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Phoenix Regional Wireless Network
Glossary of Terms
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There's almost a whole new language associated with the 800 MHz. Here's a glossary of terms that may help you understand the new communications system.800 MHz
This refers to the range of frequencies that will be utilized in the new radio network. Usually this term is applied to any network that broadcasts on frequencies between 800 and 900 MegaHertz. Specifically, the Phoenix-Mesa radio network will initially broadcast on frequencies between 821 and 824 MHz, and receive on those between 866 and 869 MHz. The FCC has reserved these frequencies for public safety purposes.Analog
Whenever a person speaks, sound is projected in the form of a sound wave. These waves move at a certain frequency that determines the pitch of the sound. An analog radio network transmits the actual wave of a person's voice over the air by modulating it onto a radio frequency carrier. An analog network operates differently from a digital network, which converts the vocal sound wave into a digital bit stream of ones and zeros. This information is then sent over the air, and eventually converted back into an analog wave to be heard. The new Phoenix-Mesa 800 MHz network uses a digital format that will replace an analog format.APCO
This stands for The Association of Public Safety Communications Officials. This agency is composed of many different public safety employees and representatives from around the world. APCO was one of the lead agencies in the development of the Project 25 Standard on which our new radio system is based.ASTRO
This is a type of radio communication system developed by Motorola that utilizes narrowband digital technology. This system makes good use of available frequencies, and allows for greater security than older systems. ASTRO can stand alone as a digital network or incorporate analog technology as well.Backward Compatibility
This term refers to the capability of a piece of equipment (i.e. software program, hardware component) to be compatible with its predecessor in all forms. For instance, Microsoft Word 2000 is backward compatible since it can create documents that will run in Microsoft Word '97.Base Station
This term refers to a stationary radio connected to an antenna. The antenna is located where it can transmit into and receive from a geographic area where mobile and portable radios are being operated. In our system the mobile and portable radios can communicate at extended distances from each other by communicating through the base stations. (See Repeaters) The mobile and portable radios can also communicate with dispatchers at radio consoles who are remotely operating the base station radios via our system.Common Air Interface (CAI)
This refers to the protocol by which handheld and mobile radios communicate with the radio system infrastructure. In modern radio systems this is typically a proprietary format, however the CAI, defined by the Project 25 Standard, makes this an open protocol. This allows different manufacturers' portable and mobile radios to work together on a single radio system.Console
A console is used by a dispatch operator to communicate with users in the field, to track radio activity, and to coordinate the efforts of various public safety agencies. A typical dispatch position consists of various types of equipment, which along with the radio console includes several different tracking and communication systems, usually running on anywhere from one to five computers. Dispatchers usually operate in a public safety facility, with consoles set up in their individual work areas.Conventional
A conventional radio network allocates specific frequencies to specific groups of radio users permanently. If nobody in a particular group is transmitting on their assigned frequency, then that channel remains open. This is in contrast to a trunking network which assigns frequencies to users only when they are needed, which can be more efficient. The Phoenix-Mesa 800 MHz network will be a trunking network, and will replace a conventional network.Coverage/Coverage Area
A radio network's coverage area refers to the entire area that gets a strong enough signal from the network for a radio in the field to transmit and receive. Once a signal from a network degrades so badly that it is essentially useless, and all transmissions are bad or impossible, then that area is considered to be out of the coverage area. The Phoenix-Mesa 800 MHz digital network has a projected coverage area that spans the entire Phoenix metropolitan area. The coverage area is often called the "footprint" of a network.Digital
The term "digital" refers to the method of expressing information in one of two different electronic states, which are usually designated as ones or zeros. These ones and zeros form a pattern that can be translated into all kinds of information. Relaying digital information through an electrical system is done by transmitting electronic pulses with one of two distinct electrical charges. These pulses are usually referred to as either "1" or "0", with the "1" pulse usually having a higher voltage, or charge, than the "0" pulse. Electronic equipment such as computers can interpret the information by: a) receiving a set of electronic pulses, b) sensing the different voltages of the pulses, therefore determining whether each pulse is a "1" or a "0", and c) combining many of these ones and zeros to form instructions that tell the computer what to do.Encryption
Digital transmissions can use encryption to secure information that is being transmitted. The reason this security technique is so effective is because the encrypted transmissions can only be deciphered by a radio with the proper decryption key. This key consists of a software application that is programmed into the authorized radios. With the new Phoenix-Mesa 800 MHz network, digital encryption is incorporated as part of the Motorola ASTRO 25 system.FCC
This stands for the Federal Communications Commission. This governmental agency decides how frequencies are to be used, as well as who can transmit on them. The FCC sets aside specific amounts of frequencies for public safety transmissions, commercial wireless carriers, television broadcasts, etc. Traditionally, the FCC grants blocks of frequencies to public safety agencies, while commercial carriers must buy a license to transmit from the FCC.Frequency
All radio networks broadcast their transmissions through antennas on a certain frequency. The number of the frequency refers to the number of times that an electromagnetic wave repeats in the span of one second. For example, a transmission being sent at 800 MHz means that its wavelength repeats 800,000,000 times per second. With sophisticated electronic equipment, these waves can be engineered to carry large amounts of information over great distances.Intelligent Site Repeater
An Intelligent Site Repeater is a radio site which utilizes a device called a site controller. This controller can perform all call processing and channel assignment tasks that are required to operate the site's base stations. Intelligent Site Repeaters will be utilized in the new Phoenix-Mesa 800 MHz digital radio network.Interoperability
This term refers to the capability of separate and independent entities to work together seamlessly. The new Phoenix-Mesa 800 MHz network will promote full interoperability between all participating agencies. For example, the Mesa Fire Department will be able to communicate with the Phoenix Police Department should the need arise. This feature is incorporated in this network as part of the Project 25 standard.IP
IP, or Internet Protocol, is a method by which data is transferred over a network. IP is widely used across the Internet. Every computer attached to the Internet is assigned a unique number, called an IP address. Using IP, a data transmission is split electronically into smaller pieces of data called packets. Every data packet contains two IP addresses: one for the sending computer, and one for the receiving computer. These addresses help route the packets of a digital message to its proper destination.Loading
The FCC awards licenses for frequency usage based on an expectation that there will be a minimum number of users on each channel by a certain time. This amount of users per channel is referred to as loading. For instance, if a wireless network builder purchased licensing for 20 channels from the FCC, then the FCC might stipulate that there must be a certain amount of loading, or users per channel, by a certain time. If the network provider does not meet the loading requirements, their license would be returned to the FCC. The FCC does this to provide incentive for carriers to make good use of their purchased frequencies. In the case of a public safety network, the FCC grants channels to government agencies (as opposed to selling them), but still requires a certain amount of loading. When all the channels that have been provided from the FCC cannot handle any additional radio users, the system is referred to as fully loaded.A second usage for the term "Loading" refers to the process of providing radios to users for operation on our system. This system loading will be accomplished in steps.
MDC
An MDC, or Mobile Data Computer, is a vehicle-mounted computer that is wirelessly linked to a radio network. An MDC can allow an operator such as a police officer or firefighter to access information from the network, such as missing persons files or driving records. In addition to this, an MDC has all the capabilities of a personal computer, so an operator may use the MDC for storing information or running various applications. This is in contrast to an MDT, which is primarily just for viewing information gathered from the network.MDT
An MDT, or Mobile Data Terminal, is a vehicle-mounted keyboard and display that is wirelessly linked to a radio network. An MDT can allow an operator such as a police officer or firefighter to access information from the network, such as missing persons files or driving records. MDT's are primarily used to view information from the network and do not have the capability of operating applications independently from the network. This is in contrast to an MDC, which is capable of many other activities.Mobile
In radio systems, the term mobile is usually used when referring to a vehicle-mounted radio unit. This is different from a portable radio, which refers to a handheld radio.Narrowband
In radio systems, the term narrowband refers to the size of a channel with regards to frequency. In the new Phoenix-Mesa digital trunked radio system, all voice channels will have a bandwidth of 12.5 kHz, which is considered to be narrowband. This will be an upgrade from the previous conventional analog network, which used 25 kHz of bandwidth per voice channel.NPSPAC
This stands for the National Public Safety Planning Advisory Committee. In the 1980's, the FCC reallocated a block of radio channels in the 800 MHz band for public safety communications. NPSPAC was set up by the FCC to determine how these channels were going to be used. NPSPAC developed a usage plan that divided the country into many different regions, and the public safety agencies in these regions would have exclusive use of the NPSPAC frequencies. These regions would then in turn develop a plan for their own respective frequency usage. The new Phoenix-Mesa 800 MHz radio network will use NPSPAC channels for their transmissions.PTT (Push to Talk)
This term refers to the button on a radio that a user pushes to transmit. When somebody wants to talk over the air, they depress the PTT on their portable radio, mobile radio, or dispatch console, and if there is an available frequency, they will be able to speak over the network. When a user presses the PTT, that is often referred to as "keying" the radio.Portable
In radio systems, the term portable usually refers to a handheld radio. This is different from a mobile radio, which would refer to a radio mounted inside a vehicle.Project 25
Project 25 is a set of guidelines developed by radio system users for the purpose of standardizing the method of designing radio telecommunications networks for public safety agencies. Agencies such as APCO, the Association of Public Safety Communications Officials, the National Association of State Telecommunications Directors (NASTD), the Telecommunications Industry Association (TIA), the International Association of Chiefs of Police, several federal agencies and radio manufacturers have all participated in building this important standard. Project 25 ensures that all systems following this standard will meet its five main objectives: to make efficient use of the limited number of available public safety frequencies; to permit interoperability among other Project 25-compliant agencies; to ensure backward compatibility of the network; to create smooth system migration via upgrades, additions, etc.; and to provide the capability for scalable trunked and conventional networks.Queue
When a radio user tries to make a call, and there are no available frequencies to transmit on, that user's call gets placed in a queue. For the most part, the first user that gets placed into a queue will get to transmit as soon as a frequency becomes available, and any subsequent users in the queue will transmit when their turn arrives.Radio
This term takes on multiple meanings when applied to a communications system. When the term radio is used, it can refer to any of the following: a portable device used to transmit audio, a base station at a transmit site that contains electronic equipment, electromagnetic waves in the air which carry a network's information, or any device used to receive and/or transmit information across a medium.Repeater
A repeater is a piece of equipment that acts as a transmitter and a receiver. In a radio communications system, repeaters are used to extend the coverage of a wireless transmission. The repeater accomplishes this by first receiving a signal that has been transmitted from some other location, then amplifying and re-transmitting that signal from an antenna, thus giving the original transmission a boost.Simulcast
A radio network that is simulcast transmits information from each of its transmission sites simultaneously. This means that when a radio user transmits from his/her radio, that transmission is rebroadcast from every tower or antenna that is part of the simulcast system. Because of this technique, any radio can pick up any transmission, regardless of its location. The Phoenix-Mesa 800 MHz network will have several simulcast networks working within the whole system.Site
Also called transmit site, cell site, radio site, or antenna site. Any radio network transmits and receives its signals through antennas that are placed strategically in different locations throughout their desired coverage area. These places are called sites. Usually the antennas at these sites are mounted high above ground on towers or on the sides of buildings. The Phoenix-Mesa 800 MHz network will utilize approximately 20 radio sites, including sites on North Mountain and South Mountain.Talkgroup
A talkgroup is a group of radio users that are linked to each other through the radio system. For instance, if any member of a talkgroup initiates a call, any member of that group will hear that transmission. The Phoenix-Mesa 800 MHz network will incorporate many different talkgroups, and the users in these groups will be able to interact with the members of their own group as well as monitor other talkgroups throughout the network.Traffic
This term refers to the number of transmissions being made on the network at any given moment. Although most networks are designed to function even when very busy, an excess of traffic on a network may cause some radios to be placed in a queue when trying to transmit. Comprehensive traffic projections have been taken into account while designing the new Phoenix-Mesa 800 MHz network, and since this network provides radio coverage to public safety agencies, the standards have been raised much higher than that of commercial wireless provider.Trunking
This term refers to a type of communications system that draws from a pool of available frequencies, and assigns them only when they are needed. For example, in the 800 MHz trunked network, when a radio user wishes to talk over the air, they push their transmit button and the system dedicates a frequency to broadcast that user's transmission. After the user lets go of the transmit button, the system can reassign that same frequency to a completely different radio. Trunking is different from a conventional radio network, which assigns one dedicated frequency to a group of radios indefinitely. In a conventional system, if nobody in a particular group is transmitting, their assigned frequency sits unused and is essentially wasted. Trunking can be more efficient, since any available frequency can be used whenever it is needed.Vocoder
This piece of equipment transforms the sound of a person's voice into a stream of digital information. It also reverses the process converting digital information back to voice. The vocoder is vital to the operation of a digital network, since without it, no audio transmissions could be sent or understood.Need more information?
The 800 MHz digital radio system transition will be a long and on-going process, and the team welcomes your questions, comments and concerns. Just contact one of the following members through e-mail by clicking HERE or by calling PFD Technical Services at (602) 495-5239.
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