Tight bounds on the randomized communication complexity of symmetric XOR functions in one-way and SMP models (1101.4555v1)

Abstract: We study the communication complexity of symmetric XOR functions, namely functions $f: {0,1}^n \times {0,1}^n \rightarrow {0,1}$ that can be formulated as $f(x,y)=D(|x\oplus y|)$ for some predicate $D: {0,1,...,n} \rightarrow {0,1}$, where $|x\oplus y|$ is the Hamming weight of the bitwise XOR of $x$ and $y$. We give a public-coin randomized protocol in the Simultaneous Message Passing (SMP) model, with the communication cost matching the known lower bound for the \emph{quantum} and \emph{two-way} model up to a logarithm factor. As a corollary, this closes a quadratic gap between quantum lower bound and randomized upper bound for the one-way model, answering an open question raised in Shi and Zhang \cite{SZ09}.