Geographical Scheduling for Multicast Precoding in Multi-Beam Satellite Systems

Abstract

Current State-of-the-Art High Throughput Satellite systems provide wide-area connectivity through multi-beam architectures. Due to the tremendous system throughput requirements that next generation Satellite Communications (SatCom) expect to achieve, traditional 4-colour frequency reuse schemes are not sufficient anymore and more aggressive solutions as full frequency reuse are being considered for multi-beam SatCom. These approaches require advanced interference management techniques to cope with the significantly increased inter-beam interference both at the transmitter, e.g., precoding, and at the receiver, e.g., Multi User Detection (MUD). With respect to the former, several peculiar challenges arise when designed for SatCom systems. In particular, multiple users are multiplexed in the same transmission radio frame, thus imposing to consider multiple channel matrices when computing the precoding coefficients. In previous works, the main focus has been on the users' clustering and precoding design. However, even though achieving significant throughput gains, no analysis has been performed on the impact of the system scheduling algorithm on multicast precoding, which is typically assumed random. In this paper, we focus on this aspect by showing that, although the overall system performance is improved, a random scheduler does not properly tackle specific scenarios in which the precoding algorithm can poorly perform. Based on these considerations, we design a Geographical Scheduling Algorithm (GSA) aimed at improving the precoding performance in these critical scenarios and, consequently, the performance at system level as well. Through extensive numerical simulations, we show that the proposed GSA provides a significant performance improvement with respect to the legacy random scheduling.

Clustering strategies for multicast precoding in multibeam satellite systems

“…Aspects related to user scheduling were discussed by the authors of this paper by introducing a novel geographical scheduling algorithm, in which clusters of users are scheduled in the same time frame only when belonging to the same zone in the beam. 19 The implementation of a cross-layer scheduler that takes into account DVB-S2 framing and the traffic class has also been recently introduced. 20 In the literature, aspects related to the choice of the users to be grouped together within the same codeword were addressed.…”

“…Since linear precoding techniques provide already significant throughput gains with a limited complexity, they might be preferred with respect to more complex techniques, ie, non‐linear precoding, for which the increase in the system complexity is not justified by an equivalent performance benefit . In this context, multicast precoding techniques have been recently proposed(): Differently from the unicast case, in multicast precoding, multiple users are multiplexed into a single codeword that is then precoded according to an equivalent channel obtained as the average of the users' channel coefficients vectors. Since the average channel coefficients exploited to compute the precoding vector depend on the selected users and the modulation and coding scheme (ModCod) used for the multiplexed users depends on the worst‐case user, ie, the user with lowest signal‐to‐interference‐plus‐noise ratio (SINR), so as to guarantee that all users can decode their information, user selection, and grouping in the same codeword directly and deeply impacts the overall system performance in terms of achievable throughput.…”

“…The design of higher rank transmissions to increase the spectrum efficiency and the design of robust beamforming to alleviate performance degradation caused by imperfect channel state information are also addressed. Aspects related to user scheduling were discussed by the authors of this paper by introducing a novel geographical scheduling algorithm, in which clusters of users are scheduled in the same time frame only when belonging to the same zone in the beam . The implementation of a cross‐layer scheduler that takes into account DVB‐S2 framing and the traffic class has also been recently introduced …”

“…Building on early works, 5,6,10 which paved the way for the application of MU-MIMO in HTS systems, the SatCom community has been intensifying the work on precoding-based satellite systems, as demonstrated by the significant contributions brought to this topic. [11][12][13][14][15][16][17][18][19][20] These works showed that significant gains can be obtained in the overall system throughput by means of both linear and non-linear precoding techniques over the multibeam fixed satellite channel. Since linear precoding techniques provide already significant throughput gains with a limited complexity, they might be preferred with respect to more complex techniques, ie, non-linear precoding, for which the increase in the system complexity is not justified by an equivalent performance benefit.…”

Code Design for Non-Coherent Detection of Frame Headers in Precoded Satellite Systems

“…Recently, it has been shown that precoding can provide significant gains in multi-beam satellite systems with interference [17], [18]. In this paper, we consider the effect of precoding on the detection of PLH and FEC frame.…”