André Puschmann

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.

SWITCH: A Multichannel MAC Protocol for Cognitive Radio Ad Hoc Networks

Cognitive radio (CR) technology will empower wireless devices with the capabilities to dynamically exploit opportunities in both licensed and unlicensed spectra. Thus, the spectrum shortage problem that occurs due to the ever-increasing of wireless devices can be handled. In CR ad hoc network, a secondary user (SU) is allowed to utilize a channel of the primary system provided the channel is idle from primary user (PU) activity. In this environment, the way the SU copes with a sudden appearance of the PU is the most important feature of distributed CR-MAC protocols. In this paper, a multichannel CR-MAC protocol, which reacts efficiently to PU appearance, is developed. The new protocol is named opportunistic Spectrum access WITh backup CHannel (SWITCH). The SWITCH protocol is a decentralized, asynchronous, and contention-based MAC protocol for CR ad hoc networks. The proposed protocol operates over both licensed and unlicensed spectra. In addition, the concept of backup channel is introduced and employed to make the SU extremely robust to the appearance of PUs. The simulation results show that SWITCH accomplishes 91% throughput gain over other CR-MAC protocols.

Implementation and evaluation of a practical SDR testbed

Software defined radios provide a perfect playground for researchers to experiment with current and future wireless communication systems. However, the benefits, especially for communication protocols, largely depend on non-functional requirements (i.e. temporal behavior) that have to be met by the system architecture. In this paper, we share our experience with a flexible SDR framework named Iris. We present an implementation of a Send-and-Wait Automatic Repeat reQuest (ARQ) protocol as well as a virtual network driver component which, in conjunction with Iris, form the core of our software defined radio networking testbed. To verify the practical suitability of the testbed and to evaluate the performance of the protocol, we are conducting end-to-end throughput and delay benchmarks.

Timings matter: standard compliant ieee 802.11 channel access for a fully software-based SDR architecture

We present a solution for enabling standard compliant channel access for a fully software-based Software Defined Radio (SDR) architecture. With the availability of a GNU Radio implementation of an Orthogonal Frequency Division Multiplexing (OFDM) transceiver, there is substantial demand for standard compliant channel access. It has been shown that implementation of CSMA on a host PC is infeasible due to system-inherent delays. The common approach is to fully implement the protocol stack on the FPGA, which makes further updates or modifications to the protocols a complex and time consuming task. We take another approach and investigate the feasibility of a fully software-based solution and show that standard compliant broadcast transmissions are possible with marginal modifications of the FPGA. We envision the use of our system for example in the vehicular networking domain, where broadcast is the main communication paradigm. We show that our SDR solution exactly complies with the IEEE 802.11 Distributed Coordination Function (DCF) as well as Enhanced Distributed Channel Access (EDCA) timings. We were even able to identify shortcomings of commercial systems and prototypes.

An architecture for Cognitive Radio ad-hoc network nodes

Cognitive Radio (CR) is considered to be the future of wireless communication. However, for a practical realization of CR, there is a need for an integrated, extensible and flexible architecture with well-defined interfaces and support for real-time adaptations. This article presents a novel architecture for CR nodes operating in an ad-hoc network scenario. Based on a highly reconfigurable software defined radio, it incorporates a Cognitive Resource Manager used for optimization, decision making and learning as well as a database-driven knowledge base called Distributed Resource Map. In contrast to other research in this field, this work focuses on practical feasibility, combines multiple hot topics in the CR domain and considers them holistically. We present implementation details and conclude the paper with intermediate results obtained in our networking testbed.

Coexistence through adaptive sensing and Markov chains

The goal of this paper is to construct a dynamic Secondary User (SU) link that can successfully coexist with a Primary User (PU).

TAG: Trajectory Aware Geographical Routing in Cognitive Radio Ad Hoc Networks with UAV Nodes

Routing real-time packets in Cognitive Radio Ad Hoc Networks (CRAHNs) with mobile nodes is a challenging task. Mobile SUs can move into PU regions where the radio spectrum may not be accessible due to PU activity. In this case, real-time packets may be delivered to their destinations beyond their latency constraints. Unmanned Aerial Vehicles (UAVs) are mobile wireless ad hoc nodes that plan for their trajectory at any given time. In this paper, a Trajectory Aware Geographical (TAG) routing for CRAHNs with UAV nodes is proposed. TAG employs the trajectory information of UAVs and avoids selecting a UAV as a next hop if the UAV will fly inside a PU region or close to it. This strategy protects real-time packets from experiencing a long delay due to the PU activity. Our simulation results show that TAG effectively decreases the average end-to-end delay compared to Greedy geographical routing in the considered scenario.

A Flexible CSMA based MAC Protocol for Software Defined Radios

Abstract In this article, we propose a flexible CSMA based MAC protocol which facilitates research and experimentation using software define radios. The modular architecture allows to employ the protocol on platforms with heterogeneous hardware capabilities and provides the freedom to exchange or adapt the spectrum sensing mechanism without modifying the MAC protocol internals. We discuss the architecture of the protocol and provide structural details of its main components. Furthermore, we present throughput measurements that have been obtained on an example system using host-based spectrum sensing.

Enhancing the performance of random access MAC protocols for low-cost SDRs

Software Defined Radio (SDR) is a technology which facilitates experimentation and the practical realization of novel wireless communication systems. Especially low-cost SDRs, however, experience high communication delays due to the connection between the radio hardware and the host computer. This delay hinders the implementation of Medium Access Control (MAC) protocols. In Carrier Sense Multiple Access (CSMA) based protocols, especially the Clear Channel Assessment (CCA) as well as the subsequent channel access phase are subject to strict temporal constraints. In this paper, we present two strategies that address both issues and aim to enhance the performance and efficiency of CSMA protocols implemented on low-cost SDRs. The first approach employs a dedicated spectrum sensing engine as a CCA agent for the SDR. The second strategy optimizes the frame transmission path inside the SDR. Experimental results indicate that both strategies have a positive impact on reducing the slot time parameter of the CSMA MAC.

A hierarchical radio resource management scheme for next generation cellular networks

Next generation cellular networks are envisioned to widely enable machine-to-machine (M2M) communication. For many applications in the M2M domain, deterministic communication latencies and high reliability are of very high importance. As a consequence, device-to-device (D2D) communication is a expected to play a key role in order to avoid from having to route the entire data through a centralized base station. Considering the large number of devices but relatively small payload lengths of many M2M applications, LTE currently fails to efficiently utilize the available radio resources. This is primarily because the granularity of resources that can be allocated to a single user is too coarse, resulting in parts of the allocation being wasted. In this paper, we present a hierarchical radio resource management scheme that allows ordinary cellular users to reuse and exploit the otherwise unused portion of a D2D scheduling grant. We show that our resource reuse scheme improves the uplink throughput of cellular users between 10% and 30%, depending on the actual number of D2D users, compared to current allocation schemes.