Daniela Laselva

An overview of downlink radio resource management for UTRAN long-term evolution

Radio resource management algorithms ranging from bearer admission control to semi-persistent and dynamic packet scheduling, fast link adaptation, and transmission control of multi-antenna transmission modes are addressed in this article for UTRAN long-term evolution. First, a high-level system overview of LTE is given, with special emphasis on the important components related to RRM. The quality of service parameter framework is outlined, as one of the main objectives for the families of RRM algorithms is to maximize system capacity while serving all users according to their minimum QoS constraints. It is demonstrated how the collocation of the RRM algorithms at the base station with easy access to air interface measurements offers opportunities for efficient cross-functional optimization between layers 1, 2, and 3. Examples of performance results for different traffic mixes and antenna transmission schemes are also presented, and the article is concluded with recommendations on how to operate the various RRM options under different load and traffic conditions.

Mobility-based strategies for traffic steering in heterogeneous networks

The large increase in size and complexity experienced by cellular networks in recent years has led to a new paradigm known as heterogeneous networks, or HetNets. In this context, networks with different cell sizes, radio access technologies, or carrier frequencies can be deployed in the same environment. As the coverage area of each of these networks is typically overlapped, operators have some degree of freedom to modify user distributions across the networks (i.e., traffic steering) in order to improve network performance. This article introduces different mechanisms of traffic steering in HetNets, clarifying the specific goals that operators can set and focusing on those techniques that adjust mobility parameters, which are typically more attractive to achieve these goals. In addition, some challenging issues arising from particular HetNet deployments are discussed and illustrated by example use cases, which are applicable to an early stage of LTE deployment. Finally, a fuzzy-logic-based algorithm that optimizes network parameters for traffic steering is proposed.

On the Impact of Realistic Control Channel Constraints on QoS Provisioning in UTRAN LTE

This paper focuses on the Physical Downlink Control Channel (PDCCH) and describes the impact of its realistic constraints. Specifically, the impact on the performance of the UTRAN LTE FDD downlink and on the QoS provisioning is studied. It is described, when adopting a QoS-aware packet scheduling policy, how scheduling limitations due to control channel may affect the scheduler behavior. It is shown that the system level performance degradation could be kept negligible utilizing the dynamic link-adaptation mechanisms available on the control channel and adopting careful control channel- related design solutions. Therefore, assuming a proper dimensioning in terms of OFDM symbols reserved for control, the PDCCH could simply be modeled for LTE FDD system level simulation purposes by limiting the number of PDCCH allocations. Such a number primarily depends on the system bandwidth.

Power Savings and QoS Impact for VoIP Application with DRX/DTX Feature in LTE

In the Long Term Evolution system Discontinuous Transmission and Reception (DRX/DTX) has been introduced to extend the terminal battery lifetime. In this paper, we study the energy-saving provided by this mechanism and the impact on the QoS performance of Voice over IP (VoIP) traffic under dynamic and semi persistent packet scheduling strategies. Simulations and analytical results show that the DRX/DTX scheme can reduce the terminal power consumption without compromising the required VoIP QoS in terms of maximum air-interface delay. However, it does not provide any further power savings if the terminal is asleep for a period longer than 20 ms. It is shown that the power savings are larger for semi persistent scheduling than for dynamic packet scheduling at the cost of a lower spectral efficiency.

UTRAN LTE Downlink System Performance under Realistic Control Channel Constraints

In the UTRAN Long Term Evolution (LTE), the downlink data channel is shared among the active users through the Orthogonal Frequency Division Multiple Access (OFDMA) technique, and high gains can be achieved by using dynamic packet scheduling. Control channels introduce an additional overhead, but also play a key role in exploiting such gains. This paper focuses on the Physical Downlink Control Channel (PDCCH) and introduces the main PDCCH related features which need to be analyzed in order to minimize its impact on the system performance.

Multi-Layer Mobility Load Balancing in a Heterogeneous LTE Network

This paper analyzes the behavior of a distributed Mobility Load Balancing (MLB) scheme in a multi-layer 3GPP (3rd Generation Partnership Project) Long Term Evolution (LTE) deployment with different User Equipment (UE) densities in certain network areas covered with pico cells. Target of the study is to evaluate MLB in terms of efficient pico cell utilization and macro layer load balancing (LB). The analysis focuses on video streaming traffic due to specific service characteristics (e.g. play-out buffer delay/jitter protection) that might make any mobility performance degradation transparent to the end user performance. Results have shown that the proposed MLB scheme can significantly improve the overall network resources utilization by eliminating potential load imbalances amongst the deployment layers and consequently enhance user experience. However this occurs at the cost of increased Radio Link Failures (RLF), a fact that might be critical for further applying MLB in real-time conversational services without additional mobility optimization and interference management techniques.

Dynamic traffic steering based on fuzzy Q-Learning approach in a multi-RAT multi-layer wireless network

The infrastructure of current cellular networks must evolve to cope with the increasing demand for mobile-broadband services. Heterogeneous networks are an attractive solution for operators to expand network capacity, based on deploying different Radio Access Technologies, cell sizes and carrier frequencies in the same environment. As a result, operators gain flexibility to distribute traffic across the different networks (or layers) in order to make a more efficient use of resources and enhance network performance. In this work, a dynamic traffic steering technique in multi-RAT multi-layer wireless networks is proposed. In particular, a fuzzy rule-based reinforcement learning algorithm modifies handover parameters according to a specific policy set by the operator, which typically searches for a trade-off between key performance indicators. Results show that the proposed optimization algorithm provides good flexibility to support different policies by simply adjusting some weighting factors. In addition, the Q-Learning algorithm is shown as an effective solution to adapt the network to context variations, such as those produced in the user spatial distribution.

On the Potentials of Traffic Steering Techniques between HSDPA and LTE

In this paper traffic steering between a High-Speed Downlink Packet Access (HSDPA) network and a 3GPP Long Term Evolution (LTE) network with different carrier frequencies is investigated. First, two traffic steering algorithms, relying on static network information, are assessed from a traffic theoretical point of view and numerically. Furthermore, numerical analysis of two traffic steering algorithms, relying on dynamic information such as user SINR and cell load, is also performed. It is shown that the dynamic traffic steering algorithms outperform the static methods in terms of end user performance. Finally, it is investigated how the LTE terminal penetration affects the performance of the proposed traffic steering algorithms. For low LTE terminal penetration all LTE capable terminals should be pushed to the LTE network, and for high LTE terminal penetration a more dynamic traffic steering scheme should be used.

Dynamic Packet Scheduling for Traffic Mixes of Best Effort and VoIP Users in E-UTRAN Downlink

This paper deals with packet scheduling for Voiceover-IP (VoIP) traffic in the Long Term Evolution (LTE) EUTRAN Downlink. The more specific target is to optimize the performance of dynamic scheduling for traffic mixes of VoIP and best effort users. To this end, we introduce the Required Activity Detection (RAD) packet scheduling algorithm with Delay Sensitivity (RAD-DS).With an appropriate delay sensitivity function, it is shown that a MACRO 1 cell with 5MHz transmission bandwidth can support up to 346 VoIP users. Furthermore, a novel delay sensitivity based soft prioritizing strategy is proposed for handling traffic mixes. It is shown that when 200 VoIP users are present in a cell along with best effort users, the proposed strategy can provide a cell throughput of up to 82% of the cell throughput with only best effort users.

Optimization of QoS-aware Packet Schedulers in Multi-Service Scenarios over HSDPA

This paper illustrates the optimization of design parameters for quality-of-service (QoS) aware packet schedulers in multi-service environments with WCDMA/HSDPA. The optimization sets the objective of maximizing the cell throughput while meeting certain minimum QoS criteria and focuses on two variants of the proportional fair with barrier function (PF-B) family of schedulers and on the proportional fair with required activity detection. The assessment on the sensitivity of the scheduler parameters to the traffic load and mixture is evaluated in scenarios with both real-time (streaming) and non real-time type of users (web browsing). This study shows that the PF-B schedulers require a per scenario dedicated optimization, while PF-RAD is quite insensitive and robust to support a general traffic mix. Overall, PF-RAD significantly outperforms PF-barrier schedulers in the investigated scenarios, providing up to 100% streaming cell throughput gain.