Efficient use of paired spectrum bands through TDD small cell deployments

©2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Traditionally, wireless cellular systems have been designed to operate in frequency division duplexing (FDD) paired bands that allocate the same amount of spectrum for both downlink (DL) and uplink (UL) communications. Such design is very convenient under symmetric DL/UL traffic conditions, as it used to be the case when voice transmission was predominant. However, due to the overwhelming advent of data services, which involves large asymmetries between DL and UL, the conventional FDD solution becomes inefficient. In this regard, flexible duplexing concepts aim to derive procedures to improve spectrum utilization by adjusting resources to actual traffic demand. In this work, we review these concepts and propose the introduction of time division duplexing (TDD) small eNBs (SeNB) to operate in the unused resources of an FDD-based system. This proposal alleviates the saturated DL/UL transmission commonly found in FDD-based systems through user offloading towards a TDD system based on SeNBs. In this context, the flexible duplexing concept is analyzed from three points of view: a) regulation, b) long term evolution (LTE) standardization, and c) technical solutions.Peer ReviewedPostprint (published version

TDD cognitive radio femtocell network (CRFN) operation in FDD downlink spectrum

Deploying cognitive radio femtocell network (CRFN) inside a macrocell network can significantly increase the utilization of the available macrocell bandwidth and increase the capacity of the macrocell. However, the success of this deployment in terms of performance degradation of the macrocell and the acceptable throughput for the CRFN is not well defined. In this paper, we propose a time division duplex (TDD) operation of a CRFN and investigate its performance inside a macrocell operating in frequency division duplex (FDD) mode. It is shown that with a proper sensing and transmission scheme the capacity of the CRFN can be increased by simultaneous transmissions on multiple channels, water-filling further improves the result when interference from the macrocell basestation is large. The proposed scheme is applicable to full duplex networks, such as LTE and GSM