Low-correlation sequences over the QAM constellation

This paper presents the first concerted look at low correlation sequence families over quadrature amplitude modulation (QAM) constellations of size M-2 = 4(m) and their potential applicability as spreading sequences in a code-division multiple-access (CDMA) setting. Five constructions are presented, and it is shown how such sequence families have the ability to transport a larger amount of data as well as enable variable-rate signaling on the reverse link. Canonical family CQ has period N, normalized maximum-cor- T relation parameter (theta) over bar (max)bounded above by less than or similar to a root N, where a ranges from 1.8 in the 16-QAM case to 3.0 for large M. In a CDMA setting, each user is enabled to transfer 2m. bits of data per period of the spreading sequence which can be increased to 3,m, bits of data by halving the size of the sequence family. The technique used to construct CC is easily extended to produce larger sequence families and an example is provided. Selected family SQ has a lower value of theta(max) but permits only (m + 1)-bit data modulation. The interleaved 16-QAM sequence family, IQ has theta(max) less than or similar to root 2 root N and supports 3-bit data modulation. The remaining two families are over a quadrature-pulse amplitude modulation (Q-PAM) subset of size 2M of the M-2-QAM constellation. Family P has a lower value Of (theta) over bar (max) in comparison with Family S Q, while still permitting (m + 1)-bit data modulation. Interleaved Family IP, over the 8-ary Q-PAM constellation, permits 3-bit data modulation and interestingly achieves the Welch lower bound on (theta) over bar (max).