  Concentration shift keying (CSK) is a widely studied modulation technique for
molecular communication-based nanonetworks, which is a key enabler for the
Internet of Bio-NanoThings (IoBNT). Existing CSK methods, while offering
optimal error performance, suffer from increased operational complexity that
scales poorly as the number of transmitters, $K$, grows. In this study, a novel
$M$-ary CSK method is proposed: CSK with common detection thresholds (CSK-CT).
CSK-CT uses \textit{common} thresholds, set sufficiently low to guarantee the
reliable detection of symbols from all transmitters, regardless of distance.
Closed-form expressions are derived to obtain the common thresholds and release
concentrations. To further enhance error performance, the release concentration
is optimized using a scaling exponent that also optimizes the common
thresholds. The performance of CSK-CT is evaluated against the benchmark CSK
across various $K$ and $M$ values. CSK-CT has an error probability between
$10^{-7}$ and $10^{-4}$, which is a substantial improvement from that of the
benchmark CSK (from $10^{-4}$ to $10^{-3}$). In terms of complexity, CSK-CT is
$\mathcal{O}\big(n\big)$ and does not scale with $K$ but $M$ ($M\ll K$),
whereas the benchmark is $\mathcal{O}\big(n^2\big)$. Furthermore, CSK-CT can
mitigate inter-symbol interference (ISI), although this facet merits further
investigation. Owing to its low error rates, improved scalability, reduced
complexity, and potential ISI mitigation features, CSK-CT is particularly
advantageous for IoBNT applications focused on data gathering. Its
effectiveness is especially notable in scenarios where a computationally
limited receiver is tasked with collecting vital health data from multiple
transmitters.
