# Daily Report 5 :::success ### Task 5 ## 23rd of July 2021 :::info **Baseband Technology** OFDM =>a multiplexing technique that divides the available bandwidth into multiple orthogonalsub-carriers. # OFDM Diagram ![](https://i.imgur.com/HqFMGo7.png) - Modulation & Demodulation 1. Modulation is the process of changing a periodic wave with acertain frequency in order to be able to carry information. 2. Demodulation is the process of returning the bit value of the modulated signal y whichconsists of Real (I)and Imaginary (Q) components received. :::spoiler =>Each sub-carrier can be modulatedindependently and carries different information. - Bandwith Efficiency o Multi-carrier method o The sub-carriers areorthogonal to eachother o Orthogonalitybetween sub-carriersobtained by IFFTprocess - Characteristic • Resistant to Fading • Supports Various Operating Modes • Make It Easier to Sync Frequency and Time • Simplify Channel Equalization - Disadvantages of OFDM System 1. Shifting the frequency of the carrier signal causes InterCarrier Interference (ICI) and Multiple Access Interference(MAI). 2. Frequency shifts or error frequencies can be caused byDoppler Shift due to device movement, or due to the useof non-precision oscillators, etc. 3. Frequency shifting by Doppler Shift can result in loss oforthogonality between sub-carriersresulting in high BitError Rate (BER). 4. This is coupled with the small frequency distance betweensub-carriers (frequency spacing). :::