  Encoding information in combinations of pre-synthesised deoxyribonucleic acid
(DNA) strands (referred to as motifs) is an interesting approach to DNA storage
that could potentially circumvent the prohibitive costs of
nucleotide-by-nucleotide DNA synthesis. Based on our analysis of an empirical
data set from HelixWorks, we propose two channel models for this setup (with
and without interference) and analyse their fundamental limits. We propose a
coding scheme that approaches those limits by leveraging all information
available at the output of the channel, in contrast to earlier schemes
developed for a similar setup by Preuss et al. We highlight an important
connection between channel capacity curves and the fundamental trade-off
between synthesis (writing) and sequencing (reading), and offer a way to
mitigate an exponential growth in decoding complexity with the size of the
motif library.
