Tractable Resource Management with Uplink Decoupled Millimeter-Wave Overlay in Ultra-Dense Cellular Networks

TL;DR

This paper proposes a tractable resource management framework for 5G ultra-dense cellular networks that overlay millimeter-wave and micro-wave frequencies, introducing mmW uplink decoupling to address uplink bottlenecks and deriving closed-form spectral efficiency expressions.

Contribution

It introduces mmW uplink decoupling allowing legacy micro-wave base stations to receive mmW signals and provides a novel closed-form spectral efficiency derivation for resource management.

Findings

mmW focuses on downlink, while μW prioritizes uplink in TDD operation.

mmW uplink decoupling alleviates uplink bottleneck in UDNs.

Spectral efficiency is a logarithmic function of BS-to-user density ratio.

Abstract

The forthcoming 5G cellular network is expected to overlay millimeter-wave (mmW) transmissions with the incumbent micro-wave ({\mu}W) architecture. The overall mm-{\mu}W resource management should therefore harmonize with each other. This paper aims at maximizing the overall downlink (DL) rate with a minimum uplink (UL) rate constraint, and concludes: mmW tends to focus more on DL transmissions while {\mu}W has high priority for complementing UL, under time-division duplex (TDD) mmW operations. Such UL dedication of {\mu}W results from the limited use of mmW UL bandwidth due to excessive power consumption and/or high peak-to-average power ratio (PAPR) at mobile users. To further relieve this UL bottleneck, we propose mmW UL decoupling that allows each legacy {\mu}W base station (BS) to receive mmW signals. Its impact on mm-{\mu}W resource management is provided in a tractable way by virtue of a novel closed-form mm-{\mu}W spectral efficiency (SE) derivation. In an ultra-dense cellular network (UDN), our derivation verifies mmW (or {\mu}W) SE is a logarithmic function of BS-to-user density ratio. This strikingly simple yet practically valid analysis is enabled by exploiting stochastic geometry in conjunction with real three dimensional (3D) building blockage statistics in Seoul, Korea.