Communications Technology To Improve The Utilization Of Channel Bandwidth

In modern communication systems, high speed data transmission and limited bandwidth is a contradiction. So researchers find so many methods to evaluate the utilization of channel bandwidth. Channel estimation is a must for reliable communication in wireless systems. In traditional channel estimation, part of the bandwidth is used for transmitting the training sequence. But in superimposed training sequence channel estimation(ST), training sequence is superimposed on the data sequence without using the bandwidth. So ST method becomes a hot research point for future wireless communication.For economic reasons and because of the characteristic of original image and sound signals, analogue optical fiber transmission systems remain attractive. Though in the reality, digital signals (control signal, synchronization signal) should also be transmitted at the same time. A PWAM optical fiber transmission system, which uses a 2-level pulse amplitude modulation (PAM) and analogue pulse width modulation (PWM) hybrid technique, can simultaneously support digital and analogue communications over the common optical fiber in a cost effective fashion. So for optical communication systems, evaluate the utilization of channel bandwidth means both digital and analogue signal can be transmitted in a common optical fiber. In this paper, we spread our work in the following aspects:1. Based on the superimposed training channel estimation method, we analyzed the steps for channel estimation and gave the mathematical model of the method. Then we analyzed how different training sequences and different power distribution impact on the channel estimation.2. We proved the periodic training sequence can reduce the complexity of the channel estimation. And then we gave the optimized training sequence for channel estimation in this paper. We also do the computer simulations for both the ST method and the ST method after excluding the mean value.3. We proposed a new frequency domain interpretation for the ST method and got the mean square error. Based on these results, we also got the data dependent superimposed training method(DDST) using frequency domain deduction. All the results were proved by computer simulations.4. In this paper an iterative channel estimator based on superimposed training (IST) is elaborated. Unlike the conventional ST scheme, IST method just uses the information in the receiver. From the computer calculations, after 3-4 iterations estimation error get significantly improved.5. We also analyzed the PWAM optical fiber transmission technique to evaluate the utilization of optical channel bandwidth. We focused on the analysis for the optical receiver technology in optical fiber communication system.6. We analysis the PWAM optical transmission system which uses self-error-correction code. Because of the PWM and PAM modulation, self-error-correction code can easily be adopted into PWAM system. The error correction effect has been estimated based on the improvement in receiver sensitivity. Compared with a conventional optical fiber transmission system, the proposed PWAM system with repetition code does not have a high complexity. Based on the computer simulation, the results indicate the improvement of the system performance.