Carl Wijting

Device-to-device communication as an underlay to LTE-advanced networks

In this article device-to-device (D2D) communication underlaying a 3GPP LTE-Advanced cellular network is studied as an enabler of local services with limited interference impact on the primary cellular network. The approach of the study is a tight integration of D2D communication into an LTE-Advanced network. In particular, we propose mechanisms for D2D communication session setup and management involving procedures in the LTE System Architecture Evolution. Moreover, we present numerical results based on system simulations in an interference limited local area scenario. Our results show that D2D communication can increase the total throughput observed in the cell area.

Device-to-Device Communication Underlaying Cellular Communications Systems

In this article we propose to facilitate local peer-to-peer communication by a Device-to-Device (D2D) radio that operates as an underlay network to an IMT-Advanced cellular network. It is expected that local services may utilize mobile peer-to-peer communication instead of central server based communication for rich multimedia services. The main challenge of the underlay radio in a multi-cell environment is to limit the interference to the cellular network while achieving a reasonable link budget for the D2D radio. We propose a novel power control mechanism for D2D connections that share cellular uplink resources. The mechanism limits the maximum D2D transmit power utilizing cellular power control information of the devices in D2D communication. Thereby it enables underlaying D2D communication even in interference-limited networks with full load and without degrading the performance of the cellular network. Secondly, we study a single cell scenario consisting of a device communicating with the base station and two devices that communicate with each other. The results demonstrate that the D2D radio, sharing the same resources as the cellular network, can provide higher capacity (sum rate) compared to pure cellular communication where all the data is transmitted through the base station.

License-exempt LTE deployment in heterogeneous network

Mobile broadband data usage in Long Term Evolution (LTE) networks is growing exponentially and capacity constraint is becoming an issue. Heterogeneous network, WiFi offload, and acquisition of additional radio spectrum can be used to address this capacity constraint. Licensed spectrum, however, is limited and can be costly to obtain. This paper investigates deploying LTE on a license-exempt band as part of the pico-cell underlay. Coexistence mechanism and other modifications to LTE are discussed. Performance analysis shows that LTE can deliver significant capacity even while sharing the spectrum with WiFi systems.

On Number of Almost Blank Subframes in Heterogeneous Cellular Networks

In heterogeneous cellular scenarios with macrocells, femtocells or picocells users may suffer from significant co-channel cross-tier interference. To manage this interference 3GPP introduced almost blank subframe (ABSF), a subframe in which the interferer tier is not allowed to transmit data. Vulnerable users thus get a chance to be scheduled in ABSFs with reduced cross-tier interference. We analyze downlink scenarios using stochastic geometry and formulate a condition for the required number of ABSFs based on base station placement statistics and user throughput requirement. The result is a semi-analytical formula that serves as a good initial estimate and offers an easy way to analyze impact of network parameters. We show that while in macro/femto scenario the residue ABSF interference can be well managed, in macro/pico scenario it affects the number of required ABSFs strongly. The effect of ABSFs is subsequently demonstrated via user throughput simulations. Especially in the macro/pico scenario, we find that using ABSFs is advantageous for the system since victim users no longer suffer from poor performance for the price of relatively small drop in higher throughput percentiles.

Energy-efficient inter-frequency small cell discovery techniques for LTE-advanced heterogeneous network deployments

Heterogeneous network, or HetNet, deployments are one of the key enablers in providing ubiquitous coverage and capacity enhancements for LTE-Advanced networks. They play an important role in achieving high data rate and quality of service requirements defined for next generation wireless networks. In this article we evaluate various cell discovery techniques tailored for energy-efficient detection of small cells deployed in a carrier other than the serving macrocell. The presented schemes are evaluated using extensive system simulations conducted in a 3GPP LTE-Advanced HetNet scenario. Shortcomings of the currently standardized mechanism are analyzed, and advantages of the evaluated schemes are presented. Both the offloading opportunity utilization and savings in UE battery power consumption are analyzed. The results show that using the considered flexible, adaptive, and intelligent schemes for small cell discovery, significant UE power savings can be achieved with small loss in offloading - giving benefits both on system level as well as in user experience.

Interference Aware Scheduling for Soft Frequency Reuse

In this paper we present an interference aware phased scheduling strategy for a soft frequency reuse (SFR) interference coordination scheme in an Orthogonal Frequency Division Multiple Access (OFDMA) network. It groups the active user terminals (UT) in a low and high signal-to-interference plus noise ratio (SINR) group and picks UTs from both groups in each scheduling round to optimally exploit the interference variations introduced by SFR. We show that the proposed interference aware phased scheduling scheme for SFR improves the 5 percentile of the user throughput cumulative distribution function (CDF) and the average cell throughput compared to reuse one. In addition to better performance the reduced feedback option of the proposed phased scheduler reduces the feedback load by two third for UTs in the low SINR group with a moderate decrease in the 5 percentile of the user throughput CDF while keeping the same average cell throughput. Further, our system simulation results show that SFR clearly outperforms fractional frequency reuse, a competing interference coordination scheme.

Smart mobility management for D2D communications in 5G networks

Direct device-to-device (D2D) communications is regarded as a promising technology to provide low-power, high-data rate and low-latency services between end-users in the future 5G networks. However, it may not always be feasible to provide low-latency reliable communication between end-users due to the nature of mobility. For instance, the latency could be increased when several controlling nodes have to exchange D2D related information among each other. Moreover, the introduced signaling overhead due to D2D operation need to be minimized. Therefore, in this paper, we propose several mobility management solutions with their technical challenges and expected gains under the assumptions of 5G small cell networks.

Key technologies for IMT-advanced mobile communication systems

WINNER is an ambitious research project aiming at identification, development, and assessment of key technologies for IMT-advanced mobile communication systems. WINNER has devised an OFDMA-based system concept with excellent system-level performance for flexible deployments in a wide variety of operating conditions. The WINNER system provides a significant step forward from current 3G systems. Key innovations integrated into the system concept include flexible spectrum usage and relaying, adaptive advanced antenna schemes and pilot design, close to optimal link adaptation, hierarchical control signaling, and a highly flexible multiple access scheme. The end-to-end performance assessment results demonstrate that the WINNER concept meets the IMT-advanced requirements.

Awareness networking in wireless environments

This article presented a platform for awareness networking, targeted for distribution of locally relevant control information between nodes in heterogeneous wireless environments. This concept can be leveraged in many different ways and purposes, as shown with the examples given, which range from network discovery, to functionalities required in cognitive radio systems to distributed services facilitating localized mobile social networking. Although a wide range of applications can be envisioned, the same basic solution for distributing locally relevant control information applies to all of them. Future research work on awareness networking is required on multiple areas, covering the technical details of the connectivity solution, details of the distributed algorithms, functionalities, and services, and the regulatory support required for their realization.

Adaptive Soft Reuse for Relay Enhanced Cells

In this paper we present an adaptive radio resource management scheme for relay enhanced cells based on soft resource partitioning. Power masks varying in the time or frequency domain are assigned to each radio access point (RAP). Thus, soft resource partitioning enables frequency reuse one and at the same time each RAP has high power resources with reduced interference available to schedule user terminals. Our scheme allows a local power mask adaptation and we present a mechanism for adapting the power mask based on the traffic load situation within the REC. We show in dynamic system simulations for a metropolitan area scenario that the radio resource management scheme based on soft resource partitioning outperform a scheme based on hard resource partitioning. Further, we show that the adaptive resource management scheme improves the throughput of low throughput users in the cell.