BAUD: Measurement of Modem Speed

Detailed explanation of BAUD, its differences from bits per second (BPS), historical context, and examples of its application in modem technology.

Definition and Distinction from BPS

BAUD is a term used to measure the speed of a modem, specifically indicating the number of times per second a communication channel changes the carrier signal it transmits. One baud corresponds to one signal change per second. For instance, a 56,000-baud (56K) modem changes its signal 56,000 times per second.

It’s essential to point out that baud and bits per second (BPS) are often confused but technically represent different measurements. Baud measures the signal changes per second, whereas BPS measures the number of bits transmitted per second. The confusion arises because in the early modems, one baud equated to one bit per second. However, modern modulation techniques enable the transmission of multiple bits per signal change, making the distinction crucial.

Mathematical Representation

In simple terms:

$$ \text{Baud Rate} = \frac{\text{Number of Symbols}}{\text{Time in Seconds}} $$

For complex signal modulations:

$$ \text{BPS} = \text{Baud Rate} \times \log_2(\text{M}) $$

where \( \text{M} \) is the number of distinct symbols a signal can take.

Historical Context

Invention and Evolution

The term “baud” is named after Émile Baudot, a pioneer in telegraphy. The measurement became particularly relevant with the advent of digital telecommunications and modems in the mid-20th century.

Changes Over Time

Earlier modems, such as those from the 1960s and 1970s, had baud rates directly equivalent to their bit rates (e.g., 300 baud = 300 bps). With the development of more advanced modulation techniques, modern modems can transmit multiple bits per signal change, distancing the baud rate from the bit rate.

Applicability

Practical Examples

• Simple Case: A traditional 300-baud modem would send 300 bits per second assuming a one-to-one correspondence between baud rate and bit rate.
• Modern Example: A 56K modem (56,000 baud) typically employs Quadrature Amplitude Modulation (QAM), allowing it to transmit data at rates exceeding 56,000 bits per second by encoding multiple bits per signal change.

Comparison with BPS

• Single-Bit Transmission: Early modems with simple modulations had baud rates equal to their bit rates.
• Multi-Bit Transmission: Modern modulations (e.g., QAM, PSK) enable several bits per baud, resulting in bit rates that are multiples of the baud rate.

Related Terms

• Bits per Second (BPS): A measurement of data transmission speed in terms of bits sent per second.
• Modem: A device that modulates and demodulates signals for communication over phone lines.
• Quadrature Amplitude Modulation (QAM): A modulation scheme that conveys data by changing the amplitude of two carrier waves.

FAQs

What is the relationship between baud and BPS in modern modems?

Modern modems utilize advanced modulation techniques that allow them to transmit multiple bits per signal change. As a result, the bit rate (BPS) is often a multiple of the baud rate.

Why is baud rate important?

Baud rate is critical because it defines the number of signal changes or symbols transmitted per second, which affects the overall data transmission efficiency and speed.

Can baud rate exceed the speed of light?

No, baud rate, like all speed measurements, is bounded by the physical limitation that information cannot travel faster than the speed of light.

References

1. Kurose, James, and Keith Ross. “Computer Networking: A Top-Down Approach.” 7th edition.
2. Peterson, Larry L., and Bruce S. Davie. “Computer Networks: A Systems Approach.” 5th edition.
3. Stallings, William. “Data and Computer Communications.” 10th edition.

Summary

BAUD is a fundamental measurement in telecommunications, indicating the number of signal changes per second in a modem. While it is often conflated with bits per second (BPS), the two metrics differ, with baud focusing on signal changes and BPS measuring the actual data transmitted. Understanding this distinction and the historical context enhances our comprehension of modern data transmission technologies and their efficiency optimizations.