Petteri Lunden

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.

Efficient Semi-Persistent Scheduling for VoIP on EUTRA Downlink

Evolved UTRA (EUTRA) is currently under standardization within 3GPP as a long-term evolution (LTE) of universal terrestrial radio access (UTRA) air interface. Due to the potentially large number of VoIP users served in this system, related control signaling overhead for VoIP transmissions with traditional full dynamic scheduling scheme could become a bottleneck and limit the system capacity to a greater extent. In this paper, we present a semi-persistent packet scheduling scheme for VoIP to explore the capacity within the limitation of control channel resources. System level simulation results show that semi-persistent scheduling scheme can reduce control channel usage without using packet bundling technique. With 6 control channels, around 310 users per sector can be supported in 5 MHz bandwidth with both discontinuous reception (DRX) enabled and without packet bundling.

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.

Enhancing Performance of VoIP over HSDPA

This paper presents a study of packet scheduling enhancements for VoIP service over high-speed downlink packet access (HSDPA) in WCDMA. Taking VoIP traffic characteristics into account in Node B packet scheduling algorithm is a key element in achieving good performance and high VoIP capacity. The novelty of this study consists of dynamic transmission resource allocation method for VoIP service. Dynamic resource allocation takes the estimated channel conditions and the transmission requirements of a user into account to increase the efficiency of resource utilization. Simulation results produced with a dynamic system simulator indicate 20 % VoIP capacity gain achieved with the proposed enhancement when compared to the conventional even share resource allocation.

Downlink VoIP Support for Evolved UTRA

This paper presents the design of VoIP optimized packet scheduler and performance simulations for supporting voice services over downlink evolved UTRA. An efficient packet scheduler taking into account the traffic characteristics and adopting optimal resource allocation is proposed. Results are given for different control channel number settings and packet bundling options. Simulation results show that downlink EUTRA VoIP capacity is mainly limited by control channel number with full dynamic scheduling and packet bundling can help to increase capacity within the control channel limitation. In summary, with packet bundling technique, around 378 and 488 users per sector can be supported in 5 MHz bandwidth with 6 and 8 control channels respectively.

Performance of VoIP over HSDPA in Mobility Scenarios

This paper presents an evaluation of Voice over IP (VoIP) system level performance in High Speed Downlink Packet Access (HSDPA) network. The main purpose is to determine how VoIP over HSDPA performance is affected by HSDPA handover i.e. serving High Speed Downlink Shared Channel (HS-DSCH) cell change. This paper studies how sensitive the capacity of VoIP service is to handover delay and User Equipment (UE) velocity. Additionally, the reliability of handover related signaling in downlink is evaluated. The system level performance of VoIP in the mobility related scenarios is evaluated with fully dynamic system level tool in which mobility of users, radio resource management functionalities and the interactions between them are explicitly taken into account. The simulation results indicated moderate sensitivity of VoIP capacity to the UE velocity. High velocities lead to capacity loss for VoIP over HSDPA. Handover delays started to have significant effect only at UE velocity of 50 km/h or more. Reliability of handover signaling does not pose any problems even at high velocity and incurs only 1% resource overhead when transmitted over HSDPA.

Energy Efficient Small-Cell Discovery Using Received Signal Strength Based Radio Maps

We consider the use of received signal strength based radio fingerprints to discover small cells in heterogeneous networks, deployed in a different carrier frequency as compared to a macro-cell network. We propose using a flexible fingerprint matching region around fingerprint reference locations in order to provide energy efficient small-cell discovery. We evaluate the scheme using extensive simulations in a heterogeneous network scenario, concentrating on the tradeoff between the energy consumed for discovering inter-frequency small cells and the offloading opportunity i.e. the fraction of time spent in the small-cell layer. Results show that we can save significant amount of battery power using fingerprint scheme with acceptable compromise in offloading opportunity.

Optimal muting ratio for Enhanced Inter-Cell Interference Coordination (eICIC) in HetNets

We calculate the optimal muting ratio for time domain Enhanced Inter-Cell Interference Coordination (TDM eICIC) in a downlink HetNet scenario, consisting of macrocell and femtocell users. First we derive analytically the optimal muting ratio in a simplified scenario, and identify a particular case where all macro users are either strongly or not at all affected by the presence of femtocells. In this case, the optimal muting ratio can be calculated from parameters that can be simply estimated by the network. Furthermore, we solve by numerical optimization the optimal muting ratio in a simulated HetNet scenario, and find that most of the network instances are described by this particular case. We conclude that in a typical femto-macro heterogeneous network, an optimal muting ratio can be approximated by a simple calculation based on parameters that can be estimated by the network.

Energy-Efficient Flexible Inter-Frequency Scanning Mechanism for Enhanced Small Cell Discovery

Heterogeneous Network deployments are one of the key enablers in providing ubiquitous coverage and capacity enhancements for satisfying high data rate and Quality of Service requirements for LTE-Advanced networks. In this paper we propose an energy efficient small cell discovery mechanism for heterogeneous networks by means of flexible inter-frequency scanning. We also propose the concept of threshold speed for inter-frequency scanning, above which mobile terminals should not search for or connect to inter-frequency small cells. Above threshold speed, the small cell connection opportunities become so short that they offer very limited benefit. The scheme is evaluated using extensive simulations conducted on HetNet scenario specified in 3GPP LTE-A system settings. Shortcomings of the currently standardized mechanism are analyzed and advantages of the proposed scheme are presented. Numerical analysis is done based on utilization of available offloading opportunities as well as savings in terminal battery power consumption. The results show that with the flexible scheme, significant power savings can be achieved with acceptable tradeoffs in offloading.

Performance of VoIP on EUTRA downlink with limited channel feedback

The emerging evolved UTRA radio system is generally envisioned to support a large number of VoIP users. This is basically enabled by efficient frequency domain packet scheduling together with accurate channel quality feedback information. In this paper, we investigate the performance of VoIP on EUTRA downlink assuming that only limited channel quality feedback information is available. System level simulation results show that by increasing the CQI measurement frequency window to 2 PRBs and using average best-4 CQI reporting scheme, the achieved VoIP capacities for no packet bundling case and packet bundling case are 201 users/sector and 353 users/sector respectively with 6 control channels. Compared with the ideal CQI measurement frequency window of 1 PRB and full CQI reporting scheme, the relative loss of VoIP capacity is negligible for no bundling case and about 9% for bundling case. On the other hand, the reported CQI wordsize in uplink can be significantly decreased by 84% from 126 bits to 20 bits.