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The C programming language is a computerprogramming language that was developed to do system programming for the operating systemUNIX and is an imperative programming language. C was developed in the early 1970s by Ken Thompson and Dennis Ritchie at Bell Labs. It is a procedural language, which means that people can write their programs as a series of step-by-step instructions. C is a compiled language.

Because the ideas behind C are kept close to the design of the computer, the compiler (program builder) can generate machine code/native code for the computer. Programs built in machine code are very fast. This makes C a good language for writing operating systems. Many operating systems, including Linux and UNIX, are programmed using this language. The language itself has very few keywords, and most things are done using libraries, which are collections of code for them to be reused.

C is available for many different types of computers. This is why C is called a 'portable' language. A program that is written in C and that respects certain limitations can be compiled for many different platforms.

The syntax of C has also influenced many other programming languages, such as C++, C#, and Java, and many more programming languages we use nowadays.

Example code[changechange source]

Here is an example of a program written in C. When built and run it will show 'Hello world!', followed by a new line on the computer screen.

  • #include<stdio.h> gets the standard input/output tools ready for the program to use. This allows text to be displayed (output).
  • intmain() is called the main function, and it is where the first code starts being run in a C program.
  • printf('Hello world!n'); is what displays text, in this case 'Hello world!' with a new line (n) at the end.
  • return0; tells the computer that the program finished and did not run into problems.
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Related pages[changechange source]

Other websites[changechange source]

  • C Programming Language in Hindi - सीखें आसानी से। (Hindi)
  • Coding Programmer Page / C Library Reference and Examples (English)
  • C (programming language) -Citizendium)


Retrieved from 'https://simple.wikipedia.org/w/index.php?title=C_(programming_language)&oldid=6765886'

In telecommunications, the carrier-to-noise ratio, often written CNR or C/N, is the signal-to-noise ratio (SNR) of a modulated signal. The term is used to distinguish the CNR of the radio frequency passband signal from the SNR of an analog base band message signal after demodulation, for example an audio frequency analog message signal. If this distinction is not necessary, the term SNR is often used instead of CNR, with the same definition.

Digitally modulated signals (e.g. QAM or PSK) are basically made of two CW carriers (the I and Q components, which are out-of-phase carriers). In fact, the information (bits or symbols) is carried by given combinations of phase and/or amplitude of the I and Q components. It is for this reason that, in the context of digital modulations, digitally modulated signals are usually referred to as carriers. Therefore, the term carrier-to-noise-ratio (CNR), instead of signal-to-noise-ratio (SNR) is preferred to express the signal quality when the signal has been digitally modulated.

High C/N ratios provide good quality of reception, for example low bit error rate (BER) of a digital message signal, or high SNR of an analog message signal.

Definition[edit]

The carrier-to-noise ratio is defined as the ratio of the received modulated carrier signal powerC to the received noise power N after the receiver filters:

CNR=CN{displaystyle mathrm {CNR} ={frac {C}{N}}}.

When both carrier and noise are measured across the same impedance, this ratio can equivalently be given as:

CNR=(VCVN)2{displaystyle mathrm {CNR} =left({frac {V_{C}}{V_{N}}}right)^{2}},

where VC{displaystyle V_{C}} and VN{displaystyle V_{N}} are the root mean square (RMS) voltage levels of the carrier signal and noise respectively.

C/N ratios are often specified in decibels (dB):

CNRdB=10log10⁡(CN)=CdBm−NdBm{displaystyle mathrm {CNR_{dB}} =10log _{10}left({frac {C}{N}}right)=C_{dBm}-N_{dBm}}

or in term of voltage:

CNRdB=10log10⁡(VCVN)2=20log10⁡(VCVN){displaystyle mathrm {CNR_{dB}} =10log _{10}left({frac {V_{C}}{V_{N}}}right)^{2}=20log _{10}left({frac {V_{C}}{V_{N}}}right)}

Measurements and estimation[edit]

The C/N ratio is measured in a manner similar to the way the signal-to-noise ratio (S/N) is measured, and both specifications give an indication of the quality of a communications channel.

In the famous Shannon–Hartley theorem, the C/N ratio is equivalent to the S/N ratio. The C/N ratio resembles the carrier-to-interference ratio (C/I, CIR), and the carrier-to-noise-and-interference ratio, C/(N+I) or CNIR.

C/N estimators are needed to optimize the receiver performance.[1] Typically, it is easier to measure the total power than the ratio of signal power to noise power (or noise power spectral density), and that is why CNR estimation techniques are timely and important.

Carrier-to-noise density ratio[edit]

In satellite communications, carrier-to-noise-density ratio (C/N0) is the ratio of the carrierpowerC to the noise power densityN0, expressed in dB-Hz.When considering only the receiver as a source of noise, it is called carrier-to-receiver-noise-density ratio.

It determines whether a receiver can lock on to the carrier and if the information encoded in the signal can be retrieved, given the amount of noise present in the received signal. The carrier-to-receiver noise density ratio is usually expressed in dBHz.

The noise power density, N0=kT, is the receiver noise power per hertz, which can be written in terms of the Boltzmann constantk (in joules per kelvin) and the noise temperatureT (in kelvins).

See also[edit]

  • C/I: carrier-to-interference ratio
  • Eb/N0 (energy per bit relative to noise power spectral density)
  • Es/N0 (energy per symbol relative to noise power spectral density)
  • Signal-to-interference ratio (SIR or S/I)
  • Signal-to-noise ratio (SNR or S/N)
  • SINAD (ratio of signal-plus-noise-plus-distortion to noise-plus-distortion)

References[edit]

  1. ^Islam, A. K. M. Najmul; Lohan, E. S.; Renfors, M. (Mar 2008). Moment based CNR estimators for BOC/BPSK modulated signal for Galileo/GPS. pp. 129–136.

This article incorporates public domain material from the General Services Administration document 'Federal Standard 1037C' (in support of MIL-STD-188). Online casinos with no deposit bonus.

Further reading[edit]

C To F

  • Digital Transmission: Carrier-to-Noise Ratio, Signal-to-Noise Ratio, and Modulation Error Ratio at the Wayback Machine (archived 2016-03-04)

C-span

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