In this paper, the user selection problem is investigated in the multi-user satellite multiple-input multiple-output (MIMO) downlink, which includes a multi-beam geostationary earth orbit (GEO) satellite in space and multiple terrestrial users on the ground. Considering that the number of users is much larger than that of beams or feeds, user selection should be performed so that multiple users can be served successively in different time slots. In order to meet the quality of service (QoS) requirements of users and maximize the system sum rate, three user selection algorithms are proposed: greedy user selection (GUS) algorithm, add swap user selection (AS) algorithm, and random add swap user selection (RAS) algorithm. Among the three algorithms, only the “add” operation is adopted in the GUS algorithm, both the “add”, and “swap” operations are considered in the AS algorithm. On this basis, heuristic search and “random swap” operation are introduced and the RAS algorithm is obtained. The complexity of the above three algorithms is analyzed analytically and the RAS algorithm is found to have the highest complexity. Besides, the performance of the three algorithms is analyzed and compared through simulations, where the random user selection (RUS) algorithm is taken as a benchmark. Numerical results show that the system sum rate and energy efficiency are greatly improved by the proposed algorithms and the RAS algorithm has the best performance.

Bundle protocol (BP) is the main protocol of delay/disruption-tolerant networking which is developed to provide reliable data delivery services in a stressed communications environment. A typical application of BP is for data delivery in a challenging deep-space communication environment. However, little work has been done in analyzing the performance of BP in deep-space communications, especially in presence of highly channel-rate asymmetry. In this paper, we present analytical modeling of the transmission performance of BP over deep-space communication channels characterized by highly asymmetric channel rates. The model is built to estimate the expected file delivery time (and goodput) of the protocol for reliable data delivery in a deep-space transmission scenario. The model is validated by conducting data transfer experiments using a PC-based experimental test bed.

A blind channel estimation algorithm is proposed in this paper by analyzing the received signal of uplink for MC-CDMA system. The proposed algorithm uses the second order statistics of the received signal and the user spreading sequences to separate the user information and to estimate the channel response. Then PIC technique is used to improve the performance of the algorithm. The proposed algorithm has nothing to do with the type of noise. And the results of computer simulation show the proposed algorithm has excellent performance in wireless channel.