# A History of Channel Coding in Aeronautical Mobile Telemetry and Deep-Space Telemetry
## 4 Aeronautical Mobile Telemetry  
### Channel Coding in the 20 th Century  
From 1966 to 1999, 245 papers mentioning what is now called channel coding appeared in the _Proceedings of the International Telemetering Conference_. The treatment of coding ranged from incidental remarks that channel coding improves link reliability to full-length treatments of code design and decoding algorithms. The most common mention of coding was the discussion of ground stations, for both satellites and space probes, that had decoding capabilities conforming to CCSDS coding standards [50]. It is clear that by the 1970s coding became permanently established in NASA circles, but was little more than \"in the air\" in aeronautical mobile telemetry circles. Of the 245 papers, only 40 target aeronautical mobile telemetry systems: ref. [112; 113; 114; 115; 116; 117; 118; 119; 120; 121] mention the use of coding in magnetic tape recording, ref. [122; 123; 124] mention the use of coding in solid state recording, ref. [125] describes the use of coded ATM technology for ground transport, ref. [126] predicts the use of channel codes for improving quality telemetry data transport on a data bus inside a Boeing aircraft, ref. [127] describes how coding might be used to assess the quality of merged PCM streams from different receivers, and [128; 129; 130; 131; 132; 133; 134; 135; 136; 137; 138; 139; 140; 141; 142; 143; 144; 145; 146; 147; 148; 149; 150] deal specifically with the air-to-ground radio link. In a 1975 \"where do we go from here\" paper, [PERSON] states [151], \"error-detecting- and correcting codes will receive much more attention\". It is interesting that [PERSON], in two \"future trends\" papers published in 1978 [10] and 1988 [152], does not mention channel coding. This is because, in the era in which he wrote, the reliability of RF transmission was not the bottleneck. The bottlenecks were recording bandwidth, ground station configuration, and the ability of data processors to produce real-time displays of telemetry data with the proper engineering units. The same is true for [PERSON]'s \"Telemetry Systems of the Future\" published in 1989 [153]. [PERSON]'s \"Airborne Telemetry Trends for the 1990's\" [154] states (rather briefly), \"convolutional encoding enhances link performance\", in the context of future breakthroughs in FM. A decade later, [PERSON] Future Trends paper [155] fails to mention coding. None of these observations are intended as criticisms. Instead, these observations reflect the reality of the times in which these papers were written. Other issues were more pressing, such as spectral congestion, the ability to automatically organize hundreds of thousands of measurements, store those measurements, and use networks to convey those measurements to the engineers and scientists who need them. The first coding study published in the open literature constrained by the aeronautical mobile telemetry environment was carried out by [PERSON] and [PERSON] [128] in 1983. They examined BPSK with the \((7,1/2)\) convolutional code whose encoder is shown in Figure 12 and described by the polynomials (6). Interleaving was applied after the encoder and the corresponding deinterleaver prior to the Viterbi decoder to \"break up\" the long error bursts caused by link outages. The decoder was able to support a 10 Mbit/s downlink. Except for the placement of the interleaver and deinterleaver, this system was the inner code for the _Voyager_ program described in Section 3.5. To the author's knowledge, this configuration was never flown on a test range. The most probable reason is that it required too much bandwidth. The next serious investigation, also performed in 1983 by [PERSON] and [PERSON] [129], addressed the bandwidth issue by exploring the same rate-1/2 constraint length 7 convolutional code with PCM/FM. The experimental configuration is shown in Figure 19. A pseudo-noise (PN) sequence was encoded and input to an FM transmitter. No pre-modulation filter was used in this experiment.