Wireless technologies in licence-free bands

What technologies are good for what product?

More and more applications are utilising the benefits of wireless communication. Users are getting used to the comfort of wirelessly connected devices. A number of licence-free bands may be used for a variety of these applications. When selecting the right wireless technology to be used in a specific application, a range of different features have to be considered.

The first choice may not always be the overall optimum choice

Some of the features to be considered first are achievable bandwidth, range, implementation and production cost. Additional considerations related to the applications include the required quality of service and the security aspects. Does the application require data and/or voice capability? The most obvious choice may not always be the overall optimum choice. You should consider the maturity of the technology candidates and the interference level in the used environment.

What else to consider

In the ISM bands, multiple devices are competing for the same spectrum. Local regulation must also be given a thought, e.g. the 2.4GHz ISM is the main part of theaccepted worldwide. What is the system topology? Is the main part of the communication between master and slave or does the main part of the communication take place between multiple devices. You should also consider whether interoperability with other devices or applications is needed.

An overview of the main features of different wireless technologies:

The traditional DECT operates in a protected  frequency band at 1.9GHz. Derivatives of DECT operating in the 900MHz, 2.4GHz and 5.8GHz ISM bands utilise either frequency hopping spread spectrum (FHSS) or dynamic channel allocations (DCS). In the protected 1.9GHz band, the technology can provide a high quality of service due to the highly specified radio access and management procedures. Where local regulations do not allow usage of the 1.9GHz band, the ISM bands may be used. Current technology seems quite mature thanks to highly optimised chipsets showing good performance, low power consumption and low cost.

The main strength of DECT is its capability to support multiple voice duplex voice channels and its packet data capability (DPRS). For example the RTX developed Cordless Voice Module (CVM) also has limited data capability.

Bluetooth

The main strength of Bluetooth is that it is a globally accepted, low-power and low-cost technology. It is intended for use in wireless personal area networks. For such a range of applications, profiles have been defined allowing devices from different vendors to inter-operate.The technology is available in highly optimised modules from multiple vendors. It is primarily intended for data applications, but has voice transfer capabilities as well. Although current chipsets and implementation seem to perform well and are maturing, there are still some basic improvements to be added to the Bluetooth specification.

802.11 a/b/g

The WLAN IEEE 802.11 technology family operates in the 2.4GHz and 5.2GHz bands. It is a true network technology that can provide high data throughput. It can be seen as a wireless version of the well-known Ethernet technology and as such it has very limited quality of service capability. Basically, it does not support voice transfer, although it may carry VoIP services. The technology is constantly being improved and standardisation is evolving with new variants and enhancements. Because the main focus is on high performance, power consumption and cost are significantly higher than other technologies discussed.

Others

The above-mentioned wireless technologies make up the most accepted and available technologies today, although new technologies are appearing on the horizon. These include Zigbee™ and standards from the IEEE 802.15™ working group. These are still very immature technologies and lack generally available silicon