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The main objectives of this project is to investigate the applicability and enumerate the potential gains of using Carrier Aggregation (CA) in satellite systems with taking into considerations the various nuances therein:
1. Define relevant scenarios for the possible implementation of CA schemes. The candidate scenarios can be characterized based on services, operational frequency bands, nature of CA (beam level, transponder level etc.).
2. Assessing the impact of CA schemes on the design and operation of gateway, payload and user terminal. The axes for impact analyses include hardware and processing complexity, modifications to existing standards and end-to-end system performance analysis.
3. Demonstrate and examine the performance of CA under different scenarios highlighting the implementation consequences on RF, PHY, MAC and link layers, where an end-to-end laboratory software-based testbed called “Carrier Aggregation Demonstrator (CAD)” is developed for this evaluation.
4. Based on the designing insights and the outcomes of the demonstration and testing, this project defines the technological roadmap to fill the gaps between the existing technologies and those of future that are needed for CA implementation.
Figure (1) Carrier Aggregation in GEO FSS forward link.
Figure (2) Multi‐Satellite CA (GEO‐GEO / MEO‐MEO / GEO‐MEO)
Applying Carrier Aggregation (CA) technique in satellite systems confronts some technological challenges from implementation perspectives. Specifically, as CA technique is applied to intra-band contiguous, intra-band non-contiguous and inter-band, additional RF chains, ADC or digital chains might be required for each user terminal. Moreover, at the gateway, smart load balancing and carrier assignment per user need to be developed. Besides, a set of standard modifications in terms of packet stream encapsulation/decapsulation into multiple packets and scheduling procedures under different channel conditions are necessary for this upgrade.
Carrier aggregation (CA) as a long-term evolution (LTE) advanced (LTE-A) technology, enables the association of multiple carriers to/from a user terminal leading to a higher peak and average data rate for the users. Given the benefits of CA in terrestrial wireless networks in exploiting the available spectrum resources to satisfy very high data rate demands as well as to manage the spectrum and interference efficiently, the attention for CA in satellite networks grows steadily. In the framework of satellite networks, CA has huge potentials in scenarios where a user can meet its demand from multiple carriers, possibly occupying spectrum in different transponders, and hence, offering possibility to exploit the underutilized resources. The CA approach facilitates decreasing gaps in transponders being unused by other services. Moreover, it enhances the user experience by delivering increased peak data rate that cannot be provided with just a single carrier. Interference management with CA can be readily conducted through an intelligent resource allocation in the assignment of multiple carriers to each user.
Carrier aggregation provides a high flexibility in spectrum aggregation and brings extraordinary system-level performance benefits comparing with the channel bonding techniques that already included in the DVB-S2 standard. Some of the new additional features that arise with carrier aggregation deployment in satellite systems are summarized as follows:
1- Unlike channel bonding, carrier aggregation technique operates with Adaptive Coding and Modulation (ACM) functionalities that are fundamental for broadband traffic
2- Aggregated channels may not be located in the same frequency band, i.e. a multibeam multicarrier scenario is feasible in carrier aggregation, whereas channel bonding requires same frequency channel band.
3- Carrier aggregation approach facilitates decreasing the gap between the underutilized and the fully occupied transponders.
4- Carrier aggregation enhances user experience by delivering a higher data rate that cannot be provided by engaging a single carrier.
Carrier Aggregation (CA) is implemented by means of three main blocks. First, at the Gateway side, a Multiuser Aggregation and Access Control (MAAC) block represents the main intelligence of the system that is in charge of designing the carrier allocation strategy for all the user terminals in the system as well as the multiplexing of each carrier. Also in the gateway side, a key module is the load balancing and PDU scheduler, that is responsible for applying the decisions of the MAAC by distributing the incoming PDUs across the available carriers. The load balancing and PDU scheduler block has to be carefully designed such that the PDUs are distributed across the selected carriers based on the link capacities so that the PDU disordering is minimized at the receiver side.
Finally, at the receiver side, the most important block is the traffic-merging block that takes the PDU streams of the aggregated carriers as input and converts them into a single stream of received PDUs.
CADSAT duration is two years, starting from January 2018.
The project is composed of four main tasks:
1- Carrier aggregation scenario definition and selection.
2- CADSAT design and implementation
3- CADSAT testing.
4- System development roadmap.
The project is running as planned and the scenario definition and selection task has been completed.
The team is currently working on the CADSAT design and implementation, which should be finalized by September 2019.
Finally, testing and roadmap will be addressed in the last phase of the project.