Wireless networks can be categorised by their topology, with star topologies and mesh topologies being the most basic variants. In a star-shaped network, all nodes are connected to a central node which usually provides the Internet connection as well. In a mesh network, however, each node can be connected to multiple nodes, and the Internet connection can also be made via one or more nodes. The ZigBee Light Link network is a common example: many lighting fixtures are connected to a mesh network in order to increase its range. Usually, one of the ZigBee nodes (coordinator) serves as the Internet gateway.
Mesh networks are more complex, and forwarding messages can take much longer than in a star network. On the other hand, mesh networks offer the advantage that their range can be extended via multiple intermediate nodes (hops) without increasing the power of the transmitters. Furthermore, improved redundancy and reliability result from the fact that messages can take multiple paths through the network. Mesh networks can potentially consist of thousands of nodes.
Making communication systems interoperable is a real challenge and cannot be done without standardisation. Today, the Wi-Fi Alliance, the Bluetooth Special Interest Group (SIG) and the ZigBee Alliance are three organisations ensuring the interoperability of devices with wirelessly connectivity.
ZigBee
Conceived as a mesh network, ZigBee (IEEE 802.15.4) mainly operates in the 2.4GHz ISM band, but it supports the 868MHz and 916MHz ISM bands as well. While ZigBee can reach a data throughput of up to 250kbps, data rates tend to be much lower in practical applications. Short active phases separated by long power-down intervals enable several years of operation with a single coin cell.
The standard is maintained by the ZigBee Alliance. It defines the protocol layers above the 802.15.4 data link layer and provides several application profiles. ZigBee has proven particularly successful in smart grid applications.
Although an IP specification exists for the ZigBee standard, it is detached from the common profiles of the main application areas and has not reached widespread adoption yet. ZigBee networks require an application-level gateway for cloud connectivity. Implemented as a node, the gateway is part of the ZigBee network while it simultaneously executes the TCP/IP stack via Ethernet or Wi-Fi.
6LoWPAN
6LoWPAN (IPv6 over Low power Wireless Personal Area Networks) is intended for devices featuring very low power consumption and limited processing performance. It is meant to provide IoT connectivity even for very small devices. In September 2011, 6LoWPAN was formalized as RFC 6282 (Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks). The standard only defines an efficient adaptation layer inserted between the 802.15.4 data link layer and the TCP/IP stack.
There is still no comprehensive standard for the entire protocol stack. In addition, certification programs for 6LoWPAN solutions do not exist yet. Due to the multiple optional modes available in the data link layer, different manufacturers can develop solutions that are not interoperable at the network layer. Nonetheless, these solutions can be designated as 6LoWPAN networks. However, 6LoWPAN devices residing in different networks can communicate via the Internet as long as they use the same Internet application protocol. 6LoWPAN devices are also able to communicate with any IP-based servers or devices on the Internet, including Wi-Fi and Ethernet devices.
The 6LoWPAN communication protocol is still quite new. Initial installations operate in the 2.4GHz, 868MHz and 916MHz ISM bands. With the advantages provided by the 802.15.4 technology (mesh network topology, large networks, reliable communication and low-power operation) and by the IP communication technology, 6LoWPAN is in a favorable position to provide further impetus to the growing market of sensors with cloud connectivity, low-data-rate applications or energy-sensitive applications.
Wi-Fi
Based on a star-shaped topology, Wi-Fi networks use the access point (AP) as their Internet gateway. Until recently, it was quite expensive to provide Wi-Fi connectivity to devices with low processing performance (e. g. thermostats or household appliances) due to the size and complexity of the Wi-Fi and TCP/IP software. However, new devices and modules often include the Wi-Fi and TCP/IP software.
Wi-Fi is based on the IEEE 802.11 standard and was designed as a wireless replacement for the widely used, cable-based IEEE 802.3 Ethernet standard. Although the Wi-Fi technology mainly defines the data link layer of a LAN, it is also integrated into the TCP/IP stack. Using Wi-Fi therefore implies that TCP/IP is used for Internet connectivity.
Due to the high power consumption required in order to achieve high data rates and good coverage in buildings, Wi-Fi often does not lend itself for battery-operated devices. This problem can be solved by activating the radio section only for short phases separated by long power-down intervals. Products providing Internet connectivity can thus be operated more than a year with two AA-size batteries.
Bluetooth
Today it is virtually impossible to find a mobile phone without Bluetooth support. As a PAN technology (Personal Area Network), Bluetooth supports data rates up to 2Mbps.
Bluetooth Low Energy (BLE) was recently included in the specification. Commonly designated as Bluetooth Smart, this technology is intended for lower data throughput. It significantly reduces the power consumption of Bluetooth devices, enabling several years of operation with a single coin cell.
Bluetooth connects wireless accessories with smartphones or tablets and can be used as an Internet gateway. Wearable heart-rate monitors uploading their data to cloud-based servers or phone-controlled door locks sending status information to security companies are just two examples of the many IoT applications that can be implemented using this technology.
SimpleLink as a Comprehensive Solution
Texas Instruments' SimpleLink portfolio includes a comprehensive range of wireless connectivity solutions. Targeting the entire embedded systems market, the Wireless MCUs, WNPs (Wireless Network Processors), RF transceivers and range extenders provided within this product family facilitate the provision of IoT connectivity for any devices and applications.
SimpleLink covers more than 14 standards and technologies including Wi-Fi, Bluetooth, Bluetooth Low Energy, ZigBee, sub-1 GHz and 6LoWPAN. This range of products effectively supports manufacturers in the provision of wireless Internet connectivity to all kinds of designs for any conceivable application.
