A receiver structure, called a "pseudo maximum likelihood sequence estimation" (pseudo MLSE), which approximates MLSE with a simple hardware configuration, was derived. By introducting a tentatively estimated sequence, the pseudo MLSE detects the received sequence symbol by symbol, retaining the MLSE optimum decision property. The number of arithmetic operations required in one symbol duration is reduced fromM^{L + 1}to(L + 1)Min anM-ary signaling case with channel memory lengthL. An adaptation algorithm for the variation in the channel characteristics was also developed. Pseudo MLSE application to quadrature phase shift keying (QPSK) for a band-limited nonlinear channel is described. The most practical application of pseudo MSLE, named the "adaptive threshold detector with estimated sequence" (ATDES), detects symbols with threshold detection and is suitable for high bit rate operation. For both the pseudo MLSE processor and ATDES, most of the hardware is occupied by a replica memory stored in the receiver. Performance in a typical nonlinear satellite channel model is evaluated by computer simulation. Simulation results show a 0.8 dB improvement by ATDES with 64 replica memories and 1.3 dB improvement by the pseudo MLSE processor with 3072 replica memories. The tentative estimation error effect is estimated to be less than 0.1 dB in the simulated satellite channel.

A new technique for parallel transmission of digital and analog signals over a single telephone channel is presented. The modulation scheme treated in this paper is quadrature amplitude modulation, wherein the digital and analog information are mapped separately as in phase and quadrature components. New decision directed schemes which are applicable to parallel transmission are derived by using an error signal measurement defined independent of the analog part. Computer simulation for the parallel transmission scheme of 4.8 kbit/s digital and 2.4 kHz sampled analog sequences is carried out for a typical dispersive telephone channel. Simulation results show that this scheme is useful for high fidelity analog signal transmission.