The Gamification of Dynamic Spectrum Access & Cognitive Radio Paul D. Sutton and Linda E. Doyle CTVR, The Telecommunications Research Centre University of Dublin, Trinity College Dublin, Ireland
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Abstract— Current wireless research is dominated by the need to satisfy ever-increasing demands for high-speed mobile wireless data. To satisfy these demands, researchers employ flexible, agile software-based radio systems which efficiently use the resources available to them. Dynamic Spectrum Access (DSA) and cognitive radio are key concepts for achieving these research goals. This paper presents Spectrum Wars, a game designed to inform about DSA and cognitive radio but which has also proven to be an effective tool in educating about many of the basic principles of wireless telecommunications. The game pits two teams of players against each other to create and maintain wireless connections in a dynamic environment in order to transfer data as quickly as possible between a transmitter and receiver. Built upon Iris, an open-source framework for software radio, Spectrum Wars is freely available to be recreated, reused, expanded and improved. The paper explains the background of DSA and cognitive radio and gives an overview of the Iris framework. It discusses related work including the MANIAC challenge and the DARPA spectrum challenge before presenting the game itself, examining the feedback of players and exploring the possibilities for future work and improvement.
cognitive radio to decision-makers (i.e. regulatory bodies /politicians). The paper is structured as follows. Section II provides some background on wireless communications, dynamic spectrum access and cognitive radio. Section III discusses some related work and draws comparisons with Spectrum Wars. Section IV introduces Iris, the software radio framework upon which Spectrum Wars was built. Section V presents the Spectrum Wars game itself. User feedback is examined in Section VI and Section VII concludes the paper. II.
DYNAMIC SPECTRUM ACCESS AND COGNITIVE RADIO
Most wireless systems use radio waves to transfer data between two points. To do so, they emit and receive electromagnetic radiation which travels in waves with a particular frequency and wavelength. Radio waves typically have frequencies between 3kHz and 300GHz and wavelengths between 100km and 1mm. The radio spectrum describes this set of frequencies which can be used by wireless systems.
Keywords—software radio, gamification, dynamic spectrum access, cognitive radio, learning through action, open source platforms
I.
INTRODUCTION
Gamification is the application of digital game design techniques to non-game problems. As Werbach notes, gamification as a business practice has gained increasing interest in the past number of years. Organizations are applying it in areas such as marketing, human resources, productivity enhancement, sustainability, training, health and wellness, innovation, and customer engagement [1]. The purpose of this paper is to present a game that has been designed to inform the player about the fundamentals of wireless telecommunications, explain dynamic spectrum access and to expose some of the features of a cognitive radio. The game is entitled „Spectrum Wars‟ and is designed for two teams who compete against each other to successfully transmit and receive data streams. The platform on which it has been developed is an open source platform that is also part of the educational experience. The game is intended for use by researchers who are new to the field as well as for use as a tool that helps explain complex concepts involved in the areas of dynamic spectrum access and This material is based upon work supported by Science Foundation Ireland under Grant No. 10/CE/I853 as part of CTVR, The Telecommunications Research Centre at University of Dublin, Trinity College, Ireland.
Fig. 1.
A wireless telecommunications signal.
The signals transmitted by wireless systems typically occupy a portion of the radio spectrum. The term carrier frequency refers to the frequency of the centre of the signal and the term bandwidth refers to the range of frequencies used (see Fig. 1). Signals transmitted with different carrier frequencies have different properties. For example, signals transmitted at low carrier frequencies typically travel further and are less affected by obstacles such as buildings and vegetation. Signals transmitted at higher frequencies don't travel as far and have less ability to pass through obstacles. The amount of information which can be carried by a signal depends on the bandwidth of that signal. A signal with a higher bandwidth can
carry more information than a signal with a lower bandwidth. At low carrier frequencies, limited bandwidth is available to transmit data. At higher frequencies in the radio spectrum, there is more bandwidth available and signals using wider bandwidths at these frequencies can carry more information. The portion of the radio spectrum with the best trade-off between transmission range and available bandwidth is between 300MHz and 3GHz. If two wireless transmitters transmit signals at the same carrier frequency, those signals will interfere with each other and receivers may not be able to successfully receive them. For this reason, different wireless systems use different portions of the radio spectrum (spectrum bands) to transmit and receive signals. Historically, countries have created spectrum regulators with responsibility for licensing the use of the radio spectrum in that country. In the US, this regulator was created with the adoption of the Radio Act of 1912, partly in response to sinking of the Titanic and the role which radio interference may have played in that tragedy [2]. Any person wishing to transmit radio signals must obtain a license from the regulator to permit them to do so. This license typically specifies the spectrum band to be used and places limits on the power of the signals which can be transmitted. In this way, interference between the signals of different wireless systems is avoided. While this command and control approach to radio spectrum management successfully avoids the creation of harmful interference, it can result in inefficient radio spectrum use and stunted wireless innovation. With the increasing demand for broadband wireless internet access, suitable radio spectrum has become a valuable resource. Spectrum licenses for new wireless systems and services are in great demand and fetch very high prices at auction [3]. Meanwhile, studies carried out worldwide indicate that although all available spectrum bands may be licensed, those bands are often severely underutilized [4,5]. In an effort to overcome this highly inefficient use of valuable radio spectrum, researchers and regulators have introduced the concept of dynamic spectrum access. Dynamic spectrum access refers to a mode of accessing spectrum that happens on a dynamic rather than static basis. Rather than being tied to specific carrier frequencies or spectrum bands, dynamic spectrum access wireless systems can flexibly adapt the carrier frequencies and bandwidths of their transmitted signals according to the environment in which they operate. In this way, they can opportunistically use spectrum bands which are not being used by other systems at that time and place. This approach results in much more efficient use of radio spectrum. The term cognitive radio may also be used to describe wireless systems which are capable of dynamic spectrum access [6]. A cognitive radio is capable of adapting the way it operates in response to observing its environment. These observations permit it to learn, plan and make decisions in order to achieve specific operational goals. Recent years have seen initial steps taken by regulators to permit dynamic spectrum access [7,8] and the emergence of the first commercial dynamic spectrum access systems. As the demand for wireless systems and services continues to grow, so
too will the need for greater spectrum use efficiency and dynamic spectrum access. III.
RELATED WORK
Related work in the field of gamification for telecommunications includes the MANIAC challenge for ad hoc networks and the DARPA spectrum challenge for agile, interference-tolerant wireless systems. The MANIAC Challenge [9] is a competition to better understand cooperation and interoperability in ad hoc networks. Competing teams of students/researchers come together to form a wireless ad hoc network, while simultaneously connected to a backbone of access points. The organizers generate traffic coming from the backbone, destined to somewhere in the network. A hop-by-hop bidding contest decides the path of each data packet towards its destination. Teams are judged based on how much of their relayed traffic reaches its destination. In 2013, 5 teams took part from North America, South America and Europe with winning participants from University of Alberta, Hamburg University of Technology, University of Bremen and University of Brasilia. In 2013, the Defense Advanced Research Projects Agency (DARPA) held the first DARPA Spectrum Challenge [10]. Participants in the challenge competed to demonstrate a radio protocol that can best use a given communication channel in the presence of other dynamic users and interfering signals. Teams used common radio hardware and designed their own software radios which used that hardware to communicate. These radios competed in head-to-head tournaments in a structured testbed environment. 90 teams from around the world registered for the challenge with 18 eventually selected to take part in the live competition. Winners of the preliminary event included Vanderbilt University and Northeastern University with the final competition scheduled for early 2014. Spectrum Wars borrows from both the MANIAC and DARPA spectrum challenges. However, while these competitions involve the design of dedicated communications systems for months before the live event, Spectrum Wars can be played by participants with no prior knowledge of the game or indeed of wireless communications systems. It is instead targeted at an educational environment, providing value for a wide range of audiences and serving as a showcase for ongoing research challenges and solutions. IV.
IRIS – THE SOFTWARE RADIO PLATFORM
Iris is a program and a set of libraries written in C++ which can be used to build software radios [11]. A software radio is a wireless system in which many of the tasks for generating a signal for transmission, or receiving and extracting data from a transmitted signal are carried out in software, often on generalpurpose processors such as those found in PCs or laptops. Here, a radio is any device which sends or receives data wirelessly (this could be anything from a digital TV receiver to
a 3GPP LTE modem used in modern mobile phones). One of the major advantages of building a radio in software is the flexibility it provides. In software, it‟s very easy to dramatically change the properties of the radio (for example, switching from a garage door opener to an 802.11 wifi access point or vice versa). Iris is designed to support and exploit this flexibility or reconfigurability. Iris is built using a plug-in architecture. Each plug-in is a library which does a specific job (e.g. data scrambling, OFDM modulation etc.) and which provides a generic API for the core Iris program to use. These libraries can be dynamically loaded at runtime and used within a software radio design. The main type of Iris plug-in is called a component. Components typically process streams of data. They have input and output ports and work by reading data from one or more of their inputs and writing data to one or more outputs. In Iris, components run within an engine. The engine is responsible for loading the component library, initializing the component, providing input data to it, calling it to work on that input data, taking output data from it, destroying it and unloading the library when the radio is shut down. Typically, a component in an Iris radio will run in a loop, repeatedly processing sets of data before it is unloaded and destroyed. Components can expose parameters which control how they operate and these parameters may be used to reconfigure a radio while it is running.
time, in addition to processing data coming from above and below. Stack component examples include complete MAC layers, network routing layers and data encryption layers. In order to run a radio in Iris, an XML configuration file is used. This file tells the core Iris program which engines will be used to create the radio, and which components will run within those engines. It also includes the initial parameter settings for each component. An example XML configuration file for a simple OFDM transmitter is shown in Fig. 2. This XML configuration specifies 4 Phy components which will run within a single Phy engine. In this radio, data is read from the file “testdata.txt”, modulated into an OFDM signal, scaled in magnitude and transmitted with a specific carrier frequency and bandwidth by a radio front-end, in this case an Ettus Research Universal Software Radio Peripheral (USRP). The radio front-end is responsible for actually transmitting and receiving the raw radio signals used by the software radio. The resulting radio can be seen in Fig. 3.
Fig. 3.
An Iris radio.
You can see that some initial parameter values are provided for some of the components in the radio. If a component has parameters which are not specified in the XML configuration, these are set to default values (as is the case for the OFDM modulator here). An XML configuration file specifies the structure of an Iris radio when it is initially loaded and run. However, it can also be used to reconfigure a radio while it is running. This can be done for example by changing the value of a parameter in the file, saving it and prompting Iris to reload it. Iris will compare the configuration in the file with that of the running radio, find that one of the parameters has changed and reconfigure that parameter as required.
Fig. 2.
An Iris configuration file.
Iris currently has two types of engines (and thus two types of components) – the Phy engine and the Stack engine. Phy components typically operate on a stream of signal data which flows in one direction from input to output and execute only when called by their Phy engine. Examples include modulators and demodulators, channel coders and decoders, data scramblers etc. Stack components on the other hand may support bidirectional data, coming both from above and below. They run their own threads and can generate sets of data at any
Using the XML configuration file, an Iris user can easily reconfigure a running radio. However, we often need a radio to reconfigure itself instead of relying on user input. This might be the case for example, when we wish to design a receiver which scans a set of channels for signals of interest. We have already discussed the main type of Iris plug-in – the component. The second type of plug-in which is used in the Iris architecture supports this self-configuring behaviour – the controller. Controllers are libraries which are loaded at runtime, just like components. However, a controller does not run in an engine and typically does not operate on streams of data. Instead, a controller has a global view of a running radio and can reconfigure any component in the radio at any time. With this global view, controllers can perform reconfigurations by adjusting parameter values in any running component. A simple controller could be used for example to scan frequencies in a wireless receiver.
Fig. 4.
An Iris controller reconfiguring a radio.
This scenario is illustrated in Fig. 4. Here, the radio consists of a Usrp front-end receiver, an OFDM demodulator and a file writer. The controller simply enters a loop, reconfiguring the receive frequency on the Usrp radio front-end and then sleeping for a set amount of time. Of course, with this design there is no mechanism for the radio to lock onto a received signal – it will simply continue scanning forever. Some mechanism is needed to allow a component to notify the controller to stop when a signal is received.
Fig. 5.
Reconfiguration within an Iris radio.
In Iris, this is what component events are used for. Building on the previous example, we could design the OFDM demodulator so that it triggers an event whenever an incoming signal is detected. This can be seen in Fig. 5. Controllers can subscribe to events on specific components in order to be notified when that event is triggered. In this way, our controller gets notified when the OFDM demodulator detects an incoming signal and exits the scanning loop, thus locking onto the signal of interest.
Fig. 6.
A Spectrum Wars control interface.
On the transmitter, the control interface directly affects the radio signal generated. On the receiver, the interface affects how the radio "listens" for incoming signals. The objective of the game is to transfer a fixed amount of data from the transmitter to the receiver as quickly as possible. The first team to successfully transmit the data wins. While the game is being played, a large screen displays the spectrum band being used. The Spectrum Wars display can be seen in Fig. 8. All signals being transmitted in the band can be seen clearly, along with the instantaneous carrier frequency and bandwidth of each team's receiver. A "waterfall" display shows how signals in the spectrum band change over time. In addition, the display shows a scoring bar for each team. The level of the scoring bar indicates the amount of data which has been successfully transferred by that team. In addition to the transmitters and receivers which are operated by players, there is also an independent transmitter operating in the same spectrum band. This is the primary user which randomly chooses a new operating frequency and sweeps to it every 5 seconds. The concept of a primary user is encountered frequently in the context of dynamic spectrum access. In a particular spectrum band, the primary user has priority and any other users can only transmit using spectrum which is not in use by that primary user. In our game, the primary user illustrates the concept of priority of access and also provides a highly dynamic environment where teams cannot simply remain at a single frequency but must constantly adapt and change the properties of their signal.
Using controllers, events and parameters in this way, we can build “smart” self-configuring radios which adapt to changes in their operating environment to maintain and optimize communications links. V.
SPECTRUM WARS
Spectrum wars is a game designed to inform players about many aspects of wireless communications. Two teams play the game, each with two team members. One team member operates a radio transmitter and the other operates the radio receiver. Both transmitter and receiver are implemented as software radios using Iris and players use a graphical interface to control their radio. The interface allows players to control the carrier frequency, bandwidth and gain (power) of their radios (see Fig. 6). These graphical interfaces are implemented as Iris controllers and so can be used to reconfigure parameters in any part of the running radio.
Fig. 7.
The Spectrum Wars layout.
Fig. 8.
The Spectrum Wars display.
Fig. 7 illustrates the layout of the game. Each team consists of a transmitter (e.g. TxA) and a receiver (e.g. RxA). A primary user transmits a fixed-bandwidth signal in the same spectrum band, periodically changing its carrier frequency. A display node observes all activity in the band of interest and represents it graphically on-screen. The game can be grasped by a wide range of players, from graduate students with a deep knowledge of wireless systems, software radio and dynamic spectrum access to early-stage undergraduate and high school students with a very limited understanding of wireless communications. For those without much knowledge of wireless communications, playing spectrum wars introduces the concepts of radio spectrum, carrier frequency and signal bandwidth. Players learn that interference can occur between signals transmitted with the same carrier frequency and that signals with a wider bandwidth can carry more information. The game illustrates the need for synchronization between a transmitter and receiver. In order to successfully transfer data between radios, both transmitter and receiver must use the same carrier frequency and bandwidth. During the game this synchronization can be achieved by using the display and through verbal communication between players. This process teaches that achieving synchronization between radios is not straightforward and is a key requirement for any wireless communications link. Furthermore, it's clear that achieving synchronization becomes more difficult as radios become more flexible and change their parameters more frequently.
For players with a greater knowledge of wireless communications, spectrum wars illustrates a number of important lessons and provides an opportunity to test various strategies. For example, players learn that as the bandwidth of a signal is increased, the power level of that signal at any given frequency also decreases. A signal with greater power is more likely to be successfully received than a signal with lower power. In order to transmit data while preventing the opposing team from doing so, a team may choose to use a high-power, narrow-bandwidth signal and move that signal to the same carrier frequency as that of the opposing team. The high-power signal may be successfully received while disrupting the lowpower, wide-bandwidth signal of the other team. Players also learn that, as the power of a transmitted signal is increased, the shape of that signal can become distorted. Unexpected signal components can occur outside the intended bandwidth of the transmitted signal. Advanced players may use this to their advantage, choosing a carrier frequency such that these out-ofband emissions interfere with the signals of the opposing team.
Fig. 9.
The Ettus USRP RF front-end.
Fig. 10.
Spectrum Wars in action.
I.
USER REACTIONS
Spectrum Wars was played and evaluated by three different groups of users. The first group consisted of a selection of researchers working in the field of communications and who understood concepts in cognitive radio. The second group of users consisted of undergraduate students who were new to the field and had no understanding of the area. The third group of users were from a wider audience. Our group of researchers required very little explanation and preparation in order to take part. They intuitively understood the control interfaces and the expected effect of each. Being accustomed to power spectrum displays and waterfall plots, they also quickly understood the main game display and set about creating wireless links and generating interference for the opposing team. Teams quickly started strategizing and using techniques which they were familiar with from their research. These including frequency hopping, where the carrier frequency of the transmitted signal was regularly changed to avoid interference. Verbal communication was used to coordinate between transmitter and receiver. In some cases, teams agreed upon a hopping sequence in advance of the game in order to minimize the amount of communication required during the game. Teams of researchers also intuitively recognized that by increasing the bandwidth of the transmitted signal, information could be transferred more quickly and the
team‟s score improved more rapidly. However, some teams were surprised to see the link between increased bandwidth and reduced power levels. This was exploited by other teams who used high-power narrow-bandwidth signals to create interference. The first version of the game permitted teams to use very wide-band signals, thus occupying the entire band of interest. However, this resulted in a “tragedy of the commons” situation where each team created and experienced a high level of interference, making it impossible to transfer data and ending up in a stalemate. This is, in fact, one of the issues with the shared use of a common resource. If participants can consume too much of the resource or if insufficient resources are available, the overall value of the resource can be reduced to zero. In response to this observed behaviour, the game was altered such that teams could only transmit signals with a bandwidth of less than 50% of the available spectrum band. In addition, the primary user was introduced to make the environment more dynamic and force teams to react and adapt to changes. Our second group of undergraduate students required more explanation and preparation for the game. However, once they became familiar with interfaces used to control and display the radios, they quickly started creating links and transferring
data. While these teams didn‟t strategize like our teams of researchers, they soon learned that wideband signals can be used to transfer more data and that carrier frequency and bandwidth must be synchronized between transmitter and receiver. Undergraduate teams were less likely to experiment with transmit and receive power levels, instead working with the more visually significant changes in carrier frequency and bandwidth. Undergraduate teams also had many more questions about the game, asking about the significance of the primary user and questioning the difference between the DSA scenario painted by the game and the environment for realworld systems. When asked for feedback, undergraduate players spoke of learning more about software radio and the flexibility which it can provide. They observed that the receiver in a wireless link has much more work to do than the transmitter and highlighted the difficulty of achieving synchronization. They especially enjoyed the experience of “feeling” and gaining a more intuitive understanding of the issues surrounding wireless telecommunications. When asked what they found difficult about the game, players often spoke about the challenge of balancing each of the parameters available to them to find a “sweet spot” where data throughput and tolerance to interference was balanced.
maintaining communications on the other. Finally, some of our research students suggested the creation of an automated team to play against. This team would not be controlled by players but rather would use some of the techniques developed for dynamic spectrum access within CTVR, detecting and avoiding other signals in order to create and maintain communication links.
Our third group of users came from a wider audience at an industry showcase where Spectrum Wars was deployed. These users typically found it more difficult to understand the key concepts behind the game and struggled more to create links and score points. However, users who observed one or two games before taking part themselves quickly got up to speed and started scoring points. These users were attracted by the large, colourful display where they could easily see how other players were performing and what approaches they were taking to win games. While users from the wider audience might not have understood the concepts behind the game as well as our researcher and undergraduate teams, they were still able to take part and enjoy it.
[1]
With the feedback we received from users were a number of suggestions for improving the game. One such suggestion was to isolate the teams from each other such that the verbal control channels could not be overheard. It would be interesting to observe the impact this would have on the game and could be implemented through the use of player headsets. A number of suggestions involved the creation of a more aggressive primary user. Rather than randomly choosing new carrier frequencies to move to, the primary user could detect the carrier frequency of a team's transmitted signal and move to the same frequency in order to create interference and force that team to adapt. Other suggestions involved the use of multiple primary users to create more interference and make the environment even more dynamic. Some users suggested that teams should be capable of transmitting more than one signal, in order to cause interference with one while
II.
CONCLUSIONS
Overall, we have found Spectrum Wars to be a strong mechanism for engaging users with the concepts of wireless telecommunications, dynamic spectrum access and cognitive radio. The game has received positive feedback from a wide range of audiences, from users with little or no knowledge of wireless communication systems to research students with experience in the fields of DSA and cognitive radio. We have received a number of invitations to showcase the work at other events and have identified a range of advancements that can be made to the system. The open-source nature of the game and of Iris, its underlying platform means that Spectrum Wars can be freely deployed, adapted and enhanced by anyone who wishes to do so [12]. REFERENCES K. Werback and D. Hunter, “For the Win: How Game Thinking can Revolutionise your Business,” Wharton Digital Press, Novemeber 2012, [2] Sharon Gaudin, “Titanic was high-tech marvel of its time”, http://www.computerworld.com/s/article/9226168/Titanic_was_high_tec h_marvel_of_its_time, visited 12/11/2013. [3] Ken Binmore and Paul Klemperer, “The Biggest Auction Ever: The Sale of the British 3G Telecom Licenses”, The Economic Journal, Volume: 112, March 2002. [4] M. McHenry and K. Steadman, “Spectrum occupancy measurements location 1of 6: Riverbend Park, Great Falls, Virginia,” Shared Spectrum Company, Tech. Rep., 2005. [5] T. Erpek, K. Steadman, and D. Jones, “Dublin, Ireland spectrum occupancy measurements,” Shared Spectrum Company, Tech. Rep., 2007. [6] Doyle, L.E., The Essentials of Cognitive Radio, Cambridge University Press, The Cambridge Wireless Essentials Series, pp240, April 2009. [7] FCC, “Second Report and Order and Memorandum Opinion and Order, In the Matter of Unlicensed Operation in the TV Broadcast Bands dditional Spectrum for Unlicensed Devices Below 900 MHz and in the 3 GHz Band”, November 2008. [8] Ofcom, “TV white spaces, A consultation on white space device requirements”, November 2012. [9] Emmanuel Baccelli, Felix Juraschek, Oliver Hahm, Thomas C. Schmidt, Heiko Will, and Matthias Wählisch, "The MANIAC Challenge at IETF 87", IETF Journal, Volume: 9, Issue: 2, November 2013. [10] DARPA Spectrum Challenge, http://dtsn.darpa.mil/SpectrumChallenge, visited 10/11/2013. [11] P. Sutton, J. Lotze, H. Lahlou, K. Nolan, S. Fahmy, B. Ozgul, T. W. Rondeau, J. Noguera and L. Doyle “Iris – An Architecture for Cognitive Radio Networking Testbeds,” Communications Magazine, IEEE Volume: 48 , Issue: 9 Year: 2010 , Page(s): 114 – 122. [12] The Iris Software Radio Project, http://www.softwareradiosystems.com/redmine/projects/iris visited 12/11/2013.
