Radoslaw Piesiewicz

Cooperative Spectrum Sensing with Noisy Hard Decision Transmissions

Most critical component of the cognitive radio paradigm is spectrum sensing and accordingly, detection of primary users. Recently proposed cooperative spectrum sensing methods do not consider errors occurring during the transmission of local cognitive radio decisions to the cognitive base station. However, perfect communication is clearly not the case in realistic cooperative spectrum sensing scenarios and might lead to misleading performance result interpretations. In this paper, we extend the simple cooperative spectrum sensing communication model to admit transmission imperfections. Specifically, we consider the case where the local hard cognitive radio decisions that are based on any local detection scheme are corrupted by additive noise during transmission from cognitive radios to cognitive base station. Utilizing this extended cooperative spectrum sensing model, we present the complex optimal and a practical and effective suboptimal detector that is capable of operating with any local cognitive radio detection scheme: Two-step detector. We present simulation results investigating the performance of the proposed detectors and the effect of parameters of interest such as number of cognitive radios and signal to noise ratio. Moreover, we provide comparisons between non-cooperative and cooperative spectrum sensing performances revealing some cases where non-cooperative scheme is more effective.

Cooperative Shared Spectrum Sensing for Dynamic Cognitive Radio Networks

Cooperative spectrum sensing for cognitive radio networks is recently being studied to simultaneously minimize uncertainty in primary user detection and solve hidden terminal problem. Sensing wideband spectrum is another challenging task for a single cognitive radio due to large sensing time required. In this paper, we introduce a technique to tackle both wideband and cooperative spectrum sensing tasks. We divide the wideband spectrum into several subbands. Then a group of cognitive radios is assigned for sensing of a particular narrow subband. A cognitive base station is used for collecting the results and making the final decision over the full spectrum. Our proposed algorithm minimizes time and amount of energy spent for wideband spectrum scanning by a cognitive radio, and effectively detects the primary users in the wideband spectrum thanks to cooperative shared spectrum sensing.

Cooperative Spectrum Sensing over Imperfect Channels

Cognitive radio has emerged as an innovative approach able to cope with the spectral limitations. Cognitive radio networks rely on detecting whether a particular segment of the radio spectrum is currently in use and to exploit the temporarily unused spectrum rapidly without interfering with the transmissions of other users. Thus, one of the most important and critical components of the cognitive radio is spectrum sensing and accordingly, detection of primary users. Recently proposed cooperative spectrum sensing methods do not consider errors occurring during the transmission of local cognitive radio decisions to the cognitive base station. However, perfect communication is clearly not the case in realistic cooperative spectrum sensing scenarios and might lead to misleading performance result interpretations. In this paper, we extend the cooperative spectrum sensing model to admit transmission imperfections and propose two simple, hardware-friendly and effective primary user detectors operating on noisy local cognitive radio decisions. We present simulation results investigating the performance loss incurred by considering realistic channels with varying signal-to-noise ratio values. Moreover, we compare the two proposed cooperative spectrum sensing algorithms in various practical scenarios.

Spectrum sensing for cognitive radios with transmission statistics: considering linear frequency sweeping

The spectrum sensing performance of Cognitive Radios (CRs) considering noisy signal measurements and the time domain transmission statistics of the Primary User (PU) is considered in this paper. When the spectrum is linearly swept in the frequency domain continuously to detect the presence of the PU the time-domain statistics of the PU plays an important role in the detection performance. This is true especially when the PUs bandwidth is much smaller than the CRs scanning frequency range. We model the transmission statistics that is the temporal characteristics of the PU as a Poisson arrival process with a random occupancy time. The spectrum sensing performance at the CR node is then theoretically analyzed based on noisy envelope detection together with the time domain spectral occupancy statistics. The miss detection and false alarm probabilities are derived from the considered spectral occupancy model and the noise model, and we present simulation results to verify our theoretical analysis. We also study the minimum required sensing time for the wideband CR to reliably detect the narrowband PU with a given confidence level considering its temporal characteristics.

Experimentally detecting IEEE 802.11n Wi-Fi based on cyclostationarity features for ultra-wide band cognitive radios

In this paper we present some experimental results on the cyclostationarity properties of the IEEE802.11n Wi-Fi transmissions, and the usage of the cyclostationarity features to detect IEEE802.11n radios in the context of ultra wide band (UWB) based cognitive radios (CR). The IEEE 802.11n lies in the UWB frequency range, at 5.2GHz, and the CR needs to successfully detect the legacy user to avoid interference. By performing cyclostationarity analysis we compute the cyclic power spectrum (CPS) of the IEEE802.11n transmissions and use it for detecting the presence of the legacy user. We conduct experimentations to perform our study under different channel conditions and perform post signal analysis to measure the detection performance using the CPS based detection technique. The probability of false alarm and the probability of missed detection are computed and the results are presented for different channel conditions, together with the CPS of the legacy users signal.

Time divisional and time-frequency divisional cooperative spectrum sensing

In this paper we present a time divisional and a time-frequency divisional cooperative spectrum sensing technique suitable for cognitive radio (CR) networks. The two methods are well suited for very high bandwidth CR networks, such as UWB networks, where the individual nodes need to scan a wide range of spectrum which is a time consuming process. With the time divisional and the time-frequency divisional cooperative spectrum sensing approaches the nodes share the spectrum sensing functions cooperatively, coordinating in time and frequency, covering the total frequency band and also in near-continuous time. In this paper we present the corresponding algorithms and techniques for the two cooperative spectrum sensing approaches, analyze their performances, and compare the advantages and disadvantages with each other. We also present simulation results to verify the performance improvements in terms of probability of miss detection and the probability of false alarm for detecting the PU. Results show that the the proposed methods are best suited for detecting the PUs having low spectral occupancy statistics who occupy the spectrum very seldom.

Preliminary experimental results on the spectrum sensing performances for UWB-Cognitive Radios for detecting IEEE 802.11n systems

In this paper we present the spectrum sensing performance for detecting the IEEE 802.11n WiFi terminals for Ultra-Wideband (UWB) based Cognitive Radio (CR) systems. The 802.11n WiFi system lies in the 5GHz un-licensed frequency band and is subjected to interferences from the UWB transmissions. The UWB based CR terminals perform secondary communications by opportunistically utilizing the available spectrum when no legacy users such as the 802.11n WiFi systems are present in the environment. Therefore, the CR nodes need to sense the spectrum to detect the presence of any legacy users in the surroundings. Here, we study the commonly known spectrum sensing technique, the energy based method, on experimentally obtained signal data for the IEEE 802.11n WiFi system, and analyze the detection performances for detecting the legacy user. We present the time-frequency measurements obtained from the experimental data, and also compute the probabilities of missed detection and false alarm for detecting the legacy user by performing post analysis on the experimental data. The results can then be used to determine the detection threshold based on the required detection criteria.

Experimental Analysis of 3.5 GHz WiMAX 802.16e Interference in WiMedia-defined UWB Radio Transmissions

The interference produced by WiMAX mobile wireless transmissions operating in the 3.5 GHz band on a WiMedia-defined ultra-wideband (UWB) wireless link is experimentally analyzed in this paper. The investigation includes standard IEEE 802.16e WiMAX, and ECMA-368 UWB equipment as defined by the WiMedia alliance. A conventional meeting room scenario has been considered for the measurements. The experimental results indicate that WiMAX transmitters must be located at distances larger than 5 m from the UWB receiver to guarantee successful UWB communication.

Cognitive Information Service: Basic Principles and Implementation of a Cognitive Inter-Node Protocol Optimization Scheme

Cognitive networks are becoming extremely popular in the network domain. This paper proposes a novel concept in cognitive network management and protocol configuration, where any protocol of the TCP/IP protocol reference model can be extended to dynamically tune its configuration parameters based on immediate past performance. The approach is focused on inter-node cognitive adaptation which is fostered by the proposed Cognitive Information Service (CIS). Performance evaluation results are obtained for cognitive adaptation of main TCP flow control parameters and show good agreement with design objectives.

UWB Cognitive Radios

In this chapter we present UWB communication as a potential candidate for cognitive radio technology. Cognitive radios are intelligent radios that could adopt itself by sensing and learning the radio environment and optimize its transmission strategies to maximize the utilization of the scarce radio resources such as the radio spectrum. This has been motivated by the radio regulatory bodies around the world (EC, 2007; FCC, 2003) to utilize unused radio spectrum known as white space in the spatio-temporal domain. In the recent years UWB communication has emerged as a potential candidate for the CR technology due to its ability to share the spectrum with others for short range wireless communications. In this context we present the concept of cognitive radios and the necessary techniques to adopt UWB as cognitive radios in this chapter. Especially, we enhance on the fundamentals of cognitive radios and spectrum sensing which enable the UWB radio to learn the radio environment. We also touch upon other cognitive radio related topics that are related to UWB communications such as dynamic spectrum access, interference mitigation and localization techniques. Furthermore, we present some potential applications for the use of UWB based cognitive radios which are derived from the European Union funded projects EUWB (EUWB, 2008) which is one of the biggest UWB projects that the world has seen so far, and the C2POWER project (C2POWER, 2010) which is related to energy efficiency in short range wireless communications with the use of cognitive radios. In this chapter we do not consider the technological aspects related to the use of cognitive radios for energy efficiency but only consider the use of cognitive radios for dynamic spectrum access. However, at the end of the chapter we present a scenario for the use of cognitive radios for energy efficiency derived from (C2POWER, 2010). In the material presented in this chapter we mainly consider the high data rate UWB radios based on the Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) technique following the Wimedia specifications (Wimedia-PHY, 2009). The OFDM based transceiver design makes it feasible for the UWB radio to sense the radio environment and dynamically change the transmission parameters accordingly. This makes the UWB 11