The forward link of an IS-2000 CDMA system may become Walsh code limited under certain scenarios. To enhance the capacity in such scenarios, alternative sets of orthogonal functions called the quasi-orthogonal functions (QOF), which possess optimal minimax cross correlation with Walsh code sets of variable length, have been incorporated in IS-2000. We discuss a method of significantly enhancing the maximum throughput in evolutions of IS-2000 systems. This method uses aggregation of multiple quasi-orthogonal functions with a relatively smaller constellation alphabet size for a single user with a joint multi-channel detector. This method is compared with the alternative method for enhancing the maximum throughput using aggregation of a relatively smaller number of Walsh functions, but with a higher constellation alphabet size (multi-level modulation). Discussions on the trade-offs and recommendations as to the better method for enhancing the throughput in evolutions of IS-2000/3G systems are then provided.

An upper hound for Weil-type exponential sums over Galois rings was derived by Kumar, Helleseth, and Calderbank (see ibid., vol.41, no.3, p.456, 1995). This bound leads directly to an estimate for the minimum distance of Z/sub 4/-linear trace codes. An improved minimum-distance estimate is presented. First, McEliece's result on the divisibility of the weights of binary cyclic codes is extended to Z/sub 4/ trace codes. The divisibility result is then combined with the techniques of Serre (1983) and of Moreno and Moreno (see ibid., vol.40, no.11, p.1101, 1994) to derive the improved minimum-distance estimate. The improved estimate is tight for the Kerdock code as well as for the Delsarte-Goethals codes.

An upper bound for a hybrid exponential sum over Galois rings is derived. This bound is then used to obtain an upper bound for the maximum aperiodic correlation of some sequence families over Galois rings. The bound is of the order of /spl radic/qlnq where q-1 is the period of the sequences.

A bound on exponential sums over Galois rings is used to construct a nested chain of Z/sub 4/-linear binary codes and binary sequences. When compared with the chain of Delsarte-Goethals'(1975) codes, the codes in the new chain offer a larger minimum distance for the same code size. The binary sequence families constructed also make use of Nechaev's (1991) construction of a cyclic version of the Kerdock code. For a given value of maximum correlation, the binary sequences are shown to have a family size considerably larger than the best sequence families known.

The rth generalized Hamming weight d/sub r/ of the Kerdock code of length 2/sup m/ over Z/sub 4/ is considered. A lower bound on d/sub r/ is derived for any r, and d/sub r/ is exactly determined for r=0.5, 1, 1.5, 2, 2.5. In the case of length 2/sup 2m/, d/sub r/ is determined for any r, where 0/spl les/r/spl les/m and 2r is an integer. In addition, it is shown that it is sometimes possible to determine the generalized Hamming weights of the Kerdock codes of larger length using the results of d/sub r/ for a given length. The authors also provide a closed-form expression for the Lee weight of a Kerdock codeword in terms of the coefficients in its trace expansion.