1. Telecom Regulatory Authority of India
Presentation on behalf of the
Association of Unified Telecom Service Providers of India
– Response to Nokia’s Paper on Interference Issues –
ITU-B Band and ITU Band 1: / MHz
Dr Y S Rao
Contribution by QUALCOMM & Lucent
13 October 2004
New Delhi

2. EXECUTIVE SUMMARY
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3. Synopsis of AUSPI’s stand
Present allocation in 800 MHz for CDMA – Not sufficient for multiple operators.
Internationally allocation for large operators varies from 10+10MHz to MHz (average allocation MHz).
CDMA operators need additional allocation in other bands to grow their networks.
Globally, CDMA systems work in 800 MHz and 1900 MHz, with the exception of Korea
– Korean PCS is unique and is not used anywhere else in the world.
AUSPI has proposed service neutral plan of 800 MHz and 1900 MHz for CDMA and 900 MHz and 1800 MHz for GSM in line with international standards.
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4. Main points of NOKIA’s presentation
GSM is opposed to 1900 MHz allocation for use by CDMA Operators
– It overlaps with WARC’92 recommended IMT-2000 Band of MHz paired with MHz
Even a small allocation of MHz for CDMA2000 operation in the USPCS Band will cause unacceptable interference to a WCDMA system in the WARC’92 IMT-2000 band
Adequate protection of the WCDMA uplink will require:
Very high rejection filters at every CDMA2000 and WCDMA Base Station
Guard bands greater than 5 MHz
Site to site coordination
15% additional IMT-2000 sites to account for lost coverage
Several thousand Euros added per site to pay for all this
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5. Main points of NOKIA’s presentation – contd…
There is no incentive for a CDMA2000 operator to invest in filters
Experience of “mixed” CDMA/GSM in 800/900 MHz in India/Asia show that CDMA operators neglect additional filtering
Operators do not coordinate in practice
Adequate protection of the CDMA downlink Interference from IMT-2000/ WCDMA User Equipment (UE) and USPCS CDMA UE is not possible
This will result in a USPCS CDMA capacity loss up to 35%
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6. Our General Response GSM opposition is unjustified:
WARC-2000 has recommended different bands for IMT-2000/3G allowing flexibility for the administration to choose any band from:
806 – 960 MHz,
1710 –1885 MHz,
2500 –2690 MHz.
ITU-R recommendation No. M identified different paired frequency arrangements for IMT-2000
A1&A2
B1 to B6
3GPP has already standardised DCS1800 for 3G/UMTS [No. TS25.105(Rel-5)] and has already been requested to quickly standardise 900 MHz for the same
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7. Our General Response – contd…
Notwithstanding its position to have the USPCS band allocated for CDMA operators, AUSPI now responds to Nokia interference issues with a mixed band plan of USPCS and the WARC IMT-2000
As per the ERC-101 Report, there are three methods to study interference between two adjacent frequency bands:
Minimum Coupling Loss (MCL)
Enhanced – Minimum Coupling Loss (E- MCL)
Monte Carlo Method
Method used by Nokia is MCL
As per the ERC-101 Report, the MCL method evaluates the worst case scenario and gives spectrally inefficient results
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8. TECHNICAL RESPONSE
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9. Clarification on band allocations near 2 GHz (ITU Definitions)
Nokia states on page 3: “even the allocation of as little as 10 MHz for PCS CDMA within / MHz will severely interfere the uplink portion ( MHz) of the ITU-R globally harmonized IMT GHz band”.
We believe this is confusing the technical discussion since IMT-2000(3G) systems can be deployed in both of these bands. In ITU-R M the ITU has stated that the following 3 bands (in addition to others-i.e MHz/ MHz) are equally valid bands for IMT-2000 and that administrations can implement all or parts of these frequency arrangements for IMT-2000 services in the 2 GHz region. It is up to the Administrations of each country to decide which arrangement, or mix of arrangements best suits its own needs.
ITU band 1, commonly termed the “UMTS” band
/ MHz
ITU band 2, commonly termed the “DCS-1800” band
/ MHz
ITU band 3, commonly termed the “USPCS” band
/ MHz
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10. Existing band allocations near 2 GHz (ITU Definitions)
We also note that each Standards Organization, eg 3GPP and 3GPP2, refer to these bands by other designations
To avoid confusion in this presentation, we will refer to these bands by their ITU designations, as shown on the previous chart
The next chart shows these bands as defined by the ITU.
Red lines indicate mobile transmit bands
Blue lines indicate BTS transmit bands
Green line indicates DECT assigned bands in India
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11. Existing ITU Band allocations near 2 GHz
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12. Frequency allocation arrangement addressed by NOKIA
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13. NOKIA’s claims on a mixed band plan
Nokia claim page 3: … allocation of even 10 MHz from the USPCS (ITU B3) band will essentially block the IMT-2000 evolution…
The previous figure shows the allocation arrangement addressed by Nokia
Our response:
Normal design practice for this arrangement will place the last WCDMA carrier 2.5MHz below the 1980 MHz boundary and the first CDMA 2000 carrier 1.25MHz above the 1980 MHz boundary. This arrangement places these carriers 3.75 MHz apart, and provides an inherent guard band of 1.2 MHz
1.2 MHz = 3.75 –( )/2
Additional guard band can be obtained without “essentially blocking” IMT evolution
Dropping 1 CDMA 2000 carrier gains 1.25 MHz
Dropping 1 WCDMA carrier gains 5 MHz
Reducing the WCDMA channel spacing to 4.8 MHz gains 2 MHz
These inherent and easily increased guard bands reduce the requirement on any filter designs needed to assure interference is not an issue
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14. NOKIA concern number 1 – CDMA2000 BTS TX Emissions to WCDMA BTS RX
Nokia claim on pages 3 and 4: “-13dBm/MHz limit for CDMA BS does not consider mixed band plan.” CDMA BS will transmit unfiltered spurious emissions and wideband noise across the uplink portion of the ITU-B1 band
Our response:
Nokia assumes the worst case noise density from a CDMA2000 BTS of – 13dBm/MHz (or -73dBm/Hz)*, but commercial BTS typically perform better, as much as 22dB better. Given that a significant number of Base Stations have been deployed, it would seem reasonable to use real data rather than worst case limits
The specification says nothing about whether a mixed band plan will work. We believe it is possible to have a mixed band plan such that operators get a fair and equitable opportunity to offer IMT-2000 services as soon as possibleIf a mixed plan is anticipated, more appropriate emissions can be specified.
The entire ITU-B1 band is not affected equally. Only the first WCDMA carrier below 1980 MHz is an issue.
* Note: this is a specification from an early version standard, which has been recently changed to -30dBm/30KHz ( or -75dBm/Hz)
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15. Interference issues with mixed band plan –Emissions contd…
Nokia claim page 4: Nokia quotes Lucent as saying 77dB of filtering at the CDMA 2000 BTS may be required to solve the BTS to BTS noise interference issue. This supports an overall Isolation target of 107dB, as derived by Lucent.
Nokia also concludes that the only way to prevent interference from spurious emissions coming from CDMA 2000 BTS transmitters in the ITU-B3 band into WCDMA BTS receivers in the ITU-B1 band is to install additional filters in all ITU-B3 base stations.
Our comments:
The requirement for 77 dB of filtering arises from Nokia’s assumption that 30dB of antenna isolation is all that can be obtained. But this limit only applies to systems sharing the same antenna, and over 50dB of isolation can be obtained in both collocated and non collocated arrangements that do not share an antenna.
A more reasonable approach, stated by Lucent, is to assume a filter with 60dB rejection. Then the required antenna isolation is 47dB, well within standard practice.
It is not the case that expensive technical modifications of infrastructure must occur to permit the use of some of the PCS and ITU-B1 frequency bands. We will later show the only modification required is to add filters.
We further believe that 60dB filter rejection is the maximum required and will show that it can be obtained in real, commercially available designs.
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16. Interference issues with mixed band plan –Emissions contd…
Our comments, contd…
In computing the -107 dB isolation requirement, Lucent used a worst case Minimum Coupling Loss (MCL) analysis procedure with CDMA 2000 emissions at -73dBm/Hz, plus assuming this interference arrived at the WCDMA BTS receiver 10dB below the noise floor, estimated at -170 dBm/Hz. ( i.e. from a 4dB noise figure receiver). This worst case analysis serves well to establish limits on the interference issue.
Even in this worst case condition we believe that coexistence is achievable.
However, ERC report 101 [1] states that the minimum coupling method yields pessimistic results when compared to real world results, and recommends a procedure if more accurate Monte-Carlo simulations are not available. One particular comment stands out:
The degradation should be estimated with the desired signal at 3dB above the minimum sensitivity.
In line with these guidelines, we believe a 1dB degradation in noise figure as more reasonable for CDMA systems, and which is actually more severe than that recommended by ERC-101.
This sets the allowable interference density at -176 dBm/Hz
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17. Interference issues with mixed band plan –Emissions continued
Our comments, contd…
Given an allowable interference density of -176dBm/Hz at the ITU-B1 BTS receiver, and a specified emission density or – 75dBm/Hz from the CDMA 2000 transmitter, the required isolation is 101 dB, not 107dB
If the emission density is at a more typical level, as much as 22 dB below the specified level, the required isolation is 79 dB, far less than the worst case estimates
Based on these values, we would consider a reasonable isolation requirement to be not more than 90 dB, which could be met with a 50 dB filter and 40 dB of antenna coupling loss
In any case, the reduction in required isolation can be used to reduce the required antenna coupling loss, the filter rejection loss, or the guard band
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18. Interference issues with mixed band plan –General
Nokia claim on page 5: use of mitigation techniques will not work because there is no incentive for the perspective PCS CDMA operator in / MHz to invest and to provide the necessary additional filtering. Severe interference has been observed in the 800 MHz band, where a similar boundary condition occurs.
Our response:
Nokia fails to consider that the ITU-B1 band can be shared** between WCDMA and CDMA CDMA 2000 may well end up on both sides of the boundary. To avoid interference later, the boundary problem must be addressed now
It is also not true that in case of CDMA 2000/GSM band plans in 800/900 MHz bands in India the operators have neglected the need for filters
It is a fact that CDMA filters have been provided to solve the 850MHz issue
In addition there was a resolution between the operators to take the necessary steps and to the best of our knowledge there are no significant interference issues between CDMA and GSM in 800/900 MHz bands
** Notwithstanding its position to have the ITU-B3 band allocated for CDMA operators, AUSPI is responding to Nokia’s interference issues concerning a mixed band plan
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19. Interference issues with mixed band plan –Blocking
Nokia claim page 6: Use of mitigation techniques, if imposed upon the operators, are not viable due to large site coordination distance, large guard bands, high cost and need for additional sites due to degradation. 114dB of total isolation will be required, and sites will need to be 300 Meters apart even when 60dB of filtering is added at WCDMA receivers
Our response:
After reviewing typical data we believe 114 dB isolation is not required for the ITU-B3 to ITU-B1 blocking interference condition
In computing this number Lucent again used a worst case analysis procedure
First, Lucent assumed a CDMA2000 transmitted power of 46.8dBm (for three carriers). We agree with this assumption
Lucent then computed the allowable blocking level at the WCDMA receiver at -66.8dBm at the receiver input from the WCDMA ACS specification
The difference of these numbers is dB, rounded to the isolation requirement of 114dB
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20. Interference issues with mixed band plan –Blocking contd…
Our response continued:
Actual blocking measurements have been performed in generic programs with co-operative partner FDD vendors and indirectly as part of co-siting tests on ITU-B1 operators’ FDD networks. These experiments were performed on six different FDD vendors equipment and across all TDD channels in the core ITUB1 bands. These measurements have been averaged to protect confidentiality and are summarised below. Note these are considerably higher than the default specification of -55 dBm. At 5 MHz offset the interfering signal was –37dBm, 18 dB larger than the specified level of -55dBm, and about 30 dB larger than the worst case calculated level of –66.8 dBm.
Interfering channel (TDD signal)
Interfering signal level for 1dB noise rise in 1922 MHz FDD UL
MHz
-9dBm
MHz
-17dBm
MHz
-27dBm
MHz
-37dBm
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21. Interference issues with mixed band plan –Blocking contd…
Our response continued:
As before, after reviewing this analysis, we believe this is too severe when using the worst case minimum coupling loss (MCL) method of computing system coexistence
Given a transmitted power of 46.8dBm from three CDMA carriers, and aspecified blocking level of -55dBm at the WCDMA receiver for a 5MHz offset, the computed isolation is 101.8dB, not 114dB
Given a transmitted power of 46.8dBm from three CDMA carriers, and a typical blocking level of -37dBm at the WCDMA receiver for a 5MHz offset, the computed isolation is 83.8dB, far less than the worst case 114dB
As before, we would consider a reasonable isolation requirement to be not more than 90 dB, which could be met with a 50 dB filter and 40 dB of antenna coupling loss
In any case, the reduction in required isolation can be used to reduce the required antenna coupling loss, the filter rejection loss, or the guard band
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22. Interference issues with mixed band plan –Blocking contd…
Nokia claim page 6: Use of mitigation techniques, if imposed upon the operators, are not viable due to large site coordination distance, large guard bands, high cost and need for additional sites due to degradation. 54 dB of antenna isolation will be required, and sites will need to be 300 Meters apart even when 60dB of filtering is added at WCDMA receivers. (This is to meet the 114 dB total isolation requirement)
Our response continued:
Site coordination distances: We do not agree with Nokia’s conclusion that a 300 meter minimum site-site distance is needed when 54dB of isolation is desired. In line 6 of their table on page 6, we see Nokia has listed 54dB as the available antenna isolation. Since the Free Space loss at 300 Meters at 1980 MHz is 88dB (as shown in the next chart) this means that Nokia has assumed BTS antenna gains of 17dB each and that they are directed exactly at each other. Nokia also neglected any cable losses in their analysis
It is recommended ( ERC-101) that 10 dB antenna gains be used when determining interference. Using these values reduces the free space loss requirement to 74dB and the site to site spacing to about 75 Meters
Analytical and measured data ( see later charts) show that 54 dB total isolation is also quite possible when antennas are mounted on the same mast
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23. Free Space loss model for BTS to BTS interference calculations
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24. Antenna coupling for antennas mounted on a common mast
The above data may be found in “prediction of Mutual Coupling between Base Station Antenna Arrays, RAWCON 2002 conference paper.
These measurements are comparable to the following table found in contribution UK WP8F WP(04)026, which was aimed at solving the boundary problem between TDD and FDD bands in Europe. The data applies equally well in the case here
Antenna configuration
Coupling loss
Dual antennas in the same radome
30dB
Default separation on the same mast <1m
45-48dB
Careful separation on the same mast >1m
55-65dB
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25. Interference issues with mixed band plan –Filter Characteristics
Nokia claim page 7: Lucent proposal that interference problems can be mitigated by providing 2.25 MHz guard band and 60 dB additional filtering at the CDMA BS and WCDMA BS is not practical
Our response:
Considering the blocks at the band edges will most likely be 5 or 10MHz wide, it is quite possible to design filters that can provide 60 dB rejection in a very small frequency range from the band edge
The next chart shows the measured response of a “low cost” BTS filter that can meet the objections from Nokia given a 5 MHz allocation at the edge of the band
This filter has 60 dB of rejection within 1 MHz from the band edge, coupled with less than 0.75 dB of insertion loss. It will easily support 3 CDMA2000 carriers or 1 WCDMA carrier
If the edge band allocations at 1980 MHz were 5MHz each, using this filter would result in the need for NO added guard band
If this filter replaced the existing filters, rather than added to the existing filter, there would be essentially no loss in coverage
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26. Suitable filter for 1980 band edge isolation for 5MHz allocations
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27. Interference issues with mixed band plan –Filter Issue (repeated)
Nokia claim page 7: Lucent proposal that interference problems can be mitigated by providing 2.25 MHz guard band and 60 dB additional filtering at the CDMA BS and WCDMA BS is not practical:
Our response:
The next chart shows the simulated response of a “low cost” BTS filter that can meet the objections from Nokia given a 10 MHz allocation at the edge of the band
This filter has 60 dB of rejection 2.5 MHz from the band edge, coupled with less than 0.5 dB of insertion loss in the desired band
This implies that some emissions would pass through and additional means for isolation are required
Some options were discussed earlier, and using the Lucent suggestion of having 4.8MHz spacing between WCDMA carriers is enough to solve this problem with no loss in the total number of carriers in either band
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28. Suitable filter for 1980 band edge isolation for 10 MHz allocations
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29. BTS to BTS interference issues – Summary
Using minimum coupling loss methods to establish Isolation requirements leads to overly pessimistic results, not representative of the real world.
Using specified performance values for transmitters and receivers to establish Isolation requirements also leads to overly pessimistic results, since they are not representative of the actual equipment performance.
We believe 90 dB isolation is adequate to meet the BTS to BTS interference conditions for both the emission and blocking issues. But that up to 114 dB can be met with a combination of filters and antenna isolation if needed in extreme cases.
60 dB rejection filters are available
50 dB of antenna isolation is quite possible with good practice, for collocated and non-collocated systems. Only 30 dB is possible for systems that share the same antenna.
50 dB of antenna isolation can be achieved with site to site spacing of 30 Meters.
40 dB of antenna isolation can be achieved with site to site spacing of 10 Meters.
If the edge band allocations at 1980 MHz were 5MHz each, filters are available which would result in the need for NO added guard band.
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30. Interference issues: IMT-2000 handset to the PCS CDMA handset, Monte-Carlo method
Nokia claim on page 9: mixed plan will result in interference between the IMT-2000 handset to the PCS CDMA handset when they are in close proximity to each other
Lucent has provided TRAI with the results of a Monte-Carlo method to estimate the issue of mobile station interference
We will not repeat that presentation here, but do restate exactly the results:
Under the assumed conditions, CDMA downlink capacity degradation is <5%
Leads to the conclusions that mobile to mobile interference is expected to occur a relatively small percentage of the time
Analysis assumed conservative full load for UMTS
Analysis assumed full-shifted overlay, which is conservative
UMTS mobile and CDMA mobile must both be active for interference to occur (all mobiles assumed active in the simulation)
CDMA mobiles could be given more power if cells are running at less than full load
If UMTS mobile spurious emissions are better than standards, interference effects are reduced. Spurious also reduces with power.
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31. Interference issues: IMT-2000 handset to the PCS CDMA handset, MCL method – contd…
In reviewing the assumptions used in the Monte-Carlo analysis, we believe adding more detailed information using an MCL method will show that the Monte-Carlo method was pessimistic.
The typical noise floor of a CDMA2000 or WCDMA handset is about -105dBm/Hz, far less than specified.
An example is shown in the following chart, for a CDMA2000 handset.
When transmitting at maximum power, this floor is reached at about +/ MHz from the center of the CDMA2000 carrier, and to not interfere with a CDMA handset, this needs to be reduced to about -170 dBm/Hz.
Allowing 3 dB of body loss, this requires 59 dB of path loss between the two CDMA2000 handsets, which at 1980 MHz occurs at less than 10 Meter separation.
This results from using a “2 slope” propagation model, show in a following chart.
If the jammer is a WCDMA handset, the floor is reached at about +/-7.5 MHz.
This is a minimum coupling loss method of analysis and as before will yield pessimistic results compared to monte-carlo methods which better reflect real world conditions, but only of real world performance is used, not justspecified performance.
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32. Typical CDMA2000 handset spectrum at maximum power
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33. Interference issues: IMT-2000 handset to the PCS CDMA handset, MCL method – contd…
Handsets at the extreme combination of maximum power from the jammer and minimum signal at the victim occur in very few cases
If the TX power of the handset is decreased 10 dB from maximum the noise floor decreases significantly, reaching -100 dBm/Hz within 2.5MHz and -115 dBm/Hz within 5 MHz
– This is shown on the next chart
This reduces the interference distance at 5MHz offset to less than 3 meters
If the victim handset signal is 10 dB above threshold, the same interference distance results
A combination of these reduces the interference range to less than a meter
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34. Interference issues: IMT-2000 handset to the PCS CDMA handset
If the TX power of the handset is decreased 10 dB from maximum the noise floor decreases significantly, reaching -100 dBm/Hz within 2.5MHz and -115dBm/Hz at 5 MHz
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35. Path loss models for mobile to mobile interference calculations
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36. Restatement of AUSPI’s position
Present allocation in 800 MHz for CDMA –Not sufficient for multiple operators
Internationally allocation for large operators varies from 10+10MHz to MHz (average allocation MHz)
CDMA operators need additional allocation in other bands to grow their networks
Globally, CDMA systems work in 800 MHz and 1900 MHz, with the exception of Korea
Korean PCS is unique and is not used anywhere else in the world
AUSPI has proposed service neutral plan of 800 MHz and 1900 MHz for CDMA and 900 MHz and 1800 MHz for GSM in line with international standards
Notwithstanding this position, we disagree with Nokia’s conclusions on a mixed band plan
Interference issues at the 1980 MHz boundary can be dealt with by providing filters where needed
Not all BTSs will require filters, and for those that do, these filters are cost effective
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37. References
European Radio communications Committee (ERC) Report 101, “A Comparison of Minimum Coupling Loss Method, Enhanced Minimum Coupling Loss Method and the Monte-Carlo Simulation”, Menton, 1999.
A.H. Mohammadian, L Golovanesky, S.S. Soliman, M.A. Tassoudji, “Prediction of Mutual Coupling between Base Station Antenna Arrays”, Proceedings of 2002 IEEE Radio and Wireless Conference, Boston, MA, August 11-14, 2002.
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38. Thank you!
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