Distributed Spectrum Management in TV White Space Networks

This paper presents a cognitive radio system (CRS) that complies with the maximum allowable transmit power and emission limits of TV band devices (TVBDs). The CRS consists of a TVBD that uses the existing Wi-Fi module and two Wi-Fi modules operating in the 2.4 GHz and 5 GHz bands. Design methods are proposed for a radio frequency (RF) module, a digital signal processing (DSP) module, and a circuit for transmit-receive mode switching in the TV band device (TVBD). The performance of the implemented TVBD is investigated in both wired and wireless environments. The measured data rates of the implemented TVBD at the application layer are approximately 60 % of the theoretical data rates at the physical layer in the Wi-Fi system. The service coverage of a TVBD network is also measured according to several modulation and coding schemes (MCSs) of the TVBD for a single spatial stream. The coverage measurements of a TVBD network are conducted in both a suburban area, Jeju Island, and a nearly open area, Incheon, South Korea. The results show that the service coverage of a mobile network in TV white space (TVWS) can be enlarged by more than 2 km in the suburban area and by more than 8 km in the nearly open area.

This paper investigates how suitable TV White Space (TVWS) is for use by cellular networks. Unlike in licensed bands, transmit power in TVWS is limited and considerable interference from TV towers exists. This suggests that evaluating TVWS only in terms of available bandwidth can be misleading, since performance of wireless networks in TVWS is likely lower than in the same amount of dedicated spectrum. We quantify TVWS at the example of Germany, using the European methodology developed in CEPT ECC SE 43. In the second step, we determine the performance of a cellular network operating in TVWS using a calibrated multi-cell and multi-user system level simulation tool. This way we also consider interference between TVWS users, which in previous TVWS studies has not been investigated in detail. Not all locally available TV channels are equally useful. We thus compare different channel selection algorithms a TVWS operator could apply to select from the set of available TVWS channels. We found that while the available spectrum for TVWS usage is in theory quite high, its actual utility strongly depends on the channel selection method and the requirements it is based on. Due to the high interference from TV towers, cellular networks based on frequency re-use one (like LTE) have difficulties finding channels that allow good performance at the cell edge. The inner part of a cell can however considerably benefit from TVWS. This indicates that for cellular networks TVWS is primarily suitable for traffic offloading and spotty coverage rather than for building large contiguous coverage networks.

This paper presents a TV white space (TVWS) field demonstration system complying with the maximum transmit power and emission regulatory requirements of the Federal Communications Commission (FCC). Recently, the service coverage measurement of a TV band device (TVBD) network has been conducted in Jeju Island, South Korea. The measurement results show that the service coverage of a mobile network can be enlarged up to more than 2 km with TVBDs operating in the available TV bands.

본 논문에서는 국내 전파 환경에서 DTV 서비스를 안전하게 보호하면서 동시에 TV 유휴 대역 기기를 효과적으로 운용하기 위해 은닉 노드에 의한 DTV 신호 감쇄 영향을 살펴본다. 이를 위해, 국내 전파 환경을 지리적 특성에 따라 해안형, 분지형, 도시형 지역으로 분류하고, 각 지역을 지형적 특징에 따라 다시 8개 지형으로 세분화하여 측정 지점을 선정한 후 DTV 신호의 은닉 노드 감쇄 정도를 측정하고 분석한다. 국내 대도시의 경우 빌딩 건물 지역과 주상 복합 지역이 다른 나라에 비해 상대적으로 밀집해 있기 때문에, 국내 DTV 서비스를 안전하게 보호하기 위해서는 은닉 노드 마진을 최소한 38 dB 이상 설정해야 한다. In this paper, we investigate hidden node problem to effectively utilize TV band devices(TVBDs) in the TV white space(TVWS), and also to protect digital television(DTV) service in Korea. Firstly, we classify the radio propagation environment into an urban area, a basin area, and a coastal area based on geographical characteristics. Thereafter, we measure and analyze local shape based hidden node attenuation at eight segmented positions in each geographic area. Because commercial buildings as well as residential and commercial buildings in Korea are located in closer proximity to each other than in other countries, hidden node margin should be more than 38 dB in order to safely protect DTV service in Korea.

TV White Space (TVWS) refers to frequency band reserved only for licensed terrestrial TV broadcasting and is opened to unlicensed use under regulatory conditions. While regulations protect licensed systems from interference, interference among unlicensed systems is left mainly to manufacturers. Consequently, there is a need to develop new coexistence approaches between TVWS networks. Busy tone broadcasting is a coexistence method, which can be used by TVWS networks to announce the selected frequency band is occupied. In this paper, a busy tone based coexistence algorithm is proposed for IEEE 802.11af and IEEE 802.22 networks and analyzed by considering different client distributions experiencing log-normal shadowing, where the exact interfering packet rate and successful packet transmission rate expressions are obtained and validated by simulations for different scenarios. The results show that with the proposed coexistence approach, a WLAN can reliably detect the busy tone signal to change its frequency band and can reduce interference to WRAN. Even if there is no available frequency band for the WLAN, the WRAN still maintains its enhanced successful packet transmission performance. The deployment of the proposed algorithm is important for successful coexistence between cognitive wireless networks, where interference is not regulated, such as in TVWS bands.

Spectrum scarcity demands for additional bandwidth where new services can be deployed on. However, today's spectrum allocation leaves almost no bands unallocated. Thus, Cognitive Radio has been studied to bring relief to the lack of spectrum, moving towards a more efficient and dynamic spectrum access. In this domain TV White Space have been proposed as a possible solution to bring new, valuable spectrum for opportunistic services. However, their availability is quite low in highly populated areas, and thus their viability is limited. This is mainly because the availability of TV White Space is typically considered at the rooftop, through two-dimensional propagation models which do not account for possible spectrum re-utilization policies within a building, or in a small-scale area. In this paper, we show that much more communication opportunities can be found when we consider also the third-dimension, i.e. the height from the terrain, and novel per-floor allocation policies. We propose three main contributions in this paper. First, we describe an analytical model through which we derive the number of available spectrum resources for indoor secondary networks, considering PU protection policies in the same building, and in surrounding buildings. Second, we estimate the number of TV Gray Space (TVGS) over realistic scenarios in candidate cities, considering realistic street topology and buildings locations, and we show that this value can be much higher than what reported in the spectrum database. Finally, we investigate co-existence of secondary networks on TVWS, when novel per-floor spectrum sharing models are used.

Cognitive radio technology, which enables an efficient use of spectrum, is expected as one of solutions for a spectrum shortage problem. Recently, spectrum sharing type cognitive radio technology in TV white-spaces has been actively promoted worldwide and technical specifications have been advanced in international standardization activities such as IEEE802.11af and IEEE802.22. These standardizing systems tend to secure more frequency channels for existing systems by simply converting their native frequency band to TV white-spaces for data traffic offload. As one of the simplest technologies to realize wireless communications in TV white-spaces, we proposed a frequency conversion system using a UHF converter. In this paper, we prototyped a tablet-type portable TV band device, which can communicate in TV band with IEEE802.11b/g-based communication systems by using the UHF converter. Also, physical features of our prototyped tablet terminal are summarized and the RF transmitter and receiver performance and spurious response are characterized.

In this paper, we propose a novel information market for TV white space networks, where the spectrum database operator sells the information regarding TV white space to secondary users. Different from the traditional spectrum market, the information market processes the unique property of positive externality, as more users purchasing the information service will increase the value of the service to each buyer. We systematically characterize the market equilibrium and the database operator's optimal information pricing strategy. Specifically, we first study how the market share dynamically evolves over time and eventually converge to a market equilibrium. We show that the market equilibrium increases with the initial market share, and there exist several tipping points of the initial market share, around which a slight change will lead to a significant change on the emerging market equilibrium. Based on the market equilibrium analysis, we further study the impact of the database operator's information pricing strategy on the market equilibrium, and derive the optimal information price that maximizes the database operator's revenue. Theoretical analysis and numerical result indicate that this is a promising business model for creating incentives for the database operator in TV white space networks.

In this paper, we propose a reinforcement learning-based approach for enabling vehicles to make intelligent channel selection choices across TV whitespace spectrum. In order for vehicle communication networks to dynamically access TV whitespace in a secondary manner, it is imperative that these communication systems be capable of coexisting with other types of secondary wireless networks operating within the same frequency range. Consequently, we first propose a TV whitespace channel sharing scheme that would facilitate the coexistence between WLAN, WRAN, and vehicular communication networks. Using the channel utilization variations observed by a collection of mobile vehicular communication systems, we then devised a reinforcement learning-based adaptive channel selection algorithm that employs channel utilization sensing in order to reinforce the decisions made by the vehicular communication system. Moreover, the parameters of the proposed learning approach are adaptively tuned in order to achieve better adaptation to a particular environment. A computer emulation environment composed of actual real-world sensing measurement data and a simulated TV whitespace network is created in order to accurately model the characteristics of future wireless environment, as well as to test the proposed learning-based channel access approach. Experimental results show a significant performance improvement with respect to vehicle communication.

Localization is the enabling technology of geolocation database assisted Cognitive Radio Networks (CRN) in TV White Space (TVWS), as the location is required in the implementation of geolocation database approach by regulators such as FCC and Ofcom. This paper proposes a novel Sensing enAbled Localization and Tracking (SALT) system, which locates Secondary Users (SUs) and tracks their movements. In particular, the system localize SUs based on their measurement of Primary User (PU) signals in the TV spectrum. SALT also uses the SU movement information to dynamically manage the available spectrum with an optimal spectrum allocation algorithm based on the location estimation, so as to maximize the uplink throughput of the entire network. The performance of the proposed localization and tracking algorithm is verified with field measurement data from complex environment through extensive experimentation.

TV white spaces (TVWS) can be used by secondary users as long as they do not cause harmful interference to primary users (PUs). Regulatory authorities worldwide have mandated the use of geo-location database (GLDB) for protection of incumbent users. In a wireless TVWS network, interference could be due to either co-channel interference or adjacent channel interference. Recent studies have shown that aggregate adjacent channel interference from a high density of mobile users using low power in multiple adjacent channels is as harmful as co-channel interference even if each single adjacent channel interference stays below the GLDB D/U (desired to undesired) ratio constraint. When there is a high density secondary users (SUs) in a TVWS network, there will high interference among SUs and a possibility of harmful interference to primary users (PUs). Power control is therefore necessary to protect PUs against harmful interference and to reduce the level of interference among SUs. In this paper we propose a firefly algorithm based power control algorithm for a GLDB based wireless TVWS network that take into consideration interference constraints at the primary user (PU) and SU. The algorithm also takes into consideration both co-channel and adjacent channel interference. Simulation results show that the proposed algorithm protects TV receivers against harmful interference and results in an improvement of signal to interference and noise ratio (SINR) for SUs.

Dynamic spectrum access (DSA) regulations and associated radio network technologies are expected to result in efficient frequency spectrum utilization by future wireless networks. TV white space (TVWS) networks supported by location aware spectrum databases (LASDs) will be the first step to realize DSA, until cost-effective cognitive radio (CR) devices are reliable enough for building future networks. This paper describes a design and development process of a LASD for rural communities in South Africa. Apart from avoiding the difficult problem of spectrum sensing, the database also protects primary TV broadcasters from any harmful interference that might be caused due to secondary spectrum usage. The LASD is designed as a tool for testing DSA policy frameworks and enables reconfigurable TVWS networks to provide full capacity and affordable wireless broadband Internet connectivity for rural communities.

The TV white spaces (TVWS) enabled infostation has received significant attention due to its wide area coverage for cost-effective and media-rich content dissemination. In this paper, we engineer WhiteFi infostation, which is dedicated for Internet-based vehicular media streaming by leveraging geolocation database. After demonstrating the empirical observations of unique TVWS features and analyzing the real-world TVWS data collected from geolocation database, we first propose an optimal TVWS network planning to deploy WhiteFi infostation with the objective of maximizing network-wide throughput. The proposed TVWS network planning jointly considers the multi-radio configuration and the channel-power tradeoff, which can be realized by decentralized Markov approximation. Furthermore, we introduce a location-aware contention-free multi-polling access scheduling scheme for vehicular media streaming, which considered both the realistic vehicular applications and dynamics of wireless channel conditions. Through extensive simulations with real-world empirical TVWS data and urban vehicular traces, we demonstrate that our WhiteFi infostation solution can well support both the delay-sensitive and delay-tolerant vehicular media streaming services.

We consider a non-cooperative Opportunistic Spectrum Access (OSA) where Secondary Users (SUs) access opportunistically the spectrum licensed for Primary Users (PUs) in TV white spaces (TVWS). As sensing licensed channels is time and energy consuming, we consider a hierarchical Cognitive Radio (CR) architecture, where CR base stations sense a subset of the spectrum in order to locate some free frequencies. Thereafter, a SU that needs to communicate through TVWS sends a request to a CR base station for a free channel. We model the problem using a Partially Observable Stochastic Game (POSG), and we take into consideration the energy consumption of CR base stations and the Quality of Services (QoS) of SUs. Since solving POSG optimally may require a significant amount of time and computational complexity, we model the OSA problem using a game theoretical approach, and we propose a symmetric Nash equilibrium solution concept. Finally, we provide some simulations that validate our theoretical findings.

In recent years, as a demand for communication services over the VANET (Vehicle Ad-hoc Network) is increasing drastically, radio frequencies to be assigned to the new communication services are becoming insufficient. In response to this problem, we consider to apply the cognitive radio technology in general, and the cognitive use of TV white space based on the white space database (WSDB) in particular, to the VANET where communication nodes (vehicles) move fast and for a long time. In order to provide stable and efficient communications over TV white space in VANET, (1) the quick acquisition of the status of license/primary users at the location and (2) the dynamic selection of an appropriate data channel are essential. To fulfill those two requirements, in this paper, we propose a database driven data channel selection scheme for VANET over TV white space. Through simulation experiments, we showed that the proposed scheme can reduce not only channel switching but also channel collision rate with a good balance, thereby improving the throughput performance as well.1