Baseband
Understanding Baseband
Baseband is where information originates and is ultimately recovered. Voice, data, and video signals exist at baseband frequencies before being modulated onto an RF carrier for transmission, and are recovered at baseband after demodulation at the receiver.
Baseband in Communications
- Voice: 300 Hz - 3.4 kHz (telephone). 20 Hz - 20 kHz (hi-fi).
- Digital data: DC to symbol rate/2. For 10 Msym/s: DC to 5 MHz.
- Video: DC to 6 MHz (analog TV). DC to 20 MHz (digital HD).
Baseband Processing
- Transmit: Source coding, channel coding, modulation, pulse shaping, DAC, I/Q generation.
- Receive: ADC, I/Q separation, matched filtering, equalization, demodulation, decoding.
Frequently Asked Questions
What is baseband?
Baseband is the original frequency range of a signal (starting from DC/0 Hz) before RF modulation or after demodulation. For digital signals, it extends from DC to approximately half the symbol rate. Baseband processing handles modulation, coding, and digital signal processing.
What is baseband processing?
Baseband processing includes all signal operations at the original signal frequencies: source/channel coding, modulation mapping, pulse shaping (transmit side), and matched filtering, equalization, demodulation, decoding (receive side). Often implemented in DSP or FPGA.
What is a direct-conversion receiver?
A direct-conversion (zero-IF) receiver mixes the RF signal directly to baseband, skipping the IF stage. This simplifies the architecture but introduces DC offset and I/Q imbalance challenges. It is the dominant architecture for cellular and Wi-Fi receivers.