We write custom essays and can help you with

The essay examples we publish have been submitted to us by students. The essays are the student's work and are not examples of our expert essay writers' work. READ MORE

See how we can help

Essential telecommunication services

Abstract- Satellite operators are using the C-Band globally to provide essential telecommunication services. In many countries it serves as the core network for national and international communication. The new terrestrial service (IMT 2000) defined by the International Telecommunication Union (ITU) uses the same spectrum (C-Band) which causes the interference in satellite downlink section. Interference is the main threat to satellite downlink performance such harmful signals originate from the terrestrial wireless application from many locations, in all directions. These signals are powerful enough to saturate the C-Band satellite receiving systems causing a potential for total loss of service in C-Band. This paper proposes a hypothesis about interference effect on satellite downlink receivers and then confirms the hypothesis with experimental results.

Keywords- Fixed Satellite Services, IMT 2000 / WiMax, Interference in C-Band, Sharing Studies, Compatibility analysis

I Introduction

C-Band is a prime band for satellite communication. There are more than 160 geostationary satellite are operating in C-Band today and are using the ITU FSS location in these bands [7]. Many more satellites today operate communication channels in other frequency bands but depend on telemetry operations (Telemetry, Tracking and Ranging) in C-band

Several administrations have allotted the Extended C-Band for this new terrestrial service "IMT 2000 / WiMax" so it become a cause of in band and out of band interference and service interruption for satellite ground station and their related services. Furthermore some administrations are looking to deploy WiMax in standard C-Band also.

Many satellite operators claim about the interference problem in different parts of world like Australia, Bolivia, the Caribbean, China, Fiji, Hong Kong, Indonesia, and Russia and in Pakistan also [1], [9].

II Types Of Interference

The interference problem that is experienced in satellite link due to the new terrestrial service, which is severely effect the satellite link, is co-frequency emission from the terrestrial link. In view of the large distances involved, satellite signals received by earth stations have very low power and are therefore, highly sensitive to interference.

The reason behind is that terrestrial wireless applications emit signals from many locations, in all directions, simultaneously. These signals are powerful enough to saturate the sensitive C-band satellite receiving systems, causing a potential for total loss of service in the C band [2].

The 2nd obsession which is experienced / observed in the satellite ground stations is the out of band emission from the terrestrial link makes a problem to the non-overlapping part of the band [2].

III Sharing Studies

The sharing study is divided into two parts. First one is called the Preliminary analysis and the second one is called the compatibility analysis.

A. Preliminary Analysis

The basis of performing preliminary analysis is to find out the coordination area around a satellite earth station. For this the help was taken from ITU Recommendation R-1448 and Appendix-7 of the ITU Radio Regulation which describe the coordination area around a receiving / transmitting earth station which share the same frequency band (100MHz-105GHz) with the terrestrial services. On the basis of these Recommendation / Radio Regulations ITU has developed software which describes the coordination area around an earth station. Its purpose is to identify the area within which detailed evaluations of the interference potential need to be performed in order to determine whether the coordinating earth station or any of the terrestrial stations, that are sharing the same frequency band, will experience unacceptable levels of interference. Hence, the coordination area is not an exclusion zone within which the sharing of frequencies between the earth station and terrestrial stations or other earth stations is prohibited, but a means for determining the area within which more detailed calculations need to be performed. The calculation is to be done for worst case on the basis of worst case the coordination contour is to be calculated.

As an illustrative example, Figure shows the coordination contour around Islamabad Earth station in Pakistan in the band 3400 - 4200 MHz. So detail analysis is required to coordinate the terrestrial and satellite earth station to operate in the same region. It can be said that the coordination area is a trigger which describes that more detailed bilateral coordination follows to find a means of enabling sharing to take place [5]-[6].

B. Compatibility analysis

Some technical parameters which are provided by ITU about FSS earth station and IMT base station to support in completion of sharing studies are as under:

FSS Earth station characteristics in 3400-4200MHz Band: For the purpose of analysis, a typical earth station is considered which can be placed at any region (Rural or Urban). The earth station antenna pattern which is used here is ITU-R S-465

The emission bandwidth which is considered here from 4 KHz to 72 MHz in the analysis.

IMT Advanced Base Station and Mobile Station Characteristic:

a) Advanced Base Station: In IMT 2000 service two types of Base stations are used, one is the macro BS and the other is the micro BS. The maximum EIRP for macro BS and micro BS is 59dBm and 35dBm respectively [3]. The reference signal bandwidth here is 20MHz to 100MHz. The RX/TX antenna which is used in the macrocell is sectored (antenna gain= 20dBi) and omni (antenna gain= 5dBi) for microcell [3].

b) Mobile Station: The EIRP value for the mobile station provided by the ITU is 24dBm. The reference signal bandwidth range is same as defined for the Advanced Base Station [3]. The RX/TX antenna which is used in the Mobile Station are omni directional (antenna gain= 0dBi).

FSS Protection Criteria: FSS protection criteria which is defined by ITU where FSS may share the band on the equal basis with the Fixed service and Mobile service. The long term interference to noise criteria defined for MS and FS is -12.2dB for the 20% of time. Here, as a standard practice, the equal noise contribution from the two interfering services is considered. The long term criteria defined in the ITU Recommendation ITU-R S.1432 [10]. For short term interference to noise criteria three equivalent and uncorrelated source of interference have been considered, then the short term protection criterion would be equivalent to an I/N of -1.3 for 0.005% of time. This criteria also appear in Annex 7 of Appendix 7 of the Radio Regulation [6].

I/N, being the most important parameter in this work. Using Recommendation S.1432 as a basis to develop long term interference criteria, [11]. Following equation is used to calculate the permissible interference level for long term criteria (refered in [6] above). The same approach is also applied for short term.

Impact of IMT-Advanced interference into FSS systems: In this paper the analysis of the single entry interference only for both short term and long term criteria is considered. The reason for doing so is that the exact no. of users accessing IMT advanced system is not known .

The analyses are based on the propagation models described in ITU-R P.452-12. Here the generic nature of the analysis is performed. For the long-term protection cases, the propagation is calculated over a smooth earth surface, utilizing the propagation model described in Section 4.3 of ITU-R P.452-12. The model in ITU-R P.452-12 includes the effects of building losses and clutter and the topography of surrounding obstacles etc. However, due to lack of information for these parameters, the building losses and clutter effects has been assumed to represent suburban environment in these analyses [3]-[4].

Furthermore, in the case of short-term propagation, the ducting mode of propagation model, as described in Section 4.5 of ITU-R P.452-12 has been utilized. In order to simplify the model, rain scatter and tropospheric scatter is not considered here.

The required isolation to mitigate interference from a macro cell base station in the IMT-Advanced system operating at its maximum transmission capability (46 dBm/MHz) would be equivalent to:

Using the propagation model of P.452-12, the following minimum separation distances between an FSS station and a Base Station were estimated, such that the identified protection criterion is achieved [3]

The mobile station in the IMT-Advanced system is assumed to be operating at its maximum transmission capability (11 dBm/MHz) TABLE III. Minimum separation distances between an FSS station and a Base Station to achieve the stated FSS protection criterion

IV Discussion & Conclusions

The studies show that when no particular shielding or blocking with the respect to the interfering signal can be guaranteed, the minimum required separation distances would be 140Km. So co existence between FSS and IMT 2000 is more difficult. In situations where IMT 2000 may be introduced on a regional basis, the following measures may be considered.

To prohibit FS deployment in areas known to have high density of FSS earth stations, such as urban areas. IMT2000 systems might be allowed in other areas where there is low density of deployment.

To establish a location database for FSS earth stations such that those earth stations with known locations in the database would be offered protection through FS services.

References

AsiaSat, Presentation On "Broadband Wireless Access and C-Band satellite. Is sharing spectrum possible?"
Asia-Pacific Telecommunity , The 3rd Interim Meeting Of The APT Wireless Forum, Document AWF-IM3/10 (Rev.1) "Report On Co-Existence Of Broadband Wireless Access Networks In The 3400-3800 MHz Band And Fixed Satellite Service Networks In The 3400-4200 MHz Band", January 2007
International Telecommunicatio Union , Radiocommunication Study Groups, Document 8F/998-E, "Study Of Interference From IMT-Advanced Into Fss, And From Fss Into IMT-Advanced In The Band 3 700-4 200 MHz", August 2007.
The ITU Radiocommunication Assembly, "Prediction Procedure For The Evaluation Of Microwave Interference Between Stations On The Surface Of The Earth At Frequencies Above About 0.7 GHz", Rec. ITU-R P.452-12, 2001
The ITU Radiocommunication Assembly, "Determination Of The Coordination Area Around An Earth Station In The Frequency Bands Between 100 MHz And 105 GHz", Rec. ITU-R SM.1448-12, 2003.
International Telecommunicatio Union, World Regional Conference, "Methods For The Determination Of The Coordination Area Around An Earth Station In The Frequency Bands Between 100 MHz And 105 GHz", Appendix 7 (Rev. WRC-03), 2003.
International Telecommunicatio Union, World Regional Conference, ARTICLE 5, "Frequency Allocations", 2003.
The ITU Radiocommunication Assembly, "Reference earth-station radiation pattern for use in coordination and interference assessment in the frequency range from 2 to about 32 GHz", Rec. ITU-R S.465-5, 2008
Robert Ames, Adam Edwards, Kenneth Carrigan, "Field Test Report WiMAX Frequency Sharing with FSS Earth Stations February 2008" Satellite User Interference Reduction Group, Oct 2008
The ITU Radiocommunication Assembly, "Apportionment of the allowable error performance degradations to fixed-satellite service (fss) hypothetical reference digital paths arising from time invariant interference for systems operating below 15 GHz ", Rec. ITU-R S.1432 , 2000
The ITU Radiocommunication Assembly, "Apportionment of the allowable error performance degradations to fixed-satellite service (fss) hypothetical reference digital paths arising from time invariant interference for systems operating below 15 GHz ", Rec. ITU-R S.1432 , 2000