Comparing Performance of Coded Communications over fading channels between the Lunar South Pole & Earth

Abstract

In this paper we design and analyze an end-to-end communication system between a lander/rover on the surface of the lunar South Pole and an Earth station. Various communication systems on the lander or rover could be used for the Earth-to-Moon communication in both the uplink and downlink direction. To communicate to and from the lander/rover on the lunar South Pole, low and/or medium directional antennas onboard the lander/rover will have to be pointed at low elevation angles between 2 to 10 degrees, thus causing multipath fading effects due to reflection of a portion of the transmitted electromagnetic waves from the surface of the Moon. These are not commonly encountered in traditional deep space communications between a spacecraft and a ground station. We investigate various design methods and analyze such communication systems, in the presence of multipath fading. We model the fading channel based on existing and simulated data. For coherent reception, the acquisition and tracking loop should acquire and track incoming carrier phase in presence of Rician multipath fading. For this communication system in addition to estimating the received carrier phase, the amplitude of the fading signal should also be estimated, in particular to be used in the decoder. We consider simple modulation and coding schemes in particular those specified in the CCSDS standards for space applications. After designing various components of the communication system, we use Simulink models to obtain the end-to-end performance of the communication link under investigation. Based on the available data, the fading channel can be accurately modeled as a Rician fading channel with various Rician parameters depending on the Earth elevation angle, which also affects the Doppler spread. Therefore, the challenge is to design a communication system robust in the presence of the multipath fading where the channel conditions change in time and thus produce fading. In summary, this paper compares possible communication system designs, performance analysis, and simulations for coded system with/without interleaving with hard/soft decision and with/without channel state information (CSI), over a communication link between a lander/rover at the Lunar south pole and a Deep Space Network station in presence of Rician fading.