A feedback-loop type transmission power control for low speed TDMA satellite communication systems

Abstract

This paper proposes a feedback-loop type transmission power control (TXPC) schcme coupled with first and second order prediction methods and analyzes the optimum control period and residual control error. In order to minimize residual control error, the three main factors contributing to residual control error are analyzed. First, to minimize level detcction error, a channel Pe estimation method is proposed and analyzed experimentally for quasi signal-level detection. Second, rain attenuation rates in Ka bands are measured and analyzed statistically. Finally, the optimum control period of the proposed TXPC scheme is analyzed. The simulation results on the prototype TXPC scheme show a maximum residual control error of k2.5dB is achievable with an optimum control period of about 2 scconds. I n t r o d u c t i o nIn satellite communication systems using frequency bands above lOGHz, Pe performance is degraded by rain attenuation not only due to decreased C/N of the desired channel, but also because of decreased D/U. The adjacent channel interference due to rain attenuation degrades system performance especially in low speed satellite communication systems in which channel filtering after a high power amplifier can no longer be used.Transmission power control (TXPC) is the most e f f e c t i v e technique f o r reducing such interference, and various kinds of TXPC schemes have been proposed such as an open-loop s c h e m e [ l I , a closed-loop schemeL2I and a feedbackloop scheme [3]. In the open-loop scheme, up-link rain attenuation is estimated measuring the beacon signal level in the down-link. However, rain attenuation can not be accurately estimated in Ka bands using this scheme, since frequency s c a l i n g F 4 ] of rain attenuation is not valid in Ka bandsL5I. Moreover, this scheme requires a lot of hardware since a beacon signal level detector is required in all earth stations. In the closed-loop schcme, up-link rain attenuation is estimated by the attenuation on self-transmitted signals in down-link. Accurate rain attenuation estimation can not be achicvcd with this scheme itself, either, since rain attenuation occurs in both the up-link and down-link. Moreover, this scheme is not suitable for multi-beam TDMA systems which generally have no closed-loop.To solve these problems, this paper proposes a feedback-loop type TXPC scheme employing prediction control. In the fcedback-loop scheme, r e c e i v i n g s t a t i o n s m e a s u r e d e s i r e d -c h a n n e l quality to estimate up-link rain attenuation of transmitting stations and send back the control data to the transmitting stations. This scheme a c h i e v e s m o r e a c c u r a t e rain a t t e n u a t i o n estimation than the open-loop and closed-loop schemes, because the system rarely suffers from simultaneous rain attenuation at two receiving reference stations backing up each other for site diversity. Moreover, this TXPC scheme requires little additional hardware when it is implemented in central controlled TDMA systcms and is suitable for mul...

Quality estimation of PSK modulated signals

“…∫ dt . (6) Only the magnitude of the signal is considered, without any knowledge of whether the bit has been correctly decoded. Function (6) can be inverted, so the E b / N 0 and the BER of the signal can be obtained from the frequency of the event S < T µ s { } .…”

“…As opposed to the traditionally used Ku band (14/12 GHz), the Ka band is much more affected by atmospheric events that lead to bad signal conditions, ranging from a slowly changing attenuation of the signal to a sudden deep fade that blocks all communication. Many methods for countermeasuring rain attenuation have been proposed [1][2][3][4][5][6][7][8][9]. Some of these methods, such as space or frequency diversity [7,9], allow a very high level of link availability to be achieved, but they are very complex and expensive.…”

Modeling Ka-band scintillation as a fractal process

“…Fade countermeasure systems, such as transmission power [9], bit and coding rates adaptation [1,2], frequency [12,13] or space diversity [10] are thus required to avoid loss of economy.…”