Reviews on cognitive access to TV White Space

Unlicensed Operations in the Lower Spectrum Bands: Why is No One Using the TV White Space and What Does That Mean for the FCCCs Order on the 600 MHz Guard Bands?

The IEEE 802.22 is a standard for wireless regional area networks to opportunistically operate in TV bands; however, sharing TV White Space (TVWS) spectrum creates a problem of coexistence because no mechanism is defined for coordinating channel usage among secondary networks. We propose a White Space Resource Sharing mechanism (WSRS) for fixed secondary and mobile IEEE 802.22 networks to improve network coexistence and spectrum efficiency. Based on power control and channel allocation, our mechanism allows the TVWS system to serve vehicular networks in scenarios where there are active secondary fixed networks and no more TVWS channels available for opportunistic usage. Unlike state-of-the-art mechanisms for coexistence in TVWS spectrum, our mechanism allocates resources to vehicles even when the density of fixed nodes and the transmission power of the fixed network cause high interference to the vehicular network. Our results show the offered channel capacity increases up to 50% using the proposed WSRS mechanism compared to the recent IEEE 802.22 standard that does not have a defined TVWS channel sharing mechanism. Furthermore, our WSRS mechanism implements a strategy to protect the fixed secondary network from interference caused by vehicular transmissions while promoting fair usage for both secondary networks.

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.

TV White Space (TVWS) spectrum utilization is totally a new idea in wireless communication technology. It refers to some portion of TV spectrum that is not used by TV channels and available for other applications. This unused spectrum has been opened up for the free and unlicensed users. This spectrum can be utilized greatly if a noninterference environment is created between the users of this spectrum. Therefore, a coexistence of multiple networks requires interference management. In this paper, an interference management algorithm is developed. It ensures that a network can access the TVWS spectrum without causing interference to other networks. This is done by using three stages. The first stage is for finding the group of networks that will not cause interference to one another. For this graph coloring algorithm is used. The second stage is for assigning different channels to each group of networks. Here, channel assignment gives priority to the user requirement of each group. If any bandwidth is left after second stage, then the third stage is performed where performance of each network will be increased. This is done by considering the number of networks in a group. Simulation results show that the proposed scheme provides better channel assignment along with bandwidth utilization.

The lack of sufficient fixed-line communication infrastructure in African rural areas has resulted in wireless communication being the only cost effective alternative solution for broadband connectivity. However, access to valuable spectrum—specifically sub-1 GHz spectrum—is mostly allocated to broadcasting or mobile telephony. The global digital switch over (DSO) of television (TV) broadcasting systems will see more sub-1 GHz TV band spectrum being made available for the digital dividend and also result in more TV white space (TVWS) spectrum. In order to ensure dynamic and efficient utilization of the TV white space spectrum, there is an increasing trend to use cognitive radiosystems that use geo-location spectrum databases and spectrum sensing as an enabling technology. In this paper, we overview the relevant signals and standards and present field measurement results showing the actual usage of TV bands before the DSO in selected urban and rural areas of Southern Africa. Measurements were conducted using low-cost and high-grade radio instruments. The low-cost spectrum analyser was built in-house using the Universal Software Radio Peripheral (USRP-2) and GNU Radio software. A metric to quantify available TV white space, based on the minimum acceptable field strength, is introduced and applied to quantify the availability of TV white space. Our results show medium spectrum usage in urban areas and very low spectrum usage in rural areas, making TVWS an attractive solution for rural broadband connectivity.

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

In this chapter, Joint Radio Resource Management (JRRM) issues in cognitive networks are discussed presenting the TV White Spaces (TVWS) spectrum exploitation use case. TVWS are portions of UHF spectrum, which will be released and interleaved according to the geographical region due to the gradual switch-off of analogue TV and the adoption of digital TV. With the availability of TVWS and their temporary lease, traditional network planning and RRM design rationale points need to be enhanced. This chapter provides state-of-the-art work for existing cognitive radio network architectures, while a reference architecture for commons and secondary TVWS trading is proposed. Subsequently, JRRM concepts for heterogeneous Radio Access Technologies’ extension over TVWS aiming to continuously guarantee the QoS, the network key performance indicators, and at the same time targeting the overall highest system capacity, are presented. Finally, a thorough classification of existing admission control and scheduling techniques are provided, outlining the need for including continuously more cognitive and context-aware features in JRRM algorithms being applicable in advanced Heterogeneous Networking (HetNet) environments.

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.

TV White Spaces (TVWS) has taken a major step forward with the UK regulator Ofcom initiating a pilot of the technology and associated procedures in the UK, and TVWS rules being harmonized at the European level. This paper considers some aspects of our trial within the Ofcom TV White Spaces Pilot, namely, investigation of aggregation in TVWS and the deployment and testing of IEEE 802.11 white space devices that are capable of aggregating up to 4 TV channels, contiguously or non-contiguously. Our trial is the only deployment of these devices, developed at InterDigital in the USA, within the Ofcom TV White Spaces Pilot. This paper discusses the specifics of the InterDigital devices, including their design and capabilities. Further, results are presented highlighting what is possible in TVWS through contiguous aggregation. These results are achieved through per-channel allowed EIRP and capacity analyses based on feedback from a TVWS database within the Ofcom Pilot, using TVWS functionality developed at King's College London. Additional results outline the added benefit of optimal non-contiguous aggregation. Finally, this paper performs a like-for-like comparison of the performance of the InterDigital devices against what is theoretically possible in TVWS through capacity analyses using feedback from the TVWS database.

In order to implement the interweave cognitive radio solutions, the research for finding sparsely utilized spectrum bands has revealed the VHF and UHF television broadcast bands, known as television white spaces (TVWS) as the foremost candidate. The TVWS quantification and throughput analysis conducted via several measurement attempts and field trials uncover various facets of the TVWS spectrum measurement. Consequently, the conclusions obtained may be processed to get a statistical knowledge about spectrum availability in a particular geographic region and hence utilized for spectrum management. This paper explores inherent methodologies used for TVWS assessment and provides a comprehensive overview of the TVWS regulatory norms, results obtained by TVWS measurement campaigns and field trials conducted worldwide. In addition, research issues, implementation challenges and future directions for TVWS measurement procedure are highlighted.

The regulatory framework for secondary utilization of TV white spaces (TVWS) is well underway in the United Kingdom, while important steps in this direction are taken within the European Union and elsewhere. Mobile network operators are interested in the use of TVWS for cellular extension and rural access, where TVWS is seen as a significant new opportunity for operators to provide new wireless services. The government's plan to close the digital divide between the urban and rural communities has motivated the efforts to develop Wi-Fi like operation in TVWS for better coverage in rural areas. The IEEE currently has a working group developing 802.11af amendment which will allow for WLAN operations in the TVWS. This paper presents a quantitative analysis of downlink throughput performance of IEEE802.11af, also known as White-Fi in a rural environment while taking into account realistic modelling of TV channel availability, wireless channel, AP density, and the effect of co-channel interference caused by secondary APs and DVB-T transmitters. The paper shows that the low operating frequency of White-Fi offers a wide coverage in a rural environment, where there is limited cellular coverage due to the cost-inefficiency of base stations deployment. The presented results also show that there are more available TVWS channels and less co-channel interferers in a rural environment, resulting in a significant throughput performance even in high mobility if suitable channel estimation is considered, making it ideal for vehicular communications with White-Fi.

The explosive growth of capacity-hungry wireless services are presenting challenges to the scarce spectrum resource. Operating LTE systems on TV white space may meet the capacity demand due to the good propagation characteristic. However, according to the decision on World Radiocommunication Conference 2012, TV white space is unable to be used by LTE systems exclusively in the near further in China. Cognitive technologies throw light on sharing TV white space between LTE and TV broadcasting systems. Taking 470– 806 MHz band as an example, the availability of deploying LTE systems on TV white spaces in China is studied in this paper. Firstly, the separation distance from LTE stations to the edge of TV coverage area is calculated. Then, the inter-site distance between TV and LTE stations are figured out using the separation distance and TV coverage radius. Combining the theoretical calculation with the deployment information of both analog and digital TV stations stored in the national station database, simulation results on the capacity distribution of cognitive LTE system in typical cities are given. The simulation results inferred that approximately 67% of TV channels are unused averaged over the cities. This result confirms quantitatively the often-stated expectation that white spaces can be shared by LTE systems to meet the capacity demand as well as improve the spectrum efficiency.

Many rural and low-income areas around the globe have poor quality (or no) internet service with limited telephone coverage due to a lack of infrastructure, insufficient power supply, and a limited core telecommunications network. Because of limited mobile device propagation capabilities, sparse population density and poor purchasing power, it is not economically feasible for mobile operators to deploy traditional communication networks in these regions. Researchers recently discovered that a portion of the underutilized TV spectrum known as TV white space (TVWS) could be suitable for those areas in terms of bandwidth, improved reception features, good penetration of buildings, and broad reach. This paper presents a comprehensive evaluation of available TVWS channels in Ethiopia using a Geolocation Database front-end (GLSD) aided by the CSIR Calculation Engine hosted by the CSIR Meraka Institute. GLSD and the CSIR calculation engine together are able to quantify the amount of TVWSs through dynamically allocating the TVWS network radio services according to the geographic position of WSDs. The GLSD was developed using the ITU-R P.1546-5 propagation model. Using the GLSD and the CSIR calculation engine, the quantification of TVWS free channels are calculated. The results show that among the 58 VHF and UHF TV channels, 52 of the channels are free (underutilized) in Ethiopia. These free channels can be employed to provide wireless broadband solutions for connecting the rural areas as well as offloading the urban traffic.

Monitoring and sensing of spectrum are becoming more and more important, as the subject of using underused TV White Spaces (TVWS) spectrum by software defined radios (SDR) and cognitive radios is advanced forward towards practical applications. Correctly identifying available TVWS bands is critical for success of TVWS based broadband communications, not causing interference to reception of TV broadcast by TV receivers. This paper discusses side effects encountered with a popular design of a wire discone antenna. AntennaCraft model ST4 is exampled as an inexpensive candidate for spectrum monitoring and sensing in UHF frequency band. The study was done by both simulation and measurements, with well matching results. The candidate antenna was found to introduce notch banded loss in the system sensitivity. The influence of a potential mechanical damage onto the sensitivity of the antenna system has also been considered, and was found to be relatively small, under 3 dB.

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.