Digital Modulation Helps MilCom Do More with Less
2019-03-29 | 4 min read
“Do more with less.” This mantra has become very popular with the trend toward minimalist lifestyles. Quite a few years ago, however, communications systems already were living by a “do more with less” mantra when it came to spectrum. Digital modulation evolved as a way to add users, provide increased data rates, and perform more tasks with the same or less spectrum.
As commercial communications evolved to higher data rate applications, military communications (MilCom) remained restricted to voice transmission for quite some time. Now, military intelligence is shared more accurately via data including video, images, and messaging. This increasing use of data translates into the rapid consumption of bigger portions of bandwidth. To maximize finite spectrum, MilCom also leverages digital modulation, packing more users securely into the same or less spectrum while enabling higher data rates.
To provide better spectrum management and enhanced communications, modulation techniques grow ever-more complex. Yet these cutting-edge techniques are still derived from the three basic forms of digital modulation: amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). For example, quadrature amplitude modulation (QAM) and quadrature phase shift keying (QPSK) build upon these formats to provide more efficient bandwidth usage and security for voice communication in the battlefield.
Depending on the digital modulation scheme(s) at the heart of the technique, enhancement methods vary. For example, improving spectral efficiency for ASK and FSK schemes depends on the correct choice of data rates, shift frequencies, and carrier frequencies. No gaps should occur when moving between different binary states. Any discontinuities create glitches, which boost bandwidth as well as harmonic content.
PSK matches ASK’s bandwidth efficiency while adding power efficiency. With the same signal-to-noise ratio (SNR), PSK will therefore have a lower bit error rate. With QPSK, the modulator produces a pair of sine carriers separated by 90 degrees. Each phase is modulated according to the binary data. This process results in four individual sine signals, with the final signal combining both phases. With every carrier phase equal to two bits of data, QPSK offers high spectral efficiency.
Amplitude phase shift keying (APSK) uses a smaller number of amplitude levels to surpass QAM. It combines ASK and PSK to make changes to the carrier wave’s amplitude and phase, thereby boosting the signal set. APSK boasts increased efficiency and output power.
Modulation schemes will continue to evolve. As the technology advances, testing will be critical to ensure proper performance, interoperability, and security. New communications approaches promise improved capabilities. In military locations and especially in conflict zones, however, new capabilities are useless if communications fail. MilCom must do even more with less spectrum going forward, but never at the expense of security and reliability.
Learn more about how Keysight supports MilCom here.