A Study to Determine the Potential for Harmful Interference from TDD LTE Systems Operating in the 2300 – 2400 MHz Band into ZigBee Devices

Background Ofcom is currently examining the potential uses of the 2300 – 2400 MHz frequency band that is being released by the Ministry of Defence in the United Kingdom. Given the rising demand for broadband communications, one possible use is to support LTE systems in a time division duplex (TDD) arrangement. The band is directly adjacent to the unlicensed 2.4 GHz industrial, scientific and medical (ISM) band, which is used by a range of different local and personal area communications technologies such as WiFi, Bluetooth and ZigBee. Although systems operating within the ISM band do so on a non-interference, non-protection basis, it is still important for Ofcom to understand the impact on these systems of introducing new technologies into the 2300 – 2400 MHz band. To this end, Ofcom has commissioned Multiple Access Communications Limited (MAC Ltd) to perform a study into the impact of a TDD LTE system operating in the 2300 – 2400 MHz band on the performance of ZigBee systems operating in the adjacent ISM band. This study consists of a brief theoretical analysis of the performance of ZigBee devices based on published literature, followed by measurements performed on representative ZigBee devices. In this report we present the results of the theoretical analysis and also the results and conclusions from the measurement programme. Theoretical Analysis Ideally it would be possible to test application-specific ZigBee devices (eg, smart meters, lighting controllers, health monitors) and determine the manner in which they perform under different interference scenarios. However, the ZigBee specifications do not mandate a test mode for the purposes of making objective radio link measurements and, therefore, this was not a viable approach for our measurement programme. Instead we selected a number of development boards based on chipsets from leading ZigBee chipset manufacturers and these Commercial in Confidence 4/69 were tested as part of our measurement programme. As part of our theoretical analysis, we identified the leading chipset manufacturers based on the presence of their products amongst the 60 ZigBee Compliant Platforms listed by the ZigBee Alliance. From this group we chose development boards based on chipsets from four vendors for the purposes of testing. We also tested a ZigBee device in a Universal Serial Bus (USB) 'stick' format based on a chipset from one of these vendors to understand the performance of devices with internal antennas. Finally we tested the performance of a ZigBee-based home automation system to …