Technical Analysis of WIA in industrial Wireless Networks

Wireless Networks for Industrial Automation (WIA) is a high-reliability, ultra-low-power smart multi-hop Wireless Sensor Network Technology with independent intellectual property rights launched by the Chinese Emy of Sciences Shenyang Automation.

Industrial wireless network WIA Technology

Wireless Networks for Industrial Automation (WIA) is a high-reliability, ultra-low-power smart multi-hop Wireless Sensor Network Technology with independent intellectual property rights launched by the Chinese Emy of Sciences Shenyang Automation, this technology provides a self-organizing and self-healing intelligent Mesh network routing mechanism that can dynamically change application conditions and environments to maintain high reliability and strong stability of network performance.

The WIA technology is based on the IEEE 802.15.4 standard for short-range wireless communication and uses a free-band that complies with the requirements of the China Wireless Communications Commission, it solves the multi-path effects of various large devices and metal pipelines distributed in the factory environment on the reflection and scattering of wireless signals, as well as electromagnetic noise interference to wireless communication During Motor and Equipment operation, it provides highly reliable and real-time wireless communication services that can meet industrial application requirements.

By using industrial wireless network WIA technology, users can achieve "ubiquitous awareness" of the entire industrial process at a low investment and cost ", obtain important industrial process parameters that cannot be monitored online due to costs, and implement Optimization Control Based on these parameters to improve product quality and reduce energy consumption.

WIA technology is mainly used in petroleum, petrochemical, metallurgy, environmental protection, sewage treatment and other fields.

Select the five most important rules for industrial Wireless Technology

Wireless applications bring many new capabilities (such as implementing new monitoring, increasing the flexibility of existing devices, and reducing operation and process management costs) into the industries they serve. In turn, many different types of wireless technologies and applications are rapidly emerging to meet this growing demand.

It should be emphasized that there are some unique challenges in the industrial field, but many traditional wireless technologies are not designed specifically to address these challenges. These challenges include the ability to require high reliability, low system power consumption, good performance in a physical environment with severe RF interference, and of course cost-effective.

The increasing number of wireless technology applications has also become a challenge. A large number of wireless applications compete for the same RF space, resulting in too crowded spectrum and intertwined with existing challenges. To select a suitable and sufficient technology for a particular application to address these challenges, engineers need to consider multiple important metrics, including reliability, simplicity, efficacy, transmission range, and cost.

Reliability

Reliability refers to the ability of wireless systems to successfully complete communications in the presence of various industrial barriers. We can evaluate the reliability of the Wireless System Based on some characteristic parameters.

The RF spectrum used:Physical RF spectrum used for Wireless System Communication

Receiving sensitivity:Minimum signal level received by the transceiver for communication

Output Power:Capable output signal level

RF Agility:Ability to move in RF spectrum to avoid interference

Anti-interference degree:The ability to communicate in a given channel when interference exists.

The physical characteristics of RF wave make the spectrum usage highly dependent on the environment. The lower the frequency, the longer the wavelength, the less likely the liquid and reinforced concrete and other typical living and building materials to absorb.

However, in order to reduce interference with other wireless communication technologies, the RF spectrum and its use are highly regulated. In the RF spectrum, local or international organizations only Reserve several frequencies for licensed communications, known as industrial, scientific, and medical (ISM) frequencies. In these frequencies, the main frequency band is 2-4 GHz. In this frequency band, due to the short wavelength, the signal is quickly absorbed by the industrial environment that is not conducive to RF transmission. We need to pay more attention to other reliability evaluation indicators.

We can combine the reception sensitivity, output power and anti-interference degree to form a more macro and more important reliability indicator-the link budget. The link budget is the comprehensive value of the reception sensitivity, output power, and anti-interference degree. The higher the system's receiving sensitivity, the greater the output power and anti-interference degree, the higher the link budget. The higher the link budget, the less likely the RF absorption and RF interference will affect the system, and the greater the potential for reliable communication.

The receiver sensitivity and output power of the transceiver are strongly dependent on the components used for easy evaluation and comparison, however, anti-interference is largely dependent on the technologies used by wireless transceiver to improve its vitality. One of the best technologies currently used to directly improve anti-interference is direct sequence spread spectrum (DSSS) modulation.

In essence, DSSS modulation reduces data loss caused by signal interference by introducing forward error correction to transmission signals. In particular, DSSS compiles data into larger bit streams based on the Pseudo-Random Noise Code shared by the transmitter and receiver.

Figure 1 shows the process of compiling 8-bit data into 32-bit Chip data. Here, 4 pieces are equivalent to one bit.

These codes are modulated into RF signals and sent out. The receiver calls out the chunks from the received signal and reverse executes the DSSS encoding scheme. Although there is a Demodulation error due to signal noise or interference, we can reproduce the original data.

RF agility improves reliability through interference avoidance technology (in the RF spectrum, such as beating or moving. The more freedom the system moves in the spectrum, the more powerful it can find RF quiet environments with less interference. Including the pseudo-random Frequency Hopping scheme or algorithm-Based Frequency Hopping scheme, currently, various RF agile technologies are used to minimize interference by continuously changing the spectrum (see figure 2 ).

From the reliability perspective, a problem with frequency hopping is that in the busy RF spectrum, the system may unintentionally jump to a Channel containing strong interference. A more intelligent solution only performs frequency hopping when interference occurs. Once a quiet and non-interfering frequency is found, the frequency hopping is stopped.

Regardless of the VPC solution, rf vpc also relies on the RF spectrum and channel scale used. The RF spectrum used affects the available space for quick change. For example, due to frequency distribution constraints, compared with systems with higher operating frequencies, systems with lower operating frequencies have less room for quick change. For example, a GHz system has a MHz available spectrum, while a MHz system only has 26 MHz.

Channel width is also an important factor affecting the RF scalability. The smaller the channel width, the larger the space for quick change in the spectrum, the stronger the RF quick change capability, the stronger the capability to avoid interference and find the proper location between interference. For example, the channel width of a system based on 802.15.4 is 5 MHz and there are only 16 available channels. A system with a channel width of 1 MHz usually has 80 available channels, therefore, there are more available anti-interference locations.

Therefore, reliability is jointly determined by the link budget, the RF agile capability, and the RF spectrum used. In the same RF spectrum, the reliability of the wireless system is positively correlated with the link budget and the RF scalability.

In addition, although low-frequency technologies have outstanding performance in certain environments (for example, when a low-frequency technology is applied to factories distributed throughout water pipes ), however, compared with technologies that can increase the link budget and RF scalability, the technology is still inferior.

Simplicity

Ideally, wireless systems in the industrial field should be able to achieve the same functions as wired systems, and simply implement them. We should consider the simplicity from two different perspectives: one is from the perspective of engineers who design end products to replace wired products, and the other is from the perspective of users who install and use these products.

From the engineer's perspective, simplicity can be defined as the ease of designing, developing, and implementing wireless systems. At this point, simplicity involves the ease of use of the contained components, the auxiliary tools available for design and development, and the existence of certified components to eliminate or reduce the daunting Local Wireless authentication process. Flexible programmable technology allows engineers to adjust the designed system to the maximum extent, improving the ease of use of wireless systems.

However, flexibility and programmability often increase complexity; therefore, development environments and tools (including hardware and software tools) must be easy to use and understand. Tools with development and evaluation kits can help you fully evaluate and understand hardware and software. Ideally, engineers should obtain the complete wireless protocol stack and application sample library, help documentation and instance code to speed up the learning process.

From the user's perspective, simplicity involves the simplicity of setting up and activating wireless devices in the target environment and the impact on related business processes. For example, the system reliability and transmission range affect the test run failure rate of wireless technology. The system that has a trial run failure will eventually determine the optimal location and communication path through on-site inspection.

In addition, technologies that adapt to business processes allow users to quickly integrate the benefits brought by this technology into daily operations. These technologies include programmable flexible interfaces for monitoring and remote control wireless actuators and their support logic for automatic response systems. These interfaces are usually called dashboards, which can easily integrate the status information of wireless networks into existing reports and analysis processes.

In general, wireless systems must eventually become as easy to manage and use as wired systems. Qualitative evaluation of the system from the perspective of engineers and users helps to understand and achieve this goal.

Efficacy

Efficacy is a measure of the power consumption level of the wireless system. The traditional method to measure the advantages and disadvantages of wireless solutions is to measure the power consumption of the components used by the system, but this is not all the problem. For example, a high-reliability system with the lowest power consumption (sleep mode) for most of the time is generally more effective than a system with low power consumption but less reliable power consumption, these unreliable systems have less time in sleep mode, and more time in high-power forwarding mode. Therefore, reliability is an important indicator to measure the effectiveness of the system.

In addition to reliability, system behaviors such as active power management (dynamic control of output power) can also reduce power consumption and improve efficiency. A system that has been committed to reducing the output power to the lowest level required for communication is not only reliable but also highly effective. Although it is not a new concept for radio technology, it is a new concept to ensure that the system reduces system power consumption.

Transmission range

The transmission range is the distance from which radio signals can be transmitted and reliably compiled into data by the receiver. Considering the changing environment in the industrial field that is not conducive to RF transmission, the most important indicator for determining the technology to get the Optimal Transmission range is the link budget and reliability.

Wireless systems can also increase their link budget through on-chip and non-chip power amplifiers. If the above power amplifier is used during implementation, the transmission range of the highly reliable system will be larger. It should also be noted that the high-performance system only uses these amplifiers that lead to increased power consumption when absolutely necessary.

Other methods to extend the transmission range of wireless systems include using technologies such as relay, router, and peer-to-peer communication. Due to great uncertainty in latency and communication paths, these wireless protocol-based technologies increase complexity, increase power consumption, and reduce reliability.

Therefore, the best way to increase the transmission range while keeping all indicators unchanged is to increase the reliability or use a power amplifier to further increase the signal amplitude, which is limited by the local frequency usage regulations.

Cost

Because the wireless system involves many metrics, the lowest cost for a specific operating environment is not always the best. On the contrary, we should focus on the cost of the entire system. For example, if a high-cost contingency plan is used due to low reliability (for example, increasing the number of power amplifiers due to low link budgets and using a wired backup system, these costs also need to be included when evaluating wireless systems.

In addition, if the system can complete more functions and bring further benefits to the system in general, we should also consider the value of these new capabilities-in fact, this value should be deducted from the total cost of the system.

Assuming that all other indicators remain unchanged, a technical method to reduce the cost of the wireless system is to increase the value of the system to users or reduce the actual acquisition cost of the system. The component cost usually needs to be negotiated by the developer and supplier, but some application systems may have relatively low requirements on performance (such as flash memory, RAM, and processing capability), thus reducing the component cost.

For example, a complex grid network protocol requires more flash memory than a simple star network protocol, because the GRID network needs to allocate routes for communications throughout the network, A star network is a simple Point-to-Point Protocol. Only the hub actually needs a certain level of routing. This comparison is performed without changing other indicators. This is not a reasonable comparison if the grid scheme is more reliable or vice versa than the star scheme.

Reliability, simplicity, efficacy, transmission range, and cost are the five most important indicators for comparison, evaluation, and selection of Industrial wireless technologies. Each metric shows the advantages of a technology from a unique perspective. To ensure that the most suitable wireless technology is selected for a given application, we must examine these indicators one by one when comparing the advantages and disadvantages of different technologies.