Some Brief Descriptions of Various Radio Systems

Frequency Division Multiple Access (FDMA)
Original cellular channels were 30 KHz wide and accommodated one voice signal subscriber.

Time Division Multiple Access (TDMA)
Increased the number of users by 3:1 by allowing each subscriber to talk for a few milliseconds in rotation, three conversations now take place within the same 30 KHz channel.

Code Division Multiple Access (CDMA)
Spread spectrum techniques Frequency Hopping and Direct Sequence. Both systems use vocoders (voice coder/decoder) to digitize the signal.

• Frequency Hopping: many different frequency changing sequences as there are radios in a given area, many conversations may occur at the same time over the same spectrum.


• Direct Sequence: transmitted digital signals are coded by a “spreading circuit” in each transmitter. Each receiver has a decoder that deciphers the spread signal and recovers the voice.

Location and Monitoring Service (LMS)
LMS systems utilize non-voice radio techniques to determine the location and status of mobile radio units (902-928 MHz).

Interactive Video and Data Service (IVDS)
An IVDS system is a point-to-multipoint, multipoint-to-point, short distance communications service for its licensees to provide information, products, or services to, and allow interactive responses from, subscribers in the licensee's service area.

Trunked Radio System (TRS)
A trunked radio system differs from a conventional system in its ability to automatically search two or more available channels and assign a user an open channel. In a conventional radio system, a radio can access only one channel at a time.

• Trunk (telephony). A one or two-way channel provided as a common traffic artery between switching equipment.


• Trunk Group. All of the trunks of a given type of characteristic that extend between two switching points.

Personal Radio Services (PRS)
Short-range, low power radio for personal communications, radio signaling, and business communications not provided for in other services.

• 218-219 MHz Service - One or two way communications for transmission of information to subscribers within a specific service area. ULS Radio Service Codes ZV - Formerly IVDS now 218-219 MHz. Band 218.0-218.5 MHz, 218.5-219.0 MHz. (Part 95)


• Citizens Band (CB) Radio Service - 1-5 mile range two-way voice communication for use in personal and business activities. Band 26.865-27.405 MHz. (Part 95.4)


• Family Radio Service (FRS) - 1 mile range Citizen Band service for family use in their neighborhood or during group outings. Band 462.5625-467.7125 MHz (Part 95.191-95.194)


• General Mobile Radio Service (GMRS) - 5-25 mile range Citizen Band service for family use in their neighborhood or during group outings. Band 462-467 MHz. (Part 95.1-95.181)


• Low Power Radio Service (LPRS) - private, one-way communications providing auditory assistance for persons with disability, language translation, and in educational settings, health care, law, and AMTS coast stations. Band 216.75-217.0 MHz. Part 95)


• Medical Implant Communications Service (MICS) - for transmitting data in support of diagnostic or therapeutic functions associated with implanted medical devices. Band 402-405 MHz. (Part 95)


• Radio Control Radio Service (R/C) - one-way non-voice radio service for on/off operation of devices at places distant from the operator. Band 72.0-73.0 MHz, 75.4-76.0 MHz. (Part 95.201-95.225)


• Wireless Medical Telemetry Service (WMTS) - for remote monitoring of patients’ health through radio technology and transporting the data via a radio link to a remote location, such as a nurses’ station. Band 608-614 MHz, 1395-1400 MHz, 1427-1432 MHz. (Part 95)

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