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In telecommunications, modulation is the process of varying a periodic waveform in order to use that signal to convey a message or to transmit information. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. Phase shift keying (PSK) is a digital modulation scheme that conveys data by modulating the phase of a reference signal (the carrier wave). PSK uses a finite number of phases, each assigned a unique pattern of binary bits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. In digital communications, a symbol is the smallest unit of data transmitted at one time.
In the simplest modulation schemes such as binary phase-shift keying (BPSK), only one bit of data (0 or 1) is transmitted at a time depending on the phase of the transmitted signal. However, in a more complex scheme such as 16-QAM, four bits of data are transmitted simultaneously, resulting in a symbol rate that is equal to one-quarter of the bit rate. Because of its simplicity, BPSK is appropriate for low-cost passive transmitters and is used in radio frequency identification (RFID) standards such as International Organization for Standardization (ISO) 14443 which has been adopted for biometric passports, credit cards such as American Express’s Express Pay and many other applications.
Advancing modulation techniques further, Navy scientists have developed a system for transmitting digital data that has a lower error probability than previous phase shift keying techniques for the same spectral efficiency. The system uses M-hyper phase shift keying (M-HPSK) basis functions – periodic functions having a duration T and a bit-to-symbol mapper for combining the bitstream and the HPSK basis functions to form a succession of 4-bit HPSK symbols for 16-HPSK, 5-bit HPSK symbols for 32-HPSK, or 6-bit HPSK symbols for 64-HPSK.
HPSK is an excellent modulation technique for energy-limited scenarios like satellite communication. Due to the great distances involved between communication satellites and earth stations, the signal is often received with a degraded signal power.
- HPSK can perform well even when the noise and signal powers are of the same magnitude with the use of error correcting codes
- 64-HPSK modulation technique is shown to have far superior bit error rates than 16-PSK and 16-QAM versus energy per bit to noise power spectral density ratio while having the same spectral efficiency
- US patent 8,064,541 available for license