Pawel Kryszkiewicz

Dynamic spectrum aggregation for future 5G communications

We discuss dynamic spectrum aggregation methods, opportunities, and issues for future 5G communication in cognitive cellular networks. We focus on multicarrier technologies, which have been recognized as capable of flexible utilization of fragmented spectrum opportunities in unlicensed frequency bands, such as enhanced NC-OFDM and NC-FBMC. These techniques can be applied to shape the signal spectrum so that it is concentrated within used frequency bands, and the out-of-band transmitted power and associated interference generated to the incumbent coexisting systems are limited. We present key issues associated with spectrum aggregation that are recognized at the transmitter and the receiver. We also discuss solutions of these issues that can make spectrum aggregation viable for 5G systems.

Protection of primary users in dynamically varying radio environment: practical solutions and challenges

One of the primary objectives of deploying cognitive radio (CR) within a dynamic spectrum access (DSA) network is to ensure that the legacy rights of incumbent licensed (primary) transmissions are protected with respect to interference mitigation when unlicensed (secondary) communications are simultaneously operating within the same spectral vicinity. In this article, we present non-contiguous orthogonal frequency division multiplexing (NC-OFDM) as a promising and practical approach for achieving spectrally agile wireless data transmission that is suitable for secondary users (SUs) to access fragmented spectral opportunities more efficiently. Furthermore, a review of the current state-of-the-art is conducted with respect to methods specifically designed to protect the transmissions of the primary users (PUs) from possible interference caused by nearby SU transceivers employing NC-OFDM. These methods focus on the suppression of out-of-band (OOB) emissions resulting from the use of NC-OFDM transmission. To achieve the required OOB suppression, we present two practical approaches that can be employed in NC-OFDM, namely, the insertion of cancellation carriers and windowing. In addition to the theoretical development and proposed improvements of these approaches the computer simulation results of their performance are presented. Several real-world scenarios regarding the coexistence of both PU and SU signals are also studied using actual wireless experiments based on software-defined radio. These simulation and experimental results indicate that OOB suppression can be achieved under real-world conditions, making NC-OFDM transmission a viable option for CR usage in DSA networks.

Out-of-Band Power Reduction in NC-OFDM with Optimized Cancellation Carriers Selection

In this letter, we propose a computationally efficient method for joint selection of cancellation carriers (CCs) and calculation of their values minimizing the out-of-band (OOB) power in non-contiguous (NC-) OFDM transmission. The proposed new CCs selection method achieves higher OOB power attenuation than algorithms known from literature as well as noticable reception performance improvement.

TVWS indoor measurements for HetNets

In this paper the results of intensive measurement campaigns performed inside the buildings in two locations (Poznań, Poland and Barcelona, Spain) are presented and analyzed to investigate their potential in the generation of digital indoor radio environment maps. The existence of such detailed and stable maps will allow for further definition of the allowed transmit power of small cell transceivers operating within indoor heterogeneous networks and making use of TeleVision White Spaces (TVWS). The analysis concentrates on the stability and repeatability of the measured values both over time and location, as key elements enabling the creation of aforementioned digital maps.

Small-Scale Spectrum Aggregation and Sharing

New spectrum bands together with flexible spectrum management are treated as one of the key technical enablers for achievement of the so-called key-performance indicators defined for 5G wireless networks. In this paper, we deal with the small-scale spectrum aggregation and sharing, where a set of even very narrow and disjoint frequency bands closely located on the frequency axis can be utilized simultaneously. We first discuss how such a scheme can be applied to various multicarrier systems, focusing on the non-contiguous orthogonal frequency division multiplexing and non-contiguous filter-bank multicarrier technique. We propose an interference model that takes into account the limitations of both transmitter and receiver frequency selectivity, and apply it to our 5G link-optimization framework, what differentiates our work from other standard approaches to link adaptation. We present the results of hardware experiments to validate assumed theoretical interference models. Finally, we solve the optimization problem subject to the constraints of maximum interference induced to the protected legacy systems (GSM and UMTS). Results confirm that small-scale spectrum aggregation can provide high throughput even when the 5G system operates in a dense heterogeneous network.

Dynamic determination of spectrum emission masks in the varying cognitive radio environment

In the context of cognitive radio it is important to obtain high spectrum utilization while limiting interference generated to licensed systems. In this paper, new method for the determination of a dynamic spectrum mask is presented that allows for higher flexibility of the cognitive radio links, systems and future standards. The solution maximizes the throughput of the secondary non-contiguous OFDM (NC-OFDM)-based system while limiting the transmission power, interference caused to the primary system and minimum power to be allocated to each OFDM subcarrier for the successful transmission. Below, we investigate coexistence of a secondary NC-OFDM system with primary wireless microphones, although our method can be easily extended to other scenarios and systems.

Flexible quasi-systematic precoding for the out-of-band energy reduction in NC-OFDM

The reduction of spurious emission is an important issue in future OFDM-based systems, especially in the context of cognitive radio, when the primary users must be protected from the interference. In this paper, flexible quasi-systematic precoder is presented for non-contiguous OFDM transmitter, which has the effect of relatively small distortion of the data symbols modulating the subcarriers. We discuss degrees of freedom in the precoding-matrix design. The quasi-systematicy allows for not only the reduction of the out-of-band emission, but also flexible reception with high performance, either with or without the knowledge of the coding-matrix.

Measurement-based coverage maps for indoor REMs operating in TV band

Radio Environment Map (REM) is a tool frequently envisaged to be one of the technical enablers for practical deployment of secondary systems operating in the legacy bands and following some of the spectrum sharing policies. However, the creation of such a map requires the detailed knowledge about the parameters of the incumbent system that has to be protected. The ways, how the information is obtained and stored in the system has to be accurate and cannot require involvement of too much resources, e.g., for collecting the measurement samples. Thus, in this paper we provide a discussion on the ways how the ordinary kriging algorithm can be applied for creation of an indoor and outdoor coverage map of the TV signal — a map that could be used by REMs for management of secondary transmission. Based on the real signal measurements conducted in Poznan, Poland, the map was calculated using various approaches, which are compared and discussed. In this paper the new approaches have been proposed on how to consider the attenuation of the walls during the creation of the map.

Reduction of subcarriers spectrum sidelobes and intermodulation in NC-OFDM systems

The paper tackles the problem of efficient reduction of the out-of-band (OOB) radiation in multi-carrier systems when considering the presence of a nonlinear power amplification. It is important to provide “green” transmitters producing less electromagnetic “pollution” out of its nominal frequency band and obtaining at the same time high energy efficiency of the used power amplifier. One of the known methods assumes appropriate modulation of dedicated subcarriers by specially calculated symbols reducing OOB radiation. The solution proposed in this paper combines two approaches, among which the first, called cancellation carriers, is used traditionally for subcarrier sidelobes minimization, and the second, called tone reservation, for peak to average power ratio reduction. The novelty of this work is in joint minimization of both aforementioned metrics in the near optimal way while keeping low computational complexity. The result is seen as a decreased power of the OOB radiation observed after signal passing through the power amplifier. The obtained results confirm that the proposed algorithm outperforms the approaches in which those metrics are minimized separately. Additionally, a number of simulations has been carried out to investigate the influence of the proposed algorithm parameters on the resultant out-of-band radiation performance.

In-Band-Interference Robust Synchronization Algorithm for an NC-OFDM System

We consider receiver synchronization in the non-continguous orthogonal frequency division multiplexing (NC-OFDM)-based radio system in the presence of in-band interfering signal, which occupies the frequency-band between blocks of subcarriers (SCs) used by this system, i.e. in-band of NC-OFDM receiver spectrum range. This paper proposes a novel preamble-based synchronization algorithm for estimation of the time and frequency offset based on the received signal cross-correlation with the reference preamble. Contrary to the existing algorithms, it is robust against in-band interference including narrowband interference at the cost of increased complexity. Moreover, in the interference-free system, the probability of frame synchronization error is improved in comparison to all simulated algorithms.