talkie radios. One- to five-channel systems may be conventional two-way radio repeaters. More than five channel systems must be trunked.

## Fees[edit]

The radio system is operated by a commercial service. Paying a fee allows users to utilize the radio system backbone, increasing their range. Some SMR systems offer telephone interconnect. This allows telephone calls to be made from the mobile radio or walkie talkie. Some systems may also offer selective calling, allowing customers to communicate with individual radios or segments of their entire radio fleet.

Users are charged a fee for some combination of:

* Air time (the amount of time any of the user's radio units is talking).
* A monthly fee covering site lease costs, engineering, maintenance, and overhead.
* Rental of radio units, in some cases.

## Conventional two-way radio SMR system[edit]

In conventional systems, units are separated into groups by selective calling. Radios are usually segmented into customers with each customer on a separate selective calling code. Systems may use continuous tone-coded squelch system for this purpose. A disadvantage is that conventional systems require the user to disable selective calling, (to monitor,) in order to see if another company is talking before using the channel. Conventional systems are usually analog FM.

Block diagram of a five channel trunked system.

## Trunked SMR system[edit]

Main article: Trunked radio system

In trunked systems, units are separated into virtual groups by the embedded radio system logic. Channel assignments are controlled by a computer and software. These virtual groups are often referred to as "fleet" and "subfleet" or "talk groups". There is no monitor function on trunked systems, but users may get busy signals or cryptic overload messages on their radio's display if an attempt is made to transmit while all channels are busy.[3]

A service operating an SMR system must maintain a certain number of users for each licensed channel. This is called loading. The service must show adequate loading before licenses for more channels can be granted.

## Quality of service[edit]

In SMR systems, many factors affect the quality of service. This may include the capacity of the radio system versus the number of radio units using the system. A talkative user community may cause busy signals while a disciplined, professional group of SMR users may keep channels idle.

Some systems experience seasonal peaks. For example, a trunked system in an agricultural area used by crop harvesting crews may overload and experience busy signals during peaks in harvesting. A system used by a ski resort may overload on a holiday weekend. Disaster planning experts like to say that trunked system users are likely to hear busy signals for the first time when a disaster occurs. A major flood or earthquake is likely to generate a level of call traffic that loads the system to capacity.[4]

Siting of the system affects coverage: the system antennas should overlook the desired coverage area. Federal Communications Commission regulations require systems using the same radio frequency to be spaced 70 miles from one another or do an engineering study to confirm there will be no interference from closer spacing.

Maintenance practices also can affect quality. In some systems, the operator may remove one channel of a trunked system from service to perform repairs. In a heavily used system, this could cause busy signals.

Engineering documentation for these systems suggests another evaluation would be delivered audio quality. This is a measurement of the sound quality over all of the involved pieces of communications equipment from end to end. The first clue this may be an issue is that radio users with normal hearing have trouble understanding others when speaking over the radio.

## See also[edit]

* Business band
* iDEN
* Mobile radio
* Professional Mobile Radio
* Motorola Type I trunked radio system

## Notes[edit]

1. ^ See External link: Federal Communications Commission definition of SMR below.
2. ^ The date is unclear. The FCC web site has a page under the Wireless Telecommunication Bureau defining Specialized Mobile Radio Service. It claims licenses were first issued in 1979. Another publication suggests licenses were first issued in 1976. See: "3.6.1 Overview," Statewide Radio Interoperability Needs Assessment, (Phoenix, Arizona: Macro Corporation and The State of Arizona, 2004) pp. 30.)
3. ^ Some Nextel phones give the message, 'Please try again' when all channels are busy.
4. ^ SMR systems are not designed and built to the same standards as government trunked systems used to manage emergencies. There are many documents addressing this issue. One article discussing this topic is, "Intra- and Inter-County Coordination and Interoperability: Existing Cooperative Agreements," Contra Costa County Public Safety Mobile Radio Master Plan, Final Report, June 18, 2002, (Fairfax, Virginia: Federal Engineering, Inc., 2002) pp. 25.

## External links[edit]

* FCC definition of Specialized Mobile Radio.
* FCC PDF file describing US private radio services.

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Cellular network standards

List of mobile phone generations

0G radio telephones (1946)|

* MTS
* IMTS
* Altai
* OLT
* MTA - MTB - MTC - MTD
* Mobile TeleSeratout
* AMTS
* Autotel (PALM)
* ARP
* B-Netz
* AMR

1G (1979)|

| AMPS family|

* AMPS - N-AMPS
* TACS - ETACS

|

Other|

* NMT
* C-450
* Hicap
* Mobitex
* DataTAC
* CT1

2G (1991)|

| GSM/3GPP family|

* GSM
* CSD - HSCSD

|

3GPP2 family|

* cdmaOne (IS-95)

AMPS family|

* D-AMPS (IS-54 and IS-136)

Other|

* CDPD
* iDEN
* PDC
* PHS
* CT2

2G transitional
(2.5G, 2.75G, 2.9G)|

| GSM/3GPP family|

* GPRS
* EDGE/EGPRS - Evolved EDGE

|

3GPP2 family|

* CDMA2000 1X (TIA/EIA/IS-2000)
* CDMA2000 1X Advanced

Other|

* WiDEN
* DECT

3G (1998)
IMT-2000 (2001)|

| 3GPP family|

* UMTS
* UTRA-FDD / W-CDMA
* FOMA
* UTRA-TDD LCR / TD-SCDMA
* UTRA-TDD HCR / TD-CDMA

|

3GPP2 family|

* CDMA2000 1xEV-DO Release 0 (TIA/IS-856)

3G transitional
(3.5G, 3.75G, 3.9G)|

| 3GPP family|

* HSPA
* HSDPA
* HSUPA
* HSPA+
* DC-HSDPA
* LTE (E-UTRA)

|

3GPP2 family|

* CDMA2000 1xEV-DO Revision A (TIA/EIA/IS-856-A)
* EV-DO Revision B (TIA/EIA/IS-856-B)
* EV-DO Revision C

IEEE family|

* Mobile WiMAX
* IEEE 802.16e
* Flash-OFDM
* iBurst (IEEE 802.20)
* WiBro

ETSI family|

* HiperMAN

4G (2009)
IMT Advanced (2013)|

| 3GPP family|

* LTE Advanced (E-UTRA)
* LTE Advanced Pro (4.5G/4.9G)

|

IEEE family|

* WiMAX (IEEE 802.16m)
* WiMax 2.1
* WiBro

5G (2018)
IMT-2020 (2021)|

| 3GPP family|

* 5G NR
* 5G-Advanced
* NR-IIoT
* LTE-M
* NB-IoT

|

Other|

* DECT-5G

Related articles|

* Cellular networks
* Mobile telephony
* History
* Comparison of standards
* Channel access methods
* FDMA
* OFDMA
* TDMA
* STDMA
* SSMA
* CDMA
* SDMA
* Spectral efficiency comparison table
* Frequency bands
* GSM
* UMTS
* LTE
* 5G NR
* CDMA
* Mobile broadband
* Multimedia Broadcast Multicast Service
* NGMN Alliance
* Push-to-talk
* MIMO
* IMS
* VoLTE
* ViLTE
* VoNR
* ViNR
* Wi-Fi Calling
* Osmocom

Telecommunication portal Telephones portal

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Two-way radio

Amateur and hobbyist|

* Amateur radio
* Amateur radio repeater
* Citizens band radio
* Family Radio Service
* Public Radio Service
* General Mobile Radio Service
* KDR 444
* LPD433
* Mobile rig
* Multi-Use Radio Service
* PMR446
* UHF CB (Australia)

Aviation
(aeronautical mobile)|

* Air traffic control
* Aircraft emergency frequency
* Airband
* Common traffic advisory frequency
* Mandatory frequency airport
* MULTICOM
* Single Frequency Approach
* UNICOM

Land-based commercial
and government mobile|

* Base station
* Business band
* Mobile radio
* Professional mobile radio
* Radio repeater
* Specialized Mobile Radio
* Trunked radio system
* Walkie-talkie

Marine (shipboard)|

* 2182 kHz
* 500 kHz
* Coast radio station
* Marine VHF radio
* Maritime mobile amateur radio

Signaling /
Selective calling|

* CTCSS
* D-STAR
* Dual-tone multi-frequency
* MDC-1200
* Push-to-talk
* Quik-Call I
* Quik-Call II
* Selcall
* SELCAL

System elements
and principles|

* Antenna
* APRS
* Automatic vehicle location
* Call sign
* CAD
* DC remote
* Dispatch
* Dynamic range compression
* Fade margin
* Link budget
* Rayleigh fading
* Tone remote
* Radiotelephony procedure
* Voting (diversity combining)

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