In this record we noted NIHON KOHDEN (日本光電) Digital Telemetry System is still using the FSK modulation technique which is one of the oldest method of sending a digital signal using analog RF wave.
NIHON KOHDEN Life Scope Digital Telemetry System is found still using FSK modulation
According to technical data provided, we are surprised to find Nihon Kohden telemetry's underlying technology is still the Frequency Shift Keying modulation. We found the demand is mainly coming from the protectively-isolated domestic market in Japan, where there is government subsidy for the use of telemetry for patient care; the manufacturer is obviously not pressured to upgrade the outdated technology.
The Frequency Shift Keying modulation is commonly referred in short as FSK and one of the oldest method of sending a digital signal using analog radio wave as carrier.
Modulation is the method to put digital information onto a radio wave; since the radio wave is carrying the information needed to a receiving end, a radio wave carrying information is also known as a Carrier Wave. Demodulation is the reverse process by extracting the digital information from the analog carrier wave at the receiving end.
The Frequency Shift Keying modulation is commonly referred in short as FSK and one of the oldest method of sending a digital signal using analog radio wave as carrier.
Modulation is the method to put digital information onto a radio wave; since the radio wave is carrying the information needed to a receiving end, a radio wave carrying information is also known as a Carrier Wave. Demodulation is the reverse process by extracting the digital information from the analog carrier wave at the receiving end.
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| The first digital telemetry system from NIHON KOHDEN |
As shown above, digital telemetry was first introduced by NIHON KOHDEN in Digital Cardiac Telemetry System WEP-8430, which was launched in February 1991. The modulation method was stated as FSK (i.e. Frequency Shift Keying). The modulation method is no different from current specification.
During the 1990s, the disruptive Digital Revolution pushed back by decades the technological progress of NIHON KOHDEN, whose strength was mainly in analog electronics and the company was no longer able to compete in foreign markets as a result! The WEP-8430 Digital Cardiac Telemetry System would have been PC-based by foreign standards but it was not, and the device had only limited processing power and storage. The minimal processing power of the WEP-8430 Digital Cardiac Telemetry System could only analyze one single ECG lead (of choice) for arrhythmia events and had not enough capability for monitoring patients with heart conditions.
The first digital telemetry system was introduced to have better noise immunity from the environment compared to older analog telemetry system, and the WEP-8430 Digital Cardiac Telemetry System was designed primarily for the need of the domestic market in Japan, which is a protective market insulated from the high-tech foreign competitors with advanced RF and digital know-how. The WEP-8430 Digital Cardiac Telemetry System for said reason did not meet the requirements and expectations of the export markets. Most foreigners only adopted the use of NIHON KOHDEN telemetry products through the Official Development Assistance (ODA) projects sponsored by the Japanese Government.
NIHON KOHDEN Frequency Shift Keying does not do Frequency Hopping
It
occurred some sales people are confused with the two terms and used
them interchangeably. It should be clarified Frequency Hopping and
Frequency Shift Keying are two very different technology for different
purposes.
Frequency Hopping is much more complicated. This technology was first developed by the military to keep changing the carrier frequency to avoid enemy eavesdropping and jamming; in telemetry application, the technology is deployed to continuously seek a new carrier frequency to get a good signal from a noisy RF environment.
| Frequency Hopping | Frequency Shift Keying |
|---|---|
| A method to pick up a better signal against a given background environment |
A method to use a Radio Wave for sending out data in the air |
| Hopping means jumping from one Carrier Wave Frequency to another Carrier Wave frequency |
In Frequency Shift Keying, the frequency of the Carrier Wave is NOT changed |
How does Frequency Shift Keying modulation work?
Frequency Shift Keying is a simpler version of your home FM radio, what the modulation does is to slightly shift the instantaneous frequency of the Carrier Wave to code a signal. It is not hopping from one Carrier Frequency to another in this case; the Carrier Frequency remains the same, the shift from the Carrier Frequency is very small and well within the bandwidth of the oscillator circuitry. In the case of FM radio, the signal is a complex analog audio wave comprising component sine waves ranging from 20Hz to 20KHz of varying amplitudes and we have a complex deviation spectrum but the Carrier Frequency is not changed.
FSK is simpler than FM radio, and the simplest FSK is binary FSK which is the method adopted by NIHON KOHDEN. There are only two shifted frequencies corresponding to the "1" and "0" logical level of a digital signal.
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| The meaning of "keying" in communication |
The image below illustrates the mechanism of Frequency Shift Keying (FSK). When the signal data is "logical "1" a fixed amount of frequency change (∆f) will be added to the the carrier wave frequency (Fc) resulting in a Carrier Wave that has frequency of (Fc+∆f) and when the signal data is logical "0" the Carrier Wave will have frequency of (Fc-∆f). The SHIFT in frequency is VERY SMALL and only a few kilo-Hertz (kHz) while the Carrier Wave is in HUNDREDS of Mega-Hertz (MHz), i.e. Fc >> ∆f, meaning it is well within the bandwidth of a FSK telemetry receiver tuned to the Fc carrier wave. The frequency change in Image 1b is exaggerated for purpose of illustration.
If only Fc is received but there is no ∆f, it means no data such as the patient is not hooked up.
If only Fc is received but there is no ∆f, it means no data such as the patient is not hooked up.
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| Illustration of Frequency Shift Keying modulation |
The technique in the NIHON KOHDEN transmitter is to convert the ECG signal obtained from the human body into a serial digital data. The serial digital data is then used to FM-modulate a voltage-controlled oscillator and radiate into space.
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| The inside schematic of a FSK transmitter |
With continued improvement in the electronics industry, it is now possible for example to effect Frequency Shift Keying modulation and demodulation completely based on software instead of traditionally relying on hardware; such advancement makes for much lighter and compact FSK transmitters and receivers. Thus, it should not surprise you to see products using this old technology becoming more compact than ever.
Current telemetry transmitters are all still using FSK modulation
Current telemetry transmitters (ZS-500 series, ZS-600 series, ZS-900 series, ZM-500 series, ZM-900 series) are no different from first generation digital telemetry products from NIHON KOHDEN, with product progression not based on wireless technology but on improving compactness and screen display on transmitter. One well-known limitation of a FSK telemetry transmitter is only allowing one-way data-sending from Transmitter to the Central Monitor but not the other way round, an obvious weakness is its low data rate.
The NTX telemetry transmitter is heavy and tiring for many patients
Image 1b shows current NTX Telemetry Transmitter using FSK Technology offered by Nihon Kohden America; there are two models namely ZM-540A and ZM-541PA. The ZM-540PA operates in the range (608.025- 613.975)MHz while ZM-541PA operates in the range (1395.025- 1431.975)MHz.
In terms of physiological data, the transmitters send out ECG, Respiration and Pulse waveform plus the SpO2 and NIBP digital values. On the screen of the transmitter, the digital data are displayed with one waveform showing either ECG or the pulse wave. The ZM-541/ 540 have a choice to make use of a 6-lead ECG cable for ECG measurement.
In terms of physiological data, the transmitters send out ECG, Respiration and Pulse waveform plus the SpO2 and NIBP digital values. On the screen of the transmitter, the digital data are displayed with one waveform showing either ECG or the pulse wave. The ZM-541/ 540 have a choice to make use of a 6-lead ECG cable for ECG measurement.
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| The heavy NTX transmitter is tiring for many patients. Patients should not be burdened with a heavy NIBP pump |
Central Monitoring
Central monitoring can be configured using PC-based CNS-6201 Central Nurse Station with ORG-9700
Multiple Patient Receiver Unit. The number of receivers in the ORG-9700
is scalable and up to 8 receivers can be installed as option.
Additional ORG-9700 Receiver Unit can also be added if deterioration of
signal/ noise ratio remains tolerable. Note the more compact ORG-9100
Multiple Patient Receiver is not configured here because it does not
have a CE Mark Certificate.
Citing a resale notice containing items CNS-9701A, ORG-9700A and NTX ZM-940PA
originally sold by Nihon Kohden America, a typical network is drawn up
to show what a physical FSK digital telemetry network infrastructure looks like.
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| The network example for a small coverage area utilizing the sales items listed below |
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| A sales notice for a FSK telemetry system using CNS-9701A as telemetry central monitor for the US Market |
The PC-based Central Monitor CNS-9701A can be substituted with the latest PC-based CNS-6201 Central Monitor or the Prefense EDNS-9000 series
Central Nurse Station. In case you have difficulties in understanding
what they are promoting, the Prefense Nurse Station is simply monitoring
patients using a scoring algorithm based on the three parameters ECG,
NIBP and SpO2. Scoring-algorithm based central monitoring is not unique
in the industry.
Compact telemetry central monitor are common in Japan
The next image shows a WEP-4208A compact central monitor with seven transmitters. The "8" shows it has 8 receivers built-in and can accommodate reception and simultaneous display of up to 8 transmitters. With the compact central monitor, you do not need the CNS-9701A and the ORG-9700A of the above configuration. The
compact telemetry central monitor is designed for simple deployment in a
confined area with two whip antennae directly fixed to its diversity
BNC connectors as is usually shown.
NIHON KOHDEN is not known for expertise in multi-lead ECG Analysis Software
The transmitter in the next image is newer ZS-620P transmitter which is small enough to hold it in your palm. However, there is no new wireless technology involved, only usual progression of the FSK technique. The ZS-620P transmitter is a simple one that does not have a choice to use the 6-lead ECG cable as is applicable to ZM-540/ 541.
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| Product progression is not based on wireless technology but improving compactness and introduction of a local display |
There is negligible demand for single-lead ECG monitoring outside of Japan, which has a subsidy system to encourage its use; demand for patients with cardiac conditions requires at least two chest leads for effective monitoring. For Cardiac monitoring, the sophistication of the ECG analysis software in the server is the most important component for product evaluation and NIHON KOHDEN is not known for such expertise.
There is no possibility of wireless patient body sensors using current FSK technology
Below image shows older transmitters (analog type telemetry) on the left and more recent ZB-800 series transmitters on the right; these are usually monitored with a telemetry central at the nurse station. As setting up a transmitter on the patient needs verification of proper sensor attachments, a local display will of be great help as the central monitor may not be near to the patient.
However, the trend is not only just moving toward a transmitter with display but also integrated short range RF link to cableless patient sensors around a body area network. There is no such possibility from NIHON KOHDEN.
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| The physical size of earlier series transmitters were not much bigger, only without a display |
Demand for the instrument telemetry transmitter is mainly from the protectively-insulated domestic market in Japan
An instrument telemetry transmitter can often be attached to most exporting devices from Nihon Kohden to allow it to participate in a telemetry network, which is rarely needed for the export market. This however, is a necessity for the Japanese domestic market because of government subsidy for telemetry use; to make use of an instrument telemetry transmitter requires a built-in interface and a power socket on the device to link to the transmitter.
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| The telemetry connectivity is costly without subsidy, and they are therefore not in demand outside of Japan |
Next image shows Life Scope PT (BSM-1700 series) equipped with an Instrument Telemetry Transmitter. This ZS-900P transmitter will allow the Life Scope PT to participate in a telemetry network.
The Life Scope PT was, however, designed to operate primarily as an input unit for Life Scope TR, to use it solely as a telemetry monitor like what is shown would be an overkill because of its price.
The Life Scope PT was, however, designed to operate primarily as an input unit for Life Scope TR, to use it solely as a telemetry monitor like what is shown would be an overkill because of its price.
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| The ZS-900P with BSM-1700 monitor is an unlikely installation in your market |
The FSK Telemetry operating environment is outdated by today's standard
The earlier network example above showed the key supporting items are the splitters (for reverse use of adding signals) and RF amplifiers (for boosting signal power).
The 4-way splitters shown are used in the reverse way, they are acting as a poor man's summing amplifier with negative amplification. The input point becomes the output and the many output points becomes multiple input points. This is a cheap but inefficient way to sum RF signals because whatever arrives at the input will be greatly attenuated at the output.
The following image illustrates this important point. When using the simplest 2-way splitter, the output power is only half (-3db) of that measured at the input point. In the case of using a 8-way splitter to join RF signals, the output power is left with only one eighth (1/8) of the input power! Splitters have no active amplification and only unfavorable power loss.
The 4-way splitters shown are used in the reverse way, they are acting as a poor man's summing amplifier with negative amplification. The input point becomes the output and the many output points becomes multiple input points. This is a cheap but inefficient way to sum RF signals because whatever arrives at the input will be greatly attenuated at the output.
The following image illustrates this important point. When using the simplest 2-way splitter, the output power is only half (-3db) of that measured at the input point. In the case of using a 8-way splitter to join RF signals, the output power is left with only one eighth (1/8) of the input power! Splitters have no active amplification and only unfavorable power loss.
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| Notice the power of both "Signal AA" and "Signal BB" drops by half after passing through a 2-way splitter |
All
things being equal, the more antennae deployed the more inferior will
be the signal received at the ORG-9700A Multiple Patient Receiver Unit.
Below image shows an arrangement using one two-way and two four-way splitters as summers and the total power loss from each antenna to the receiver input point is close to -12db. A -3db drop means a power loss of 50% and a -12db drop means the power reaching the receiver is only 6.25% of what was picked up by the antenna.
Below image shows an arrangement using one two-way and two four-way splitters as summers and the total power loss from each antenna to the receiver input point is close to -12db. A -3db drop means a power loss of 50% and a -12db drop means the power reaching the receiver is only 6.25% of what was picked up by the antenna.
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| Example of loss calculation |
An RF Booster Amplifier is shown together with a 3-way and 8-way splitters in below image.
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| Other types of RF splitters (top) and booster amplifier |
RF Booster Amplifiers are used in general to boost the weakened signals after the splitters but this approach has limitation. The amplification cannot restore back the original Signal/ Noise ratio and is useless if the internal noise of the RF booster amplifier is bigger than the attenuated signal.
The RF Booster Amplifiers will also need AC Power Line outlets and these booster amplifiers are usually mounted on the ceiling; many power line points are needed along the side of the ceiling in each installation.
Attenuation and noise are the major weakness of such network because splitters with large attenuation are being used to sum (join) RF pickups from different antennae and analog RF signals have to travel long distance on coaxial cables (which also attenuates the RF signal). Due to the large frustration of attenuation encountered at every turn, coverage area easily reaches limit point when noise level becomes intolerable and the signal and noise are indistinguishable.
Access point technology is mandatory today for a wide coverage area
To have a wide coverage area today where patients are free to move within, Access Point technology is needed.
The ORG-9700A Multiple Patient Receiver Cabinet can accommodate only up to a maximum number of eight receivers (scalable); when the quantity of eight receivers is reached, another ORG-9700A Multiple Patient Receiver unit needs to be added to accommodate more transmitters. The RF Signal going into existing ORG-9700A Receiver Unit will need to be shared with the additional ORG-9700A Receiver Unit, resulting in overall system degeneration (i.e. lower signal to noise ratio) since a 2-way splitter must be introduced to split the signal as shown.
The ORG-9700A Multiple Patient Receiver Cabinet can accommodate only up to a maximum number of eight receivers (scalable); when the quantity of eight receivers is reached, another ORG-9700A Multiple Patient Receiver unit needs to be added to accommodate more transmitters. The RF Signal going into existing ORG-9700A Receiver Unit will need to be shared with the additional ORG-9700A Receiver Unit, resulting in overall system degeneration (i.e. lower signal to noise ratio) since a 2-way splitter must be introduced to split the signal as shown.
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| Adding a new expansion unit degenerates the existing system; it will get worse if another is added, and so on. |
Since adding more transmitters to an existing installation can result in a lower signal/noise performance, it is important to get the vendor's prior commitment how many transmitters can be totally deployed in a given coverage area; the number may be too small for your future need.
Use of Access Point Technology for telemetry
Philips MX40 is newer type digital telemetry device which has color display and also support for cableless patient sensors.
The Philips MX40 uses a newer type telemetry infrastructure using Access Points as shown. Similar to a Access Point in a home environment, the output of an Access Point is digital and can go straight to an Ethernet Switch. Ethernet signals can travel 100 meters without loss trouble, which is very different to handling analog RF signal traveling along coaxial cable in older infrastructure. Philips claims they can accommodate 1000 transceivers in such a network.
You may think the Life Scope G3 being the last of many to appear on the scene should be able to set a new level of sophistication but it fails miserably even on basic counts.
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| Philips MX40 wearable telemetry patient monitor |
The Philips MX40 uses a newer type telemetry infrastructure using Access Points as shown. Similar to a Access Point in a home environment, the output of an Access Point is digital and can go straight to an Ethernet Switch. Ethernet signals can travel 100 meters without loss trouble, which is very different to handling analog RF signal traveling along coaxial cable in older infrastructure. Philips claims they can accommodate 1000 transceivers in such a network.
You may think the Life Scope G3 being the last of many to appear on the scene should be able to set a new level of sophistication but it fails miserably even on basic counts.
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| Access point controllers and synchronization units are needed for proper functioning of such a network |
The next image shows an access point and controller with power provided via POE (Power Over Ethernet), very different from first generation RF amplifiers requiring many mains supply points near to the ceilings. New type transceivers can have two-way communication with Central Station, it is therefore possible to change settings at the transceiver end.
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| By incorporating newer technology, the size of newer type transceiver using Access Points and Controllers is seen to be slightly bigger than the older series transmitter |
Brief summary of current Philips Telemetry System
The official name
for current Philips telemetry system is IntelliVue Instrument Telemetry
System (IIT) and this is a newer generation bi-directional communication
system operating in groups of channels within the 2.4GHz ISM band utilizing
frequency hopping algorithm. The adoption of frequency hopping is to improve real-time performance
in a crowded band since the 2.4GHz ISM band is a real radio waves
jungle today. In the US market, Philips also offers the same IIT
system using the
protected WMTS bands in line with FCC initiative. This is done easily
by
replacing the internal ISM adapter (for International market) with WMTS adapter.