Multi-carrier code-division multiple access: Difference between revisions

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'''Multi-Carriercarrier Codecode-division Divisionmultiple Multiple Accessaccess''' ('''MC-CDMA''') is a [[multiple access]] scheme used in [[OFDM]]-based telecommunication systems, allowing the system to support multiple users at the same time.

MC-CDMA spreads each user symbol in the frequency ___domain. That is, each user symbol is carried over multiple parallel subcarriers, but it is phase -shifted (typically 0 or 180 degrees) according to a code value. The code values differ per subcarrier and per user. The receiver combines all subcarrier signals, by weighing these to compensate varying signal strengths and undo the code shift. The receiver can separate signals of different users, because these have different (e.g. orthogonal) code values.

Since each data symbol occupies a much wider bandwidth (in hertz) than the data rate (in bit/s), a ratio of signal- to- noise-plus-interference ratio (if defined as signal power divided by total noise plus interference power in the entire transmission band) of less than 0 dB is feasible.

One way of interpreting MC-CDMA is to regard it as a direct-sequence CDMA signal ([[DS-CDMA]]), which is transmitted after it has been fed through an inverse FFT ([[fast Fourier transform]]).

which is transmitted after it has been fed through an inverse FFT ([[Fast Fourier Transform]]).

== Rationale ==