Adrian Kliks

Energy-Efficient Cooperative Spectrum Sensing: A Survey

The article analyzes the problem of energy efficient techniques in cooperative spectrum sensing (CSS). Although it was proven that single-device sensing is not sufficient for reliable sensing, cooperative spectrum sensing was proposed, burdened, however, with great overhead. Thus, work on the topic of energy efficient cooperative schemes gained more interest, which resulted in a number of energy efficient cooperative algorithm proposals. In this work, we try to classify the possible directions in energy efficient CSS and present a limited set of works introducing new ideas to an energy efficient CSS algorithm.

Spectrally agile multicarrier waveforms for opportunistic wireless access

Multicarrier modulation has been employed in numerous modern wireless communications standards due to its ability in providing high data rates while simultaneously counteracting the effects of intersymbol interference due to multipath fading channels. In the recent years, multicarrier modulation is being investigated as a possible candidate data transmission scheme for achieving spectrally agile wireless access in scenarios where unlicensed users temporarily borrow unoccupied licensed frequency bands while minimizing interference with spectrally adjacent signals, i.e., opportunistic wireless access. Specifically, the divide-and-conquer data transmission approach employed by multicarrier modulation makes it an attractive option for realizing wireless communication systems that do not require a single continuous transmission frequency band. In this article, we present several multicarrier transmission solutions designed for efficiently achieving opportunistic wireless access. In particular, we shall investigate two types of spectrally-agile multicarrier modulation schemes, namely, non-contiguous orthogonal frequency-division multiplexing and non-contiguous nonorthogonal frequency-division multiplexing. The viability of these two techniques employed within an opportunistic wireless access scenario is assessed using actual spectrum measurement data, and a comparative study in terms of out-of-band interference mitigation as well as implementation complexity is provided.

Spectrum and license flexibility for 5G networks

Spectrum sharing is a key solution facilitating availability of the necessary spectrum for 5G wireless networks. This article addresses the problem of flexible spectrum sharing by the application of adaptive licensing among interested stakeholders. In particular, it acts as a proponent of “pluralistic licensing” and verifies it in three simulation scenarios that are of strong interest from the perspective of 5G networks. The concluding analysis offers discussion of the potential benefits offered to spectrum holders and other interested players through the application of the pluralistic licensing concept.

Optimal beamforming in MISO cognitive channels with degraded message sets

In this paper we consider the coexistence of a single-input single-output (SISO) primary link with a multiple-input single-output (MISO) secondary user pair that has non-causal knowledge of the primary message. We study an achievable rate region that exploits this knowledge by combining selfless relaying to maintain the rate supported by the primary link with dirty paper coding to pre-cancel the interference at the secondary receiver. We find the optimal choice of power allocation between these operating modes at the secondary transmitter as well as the optimal beamforming vectors. Moreover, we address the robustness of the solution to uncertainties in the channel knowledge. Finally, we show by numerical evaluation the gains obtained due to the additional knowledge of the primary message.

Improving Effectiveness of the Active Constellation Extension Method for PAPR Reduction in Generalized Multicarrier Signals

In this paper, the Active Constellation Extension (ACE) method of Peak-to-Average Power Ratio (PAPR) reduction is studied for the application in Generalized Mulicarrier (GMC) transmission using nonorthogonal subcarriers. It is shown, that GMC signaling is advantageous for modern wireless communications due to its high spectral efficiency, however, it faces even higher PAPR than in the case of the conventional Orthogonal Frequency Division Multiplexing (OFDM) transmission. The modification of the ACE method for the GMC signals is presented, which takes into account overlapping of data symbol pulses and of their subband spectra. Further improvements of the proposed method are suggested that lead to the decrease of the computational complexity and to more efficacious PAPR reduction in comparison with the conventional ACE scheme. With these improvements, the PAPR reduction for the GMC signaling is the same as for OFDM.

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.

On non-contiguous multicarrier waveforms for spectrally opportunistic cognitive radio systems

Multicarrier modulation is well suited for future wireless communication systems due to its ability to opportunistically transmit across unoccupied frequency bands. In addition to multicarrier modulation being able to attain high data rates with a sufficient level of error robustness, it also has the potential to achieve transmission flexibility via the non-contiguous access of wireless spectrum. In this paper, we shall investigate two approaches for enabling non-contiguous multicarrier modulation that can be used to facilitate spectrally opportunistic cognitive radio systems. One of the approaches is a variant of orthogonal frequency division multiplexing (OFDM), called non-contiguous OFDM (NC-OFDM), while the other approach is based the noncontiguous version of the filter bank approach non-orthogonal frequency division multiplexing (NOFDM), referred to as noncontiguous NOFDM (NC-NOFDM). The performance of these two approaches is assessed in terms of interference mitigation, which involves the use of actual spectrum measurement data, as well as computational complexity.

Cross-Layer Analysis in Cognitive Radio—Context Identification and Decision Making Aspects

Research on context-aware communications has recently led to the introduction of features and algorithms relying on the presence of rich, accurate context information, and requiring however, the introduction of cross-layer information exchanges. Cognitive radio (CR), in particular, is expected to benefit from context awareness, as the cognitive engine (CE) relies on the availability of multiple information sources to operate efficiently. In this context, this work delivers a detailed, yet concise classification and description of the information exchanged in a CR network between the layers of a generic protocol stack, and between each layer and the CE. For each layer, the key services provided and delivered are presented, followed by a catalogue of exchanged parameters. The analysis, supported by a set of use cases providing a quantitative assessment of the impact of crosslayer information exchanges in a CR framework, is the basis for the discussion of key implementation challenges and the identification of the most promising partition of functions and tasks between layers and CE.

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.

Capacity analysis of WCC-FBMC/OQAM systems

This paper evaluates the capacity of weighted circularly convolved FBMC/OQAM systems. A rigorous mathematical model is derived to calculate the increase of capacity that can be obtained thanks to the lattice structure of the modulation and the exploitation of the intrinsic interference. The numerical results reveal that a signal to noise ratio gain of 2dB is obtained in one resource block of 12 subcarriers, translating into a capacity increase of 11% with respect to OFDM, which nuances some previous results on this topic in the literature.