  Modern wireless systems such as the Long-Term Evolution (LTE) and 5G New
Radio (5G NR) use pilot-aided SINR estimates to adapt the transmission mode and
the modulation and coding scheme (MCS) of data transmissions, maximizing the
utility of the wireless channel capacity. However, when interference is
localized exclusively on non-pilot resources, pilot-aided SINR estimates become
inaccurate. We show that this leads to congestion due to retransmissions, and
in the worst case, outage due to very high block error rate (BLER). We
demonstrate this behavior through numerical as well as experimental results
with the 4G LTE downlink, which show high BLER and significant throughput
detriment in the presence of non-pilot interference (NPI). To provide useful
insights on the impact of NPI on low-latency communications, we derive an
approximate relation between the retransmission-induced latency and BLER. Our
results show that NPI can severely compromise low-latency applications such as
vehicle-to-vehicle (V2V) communications and 5G NR. We identify robust link
adaptation schemes as the key to reliable communications.
