3 research outputs found
Analysis of Non-Pilot Interference on Link Adaptation and Latency in Cellular Networks
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.Comment: 6 pages, 9 figures, accepted for publication at the 89th IEEE
Vehicular Technology Conference (IEEE VTC Spring 2019
Probability of Pilot Interference in Pulsed Radar-Cellular Coexistence: Fundamental Insights on Demodulation and Limited CSI Feedback
This paper considers an underlay pulsed radar-cellular spectrum sharing
scenario, where the cellular system uses pilot-aided demodulation, statistical
channel state information (S-CSI) estimation and limited feedback schemes.
Under a realistic system model, upper and lower bounds are derived on the
probability that at least a specified number of pilot signals are interfered by
a radar pulse train in a finite CSI estimation window. Exact probabilities are
also derived for important special cases which reveal operational regimes where
the lower bound is achieved. Using these results, this paper (a) provides
insights on pilot interference-minimizing schemes for accurate coherent symbol
demodulation, and (b) demonstrates that pilot-aided methods fail to accurately
estimate S-CSI of the pulsed radar interference channel for a wide range of
radar repetition intervals.Comment: 13 pages, 5 figure
Semi-Blind Post-Equalizer SINR Estimation and Dual CSI Feedback for Radar-Cellular Coexistence
Current cellular systems use pilot-aided statistical-channel state
information (S-CSI) estimation and limited feedback schemes to aid in link
adaptation and scheduling decisions. However, in the presence of pulsed radar
signals, pilot-aided S-CSI is inaccurate since interference statistics on pilot
and non-pilot resources can be different. Moreover, the channel will be bimodal
as a result of the periodic interference. In this paper, we propose a max-min
heuristic to estimate the post-equalizer SINR in the case of non-pilot pulsed
radar interference, and characterize its distribution as a function of noise
variance and interference power. We observe that the proposed heuristic incurs
low computational complexity, and is robust beyond a certain SINR threshold for
different modulation schemes, especially for QPSK. This enables us to develop a
comprehensive semi-blind framework to estimate the wideband SINR metric that is
commonly used for S-CSI quantization in 3GPP Long-Term Evolution (LTE) and New
Radio (NR) networks. Finally, we propose dual CSI feedback for practical
radar-cellular spectrum sharing, to enable accurate CSI acquisition in the
bimodal channel. We demonstrate significant improvements in throughput, block
error rate and retransmission-induced latency for LTE-Advanced Pro when
compared to conventional pilot-aided S-CSI estimation and limited feedback
schemes.Comment: 33 pages, 26 figure