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Technology and Components. Two-Way Radio Explained.

There are many two-way radio technology available today. The table shows each of technology in terms of whether it is analog or digital, and whether it is conventional or trunked. Note that the analog conventional is the most basic and well known technology. We will not discuss analog conventional system.

The ComponentsThe following diagram illustrate major components in two-way radio system. The diagram shows a typical wide area network.Typical Network ComponentIn a typical configuration, a wide area radio network consists of 3 major components:

–         Switching system

–         Base Stations

–         Radio Terminal

Note that the above configuration applies to a wide area radio network. For a single site radio network, typically there is no centralized switching system. Its ‘switching’ or commonly known as controller resides in the same physical location as Base Station. Thus, a single-site radio network consists of:

–         Base station or site repeater (which includes site controller)

–         Radio Terminal

Radio Terminal

Also known as: Subscribers Unit, Radio Unit, Mobile Station, Portable Radio, Mobile Radio, Fixed-Station Radio

This is a device for the user to communicate and interface to the network. For end-users, they will mostly see these devices more often than the radio infrastructure itself. Thus, the ergonomics and performance of radio terminal (i.e. size, weight, battery life, user interface and ease of use) plays important role for end-user’s acceptance of radio system.

In general, radio terminal can be classified into:

–         Portable Radio

This is the device that users can carry while in the move. Since users carry this device most of the time, the ergonomics of portable radio (i.e. size and weight) is one of the important factors for users. However, size, weight and battery life are, among others, factors that limit the performance of radio unit. Portable radios usually have lower power output compared to mobile or fixed-station radio due to the above limitation factors. Thus, the range of portable radio is typically smaller than mobile or fixed-station radio. In many cases, portable radio with higher power comes with bigger form factors. Usually there will be a trade-off between the size of portable and power output. You can have either a smaller form factor radio but lower power or bigger form factor with higher power.

–         Mobile Radio

This is the device that is permanently installed in a vehicle or a car. The size and weight of this mobile radio is bigger than a portable radio but it usually does not really matter to user because mobile radio is permanently fixed into the vehicle (i.e. users do not have to ‘carry’ a mobile radio). Typically a mobile radio has higher power output than a portable radio due to its form factor which facilitates more components to produce higher power as well as it does not have issue with battery life (it uses vehicle battery for its power). Thus, the range of a mobile radio is usually greater than portable radio.

–         Fixed-Station Radio

This device is usually installed in a fixed location such as a branch office or a field post. Typically, a fixed-station radio is a mobile radio with a power supply, external microphone or speaker and better antenna system (such as directional antenna). Thus, the range of fixed-station radio is greater than mobile and portable radio.

Base Station or Repeater

Also known as: Site repeater, RF Repeater, Site

This is a network component that provides RF coverage in a radio network. In typical configuration, a base station can consist of RF Repeater(s), Controller(s), antenna distribution system (i.e. duplexer, combiner, etc) and Power Supply.

In the traditional Two-way Radio world, the term Base Station is also known as a fixed station that receives a signal but does not re-broadcast the signal to other radio users in the system. This configuration allows an operator, commonly known as the dispatcher, sitting in the office to communicate with the radio terminals in the field. The term Repeater is used referring to a transceiver that receives a signal and re-transmits it at the same time. The primary purpose of repeaters is to extend coverage. The main difference between base station and repeater is that a repeater repeats a signal that it receives, a base station doesn’t.

Nowadays, the term of Base Station and Repeaters are often mixed referring to network components that provides RF coverage.

In one radio network, there can be multiple base stations or repeaters to provide necessary coverage. In a wide area configuration, these base stations are connected to a central switch that manages the entire network. The connection from the base stations to switch is called a Site Link.

Switching System or Controller

Also known as: Central controller, central switch, Mobile Switching Office (MSO)

This is a network component that manages the entire network. The switching system, for example, manages the traffic in and out and routes the communication to and from base stations. The switching system is the brain of the network without which the network will not be able to handle wide area network calls.

In typical configuration, a switching system can consist of multiple devices or equipments. Each equipment handles specific function. For example, one equipment handles the routing of the calls while the other handles interaction with base stations. More often than not, these devices or equipments are placed in rack(s) or cabinet(s). Depending on the complexity of the network, the switching system can have from one to well over ten racks.

Mobile Switching Office (MSO)

Also known as: Switching system, Controller, Central controller, central switch

This refers to physical location where all of network switching or controller is placed. This term is derived from cellular network for a common term to refer to its switching system. Since the switching system is located in one physical location, the “generic” term is Mobile Switching Office (MSO) with an “office” word added to emphasize a location that accommodates various equipment of the switch.

In two-way radio, this term is sometimes also used to refer to the radio switching system, especially for radio network with complex switching system. A digital trunked radio system, like iDEN for example, has architecture similar to a cellular system. Its switching system is as complex as the cellular system. Thus, the iDEN switching system sometimes refers to iDEN MSO.

Site Link

This is a facility to connect base station(s) to its switching system. Depending on the technology and products, site link can be E1, partial E1, microwave, 4W, fiber-optic network and any other means to connect base station to its switching with necessary bandwidth and performance. In many radio network installations, site link(s) can be leased from a telecom provider (i.e. E1 line) or owned by the organization (i.e. microwave). Leased line will typically incur a monthly recurring cost but has lower maintenance cost while privately owned link will need a higher capital expenditure to buy the equipment and maintenance expenses but organizations do not to need to pay monthly subscription like leased line.

There are several discussions on the use of satellite as site link. The long delay of satellite link is one of the main factors that need to be considered for two-way radio network implementation, especially for group call type of communication. The use of satellite link for two-way radio is discussed in the Advanced Topics.

Antenna System

This is a device connected to the base station / repeater to propagate the Radio Frequency (RF) energy. Antenna system plays an important role to determine the efficiency of converting electrical energy into RF energy. Thus, determine the area of coverage.

There are several antenna configurations to meet various condition and terrain.

Typical antenna parameters are:

  • Frequency Band: This is the range of the band that the antenna will operate in (i.e. 806-870 MHz). This only means that the antenna will operate within this band.  It usually does not necessarily mean that the antenna will operate over the entire band.
  • Bandwidth: The maximum frequency separation that this antenna will operate within the frequency band.
  • Gain: Antenna gain is proportional to the product of directivity and the antenna’s efficiency. Directivity is a measure of how an antenna focuses energy. Antenna’s efficiency accounts for loss associated with antenna. Gain is achieved in an antenna by re-directing energy from some directions into the desired directions. The higher the gain of the antenna, the further the coverage obtained. However, a higher gain antenna typically means higher cost.
  • Radiation Pattern: In Two-Way Radio there is usually a uni-directional antenna or omni-directional antenna. The names reflect the radiation pattern produced by each type of antenna.
  • Maximum Input Power: Look for the specs that the maximum input power rating of the antenna is greater than the RF power output rating of the transmitter(s).
  • VSWR (Voltage Standing Wave Ratio):A high VSWR (Voltage Standing Wave Ratio) implies a large amount of reflected power.  This means that the amount of forward power is less. Rule: The higher the VSWR, the less efficient the antenna.
  • Length: This refers to the physical length of the antenna.A long antenna is cumbersome to ship, store or install.
  • Wind Loading:In windy areas, the load of the wind on the antenna must be taken into account.

Dispatcher or Console System

This is a network sub-system where an operator, commonly known as dispatcher, interfaces with the network to monitor users’ activities and communicate with users in the field. The dispatcher acts as the central focus of the most two-way radio system and usually has more powerful features to allow the dispatcher operator to effectively monitor and manage the users in the field. The dispatcher is usually located at organization’s control center (also known as: Command and Control room or Monitor room).

In traditional two-way radio system, console or dispatcher system has various buttons and LEDs to facilitate monitoring and managing various talk group. In a modern two-way radio system, these buttons and LEDs are replaced with Personal Computer equipped with specialized Digital Sound Processing (DSP) card and other specialized equipment to facilitate monitoring and managing users effectively. Many dispatcher and console system has a Graphical User Interface (GUI) for ease of use.

Network Management System

This is a network sub-system to monitor and manage all related components in the entire network. Depending on the products, Network Management System can vary in term of functionalities and performance. An industry standard for network management which follows the Open System Interconnection (OSI) reference model will have, at least, the following functional management known as FCAPS:

–         Fault management

–         Configuration management

–         Accounting management

–         Performance management, and

–         Security management

In modern two-way radio system, the Network Management System uses computerized system, such as Personal Computer with specialized hardware and software to perform the function. The use of Personal Computer with Graphical User Interface (GUI) will make it easier for network manager to monitor and manage the network.

Area of Coverage

Area of coverage indicates the area where the radio terminals have usable signal (uplink and downlink) to use the radio network. The usable signal means an acceptable signal level that allows user to communicate. A term that is mostly used in area of coverage is coverage reliability. A 95% coverage reliability means that there is 95% chance that user will have the acceptable signal level in particular area of coverage. The higher the number, the better the coverage but it usually comes with higher cost due to the need to build more base station or repeater sites.

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