Thomas Jacobsen

Interval Abstraction Refinement for Model Checking of Timed-Arc Petri Nets

State-space explosion is a major obstacle in verification of time-critical distributed systems. An important factor with a negative influence on the tractability of the analysis is the size of constants that clocks are compared to. This problem is particularly accented in explicit state-space exploration techniques. We suggest an approximation method for reducing the size of constants present in the model. The proposed method is developed for Timed-Arc Petri Nets and creates an under-approximation or an over-approximation of the model behaviour. The verification of approximated Petri net models can be considerably faster but it does not in general guarantee conclusive answers. We implement the algorithms within the open-source model checker TAPAAL and demonstrate on a number of experiments that our approximation techniques often result in a significant speed-up of the verification.

On the performance of one stage massive random access protocols in 5G systems

The next generation of cellular systems are expected to experience a proliferation of the number of emerging use cases alongside supporting high speed mobile broadband services. Massive Machine Type Communication (mMTC), which caters to a large number of low-data rate and low-cost devices, is such an use case. Smart utility meters, automated sensors in farms, and vehicle tracking nodes for logistics monitoring are all examples of emerging mMTC devices. Ensuring efficient mechanisms to access the wireless channel for such a massive number of densely deployed devices is the key challenge posed by mMTC applications. A framework for the analysis of the one-stage massive access protocol is proposed in this paper, which allows to model and evaluate its performance with respect to important performance metrics for mMTC services.

Power control optimization for uplink grant-free URLLC

Ultra-reliable and low latency communication (URLLC) presents the most challenging use cases for fifth generation (5G) mobile networks. Traditionally the focus for mobile broadband has been to optimize the system throughput for high speed data traffic. However the optimization criteria for URLLC should focus on achieving small packets transmissions under strict targets such as 99.999% reliability within 1 ms. Power control is one candidate technology component for improving reliability and latency. In this work we investigate the power control for grant-free URLLC transmissions through extensive system level simulations in a urban outdoor scenario. We initially compare different settings for open loop power control (OLPC) with full and with fractional path loss compensation. Then we evaluate whether power boosting the retransmission can reduce the probability of packets delays under the 1 ms constraint. We also discuss the practical implication of applying power boosting. With full path loss compensation and boosting retransmissions, we show that a URLLC load such as 1200 small packets per second per cell can be achieved in the considered scenario.

Reliability Analysis of Uplink Grant-Free Transmission Over Shared Resources

Uplink grant-free schemes have the promise of reducing the latency of a user-equipment-initiated transmission by avoiding the handshaking procedure for acquiring a dedicated scheduling grant. However, the possibility of successfully delivering a payload within a latency constraint may be severely compromised in case of grant-free operations over shared radio resources. In this paper, we study the performance of two different uplink grant-free schemes over shared resources recently discussed within the fifth generation new radio standardization, namely, a solution based on a stop-and-wait (SAW) protocol and a blind retransmission approach. Performance is evaluated assuming Rayleigh fading channels with a maximum ratio combining (MRC) multi-antenna receiver. Analytical results show the benefits of grant-free transmission with respect to the traditional grant-based approach for a tight latency constraint. A high-order receive diversity is beneficial to leverage the MRC gain and enables the possibility of achieving the 10−5 outage probability target set for ultra-reliable low-latency communication services. The blind retransmission approach is significantly penalized by identification and signaling errors, while a SAW solution with potentially scheduled retransmissions out of the shared bandwidth leads to the lowest outage probability, at least for frequent packet arrivals.

LTE IoT link budget and coverage performance in practical deployments

This paper provides an updated analysis of link-budget and coverage performance for LTE IoT technologies: enhancements for machine type communications (eMTC) and narrowband Internet of Things (NB-IoT). Previous studies have used the 3GPP evaluations assumptions and have demonstrated the coverage capabilities of these technologies when they are independently deployed. Some operators are, however, likely to deploy dual-mode networks — eMTC and NB-IoT — with the intent of supporting different applications in the two systems. With all conditions being equal for the two systems in such a scenario, comparison of the eMTC and NB-IoT technologies then requires that all assumptions are aligned. This paper extends the previous studies with the assumptions aligned for eMTC and NB-IoT systems to provide a fair coverage performance comparison. The study shows that compared to the 3GPP assumption, under the aligned assumptions, both eMTC and NB-IoT can support up to 5dB and 3dB higher uplink coverage, respectively. We further show these link budget improvements yield significantly reduced LTE IoT coverage outage in two simulated scenarios based on real network deployments: a wide area rural case and an urban deep indoor case. The results further demonstrate the potential of these LTE IoT technologies in realistic network deployment conditions.

Generic Energy Evaluation Methodology for Machine Type Communication

It is commonly accepted that the 3rd Generation Public Partnership Long Term Evolution (also known as 3GPP LTE) standard is likely to be unfit for future large scale machine type communication (MMTC). As a result, a new standard, LTE Narrow-Band Internet of Things (NB-IoT) and several radio protocol proposals are being developed. One of the main performance indicators for MMTC is the radio energy consumption. It is important to be able to evaluate the energy consumption of the new standard and the proposed protocols, therefore a generic energy consumption evaluation methodology tailored for MMTC devices is required. Such methodology is the contribution of this paper. It is developed by defining a generic radio transmission and describing the factors which affect the energy consumption. Special attention is put on the factors; power control, link-level performance and a radio power model with a non-constant power amplifier (PA) efficiency model intended for MMTC devices. The results show the impact of the factors and highlight first that applying a commonly used constant radio PA efficiency model can result in an overestimation of the battery life of up to 100% depending on the traffic scenario. It is also highlighted that combining power control, transmit repetitions and the radio power model opens for new methods to minimize the radio energy consumption.

Combining Constraint Types From Public Data in Aerial Image Segmentation

We introduce a method for image segmentation that constraints the clus- tering with map and point data. The method is showcased by applying the spectral clustering algorithm on aerial images for building detection with constraints built from a height map and address point data. We automatically detect the number of clusters using the elongated K-means algorithm instead of using the standard spec- tral clustering approach of a predefined number of clusters. The results are refined by filtering out noise with a binary morphological operator. Point data is used for semi-supervised labelling of building clusters. Our evaluation show that the com- bination of constraints have a positive impact on the clustering quality achieved. Finally we argue how the presented constraint types may be used in other applica- tions.