M. Dohler

Impact of Interfering Bluetooth Piconets on a Collocated

In this paper, the effect of cochanneled Bluetooth (BT) piconets on a carrier-sense multiple-access (CSMA)-based wireless local area network (WLAN) is investigated. Specifically, the p-persistent CSMA protocol is considered for WLANs, and the probability of error of a WLAN packet is calculated in the presence of interfering BT packets of different lengths and variable piconet traffic loads and as a function of the BTs frequency-hopping guard time. The probability derivation is then used in conjunction with the p-persistent CSMA throughput and delay formulations to examine its net performance in the presence of BT interference. Simulations have been used to corroborate the analytical results, which indicate that the presence of just one fully loaded interfering BT piconet reduces the peak CSMA throughput by 42%. Furthermore, we show that under fully loaded BT traffic conditions, the effect of more shorter BT packet transmissions on the CSMA delay performance can outweigh the interference impact of a higher number of BT piconets with longer packet transmissions.

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To underpin the predicted growth of the Internet of Things (IoT), a highly scalable, reliable and available connectivity technology will be required. Whilst numerous technologies are available today, the industry trend suggests that cellular systems will play a central role in ensuring IoT connectivity globally. With spectrum generally a bottleneck for 3GPP technologies, TV white space (TVWS) approaches are a very promising means to handle the billions of connected devices in a highly flexible, reliable and scalable way. To this end, we propose a cognitive radio enabled TD-LET test-bed to realize the dynamic spectrum management over TVWS. In order to reduce the data acquisition and improve the detection performance, we propose a hybrid framework for the dynamic spectrum management of machine-to-machine networks. In the proposed framework, compressed sensing is implemented with the aim to reduce the sampling rates for wideband spectrum sensing. A noniterative reweighed compressive spectrum sensing algorithm is proposed with the weights being constructed by data from geolocation databases. Finally, the proposed hybrid framework is tested by means of simulated as well as real-world data.

-Persistent CSMA-Based WLAN

In this paper, we aim to obtain optimal space-time trellis codes and propose novel methods for reducing the highly growing full code search. We show that by exploiting the symmetry in the QAM and PSK constellations, the number combinations in the generator matrix of the encoder can be halved. We also show that for the same set of columns of the generator matrix, interchanging the columns give identical results hence reducing the full code search by the factorial of the number of transmit antennas. Using the suggested methods, we obtain novel space-time codes for slow Rayleigh fading environments and evaluate their performance by simulation, described by frame error probabilities. Furthermore, the performance of the obtained novel codes is evaluated in a multi-user code division multiple access (CDMA) system.

Scalable and Reliable IoT Enabled by Dynamic Spectrum Management for M2M in LTE-A

The recently introduced concept of virtual antenna arrays (VAAs) promises a significant increase in link and system capacity. VAAs therefore constitute a promising candidate for ad-hoc oriented 4G networks. VAAs successfully emulate a multiple-input multiple-output (MIMO) transmission channel to which space-time codes (STC) can be applied. The realisation of VAAs is accomplished by letting spatially close mobile terminals communicate with each other, which overcomes the disadvantage of having only one receiving antenna in a mobile handset. The thus created ad-hoc network represents a general form of MIMO channels for which different link level performance results apply. The work presented analyses the link level performance of a VAA system with deployed higher order space-time block codes (STBCs) in dependency of the prevailing channel conditions within the generated ad-hoc network. As such, the influence of Rayleigh, Rice and Nakagami flat fading channels with a varying parameter set onto the performance of generic STBCs with associated VAA is investigated. It is known that for close antenna spacing and/or high Rice K-factors (Nakagami m-factors) the correlation at the receiving end increases, which is shown to be successfully mitigated by the deployment of VAAs.

Fast search techniques for obtaining space-time trellis codes for Rayleigh fading channels and its performance in CDMA systems

Splitting functionalities of radio access network (RAN) and cloudiamp;#64257;cation of such functionalities is considered as oneofthekeyenablersofthenextgenerationmobileandwireless networking, i.e. 5G, and is often referred to as software-deamp;#64257;ned RAN, virtualized RAN or Cloud RAN. Deamp;#64257;ning the splitting point, and maintaining the tight interaction between different functionalities in the RAN is, however, critical. Success of such cloudiamp;#64257;cation depends on the availability of high speed fronthaul, while high speed fronthauling is costly. In this paper we experiment splitting MAC and PHY layer with fronthauling through Ethernet that allows using commodity and low-cost industry standard equipment. We examine the effect of packetization on latency, and study the pros and cons of splitting MAC and PHY layer, within a hardware-based testbed.

Influence of channel characteristics on the performance of VAA with deployed STBCs

In this paper, we study the effect of channel estimation error on transmitter design in a multiple input multiple output (MIMO) channel. We assume that only knowledge of either the channel correlation or mean is available at the transmitter and find the transmitting strategy. Under covariance feedback, at the transmitter the channel is modelled as a matrix of zero mean circularly symmetric complex Gaussian (ZMCSCG) random variables with known covariances. We assume that only rows of channel matrix are correlated. Under mean feedback the covariance of channel is modelled as white. We determine the necessary and sufficient conditions under which a unit rank input covariance matrix, i.e. eigen-beamforming, can achieve capacity lower bound. Numerical simulations are conducted to corroborate theoretical results.

On the Feasibility of MAC and PHY Split in Cloud RAN

The traffic growth as well as the diversity in Quality of Service (QoS) requirements are drastically increasing the challenges in achieving effective network management. The need to handle dynamic QoS requests exacerbates such challenges and dictates novel solutions able to make network management more flexible and adaptable to traffic changes. To this aim, in this paper we propose a novel approach aiming at dynamically managing the QoS within the Software-defined Networks through flow initialization and termination requests from the end-client. This approach allows management and control planes to be informed as soon as possible about the changes in the traffic requirements of the network, thus introducing a more flexible (re)configuration of the network according to the actual traffic demands. Such flexibility is particularly interesting within the next generation networks that aim to serve a diverse set of vertical industries. While the full picture of the network architecture is depicted in this paper, we also present the prototype implementation of this novel approach. The latency and overhead as introduced by the proposed approach in this paper are studied using the prototype implementation.

Transmitter design in partially coherent antenna systems

The road to 5G is posing challenging requirements to the cellular network to introduce more applications from several industry verticals. Low delay, high scalability, ultra-reliability and device-centric procedures are some of these requirements. Decoupled Uplink (UL) and Downlink (DL), DUDe, is a key enabler of the device-centric network, and provides a good solution to the UL and DL imbalance problem in heterogeneous networks, improving the UL reliability and load balancing. However, the direct applicability of this technique in 4G networks is subject to either very low backhaul latency between both cooperative base stations, or assisting UL and DL connections that can carry the user plane control signals. This article does a comprehensive study of the enabling architectures for DUDe; the proposed architectures are based on two well- known techniques, Dual Connectivity and Cloud Radio Access Networks. The impact of high latency fronthaul and X2 interfaces is studied and compared to the upper bound UL reliability and throughput obtained with regular round trip time (RTT) values. Results show that even if the radio access network RTT is doubled, DUDe provides an improvement in the UL reliability compared to the classical DL received power cell association.

Can QoS be dynamically manipulated using end-device initialization?

The Device-to-Device (D2D) communication principle is a key enabler of direct localized communication between mobile nodes and is expected to propel a plethora of novel multimedia services. However, even though it offers a wide set of capabilities mainly due to the proximity and resource reuse gains, interference must be carefully controlled to maximize the achievable rate for coexisting cellular and D2D users. The scope of this work is to provide an interference- aware real- time resource allocation (RA) framework for relay- aided D2D communications that underlay cellular networks. The main objective is to maximize the overall network throughput by guaranteeing a minimum rate threshold for cellular and D2D links. To this direction, genetic algorithms (GAs) are proven to be powerful and versatile methodologies that account for not only enhanced performance but also reduced computational complexity in emerging wireless networks. Numerical investigations highlight the performance gains compared to baseline RA methods and especially in highly dense scenarios which will be the case in future 5G networks.

On the Performance Evaluation of Enabling Architectures for Uplink and Downlink Decoupled Networks

Operating at ultra-high frequency (UHF), TV white space (TVWS) can achieve long-distance communication and good in-building penetration, and has attracted increasing attention of regulators, researchers and stakeholders. This paper explores the potential of TVWS for network provisioning within a cluster of buildings, through a succession of tests. Different transmission distances, from 10m to over 120m, and through multiple layers of walls as well as complex transmission environment imposed by other factors like office and construction facilities, are considered. Further, a compact ultra-wide band (UWB) printed monopole antenna is designed for the client white space terminal, and compared with a commercial directional UHF antenna on the same client. Measurement results show that the in-house compact antenna achieves fast network speed and a high signal-to-interference-plus-noise ratio (SINR), and it is orientation independent.