Digital modulation waveforms are used extensively in broadband communications and home networking. BPSK is the simplest form of phaseshift keying; it shifts the carrier 0 or 180 degrees. QPSK is used to increase data rates or to provide for multiple channels. Differential techniques are used to provide simpler demodulation methods and are acceptable with all types of modulations. OQPSK is used to minimize amplitude modulation by eliminating the 180-phase shift possibility and provides another method to generate MSK and GMSK. Higher order PSK systems can be analyzed much the same way only with more phase states and phase transitions. However, the more phase shift possibilities, the harder it is to detect and resolve the different phase states. Therefore, there is a limit on how many phase states can be sent for good detection. This limit seems to grow with better detection technology, but caution must be given to the practicality of how many phase states can be sent out for standard equipment. Amplitude modulation points are combined with phase states to produce a hybrid QAM to further increase the data capacity for the bandwidth channel. FSK is another method of encoding data using two frequencies. Minimum spacing provides another method of producing MSK. TDMA, CDMA, FDMA are techniques to allow multiple users. Parallel systems can be implemented to increase the data rate, which is dependent on the number of parallel channels used. OFDM is a way to transmit parallel overlapping channels for bandwidth efficiency. OFDM can also be used to allow multiple users to operate in an FDM mode, with more users for a given bandwidth. Spread spectrum techniques are used to provide process gain to reduce the effects of jammers and allow more efficient use of the spectrum for multiple users.

Chapter Contents:

• 3.1 Phase-Shift Keying (PSK)
• 3.2 Frequency Shift Keying (FSK)
• 3.3 Multiple Users
• 3.4 Parallel Techniques to Increase Data Rates
• 3.5 Orthogonal Frequency Division Multiplexing (OFDM)
• 3.6 Spread Spectrum Systems
• 3.7 Summary
• 3.8 References

Inspec keywords: broadband networks; modulation

Other keywords: digital modulation; bandwidth channel; phase-shift keying; bandwidth efficiency; CDMA; GMSK; broadband communications; OQPSK; OFDM; TDMA; home networking; BPSK; amplitude modulation; differential techniques; hybrid QAM; FSK; parallel systems; FDMA

Subjects: Modulation and coding methods