The user equipment (UE) of cellular systems operating in frequency division duplexing (FDD) mode feeds back (report) the channel state information (CSI) to the new generation base node (gNB). We exploit the correlation between the uplink and downlink channels, although they are at different frequencies, to obtain a two-way protocol to report the downlink CSI. First, the gNB estimates the uplink channel and sends a feedforward message to the UE to select the codebook used by the UE to quantize the downlink CSI; then, the UE transmits the index of the quantized code vector in feedback to the gNB. This protocol is modeled as the cascade of two rate-distortion source coding schemes, for the feedforward and feedback signals, where the feedback scheme also has mixed-side information. We design both encoders and compare their performance with existing schemes, including an approach using natural networks.
Search Engines represents an important application of Information Retrieval. In particular, a major branch of Search Engines is devoted to web search. In this document we summarize our work to produce a submission for the CLEF LongEval initiative, primarily concerning web search. The described activity first focuses onto the development of an indexing and searching IR system with the best possible performance based on the provided training data then evaluates its performance on test data coming from different scenarios. We first introduce the task and related problems. Subsequently we present the retrieval systems that we have used for the program submission.
Afterwards, we discuss the results obtained with the various systems and compare them in the training scope to explain why some systems perform better than others. Finally, metrics analysis is extended to the additional scenarios LongEval focuses on, along with statistical considerations over the systems’ output.