arXiv:2611.07577v1 Announce Type: new Abstract: In networked integrated sensing and communication (ISAC), a base station (BS) performing sensing using its own downlink signals is subject to interference from the downlink transmissions of neighboring BSs. This paper investigates the impact of the signal constellation and waveform on the sensing performance in the presence of such inter-BS interference. For any linear receiver, we show that the mean-squared cross-ambiguity between two random ISAC signals is invariant to the modulation bases and constellations. We then derive the exact Fisher information under finite-alphabet interference with a flat-fading link, which equals the interference-free Fisher information scaled by $1-\gamma\,\mmse_{\C}(\gamma)$, where $\gamma$ denotes the interference-to-noise ratio (INR) and $\mmse_{\C}$ is the minimum mean-square error (MMSE) in estimating an interfering data symbol from its noise-corrupted observation at the sensing receiver. Consequently, Gaussian interference is the worst case and corresponds to the CRB loss of the matched filtering, whereas finite-alphabet interference induces a non-monotonic CRB loss that peaks at intermediate INR and vanishes at high INR. The loss is waveform-independent for the flat-fading BS-BS link, and an expectation-maximization (EM) interference-cancellation receiver approaches the theoretical bound for delay estimation.