  As a special case of sparse code multiple access (SCMA), low-density
signatures based code-division multiple access (LDS-CDMA) was widely believed
to have worse error rate performance compared to SCMA. With the aid of
Eisenstein numbers, we present a novel class of LDS which can achieve error
rate performances comparable to that of SCMA in Rayleigh fading channels and
better performances in Gaussian channels. This is achieved by designing
power-imbalanced LDS such that variation of user powers can be seen both in
every chip window and the entire sequence window. As LDS-CDMA is more flexible
in terms of its backwards compatibility, our proposed LDS are a promising
sequence candidate for dynamic machine-type networks serving a wide range of
communication devices.
