Application and Prospect of Electricity Meter Billing Based on Bluetooth Wireless Technology

The existing manual meter reading method is labor-intensive and inaccurate, and can only reflect electricity consumption once a month or so. Its information feedback speed is far behind the instantaneous operation of power dispatching, so it is impossible to achieve the requirement that the electricity prices should be different during peak and low peak periods, making the manual meter reading method urgently need to be reformed. Some automatic meter reading schemes currently proposed use infrared transmission to transmit the electricity consumption information of digital meters to the receiving end (such as property management companies or power management departments) through telephone lines or local area networks. There are three problems with this type of scheme: (1) Too many infrared control signals in the home (such as multiple home appliance remote controls) will interfere with the accuracy of the data; (2) It is impossible to achieve real-time transmission using telephone lines, and the cost of the modem pool required by the receiving end is too high; (3) Using local area network transmission is limited to the need to reinstall the household lines of thousands of households and the long-distance transmission of digital signals.

The key to solving the above problems is to find a wireless or wired transmission method, and to transmit the power consumption information to the receiving end in a timely and accurate manner. Through the comparison of various methods, the combination of Bluetooth technology (BlueTooth) and cable television (CATV) equipment is a method that can avoid the above problems and achieve real-time control better. That is, using the characteristics of wireless transmission, short transmission distance (within 10m) and strong anti-interference of Bluetooth technology, the DC signal of the billing meter is first wirelessly transmitted to the uplink channel in the CATV line through the loaded BlueTooth chip, and then directly transmitted to the property company or the dispatching department of the power industry through the CATV network throughout the city and the countryside. After that, the digital signal is demodulated again and can be input into the computer to complete the automatic inquiry of the electricity bill of any user on the Internet. Of course, it can also be connected to the existing electricity bill collection network system, and connected to the dispatching command center of the power grid to form a complete electricity management network.

2 Anti-interference characteristics of BlueTooth

The Bluetooth chip is only 9mm×9mm and currently costs about 50 yuan. It can be directly embedded in a digital meter. It uses the ISM (Industrial, Scientific and Medical) frequency band of 2400~2483.5MHz. This is because there is no fixed signal interference from other systems in this band. At the same time, the band is open to the public and is valid worldwide. However, as an open band, any use of the ISM band will encounter unpredictable random interference sources (such as some household appliances, cordless phones, and car door openers) [1]. Therefore, different technologies are used to deal with interference sources from external and other Bluetooth users.

For example: frequency hopping technology is used to resist signal fading; fast frequency hopping and short packet technology are used to reduce co-frequency interference and ensure the reliability of transmission; forward error correction (FEC) coding technology is used to reduce the influence of random noise during long-distance transmission; FM modulation is used to reduce the complexity of equipment, etc. At present, the transmission rate of Bluetooth technology is designed to be 1MHz, and full-duplex communication is carried out in time division. Its baseband protocol is a combination of circuit switching and packet switching, which fully meets the real-time requirements of meter charging. One frequency hopping frequency sends a synchronous packet, each packet occupies one time slot, and can also be expanded to 5 time slots. Bluetooth technology also supports an asynchronous data channel, or 3 concurrent synchronous voice channels, or a channel that transmits asynchronous data and synchronous voice at the same time. The asynchronous channel supports asymmetric connections with a maximum rate of 72kbps and a reverse response rate of 57.6kbps, or a symmetrical connection of 432.6kbps, so that it can be flexibly selected according to the interference source.

Bluetooth technology enables devices to work without connections, provides the function of accessing the data network, and has peripheral device interfaces, which can form a specific small network (piconet), also known as a micro-network. The Bluetooth system uses packet-based transmission: the information stream is divided into slices (groups) and only one data packet is sent in each time slot. All data packets have the same format, starting with an access code, followed by a header, and finally a payload.

The access code has a pseudo-random nature, and direct sequence coding can be used in some access operations. The access code includes the micro-net master unit flag. On this channel, all packet exchanges are identified by the master unit flag. Only when the access code matches the access code of the micro-net master unit can it be received, thereby preventing a micro-net data packet from being received by another micro-net unit that happens to be loaded on the same frequency hopping carrier. In this way, the signals of different users between building groups can be easily distinguished.

3 Transmission between BlueTooth and CATV

CATV is a broadband network that covers urban and rural areas. Its uplink channel has abundant frequency band resources of 5 to 65 MHz. We use 34.45 MHz as the carrier frequency. Using the Bluetooth interface installed at the user's line end, we directly use the Bluetooth core protocol to define and provide a secure RF method to send it to the receiver of the property company or the dispatching department of the power industry management, and then modulate it into a digital signal to the corresponding computer. As shown in the figure.

Application of Bluetooth Technology in Electricity Meter Billing

The connectionless feature of CATV can transmit real-time data to the remote receiving end at any time on the Internet, which is an advantage that the PSTN and LAN network solutions do not have. As for how to distinguish the data signals from different users at the receiving end, we use the unique feature of each main unit mark. Although the carrier frequency of the data transmission of each user on the network is the same, the main unit mark is used as an identification code during CATV transmission.

Demodulation at the receiving end can be accomplished using existing cable modems, but this is costly. This can be achieved by modifying a dedicated addressable modem, that is, by changing its corresponding crystal oscillator and receiving circuit [2].

The demodulated digital signal is sent to the Oracle database based on the Windows platform, which can complete the corresponding data query, retrieval, and statistical summary, and directly provide the power dispatching department with a basis for decision-making, so as to realize the real planned electricity consumption and time-of-use electricity price requirements.

4 Outlook

If it is further extended to other digital metering devices, it can also be connected to an automatic water fee inquiry system, a gas fee inquiry system, a heating fee inquiry system, a home security alarm system, etc. The biggest advantage of combining Bluetooth technology with CATV over infrared control is that it can form a two-way transmission, because CATV is also a two-way network. For example, in heating control, if the user is temporarily unoccupied, the heating can be stopped at any time by sending a command to the designated Bluetooth chip at the receiving end. Of course, the heating valve of each household must be modified to be controllable.