Przemyslaw Pawelczak

Cognitive functionality in next generation wireless networks: standardization efforts

This article discusses recent standardization efforts related to cognitive radio focusing on the work of IEEE Standards Coordinating Committee 41, formerly known as IEEE 1900. Some important tasks to be performed by the CR standardization community also are presented. These tasks will expedite the introduction of CR devices to the market while promoting a fair use of scarce radio resources. Some avenues for using the currently available standards for rapid deployment of CR devices, such as ISO standards, also are discussed.

Cognitive radio: Ten years of experimentation and development

The year 2009 marked the 10th anniversary of Mitola and Maguire Jr. introducing the concept of cognitive radio. This prompted an outpouring of research work related to CR, including the publication of more than 30 special issue scientific journals and more than 60 dedicated conferences and workshops. Although the theoretical research is blooming, with many interesting results presented, hardware and system development for CR is progressing at a slower pace. We provide synopses of the commonly used platforms and testbeds, examine what has been achieved in the last decade of experimentation and trials relating to CR, and draw several perhaps surprising conclusions. This analysis will enable the research community to focus on the key technologies to enable CR in the future.

Cognitive radio emergency networks - requirements and design

Currently deployed wireless emergency networks possess low spectrum efficiency, similar to their civilian wireless counterparts. Its due to the traditional radio frequency partitioning where each service has uniquely assigned bandwidth. To alleviate the problem one can propose dynamic channel assignment as a promising foundation for physical and link layer design of future wireless emergency communication networks. Here we identify functional requirements and system specifications for mobile ad hoc emergency networks built on top of cognitive radio. We also propose a simple Cognitive Radio medium access control protocol applicable to our network model, adopted from distributed channel assignment algorithm of IEEE 802.11

Multinode Spectrum Sensing Based on Energy Detection for Dynamic Spectrum Access

Sharing of the frequency spectrum between licensed primary users and unlicensed secondary users (SUs) requires reliable detection of spectrum occupancy by the SUs. Due to fading, single terminal detection is unreliable and results in a high probability of missed detection. This problem is solved by applying cooperative detection. In this paper two novel energy-based cooperative detection methods using weighted combining for Dynamic Spectrum Access are presented and analyzed. Weighting is based on the local mean SNR and the optimum log-likelihood ratio. Simulation results show a substantial improvement for the proposed weighting methods compared to equal gain combining and hard decision combining.

Performance Analysis of Multichannel Medium Access Control Algorithms for Opportunistic Spectrum Access

In this paper, different control channel (CC) implementations for multichannel medium access control (MAC) algorithms are compared and analyzed in the context of opportunistic spectrum access (OSA) as a function of spectrum-sensing performance and licensed user activity. The analysis is based on a discrete Markov chain model of a subset of representative multichannel OSA MAC classes that incorporates physical layer effects, such as spectrum sensing and fading. The analysis is complemented with extensive simulations. The major observations are given as follows: 1) When the CC is implemented through a dedicated channel, sharing such dedicated channel with the licensed user does not significantly decrease the throughput achieved by the OSA network when the data packet sizes are sufficiently large or the number of considered data channels is small. 2) Hopping OSA MACs, where the CC is spread over all channels, are less susceptible to licensed user activity than those with a dedicated CC (in terms of both average utilization and on/off times). 3) Scanning efficiency has a large impact on the achievable performance of licensed and OSA users for all analyzed protocols. 4) The multiple rendezvous MAC class, which has yet to be proposed in OSA literature, outperforms all the multichannel MAC designs analyzed in this paper.

Performance of Transport Control Protocol Over Dynamic Spectrum Access Links

Dynamic Spectrum Access (DSA) radio devices look for temporarily unoccupied frequency bands and attempt to communicate in them. It is envisioned that DSA can substantially increase the capacity of wireless networks by broadening the utilization of radio resources. Given the ubiquitous use of Internets Transport Control Protocol (TCP), it can be expected that TCP will be used in DSA networks in the future. Whether TCP can efficiently provide stable end-to-end transmissions over DSA links, given their dynamic and unpredictable nature, remained unclear. Therefore, we have studied by simulation the ability of various TCP flavors to efficiently utilize DSA links. We have performed simulations using the TCP stack from the Linux operating system. Our simulations show that modern TCPs can efficiently make use of the dynamic capacity of DSA links for bulk data transmission, under a wide range of conditions, but only if certain requirements are met. We also analytically determine the effect of Primary User (PU) detection errors on TCP performance and conclude that the dominating component responsible for TCP throughput reduction in a DSA environment is the observation time, not, as one might expect, PU detection errors.

Performance of Joint Spectrum Sensing and MAC Algorithms for Multichannel Opportunistic Spectrum Access Ad Hoc Networks

We present an analytical framework to assess the link layer throughput of multichannel Opportunistic Spectrum Access (OSA) ad hoc networks. Specifically, we focus on analyzing various combinations of collaborative spectrum sensing and Medium Access Control (MAC) protocol abstractions. We decompose collaborative spectrum sensing into layers, parametrize each layer, classify existing solutions, and propose a new protocol called Truncated Time Division Multiple Access (TTDMA) that supports efficient distribution of sensing results in “K out of N” fusion rule. In case of multichannel MAC protocols, we evaluate two main approaches of control channel design with 1) dedicated and 2) hopping channel. We propose to augment these protocols with options of handling secondary user (SU) connections preempted by primary user (PU) by 1) connection buffering until PU departure and 2) connection switching to a vacant PU channel. By comparing and optimizing different design combinations, we show that 1) it is generally better to buffer preempted SU connections than to switch them to PU vacant channels and 2) TTDMA is a promising design option for collaborative spectrum sensing process when K does not change over time.

Computationally Efficient Modulation Level Classification Based on Probability Distribution Distance Functions

We present a novel modulation level classification (MLC) method based on probability distribution distance functions. The proposed method uses modified Kuiper and Kolmogorov-Smirnov distances to achieve low computational complexity and outperforms the state of the art methods based on cumulants and goodness-of-fit tests. We derive the theoretical performance of the proposed MLC method and verify it via simulations. The best classification accuracy, under AWGN with SNR mismatch and phase jitter, is achieved with the proposed MLC method using Kuiper distances.

Planning of Cellular Networks Enhanced by Energy Harvesting

We pose a novel cellular network planning problem, considering the use of renewable energy sources and a fundamentally new concept of energy balancing, and propose a novel algorithm to solve it. In terms of the network capital and operational expenditure we conclude that savings can be made by enriching cellular infrastructure with energy harvesting sources, in comparison to traditional deployment methods.

Primary User Traffic Estimation for Dynamic Spectrum Access

This paper presents a mathematical analysis of the accuracy of estimating Primary Users (PUs) mean duty cycle u, as well as the mean off- and on-times, where the estimation accuracy is expressed in terms of the Cramer-Rao bound on the mean squared estimation error. For estimating u, we derive the mean squared estimation error for uniform, non-uniform, and weighted sample stream averaging, as well as maximum likelihood (ML) estimation. The estimation accuracy of the mean PU off- and on-times is studied when ML estimation is employed. Besides, the impact of spectrum sensing errors on the estimation accuracy is studied analytically for the averaging estimators, while simulation results are used for the ML estimators. Furthermore, we develop algorithms for the blind estimation of the traffic parameters based on the derived theoretical estimation accuracy expressions.