C

Call Forwarding - A feature allowing the subscriber to forward a call to another telephone number.

Call Processing - The complete process of routing, originating, terminating cellular telephone calls, along with the necessary billing and statistical collection processes.

Call Record - A record stored on DAS tape containing mobile number, dialed digits, time stamp information, and other data needed to bill or 'ticket' a cellular telephone call.

Call Setup - The call processing events that occur during the time a call is being established, but not yet connected.

Call Waiting - A feature allowing the subscriber to be alerted of another call during a current conversation. User can answer the call waiting, but cannot connect all parties (connecting all parties is considered a conference call).

Carrier - The operating frequency of a wireless system. A fixed frequency radio signal which is shifted up and down (modulated) in either frequency (FM) or level (AM) by the audio signal.

CDMA - Code Division Multiple Access.

CDPD - Cellular Digital Packet Data - sending digital data over the existing AMPS system, by transmitting dense packets on vacant analog channels

CDPD Forum - Cellular Digital Packet Data Forum. A trade association to promote the development of the cellular data industry and, in particular, to the standardization and effective use of cellular digital packet data (CDPD technology). This group maintains the CDPD protocol specification that allows the transmission of packet data over analog cellular channels.

Cell - The RF coverage area in the cellular system resulting from operation of a single multiple-channel set of base station frequencies. Cell can also refer to the base site equipment servicing this area. A city or county is divided into smaller "cells", each of which is equipped with a low-powered radio transmitter/receiver. The cells can vary in size depending upon terrain, capacity demands, etc. By controlling the transmission power, the radio frequencies assigned to one cell can be limited to the boundaries of that cell.

Cell splitting - A means of increasing the capacity of a cellular system by subdividing or splitting cells into two or more smaller cells.

CELP - Code Excited Linear Predictive compression algorithm.

Central Office (CO) - The switching office that connects the MTSO (Mobile Telephone Switching Office) to the PSTN (Public Switched Telephone Network). The CO is also known as a Class 5, or 'end' office.

CGSA - Cellular Geographic Service Area. The actual area in which a cellular company provides cellular service.

Channel - A unique RF frequency that is used for communication between subscriber unit and cell site base station. Must be assigned by the FCC (Federal Communications Commission).

Chip - The time it takes to transmit a bit or single symbol of a PN code.

Click Tone - A particular progress tone injected onto the forward voice channel (mobile unit receive, base station transmit) to indicate to the subscriber that the call has not been abandoned by the system.

Cochannel interference - Cochannel interference refers to the interference caused between two cells transmitting on the same frequency within a network. Since cochannel interference is caused by another cell transmitting the same frequency, you can't simply filter out the interference. You can only minimize the cochannel interference through proper cellular network design. A cellular network must be designed to maximize the C/I ratio. The C/I ratio is the carrier-to-cochannel interference ratio. One of the ways to maximize the C/I ratio is to increase the frequency re-use distance, I.E. increase the distance between cells using the same set of transmission frequencies. The C/I ratio in part determines the frequency re-use distance of a cellular network.

Compandor - A combination of a compressor at the transmitter to reduce the dynamic range of the transmitted signal and an expander at the receiver to recover this signal to the original dynamic range. The transmitter encodes (compresses) the dynamics of the audio signal and the receiver decodes (expands) the dynamics of the audio signal. Used in communications systems to improve signal-to-noise as a result of reduced transmitted dynamic range. In analog cellular, 2:1 syllabic compression is used to limit the maximum peak voice deviation to +/- 2.9 KHz.

Constructive interference - Interference that occurs when waves occupying the same space combine to form a single stronger wave. The strength of the composite wave depends on the how close in phase the two component waves are. For example if you transmitted two waves of the same phase, each with an amplitude of 10, they would combine into a composite wave of amplitude 20, but two waves slightly out of phase would combine into a composite wave of amplitude less than 20.

Control Channel - A unique RF channel used by each base station dedicated for the transmission of digital control information from the base station to the mobile unit. Used to assign voice channels, control mobile power, authorize handoffs, etc.

Correlator - The receiver component that demodulates a spread spectrum signal; a device that measures the similarity of of an incoming signal and a stored reference code.

COTS - Commercial Off The Shelf.

Cross-correlation - A measure of the similarity of two different signals.

CT2 - Cordless Telephone 2.

CTIA - Cellular Telecommunications Industry Association.

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