Study On The Characteristics Of Wait-receiving Reentry-telemetry Channel

In order to improve the transmited rate via compensating the channel's attenuations, it is significant to research the the characteristics of reentry telemetry channel. So this dissertation deeply studies the modulation-channel and wireless transmited channel. After analyzing the relationships between the each parameterof the modulation-channel and modulation-channel's performance, it puts forward some rules that should be followed in the design of the modulation-channel. It also establishes the fading models of wait-recesiving reentry telemetry channel. There are two kindes frequency-nonselective models: one is a two paths model basing on the wait-receiving antenna's specialties, the other is the near-to-ground fading model basing on the terrain's character of shooting range and the location of the ground-receiving station and the configuration of the wait-receiving antennae and transmitting antennae and the antenna gain pattern which is a product process of a Rice process and a lognormal process. And there are two kindes frequency-selective models: one is a three paths model basing on different dalay times and attenuations, the other is an exponential basis expansion model basing on the environment that multipath is caused by a few strong reflectors and the hypothesis that the transmit-receive filters are time-invariant (TI). In this model, the channel's time-varying (TV) taps are expressed as a superposition of TV exponentials bases with TI coefficients. This dissertation brings forward the estimating methods of channel's parameters and analyzes the channel's characteristics using the computer simulating.Then roundly considering the effects of multipath interference and filter bandwidth and antenna gain pattern and white noise, it quantitatively analyzes how the multipath interference affects the performance of the re-entry telemetry system and the variety disciplinarian of received signal in wait-receiving telemetry system. It gets the up-bounded of system performance loss coursed by multipath interference and how the ground station and the antennas affect the received signal.The final aim of researching the reentry telemetry channel's characteristics is to gain a suitable signal processing method to compensate the channel's distortions and attenuations. According to the established channel model, the dissertation studies the blind channel identification and equalization, and analyzes its performances by computer simulating and calculating and validates the validities of these methods. In addition, according to the slowly variety of the channel (compare with the code rate) and a short time between the missile out from the black area and touchdowns, it researches a simple, flexible and fast adaptive equalizer to compensate and equalize the channel's distortions and attenuations. So use the combined DFE/MLSE equalizer based on predicted signal to compensate the reentry telemetry channel distortions. Simulation results suggest that the DFE/MLSE is excellent. Finally, using two DSP chips and one FPGA chip, it accomplishes the hardware system design and debug for DFE/MLSE equalizer. It proves that the hardware can satisfy the requirements of performance and real-time processing.The main contributions in this dissertation are as follows:1. In the engineering design, the research results of the modulation-channel will be important references.2. The model of the wait-receiving reentry telemetry channel and the analysis results of the channel characteristics all are the theory base of researching the signal processing method to compensate channel's distortions and attenuations.3. The researching results of the multipath interference and the filter bandwidth and the antenna gain pattern affectting the system performance and receiving signal will be very important in the system design and in a flight test to configure the antenna and locate the ground station.4. The signal processing method based on the characteristics of reentry telemetry channel can compensate the channel's distortions and attenuations.5. Using the all-digital method (DSP+FPGA), it implements this adaptive equalizer. So it validates that the project is realizable.