Citation
Abstract
The concept of using a relay satellite which receives information from deep space vehicles over an optical channel and relays this information to Earth over a microwave channel has been considered in the past. An important consideration in such a system is the nature of the optical-microwave interface aboard the relay satellite. In order to allow for the maximum system flexibility, without overburdening either the optical or RF channel, this paper considers the option of demodulating the optical channel on board the relay satellite but leaving the optical channel decoding to be performed at the ground station. This not only removes some degree of complexity from the relay satellite but more importantly it circumvents restricting all deep space vehicles to a specific channel coding for which the decoder is provided on board the relay. For this scheme to be viable, the occurrence of erasures in the optical channel must be properly treated. A hard decision on the erasure (i.e., the relay selecting a symbol at random in case of erasure occurrence) seriously degrades the performance of the overall system. In this paper, we suggest coding the erasure occurrences at the relay and transmitting this information via an extra bit to the ground station where it can be used by the decoder. Many examples with varying bit/photon energy efficiency and for the noisy and noiseless optical channel have been considered. It is shown that coding the erasure occurrences dramatically improves the performance of the cascaded channel relative to the case of hard decision on the erasure by the relay.
Details
- Volume
- 42-70
- Published
- August 15, 1982
- Pages
- 117–131
- File Size
- 739.3 KB