Cognitive SatCom Simulator for Non-Exclusive Ka-band multibeam systems

1.     Short Description

The Cognitive SatCom Simulator demonstrates the optimal resource allocation techniques (carrier/power) for a cognitive spectrum utilization scenario where the satellite system aims at exploiting the spectrum allocated to terrestrial networks as the incumbent users without imposing harmful interference to them.

In particular, we focus on cognitive Ka-band multibeam satellite systems exploiting the microwave frequency bands (17.7-19.7 GHz for the cognitive satellite downlink and 27.5-29.5 GHz for the cognitive satellite uplink) which are licensed to terrestrial Fixed-Service (FS) links.

2.     Functionality

Figure 1 shows the schematic plan of the cognitive satellite simulator. We can differentiate 3 main parts whose functionalities are described below.

Figure 1. Cognitive Satellite Simulator Schematic Plan

Blocks and functionalities:

• Radio Environment Mapping:this unit is responsible to calculate the received/imposed interference from/to the incumbent users, based on the information obtained through databases (or spectrum sensing/estimation if database is not available). For interference modeling, ITU-R interference model between the earth stations is applied. Another part of this unit is responsible to feed the fixed satellite service (FSS) link budget information to the network management unit in order to calculate the SINR over each carrier and in each FSS terminal.

• Network management:based on the interference levels and FSS link budget received from radio environment mapping, first the SINRs are calculated. If the SINR over specific carriers and in specific terminals does not satisfy the minimum requirements, beamforming is applied in order to improve the SINR in the mentioned terminals. The final calculated SINRs are fed to the carrier allocation unit, which assigns the carrier optimally to the terminals so as to maximize the system capacity. Note that the role of power control in this unit is applied to the scenarios where the cognitive terminal works in the uplink. Therefore, power management is required so as to satisfy the regulatory interference limit and maximize the throughput.

• Performance evaluation:the final block is responsible to calculate the system throughput, and availability based on the assigned carrier and power levels from the network management unit. 

3.     Sample Results

Results show that the combination of the exclusive Ka-band frequency assignment with the non-exclusive frequency bands that are primarily assigned to FS microwave links provides significant throughput gains to the FSS system.

In particular, the simulator evaluates the 3 following cases:

• Case 1- This denotes the conventional system without the use of cognitive SatCom. Only the convetional exclusive frequency bands are considered.
• Case 2- This represents the scenario where the non-exclusive spectrum is allocated exclusively to FSS system (without the presence of FS system). This case does not exist in practice but is considered for comparison purposes.
• Case 3- This depicts the scenario where FSS system considers both the exclusive plus the non-exclusive bands, which are shared with the FS system.

Fig. 2 shows the average throughput per beam obtained for the cognitive satellite downlink scenario. As expected, the per beam throughput is improved when using the 2 GHz extra bandwidth. Even without considering any resource allocation strategy, the cognitive satellite system increases its overall throughput from 0.77 to 3.09 Gpbs by accommodating some terminals in the shared band. Therefore, exploitation of spectrum opportunities in the cognitive SatCom resulted in an approximately 300% throughput improvement with respect to the conventional fixed spectrum allocation. Note that this gain can be further increased by considering carrier allocation and beamforming techniques.

Figure 2. Cognitive satellite downlink results (w/o CA: without carrier allocation; w/CA: with carrier allocation; w/ CA+BF: with carrier allocation and beamforming).

Table 2 summarizes the throughout per beam obtained for the cognitive satellite uplink scenario. Again, it is demonstrated that the cognitive satellite system throughput can be significantly improved by using the non-exclusive bands. Note that, in the uplink case, the application of the resource allocation techniques guarantee that the cognitive satellite system never exceeds the prescribed interference threshold of the FS microwave stations. This can be observed in Fig, 3, which shows the aggregate interference caused by the cognitive satellite system and received at the FS stations in terms of Cumulative Distribution Function (CDF) with and without the proposed power and carrier allocation (PCA) module. The minimum aggregate interference threshold is depicted as well in Fig. 3 for comparison purposes. It can be observed that the interference generated by the cognitive satellite system at the incumbent system exceeds the acceptable threshold when no optimal resource assignment is employed, while it is kept always below the threshold when using the proposed PCA technique.

Table 1. Cognitive satellite uplink results (w/o CA: without carrier allocation; w/CA: with carrier allocation; w/ PCA: with carrier and power allocation).

Figure 3. Cognitive satellite uplink results (w/o PCA: without power and carrier allocation; w/ PCA: with power and carrier allocation).

4.     Related Publications

• Book: "Cooperative and Cognitive Satellite Systems", Editors:S. Chatzinotas, B. Ottersten, R. De Gaudenzi. Elsevier, 2015.
• E. Lagunas, S.K. Sharma, S. Maleki, S. Chatzinotas, B. Ottersten, “Resource Allocation for Cognitive Satellite Communications with Incumbent Terrestrial Networks”, under review, IEEE Trans. On Cognitive Communications and Networking, September 2015.
• E. Lagunas, S.K. Sharma, S. Maleki, S. Chatzinotas, B. Ottersten, “Impact of Terrain Aware Interference Modeling on the Throughput of Cognitive Ka-Band Satellite Systems”, Ka and Broadband Communications Conference (KaConf), October 2015.
• E. Lagunas,S.K. Sharma, S. Maleki, S. Chatzinotas, B. Ottersten, “Power Control for Satellite Uplink and Terrestrial Fixed-Service Co-existence in Ka-band”, IEEE Vehicular Technology Conference (VTC-Fall), September 2015.
• B. Evans, P. Thompson,E. Lagunas, S.K. Sharma, D. Tarchi and V. Icolari, “Extending the Usable Ka Band Spectrum for Satellite Communications: The CoRaSat Project”, Advanced Next Generation Broadband Satellite Systems Workshop,International Conference on Wireless and Satellite Systems (WiSATS, formerly PSATS), July 2015.
• A. Guidotti, V. Icolari, D. Tarchi, A. Vanelli-Coralli,S.K. Sharma,E. Lagunas,S. Maleki, S. Chatzinotas,J. Grotz, J. Krause, E. Corbel, B. Evans, P. Thompson, “Spectrum Awareness and Exploitation for Cognitive Satellite Communications”, European Conference on Networks and Communications (EuCNC), June 2015.
• Maleki, S.; Chatzinotas, S.;Krause, J.; Liolis, K.;Ottersten, B.,"Cognitive Zone for Broadband Satellite Communications in 17.3–17.7 GHz Band," in IEEE Wireless Communications Letters,  vol.4, no.3, pp.305-308, June 2015.
• S. K. Sharma, S. Maleki, S. Chatzinotas, J. Grotz, J. Krause, andB. Ottersten, "Joint Carrier Allocation and Beamforming for Cognitive SatComs in Ka-band (17.3-18.1 GHz)," IEEE International Conference on Communications (ICC), June 2015.
• S.K. Sharma,E. Lagunas,S. Maleki, S. Chatzinotas, J. Grotz, J. Krause,B. Ottersten, “Resource Allocation for Cognitive Satellite Communications in Ka-band (17.7-19.7 GHz)”, Workshop on Cognitive Radios and Networks for Spectrum Coexistence of Satellite and Terrestrial Systems, IEEE Int. Conf. On Communications (ICC), June 2015.
• Chuberre, N.; Evans, B.; Vanelli-Coralli, A.; Krause, J.; Grotz, J.;Sharma, S.K.; “FP7 PROJECT CoRaSat intermediate results and standardization strategy - Cognitive radio techniques in Ka band SatCom context”, European Conference on Networks and Communications (EuCNC), May 2014.
• E. Lagunas, S.K. Sharma, S. Maleki, S. Chatzinotas, J. Grotz, J. Krause,B. Ottersten, “Resource Allocation for Cognitive Satellite Uplink and Fixed-Service Terrestrial Coexistence in Ka-band”, International Conference on Cognitive Radio Oriented Wireless Networks (CROWNCOM), Doha, Qatar, April 2015.
• Maleki, S.; Chatzinotas, S.;Evans, B.; Liolis, K.; Grotz, J.; Vanelli-Coralli, A.; Chuberre, N., "Cognitive spectrum utilization in Ka band multibeam satellite communications," in IEEE Communications Magazine, vol.53, no.3, pp.24-29, March 2015.
• S.K. Sharma, S. Maleki, S. Chatzinotas, J. Grotz,B. Ottersten, "Implementation Issues of Cognitive Radio Techniques for Ka-band (17.7-19.7 GHz) SatComs," Advanced Satellite Multimedia Systems Conference and Signal Processing for Space Communications Workshop (ASMS/SPSC), September 2014.
• S. Maleki, S. Chatzinotas, S.K. Sharma,A. Guidotti, D. Tarchi, A. Vanelli-Coralli, W. Tang, B. Evans, J. Grotz, K. Liolis, J. Krause, N. Chuberre, "Cognitive radio for Ka band satellite communications," AIAA International Communications Satellite Systems Conference (ICSSC), August 2014.
• Tarchi, D.; Guidotti, A.; Icolari, V.; Vanelli-Coralli, A.;Sharma, S.K.; Chatzinotas, S.; Malekil, S.;Evans, B.; Thompson, P.; Tang, W.; Grotz, J., "Technical challenges for cognitive radio application in satellite communications," in Cognitive Radio Oriented Wireless Networks and Communications Conference (CROWNCOM), June 2014.
• Liolis, K.; Schlueter, G.; Krause, J.; Zimmer, F.; Combelles, L.; Grotz, J.;Chatzinotas, S.;Evans, B.; Guidotti, A.; Tarchi, D.; Vanelli-Coralli, A., “Cognitive Radio Scenarios for Satellite Communications: The CoRaSat Approach”, in Future Network and Mobile Summit (FutureNetworkSummit), July 2013.

Acknowledgments

The research leading to this simulator has received funding from the European Commission FP7 project “COgnitive RAdio for SATellite Communications ” - CoRaSat (funded under the ICT Call 8), and by the National Research Fund, Luxembourg, under CORE project “Spectrum Management and Interference Mitigation in Cognitive Radio Satellite Networks” - SeMIGod.