VSAT Bandwidth vs. Data Rate: Understanding the Difference

This page breaks down the difference between VSAT bandwidth and VSAT data rate. Both concepts are crucial when discussing the capacity of any transmission medium. Think of it this way: different mediums have different limitations. Generally, a higher bandwidth allows for a higher data rate. The channel capacity represents the maximum data rate a channel can handle.

If the bandwidth is equal to W, then:

$Data\ Rate \le 2 \* W$

The core concepts of bandwidth and data rate apply universally, regardless of the specific communication system or transmission medium.

VSAT Bandwidth Explained

In the context of VSAT (Very Small Aperture Terminal), bandwidth refers to the total frequency allocation assigned to a specific VSAT at its RF center frequency by RF engineers.

For instance, imagine a VSAT with an allocated IF (Intermediate Frequency) of 71.02 MHz, and it’s running one voice channel at 19.2 Kbps and one data channel at 9.6 kbps.

The total VSAT bandwidth in this scenario is:

$(19.2 + 9.6) = 28.8 \text{ KHz}$

This calculation assumes 1 bit is used per carrier (meaning BPSK modulation is used).

VSAT Data Rate Defined

VSAT data rate represents the speed at which information is transmitted via a VSAT. It’s essentially the ratio of the amount of information transmitted (in bits) to the duration of the transmission (in seconds).

$\text{VSAT Data Rate} = \frac{\text{Information in bits}}{\text{Duration for information transmission in seconds}}$

The Relationship Between Bandwidth and Data Rate in VSAT

VSAT bandwidth and data rate are directly related through the following equation:

$\text{VSAT Bandwidth} = \frac{1}{\text{Modulation Level}} \times \text{VSAT Data Rate}$

Example: Consider QPSK (Quadrature Phase Shift Keying) modulation. In QPSK, the modulation level is 2, meaning 2 bits are transmitted per carrier.

• 1 symbol = 2 bits in QPSK
• 1 symbol = 4 bits in 16QAM (16-Quadrature Amplitude Modulation)
• 1 symbol = 1 bit in BPSK (Binary Phase Shift Keying), ASK (Amplitude Shift Keying), FSK (Frequency Shift Keying), or PSK (Phase Shift Keying)

Therefore, if a VSAT modem uses QPSK, the required VSAT bandwidth is halved compared to using BPSK for the same data rate.