It is predicted that there will be approximately 50 billion devices using wireless communication by 2020. According to data from the GSM Alliance, mobile handheld and personal computers account for only a quarter, and the rest are autonomous interconnects that communicate with other machines in a non-user-interactive manner. Our Internet is rapidly evolving into the World Wide Web - Internet of Things (IoT) for wireless devices.
Core features and capabilities of wireless network technologyWi-Fi is a communication technology based on the 2.4 GHz band. It excels at quickly transferring large amounts of data between two nodes, but at the same time consumes a lot of energy, and in a star configuration, each AP is limited to no more than 15-32 clients. .
Bluetooth is another 2.4 GHz technology for portable devices, primarily as a point-to-point solution that supports only a few nodes.
ZigBee shares the same wireless spectrum as Bluetooth and Wi-Fi, but is only used to meet the special needs of low-power wireless sensor nodes.
Table 1 summarizes the core features and capabilities of current wireless network technologies.
ZigBee: Optimized solution for wireless mesh networksBased on global standards, ZigBee is an open wireless mesh network technology. Unlike traditional network architectures, such as star and peer-to-peer, mesh networks use the lowest cost node to provide reliable coverage for all locations within a building (see the network topology option comparison in the figure below). ZigBee uses a dynamic, autonomous routing protocol based on AODV (Ad Hoc On-demand Distance Vector) routing technology. In AODV, when a node needs to connect, it will broadcast a route request message, and other nodes look up in the routing table. If there is a route to the destination node, it feeds back to the source node, and the source node picks a reliable number of hops. The smallest route, and store information to the local routing table for future needs, if a routing line fails, the node can simply choose another alternative routing line. If the shortest line between the source and destination is blocked due to wall or multipath interference, ZigBee can adaptively find a longer but available routing line.
Network topology comparisonFor example, wireless sensor networks based on the Silicon Labs EM35x Ember ZigBee SoC and EmberZNet PRO stacks provide self-configuring and self-healing mesh network connectivity that can extend hundreds or thousands of nodes in a single network. The rapid development of "ZigBee Certified Products" benefited from Ember AppBuilder, which hides the details of the protocol stack and focuses on the development tools implemented by ZAP (ZigBee ApplicaTIon Profiles). Through the graphical interface, developers can quickly select the properties required by the application, and then the AppBuilder automatically generates the required code.
To take advantage of the ZigBee network's flexibility, efficient debugging tools are needed. The complexity of mesh networks makes traditional network analysis tools (such as Packet sniffer) more difficult to use. In fact, since the packet may travel through multiple hops to the destination, many intermediate transmissions are beyond the scope of the analyzer. For this problem, the only solution currently is to use the Silicon Labs Desktop Network Analyzer. This analysis tool is powerful enough to display the full picture of each packet in the network in a graphical interface, and built-in protocol analysis. And visual tracking engine, developers can coordinate the tasks of network communication and devices.
In some cases, mesh networks are not a good choice because node density is too low to provide effective failover support. For example, a road or rail network topology requires nodes to be deployed at wide spans along narrow paths. Similarly, the campus's external facilities are too sparse to adopt a mesh network. In these environments, star topology combinations can span longer distances and are therefore more reliable and appropriate.
Sub-GHz: Ideal for long distance and low power communicationWireless propagation is inversely proportional to frequency, and sub-GHz RF is more advantageous in terms of low power consumption, long distance communication or wall penetration. For many applications, 433MHz is a global replacement for 2.4GHz (but Japan does not allow it for wireless applications). Designs based on 868MHz and 915MHz are available in the US and European markets. There are many frequency bands available that are not authorized or require authorization. For system integrators, you can choose to optimize performance in certain areas or with utility companies designing systems in a wide area. In this diversification, the sub-GHz band has less spectral interference than the 2.4 GHz band. A frequency band with less interference can improve the overall performance of the network and reduce the number of retransmissions in transmission.
Third-party and standards-based network stacks are available for sub-GHz radios, but many vendors still choose proprietary solutions to address their specific needs. Many wireless protocols face a problem in that the interface constantly activates "listening" traffic in the network. Data transmission consumes more energy than data reception, but the emissions are short-lived and have long intervals, so long-term average energy consumption is usually lower. In many wireless protocols, the receiver does not know when the message will arrive. Therefore, it is necessary to keep listening so that no data is lost, so even if there is no message, the receiver cannot completely turn off the power consumption. This situation will limit the battery autonomy of the node and require periodic replacement or charging of the battery.
Sub-GHz transceivers, such as the Silicon Labs Si446x EZRadioPRO IC, support a frequency range from 119MHz to 1050MHz, a link budget of up to 146dB, and only 50nA of current consumption in sleep mode. To mitigate the effects of multipath fading, the EZRadioPRO chip supports dual antennas and integrates antenna diversity logic algorithms within the chip. By combining frequency hopping and clock synchronization techniques, system integrators can implement a sub-GHz network spanning several kilometers between the coordinator and the end node, while the end node can operate for more than a decade with a single battery. This allows system integrators to reliably cover specific areas with a small number of coordinators and place the end nodes where the main power supply cannot be connected.
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