NASA's Mars laser communications demonstration (MLCD) project (since discontinued) was designed to achieve data rates greater than 1 Mb/s from the farthest Mars range and greater than 30 Mb/s from the nearest Mars range. We present here pathways whereby ongoing optical technology advances should allow 30 dB of increased data rates relative to MLCD by 2020. In other words, technical advances should soon allow the return of deep-space data at rates of 1 Gb/s from the maximum Mars range, 100 Mb/s from Jupiter distances, and 10 Mb/s from Uranus, all many orders of magnitude greater than present radio-frequency capabilities. The potential for realizing the stated capability with less than a three times increase in dc power required from the spacecraft and no increase in payload mass is discussed.

Demand for increased capacity in deep-space to Earth communications systems continues to rise as sensor data rates climb and mission requirements expand. Optical free-space laser communications systems offer the potential for operating at data rates 10 to 1000 times that of current radio-frequency systems. A key element in an optical communications system is the Earth receiver. This paper reviews the design of a distributed photon-counting receiver array composed of four meter-class telescopes, developed as a part of the mars laser communications demonstration (MLCD) project. This design offers a cost-effective and adaptable alternative approach to traditional large, single-aperture receive elements while preserving the expected improvement in data rates enabled by free-space laser communications systems. Key challenges in developing distributed receivers and details of the MLCD design are discussed.

A new, relatively simple architecture for generating continuous phase modulation (CPM) signals is presented. It can produce arbitrary frequency pulses for binary full-response signals with arbitrary modulation indexes. It can also produce partial-response signals or M -ary signals with reasonable accuracy. The method filters and then hard limits the switched and summed outputs of a 90 degrees hybrid.>

An error to equation (25) in the above-named work (ibid., vol. COM-27, pp. 1519-1527, Oct. 1979) is corrected.

Frequency division multiplexed, orthogonalM-ary FSK modulated signals transmitted over a frequency hopping channel (with one channel use per hop) interfere with each other unless perfectly synchronized in time and frequency with the receiver. In order to maintain the interfering "crosstalk" energy at harmless levels, even in the case of grossly power unbalanced users, the frequency separation between assigned signaling frequencies must be expanded beyond the orthogonal spacing. It is found that the required bandwidth expansion can be significantly reduced by amplitude windowing at the receiver, at a cost of a slight decrease in detectability. This effect is evident through examination of both worst case, single source crosstalk and average, multiple user crosstalk.