Christian Hoymann

Relaying operation in 3GPP LTE: challenges and solutions

With the ever growing demand of data applications, traditional cellular networks face the challenges of providing enhanced system capacity, extended cell coverage, and improved minimum throughput in a cost-effective manner. Wireless relay stations, especially when operating in a halfduplex operation, make it possible without incurring high site acquisition and backhaul costs. Design of wireless relay stations faces the challenges of providing backward compatibility, minimizing complexity, and maximizing efficiency. This article provides an overview of the challenges and solutions in the design of relay stations as one of the salient features for 3GPP LTE advanced.

A Lean Carrier for LTE

The next major step in the evolution of LTE targets the rapidly increasing demand for mobile broadband services and traffic volumes. One of the key technologies is a new carrier type, referred to in this article as a Lean Carrier, an LTE carrier with minimized control channel overhead and cell-specific reference signals. The Lean Carrier can enhance spectral efficiency, increase spectrum flexibility, and reduce energy consumption. This article provides an overview of the motivations and main use cases of the Lean Carrier. Technical challenges are highlighted, and design options are discussed; finally, a performance evaluation quantifies the benefits of the Lean Carrier.

Distributed Uplink Macro Diversity for Cooperating Base Stations

Nowadays cellular systems operate with frequency reuse one, where adjacent cells use the same frequency band. Use equipments (UEs) located at cell edge are mostly affected by the resulting co-channel interference. In addition, cell edge UEs suffer from their weak carrier signal strength. This paper proposes a new method to increase the performance of cell edge UEs by means of information exchange between base stations (BSs). A BS serving a cell edge UE requests support from a co-channel BS. The supporting BS transfers demodulated or decoded bits received from the cell edge UE back to the serving BS. The serving BS then combines the information. The concept of cooperative BSs described in this paper is based on a request-response mechanism and does not require a central control node. Performance evaluation by means of simulation shows the capability of BS cooperation applied to 3GPP long-term evolution (LTE) in terms of user throughput and emphasizes the trade-off in terms of increased backhaul requirement due to BS-BS communication.

LTE release 14 outlook

Todays 4G LTE systems bring unprecedented mobile broadband performance to over a billion of users across the globe. Recently, work on a 5G mobile communication system has begun, and next to a new 5G air interface, LTE will be an essential component. The evolution of LTE will therefore strive to meet 5G requirements and to address 5G use cases. In this article, we provide an overview of foreseen key technology areas and components for LTE Release 14, including latency reductions, enhancements for machine-type communication, operation in unlicensed spectrum, massive multi-antenna systems, broadcasting, positioning, and support for intelligent transportation systems.

Codebook based Inter-Cell Interference Coordination for LTE

Current cellular systems suffer from co-channel interference, when simultaneous transmissions in other cells use the same physical resources. Schemes involving cooperation between Base Stations (BS) are currently discussed for further releases of the 3GPP Long Term Evolution (LTE) system as a promising method to mitigate co-channel interference for users located at cell-edge. The BS cooperation approach proposed in this paper applies to the Downlink (DL) of cellular systems and can be considered as an expansion of Inter-Cell Interference Coordination (ICIC) techniques to the spatial domain. Cooperating cells coordinate their antenna weights to reduce interference caused to selected users. This scheme uses an extension of the implicit DL channel feedback mechanism defined in current Frequency Division Duplex (FDD) cellular systems that is based on predefined codebooks of antenna weights. Performance evaluations by means of simulation show the capability of codebook based ICIC applied to LTE in terms of mean and cell-edge user throughput.