1、 % STD-CEPT ERC REPORT SB-ENGL 1999 H 232b414 0017093 214 c ERC REPORT 98 European Radiocommunications Committee (ER0 within the European Conference of Postal and Telecommunications Administrations (CEFT) COMPATIBILITY OF SFtDS AT WO MHZ WITH ADJACENT SERVICES Marbella, February 1999 ERC REPORT 98 E
2、XECUTiVE SUMMARY This report has been compiled to examine the impact of the introduction of SRDs (Short Range Devices) in the band 868 - 870 on the services in adjacent bands (TETRA and CT2 - Cordless Telephone 2), but has not considered how these devices may be affected by other services elsewhere
3、in the 900 MHz bands. The segmentation in sub-bands is detailed in ERC/REC 70-03, produced originally by SE24 and FM26. A maintenance group has now been created to address future modifications. One of the relevant ETSI standards for SRDs is prEN300 220. Because of their low power and defined transmi
4、tter spectrum mask, it is possible for low power SRDs (up to 25 mW) to operate in bands adjacent to other services without causing unacceptable interference, provided that: SRDs up to 25 mW e.r.p. in the 868 - 870 band can coexist with CT2 in 864.1 - 868.1 MHz, provided that SRDs at 868 - 868.5 MHz
5、are subject to a power restriction of 25 mW and have dynamic frequency allocation. Narrow band SRDs can coexist with TETRA but wideband SRDs need a minimum carrier separation of 500 kHz. The implications of introducing higher power SRDs (500 mW), based upon minimum performance specifications, are gi
6、ven below: Interference to the adjacent band services (and other SRDs within the band) should be expected if very large numbers of 500 mW SRDs become widely used. The cost of 500 mW SRDs will be insufficient to adequately restrict the number of these SRDs, and wide geographical distribution (includi
7、ng in the domestic environment) should be expected, because its highly likely that mass-market applications are found. Therefore it is unlikely that an immediate compatibility problem could arise, but if the potential (currently not quantifiable) future interference to the adjacent band services is
8、to be avoided, an acceptable method of limiting the deployment of 500 mW SRDs may need to be identified before this type of SRD is permitted to operate within the 868 - 870 MHz frequency band. A request for an allocation for high performance and high price SRDs has been submitted to WG FM. An uncont
9、rolled increase of production of SRDs for different applications than those envisaged at the moment could cause the unavailability of the band for those specific applications (e.g. professional telemetry). An uncontrolled and permanent increase of the generic pollution of this band could cause probl
10、ems initially to the lower power SRDs in adjacent bands and later to the other services allocated in 900 MHz band, such as CT2 in some particular environments such as domestic applications or radio PABX, and to a lesser extent TETRA. In particular it is highly likely that social alarms and security
11、systems within the harmonised SRD 900 MHz band could be frequently affected by uncontrolled deployment of 500 mW devices. In a precedent ERC report dealing with the compatibility between CT2 and CAD (Cordless Audio Devices) it has been stated that “It is important that the non-shared band (865 - 868
12、.1 MHz), having a capacity of about 28 channels is not further interfered with by possible future new applications so as to ensure a proper call capacity / reserve for the system. ” In the absence of other sources of interference a CT2 system still has 14 free channels in the presence of 500 mW SRDs
13、 at more than 6.2 m; but if the lower part of the band is made unusable by CAD, then all the CT2 capacity may be lost in presence of 500 mW SRDs at less then 70 m (free space). CT2 and CAD may occur together in domestic environment and introducing 500 mW SRDs into this environment will cause problem
14、s. It is recognised that, in general, a limited duty cycle can be a useful factor in the aim of limiting interference (even in the absence of specific means for evaluating the precise effkt). In the current version of the ERCREC170-O3 the definition of duty cycle is inappropriate for the purpose of
15、considering it when producing compatibility studies. In the case of frequency hopping applications, the duty cycle time, for adjacent band compatibility studies, has to be the total transmitter on time and not the time of a selected frequency channel (1 frequency hop). Also it should be clarified, t
16、hat it must be ensured, that the broad band noise, the switching transient and other effects of SRDs with frequency hopping are not higher than the limit for the unwanted emissions at the appropriate SRDs standards. It is recommended that SRDs intended for operating in a frequency-hopping mode be te
17、sted in that mode for type approval. ERC REPORT 98 Further work would be required to: 0 0 Ensure high channel availability for social alarms and security systems within the harmonised SRD band. Determine the effects of spurious emissions. Define the situations in which these units are to be used. Id
18、entify typical scenarios depending on the envisaged applications. The SRD industry and ETSI are encouraged to draft further standards for specific SRD applications. In particular the presence of a standard for the definition of the minimum SRDs receiver performances would be useful for evaluating th
19、e impact of other services towards the SRDs. Furthermore it was not possible to take into account the mitigation effect of low duty cycles, due at this time to the lack of a precise definition in ERCREC 70-03 and concerns were raised concerning the wide band noise that could be generated by systems
20、using frequency hopping. It is recommended that SRDs intended for operating in a frequency-hopping mode be tested in that mode for type approval. This report has not examined the effect of 500 mW SRDs on the other SRDs operating within the band. Harmful interference is possible and further work shou
21、ld be carried out within WG SE. SRD manufacturers should be aware of adjacent services (CT2, TETRA and other SRDs) when specifying and designing systems. This report has not examined the effect of 500 mW SRDs on the other SRDs operating within the band. Harmful interference is possible and further w
22、ork should be carried out within WG SE. STD*CEPT ERC REPORT SB-ENGL 1999 D 2326434 0037096 T23 ERC REPORT 98 INDEX TABLE 1 INTRODUCTION 1 2 STUDY 1 3 CONCLUSIONS . 6 ANNEX 1: THEORETICAL STUDY . 7 STDmCEPT ERC REPORT SB-ENGL 1977 232b414 0037097 7bT ERC REPORT 98 Page 1 COMPATIBILITY OF SRDS AT 900
23、MHZ WITH ADJACENT SERVICES 1 INTRODUCTION Producers and users of SRDs have indicated a need for spectrum in the 900 MHz region. The main requirement is for professional telemetry purposes but there is also demand for low cost equipment for less critical applications. Short Range Devices (SRDs) are l
24、ow power transmitting devices for which an end user license is not needed. They are used in domestic circumstances for remote control, e.g. garage door openers, car key fobs, and also for professional telemetry, e.g., instrumentation and process control. Another large use is for alarms, e.g Social a
25、larms and security systems. The use of SRDs is deregulated and no central records are kept of their numbers and locations. Very large numbers are in use and existing allocations for SRDs are becoming crowded. There are no guaranteed clear channels or time slots for SRDs and no agreed formats for tra
26、nsmissions. Mutual interference occurs but its effects are reduced because of the low duty cycles often employed and the short ranges of the transmissions. The level of mutual interference acceptable depends on the nature of the applications. There are some obstacles, which are making it difficult t
27、o make compatibility analysis on SRDs. The receivers of SRDs and the bandwidth are not specified, so the calculations can only be made based on the acceptance of some parameters for SRDS. The SRD applications and their quality (e.g. transmitter, receiver, operation area, number of equipment, locatio
28、n, modulation, multiplex access techniques, etc.) are diverse and different. For example a medical implant has generally different qualities than a container identification system or a garage door opener. The previous name for SRDs, Low Power Devices (LPDs) included in most European countries equipm
29、ent with a maximum output power of 10 mW e.r.p. Because of their low power it was assumed, that LPDs would not interfere with other radio services up to now. Under certain circumstances these LPDs didnt need to be licensed and regulated. The LPDs were operating mainly at ISM frequencies and without
30、charge, there was no demand for the customers of the equipment for protection. But the number of LPDs had been not so high. Some of the characteristics of LPDs are not applying to SRDs and the number of SRDs had been increased the last years. New applications brought new problems, e.g. the interfere
31、nce of garage door openers due to permanently active unwanted emissions from wireless headphones at the 433 ISM (Industrial Scientific and Medical) applications band. The additional relief of the licensing (e.g. no receiver parameters had been created) and also the increase of e.r.p. output power fo
32、r SRDs to a maximum limit of 500 mW made it questionable to speak about low power application. During this time the number of devices and applications have grown, operating without licensing and with free circulation and use on a European basis. With SRDs it is assumed that most of them are aimed at
33、 low cost mass-produced equipment. This means, that in high population density areas thousands of equipmentkm2 are coming in operation with varying quality and technical design (mobile, fixed, different modulations, duty cycles.). The probability of SRD transmissions is now therefore very high. 2 ST
34、UDY Equipment Regulations SRDs have to meet type approval requirements before being marketed. The generally adopted specification is prEN 300 220. This specifies certain requirements for spurious emissions, etc. To make a complete technical specification, further restrictions on operating frequency
35、and radiated power need to be added. It is noted that prEN 300 220 sets limits on the transmitter spectrum but does not specify the signalling protocols or modulation techniques. It is intended that the SRD bands will be available for emerging technologies and also for derivatives of existing techno
36、logies, including for instance, CT2, DECT, GSM etc. In order to produce a complete study including the analysis of the possible interference produced by services using adjacent bands to SRDs, the receiver characteristics of SRDs would be needed. Neither prEN 300 220 nor the individual national requi
37、rements specify receiver selectivity parameters or overall system performance levels for general applications. This is STD-CEPT ERC REPORT 98-ENGL 1999 2326414 0017098 8Tb Ref 70-03 If 7a 1g 7d 7b lh 11 7c lk ERC REPORT 98 Page 2 Frequency Band, Power Channel spacing, Duty cycles Applications MHz e.
38、r.p., kHz Footnote 1 mW 868 -868.6 25 25 Low N.S. 868.6-868.7 10 25 Very Low Alarms in general 868.7-869.2 25 253,4 Very Low N.S. 869.2-869.25 10 25 Very Low Social alarms 869.25-869.3 10 25 Very Low Alarms in general 869.3-869.4 t.b.d. 25 t.b.d. N.S. 869.4-869.65 500 255 High N.S. 869.65-869.7 25 2
39、5 High Alarms in general 869.7-870.0 5 25, 503 Very High N.S. Footnote2. 33 49 40 25 d49 40 25 d 15.5 40 500 d 69.2 40 The following table proposes the same results in a different way: Table 4: Results (distances in metres) Three considerations have to be made. - - It should be noted that these calc
40、ulations are based on a CT2 system operating 5 dB above its sensitivity. Each calculated distance is the needed distance from the CT2 device to the SRD. But the cumulative effect of more than one SRD can interfere at the same time due to the natural deployment scenario of an unlicensed mass market.
41、All the free channels are in the lower part of the band. That means that if the lower part of the band is free from interference the CT2 equipment can work. It has to be noted that the part of the band 863 - 864 MHz is allocated in Europe to cordless audio devices (CAD) and that in WG SE report SE(9
42、7)3 lannex 7 dealing with the compatibility between CT2 and CAD it has been stated that “It is important that the non-shared band (865 - 868.1 MHz). having a capacity of about 28 channels is not further interfered with by possible future new applications so as to ensure a proper call capacity / rese
43、rve for the system.“. Looking at the table above, it is showed that in the absence of other sources of interference a CT2 system still has 14 free channels in the presence of 500 mW SRD at more than 6.2 m; but if the lower part of the band is made unusable by CAD, then all the CT2 capacity may be lo
44、st in presence of 500 mW SRD at less then 70 m (free space). CT2 and CAD may occur together in domestic environment and introducing 500 mW SRDs into this environment will cause problems. Another type of calculation can be produced. We can imagine that a communication occurs; CT2 is at a certain dist
45、ance Dc from its base, the SRD is at a distance Dint. Maybe the CT2 terminal is far from working at the sensitivity limit, but the interferer is closer to CT2 base than the terminal. In this case blocking can occur. We can try to calculate the ratio between the two distances that gives the limit of
46、CT2 being able to communicate. In this case, if we consider very simply the useful power PcB, the interfering power Pint, the free space path loss of both devices, Lct2 and Lint and a value of VC of 38 dBc or 48 dBc depending on the frequency, we can write (all values in dB/dBm): Pct2 - Lct2 = Pint
47、- Lint -UC; after some rearranging we can deduce following relationship: ERC REPORT 98 Page 10 - 10 25 500 Using this formula, we obtain the following table: 79 (7a); 251 (7b, 7d) 50 (If); 158 (lg, 7c) 35 SRD power (mW) 5 I155 1 Necessary Dct2/Dint 7b 7c li SRD power Frequency separation (nearest IS
48、OLATION (dB) Distance in TETRA Distance (main (mW TETRA channel, kHz) (TETRA blocking side lobes (m) beam, m) level) 25 325 55 (-30 dBm) 4.3 15.4 500 375 68 (-30 dBm) 11.8 42 10 725 46 (-25 dBm) 1.5 5.5 Table 5: Results for CT2, alternative approach 5 10 25 The two tables above may look different, b
49、ut they reflect different aspects of the same problem. In both cases there is the limitation of using free space propagation which strictly is not applicable to large distances or to indoor environments. The first calculation is more classical, but may be considered as pessimistic. The second one is not a standard calculation, but it seems that this method can represent the real effect of introducing SRDs in the band adjacent to CT2. The considerations at the end of the first calculation are obviously still valid. 2.5 x io3 10.00 x io3 6.31 x io3 The isolations and distances are s
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