Extension of the Ozarow capacity theorem [1] for two transmitter Gaussian multiple access channel with feedback (TT-GMAC-F) to the channels with more than two transmitters is a widely studied and long standing problem (for example, see the Kramer sum capacity region [2]). In this paper, we investigate and analyse this possible extension. Specifically, exploiting a class of Schalkwijk-Kailath linear feedback codes, we obtain an achievable rate region for 3-user Gaussian MAC with full feedback and also, a capacity outer bound. Then, the results are extended for a case where there is no feedback link for one user and the corresponding achievable rate region and capacity outer bound are computed. Furthermore, the gap between the derived rates and the sum-capacity of 3-user Gaussian MAC with full and partial feedback is computed under special assumptions.

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