State-of-the-art space mission telecommand receivers

Theoretical Analysis and Implementation of Effective Receivers for Telecommand Space Links

“…In fact, carrier acquisition is common to both scenarios since it is performed under carrier modulation mode CMM1, which only contains the unmodulated carrier. As reported in [2], [3] and [10], replacing the current carrier sweeping scheme and the standard Phase Locked Loop (PLL) at the receiver with spectral estimation techniques overcomes the bottleneck for low symbol rate at the target Es/N0 ≈ 2 dB, where Es is the symbol energy and N0 the one-side spectral density of the thermal noise (operative SNR reached with the new LDPC codes at CER = 10 −5 ), and can also relax the requirements on the carrier loop enforced by the on-ground sweeping procedure. Such an approach has several advantages: i) FFTbased carrier acquisition does not require on-ground sweeping, ii) allows faster acquisition, and iii) can reach lower estimation errors on carrier frequency.…”

“…However, despite the improvements introduced by FFTbased carrier acquisition, the carrier and subcarrier tracking persist as a bottleneck for some of the selected scenarios. A detailed list of the performance limits for the most promising techniques addressed in the project is reported in [2], [3] and [10]. To summarize, from the evaluated enhanced approaches, aimed at reducing the loop bandwidth, FFT-aided Costas subcarrier acquisition and tracking provides gains in the low SNR region, yet they do not meet the target Es/N0 at the lowest symbol rate scenarios.…”

“…Introduction of the new LDPC codes has implied lengthening of the start sequence, that is passed from 16 bits to 64 bits, in order to compensate the impact of the potential operation at a reduced SNR [2], [3]. The tail sequence is also affected by the new codes, and has been lengthened as well, passing from 64 bits to 128 bits ( Fig.…”

“…Such metric is based on standard soft and hard correlation, which results in a receiver bottleneck for the target SNR and the start sequence length. The proposed Simplified Likelihood Ratio Test (S-LRT) metric introduced in [2], [3], has been implemented in the breadboard and its performance contrasted with previous simulation results. This nearoptimum metric accounts for the sign ambiguity inherent in the TC binary modulation scheme, which as a by-product, and provides the sign of the received symbols required for decoding without the need for differential modulation.…”

“…A first series of results from the NEXCODE project has been presented in [2], [3]. In this paper we deepen the subject, with special emphasis on the implementation issues.…”