Modulation and Estimation with a Helper

The problem of transmitting a parameter value over an additive white Gaussian noise (AWGN) channel is considered, where, in addition to the transmitter and the receiver, there is a helper that observes the noise non-causally and provides a description of limited rate $R_\mathrm{h}$ to the transmitter and/or the receiver. We derive upper and lower bounds on the optimal achievable $\alpha$-th moment of the estimation error and show that they coincide for small values of $\alpha$ and for low SNR values. The upper bound relies on a recently proposed channel-coding scheme that effectively conveys $R_\mathrm{h}$ bits essentially error-free and the rest of the rate - over the same AWGN channel without help, with the error-free bits allocated to the most significant bits of the quantized parameter. We then concentrate on the setting with a total transmit energy constraint, for which we derive achievability results for both channel coding and parameter modulation for several scenarios: when the helper assists only the transmitter or only the receiver and knows the noise, and when the helper assists the transmitter and/or the receiver and knows both the noise and the message. In particular, for the message-informed helper that assists both the receiver and the transmitter, it is shown that the error probability in the channel-coding task decays doubly exponentially. Finally, we translate these results to those for continuous-time power-limited AWGN channels with unconstrained bandwidth. As a byproduct, we show that the capacity with a message-informed helper that is available only at the transmitter can exceed the capacity of the same scenario when the helper knows only the noise but not the message.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

A combined PSK/ASK transmission system for commercial telephony via satellite

This study addresses three modulation schemes capable of increasing the voice channel capacity of the INTELSAT TDMA/DSI System operating with INTELSAT V spacecraft. In particular, a combination digital Amplitude-Shift Keying/Phase-Shifting Keying (APK) technique is evaluated with respect to signal design, thermal noise performance, bandwidths limitations, co-channel interference, adjacent channel interference, TWT distortion and modem complexity in an INTELSAT TDMA system environment. In a linear channel some APK signal designs are known to require significantly less average SNR than PSK to achieve the same probability of symbol error. However, when operated through a satellite channel containing at least one TWT, the reduction in average power required to accommodate amplitude variations causes APK performance to fall below that of PSK for the same alphabet size. Signal predistortion and/or TWT linearization can eliminate the effect of TWT distortion and restore the performance advantage, although the overall performance of APK is still inferior to PSK. However, in a heavily interference limited environment, such as INTELSAT V, the lower average power requirements caused an APK system to perform better, in some cases considerably better, than the corresponding PSK case. Modem implementation considerations include how the signal set can be generated, the type and method of predistortion compensation, the detection method and the equipment required for the reconstruction of phase and amplitude references. The evaluation techniques of APK described include mathematical models, computer simulations (including the development of a unified error performance expression) and logical extrapolation from the QPSK case. Finally, a simple 8 level APK hardware modem was constructed and evaluated. It is concluded that an APK system may be of advantage as a retrofit in the INTELSAT TDMA system operating at 6/4 GHz, but be of significant advantage at 14/11 Ghz where the higher signal/noise ratios can yield an increase in capacity of up to 50 percent

Voyager Spacecraft Phase B, Task D. Annex to Volume 4 - Spacecraft Electrical Subsystems Definition Final Report

Systems analysis and tradeoff data on electrical subsystems for recommended Voyager spacecraft configuratio