Research On Uplink Of Land Mobile Satellite Cooperative Systems

In order to provide communication service everywhere and anytime, International Telecommunication Union (ITU) is currently developing a vision of Next-Generation Networks (NGN) with the objective of providing a means for network integration. Satellite communications are successful for their wide area coverage and being immune to terrestrial events, but mainly rely on Line-of-Sight (LOS) path. Land mobile satellite (LMS) communication is limited by the masking effect caused by obstacles that block the LOS path. One goal of an integrated satellite-terrestrial system is to improve the reliability of the uplink in LMS system. Cooperative diversity technique, which is based on user and relay cooperation, can achieve spatial diversity and mitigate multipath fading. Thus, using cooperative diversity in integrated satellite-terrestrial systems will be a promising way to overcome the limitation of LMS communication.The performance of the uplink of LMS cooperative system is analyzed. A fixed terrestrial node is used as cooperative relay through three different cooperative protocols. The outage probability, average symbol error rate (ASER) and ergodic capacity of the proposed system are examined separately. We derive closed form expression for the joint cumulative density function (CDF) of signal to noise ratio (SNR) of the combined signal at satellite through trapezoidal rule and inverse Laplace. The CDF is used to determine the outage probability. The moment generating functions (MGF) of SNR of the combined signal are also derived for the closed form expression for the ASER and ergodic capacity. The simulations with different channel environments verify the proposed theoretical solutions.Two optimized transmitting power allocation schemes between the land mobile user and the relay node are investigated, maximizing the derived ergodic capacity and the instantaneous SNR of the combined signal, respectively. The statistic coefficients and instantaneous estimations of the channel fading in the LMS cooperative system are used in the two schemes separately. For the same system performance, the optimized transmitting power allocation schemes outperform the uniform power allocation scheme at low total transmitting power. Moreover, a channel feedback adaptation transmitting strategy is proposed for the LMS cooperative system. The mobile user and the relay node adaptively transmit the signal according to the feedback information about the link between the mobile user and satellite. The proposed strategy not only improves transmission efficiency and ergodic capacity but also ensures transmission reliability.