Vlad Popescu

On the feasibility of unlicensed communications in the TV white space: Field measurements in the UHF band

In practical unlicensed communications in TV band, radio devices have to identify, at first, the transmission opportunities, that is, the portion of the spectrum licensed for broadcasting services unoccupied in a certain region at certain time, that is, the so-called TV white space. In this paper the outcome of field measurements in the UHF TV band (470–860 MHz) conducted in EU is presented. To obtain empirical values for the parameters upon which unlicensed radio devices are able to distinguish in a real scenario between empty and occupied TV channels, signal power measurements have been performed in Italy, Spain, and Romania on rural, suburban, and urban sites, at different heights over the ground by using different analysis bandwidths. The aim of this work is to provide a set of practical parameters upon which harmless unlicensed communication in the UHF TV white space is feasible. The results have been analyzed with respect to the hidden node margin problem, spectrum sensing bandwidth, and occupancy threshold.

PAPR reduction in multicarrier modulations using Genetic Algorithms

This work presents a novel approach to the reduction of Peak-to-Average Power Ratio (PAPR) in multicarrier modulation: Partial Transmit Sequence (PTS) is optimized by opportune tailored Genetic Algorithms (GA) which allow achieving solution with pre-selected accuracy and reduced computational burden. A comparative study on both Orthogonal Frequency Division Multiplexing (OFDM) and Wavelet Packets Multi-Carrier Modulation (WP-MCM) has been conducted. Results show that although WP-MCM outperforms conventional OFDM schemes in terms of PAPR, GA applied to PTS are more effective in reducing PAPR for OFDM rather than for WP-MCM.

TV white spaces exploitation for multimedia signal distribution

The new spectrum regulation policies for dynamic spectrum access, especially those concerning the use of the white spaces in the Digital Terrestrial Television (DTT) bands, arise the need for fast and reliable signal identification and classification methods. In this paper we present a two-stage identification method for signals in the white spaces, using combined energy detection and feature detection. The band of interest is divided by means of the Discrete Wavelet Packet Transformation (DWPT) in sub-bands where the signal power is calculated. Modulation classifiers taking into account the statistical parameters of the signal in the wavelet domain are used as features for identifying the modulation schemes, in this case specifically for the DVB-T broadcast standard. Finally, a signal transmission architecture based on Motion JPEG XR has been implemented in order to explore and evaluate a practical application of indoor signal distribution over white-spaces.

Co-Channel and Adjacent Channel Interference and Protection Issues for DVB-T2 and IEEE 802.22 WRAN Operation

This paper presents a study on the coexistence issue of digital terrestrial TV broadcasting and cognitive broadband access operation in the TV white spaces (TVWS). Extended measurements were performed to evaluate the protection of the existing Second generation of digital video broadcasting terrestrial standard (DVB-T2) services in the presence of IEEE 802.22 WRAN co-channel and adjacent channel interference. The absence of picture failure over 30 consecutive seconds on decoded DVB-T2 streams has been monitored to obtain the maximum tolerable level of IEEE 802.22 WRAN interference, which ensures the protection of the primary broadcast system. This paper considers practical DVB-T2 system configuration options by varying parameters of the standard, such as constellation and code rate, FFT size, pilot pattern and guard interval, and rotated constellations and compares them in terms of robustness with respect to the interference generated by IEEE 802.22 WRAN operation. The goal is to provide cognitive broadband operators in the TVWS with guidelines to optimize their network by choosing the parameters that best fit their needs in case of coexistence with DVB-T2 broadcasting services.

An Unlicensed Indoor HDTV Multi-Vision System in the DTT Bands

Multimedia contents distribution through wireless networks in the home environment is a challenging issue. At present, several systems are proposed mainly relying on 802.11g/n standards which offer adequate bandwidth for HD video contents. However, the rapid revolution in wireless communication in past years has increased the demand of radio spectrum to fulfill the requirements of wireless applications, leading to spectrum overcrowding. The licensed-free ISM band is now overexploited and experiences serious coexistence issues. However, the transition from analog to digital TV is in progress worldwide and digital switchover plans have driven a thorough review of TV spectrum exploitation. Huge debates are taking place within the wireless world about the possible exploitation of the unused portion of the TV spectrum. Within this framework, this paper proposes a multi-vision system working on the TV band for the short-range indoor transmission of HDTV contents. The proposed system relies on geo-location databases for the TV band, it is based on the OFDM core technology and it is compliant with the DVB-T/T2 standard for HDTV. The authors investigated the feasibility of the system whereas preserving the integrity of incumbent services: computer simulations have been supported by hardware implementations on USRP2 SDR board for test-bed measures and transmission in real conditions.

Interference Issues for VANET Communications in the TVWS in Urban Environments

Within the scenario of the proliferation of smart vehicles, a novel tendency is to exploit the cooperation between vehicles to create vehicular ad hoc networks (VANETs) using the IEEE 802.11p standard. IEEE 802.11p includes dedicated short-range communications (DSRC) between high-speed vehicles and between the vehicles and the roadside infrastructure in the licensed intelligent transportation system (ITS) band at 5.9 GHz. At such frequencies, fading problems caused by the Doppler effect and/or multipath adversely affect propagation, particularly in dense urban environments. To reduce such propagation impairments, the use of lower frequencies has been proposed in literature, namely the TV white spaces (TVWS) in the ultrahigh-frequency (UHF) band. TVWS is the part of the spectrum licensed to broadcasters that is not occupied at a given time in a given geographical area on a noninterfering/nonprotected basis with regard to primary services. This paper analyses coexistence issues between digital video broadcasting-terrestrial (DVB-T)2 and IEEE 802.11p transmission in the TVWS. The aim of this paper is twofold: to evaluate the protection of DVB-T2 broadcasting services interfered by IEEE 802.11p communications and the impact of adjacent DVB-T2 services on IEEE 802.11p communications in the TVWS. The main outcomes of this paper are the maximum transmission power level and bandwidth configuration of an 802.11p signal in the adjacent channel (i.e., TVWS) of an active DVB-T2 system while protecting the broadcast service, as well as the error rate curves for each allowed mode of IEEE 802.11p in the TVWS to evaluate the performance of VANETs communications coexisting with DVB-T2 regular services in the licensed TV band.

Performance analysis of IEEE 802.22 wireless regional area network in the presence of digital video broadcasting – second generation terrestrial broadcasting services

In Cognitive Radio (CR) networks unlicensed secondary users aim at transmitting in licensed bands while preserving primaries from harmful interference. CR communications have been especially studied in the white spaces of TV band (TVWS), defined as the TV free channels left unused in each territorial area by the reallocation of TV services as a direct consequence of the switchover plans. The first full CR standard, the IEEE 802.22 Wireless Regional Area Network (WRAN), has been developed to bring wireless broadband access to remote, rural areas where other wireless networks are not present due to low revenue impact or critical network deployment. IEEE 802.22 WRAN devices are designed to operate in the range of frequencies between 54MHz and 862MHz alongside digital terrestrial television (DTT) operation. In this work we perform a complete analysis to evaluate the performance of IEEE 802.22 WRAN devices coexisting with DVB-T2 adjacent channel transmission in the TV bands in a rural environment. The link budget analysis for IEEE 802.22 WRAN in different coexistence scenarios, such as fixed DTT reception with indoor/outdoor IEEE 802.22 WRAN reception shows that its robustness is comparable to long term evolution (LTE) which represents the state-of-the art of cellular networks in rural scenario.

Hidden node margin and man-made noise measurements in the UHF broadcasting bands

This paper presents an extended study of the spectrum occupancy in the UHF frequency band (470-870MHz) in Spain and in Italy. The objective of the study is to establish by signal power measuring if cognitive devices are able to detect and distinguish in a Hidden Node scenario between empty and occupied TV channels. The study has been performed, for each of these two countries, at three different sites and at different heights over the ground for assessing the hidden node margin. The measurements in Spain were carried out in urban, suburban and rural environments close to the city of Bilbao while the measurements in Italy were carried out in Sardinia, in different urban areas of the city of Cagliari, surrounding suburban spots and a rural location 50 km west. The measurement methodology was the same in both scenarios. The results from the spectrum measurements performed in the various scenarios have been analyzed and conclusions have been drawn.

A cognitive radio indoor HD1T V multi-vision system in the TV white spaces

This paper proposes a cognitive radio (CR) indoor distribution system of HDTV contents in the TV white spaces, with immediate implementations as home entertainment system. A proof-of-concept digital terrestrial television (DTT) compliant prototype has been implemented on a test-bed based on commercial DTT receivers in combination with software defined radio (SDR) hardware devices. Extended measurements performed in real indoor environments assessed the feasibility of the proposed system with respect to the protection of the existing broadcasting TV services.

RFID sensor network for workplace safety management

Large industrial environments are inherently complex systems to be monitored and controlled, given the presence of vehicles, people and industrial plants. In a context dominated by strict regulations for workplace safety, systems for monitoring and preventing workplace risks can have a particular importance. This paper describes the work in progress on designing and implementing an RFID-based sensor network for workplace safety management. The proposed system is based on Body Area Networks and passive RFID tags and sensors. The goal of the proposed system is to offer a detailed, constantly updated overview of an industrial environment in terms of workplace safety.