Capacity of Generalized Discrete-Memoryless Push-to-Talk Two-Way Channels

Abstract

In this report, we generalize Shannon's push-to-talk two-way channel (PTT-TWC) by allowing reliable fullduplex transmission as well as noisy reception in the half-duplex (PTT) mode. Viewing a PTT-TWC as two state-dependent one-way channels, we introduce a channel symmetry property pertaining to the one-way channels. Shannon's TWC capacity inner bound is shown to be tight for the generalized model under this symmetry property. We also analytically derive the capacity region, which is shown to be the convex hull of (at most) 4 rate pairs. Examples that illustrate different shapes of the capacity region are given, and efficient transmission schemes are discussed via the examples. fa@queensu.ca, linder@mast.queensu.ca). This work was supported in part by NSERC of Canada. 1 A formal proof of this statement via the Lagrange multiplier method can be found in [2, Section 2.5.3].

Two-Way Source-Channel Coding

“…In [4], Shannon presented a random coding inner bound and a cut-set outer bound to the capacity region. He also exploited channel symmetry properties [4, Section 11] to determine the capacity region in some special cases, which are further generalized in [9]- [14]. For DM-TWCs with symmetry properties, it was shown that Shannon's inner bound is tight, and hence adaptive coding is not needed to achieve capacity.…”