21 22 September 2007, BULGARIA 113 Proceedings of the International Conference on Information Technologies (InfoTech-2007) 21 st 22 nd September 2007, Bulgaria vol. 2 AUDIENCE MEASUREMENT SYSTEM BASED ON BLUETOOTH CORDLESS COMMUNICATION Jivko Georgiev, Daniel Tzvetanov, Petya Kisheva-Vitanova, Simeon Hristov TEKOM-3 Industrial zone Microelectronica 2140 Botevgrad e-mail: tekom3@botevgrad.com Bulgaria Abstract: The paper describes the results from an investigation for using a new approach in implementing a peoplemeter system. Its essence is in using a wireless communication interface such as Bluetooth with a master module from the site of measured device and slave devices from the site of metering audience. Key words: peoplemeter, audience, wireless, cordless, Bluetooth INTRODUCTION One of the major issues for the nowadays television program producers is that they do not have enough information about the size and demographics of the television viewing audience. Such kind of information helps the television program producers to improve their TV programs and determine the correct price to be charged for the broadcasted advertising. In addition, the accurate information about the television viewing demographics allows the advertisers to target precisely the audiences of desired size, characteristics (e.g., income level, age, interests, etc.) and etc.. The configurations of the systems gathering audience information vary depending on the equipment used to acquire, process, and display television programs information in each home being monitored. The traditional audience measurement systems use client/server architecture with the client being the metering device and the server the data collection unit to collect data from the metering device. The main disadvantage for the today s systems is that they are working at fixed physical locations and hence they are giving inaccurate information about the people (audience) status, which are moving and are not
114 PROCEEDINGS of the International Conference InfoTech-2007 always in front of the working TV. A solution for gathering more précised information is to have a short range wireless system with a client device attached to the people body, and a server device, found in the TV set. In such a system, the metering device (server, also called peoplemeter ) accumulates the viewing and demographic data and typically use a proprietary data transfer protocol to communicate with a dedicated data collection unit (the client device, attached to the human body). The main advantage of such system are the following: 1) By measuring a human vital parameter (body temperature or heart rate), the client device always has information if the TV audience is active (and not sleeping, in the bathroom or doing some other work). 2) By having a wireless peoplemeter system, the audience is not wired (attached) to the TV, but can seamlessly move around, and as long is in range (which usually is the TV room range), the server knows that the client is there watching TV. EP1524809 [1] investigated different wireless systems and approaches for tracking the audience state (vital parameters) and proposed the Bluetooth wireless system described in this article. PROBLEM DEFINITION The problems that a typical wireless peoplemeter system should solve are the following: 1) High power consumption at the client side. The device should be able to work with a wearable battery for 24 hours. This requires power consumption not more than 5mA. 2) Wireless communication immunity. The wirelessly transferred data should be received with BER (bit-error ratio) not bigger that 0,01% in environment with powerful electromagnetic noises (microwave ovens, wireless access points and etc.). 3) Body vital parameter measurement. The client device should be designed in such a way, which can measure at least one vital parameter like body temperature or heart rate. PROBLEM SOLUTION In order to solve the wireless communication problem, a number of communication interfaces were investigated. The results are summarized in Table 1.
21 22 September 2007, BULGARIA 115 Table 1. Wireless interfaces comparison Speed IrDa AM/FM Bluetooth ZigBee RFID 802.11 115.2 Kb/s & 4 Kb/s & 16 Mb/s 100 Kb/s 1 Mb/s & 2 Mb/s 20 Кb/s & 40 Кb/s & 250 Кb/s 500 b/s 11 Mb/s & 54 Mb/s Frequency (800-900 nm) 433,9 MHz, 914,5 MHz 2443 MHz 868 MHz, 915 MHz, 2450 MHz 125kHz 148kHz 2450 MHz, 5100 MHz Modulation АSK PCM. PPM AM & FM FHSS DSSS ASK, FSK, PSK DSSS Range 1-4 m 20-100 m 10-100 m 10-70 m 0.1 1 20-150 m Noise immunity Only in sight High influence from side RF sources Very good Good Fair Good Security None None 64-bit or 128-bit key 128-bit AES+ None 40-bit RC4 Consumption 10 ma @ 35 ma @ 5 ma @ 15 ma @ None 300 ma @ Size Small Small Small Small Big Big The table shows that the IrDA interface is not applicable because it needs direct line of sight, the AM/FM and 802.11 interfaces are not applicable because their power consumption and size are too high, and the RFID would be difficult to cooperate with a vital parameter measurement. As a result, the only interfaces that are efficient for peoplemetry are the Bluetooth and Zigbee. Bluetooth was chosen because of its lower power consumption and higher noise immunity (coming from the very fast frequency hopping). Audience measurement system using wireless protocol such as Bluetooth uses a master Bluetooth module [2] from the site of measured device and slave Bluetooth devices from the site of metering devices. As a vital parameter it was chosen the
116 PROCEEDINGS of the International Conference InfoTech-2007 temperature because it is relatively easier to measure and analyze with electronic equipment, instead of heart rate, which requires differential electrodes and special type of filtering. The body temperature is measured directly from the Bluetooth module. It determines if the slave devices are active. Temperature, coming from the human body, is an indicator for active peoplemeter devices. Each slave device has unique identification code derived from the standardized Bluettoth address. The advantage of an audience measured system using Bluetooth protocol are: High electromagnetic noise proof Low energy consumption Possibility for simultaneously tracking more than one object Built-in unique tagging, through Bluetooth address Small operating range and a possibility for precise localization of the object under investigation Possibility for precise definition of the operating perimeter The limitations of the Bluetooth comunications are: Relatively long time for connection establishment. By applying some programming techniques for managing Bluetooth stack and communication channel, it is possible to reduce the aforementioned shortcoming and successfully use Bluetooth for effective audience measurement. EXPERIMENTAL RESULTS AND DISCUSSION The master Bluetooth unit, shown on Fig. 1, is used for locating slave Bluetooth units in the operating range. Fig.1 Master Bluetooth unit It is powered with filtered 3,3 Vdc. By optimization and using the Bluetooth low power modes (Park, Sniff and Hold), the power consumption current is reduced to less than 5mА. Connection of the Bluetooth module with head system is realized by means of UART interface. The Bluetooth module is programmed for work with bit rate BR=19,2 Kbps. Levels are 3,3V.
21 22 September 2007, BULGARIA 117 By means of UART-RS232 converter, the master Bluetooth module is able to transfer the information to a personal computer and thus its operation can be investigated with a COM Terminal. The prototype of the subordinate Bluetooth, being Bluetooth module with supplying jack, is shown on fig.2. The module is supplied with filtered 3,3 Vdc. It s size is 15mm x 23mm The course of action is as follow: The master Bluetooth module continuously scans the whole Bluetooth frequency range (79 channels), searching for secondary units. When it finds one, a connection is established and the master module starts sending the people information (the unique Bluetooth address and the temperature) over the UART interface. The information is updated in 1 second intervals. When the slave device goes out of range, the master device does not receive information any more. Fig. 2. Secondary Bluetooth module The slave Bluetooth device continuously sends its ID over the whole Bluetooth range, trying to indicate to the master device that it is there. When a master device is in range, the secondary device identifies itself and a connection between them is established. When no data is transferred during the connection, the slave devices go in low power mode. The data exchanged via the URAT interface is represented as ASCII symbols so it is possible for them to be visualized by means of PC terminal programs. The UART message separator is CR (Carriage Return) + LF(Line Feed) The address of the remote Bluetooth device is represented as HEX format, where the three Bluetooth address parts (LAP, UAP, NAP) are separated with the symbol :.
118 PROCEEDINGS of the International Conference InfoTech-2007 CONCLUSION We have investigated the use of various wireless communication techniques for registration and acquisition of data relating to TV audience rating measurements. As a result the Bluetooth interface was chosen as the most suitable and applicable. Using some software techniques it is possible to overcome the relatively high access time during connecting between the Bluetooth devices. Also, by efficient using of the Bluetooth low power modes, the power consummation can be reduced to less than 5mA, no matter if the slave device is in range or not.. REFERENCES [1] EP1524809 Method and system for determining audience members by using Bluetooth [2] Perseus Tech International Corporation BTM-CSR-FM4-C2 Specification