QBICM Quantized BICM

combines bit-interleaved coded modulation (BICM) with quantization to improve the performance of digital communication systems. QBICM is commonly used in scenarios where the communication channel has limited capacity or the transmitted signals need to be robust against noise and interference.

To understand QBICM, let's break down its two main components: bit-interleaved coded modulation (BICM) and quantization.

Bit-Interleaved Coded Modulation (BICM):

BICM is a modulation scheme that combines error correction coding and modulation. It interleaves the coded bits before modulation, allowing for more robust communication. The encoding process involves adding redundancy to the original information bits, which enables error detection and correction at the receiver.

BICM typically consists of the following steps:

a. Source Encoding: The original data bits are encoded using an error correction code such as convolutional codes or turbo codes. This process adds redundancy to the data, enabling the receiver to detect and correct errors.

b. Bit Interleaving: The coded bits are rearranged to form a bit-interleaved sequence. This interleaving process spreads out consecutive coded bits across multiple symbol intervals.

c. Modulation: The bit-interleaved sequence is mapped onto a set of symbols, which are then transmitted over the channel. The modulation scheme used can be binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), or higher-order modulation schemes.

Quantization:

Quantization is the process of representing continuous signals with a finite set of discrete values. In digital communication systems, quantization is used to convert the continuous analog signal into a discrete digital form suitable for transmission over the channel.

Quantization involves the following steps:

a. Analog-to-Digital Conversion: The continuous analog signal is sampled at regular intervals, and each sample is quantized. The quantizer maps each sample to the nearest discrete value in a finite set of levels.

b. Bit Assignment: Each quantized sample is represented using a fixed number of bits. The number of bits assigned to each sample determines the precision or resolution of the quantized signal. In QBICM, different bit assignments can be used for different samples, allowing for more efficient representation of the signal.

c. Digital Modulation: The quantized samples are modulated using a digital modulation scheme, similar to the modulation step in BICM. The modulated symbols are then transmitted over the channel.

QBICM combines BICM and quantization to achieve improved performance. The bit-interleaved coded bits are quantized before modulation, enabling efficient representation of the signal while maintaining error correction capability. This approach is especially useful in scenarios with limited channel capacity or high noise and interference levels.

At the receiver, the QBICM scheme is reversed. The received symbols are demodulated and quantized, and the quantized bits are de-interleaved. The error correction decoder then performs decoding to recover the original information bits.

Overall, QBICM provides a powerful technique to enhance the performance of digital communication systems by combining the benefits of bit-interleaved coding and quantization. It allows for more efficient use of the available channel capacity while maintaining robustness against noise and interference.