Minimum Shift Keying
Table of Contents
Another type of digital modulation technique used to transform a digital signal into analog signals is minimum shift key modulation. It is also known as Minimum-shift keying (MSK) or Advance Frequency Shift Keying because it is a type of continuous-phase frequency-shift keying.
Key features of Minimum shift keying (MSK)
- Melvin L. Doelz and Earl T. Heald, who worked for Collins Radio, invented MSK in the late 1950s.
- It is encoded using bits that alternate between quadrature components, with the Q component being half a symbol period behind the other components.
- The most efficient digital modulation method is minimum shift keying. Compared to the Phase Shift Key, Frequency Shift Key, and Amplitude Shift Key of the digital modulation technique, it is much simpler to implement for almost every stream of bits.
- The idea behind Minimum Shift Keying is based on the bit positioning frequency generating table and the positioning of bits such as even bits and odd bits for the given bitstream.
- MSK is the most popular digital modulation technology because it can handle binary bit transitions of “One(1)” and “Zero(0)” with ease and flexibility.
Working of MSK
- Bits are divided into even and odd bits and each bit’s duration is doubled in MSK.
- Following that, frequency is divide into two categories, f1 and f2. In this case, f1 identifies or indicates the low frequency, and f2 identifies the high frequency.
- Depending on whether the bit values are even or odd, the frequency generating table selects original or inverted signals.
- The curve for higher frequency takes a complete wave from 0 to π, and the curve for low frequency takes a wave 0 to π/2 within the same interval of time.
Gaussian Minimum Shift Keying (GMSK)
Similar to standard MSK, Gaussian Minimum Shift Keying (GMSK) shapes the digital data stream with a Gaussian filter before applying it to a frequency modulator. The frequency shift keying technique used in GMSK modulation has no phase discontinuities. It allows for high-efficiency radio power amplifiers and efficient spectrum utilization. Compared to the majority of MSK modulation systems, it has much smaller phase shift angles.
Usage of GMSK
GMSK is mainly use in the following technologies:
- Global System for Mobile Communications (GSM)
- Automatic Identification System (AIS) for maritime navigation.
- Satellite Communications
Advantage of Gaussian Minimum Shift Keying
- GMSK provides high spectral efficiency.
- Utilizing GMSK has the biggest benefit because it lowers sideband power,. Which lessens out-of-band interference between signal carriers in adjacent frequency channels.
The disadvantage of GMSK
- It necessitates more sophisticated channel EQ algorithms, like an adaptive EQ at the receiver.
- It has high power consumption.
- It makes it harder to distinguish between various transmitted data values by increasing the modulation memory in the system that leads to interference within a symbol.