Distributed Base Station: A Concept System for Long-Range Broadband Wireless Access

TL;DR

The paper introduces a distributed base station system that uses distributed transmit beamforming at large wavelengths to significantly extend range and increase data rates for rural broadband, addressing key technical challenges.

Contribution

It presents a robust feedback-based adaptation strategy, extends narrowband algorithms to wideband channels, and analyzes system performance considering practical constraints.

Findings

N^2-fold increase in received power with N transmitters

Effective range extension achieved through feedback-based algorithms

Acceptable performance with standard uplink reception under slow channel variations

Abstract

We propose a concept system termed distributed base station (DBS), which enables distributed transmit beamforming at large carrier wavelengths to achieve significant range extension and/or increased downlink data rate, providing a low-cost infrastructure for applications such as rural broadband. We consider a frequency division duplexed (FDD) system, using feedback from the receiver to achieve the required phase coherence. At a given range, $N$ cooperating transmitters can achieve $N^2$-fold increase in received power compared to that for a single transmitters, and feedback-based algorithms with near-ideal performance have been prototyped. In this paper, however, we identify and address key technical issues in translating such power gains into range extension via a DBS. First, to combat the drop in per-node SNR with extended range, we design a feedback-based adaptation strategy that is suitably robust to noise. Second, to utilize available system bandwidth, we extend narrowband adaptation algorithms to wideband channels through interpolation over OFDM subcarriers. Third, we observe that the feedback channel may become a bottleneck unless sophisticated distributed reception strategies are employed, but show that acceptable performance can still be obtained with standard uplink reception if channel time variations are slow enough. We quantify system performance compactly via outage capacity analyses.