The Linx NT module is designed to simplify the addition of wireless communications capabilities at ISM frequencies from 902 to 928 MHz.
Medical and industrial wireless applications often involve machine-to-machine or machine-to-human communications. Typically using unlicensed frequencies in the industrial-scientific-medical (ISM) bands, these applications are considerably different from what most wireless users consider communications. Yet, these frequencies and the devices that support them are among the fastest growing applications for wireless technology—including for emerging applications in healthcare; in home and factory automation; in smart meters and wireless sensor networks; and in the wireless hospital of the future.
Most industrial and medical wireless applications are short range in nature, such as within a factory or a hospital, and many require low-power operation. Other important considerations for these applications include the potential of a wireless system to interfere with other electronic systems, or itself to be subject to interference; how the choice of operating frequency translates into desired propagation characteristics (for high reliability of transmissions through walls, for example); how long the system must be able to operate on a given power supply, such as a battery; the security of the transmission; and the amount of data or other content that must be transmitted and received. All of these factors help determine which wireless system or technology to select for a specific environment.
The healthcare industry received a recent boost with the United States’ Federal Communications Commission (FCC; www.fcc.gov) ruling to allocate additional spectrum for medical wireless applications, known as medical body area networks (MBANs). The use of this spectrum (from 2360 to 2400 MHz) for medical applications was supported by two large companies in the electronic healthcare industry: General Electric Healthcare (www.gehealthcare.com) and Phillips Electronics NV (www.phillips.com).
However, it was opposed by an even larger aerospace company, Boeing (www.boeing.com). Since this bandwidth was already occupied by aerospace applications—notably for flight testing—Boeing had initially blocked the use of this bandwidth for medical purposes. The positive ruling for the health-care industry comes after both sides submitted a joint proposal to the FCC on how the bandwidth could be effectively shared. The FCC’s rule aligns with its National Broadband Plan, which set the goal of advancing several specific “national purposes” including healthcare.
This ruling provides more available spectrum for the development of MBAN devices, typically health-sign monitors worn by a patient that detect and transmit information about a patient’s vital signals to a central monitoring station. The first 30 MHz of the newly available 40-MHz bandwidth is intended for indoor use (such as in hospitals) and will be regulated. The last 10 MHz can be used in any environment, including in the home.
“MBANs represent the next evolution in monitoring a patient’s health status,” says Dr. Richard Katz, Director of the Division of Cardiology at The George Washington University Hospital. “These wireless innovations can enhance patient safety by giving caregivers the ability to monitor many clinical measurements, wherever the patient is located.” Mike Harsh, Vice President and Chief Technology Officer at GE Healthcare, adds that, “The FCC’s ruling is the culmination of strong collaboration between the medical industry, regulatory officials, and aeronautical stakeholders. This is an important inflection point, as it enables advances in miniaturized wireless sensors leveraging the latest chip design and clinical measurement technologies. MBANs could significantly enhance quality and access to patient care, while supporting reduced costs.”
Prior to the availability of this bandwidth, the FCC had established several frequency bands for use by the wireless medical telemetry service (WMTS) for medical telemetry over radio, such as ECG waveforms. These bands include 608 to 614 MHz, 1395 to 1400 MHz, and 1427 to 1432 MHz. WMTS electronic devices are licensed by rule under FCC Part 95 guidelines—that is, individual licenses are not required for each product; they must only comply with the established regulations for frequency occupancy, transmitted power, spurious levels, and other parameters.
As emerging WBAN device may still have interference problems under certain circumstances with flight-data recorders and other transmitters in their band, WMTS devices have had some history of problems with higher-power digital-television (DTV) transmitters operating within their bands, notably in the lower-frequency channels. Effective WMTS designs require adequate filtering to remove adjacent-channel interference from nearby DTV transmitters. For hospitals considering the use of such devices for wireless medical telemetry applications, organizations such as American Society for Health Care Engineering (ASHE; www.ashe.org) can offer assistance. They perform risk assessments on potential interference to and from other electronic emitters.
Both GE Healthcare and Phillips are major suppliers of wireless healthcare products, such as the ApexPro® CH hospital telemetry system from GE for use in the WMTS frequency bands. It is designed to provide continuous patient surveillance, operating in both the 608-to-614-MHz and 1395-to-1400-MHz bands for flexibility and scalability. Patient information is available through a variety of viewing devices, allowing hospital staff convenient monitoring of patient vital signs. Phillips offers medical telemetry solutions for both the US and Europe, such as its 2.4-GHz IntelliVue Telemetry System (not for use in the US).
A somewhat smaller medical electronics supplier specializing in wireless electrocardiogram (ECG) monitors, Great Lakes Neurotechnologies (www.glneurotech.com), has developed a lightweight monitor for reading heart, brain, and muscle electrical activity. The firm’s BioRadio™ product provides 12 channels: eight for external sensors; three embedded channels for accelerometry, pulse oximetry, and pressure-based airflow; and an embedded DC auxiliary channel. The physiological monitor operates from 2400 to 2484 MHz and provides a line-of-sight (LOS) range of about 100 ft. It measures 5.25 x 2.50 x 1.10 in. and weighs 7.4 oz. with batteries. The operating voltage range can be configured from +750 µV to +2 VDC, while sampling rates can be configured from 128 to 960 Samples/s per channel. It is designed to operate continuously for 10 hrs. on batteries.
These wireless telemetry products require reliable but low-cost wireless technology, usually in the form of low-power integrated circuits (ICs). A number of IC manufacturers have responded to the needs of medical and industrial wireless electronic product developers with highly integrated transceivers capable of low-power operation in the WMTS, ISM, and other frequency bands.
Analog Devices (www.analog.com) offers a wide range of transceiver ICs for ISM-band applications through 2.4 GHz including its model ADF7021 narrowband transceiver IC for WMTS applications. It operates over frequency ranges of 80 to 650 MHz and 862 to 950 MHz supporting data rates to 32.8 kb/s by means of various modulation schemes, including two-state frequency-shift-keying (2FSK) and minimum-shift-keying (MSK) modulation. The chip can operate on voltages from +2.3 to +3.6 VDC, with only 0.1 µA leakage current in power-down mode.
This is a highly integrated device that requires only a handful of external components to fashion a complete WMTS transceiver. It features an on-chip voltage-controlled oscillator (VCO) and fractional-N frequency synthesizer, automatic frequency control (AFC) loop, and an on-chip temperature sensor with 7-b analog-to-digital converter (ADC) for readback of the sensor, as well as monitoring of battery voltage. The transceiver IC can set transmit levels from -16 to +13 dBm in 63 steps and provides receiver sensitivity of -130 dBm at 100 b/s with 2FSK and -122 dBm at 1 kb/s with 2FSK. It meets FCC Parts 15, 90, and 95 requirements for use in the US, ARIB STD-T67 requirements for use in Japan, and ETSI EN 300 220 requirements for use in Europe. It can be used across operating temperatures from -40 to +85°C.
The company also offers a device specifically for home and building automation, its ADF7022 transceiver (Fig. 1). Designed to operate at 868 to 869 MHz, it supports one-way and two-way communications at extremely low power levels. It runs on voltages of +1.8 to +3.6 VDC and consumes only 24.1 mA when transmitting at +10 dBm and only 12.8 mA in receive mode with the automatic-gain-control (AGC) circuitry active. Current consumption can be cut down as far as 0.75 µA in sleep mode. The chip is supplied in a 5 x 5 mm package.
Analog Devices also took a major step towards unleashing software-defined-radio (SDR) technology on any number of medical and industrial wireless applications. The technology allows radio frequencies and characteristics to change under software control. During the recent 2012 IEEE International Microwave Symposium (IMS) in Montreal, Canada, the company announced its collaboration with Avnet Electronics Marketing Americas (www.em.avnet.com) on the Zynq™-7000 Extensible Processing Platform (EPP), along with its own software-defined-radio (SDR) kit. The kit includes the FMCOMMS1-EBZ field-programmable-gate-array (FPGA) mezzanine card from Analog Devices, facilitating wireless radio design.
Silicon Labs (www.silabs.com) offers a diverse portfolio of devices for wireless portable medical products, such as its Si446x EZRadioPro® transceiver IC family for ISM-band use in medical monitoring, industrial control, and home automation applications. The low-power transceivers offer continuous coverage from 119 to 1050 MHz. The firm also strengthened its position in ISM-band products with the acquisition earlier this year of Ember Corp. (www.ember.com) and their 2.4-GHz wireless mesh networking solutions, including the EM300 series of system-on-chip (SoC) devices. Based on the ZigBee low-power 2.4-GHz protocol, these devices combine a 2.4-GHz IEEE 802.15.4 radio transceiver with a 32-b microprocessor, Flash memory, and random-access memory (RAM).
For industrial and medical wireless system developers who want a ready-to-use wireless subsystem, Linx Technologies (www.linxtechnologies.com) offers a series of transceiver modules that can simply be added to a higher-level design and integrated with some additional programming. For example, the firm’s NT module uses what the company calls its True Transparency™ interface to allow users to create a “wireless wire”for use at nonstandard data rates, with custom protocols, and user-selected encoding, such as pulse-width-modulated (PWM) or Manchester encoding. The module is completely hardware-configurable. Although programming is not required, the NT Series allows for communication and microcontroller programming over a UART connection, which lets the user implement a frequency agility scheme such as frequency hopping or listen before talk.
The Linx NT module (Fig. 2) operates at ISM frequencies from 902 to 928 MHz with transmit power levels from -15.5 to +12.5 dBm and receiver sensitivity from -102 to -113 dBm, depending on bit rate. The transceiver, which can be used with frequency-shift-keying (FSK) or Gaussian FSK modulation, provides data rates from 1 to 300 kb/s. It operates on supplies of +2.5 to +5.5 VDC, and consumes 15 mA current at 0-dBm transmit power and 19.2 mA current in receive mode, with less than 1 µA current in power-down mode. It is designed for operating frequencies from -40 to +85°C. To aid developers, the module is part of a master development system complete with two boards—each populated with a transceiver module for benchmarking and prototyping.
Anaren Integrated Radio (AIR) modules from Anaren (www.anaren.com) are designed for use as embedded or stand-alone radio transceivers for industrial control, meter reading, and building automation applications. They are based on low-power transceiver ICs from Texas Instruments (www.ti.com) and available for ISM frequency bands of 433 MHz, 915 MHz, 2.4 GHz, as well as dual-band operation at 868 and 915 MHz. For example, model A1101R04C is an AIR module based on the model CC1101 transceiver IC from Texas Instruments. The radio module measures just 9 x 12 mm and operates from 433.05 to 434.79 MHz. It offers receiver sensitivity of -112 dBm at a data rate of 1.2 kb/s and is certified to ETSI EN 300 220 for use in European applications. It operates from a supply at +1.8 to +3.6 VDC and draws only 15 mA current in receive mode and 200 nA in sleep mode. It includes a simple-to-use serial peripheral interface (SPI) bus.
For any wireless solutions to be effective in medical environments or in long-term factory-automation applications, they must operate at low power levels. The most recent version of Bluetooth (Version 4.0) is aimed at low-power consumption, such as in medical applications. Operating in the band from 2400 to 2480 MHz, this version of Bluetooth, also known as Bluetooth Smart and Bluetooth low energy (BLE), employs a new protocol stack designed to conserve power and to provide various power-saving modes.
The official Bluetooth website (www.bluetooth.com) has declared the new standard to be the future of medical wireless applications. The research firm IMS Research (www.imsresearch.com) has projected that Bluetooth Smart will be the most dominant wireless technology for medical devices in the years to come, with more than 4.7 million medical devices shipped in 2016 with Bluetooth Smart wireless capability. Whether it is Bluetooth Smart or another approach, it is clear that the use of wireless technology for medical and industrial applications is growing rapidly.