Sharing in the 1710-1755 MHz Band Segment. The 1710-1755 MHz band was identified to be transferred to the FCC under OBRA-93 as a mixed-use band.⁽¹⁸⁾ Certain military facilities, safety-of-life and power distribution fixed links were exempted from the reallocation. Protection Areas were established around the military facilities as shown in the NTIA Final Reallocation Report. In this segmentation option, IMT-2000 mobiles would transmit in this portion of the band. To allow IMT-2000 operation within the protection areas, IMT-2000 base stations would need their operation coordinated with military operations. One option would be for IMT-2000 base stations to be designed with a listen-before-transmit feature to avoid interference to and from military systems in the band. The base stations within the protection areas would listen on each of the IMT-2000 mobile channels, and would not assign a mobile to that channel if it detected a signal above a pre-determined threshold level.

Federal stations operating in the 1710-1755 MHz band are eligible for compensation for relocation to another frequency band. Therefore, the currently-exempt fixed links could be moved at the expense of commercial IMT-2000 operators. This would clear the band of most Federal operations, with the exception of the 17 protected military operations areas, and various other Federal users.

Sharing in the 1805-1850 MHz Band Segment. The 1805-1850 MHz portion of the band is currently used as described earlier in this report. This part of the band includes one-half of the SGLS channels, i.e. channels 11 through 20. This band also includes 5 ACTS ground-to-ground frequencies, and two ground-to-air frequencies. The MSE also operates in this band with assignments generally spaced 500 kHz apart.

A large number (3,836) of Federal frequency assignments for stations in the fixed service are in this portion of the band. These conventional fixed stations are eligible for compensation for relocation by IMT-2000 operators. It is postulated that this band could be cleared of most conventional fixed systems by a reimbursement process.

There are also a variety of other Federal operations not detailed in this report. Many of these operations involve law enforcement, and operate nation-wide. These systems would also need to be relocated from the 1710-1755 MHz and 1805-1850 MHz segments by a reimbursement process.

2. Potential Sharing Conflicts

In this interim report we are postulating that it might be possible to share the 1710-1850 MHz band with IMT-2000 systems, under certain conditions. The first condition is that the 17 protected areas as shown in the NTIA Final Reallocation Report remain, and DOD operations within these areas are not impacted. Second, that it would be possible to determine protection areas around other Federal operations, such that IMT-2000 systems operate normally outside of these areas, but would need coordination with Federal operations within the areas. Third, that it would be necessary to relocate most conventional Federal fixed service systems to alternate bands by a method of reimbursement. Further, various other Federal operations would need to relocate to other bands or re-tune to the remaining 1755-1805 MHz segment. The size of the protection areas will vary from the preliminary values shown in this report, and would be determined by either a detailed analysis of each site, using terrain data, or by field measurements of signal strengths.

1710-1755 MHz Segment

Tactical Radio Relay. The MSE system is used to support the warfighters' data communications capabilities at all echelons of tactical operations. Because MSE systems are transportable and used to support total Army missions, they can be in operation at any time. Unlike conventional fixed systems, the antennas associated with MSE systems are pointed in different directions when activated at new locations. Using the data from the DOD Initial Report, IMT-2000 mobile stations could cause interference to MSE receivers at distances from 9 to 20 km for 3.75 MHz IMT-2000 systems, and from 11 km to 23 km for 1.25 MHz systems, depending on the position of the mobile station relative to the main beam of the MSE antenna.⁽¹⁹⁾

The MSE transmitters could cause interference to IMT-2000 base receivers at ranges from 60 to 75 km for 3.75 MHz systems, and from 62 to 82 km for 1.25 MHz systems, depending on the location of the base station antenna relative to the main beam of the MSE antenna, and interference thresholds for different IMT-2000 systems.⁽²⁰⁾

Since the required separation distance, as a factor of the antenna coupling of the IMT-2000 station to the MSE antenna, is shown to be less outside of +/- 20 degrees of the MSE antenna boresight, and minimum outside of +/- 90 degrees, there is about a 50 percent probability of a IMT-2000 station being in a minimum interference zone for any given MSE station. Within this minimum interference zone, the protection distances would be from 9 km to11 km for co-channel mobile transmitters (3.75 MHz and 1.25 MHz systems respectively),⁽²¹⁾ and from 60 km to 62 km for IMT-2000 base receivers (3.75 MHz and 1.25 MHz systems respectively).⁽²²⁾ The AN/GRC-245 and other similar radios performing radio relay functions have nominally the same protection distances.

Conventional Fixed. The Federal Government operates many fixed, point-to-point service links in the1710-1755 MHz band. This band will be transferred to the FCC in 2004 on a mixed-use basis. Fixed links in this band that are within the military protection areas, and those power distribution and public safety links shown in the NTIA Final Reallocation Report, will be protected. These protection areas vary in size from 50 to 120 km. However, Federal stations may be reimbursed for relocation to alternate frequency bands. ITU-R Recommendations have concluded that separation distances up to 120 km are necessary to prevent interference between mobile and fixed stations.⁽²³⁾ Due to the significant number of protected fixed systems, the establishment of protection areas surrounding each of these protected fixed service links is not practical.

1805-1850 MHz Segment

Government Satellites. Under this segmentation option, the IMT-2000 base stations would be transmitting (and mobile stations receiving) in the 1805-1850 MHz portion of the band. A large number of base stations transmitting simultaneously would cause interference to the satellite uplinks. The DOD Initial Report shows that IMT-2000 base station transmitters would cause a degradation to the link margin of DOD satellites from 27 to 37 dB, depending on degree of IMT-2000 build-out.⁽²⁴⁾ It is doubtful that sharing would be feasible under this scenario. If further analysis shows that the link margin will not so severely degraded in an environment of IMT-2000 base transmitters, then the 1805-1850 MHz band might be shared with IMT-2000 base stations, using a combination of geographical and time separation.

Satellite Control Stations. Data from Tables 7 and 8 show that when satellite control stations are transmitting, the IMT-2000 mobile receivers could receive interference at distances from 31 km to 121 km for 3.75 MHz mobile systems, and from 42 km to 151 km for 1.25 MHz mobile systems, depending on SGLS transmitter power and antenna elevation. Actual distances will be less than was calculated using a smooth-Earth model, because actual SGLS signals will be propagated over rough terrain. For comparison, several plots of interference contours surrounding SGLS sites, using actual terrain data, are included in the DOD Initial Report.⁽²⁵⁾

Tactical Radio Relay. The MSE system is used to support the warfighters' data communications capabilities at all echelons of tactical operations. Because MSE systems are transportable and used to support total Army missions, they can be in operation at any time. Unlike conventional fixed systems, the antennas associated with MSE are pointed in different directions when activated at new locations. Using the data from the DOD Initial Report, IMT-2000 base stations could cause interference to MSE receivers at distances ranging from 61 km to 78 km for 3.75 MHz systems, and from 64 km to 87 km for 1.25 MHz systems, depending on the position of the mobile station relative to the main beam of the MSE antenna.⁽²⁶⁾ The MSE transmitters could cause interference to IMT-2000 mobile receivers at ranges from 18 km to 32 km for 3.75 MHz systems, and from 20 km to 34 km for 1.25 MHz systems, depending on the location of the mobile station relative to the main beam of the MSE antenna, and the interference threshold used.⁽²⁷⁾

Since the required separation distance, as a factor of the antenna coupling of the IMT-2000 station to the MSE antenna, is indicated to be minimum outside of +/- 20 degrees of the MSE antenna boresight, and minimum outside of +/- 90 degrees, there is about a 50 percent probability of a IMT-2000 station being in a minimum interference zone for any given MSE station. Within this minimum interference zone, the protection distances would range from 61 km to 64 km for co-channel base transmitters (3.75 MHz systems and 1.25 MHz, respectively).⁽²⁸⁾ Protection distances would range from 18 km to 20 km for co-channel IMT-2000 mobile receivers (3.75 MHz systems and 1.25 MHz systems respectively).⁽²⁹⁾ The AN/GRC-245 and other similar radios performing radio relay functions have nominally the same protection distances.

Air Combat Training Systems. Generally, the analysis in the DOD Initial Report shows that the airborne receiving component of the air combat systems would suffer degradation throughout much of the United States, with up to 29 dB reduction in link margin in fairly large areas due to IMT-2000 base stations transmitting (the only ACTS aircraft links in this band segment are ground-to-air links).⁽³⁰⁾ Five remote-to-master ground links would be affected, as well as the two ground-to-air links. Data from the DOD Initial Report, indicates that the ACTS ground stations would require separation distances ranging from 70 km to 146 km from transmitting IMT-2000 base stations,⁽³¹⁾ but the mobile stations could operate at distances of from 12 to 48 km from transmitting ACTS ground stations.⁽³²⁾ Operation of the ACTS system without the use of ground stations, (rangeless operation) would not be feasible due to the widespread interference.

Unlike the ACMI/TACTS, the JTCTS will employ an air-to-air communication function as its primary link. The EMC between IMT-2000 systems and this JTCTS air-to-air link needs to be investigated to determine the feasibility of sharing.⁽³³⁾ The separation distances for the air-to-ground function of the JTCTS, which is similar to ACMI/TACTS, are nominally the same.⁽³⁴⁾ This function will be a secondary link for JTCTS. The ground-to-ground function of the JTCTS will be considered a tertiary data link and will not always be used.

Interference Mitigation. If the IMT-2000 base stations were to monitor the IMT-2000 mobile channels on a listen-before-transmitting protocol, interference would be mitigated at the expense of IMT-2000 system capacity. It should be noted, in a general sharing scenario, that there will be a greater potential for interference to and from IMT-2000 systems when both links (mobile and base) are within the 1710-1850 MHz band as opposed to only one link being in the band.

Option 2: Dual-Band pairing using the 1710-1790 MHz Band

1. Discussion

Under this arrangement (Option 2), IMT-2000 mobiles would transmit from 1710 MHz up to 1790 MHz in phases,⁽³⁵⁾ and base stations would transmit in frequency bands above 2110 MHz. This would, in the long-term, yield up to 2x80 MHz for IMT-2000 implementation. This pairing arrangement is included in the work being undertaken by ITU-R Working Party 8F, which had the preliminary comments: "[This pairing] could provide global arrangements in the longer term and hence economies of scale, but would require substantial re-planning of existing allocations, might provide not enough forward-link capacity, and accommodation of TDD requirements needs to be considered."⁽³⁶⁾ Some countries in the Americas have endorsed this approach in order to promote long-term harmonization.⁽³⁷⁾

The analysis of the DOD Initial Report shows that IMT-2000 mobile transmitters would cause from 10 to 20 dB degradation to the link margin of DOD satellites as a function of IMT-2000 build-out. If further analysis shows that the degradation of link margin is less, or will not severely impact DOD satellite operations, then the 1760-1790 MHz portion of the band could also be considered for sharing with IMT-2000 mobiles, using a combination of geographical and time separation. This sharing arrangement would consist of three phases. For this report, no estimate of the timing of Phases 2 or 3 is given. The three phases are as follow:

Phase 1. In Phase 1, IMT-2000 mobiles would transmit in the 1710-1755 MHz band, under conditions similar to the 1710-1755 MHz part of the in-band sharing Option 1 described above, except that the mobile stations are now paired with base stations transmitting above 2110 MHz. Protection Areas are protected areas around military facilities as shown in the NTIA Final Reallocation Report.⁽³⁸⁾ The 1710-1755 MHz band was identified for transfer to the FCC under OBRA-93 as a mixed-use band. Certain military facilities, safety-of-life and power distribution fixed links were exempted from the reallocation.

As an option to allow IMT-2000 operation within the protection areas, IMT-2000 base stations would need to be designed with a listen-before-transmit feature to avoid interference from military systems in the band. Within the protection areas, IMT-2000 base stations monitor the mobile station's transmit channel frequencies. If signals are detected on a transmit channel, mobiles are prohibited from transmitting on that channel. The base station will assign a transmit channel to a mobile only on a channel in which no other signal is detected.

Federal stations operating in the 1710-1755 MHz band are also eligible for compensation for relocation to another frequency band. Therefore, the currently-exempt fixed links could be moved at the expense of commercial IMT-2000 operators. This would clear the band of most Federal operations, with the exception of the 17 protected military operation areas.

Phase 2. In Phase 2, the 1755-1780 MHz band is added for sharing with mobiles, paired with base stations above 2110 MHz. The potential for interference to satellite control uplinks is also added, since this band segment contains SGLS channels 1-5. IMT-2000 mobile transmitters would cause from 10 to 20 dB degradation to the link margin of DOD satellites as a function of IMT-2000 build-out. If further analysis shows that the degradation of link margin is less, or will not severely impact DOD satellite operations, then the 1761-1780 MHz portion of the band could be considered for sharing with IMT-2000 mobiles. The 1780 MHz end point for Phase 2 was chosen to avoid IMT-2000 interference to the GPS uplink control channel (SGLS channel 6) at 1783.74 MHz (+/- 2.002 MHz). If further analysis shows possible interference to GPS, then the Phase 2 additional band would be reduced. New protection areas could be established around satellite control sites for a -123 dBm base station received signal with maximum transmit power of that control site (but not to exceed 7 kW) and antenna elevation of 3 degrees. Federal conventional fixed stations are assumed to be relocated from the 1755-1780  MHz band by a reimbursement process.

The ACTS would not be able to share co-channel with IMT-2000 systems. Therefore, the frequencies of 1768 MHz and 1778 MHz would need to be relocated by a reimbursement process (alternately, establish protection areas around Air Combat Training areas for the frequency 1778 MHz⁽³⁹⁾). Within the protection areas for ACTS and satellite control sites, IMT-2000 base stations would monitor the mobile station's transmit channels. If signals are detected on the transmit channel, mobiles would be prohibited from transmitting on that channel. The base station will assign a transmit frequency to a mobile only on any frequency on which nothing is heard on the transmit frequencies. Within the protection areas, IMT-2000 channels in the 1710-1755 MHz band will be assigned first. If those channels are used within a given cell, only then will the channels in the 1755-1780 MHz band be assigned.⁽⁴⁰⁾

1755-1780 MHz Segment. This band segment contains 1,225 frequency authorizations, distributed among the following categories as follows:

Phase 3. In Phase 3, the1780-1790 MHz band is added for mobiles to transmit, paired with base stations above 2110 MHz. SGLS channels 6, 7 and 8 are in this band. IMT-2000 mobile transmitters would cause from 10 to 20 dB degradation to the link margin of DOD satellites as a function of IMT-2000 build-out. If further analysis shows that the degradation of link margin is less, or will not severely impact DOD satellite operations, then the 1780-1790 MHz portion of the band could be considered for sharing with IMT-2000 mobiles. Federal conventional fixed stations could be relocated from the 1780-1790 MHz band by a process of reimbursement. Within the protection areas, IMT-2000 base stations monitor the mobile station's transmit channels as above. IMT-2000 channels in 1710-1780 MHz band would be used first. If all those channels are busy, then channels in the 1780-1790 MHz band will be assigned.

1780-1790 MHz Segment. This band segment contains 498 frequency authorizations, distributed among the following categories as follows:

2. Potential Sharing Conflicts

1710-1755 MHz Segment

The sharing potential would be the same as discussed under sharing Option 1. It is assumed that in the long-term, most conventional fixed links outside on the protection areas will be relocated to alternate frequency bands by a reimbursement process. Fixed links within the protection areas may remain indefinitely, or be relocated by reimbursement.

1755-1790 MHz Segment

The 1755-1790 MHz segment has in it the kinds of Federal systems seen in both the 1710-1755 MHz and the 1805-1850 MHz segments .

Government Satellites. An analysis of the potential for IMT-2000 mobile (handheld) stations to interfere with the SGLS uplink is contained in the DOD Initial Report. This analysis shows that the uplink signal margin would be degraded from 10 dB (in 2003) to 20 dB (full IMT-2000 build-out)⁽⁴¹⁾.

A conclusion taken from the DOD Initial Report states "Interference from IMT-2000 base stations is much more severe than from the mobile stations, but both represent significant interference to SATOPS (satellite operations). The higher the orbit and the lower the elevation angle the more degradation in the link margin, given a constant transmit power. The negative net margins predicted for the GPS and geostationary orbits indicate that co-channel sharing with IMT-2000 base stations may not be feasible even in the initial stages of IMT-2000 implementation. With a fully built out IMT-2000 system, interference to spacecraft in lower orbits is predicted to be significant. Sharing with mobile stations will be less of a problem. Even so, negative net margins are predicted at the geostationary orbit in 2003 and at the GPS orbit by 2010. Increasing AFSCN transmitter power will minimize the interference on the uplink, but will increase interference to IMT-2000 receivers. Note that these predictions are based on traffic loading at the busy hour. Interference levels at other times will be less, but may not be low enough to be negligible.⁽⁴²⁾

Satellite Control Stations. The IMT-2000 mobile stations would be transmitting (and base stations receiving) in the1755-1790 MHz portion of the band. This portion of the band contains SGLS channels 1-8, including the GPS uplink channel. The data from Tables 7 and 8 show that the radius of the protection areas surrounding satellite control sites would vary from 148 km to 406 km for 3.75 MHz systems, and 174 km to 448 km for 1.25 MHz systems, based on a smooth-Earth propagation model, depending on the uplink transmitting power and the antenna elevation angle. Actual distances will be less due to propagation over rough terrain. For comparison, several plots of interference contours surrounding SGLS sites, using actual terrain data, are included in the DOD Initial Report.

Tactical Radio Relay. The assessment for tactical radio relay in the 1755-1790 MHz segment is the same as for the 1710-1755 MHz segment.

Air Combat Training Systems. Generally, the DOD Initial Report shows that the ACTS downlink at 1778 MHz and the ACTS master ground station transmitting at 1768 MHz would cause interference to IMT-2000 receiving base stations at distances ranging from 48 km to 405 km (slant range from aircraft)⁽⁴³⁾ and from 49 km to158 km from the ground stations,⁽⁴⁴⁾ respectively.

Unlike the ACMI/TACTS, the JTCTS will employ an air-to-air communication function as its primary link. The EMC between IMT-2000 systems and this JTCTS air-to-air link needs to be investigated to determine the feasibility of sharing.⁽⁴⁵⁾ The separation distances for the air-to-ground function of the JTCTS, which is similar to ACMI/TACTS, are nominally the same.⁽⁴⁶⁾ This function will be a secondary link for JTCTS. The ground-to-ground function of the JTCTS will be considered a tertiary data link and will not always be used.

Other Issues

1. International Issues

The possibility exists that other countries will implement IMT-2000 systems in the 1755-1850 MHz frequency band and the United States will not. A particular concern in this case is the potential impact to United States space borne and airborne receivers since these receivers will be especially subject to the emissions of IMT-2000 systems operating in other countries.

2. National Defense Authorization Act of 2000⁽⁴⁷⁾

Sharing scenarios have been postulated in this report as a means of accommodating IMT-2000 systems. However, if sharing is determined not to be feasible, then either Federal systems in the band segments required for IMT-2000 operation would be relocated, and the band reallocated, or IMT-2000 services will not be implemented in the band. It must be noted that the NDAA-FY00 contains provisions that restrict certain frequency reallocation actions. Specifically, before DOD can surrender any bands of frequencies in which is a primary user, (1) NTIA, in consultation with the FCC, must identify and make available to the DOD an alternative band or bands of frequencies as a replacement; and (2) The Secretary of Commerce, the Secretary of Defense, and the Chairman of the Joint Chiefs of Staff have jointly certified to both the Committee on Armed Services and the Committee on Commerce, Science and Transportation of the Senate, and the Committee on Armed Services and the Committee on Commerce of the House of Representatives, that the replacement band or bands of frequencies as identified above provides comparable technical characteristics to restore essential military capability that will be lost as a result of this reallocation.

The DOD would be regarded as a primary user in the1755-1850 MHz band, thus requiring the approval actions noted above.

3. Sharing Issues

The sharing options presented in the sections above are preliminary, based on current EMC studies, assumptions of IMT-2000 parameters, and the assumed ability of base stations to "listen" before assigning transmit frequencies to the mobile stations. These and other technical factors will need to be studied further to determine the degree of merit these sharing options possess.

1. National Telecommunications and Information Administration, U.S. Department of Commerce, NTIA Special Publication 94-27, Preliminary Spectrum Reallocation Report (1994).

2. International Telecommunication Union, Use by the Mobile Service of the Frequency Bands 2025-2100 MHz and 2200-2290 MHz, Resolution 211, WARC-92 (Malaga-Torremolinos, 1992).

3. See DOD Initial Report, supra note 3 at Appendix B (Interference to Satellite Operations) and Appendix C (Interference to IMT-2000 receivers).

4. Id. at B-3.

5. Id. at B-5 through B-12.

6. Id. at C-11 through C-14.

7. International Telecommunication Union, Geneva, Switzerland, ITU-R Recommendation F.1334 [hereinafter ITU-R F.1334].

8. See NTIA Final Reallocation Report, supra note 12 at F-4.

9. See ITU-R F.1334, supra note 23.

10. Id.

11. See DOD Initial Report, supra note 3 at D-6 through D-10.

12. See NTIA Final Report supra note 12 at 4-11 and D-14 through D-18.

13. Id.

14. See DOD Initial Report, supra note 3 at E-1.

15. Id. at E-16.

16. Report of the San Diego Meeting of ITU-R 8F, August 2000, ITU-R 8F/63 at 55.

17. NTIA is drafting a Notice of Proposed Rulemaking to address reimbursement of costs incurred for relocating Federal radio systems as a result of Omnibus Budget Reconciliation Act of 1993 and the Balanced Budget Act of 1997.

18. "Mixed Use" is a term defined in the Omnibus Budget Reconciliation Act of 1993 for frequency bands reallocated from Federal to private use in accordance with this Act, which are partially retained for continued use by Federal stations.

19. See DOD Initial Report, supra note 3 at D-6.

20. Id. at D-7.

21. Id. at D-6.

22. Id. at D-7.

23. See ITU-R F.1334, supra note 23.

24. See DOD Initial Report, supra note 3 at B-9 and B-12.

25. Id. at C-11 through C-14.

26. Id. at D-6.

27. Id. at D-7.

28. Id. at D-6.

29. Id. at D-7.

30. Id. at E-10.

31. Id. at E-13.

32. Id. at E-15.

33. Id. at E-23.

34. Id. at E-13, E-19.

35. Id. at 1-3

36. Report of the San Diego, CA meeting of ITU-R 8F, August 2000, ITU-R 8F/63 at 62 .

37. See October 2000 contribution to ITU-R WR8F, ITU-R Doc 8F/148, Oct 20, 2000.

38. See NTIA Final Reallocation Report, supra note 12 at F-4.

39. This is the aircraft downlink frequency, and would be more difficult to move than the ground station frequency.

40. This gives maximum protection to the satellite uplinks.

41. Id. at B-5 and B-8.

42. Id. at B-3.

43. See DOD Initial Report, supra note 3 at E-16.

44. Id. at E-15.

45. Id. at E-23.

46. Id. at E-13, E-19.

47. See National Defense Authorization Act 1999, Pub. L. No. 106-65, 113, Stat. 512 (October 5, 1999).