Future NASA missions such as the Lunar Reconnaissance Orbiter, Kepler, James Webb Space Telescope, and Space Interferometry Mission will use Ka-band frequencies (26.5- and 32-GHz bands) for their primary science downlink instead of X-band frequencies (8.42-GHz band) due to scarcity of spectrum at X-band. At Ka-band frequencies, adverse weather events degrade the telemetry link performance to a greater degree than they do at X-band. The uncertainty about the weather losses at Ka-band is much greater than the uncertainty about all other losses on the link combined. Therefore, the traditional link design approach used for X-band links has to be modified. In this paper, we propose a link design approach where the atmospheric noise temperature statistics along with the ground antenna characteristics are used to optimize the average data return on the link. We introduce the mathematical foundations of this approach and present optimal link design strategies for using Ka-band both at 26.5- and at 32-GHz bands for future NASA missions.

During the last 40 years, deep space radio communication systems have experienced a move toward shorter wavelengths. In the 1960s, a transition from L- to S-band occurred, which was followed by a transition from S- to X-band in the 1970s. Both these transitions provided deep space links with wider bandwidths and improved radio metrics capability. Now, in the 2000s, a new change is taking place: namely, a move to the Ka-band region of the radio frequency spectrum. Ka-band will soon replace X-band as the frequency of choice for deep space communications, providing ample spectrum for the high data rate requirements of future missions. The low-noise receivers of deep space networks have a great need for link management techniques that can mitigate weather effects. In this paper, three approaches for managing Ka-band Earth-space links are investigated. The first approach uses aggregate annual statistics, the second one uses monthly statistics, and the third is based on the short-term forecasting of the local weather. An example of weather forecasting for Ka-band link performance prediction is presented. Furthermore, spacecraft commanding schemes suitable for Ka-band link management are investigated. Theses schemes will be demonstrated using NASA's Mars Reconnaissance Orbiter spacecraft in the 2007-2008 period, and the demonstration findings will be reported in a future publication.

Consider an area, such as a shopping mall, which is covered by a network of micro-cells. Assume a user entering this area to have a packet that he wishes to transmit during his/her residence time in the area. The user spends a limited period of time (system time) moving across the area while visiting through a number of cells. We consider a number of access control algorithms that regulate the transmission of user packets. Performance measures include: system throughput, user blocking probability (expressing the probability that the user is not able to transmit the packet) and the packet delay (for transmitted packets). We analyze and compare three access algorithms by considering an area that consists of three cells. The algorithms are differentiated by providing different access priorities to users based on their time left in the system. We can also modify the priority level to include differentiation between new arrivals and handoff users.