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(Abridged) Noise considerations for experiments that aim to statisticallyestimate the 21 cm signal from high redshift neutral hydrogen during the Epochof Reionisation (EoR) using interferometric data are typically computedassuming a tracked observation, where the telescope pointing centre andinstrument phase centre are the same over the observation. Current lowfrequency interferometers use aperture arrays of fixed dipoles, which aresteered electronically on the sky, and have different properties tomechanically-steered single apertures, such as reduced sensitivity away fromzenith, and discrete pointing positions on the sky. Use of two additionalobserving modes is encouraged: (1) zenith drift, where the pointing centreremains fixed at the zenith, and the phase centre tracks the sky, and (2)drift+shift, where the telescope uses discrete pointing centres, and the skydrifts during each pointing. The coherence of measurements in these modesdictates the optimal reduction in thermal noise by combination of coherentmodes, and the reduction in cosmic variance by combination of incoherent modes(views of different patches of the sky). The balance between these noisecomponents provides one measure for the utility of these three modes formeasuring a statistical EoR signature. We provide a general framework forestimating the uncertainty in the power spectrum for a given observing mode,telescope beam shape, and antenna distribution. We apply this framework to theMurchison Widefield Array (MWA) using an analysis of the 2D and 1D powerspectra for 900 hours of observing. We demonstrate that zenith drift scans canyield marginally lower uncertainty in the signal power compared with trackedscans for the MWA EoR experiment.

Comparison of observing modes for statistical estimation of the 21cm signal from the Epoch of Reionisation