# Analysis of Non-Pilot Interference on Link Adaptation and Latency in Cellular Networks

## TL;DR

This paper investigates how non-pilot interference affects link adaptation and latency in LTE and 5G NR, revealing significant impacts on throughput and latency, especially for low-latency applications, and emphasizes the need for robust link adaptation schemes.

## Contribution

It provides the first detailed analysis of non-pilot interference effects on SINR estimation, throughput, and latency in cellular networks, with experimental validation and insights for improving link adaptation.

## Key findings

- Non-pilot interference causes high BLER and throughput loss.
- NPI significantly increases retransmission-induced latency.
- Robust link adaptation schemes are essential for reliable low-latency communication.

## Abstract

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.