White Space Devices Research Articles

Some Are Born With White Space, <italic>Some Achieve White Space</italic>, and Some Have White Space Thrust Upon Them

A few steps from Shakespeare's spiritual home The Globe Theatre in London, the U.K. regulator Ofcom is formulating its own well-crafted play based on TV white spaces (TVWSs). Such work comfortably fits into the Shakespearean analogy of “some achieve white space” through implementation of clever twists to make white space available while not causing harmful interference to incumbents, noting that the U.K. is extremely busy in terms of spectrum usage. This paper reports on some of the work of by our trial within the Ofcom TVWS Pilot, building key observations on beneficial usage scenarios for TVWS through link testing examples. It also particularly investigates performance of TVWS in terms of availability and capacity, through these scenarios and more generally, strongly focusing on aggregation of TVWS resources. A number of key observations result from this paper, some of which we highlight here. First, in the U.K., and in Europe in general where local DTT deployment characteristics and landscapes are similar to the U.K., TVWS has most benefit potential in below-rooftop receiver and indoor deployments. This is even more so if local white space device (WSD) deployment is extensive. Given this, we define and assess key baseline scenarios that we term as “mobile broadband downlink” and “indoor broadband provisioning” (akin to Wi-Fi or small cells in TVWS). We also argue comparison with other scenarios/topologies through parameter changes, and we further demonstrate the strength of TVWS for the indoor case through link performance tests. A second key observation is that good TVWS availability is achieved through the sophisticated regulatory approach of Ofcom, noting that the same approach to TVWS is harmonized across Europe through the ETSI EN 301 598 standard. However, this is affected by scenario: high power, high transmitter (e.g., 30 m above ground level) scenarios have a particularly reduced and variable availability. Further, high capacities are achieved by aggregating TVWS channels, especially if non-contiguous aggregation is supported; and moreover, profound implications for WSD RF design are derived based on such results, particularly under contiguous aggregation or channel bonding. A third key observation is that TVWS yields significant future potential, despite headwinds such as the WRC 2015 decision to allocate 694-790 MHz to mobile broadband on a co-primary basis in ITU region 1.

High Dynamic Range Cognitive Radio Front Ends: Architecture to Evaluation

AbstractAdvent of TV white space digitization has released frequencies from 470 MHz to 790 MHz to be utilized opportunistically. The secondary user can utilize these so called TV spaces in the absence of primary users. The most important challenge for this coexistence is mutual interference. While the strong TV stations can completely saturate the receiver of the cognitive radio (CR), the cognitive radio spurious tones can disturb other primary users and white space devices. The aim of this paper is to address the challenges for enabling cognitive radio applications in WLAN and LTE. In this process, architectural considerations for the design of cognitive radio front ends are discussed. With high-IF converters, faster and flexible implementation of CR enabled WLAN and LTE are shown. The effectiveness of the architecture is shown by evaluating the CR front ends for compliance of standards namely 802.11b/g (WLAN) and 3GPP TS 36.101 (LTE).

MINE GOLD to Deliver Green Cognitive Communications

Geo-location database-assisted TV white space network reduces the need for energy-intensive processes (such as spectrum sensing), and hence can achieve green cognitive communication effectively. The success of such a network relies on a proper business model that provides incentives for all parties involved. In this paper, we propose a Model of INformation markEt for GeO-Location Database (MINE GOLD), which enables databases to sell spectrum information to unlicensed white space devices (WSDs) for profit. Specifically, we focus on an oligopoly information market with multiple databases, and study the interactions among databases and WSDs using a two-stage hierarchical model. In Stage I, databases compete to sell information to WSDs by optimizing their information prices. In Stage II, each WSD decides whether and from which database to purchase the information, to maximize his benefit of using the TV white space. We first characterize how the WSDs’ purchasing behaviors dynamically evolve, and what is the equilibrium point under fixed information prices from the databases. We then analyze how the system parameters and the databases’ pricing decisions affect the market equilibrium, and what is the equilibrium of the database price competition. Our numerical results show that, perhaps counter-intuitively, the databases’ aggregate revenue is not monotonic with the number of databases. Moreover, numerical results show that a large degree of positive network externality would improve the databases’ revenues and the system performance.

Toward dynamic real-time geo-location databases for TV white spaces

Recent FCC regulations on TV white spaces allow geo-location databases to be the sole source of spectrum information for white space devices. Geo-location databases protect TV band incumbents by keeping track of TV transmitters and their protected service areas, based on each transmitter location and transmission parameters using sophisticated propagation models. In this article, we show that keeping track of both TV transmitters and TV receivers (i.e., TV sets) can achieve significant improvement in the availability of white spaces. We first identify temporal and spatial wasted spectrum opportunities due to the current approach to white space detection. We then propose our DynaWhite architecture, which is responsible for orchestrating the detection and dissemination of highly dynamic, real-time, and fine-grained TV white space information, based on both TV transmitter and receiver information. DynaWhite proposes the development of a new generation of geo-location databases that combine conventional geo-location databases with novel unconventional sensing approaches based on the detection of passive TV receivers using standard cell phones. We present a quantitative evaluation of the potential gains, reaching 24 extra 6 MHz channels in some cases, in white space availability for potential deployments of DynaWhite. We finally identify research challenges associated with the adoption of our DynaWhite architecture.

Pricing Model for TV White Spaces Channels With Different Priorities

A new type of TV white space (TVWS) channel called the high priority channel (HPC) has been proposed by the regulator of Singapore. The HPCs are TVWS channels that will always be available to unlicensed white space devices (WSDs) although a white space database (WSDB) provider may impose fees to WSDs for using HPCs. The HPC is of interest to WSDB providers since it creates a new business opportunity for them. In this letter, we investigate the optimal fee for using HPCs such that the WSDB provider achieves the maximum revenue. The solution of the optimal fee is provided in this letter. From this study, it is observed that WSDB provider should not always increase the fee when the total number of WSDs increases as our results show that sometimes lowering the fee to attract more WSDs to use HPCs actually increases the revenue.

Spectrum Reservation Contract Design in TV White Space Networks

In this paper, we study a broker-based TV white space market, where unlicensed white space devices (WSDs) purchase white space spectrum from TV licensees via a third-party geo-location database (DB), which serves as a spectrum broker, reserving spectrum from TV licensees and then reselling the reserved spectrum to WSDs. We propose a contract-theoretic framework for the database's spectrum reservation under demand stochasticity and information asymmetry. In such a framework, the database offers a set of contract items in the form of reservation amount and the corresponding payment, and each WSD chooses the best contract item based on its private information. We systematically study the optimal reservation contract design (that maximizes the database's expected profit) under two different risk-bearing schemes: DB-bearing-risk and WSD-bearing-risk, depending on who (the database or the WSDs) will bear the risk of over reservation. Counter-intuitively, we show that the optimal contract under DB-bearing-risk leads to a higher profit for the database and a higher total network profit.

Geo-location White Space Spectrum Databases: Models and Design of South Africa’s First Dynamic Spectrum Access Coexistence Manager

Geo-location white space spectrum databases (GL-WSDBs) are currently the preferred technique for enabling spectrum sharing between primary users and secondary users or white space devices (WSDs) in the very-high frequency (VHF) and ultra-high frequency (UHF) bands. This is true because technologies for making low-cost WSDs capable of autonomous sensing and detection of available white space (WS) spectrum are not yet feasible. This paper reviews the necessary enabling technical conditions to allow coexistence of primary and secondary systems in the VHF and UHF spectrum through a GL-WSDB approach. The practical implementation of South Africa`s first GL-WSDB was performed. Results of WS channels available from five cities in South Africa calculated from the implemented GL-WSDB was compared with a commercially available GL-WSDB and was found to be 68% similar. Additionally, results from the implemented GL-WSDB were compared with measurements obtained from field spectrum scanning campaigns at two different locations in Cape Town, South Africa, and was found to be 64% similar.

Interference-constrained coverage algorithms in the protocol and SINR models

A wireless network's design must include the optimization of the area of coverage of its wireless transmitters--mobile and base stations in cellular networks, wireless access points in WLANs, or nodes on a transmit schedule in a wireless ad-hoc network. Furthermore, with increasing densities of wireless network deployments, paucity of spectrum, and new developments like whitespace devices and cognitive networks, there is a need to study the computational efficiency of managing interference and optimizing coverage. This work presents new algorithms for computing and optimizing interference-limited coverage of wireless networks under protocol and Signal-to-Interference-and-Noise Ratio (SINR) models. For the protocol model we demonstrate lower bounds on computation of the coverage area for an $$n$$n transmitter topology. We first show that any offline computation has a run-time of $$\varOmega (n\log {n})$$Ω(nlogn), and any dynamic update takes $$\varOmega (\log {n})$$Ω(logn) time to locate transmitters whose coverage is modified and $$\varOmega (k)$$Ω(k) time to update $$k$$k affected coverage regions. We then demonstrate an extension of an offline algorithm to a dynamic algorithm that achieves the lower bound. For coverage in the SINR model, we demonstrate the difficulty of geometric direct computation, and report a flexible coverage area estimation method. We then propose a Random Hill Climbing method for optimizing the coverage area measure, and demonstrate the efficacy of this method by experimental comparison with the Nelder---Mead and exhaustive search optimization methods.

White space cognitive radio prototype and its test results for white space trial

This study introduces a white space device (WSD) prototype developed for the white space technology trial organised by Infocomm Development Authority of Singapore (Singapore Trial). A draft regulation was issued by the Infocomm Development Authority for the Singapore Trial. To meet the strict requirements on some performance criteria defined in the draft regulation, some solutions on designs of the system and algorithm are developed and adopted to the WSD prototype. The prototype has a complete design of hardware and software to realise real-time and intelligent operations of periodical spectrum sensing and database access, dynamic frequency selection and non-continuous transmission featured with low adjacent channel power leakage and power control. During the Singapore Trial, tests were conducted to check the above cognitive radio (CR) technologies and CR-enabled operations. The official test results verify the effectiveness of implemented system and algorithm designs.

Analyzing the availability of TV white spaces in dynamic broadcast

TV White Spaces (TVWS) are a promising frequency resource which will potentially enable various new wireless applications in the field of consumer electronics. Typically, the availability of TVWS is calculated assuming a static frequency allocation of traditional digital terrestrial TV (DTT) networks. In the present paper, additionally, a flexible frequency allocation of a Dynamic Broadcast system is analyzed. A realistic case study is depicted, comparing a traditional DTT network and Dynamic Broadcast with respect to the available amount of TVWS. The outcome indicates that the freed capacity by implementing Dynamic Broadcast can result in a significant increase of available frequency resources for white space devices, as long as an appropriate allocation strategy is chosen. The differences of individual network configurations are studied by means of computer simulations and conclusions are drawn with regard to the network optimization process of Dynamic Broadcast.

Enhanced the Accuracy of Specification of Maximum Permitted Emission Levels for TV White Space Devices

In this paper, we present a proposed geo-location database calculations which needs to perform in order to obtain high accuracy of maximum permitted emission levels for TV white space devices (WSDs) operating in the digital terrestrial television (DTT) frequencies. The study is mainly aimed at to analuze the impact of channel power condition in band ( ) and power out band ( ) for WSD for DTT reception in hilly environment under different altitudes. The proposed methodology for the calculation of such emission levels considers the effect of environment and hight of DTT reception. Both theoretical study and mathematical investigations are conducted in order to model and characterize such complex communication medium for WSDs. The propagated maximum permitted emission levels varies from one place to another due to time varying channel condition as a result of obstacles and distance between the transmitter and receiver. The study achieved according to the methodologies, results and recommendations addressed by the European Conference of Postal and Telecommunication administration CEPT. The comparison between proposed model and traditional one has been done by CEPT. The result shows that the proposed model with various altitudes in the hilly terrain environment obtain more accurate maximum permitted emission levels for WSDs, Which increase by 25.609 dBm and 25.61 dBm for and respectively at 100 altitude accordingly.

A Hybrid Pricing Framework for TV White Space Database

According to the recent rulings of the Federal Communications Commission (FCC), TV white spaces (TVWS) can now be accessed by secondary users (SUs) after a list of vacant TV channels is obtained via a geo-location database. Proper business models are therefore essential for database operators to manage geo-location databases. Database access can be simultaneously priced under two different schemes: the registration scheme and the service plan scheme. In the registration scheme, the database reserves part of the TV bandwidth for registered White Space Devices (WSDs). In the service plan scheme, the WSDs are charged according to their queries. In this paper, we investigate the business model for the TVWS database under a hybrid pricing scheme. We consider the scenario where a database operator employs both the registration scheme and the service plan scheme to serve the SUs. The SUs' choices of different pricing schemes are modeled as a non-cooperative game and we derive distributed algorithms to achieve Nash Equilibrium (NE). Considering the NE of the SUs, the database operator optimally determines pricing parameters for both pricing schemes in terms of bandwidth reservation, registration fee and query plans.

On the Benefits of Polarization for Fixed Area Television White Space Devices

The frequency spectrum offered by television white spaces provides an attractive solution to supplying extra bandwidth within large wireless local area networks or wireless backhaul links. However, it is still necessary to ensure for deployment purposes that the primary users, broadcasting services in this case, do not interfere with the white space devices but more importantly that the white space devices do not interfere with the television receivers or television re-transmitters. Given the increased use of vertical polarization as opposed to horizontal polarization in digital television transmission, this paper investigates the benefits of using horizontal as opposed to vertical polarization for white space devices operating within a restricted area. For white space devices such as access points or backhaul links placed at a high height, use of horizontal polarization will reduce their vulnerability to interfere with the primary user regardless of what polarization it has, while also they will be less susceptible to interference from the primary user in locations where vertically polarized television transmitters are deployed.

Technical Configuration of Portable/Mobile TV White Space Devices: A Conceptual View

As is known, to eliminate interference, the frequency reuse approach is followed in Digital TV planning similar to cellular network, avoiding the use of the same channel in two neighboring allotments. There are large areas where a certain group of TV channels are deliberately not used. They are called white spaces in TV spectrum (TVWS). Considering the great economical value of TV spectrum, it was proposed to use TVWS for low-power wireless networking on non-interfering (secondary) basis with the licensed (primary) DTV service. At the same time, restrictions imposed on white space devices (WSDs) to protect primary users should not devaluate spectrum for secondary use. The lack of knowledge about the locations of primary receivers as well as unreliability of estimation of the aggregate interference impact caused by the large number of secondary devices accessing the spectrum are reported to be among the key challenges for the use of TVWS. In our view, parameters for protection of primary system should be based on the determination of minimum separation distance, observance of which at a certain area could be ensured. The required shadow margin as well as multi-user margin will be calculated for such minimum safety range. To reuse spectrum efficiently mobile/portable WSDs should support dynamic power control ability which has to be a key role of sensing and operate with the lower power where TV signal is weak. Except of providing WSDs with a list of available channels, the geolocation database should contain recommended parameters for path loss calculations as well as minimum distances which could be ensured for a certain inhabited locality.

Database-Assisted Distributed Spectrum Sharing

According to FCC's ruling for white-space spectrum access, white-space devices are required to query a database to determine the spectrum availability. In this paper, we study the database-assisted distributed white-space access point (AP) network design. We first model the cooperative and non-cooperative channel selection problems among the APs as the system-wide throughput optimization and non-cooperative AP channel selection games, respectively, and design distributed AP channel selection algorithms that achieve system optimal point and Nash equilibrium, respectively. We then propose a state-based game formulation for the distributed AP association problem of the secondary users by taking the cost of mobility into account. We show that the state-based distributed AP association game has the finite improvement property, and design a distributed AP association algorithm that can converge to a state-based Nash equilibrium. Numerical results show that the algorithm is robust to the perturbation by secondary users' dynamical leaving and entering the system.

Dynamic usage of narrowband spectrum

We examine the potential for expansion of the white space spectrum sharing model in the 400MHz band. As opposed to UHF broadcast spectrum, which contains unassigned or idle segments known as white spaces, the 400MHz band is characterised by intensive licence usage. However, productive spectrum usage does not guarantee allocative efficiency, which would require knowledge of the highest value service for each licence. 400MHz frequencies are not priced on opportunity cost. It is therefore difficult to ascertain the economically efficient mix of services to deploy in the 400MHz band. Drawing parallels with the high-economic value revealed and generated through the operations of unlicensed white space devices in UHF broadcast spectrum, we identify untapped 400MHz spectrum capacity, which we refer to as narrowband spaces. Encouraging dynamic spectrum usage of narrowband spaces could, similarly to TV white space usage help realise the efficient allocation of the 400MHz band. However, the narrowband nature of the 400MHz licences and high licensing turnover imply a significantly different concept of dynamic spectrum access than that considered for TV Bands. The paper discusses regulatory implications and the type of services suited to exploit narrowband spaces.

IEEE 802.11af: a standard for TV white space spectrum sharing

Spectrum today is allocated in frequency blocks that serve either licensed or unlicensed services. This static spectrum allocation has limited resources to support the exponential increase in wireless devices. In this article, we present the IEEE 802.11af standard, which defines international specifications for spectrum sharing among unlicensed white space devices (WSDs) and licensed services in the TV white space band. Spectrum sharing is conducted through the regulation of unlicensed WSDs by a geolocation database (GDB), the implementation of which differs among regulatory domains. The main difference between regulatory domains is the timescale in which WSDs are controlled by the GDB, resulting in different TVWS availability and WSD operating parameters. The IEEE 802.11af standard provides a common operating architecture and mechanisms for WSDs to satisfy multiple regulatory domains. This standard opens a new approach to treat spectrum as a single entity shared seamlessly by heterogeneous services.

A Channel Allocation Algorithm Based on Geo-location and Positioning Accuracy in Geo-location Database

Abstract In this paper, we investigate how to acquire spectrum information for accessing the available TV white space quickly. It is known that the load of secondary device can be reduced by utilizing geolocation database. A channel allocation algorithm based on geo-location and positioning accuracy is proposed by using geo-location database in order to further reduce the secondary device's load and sensing cost. Based on the geo-location and positioning accuracy of white space devices (WSDs), the proposed algorithm first allocates the available channels to the WSD which locates outside the keepout region of TV stations. Then, it allocates the channels to the WSDs within the scope of protection of TV station, and in this case the WSD has to sense the allocated channels to determine whether they are idle using the energy detection algorithm. Detailed simulations show that the proposed algorithm effectively reduces the sensing costs and information feedback overhead, and improves the throughput and spectrum efficiency of the whole system.

An integrated low power system architecture for spectrum sensing enabled cognitive radios

Continuous rise in the number of users as well as the increased requirement of bandwidth per user has created a need to use the spectrum efficiently. Cognitive radios are solutions proposed to address the problem of using the spectrum efficiently. Regulatory bodies around the world, FCC included, have introduced specifications intended for cognitive radio applications. TV White Space devices, which operate in the spectrum holes caused by transition from analog to digital transmission, were the first targeted applications for cognitive radio specifications (IEEE 802.22, ECMA-392). However, to maximize the potential of the idea of cognitive radios it is desirable to be able to sense the spectrum across a wide band and accordingly transmit ‘smartly’. This paper presents a possible transceiver architecture meant for integrated solutions while providing tentative block level specifications for the proposed architecture. Existing spectrum sensing techniques are discussed and an integrated low power system architecture at the PHY level suitable for waveform-based spectrum sensing technique that utilizes co-operative spectrum sensing methods is proposed.

SenseLess: A Database-Driven White Spaces Network

The 2010 FCC ruling on white spaces proposes relying on a database of incumbents as the primary means of determining white space availability at any white space device (WSD). While the ruling provides broad guidelines for the database, the specifics of its design, features, implementation, and use are yet to be determined. Furthermore, architecting a network where all WSDs rely on the database raises several systems and networking challenges that have remained unexplored. Also, the ruling treats the database only as a storehouse for incumbents. We believe that the mandated use of the database has an additional opportunity: a means to dynamically manage the RF spectrum. Motivated by this opportunity, in this paper, we present SenseLess, a database-driven white spaces network. As suggested by its very name, in SenseLess, WSDs rely on a database service to determine white spaces availability as opposed to spectrum sensing. The service, using a combination of an up-to-date database of incumbents, sophisticated signal propagation modeling, and an efficient content dissemination mechanism to ensure efficient, scalable, and safe white space network operation. We build, deploy, and evaluate SenseLess and compare our results to ground truth spectrum measurements. We present the unique system design considerations that arise due to operating over the white spaces. We also evaluate its efficiency and scalability. To the best of our knowledge, this is the first paper that identifies and examines the systems and networking challenges that arise from operating a white space network, which is solely dependent on a channel occupancy database.