1、 Rec. ITU-R RS.1346 1 RECOMMENDATION ITU-R RS.1346*SHARING BETWEEN THE METEOROLOGICAL AIDS SERVICE AND MEDICAL IMPLANT COMMUNICATION SYSTEMS (MICS) OPERATING IN THE MOBILE SERVICE IN THE FREQUENCY BAND 401-406 MHz (Question ITU-R 144/7) (1998) Rec. ITU-R RS.1346 The ITU Radiocommunication Assembly,
2、considering a) that the band 401-406 MHz is allocated to the Meteorological Aids Service on a primary basis; b) that Recommendation ITU-R RS.1165 specifies the technical characteristics of radiosonde systems in the Meteorological Aids Service, and that Recommendation ITU-R RS.1262 specifies the shar
3、ing and coordination criteria for Meteorological Aids operated in the band 401-406 MHz; c) that the Medical Implant Communication Systems are comprised of an implantable device which is installed within the human body, and a programmer, which is designed for radiocommunication operation at 2 metres
4、away from the body for the programming and occasional communications with the implant device; d) that Medical Implant Communication Systems require a single band available worldwide, and may operate in the mobile service currently allocated on a secondary basis in the band 401-406 MHz; e) that with
5、a limit of 16 dBm on the e.i.r.p. of Medical Implant Communication Systems (MICS), no harmful interference would occur to the operation of Meteorological Aids from the MICS; f) that interference mitigation techniques used by the Medical Implant Communication System equipment, as described in Annex 1
6、, provides a high level of protection to their operation from possible interference by Meteorological Aids systems, recommends 1 that sharing is feasible in the band 401-406 MHz between the Meteorological Aids Systems, and Medical Implant Communication Systems which are in compliance with recommends
7、 2 and 3 and with the technical and operational characteristics described in Annex 1; 2 that the e.i.r.p. of Medical Implant Communication System transmitters be limited to 16 dBm (25 W) in a reference bandwidth of 300 kHz in order to provide adequate protection of Meteorological Aids Systems; 3 tha
8、t interference mitigation techniques, as discussed in Annex 1, should be used by Medical Implant Communication Systems to protect their operation. ANNEX 1 Feasibility of co-channel sharing between Meteorological Aids and ultra-low power implantable medical devices in the 401-406 MHz band 1 Backgroun
9、d Millions of people worldwide depend upon active implanted medical devices to support and improve the quality of their lives. Active implants perform an expanding variety of therapeutic functions: regulating heart rates (via pacing and/or defibrillation), controlling pain, administering pharmaceuti
10、cals, controlling incontinence, and treating neurological _ *Radiocommunication Study Group 7 made editorial amendments to this Recommendation. 2 Rec. ITU-R RS.1346 tremors to name just a few. As the technology continues to evolve and the population ages, service to humanity from these devices will
11、rapidly increase from an already large base. Communication links to implanted medical devices serve a variety of purposes, with new opportunities to improve patients quality of life constantly arising. Today, communication links are used for: device parameter adjustment (e.g. pacing rate), transmiss
12、ion of stored information (e.g. stored electrocardiograms), and the real time transmission of vital monitoring information for short periods (e.g. cardiac performance during the implant procedure). A communications system for medical implant devices includes a programmer and an implanted device. The
13、 programmer transmits data to the implanted device and receives data from the implanted device. The programmer operates outside the human body and contains an ultra low power transceiver and an antenna. The implanted device also contains an ultra low power transceiver and an antenna, but operates in
14、side the human body. The implanted device receives data from the programmer and transmits data to the programmer. Current technology that relies on RF induction cannot support the requirements for higher data rates (e.g. 100 kbit/s). Implanted medical device communications systems are inherently por
15、table. Patients travel around the world and can be far from their primary physician when an emergency arises and the need for device communication occurs. Likewise, programmers are often moved between medical facilities and countries. This mobility requirement and the constraints on the system desig
16、n require the availability of at least a single channel between 250 and 450 MHz for use worldwide. For medical implant communication systems (MICS) to be successful, the identification of a single, worldwide band 3 MHz wide for use by all manufacturers is vital. Operation in a portion of the band (4
17、01-406 MHz) appears to be the only viable option. For effective MICS operations, the effective radiated power needs to be in the range of 20 dBm (10 W) to 16 dBm (25 W). This low ERP in combination with the link being used almost exclusively indoors and in urban areas virtually eliminates the potent
18、ial for MICS operations to interfere with Metaids. Note also that because the devices primary purpose is therapeutic, the communication link is used only 0.005% of the devices lifetime further limiting its interference potential. 2 MICS characteristics 2.1 Frequency of operation The focus on 401-406
19、 MHz as the frequency band for MICS operation is the result of many factors. The frequency band selected must be capable of reliably supporting high data rate transmissions, lend itself to small antenna designs, fall within a relatively low noise portion of the spectrum, propagate acceptably through
20、 human tissue, and be feasible with circuits that require a minimal amount of electrical power. 2.2 Total required bandwidth MICS operations require 3 MHz of available spectrum for the creation of at least 10 channels. These channels are used to avoid interferers and support the simultaneous operati
21、on of multiple devices in the same area (such as clinics with multiple rooms). International spectrum studies have shown that even with 3 MHz available only one or two channels will be usable in many environments. Rec. ITU-R RS.1346 3 2.3 MICS link budget calculation The parameters used for the anal
22、ysis of MICS links are: 2.4 Duty cycle The primary purposes of the devices with MICS capabilities are diagnosis and therapy. Since use of the communications system reduces the device lifetime for these operations it is used only when necessary. As an example, todays low frequency RF inductive commun
23、ication system is activated for only 0.005% of the implanted devices lifetime (about 4 hours out of 9 years). In the case of the programming device used by the physician the duty cycle will be much higher. In the case of a clinic with multiple programmers, overall use of the band could approach 50%
24、during business hours. Uplink (Implant Programmer) Downlink (Programmer Implant) Frequency 403.5 MHz +/ 1.5 MHz Modulation type FSK Receiver noise bandwidth 200 kHz 25 kHz Ambient noise at receiver input 20 dB above kTB kTB (due to tissue loss) Receiver noise figure 4 dB 9 dB Receiver noise floor 10
25、1 dBm 121 dBm Receive antenna gain 2 dBi 31.5 dBi Required SNR (BER = 1E-5) 14 dB Free space loss at 2 metres 30.5 dB Fade margin(1)(with diversity) 10 dB Excess loss(2)(polarization, etc.) 15 dB Transmit antenna gain 31.5 dBi 2 dBi Power into antenna 2 dBm 22 dBm ERP 33.5 dBm (at body surface) 20 d
26、Bm(3)(1)By using the same antenna as selected for uplink and keeping the downlink message time short relative to the 4 Hz fade rate, link reciprocity keeps the downlink fade depth to 10 dB in spite of the absence of spatial diversity in this direction. (2)Excess loss in the link is the result of pat
27、ient orientation, antenna misalignment, obstructions (such as a physician) in the main line of sight path and polarization losses. These statistically independent processes can be meaningfully modelled by adding 15 dB of margin. Note that polarization loss occurs to varying degrees for all antenna c
28、onfigurations. (3)For this analysis, 20 dBm(10 W) was used as the effective radiated power. Additional margin is desirable provided that it can be obtained without jeopardizing interference-free operation in the Metaids band and can be achieved within the design constraints imposed by the environmen
29、t in which MICS stations will operate.4 Rec. ITU-R RS.1346 3 Analysis of Metaids susceptibility to MICS interference 3.1 Interference to radiosondes Maintaining the viability of the extensive Metaids infrastructure is of great importance to the public. Current users of the band include radiosondes,
30、rocketsondes, dropsondes and data collection platforms. Of these users, radiosondes appear to have the greatest susceptibility to interference. The e.i.r.p. of MICS programmers needs to be limited in order to accomplish the desired communications without causing interference to Metaids. Recommendati
31、on ITU-R RS.1262 specifies that the interfering power to be received no more than 20% of the time is -161.9 dBW/300 kHz. Using the CCIR Standard Propagation Model1and 20 dB for building attenuation2, it is determined that a MICS device must be within 421 m to interfere with radiosonde operation. Not
32、e the use of the conservative assumption that the MICS frequencies and the radiosonde frequencies are perfectly aligned. Clearly, the ultra low transmit power of the MICS equipment greatly reduces the interference potential. However, the probability of interference is also reduced by other factors t
33、hat, while difficult to quantify, remain important: Channelization. MICS operation will be channelized with the channel of operation selected based upon the lowest ambient noise level. A radiosonde operating at a given frequency will look like a narrow-band noise source in the MICS band, causing the
34、 MICS equipment to select a different channel. Thus, when a MICS programmer detects a radiosonde, it will respond in such a way that the radiosonde and the MICS programmer do not interfere with each other. Interferer density. Due to the attenuation of waves launched from the body, the programmer is
35、the only potential source of interference for Metaids users. Additionally, implanted device proliferation is limited by medical need, not consumer desire. This holds down the number of potential interferers to something much less than could be expected from a consumer or commercial application. Inte
36、rferer duty cycle. Implanted devices have a communications duty cycle of about 0.005% over their lifetime. The programmer, of which there are several orders of magnitude fewer, may have a much higher duty cycle. Downlink duty cycle. Due to tissue attenuation, only communication to the implanted devi
37、ce has the potential to interfere with Metaids. The communication exchange will likely be half-duplex and highly asymmetric, with transmission to the implanted device occurring only a fraction of the time that the link is active. Typically, downlink will occur for only 10 ms out of every 250 ms of c
38、ommunication. Thus, the typical radii for a MICS programmer to interfere with a radiosonde will be much less than 500 m. In the rare case where a MICS programmer is within range, the probability of interference would be reduced by the need for MICS equipment to employ an interference avoidance algor
39、ithm to operate on a channel found to have a low noise level. The use of a low duty cycle and half-duplex operation by the MICS equipment, along with the duty cycle of the radiosonde system, also reduce the possibility of interference to Metaids. 3.2 Interference to the radiosonde ranging adjunct Th
40、e MICS signal will not interfere with the radiosonde ranging adjunct. The 25 W transmission power of the ranging adjunct is 60 dB higher than the MICS transmission power. The following formula predicts the carrier-to-interference ratio (note that this model would predict a higher C/I if building los
41、ses and MICS antenna directivity were included). _ 1OKUMURA et al. 1968. 2KOZONO, S. and WATANABE, K. October 1977 Influence of environmental building on UHF land mobile radio propagation. IEEE Trans. Commun., Vol. Com-25; WALKER, E. H. November 1983 Penetration of radio signal into building in the
42、cellular radio environment. Bell Sys. Tech. J., 62: 9 Pt. I; RAPPAPORT, Ted. Wireless Communications (Prentice Hall PTR), p. 131-132; Tur87 TURKMANI, A. M. D., PARSON, J. D. and LEWIS, D. G. December 1987 Radio propagation into buildings at 441, 900, and 1 400 MHz. Proc. of the 4th International Con
43、ference on Land Mobile Radio; Tur92 TURKMANI, A. M. D. and TOLEDO, A. F. 1992 Propagation into and within buildings at 900, 1 800, and 2 300 MHz. IEEE Vehicular Technology Conference. Rec. ITU-R RS.1346 5 The worst case occurs at the end of flight when the balloon is at its maximum range from the tr
44、ansmitter (x25 km). Under these conditions a C/I of 37 dB is predicted. C/I = 4.34(12.89 + 2 ln(2rh) + x2+ h2+ r2)1/2 r) ln(x2+ h2) where: h: height (km) x: range (km) r: effective radius of the Earth (km). 4 Analysis of MICS interference mitigation Clearly, it is vital patients suffer no harmful ef
45、fects from interference. This must be true for potential interference from Metaids, other intentional radiators, and unintentional radiators. Patient harm can arise in three ways: the implant device communications circuitry depletes the device battery responding to false activation, the link is unav
46、ailable when needed, and data are corrupted by interference. MICS equipment can protect the patient and implanted devices using a variety of techniques. 4.1 False alarm tolerance To meet the longevity requirements of the device, the MICS implant device communications circuitry must be active only wh
47、en communicating. It is, however, also necessary that the link be available on demand. To meet these conflicting requirements, the detection of a strong DC magnetic field (14 Gauss) can be used to activate the implant device communications circuitry. Upon detecting the magnetic field, the system wou
48、ld go through a channel identification and acquisition algorithm. Should link establishment be unsuccessful, the implant communications circuitry would return to dormancy, conserving battery energy. This method is used today for most implanted devices and has an extremely low false alarm rate. In ca
49、ses such as home monitoring where availability on demand is not a requirement, the system could poll at a long interval (typically for less than a second every 30 to 120 min) to determine if the establishment of a link is desired. The presence of interference prolongs the signal qualification and channel acquisition process, wasting battery energy. To avoid this, the microprocessor could program an increased polling interval until the interference subsides. For troubleshooting purposes the MICS transceiver could also
