آژانس هواپیمایی
pop up

OFDM و SSID یعنی چه؟!

شروع موضوع توسط greenday ‏4 سپتامبر 2007 در انجمن شبکه

  1. greenday

    greenday کاربر تازه وارد

    تاریخ عضویت:
    ‏18 آگوست 2007
    نوشته ها:
    29
    تشکر شده:
    0
    منظور از OFDM در وایمکس یعنی چه؟!
    منظور از SSID یعنی چه؟!
     
  2. Bhrzk

    Bhrzk مدیر بازنشسته

    تاریخ عضویت:
    ‏1 آگوست 2005
    نوشته ها:
    10,543
    تشکر شده:
    3,020
    محل سکونت:
    توی جیب کوچولوت
    این در مورد OFDM می تونه اطلاعات فوق العاده ای باشه :

    Orthogonal Frequency-Division Multiplexing (OFDM) — essentially identical to Coded OFDM (COFDM) — is a digital multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation) at a low symbol rate, maintaining data rates similar to conventional single-carrier modulation schemes in the same bandwidth. In practice, OFDM signals are generated using the Fast Fourier transform algorithm.

    The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions — for example, attenuation of high frequencies at a long copper wire, narrowband interference and frequency-selective fading due to multipath — without complex equalization filters. Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. Low symbol rate makes the use of a guard interval between symbols affordable, making it possible to handle time-spreading and eliminate inter-symbol interference (ISI).