We propose a novel simplified Viterbi equalizer for high symbol rate FWA (Fixed Wireless Access) systems carrying 64QAM signals. Reduced complexity and improved performance are achieved adopting two approaches. The first one is reducing the number of survival paths, taking advantage of the large D/U common in LOS (line of sight) communications. The second one is using a multi-stage process to generate desired signal replicas based on their likelihoods. Computer simulations confirm that the proposed replica generation method offers a performance improvement of about 1 dB and the proposed Viterbi equalizer offers reduced complexity with no performance penalty compared to full Viterbi equalizer.

We propose a new receiver structure to mitigate interpath interference (IPI) in W-CDMA systems. We model IPI in RAKE combining as intersymbol interference (ISI) and use a two-stage receiver structure. The first stage is a RAKE receiver and the second stage is an equalizer. In cases of multi-code transmission, interference among code channels causes extra impairments which can not be modelled as ISI. Under these circumstances, they are estimated by using decisions from the first stage and then subtracted from the input of the equalizer. The residual interference is equivalent to ISI and can be mitigated by the equalizer. Simulation results show that the proposed receiver provides very promising performance in low spreading factor W-CDMA.

Achieving optimal performance with minimal complexity are conflicting problems encountered in constructing receivers. In this paper, to solve the problem, we propose sector beamed space hopping which utilizes a Viterbi equalizing receiver. Reduction of the number of RF circuit sets, system complexity and decreasing the computational burden of the Viterbi equalizer through the use of sector beamed space hopping is presented. This is achieved using a sector beamed antenna which limits the number of paths in the multipath channel environment. This paper describes each key component which comprises the system and discusses the application of FH-SS communication. The channel is assumed to be an industrial indoor propagation channel, such as those found in a factory, where high reliability is required and many complex multipaths exist. We confirm through simulation that Viterbi equalization using less computational complexity can be obtained. It is found that there exists a trade off between system complexity and performance. Through the discussion of power consumption, cost and BER performance, we show that the proposed system achieves acceptable performance while having a low system complexity.

Phase locked loops (PLL's) are well known as a threshold extension demodulator for analogue FM signals. This capability may lead to the low bit error rate demodulation for digital FM signals. A PLL has also its native frequency tracking ability and is suited to the demodulation of the signals having large Doppler shifts, for example signals from Low Earth Orbit (LEO) satellites. In this paper, we study the demodulation scheme of Continuous Phase FSK (CPFSK) and Gaussian filtered MSK (GMSK) signals using a Digital Signal Processing type Digital PLL (DSP DPLL). First we propose a DSP DPLL completely equivalent to an Analog PLL (APLL). Next we adopt the sequence estimation scheme to compensate the Inter-Symbol Interference (ISI) associated with the finite loop bandwidth of the DSP DPLL. Through computer simulations it is clarified that the proposed DSP DPLL with sequence estimator can achieve better BER performance compared with the conventional Limiter Discriminator (LD) detection on the AWGN channel. We have also shown that the DSP DPLL with sequence estimator has excellent BER characteristics on Rician fading channels having actual large Doppler shifts.

This paper presents a novel approach to a soft-output equalizer, which makes a symbol-by-symbol soft-decision based on a posteriori probabilities (APP's) criterion in the presence of intersymbol interference. The authors propose a soft-output Viterbi equalizer (SOVE) employing expanded memory length in a trellis of the Viterbi algorithm with small arithmetic complexity. The proposed equalizer gives suboptimum soft-decision closer to that of a equalizer with the maximum a posteriori probabilities (MAP) algorithm than the conventional SOVE.

This paper proposes and investigates a tap selectable Viterbi equalizer for mobile radio communications. When the multipath channel is modeled by a tapped delay line only, the taps which may seriously affect the data sequence estimation are selected and used to calculate the trellis metric in the Viterbi algorithm. The proposed equalization algorithm can reduce the number of path metric calculations and the number of path selections in the Viterbi algorithm. Moreover, we propose an extended equalizer which has antenna diversity. This equalizer calculates the path metric using the antenna outputs and results of channel estimators. Computer simulation is used to evaluate the BER performance of the proposed equalizer in a multipath radio channel.