Cross-layer optimization of TCP throughput for DVB-S2 links

Abstract

Abstract-This paper presents a methodology to optimize the use of the forward link DVB-S2 capacity. Our interest is optimizing the switching E b /N0 thresholds for adaptive coding and modulation selection in DVB-S2 in order to maximize the TCP goodput according to a cross-layer design approach.Index Terms-Adaptive Coding and Modulation (ACM), Crosslayer design, DVB-RCS, DVB-S2, PER, TCP. I. INTRODUCTIONCurrently, most Internet applications such as file transfer, Web browsing and email services are running over the TCP-IP protocol stack. TCP permits to achieve a reliable end-to-end connection for data delivery. TCP operates in a full-duplex way: all data sent must be acknowledged via a return link.Satellite communications represent a viable solution for Internet access for wide areas. For a satellite interactive network, the second-generation of DVB-S, DVB-S2 [1], shall be considered with a return link according to DVB-RCS [2]. In this framework, the forward link is referenced as DVB-S2 link and the return link as DVB-RCS link.DVB-S2 provides an increase in capacity of up to 30% [3] compared to the older first-generation of DVB-S using the same bandwidth and power and under the same channel conditions. This improvement is achieved by applying higher order modulations and by the use of Low Density Parity Check (LDPC) codes and Bose-Chaudhuri-Hochquenghem (BCH) codes. The main novelty is the possibility of using Adaptive Coding and Modulation (ACM). In such a scenario, the selection of the suitable spectral efficiency (η) and the related Modulation and Coding (ModCod) level must be carried out considering the state of the channel. If a spectral efficiency higher than appropriate is used, the system will perceive higher capacity than actually available, but with an excessive Bit Error Rate (BER). Alternatively, if a too low spectral efficiency is selected, there is a waste of capacity. The DVB-S2 standard allows the choice between different ModCods providing a Quasi Error Free (QEF) quality target; this is performed on the basis of suitable E b /N 0 threshold values. In this work we refer to the QEF definition provided in the DVB-S2 standard as "less than one uncorrected error-event per transmission hour at the level of a 5 Mbit/s single TV service decoder", approximately corresponding to a transport stream Packet Error Rate (PER) equal to 10 −7 .

Transmission control protocol performance enhancement for mobile broadband interactive satellite communication system: a cross‐layer approach

“…Our objective is to choose the optimal bandwidth and ModCod mode for each user to maximize the total TCP throughput. Inspired by [33], we assume that there is an infinite space at the receiver buffer of each user, that is, rwnd ! 1.…”

“…Our objective is to choose the optimal bandwidth and ModCod mode for each user to maximize the total TCP throughput. Inspired by , we assume that there is an infinite space at the receiver buffer of each user, that is, rwnd → ∞ . Hence, we can reformulate the TCP throughput as Moreover, for each user, the satellite capacity in the PHY layer must be able to support the maximum of TCP throughput.…”

DVB-S2 Model in Matlab: Issues and Impairments

“…In case of clear sky by choosing higher coding rate and higher modulation orders spectral efficiency will be increased and system provides a higher throughput.The trade-off between spectral efficiency and BER is crucial in system performance and also transmission cost.In one hand, keeping in to account that although a spectral efficiency higher than appropriate according to channel state will increase system throughput ,it will introduce excessive BER to the system as well. On the other hand, if a ModCod with too low spectral efficiency is selected when the channel quality is in a good condition then capacity of the system will be wasted [4].…”