Hanna Bogucka

Degrees of freedom for energy savings in practical adaptive wireless systems

We present a new design concept for adaptive wireless communications with new trade-offs between system performance and energy consumption. The system performance, in terms of bit error rate, outage probability, and achieved spectral efficiency, depends on constellation signaling, applied diversity, and channel estimation. Resources dedicated to channel estimation and feedback traffic contribute to the overall system and network energy consumption, and the resulting CO2 emission. We consider the trade-offs among different methodologies and parameters toward an energy-efficient green communication system design. Below, we discuss the degrees of freedom in the design of communications systems with imperfect channel estimation and diversity, and investigate their energy saving options. We present the case studies of single- and multicarrier systems applying both margin-adaptive and rate-adaptive pilot-assisted transmission.

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.

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.

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.

Non-identical objects auction for spectrum sharing in TV white spaces — The perspective of service providers as secondary users

The paper considers a new spectrum sharing approach in TV white spaces (TVWS) areas using an auction of non-identical objects taking the bandwidth and power requirements of the secondary users into account. The commodity of the auction is the available frequency band with propagation-signal power limitations. These frequency resources available in TVWS may be distributed among the telecommunication operators and service providers of various types (called players) operating in a given area. The available spectrum-band may be divided into blocks having the same or different sizes and different maximum allowable power. The resource allocation problem in frequency and power domain has been defined as an optimization problem where maximum payoff of the central trading entity (called spectrum broker) is the optimization goal. The problem of the best matching of the players demands, their bids and the auction solution to the available spectrum-holes have been discussed and highlighted. In the auction solution the branch and cut technique, known from integer programming, was applied so the complexity of the optimization algorithm was reduced significantly. Simulations results are also provided.

Game theory in wireless networks

Game theory has been employed in the analysis of resource management in telecommunications networks for at least 20 years. As game theory has been traditionally applied to economic problems, it is not surprising that one of its first applications in telecommunications was in the study of pricing. In the early 1990s, researchers used game theory to propose new pricing strategies for Internet services. In the same decade, game theoretic models were developed for non-economic problems in networks, such as flow, admission, and congestion control. By the late 1990s and early 2000s, game theory was being applied to wireless networks.

Toward secure energy harvesting cooperative networks

The concept of energy harvesting cooperative networks is an emerging technology that has very high potential for a large variety of applications. However, energy transfer capability may lead to unprecedented security challenges. In this article, we study energy security issues and the solutions in energy harvesting networks. We first identify typical energy related attacks and then propose defense solutions against these attacks. We also carry out security analysis and performance analysis to evaluate our proposed solutions. Simulation results have shown that the proposed defense solutions are effective and efficient.

Frequency-domain echo cancellation in digital multicarrier modulation systems

The data driven frequency-domain echo canceller (EC) for a multicarrier modulation system is considered. An EC in such a system has to deal with both the interchannel and intersymbol interference occurring in the echo signal. For this reason, the main disadvantage of the data driven EC structure is the large computational complexity. Here, the solution of the computational complexity problem is presented. It is based on assumption that in practice, interchannel interference has a limited range. The number of operations per symbol as a measure of the EC computational complexity is given. Simulation results present echo attenuation in the frequency-domain EC, operating in the orthogonally multiplexed quadrature amplitude-shift keying system. Modifications of the proposed EC structure and its computational complexity in the systems with pulse shaping are discussed.

On the benefits of bandwidth limiting in decentralized vector multiple access channels

We study the network spectral efficiency of decentralized vector multiple access channels (MACs) when the number of accessible dimensions per transmitter is strategically limited. Considering each dimension as a frequency band, we call this limiting process bandwidth limiting (BL). Assuming that each transmitter maximizes its own data rate by water-filling over the available frequency bands, we consider two scenarios. In the first scenario, transmitters use non-intersecting sets of bands (spectral resource partition), and in the second one, they freely exploit all the available frequency bands (spectral resource sharing). In the latter case, successive interference cancelation (SIC) is used. We show the existence of an optimal number of dimensions that a transmitter must use in order to maximize the network performance measured in terms of spectral efficiency. We provide a closed form expression for the optimal number of accessible bands in the first scenario. Such an optimum point, depends on the number of active transmitters, the number of available frequency bands and the different signal-to-noise ratios. In the second scenario, we show that BL does not bring a significant improvement on the network spectral efficiency, when all transmitters use the same BL policy. For both scenarios, we provide simulation results to validate our conclusions.