Continuous phase modulation

About: Continuous phase modulation is a research topic. Over the lifetime, 3199 publications have been published within this topic receiving 37245 citations. The topic is also known as: CPM.

An orthogonal space-time coded partial response CPM system with fast decoding for two transmit antennas

Abstract: In this paper, an orthogonal space-time coded partial response continuous phase modulation (OST-PCPM) system with two transmit antennas is proposed. It can achieve full diversity with arbitrary inner memory length and phase smoothing functions of CPM schemes. Based on the orthogonality between signals from two transmit antennas and the proposed differential encoding scheme, a fast decoding algorithm is developed for some special cases. Simulation results show that this scheme can provide much better performance with a reasonable complexity, as compared to one transmit antenna CPM scheme. We also give a suboptimal decoding method that provides a tradeoff between complexity and performance.

Method and apparatus for controlling the modulation index of continuous phase modulated (CPM) signals

Abstract: A transceiver uses feedback control to monitor a transmitted continuous phase modulation (CPM) waveform, such as a spread spectrum CPM waveform, and adjust the modulation index in response thereto. Codewords are selected from a table according to a data signal and applied to a pulse shaping network. The pulse shaping network outputs a CPM waveform to a prefilter. The prefilter is connected to an FM modulator, such as a voltage controlled oscillator. In one embodiment, a correlator in the transceiver monitors the transmitted waveform during times when the transceiver is not receiving signals, and provides a correlation signal to a feedback control circuit. The feedback control circuit dynamically adjusts the gain of the prefilter, and may comprise, e.g., a second order tracking loop filter. The feedback control signal thereby tracks the amplitude of the transmitted waveform and adjusts the output gain of the prefilter so as to maintain a constant signal envelope. A tau-dither algorithm may be employed as part of the tracking circuit. In an alternative embodiment, a gradient search is used to adjust the output amplitude of the transmitted signal, wherein the step size of the gradient search is based on the slope of the signal amplitude and varied dynamically over time. In another embodiment, a two bandwidth differencing circuit is used to adjust the output amplitude of the transmitted signal.

Transmitter circuit for efficiently transmitting communication traffic via phase modulated carrier signals

Abstract: Transmitter for transmitting communication traffic via phase modulated carrier signals. The device provides for an efficient amplification of a phase modulated carrier signal using Class C amplifier (19) technology. An envelope function is applied to the carrier signal by modulating the Class C amplifier (19) with a related spectrum-suppressing amplitude envelope signal. Phase distortion accompanying the amplitude modulation of the Class C amplifier is compensated by generating a phase offset for the carrier signal. As each envelope function for suppressing the spectrum is generated, a corresponding phase offset may be applied to the carrier signal, avoiding the consequences of phase shift resulting from amplitude modulating the carrier signal in the Class C amplifier (19).

Carrier Phase Estimation Through the Rotation Algorithm for 64-QAM Optical Systems

Abstract: A novel low-complexity two-stage digital feed-forward carrier phase estimation algorithm based on the rotation of constellation points to remove phase modulation for a 64-ary quadrature amplitude modulation (QAM) system is proposed and analyzed both experimentally and through numerical simulations. The first stage is composed of a Viterbi and Viterbi (V&V) block, based on either the standard quadrature phase shift keying (QPSK) partitioning algorithm using only Class-1 symbols or a modified QPSK partitioning scheme utilizing both Class-1 and outer most triangle-edge (TE) symbols. The second stage applies the V&V algorithm after the removal of phase modulation through rotation of constellation points. Comparison of the proposed scheme with constellation transformation, blind phase search (BPS) and BPS+MLE (maximum likelihood estimation) algorithm is also shown. For an OSNR penalty of 1 dB at bit error rate of $10^{-2}$ , the proposed scheme can tolerate a linewidth times symbol duration product ( $\Delta \hbox{$ u $}\cdot T_{s}$ ) equal to $3.7\times 10^{-5}$ , making it possible to operate 32-GBd optical 64-QAM systems with current commercial tunable lasers.

Soft-output demodulator in space-time-coded continuous phase modulation

Abstract: Space-time coding has shown great promise for digital transmission in wireless communication links, especially when the channel response is known at the receiver. Space time coding combined with continuous phase modulation (CPM) can offer better tradeoffs in bandwidth and power efficiency. Because of the memory inherent in CPM, channel estimation is often harder than for linear modulations. We present an adaptive soft algorithm that performs joint channel estimation and data detection for space-time CPM systems. Properly designed pilot symbols are inserted at the very beginning to give good initial estimates of the channels. This soft receiver is further applied to the interleaved space-time CPM system to yield better performance with moderate complexity through iterative processing. Simulation results show that the receiver can often achieve near-coherent performance in quasistatic fading as well as in time-varying fading.