A Quality of Experience (QoE) parameter of increasing importance is the time that a battery powered communication device (e.g. smartphone) can be operated before it needs to be recharged. However, due to the fact that battery capacity is not evolving as fast as the power requirement, the battery lifetime of modern user equipment is stagnating or even decreasing from one device generation to another. In parallel, a major challenge for the design of next generation wireless systems such as LTE-Advanced (LTE-A) is that the required high portion of spectrum is not available in a consecutive portion. For this reason, a procedure called interband non-continuous Carrier Aggregation (CA) will be introduced in LTE-A which allows for the combination of multiple spectrum pieces from different frequency bands. This procedure however requires the parallel operation of multiple power amplifiers that are characterized by a high energy demand. In this paper, we quantify the impact of CA on the power consumption of LTE-A enabled communication by means of a Markovian based power consumption model that incorporates system parameters as well as context parameters. The results show that the suitability of CA does from a battery lifetime perspective strongly depend upon the actual device characteristics as well as the resource availability is the various frequency bands. Furthermore, the application of the sophisticated Kinetic Battery Model (KiBaM) shows that the charge recovery effect during idle periods does significantly affect the battery lifetime.

Due to continuously growing communication traffic of emerging mobile phone applications, resource-efficient communication is a key to affordable network services with high Quality of Experience. While some communication traffic requires immediate resource allocations (such as voice services), an increasing number of mobile phone applications produce a lot of background communication traffic (e.g. social network apps, crowd sensing services). In this paper we discuss the predictive Channel-Aware Transmission (pCAT) scheme, which leverages the fact, that favorable channel conditions require much less spectrum resource allocation than bad channel conditions. By leveraging the knowledge of user trajectories and recurring spots with favorable channel conditions, the so-called LTE connectivity hot spots, background traffic transmissions can be scheduled by the client according to expected channel quality and application data priority. Thereby, the spectrum consumption of background traffic of applications can be reduced significantly. At the same time, the efficient usage of spectrum resources has also an impact on the battery lifetime of the mobile devices. By introducing the Context-Aware Power Consumption Model (CoPoMo) for LTE communications, we highlight, how decisions about the spectrum resource allocation by the network will impact the battery lifetime. One case study will show, that by simply changing the resource allocation scheme and without the need for spending more spectrum resources, the power consumption can be reduced by more than 70% using the Energy-Efficient Scheduling (EES) introduced in this paper.

In Long Term Evolution (LTE), Voice over Internet Protocol (VoIP) is used for the delivery of the voice data. One of the major challenges for VoIP over LTE is to guarantee the Quality of Experience (QoE) of the VoIP calls. This paper uses an LTE base station emulator and a radio channel emulator to evaluate the impacts of different User Equipment (UE) velocities and Radio Link Control (RLC) parameter values on the QoE of the calls in the vehicular environment. Our study shows that LTE can provide acceptable VoIP quality in the high-speed scenarios (e.g., high-speed train). This paper provides the guidelines for the telecommunications operators to select the appropriate parameter values when deploying their VoIP services in LTE.

One important advantage of the Orthogonal Frequency Division Multiple Access (OFDMA) based cellular communication system Long Term Evolution (LTE) is its robustness against different kinds of impairments as they may occur on the mobile radio communication channel. This includes an increased toughness not only in harsh multi path scenarios, but also for the case of extremely high user velocities. In this paper, the applicability of the LTE system for two example applications (LTE based backhaul for high speed trains and live transmission of flight recorder data) is investigated by means of extensive throughput measurements (TCP and UDP) incorporating a radio channel emulator. The measurement results show that LTE in general is capable to provide reliable communication links for both considered scenarios. However, extreme velocities as they occur in a “flight data transmission at cruising speed” scenario rely on a specialized cross-layer parameterization.

The interaction between Machine-to-Machine (M2M) Communications, also known as Machine-Type Communications (MTC), and Human-to-Human (H2H) Communications is a recent topic in the context of cellular networks like Long Term Evolution (LTE). In this paper, we evaluate the performance of Channel-Aware MTC (CAT) based on LTE resource allocation measurements of a real LTE deployment. By means of a novel measurement setup, which uses a real-time spectrum analyzer, the LTE resource utilization in terms of occupied Resource Blocks (RBs) of the uplink is quantified for different channel conditions. Furthermore, the resource distribution in time and frequency domain, which is determined by the scheduler, is analyzed in this paper allowing for the calculation of average data rates and the spectral efficiency. The measurement results are used to quantize the potential gain of CAT. It is shown that by means of the scheme, the influence of MTC on other LTE users can be significantly reduced. In addition, the fraction of available RBs can be increased by 47%.

LTE heterogeneous networks (HetNets) are deployed in areas of high user density in order to increase the capacity in the cellular mobile network. However, they are raising two problems: fixed cell sizes and interference. In our work, we propose a technique, which is maximizing the throughput of the users while considering fairness, dynamically adapting cell sizes and reducing interferences. Moreover, we included the concept of cell selection offsets (CSOs) for the adaptation of the cell sizes and we applied protected subframes, a time domain intercell interference coordination technique in LTE advanced. In our results, we consider the system throughput and the 5-percentile UE throughput and show, that our technique outperforms the best static HetNet configurations achieving a gain up to 16.5% in terms of the fairness based system throughput and a gain up to 37.0% in the 5-percentile UE throughput.

The average operational time of today's smart phones with one filling of the accumulator is one of the most important performance parameters for the customers of new devices. Nevertheless, this value is remaining constant or even decreasing in the last few years due to the continuously increasing complexity. On the other hand, for ensuring the fulfillment of the high user-requirements even under worst case conditions, novel cellular systems such as Long Term Evolution (LTE) are usually over-dimensioned in terms of the maximum available capacity. In this paper, a novel approach is presented which allows for trading in unused cell capacity for battery lifetime extension of the mobile devices. The basic idea in this context is to increase the robustness of the submitted uplink (UL) signal by decreasing the order of the modulation and coding scheme used. If the provided data rate is kept constant, this comes along with an increasing number of allocated Resource Blocks (RB) and therefore a decreased overall cell capacity. Nevertheless, the more robust signal allows for reducing the uplink transmit power while the Quality of Service (QoS) parameters are still met. The results for exemplary Voice over IP (VoIP) traffic show that for users originally submitting at the maximum available transmit power, the consumed energy of the LTE chip-set can be reduced by up to 27.5 % applying this novel approach.

In this paper, we present a channel sensitive transmission scheme which reduces the negative impact of Vehicle-to-Infrastructure (V2I) traffic on the Quality of Services (QoS) of Human to Human (H2H) communication in cellular networks. The performance evaluation of Long Term Evolution (LTE) for different traffic characteristics is based on an introduced Markovian model. This describes the utilization of the shared LTE Resource Blocks (RBs). The model is parameterized by laboratory measurements and ray tracing simulations. We present blocking probabilities for an LTE network with heterogeneous V2I and H2H traffic and propose different transmission strategies for V2I data with the goal to minimize the impact on human users. The results show that the number of V2I devices can be doubled by using channel sensitive transmission schemes ensuring equal QoS for H2H communication compared to periodically data transmission.

In this paper, an energy efficient approach for the transmission of Floating Car Data (FCD) via Long Term Evolution (LTE) is presented. Applying channel sensitive transmission, FCD is collected by mobile devices in cars and transmitted preferably if the channel conditions are good. The results show that this approach reduces the negative impact on the utilization of the LTE air interface as well as on the energy consumption of the mobile devices. For the performance evaluation of the LTE system, a close to reality parametrized Markovian model is used. The parameters of the model are determined by laboratory measurements and ray tracing simulations. In the laboratory, also the energy consumption of the used LTE USB stick is measured. Hence, we evaluated that the channel sensitive transmission allows for an energy saving of up to 54 % for the transmission of the FCD.

The energy that has to be spent for the successful submission of one Bit is an important figure of merit for the performance analysis and optimization of modern wireless communication systems. The many factors which are influencing this performance parameter range from the efficiency of the User Equipment's (UE) power amplifier to the average path loss, the Transmit Power Control (TPC) parametrization and the fading characteristics of the radio channel. Although many of the relationships can be analytically modeled, the aim of this paper is to present reliable measurements based on commercially available Long Term Evolution (LTE) hardware. Therefore, extensive User Datagram Protocol (UDP) data rate measurements have been performed in a mobile communications laboratory for different radio channel conditions. The impact of the mobile fading channel was emulated by a sophisticated radio channel emulator. Beside this, the on average consumed power of the LTE UE was measured during data transmission. From the results of these measurements, quantitative figures on the energy efficiency are presented for different LTE frequency bands and different radio channels. The results show that major energy savings are possible if the 800 MHz frequency band, which becomes available as part of the digital dividend, can be used for user with bad channel conditions. Considering energy efficiency as a Quality of Service (QoS) parameter of increasing importance the results presented in this paper allow for a context sensitive optimization in a way that the Modulation and Coding Scheme (MCS) switching points as well as the frequency band are chosen with respect to the UE's condition.

The operational time of modern smart-phones with one filling of the accumulator is one of the most important performance parameter for the customers of new devices. This is the reason why extensive research has been performed in the fields of battery design and system optimization with regard on energy consumption. Due to the fact that the radio part of a smart-phone is one of the major energy consumers, a special focus has to be set on different approaches and strategies how to reduce the energy that has to be spent for the transmission of a certain amount of data. However, before new energy saving protocols can be efficiently developed one needs to have detailed knowledge on the different factors which impact the energy efficiency. In this paper, we present a measurement based energy model for IEEE 802.16e conform Mobile WiMAX devices. For this purpose, extensive measurements of the energy consumption of a Mobile WiMAX USB Stick have been performed for different system parameterizations, different data sizes and different application data rates. From the results of the measurements analytic models have been derived which allow for the calculation of the energy that has to be spent per successfully submitted bit. These analytic formulas can now be integrated in system level simulators for the evaluation of the energy efficiency of newly designed protocols.

For the reliable control of Micro Unmanned Aerial Vehicles (MUAV) using IP based networks it is of high importance to assure certain quality of service warranties for the transmission of control information. The mobile WiMAX standard IEEE 802.16e defines five QoS Classes which represent different requirements concerning data rate and delay. The scheduling scheme which is used to fulfill these requirements can be independently chosen by the network operator. In this paper we present a novel QoS aware scheduling scheme which can be parameterized in a very flexible and simple way and therefore enables the network operator to set up the service guarantees very accurate depending on the specific requirements. This is of special importance in the case that WiMAX is used for untypical applications such as for example the control of UAVs and therewith the requirements do not exactly match the predefined QoS classes.

The performance evaluation of mobile communication systems for time varying environments poses a major challenge. To address this issue, in this paper we propose an approach which extends a common laboratory environment by a fading channel emulator. Hereby, we analyze OFDM based links under complex and realistic radio channel conditions including upper layer protocols. By means of this setup, the influence of velocity on the data rate and Packet Error Rate (PER) of a Mobile WiMAX system is investigated for various Signal to Noise Ratios (SNR) assuming vehicular and pedestrian channel models defined by the ITU. As a result, we analyzed the performance of Mobile WiMAX for Adaptive Modulation and Coding (AMC) dependent on the QoS target, the channel model, the user velocity and the SNR. Hereby, we assumed two partially contrary QoS targets, high data rate and target PER.