Satellite Channel Emulation¶
This is the Wiki page for the SCS 2014/2015 project #1. It deals with DVB-S2 and its novel ACM feature.
Table Of Contents¶
- Lab Setup
- Information Sources
Why ACM is necessary.
Block diagram of ACM functionality.
A little bit of history.
Features vs DVB-S.
Coding and modulation schemes.
Test Setup Section:
Modem configuration, ethernet bridge. Explain as in manual (both modems on same subnet, etc...)
Introduction Link Emulation system
Network diagram of full setup
Single diagram for each modem and associated client PC
Full settings for modems (ACM mode as well as CCM mode)
Table with IPs
Task 1, Status: DONE
Task 2, Status: TODO
SubTask 1, Status: URGENT
Satellite systems based on the DVB-S standard are inevitably forced to adhere to fixed MODCOD parameters, that is, a fixed coding rate and modulation scheme. This in turn leaves the designer with no choice other than to dimension the system for the worst-case propagation conditions in order to have link-closure and meet availability, coverage and performance requirements.
This approach has the disadvantage that high margins in the carrier-to-noise-and-interference ratios (CNIRs) occur in the majority of cases when propagation conditions allow for it. In the case of broadcasting services, where we have a multitude of users spread over very large areas, this waste of power cannot be easily avoided. However, in point-to-point links if a return channel is present it is possible to report channel state conditions and exploit its temporal variations by adapting the code rate and modulation scheme being used so as to best match the CNIR. This way a fixed link is avoided and considerable improvements in system capacity are obtained with better utilization of power resources.
The DVB-S2 standard introduces adaptive coding and modulation (ACM) enabling better use of transponder resources when high carrier-to-noise-plus-interference ratios occur due to favorable propagation conditions. ACM allows for different coding rates and modulation schemes to be used and dynamically changed on a frame-by-frame basis.
(Similar to fig12 in ETSI-TR.102376)
The laboratory setup consists of the following:
(EQUIPMENT LIST AND DESCRIPTION)
All two modems will be working in L2 Ethernet bridging mode. This means that we could use PCs to generate traffic between HUB and station or we could attach other devices such as VoIP phones or any other IP capable device.
The Newtec EL470 can output a ACM log containing all MODCOD states. This is information is stored in a .csv file similar to the following example:
Timestamp,Demod,RqModCod,EsNo,CarrierBitrate 2014-11-20 16:15:17,1,16APSK-9/10,28.06,6304 2014-11-20 16:15:21,1,16APSK-9/10,28.05,8877 2014-11-20 16:15:25,1,16APSK-9/10,27.01,8877 2014-11-20 16:15:29,1,16APSK-9/10,27.06,5836 2014-11-20 16:15:33,1,16APSK-9/10,27.24,5836 2014-11-20 16:15:34,1,16APSK-9/10,27.09,5836 2014-11-20 16:15:35,1,16APSK-8/9,27.21,5836 2014-11-20 16:15:35,1,16APSK-9/10,27.05,5836 2014-11-20 16:15:36,1,16APSK-9/10,27.25,5836 2014-11-20 16:15:37,1,16APSK-5/6,27.19,5836 2014-11-20 16:15:38,1,16APSK-8/9,27.11,4250 2014-11-20 16:15:39,1,16APSK-5/6,27.22,4250
From this log we can extract the following information:
- Timestamp (in seconds)
- Modcod parameter (modulation + coding rate)
- Estimate of E s / N 0
- Information bitrate (in bps)
This is done by a parser (EL470_LogParser_ACM.m) in Matlab which also does some plotting of values.