This paper introduces an improved nonlinear parallel interference cancellation scheme for code-division multiple access (CDMA) that significantly reduces the degrading effect on the desired user of interference from the other users that share the channel. The implementation complexity of the scheme is linear in the number of users and operates on the fact that parallel processing simultaneously removes from each user a part of the interference produced by the remaining users accessing the channel the amount being proportional to their reliability. The parallel processing can be done in multiple stages. The proposed scheme uses tentative decision devices at the multiple stages to produce the most reliably estimated received data for generation and cancellation of user interference. Simulation results are given for a multitude of different situations, in particular, those cases for which the analysis is too complex.

:The Digital Signature Algorithm (DSA) was l~Oposed in 1991 by the US National Institute of Standards and Technology to provide an appropriate core fur applications requiring digital signatures. Undoubtedly, many applications will include this standard in the future and thus, the foreseen domination of DSA as a legal certification tool is sufficiently important to focus research endeavours on the suitebility of this scheme to various sitnatic~s.In this paper, we prcsant s~x new DSA-based protocols for :9 Perforn~ng a quick batch-verification of, signatures. The proposed scheme allows to make the economy of = 450, modular multiplications. 9 Avoiding the cumbersome calculation of 1 / k rood q by the signer. 9 Compressing sets ofDSA transact/ons into shorter archive signatures. 9 Generating signatures from poe-calculated "Use & Throw" 224-bit signature-coupons. 9 Self-~.ertifying the moduli and bit-patterning directly q on p (gain of 60.4% in key size).All our schemes combine in a natural way full DSA compatibility and flexible U'ade-offs between computational complexity, transmission overheads and key sizes.

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