Alternating-coded multipulse codes for incoherent scatter experiments

Abstract

A possibility of using strong alternating codes as a phase modulation pattern in multipulse incoherent scatter experiments is investigated. It is shown that such a modulation leads to a high range resolution much in the same way as the use of Barker codes does. The suggested modulation gives two types of data, one with a range resolution corresponding to the pulse length in the pulse code and the other with that corresponding to the bit length in the alternating code. Most of the efficiency of the experiment goes to high resolution data; when long alternating codes are used, the proportion of low resolution data is negligible. Practical examples using this idea are constructed and their speeds are compared with those obtained using Barker codes. The comparison is made using the GUISDAP package; hence this paper also demonstrates the capabilities of GUISDAP in planning the experiments. It is found that an alternating-coded pulse code is approximately as fast as a Barker-coded pulse code and its speed is about one third of that of a Barker-coded alternating code. Barker-coded pulse codes have small range ambiguities within a wide altitude range, which make the fit residual depart from the theoretical value of unity in the least squares parameter fits and put an upper limit to the working range of the experiment. These limitations can only partly be removed by the range ambiguity correction. The suggested modulation has the benefit that it has no range ambiguities. As a result, no systematic errors should occur and the experiment is expected to work at greater heights. Although Barker-coded alternating codes also have range ambiguities, they are always situated close to the main peak of the range ambiguity function and are therefore much less harmful. The suggested modulation is not expected to surpass Barker-coded alternating codes, except perhaps in the presence of intense sporadic E layers.