  Evaluating a building's wireless performance during the building design
process is a new paradigm for wireless communications and building design. This
paper proposes the earliest building wireless performance (BWP) evaluation
theory focusing on the channel delay spread (DS). The novel contributions of
this paper lie in the following aspects. 1) We define a new metric called DS
gain, which is the first metric for evaluating the channel DS performance of a
building under design. 2) We propose an analytical model to compute the metric
quickly and accurately. 3) The proposed scheme is validated via Monte-Carlo
simulations under typical indoor scenarios. Numerical results reveal that
building design has a clear impact on the root mean square (RMS) DS. In the
future, architects need to design a building taking its DS gain into account
carefully. Otherwise, indoor networks in it will suffer from severe signal
inter-symbol interference (ISI) due to an over large DS gain.
