This paper proposes performance improvement schemes for multiple-input multiple-output (MIMO) communication systems employing per transmit antenna differential encoding (PADE), which generates an independent differentially encoded sequence for each of the multiple transmit antennas by means of space-time coding and mapping. PADE can operate without channel state information (CSI) at both the transmitter and the receiver. This paper proposes the following schemes suitable for PADE: 1) novel mapping schemes for transmit diversity (TD) and spatial multiplexing (SM); 2) introduction of the state-reduction algorithm for per-survivor processing (PSP), if the channel is estimated by a large number of observation symbols of the received signal. Next, computer simulation confirms that the proposed schemes can improve bit error rate (BER) performance and can mitigate floor of BER on slowly time-varying fading channels, keeping small hardware complexity.

By directly detecting the phase of a baseband signal from the ratio of the in-phase and the quadrature phase components, a delta-sigma phase detector can realize an AGC-free mobile communication receiver. The paper studies the performance of the phase detector applied to digital communication systems. We explain theoretically the phase quantization noise of the detector and show the performance of a PSK/FSK receiver using it. Simulation results tell that the required clock frequency of the phase detector is less than a tenth of that of a conventional scheme which detects the phase of a limiting-amplified IF signal by digital processing.

This paper compares the following two maximum likelihood sequence estimation schemes incorporating carrier phase estimation for coded MPSK: (1) the respective-state channel estimation and (2) the multiple differential detection. This paper confirms by analysis and computer simulation that both schemes have similar performance in the absence of intersymbol interference.

This paper proposes an adaptive maximum-likelihood sequence estimation (MLSE) by means of combined equalization and decoding, i.e., adaptive combined MLSE, which employs separate channel estimation for respective states in the Viterbi algorithm. First, an approximate metric including channel estimation is derived analytically for this proposed adaptive combined MLSE. Secondly, procedures to accomplish blind equalization are investigated for the proposed MLSE. Finally, its excellent BER performance on fast time-varying fading channels is confirmed by computer simulation, when the proposed MLSE operates as a blind equalizer.>

This paper proposes an adaptive equalization scheme in dual diversity reception and assesses its performance by computer simulation over fading multipath channels. This scheme is composed of adaptive decision feedback equalizers (DFEs) in each diversity branch, a least-squares combiner (LSC) and a decision device. In the LSC, the output signals of DFEs are multiplied by controllable weights based on mean square error criterion and summed. The output of the LSC is applied to the decision device to obtain a receiver estimate of the transmitted sequence. The receiver estimate is applied to DFEs as the input of the feedback section and the reference of the tap coefficient-update algorithm. In the DFEs and the LSC, the tap coefficients are updated independently according to the Kalman algorithm. Such an arrangement of the scheme reduces the computational complexity compared with a conventional DFE transversal-combining diversity reception scheme. Simulation results confirm the effectiveness of this proposed scheme over fading multipath channels with transmission bit rate of 40 kbps and the maximum Doppler frequency of 160 Hz observed in 1.5 GHz-band digital mobile radio communication systems.

This paper proposes an adaptive maximum-likelihood sequence estimator (MLSE), which is a suboptimum approximation to the adaptive maximum-likelihood detector and is capable of tracking fast time-varying intersymbol interference (ISI) channels. The adaptive MLSE consists of a channel estimator and an MLSE implemented by the Viterbi algorithm (VA). The novel feature of the proposed adaptive MLSE is a channel estimation scheme, where the channel estimation is accomplished for each state in the VA along the surviving path connected to each state. This MLSE makes it possible to estimate a channel impulse response without an influence of a decision delay inherent in the VA, and the performance and complexity of the proposed procedure is controlled by the memory length of the VA. The bit error rate performance of the proposed MLSE is confirmed by experimental results. It is shown that the proposed MLSE has a capability of excellent tracking performance in a severe environment caused by fast time-varying ISI, for example frequency selective multipath fading in digital mobile radio communications.>