This work studies a point-to-point MIMO uplink in which user equipment transmits data to a base station employing a massive array. Signal detection is noncoherent and fading is assumed to follow the Weichselberger model. By exploiting the spatial stationarity of fading at the base station, a cyclostationary structure emerges naturally in the space-time representation, which suggests formulating the statistical properties of the received signal in the Karhunen-Loève domain. This allows the derivation of a low-complexity receiver that approximates maximum likelihood detection even for a moderate array size. The spectral analysis of the problem provides valuable insights on the design of space-time codewords.