Wireless link solutions improve efficiency of medical applications

    Two things happened recently that inspired me to write this article. I have written several articles about field programmable radio frequency (FPRF) devices, which can become almost universal wireless devices. I just happened to be in hospital for two weeks, which gave me plenty of time to think about wireless applications in hospital wards.

    An important task for nurses is to record blood pressure, temperature, blood oxygen saturation and heart rate every 1, 2 or 4 hours. This task is called monitoring vital signs. In practice it involves scanning the bar code on the patient's wristband, connecting the device to the patient (if it is not already connected), and then manually recording the measurements.

    In the UK we have the National Health Service (NHS), which covers the entire country. Newspaper headlines about the use of technology to improve the efficiency of the NHS often focus on some major initiative, such as trying to create a unified software environment. In this case, the goal is to connect larger general hospitals, regional health centers, small community hospitals and family doctor offices (also known as general practitioners in the UK). However, there is a high degree of local autonomy under the NHS, and the hospital where I live has already begun to popularize electronic computers. However, the computer is mainly used to record medication use, not vital signs data, which still needs to be entered manually into paper medical records.

    If each patient has vital signs that need to be read, say, six times a day, and each reading takes 10 minutes, then this task will take the nursing staff 60 minutes per patient per day, which is a bit surprising. Adding a simple wireless link can quickly drive automation of this process.

    So I wondered, what exactly is preventing automation? Dedicated instruments seem to be an obvious obstacle. There are many major vendors that produce equipment, but they may not be interested in networking the machines. Security is another major factor. The

    dedicated machines actually used in hospitals are generally equipped with a data interface connector in the form of a 15-pin D-type RS-232 serial port. However, in the cluttered environment of a hospital ward, the idea of ​​connecting a cable to a wall socket every time is impractical. In other words, an external wireless communication module with a barcode scanner seems to be a viable "second best" option.

Implementing the wireless link

    Modern wireless systems provide a reliable link that can connect hospital equipment to local computers. Bluetooth Low Energy (BLE), branded as Bluetooth Smart, is a good example, with existing profiles for specific medical applications. The first major limitation of BLE is range, which can theoretically extend to 100 meters (330 feet), but may be practically limited to a single room when used in a building. The second is the spectrum it uses—the risk of interference in the crowded 2.4000 to 2.4835 GHz band.

    However, to fully realize the benefits of an integrated wireless system, sufficient reliability is required over longer distances so that any data read can be sent directly to a central control system at the nursing station, which involves the signal passing through several intermediate patient room walls and still being detected 100-150 meters away (300 to 500 feet). Lower RF frequencies, such as below 1 GHz, can provide better penetration of building materials. For this reason, the 915 MHz ISM band used in the United States, 433.920 MHz used in Europe, the Middle East and Africa (EMEA), and other VHF/UHF frequencies used in Asia all provide very good distance performance. The

    newly released FPRF devices are considered an ideal solution to solve the wireless part of the problem. The chip (model LMS7002M) is user programmable over an extended range from 100kHz to 3800MHz, making it easy to cover the frequencies of interest to the user. In addition to programmable frequencies, the user can also control bandwidth and gain in real time. The

    chip uses a dual transceiver architecture, which uses a low-power, cost-effective solution for the RF section from the input/output of digitized data to the modulated RF signal. The data input is in the form of a data bit stream representing the in-phase (I) and quadrature (Q) components of the modulation. These data streams are filtered, converted to analog signals, and then processed through separate I and Q paths, mixed with the programmed RF carrier frequency, and finally provide the modulated RF signal at the chip output.

    The function of the receiver is to receive the wireless signal and demodulate it into analog signals representing the I and Q components of the data. The receiver filters and amplifies the signal before converting it to a digital output stream.

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    In the application under consideration, the wireless network can be configured in a variety of topologies, but given the relatively short cycle time (i.e., once every hour), a random access mechanism is preferred. The most common configuration is called carrier sense multiple access with collision avoidance (CSMA/CA). In this case, when the system needs to send data, it first "listens" on the carrier frequency to ensure that the carrier frequency is idle before sending a packet. To facilitate this mechanism, the FPRF device includes a received signal strength indication (RSSI) function that can detect transmission signals on the wireless link. If the link is already in use, the device can be configured to wait for a preset period of time and then retry, or use a different frequency.

    To enhance the reliability of the system, the central control system can be designed to send an acknowledgment signal back to the vital signs monitor, and the signal can also be sent back on a separate RF channel. The transmitting node waits for an acknowledgment packet from the nursing station access point to indicate that the packet has been correctly received, decrypted, and passed the checksum check.

    There are many options for the transmission modulation mechanism. The simplest technology uses 2 bits per symbol and quadrature phase shift keying (QPSK), in which the carrier is modulated to one of four different phases with a single amplitude. QPSK supports low data rate transmission and is well suited for situations with poor signal conditions. In quadrature amplitude modulation (QAM), the phase is shifted to one of several different angles and amplitudes to define different bit positions in the constellation diagram, while data is carried up to 6 bits per symbol. QAM provides a modulation scheme that uses spectrum more efficiently, but only works under conditions with good signal-to-noise ratios, which is not suitable for this application.

    However, the latest transmission mechanism is called multiple-input multiple-output (MIMO), which is a complex configuration structure that uses two or more antennas separated by a short distance physically. MIMO technology can improve spectral efficiency and achieve diversity gain that can improve link reliability. A key attribute of MIMO signals is that they can provide more robust performance. The technology has been developed to cope with signal degradation caused by fading and interference, and can also be used in multipath transmission conditions. In multipath transmission conditions, the signal reflected from the building will form a distorted signal at the receiving end. The LMS7002M is MIMO-enabled and can provide the reliability and signal integrity required by medical applications.

The baseband function

    FPRF is controlled by the baseband chip. The main function of this baseband chip is to receive data from vital sign devices, time stamp them, and then group them into Ethernet packets for transmission. The chip will encode or decode the I and Q data streams and then load the LMS7002M through its JESD207 interface. It can program the FPRF to set the transmit and receive frequencies, gain, and bandwidth through the SPI interface. The

    baseband function is generally implemented using a field programmable gate array (FPGA), such as the Altera Cyclone V SE for cost-sensitive applications. These FPGAs have rich logic, memory, and DSP functions and one or two embedded ARM processors. The internal devices provided by the 32-bit ARM core can be connected to the logic matrix or execute external code. For example, the logic matrix, memory, and DSP units can be configured to execute control logic, packetize data, and generate modulation patterns for MIMO technology. These functions can be configured according to the requirements of the ARM core on the chip, and then the required combination of functions can be instantiated.

    The software running on the on-chip ARM core can also connect to a barcode reader to identify the patient. It is then used to find and load the encryption key unique to the patient. This key is used to encrypt the data to be sent to provide a high level of security. The core also provides device intelligence to calculate and convert digital signals from vital sign sensors. The chip can also connect to the front panel controller and display.

    This type of FPGA is configured at power-on. The configuration file is usually stored in an external non-volatile memory (NMV) (such as flash memory) and can be used to program the logic matrix and ARM core. The ARM executable code is also usually stored in the NMV, which helps the user to update the NVM with new barcodes and related key files in the hospital.

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Benefits for hospitals

    Using manual methods to read and record vital signs data requires nursing staff to spend about 60 minutes per patient per day. In the ward where I was a patient, there were a total of 40 beds, which means that this task requires about 40 nursing hours per day. If automation can save even 25% of this time, it can free up 10 hours of nursing staff work per day, which will directly save costs.

    The accuracy and availability of the transmitted data are equally important. Obviously, the automation process can avoid errors in transcribing readings, thereby reducing the possibility of misdiagnosis. In addition, reminders and alarm limits can be easily set on a "per patient" basis, so that any abnormalities in vital signs can be promptly alerted to the doctor, and remedial actions can be taken immediately. The results can also be recorded directly into a spreadsheet, and the data can be displayed in a tabular or graphical form. This approach can help doctors in their daily routine and show results over time.

    In the case of a vital sign monitor permanently connected to the patient, such as in the intensive care unit (ICU), a central controller can command the device to read the data when needed. This use model requires local smart devices to monitor the wireless link for command information. Signal encryption ensures that each monitor responds only to messages that are relevant to it and ignores messages from other devices.

Benefits for equipment suppliers

    Equipment manufacturers can add cost-effective features to their equipment to differentiate from competitors' products. They can demonstrate the efficiency gains brought about by innovation and the improved standard of medical care provided by the hospital. In addition, any marginal cost increase of the machine will be quickly offset by the savings in nursing man-hours.

    Equipment manufacturers can also provide complete system solutions, including vital signs monitors, central stations and report generators, thus bringing real practical added value to their customers.

Summary

    The solution proposed in this article can provide the latest electronic innovations that are worth using, thereby improving the efficiency of medical caregivers in difficult situations. This is a high-volume application scenario, and the time spent on collecting and collating data is quite long. In addition, I am sure there are many other applications in the field of medical devices that can benefit from a reliable and secure wireless link. What do you think?