Quaternary Phase Shift Keying (QPSK)
Also referred to as Quadrature Phase Shift Keying. A method of modulating digital signals onto a radio-frequency carrier signal using four phase states to code two digital bits. QPSK is a four level use of digital phase modulation (PM). Quadrature signal representations involve expressing an arbitrary phase sinusoidal waveform as a linear combination of a cosine wave and a sine wave with zero starting phases.
A digital signal having four significant conditions. [Fib111]
Radio Detecting and Ranging; a method of detecting distant objects and determining their position, velocity, or other characteristics by analysis of very high frequency radio waves reflected from their surfaces; and, the equipment used in such detection. [Ans11] Read more: http://www.answers.com/topic/radar#ixzz1H3jl3dY1
Energy (joules) which is transferred via electromagnetic waves; there is no associated transfer of matter. [Arr11]
An optical fiber made with core and cladding materials that are designed to recover their intrinsic value of attenuation coefficient, within an acceptable time period, after exposure to a radiation pulse. [Fib111]
The function of this sleeve is to support the aluminum sheath of the cable. As the ferrule closes down to grip the sheath, the sleeve maintains the size and shape of the aluminum sheath. If the sheath were to crush down unsupported, mechanical and electrical problems could occur. [Arr11]
Radio Frequency (RF)
Analog electrical signals sent over the cable. Conventional (broadcast) television and radio, as well as cable TV, deliver RF signals to your television/radio. RF is quickly becoming yesterday's news to many cable TV providers who are installing fiber-optic lines that will replace today's cables. Or in cable television systems, this refers to electromagnetic signals in the range 5 to 1000 MHz.
Radio Frequency Interference (RFI)
Undesired signals received by a user; those signals that miss their desired user become interference energy to users in the same or adjacent cells.
An instrument, distinct from a photometer, to measure power (Watts) of electromagnetic radiation. [Fib111]
The science of radiation measurement. [Fib111]
Remote Access Dial-In User Service
Loss of signal at Ku or Ka Band frequencies due to absorption and increased sky-noise temperature caused by heavy rainfall. [Sat07]
Random Access Memory
An optical amplifier based on Raman scattering which generates many different wavelengths of light from a nominally single-wavelength source by means of lasing action or by the beating together of two frequencies. The optical signal can be amplified by collecting the Raman scattered light. [Fib111]
Regional Area Network
Random Jitter (RJ)
Random jitter is due to thermal noise and may be modeled as a Gaussian process. The peak-to-peak value of RJ is of a probabilistic nature, and thus any specific value requires an associated probability. [Fib111]
Random Jitter (RMS) versus Optical Loss in dB Graph courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/r
The process by which a cable modem learns its distance from the headend. Ranging is a continual process, due to the expansion and contraction of cable that occurs during the day.
Registration, Admission, and Status
The scanned (illuminated) area of the cathode ray picture tube. The random pattern of illumination seen on a television screen when no video signal is present. [Cha07]
A relative size of two quantities indicated by the quotient obtained by dividing one quantity by the other. [Arr11]
A geometric representation of a light path through an optical device: a line normal to the wave front indicating the direction of radiant energy flow. [Arr11]
Scattering of a lightwave propagating in a material medium due to the atomic or molecular structure of the material and variations in the structure as a function of distance. The scattering losses vary as the reciprocal of the fourth power of the wavelength. The distances between scattering centers are small compared to the wavelength. Rayleigh scattering is the fundamental limit of fiber loss in the operating wavelength region (0.8 - 1.6 µm) of optical fiber systems. [Arr11]
Lines that represent the path taken by light. [Fib111]
Regional Bell Operating Company
Regional Bell Operating Companies
Rivest Cipher 4
Real-time Protocol/Real-time Control Protocol (RTP/RTCP)
The Internet Engineering Task Force (IETF) specification for audio and video signal management. RTP provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video or simulation data, over multicast or unicast network services. The data transport is augmented by a control protocol (RTCP) to allow monitoring of the data delivery in a manner scalable to large multicast networks, and to provide minimal control and identification functionality. RTP and RTCP are designed to be independent of the underlying transport and network layers.
Rural Electrification Administration
The act of reloading the operating system of a computer, usually by resetting the power to the computer with the power switch, or selecting Start/Shutdown/Restart in Windows.
The physical upgrade of a cable system, often involving the replacement of amplifiers, power supplies, passive devices and sometimes the cable, strand, hardware and subscriber unit.
Electronic device which can convert electromagnetic waves into either visual or aural signals, or both. For cable television, usually the subscriber's television set.
A unit including a detector and signal-processing electronics that converts optical input into electronic output; often used in communications. [Arr11]
The attenuation between any two receivers connected to the system.
The maximum acceptable value of average received power for an acceptable BER or performance. [Fib111]
Expressed in dBm this tells how much power the detector must receive to achieve a specific baseband performance, such as a specified bit error rate or signal to noise ratio. [Sat07] Also, the minimum acceptable value of received power needed to achieve an acceptable bit error rate (BER) or performance. It takes into account power penalties caused by use of an optical transmitter with worst-case values of extinction ratio, jitter, pulse rise times and fall times, optical return loss, receiver connector degradations, and measurement tolerances. The receiver sensitivity does not include power penalties associated with dispersion, or back reflections from the optical path; these effects are specified separately in the allocation of maximum optical path penalty. Sensitivity usually takes into account worst-case operating and end-of-life (EOL) conditions. [Fib111]
Combination of an electron and a hole in a semiconductor that releases energy, leading to light emission. [Fib111]
Record Keeping Server (RKS)
In a PacketCable network, the RKS is responsible for accepting partial billing information generated by a distributed set of PacketCable elements and correlating this information into a single coherent record that describes the resources used during the service.
Rectangular QAM, also known as “square” constellations have evenly divisible by two (2) symbols per rectangular quadrant and are, in general, sub-optimal in the sense that they do not maximally space the constellation points for a given energy. However, they have the considerable advantage that they may be easily transmitted as two pulse amplitude modulation (PAM) signals on quadrature carriers, and can be easily demodulated. The non-square constellations achieve marginally better bit-error rate (BER) but are harder to modulate and demodulate. The first rectangular QAM constellation usually encountered is 16-QAM, the constellation diagram for which is shown here.
Constellation diagram for rectangular 16-QAM
A Gray coded bit-assignment is also given. The reason that 16-QAM is usually the first is that a brief consideration reveals that 2-QAM and 4-QAM are in fact binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK), respectively. Also, the error-rate performance of 8-QAM is close to that of 16-QAM (only about 0.5 dB better, but its data rate is only three-quarters that of 16-QAM). [Wik1115]
The part of a system that duplicates the essential tasks in order to take over should the original fail. [Arr11]
The negative of return loss. In many instances, reflectance and return loss are used synonymously. Minimum directivity and return loss are the lower limits which apply over the entire wavelength range specified in the bandpass. [AOF11]
1. Reflected energy which substantially covers the spectrum occupied by the originating signal. 2. The abrupt change in direction of a light beam at an interface between two dissimilar media so that the light beam returns into the medium from which it originated. [Arr11]
Ratio of reflected wave to incident wave.
Reflections or Echoes
In video transmission this may refer either to a signal or to the picture produced. In a signal it is either waves reflected from structures or other objects or waves which are the result of impedance or other irregularities in the transmission medium. In a picture, “Echoes” observed in the picture produced by the reflected waves.
The abrupt change in direction of light as it travels from one material to a dissimilar material. Some of the reflected power in a fiber gets transmitted back to the source. [Arr11] Also, the changing of direction of a lightwave in passing through a boundary between two dissimilar media in a graded-index medium where refractive index is a continuous function of position. [Fib111]
A number that indicates the ratio of the speed of light in a vacuum to the speed of light in a specified. material; abbreviated as n. The higher the number, the slower the speed of light. [Arr11]
Refractive Index Gradient
The description of the value of the refractive index as a function of distance from the optical axis along an optical fiber diameter. Also called refractive index profile. [Fib111]
A repeater, designed for digital transmission, in which digital signals are amplified, reshaped, retimed, and retransmitted. [Fib111]
Regenerative Repeater Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/r
Synonym for regenerative repeater. [Fib111]
Regional Bell Operating Company (RBOC)
RBOC comprises the U.S. local carriers created in the 1982 Consent Decree to break up AT&T. Seven were formed to serve as parent companies for the 22 then-existing Bell Operating Companies.
Registration, Admission, and Status (RAS)
RAS Channel is an unreliable channel used to convey the RAS messages and bandwidth changes between two H.323 entities.
Remote Access Dial-In User Service (RADIUS)
An internet protocol (IETF RFC 2138 and RVC 2139) originally designed for allowing users dial-in access to the internet through remote servers. Its flexible design has allowed it to be extended well beyond its original intended use.
Remote Method Invocation (RMI)
A Java programming feature that allows a program running on one computer to access the objects and methods of another Java program running on a separate computer.
A network device that repeats signals from one cable onto one or more other cables, while restoring signal timing and waveforms. Also, a receiver and transmitter set designed to regenerate attenuated signals. Used to extend operating range. [Fib111]
Repeater Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/r
The term given to the process of resetting a cable modem by removing its entry from the cable router, then adding it back on to re-establish the connection.