MODCODModulation and Coding
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Buffer overflow can be experienced when bandwidth is changed from a high bandwidth with a high MODCOD to a low bandwidth with a low MODCOD.
The data are then classified according to the MODCOD level, and converted into traffic data formats for ACM transmission.
Classified packets are processed by the IP layer QoS scheduler, and transferred to the MODCOD queues.
Each MODCOD queue is processed using a weighted round-robin scheduling algorithm to provide fairness for the RCSTs.
i] is the transmission capability of the modem according to a certain MODCOD.
To provide fairness to the RCSTs and use the ACM scheme, we share the timeslots with a region with poor weather conditions having low MODCOD.
Because the weight value in each MODCOD is perfectly equal, the round-robin scheduling does not offer a guarantee of QoS, as shown in Fig.
More timeslots are allocated in regions with poor conditions and low MODCOD than in regions with clear skies and high MODCOD, as shown in Fig.
Absolutely, satellite communication system with ACM scheme has higher transmission efficiency, but it does not offer earth station fairness because the data are transmitted with high MODCOD in regions with clear skies, and are transmitted with low MODCOD in regions experiencing rain event.
To achieve our goals which throughput fairness and Qos support, we propose fairness improvement-weighted round robin (FI-WRR) scheduler which the allocation timeslot is calculated by the transmission rate of each MODCOD queue.
Simulation Configurations Simulation Parameters Values Simulation time 100sec Bandwidth 120Mbps ~ 300Mbps Propagation delay 5ms (wired link for Hub system) for DVB-S2 link 250 ms (satellite link) 10ms (wired link for VSAT) Traffic packet size 1500 bytes Input traffic ratio 1:1:2 (EF:AF:BE) MODCODs MODCOD 8 (QPSK, 4/5) for ACM MODCOD 13 (8PSK, 2/3) MODCOD 19 (16APSK, 3/4) MODCOD 25 (32APSK, 4/5)