Bjoern Almeroth

Latency Critical IoT Applications in 5G: Perspective on the Design of Radio Interface and Network Architecture

Next generation mobile networks not only envision enhancing the traditional MBB use case but also aim to meet the requirements of new use cases, such as the IoT. This article focuses on latency critical IoT applications and analyzes their requirements. We discuss the design challenges and propose solutions for the radio interface and network architecture to fulfill these requirements, which mainly benefit from flexibility and service-centric approaches. The article also discusses new business opportunities through IoT connectivity enabled by future networks.

Analyzing the signal-to-noise ratio of direct sampling receivers

The increasing demand for multi-mode multi-band operation in mobile communications requires flexible radio frontends. Direct sampling receivers are very promising for this purpose. For this class of receivers, a proper parameterization of the analog-to-digital converter, in terms of input bandwidth, sampling frequency, and quantization resolution, is essential for its operation. This paper evaluates prospects and challenges of direct sampling receivers analytically. The impact of the sampling frequency and the quantization resolution on the signal-to-noise ratio of the received bandpass signal is approximated with a closed-form analytical expression. This is used to compare the performance of direct sampling receivers to the performance of traditional homodyne receiver concepts. Furthermore, an optimal choice and the trade-off between sampling rate and quantization resolution are discussed for direct sampling receivers that are intended for the reception of LTE signals.

Analytical interference models for the downlink of a cellular mobile network

Today, either simulations or simplified analytical models are commonly used to solve the problem of statistical signal-to-interference-and-noise-ratio (SINR) description in homogeneous cellular networks. But for dynamic cellular communication systems compact formulations that are close the exact behavior of the SINR are indispensable. To overcome this issue a new approach with increased accuracy is contributed. The derived functions are applied to omni-directional and sectored scenarios. These modeling techniques for an exact statistical analysis of a given cell structure are more and more important for an efficient use of the given resources from a system-level point of view. In combination with the analysis of power consumption in cellular networks it is possible to identify general design rules for future energy-efficient networks.1

Towards a wireless medical smart card

Wireless data transmission has become an integral part of modern society and plays an increasingly important role in health care. Technology scaling is continuously increasing wireless data rates, thus allowing for more flexible high-speed interfaces, e.g., between medical imaging equipment and mass storage devices. However, one issue remains: The power consumption of high-speed wireless transceivers and non-volatile memory grows with the data rate. This prevents from innovations using these high-speed wireless interfaces in ultra-low power (or even energy-passive) medical equipment that can be used by patients without a heavy power source. Clear efforts are required to close this gap, i.e., to provide high-speed wireless solutions with reduced energy consumption per transmitted bit. As a very example, this work presents the concept of a wireless medical smart card that combines near field communication for authentication and low-speed signaling together with a 60GHz interface for fast wireless memory access in a single patient-owned ID card. The basic architecture, functionality and prospects of the concept are discussed. A power budget is calculated based on state-of-the-art technologies. To put the concept into practice, some necessary developments for a reduction of the power consumption are outlined.

Twitter as a Source for Spatial Traffic Information in Big Data-Enabled Self-Organizing Networks

Cellular network performance is predominantly driven by the spatial distribution of the data traffic demand. We investigate the spatio-temporal correlation between the spatial mobile data traffic and spatially resolved information obtained from Twitter. The data stems from the centers of two European cities and is largely independent of the user device type and the wireless technology. We observe a high temporal and a moderate to high spatial correlation. In order to assess the actual suitability of Twitter data as input for self-organizing networks, we make use of a queuing-theoretic network performance evaluation tool and quantify cell utilizations and average flow sojourn times within an example network. We find that both metrics obtained with the linearly scaled Tweet density strongly correlate with the ones obtained with the actual data traffic density for reasonably chosen inter-site distances. The insights presented can help network operators to plan their cellular networks in regions with little information about spatially resolved traffic demand but high social media activity, and to further develop Big Data- enabled self-organizing networks.

The Impact of Jitter on the Signal-to-Noise Ratio in Uniform Bandpass Sampling Receivers

Receiver front-ends, enabling multi-mode multi-band operation, are essential for future efficient mobile communications and require a proper parametrization to achieve certain performance requirements. A key component in the receive chain is the analog-to-digital converter (ADC). To determine feasible configurations of the ADC, an abstract model is investigated in order to evaluate the performance in terms of the signal-to-noise ratio (SNR) of bandpass sampling receivers. It models the available types of sampling circuits, the impact of stationary and non-stationary jitter processes, as well as limited quantization resolution. The derived ADC model is used to determine the dominating jitter effect, either aperture or clock jitter, depending on the receiver setup. Furthermore, required root mean square jitter values are derived analytically for a predefined receiver noise figure. A properly designed bandpass sampling receiver, matching the proposed maximum jitter requirements, avoids significant SNR performance losses and can be employed in mobile communications.

Jitter requirements for bandpass sampling receivers utilizing sample-and-hold circuits

The uncertainty of the sampling time is of major concern for bandpass signal reception. It reduces the achievable signal-to-noise ratio of the bandpass sampling receiver. Traditionally, only the absolute sampling time is considered to be subject to timing errors, which then result in corresponding amplitude errors. But jitter also has an impact on the integration duration of the sample-and-hold circuit. In this paper we investigate the impact of jitter on the signal-to-noise ratio performance of the bandpass sampling receiver utilizing a sample-and-hold sampling circuit. In addition, a bound on the acceptable standard deviation of the jitter for different receiver setups is given.

Signal-to-Noise Ratio of Direct Sampling Receivers with Realistic Sampling Circuit Models

Employing direct sampling receivers for multi-mode multi-band operation in mobile communications is advantageous due to their high flexibility and programmability. But this type of receiver needs to be properly adjusted regarding the parameters of the sampling and the quantization stage of the analog- to-digital converter to comply with certain performance requirements. This paper studies the impact of the ideal, the track-and-hold and the sample-and-hold sampling circuit on the effective in-band signal-to-noise ratio of the receive signal. It also proposes sets of valid parameters of the complete analog-to- digital converter in terms of the duty cycle, the sampling rate, and the quantization resolution for a given band-pass input signal to limit the maximum performance loss. Moreover, the investigations for the different samplers and the overall analog-to- digital converter are used to trade-off the individual parameters in case of an exemplary LTE signal reception.