Hi Malar,
In FBMC (Filter Bank Multicarrier) modulation, the real and imaginary parts of the complex-valued symbols are separated before passing them through an IFFT (Inverse Fast Fourier Transform) operation. If they are not separated, it would fundamentally alter the nature of the modulation scheme and would lead to significant issues like:
- Loss of Orthogonality: The orthogonality of subcarriers in the frequency domain, which is a key feature of FBMC, would be lost. In FBMC, subcarriers are designed to be orthogonal to each other, meaning they don't interfere with each other. If you don't separate the real and imaginary parts and treat them as independent subcarriers, they would no longer be orthogonal, leading to interference between subcarriers.
- Increased Interference: Without orthogonal subcarriers, the interference between subcarriers would lead to a degradation in the quality of the received signal. This interference would make it much harder for the receiver to correctly demodulate and decode the data.
- Complexity and Efficiency Issues: FBMC is designed to work with real-valued signal processing, which simplifies hardware and software implementations. If you were to use complex-valued symbols directly without separation, it would complicate the signal processing operations and potentially increase computational complexity.
SI Overhead:
SI overhead stands for "Side Information overhead." In communication systems, side information refers to additional information that needs to be transmitted alongside the actual data to aid in the decoding process at the receiver. Side information can include information about the modulation scheme, channel conditions, synchronization, etc.
In the context of FBMC or other modulation schemes, SI overhead refers to the extra bits or information that are required to be transmitted alongside the modulated symbols to help the receiver properly demodulate and decode the received signal. The specific nature and amount of SI overhead can vary depending on the modulation scheme, the channel conditions, and the communication system's requirements.
Minimizing SI overhead is important in communication systems because it directly affects the efficiency of data transmission. Systems that can transmit data with lower SI overhead are typically more spectrally efficient and have better overall performance.
To learn more, you can refer to the following links:
