On a Multiple-Access in a Vector Disjunctive Channel

We address the problem of increasing the sum rate in a multiple-access system from [1] for small number of users. We suggest an improved signal-code construction in which in case of a small number of users we give more resources to them. For the resulting multiple-access system a lower bound on the relative sum rate is derived. It is shown to be very close to the maximal value of relative sum rate in [1] even for small number of users. The bound is obtained for the case of decoding by exhaustive search. We also suggest reduced-complexity decoding and compare the maximal number of users in this case and in case of decoding by exhaustive search.Comment: 5 pages, 4 figures, submitted to IEEE ISIT 201

On the capacity of the asynchronous T-user M-frequency noiseless multiple-access channel without intensity information

We discuss an achievable rate region for the asynchronous T-user M-frequency multiple-access channel without intensity information. The problem is formulated in terms of frequencies, but the results are also applicable to pulse position modulation (PPM) schemes. It is shown that the achievable sum rate for T users reduces from (M-1) bits per channel use in the synchronous multiple-access situation to at least (M-1)·ln (2) bits per channel use in the asynchronous situation. In particular, the result shows that for instance, for multitone M-ary frequency shift keying multiple access, in asynchronous operation, multiple user interference reduces the capacity maximally by a factor ln(2)=0.693 relative to the ideal TDMA system

On the capacity of the asynchronous T-user M-frequency noiseless multiple-access channel without intensity information

We discuss an achievable rate region for the asynchronous T-user M-frequency multiple-access channel without intensity information. The problem is formulated in terms of frequencies, but the results are also applicable to pulse position modulation (PPM) schemes. It is shown that the achievable sum rate for T users reduces from (M-1) bits per channel use in the synchronous multiple-access situation to at least (M-1)·ln (2) bits per channel use in the asynchronous situation. In particular, the result shows that for instance, for multitone M-ary frequency shift keying multiple access, in asynchronous operation, multiple user interference reduces the capacity maximally by a factor ln(2)=0.693 relative to the ideal TDMA system