# Generalized Degrees-of-Freedom of the 2-User Case MISO Broadcast Channel with Distributed CSIT

## TL;DR

This paper analyzes the GDoF of a 2-user MISO broadcast channel with distributed CSIT, revealing that decentralized precoding can match centralized performance using Active-Passive Zero-Forcing, despite imperfect and shared CSIT.

## Contribution

It derives the GDoF for the distributed CSIT regime and introduces AP-ZF precoding to achieve centralized-like performance in decentralized networks.

## Key findings

- Distributed CSIT can achieve centralized GDoF with proper accounting.
- Active-Passive Zero-Forcing enables optimal precoding with local CSIT.
- Decentralized networks can match centralized performance under certain conditions.

## Abstract

This work analyses the Generalized Degrees-of-Freedom (GDoF) of the 2-User Multiple-Input Single-Output (MISO) Broadcast Channel (BC) in the so-called Distributed CSIT regime, with application to decentralized wireless networks. This regime differs from the classical limited CSIT one in that the CSIT is not just noisy but also imperfectly shared across the transmitters (TXs). Hence, each TX precodes data on the basis of local CSIT and statistical quality information at other TXs. We derive the GDoF result and obtain the surprising outcome that by specific accounting of the pathloss information, it becomes possible for the decentralized precoded network to reach the same performance as a genie-aided centralized network where the central node has obtained the estimates of both TXs. The key ingredient in the scheme is the so-called Active-Passive Zero-Forcing (AP-ZF) precoding, which lets the precoder design adapt optimally with respect to different local CSIT qualities available at different TXs.