The data rate of QPSK is ______ as that of BPSK for the same symbol rate.
Twice
QPSK and BPSK Data Rate Comparison
When discussing digital modulation techniques like BPSK and QPSK, it is essential to understand the difference between data rate and symbol rate. The symbol rate, also known as baud rate, refers to the number of symbols transmitted per second. The data rate, on the other hand, is the actual speed at which information (bits) is transmitted, typically measured in bits per second (bps). The relationship between data rate and symbol rate depends on how many bits each symbol carries.
BPSK Modulation Explained
BPSK stands for Binary Phase Shift Keying. In BPSK, there are two possible phase states for the carrier signal, typically 0 degrees and 180 degrees. Each of these phase states represents one binary bit.
- BPSK transmits 1 bit per symbol.
- Therefore, for BPSK, the data rate is equal to the symbol rate.
- Mathematically, this can be expressed as: \[ \text{Data Rate}_{\text{BPSK}} = \text{Symbol Rate} \times 1 \frac{\text{bit}}{\text{symbol}} \]
QPSK Modulation Explained
QPSK stands for Quadrature Phase Shift Keying. In QPSK, there are four possible phase states, typically 45, 135, 225, and 315 degrees (or 0, 90, 180, 270 degrees in some conventions). Each of these four phase states can represent a unique combination of two binary bits.
- QPSK transmits 2 bits per symbol.
- Therefore, for QPSK, the data rate is twice the symbol rate.
- Mathematically, this can be expressed as: \[ \text{Data Rate}_{\text{QPSK}} = \text{Symbol Rate} \times 2 \frac{\text{bits}}{\text{symbol}} \]
QPSK Data Rate Comparison with BPSK
To directly compare the data rate of QPSK with that of BPSK, let's consider a scenario where both modulation schemes operate at the same symbol rate.
| Modulation Scheme | Bits per Symbol (\(k\)) | Data Rate (\(R_b\)) vs. Symbol Rate (\(R_s\)) |
|---|---|---|
| BPSK | 1 | \(R_b = R_s \times 1\) |
| QPSK | 2 | \(R_b = R_s \times 2\) |
As shown in the table and explained above, if both QPSK and BPSK maintain the same symbol rate, QPSK transmits 2 bits per symbol while BPSK transmits only 1 bit per symbol. This means that for every symbol transmitted, QPSK carries twice the amount of information (bits) compared to BPSK.
Hence, for the same symbol rate, the data rate of QPSK is twice that of BPSK. This makes QPSK more spectrally efficient, meaning it can transmit more data within the same bandwidth, given the same symbol rate.
Important Questions from Introduction To Digital Modulation
In digital data transmission, a line code should have the following properties
(A) Transmission bandwidth should be as small as possible
(B) Transmitted power should be as high as possible
(C) Transmission bandwidth should be as high as possible
(D) Transmitted power should be as low as possible
Choose the correct answer from the options given below:
If the in‐phase and quadrature components in an M‐ary PSK system are permitted to be independent, then this scheme becomes a:
Which of the following statements are correct?
A. M‐ary modulation scheme is preferable where the bandwidth requirement is important.
B. M‐ary PSK system considers 'M' different phases in the range 'π/2'.
C. In M‐ary modulation scheme, only coherent detection is possible.
D. M‐ary QAM scheme uses 'm 2' carrier signals having the same frequency.
Choose the correct answer from the options given below:
In digital communication, Inter Symbol Interference (ISI) is a form of distortion where one symbol interferes with subsequent symbols. An eye diagram is used to study the extent of ISI in a communication channel. Which of the following is FALSE?
In ASK modulation:
