What is OBW (Occupied bandwidth)

Occupied Bandwidth (OBW) Explained Technically

In communication systems, Occupied Bandwidth (OBW) refers to the minimum bandwidth required to transmit a signal while capturing most of its essential information content. It essentially represents the portion of the frequency spectrum that a particular signal occupies with a specified power level.

There are several ways to define and measure OBW, depending on the specific application and signal characteristics. Here's a breakdown of the technical aspects of OBW:

Concepts related to OBW:

• Signal Bandwidth: The theoretical bandwidth of a signal can be determined by its Fourier transform. However, in practical scenarios, a signal doesn't have a sharp cutoff frequency and its energy extends beyond the theoretical bandwidth.
• Essential Bandwidth: This refers to the minimum bandwidth required to transmit a signal with minimal distortion or loss of information. It's a practical definition of OBW, often specified at a certain power level below the peak power. Common choices include 99%, 95%, or 90% of the total signal power.
• Emission Mask: Regulatory bodies often define emission masks that specify the maximum allowable power levels for a signal at different frequencies within its allocated band. OBW can be measured based on the portion of the spectrum where the signal power exceeds the emission mask limits.

Applications of OBW:

Understanding OBW is crucial in various communication system aspects:

• Spectrum Allocation: Regulatory bodies allocate spectrum resources to different users based on their OBW requirements. This ensures efficient spectrum utilization and minimizes interference between users.
• Filter Design: Filters are used in transmitters and receivers to limit the bandwidth of signals. Knowing the OBW helps design filters that efficiently pass the desired signal while attenuating unwanted out-of-band components.
• Data Rate Estimation: In some modulation techniques, there's a relationship between OBW and the maximum achievable data rate for a given channel. Knowing the OBW can provide an estimate of the system's capacity.

Measuring OBW:

There are several techniques for measuring OBW, depending on the specific signal and desired accuracy:

• Spectrum Analyzer: This instrument can be used to display the power spectrum of a signal. By observing the power distribution and defining a specific power level threshold (e.g., 99%), the occupied bandwidth can be estimated.
• Signal Processing Techniques: Mathematical calculations based on the signal's frequency domain representation like its power spectral density (PSD) can be used to determine the OBW.

Factors Affecting OBW:

Several factors can influence the OBW of a communication signal:

• Modulation Technique: Different modulation techniques like Amplitude Modulation (AM), Frequency Modulation (FM), and various digital modulation schemes (e.g., QPSK, 16QAM) have different inherent bandwidth requirements.
• Data Rate: In digital communication systems, higher data rates typically lead to a wider OBW.
• Coding Techniques: Error correction coding schemes can introduce redundancy into the signal, potentially increasing its OBW.
• Filtering: Filters used in the transmitter can shape the signal spectrum and impact the OBW.

Conclusion:

OBW is a crucial concept in understanding spectrum utilization and designing efficient communication systems. By minimizing OBW, communication systems can operate within their allocated bandwidth and minimize interference with other users. As spectrum becomes a valuable resource, techniques to achieve efficient communication with minimal OBW become increasingly important.