RF Design: MBAN: Questions & Answers
Question: Why does the FCC allow the 2390-2400 MHz portion of the spectrum, which is allocated for home use, allow higher transmitter power (20 mW) compared to the rest of the band?
Answer: The higher TX power is intended to provide whole home coverage, with margin, in case the patient fell on the device and blocked the signal, to minimize potential for interference from adjacent band WiFi and BT devices.
Question: Will the performance of WiFi, Bluetooth and ZigBee devices be degraded by operation of nearby MBAN devices as the two frequency bands are adjacent?
Answer: It depends on the transmit power and relative separation between devices. The Electronics Communications Committee (ECC) is currently drafting a Compatibility Study between MBAN devices and other systems operating in the same or adjacent bands. This should be available sometime soon. Commercial single chip transceivers such as the CC2530 from Texas Instruments have a blocking/desensitization specification of about -32 dBm at 20 to 50 MHz offsets. This should allow for fairly robust radio performance, however, close proximity to high power devices such as WiFi routers could present a problem. Further rejection can be provided by the use of narrow bad SAW filters. These are currently available for the 2.4 MHz band only, although similar devices for the MBAN frequencies may be available in the future.
Question: Where can I find out more information on the proposed European requirement for MBANs?
Answer: ETSI has published a Technical Report that addresses this: ETSI TR 101 557 V1.1.1 (2012-02) “Electromagnetic Compatibility and Radio Spectrum Matters (ERM); System Reference Document (SRdoc); Medical Body Area Networks (MBANSs) in the 1785 to 2500 MHz range”. This can be downloaded from the ETSI Publications Download Area here.