This document contains the NI-LabVIEW Modulation Toolkit known issues that were discovered before and since the release of NI-RFmx SpecAn. Not every issue known to NI appears on this list; it is intended to show the most severe and common issues that can be encountered.
Each issue appears as a row in the table and includes the following fields:
Issue ID - The number in at the top of each of the cells in the first column. When you report an issue to NI, you may be given this ID, you can also find IDs posted by NI on the discussion forums or in Knowledge Base articles. "N/A" indicates that there is no ID assigned to the issue.
Issue Title (in italics) - Describes the issue in one sentence or less.
Problem Description - A few sentences which describe the problem in further detail. The brief description given does not necessarily describe the problem in full detail, and it is expected that you may want more information on an issue. If you would like more information on an issue, contact NI and reference the ID number given in the document.
Workaround - Possible ways to work around the problem. The workarounds that appear in the document are not always tested by NI and are not guaranteed to resolve the issue. If a workaround refers you to the NI KnowledgeBase, visit www.ni.com/kb/ and enter the KnowledgeBase number in the search field to locate the specific document.
Reported Version - The earliest version of NI Modulation Toolkit in which the issue was reported. If you discover the issue appears in an earlier version of NI Modulation Toolkit than is reported in this field, report the discrepancy to NI to have the field updated.
Resolved Version - Version in which the issue was resolved or was no longer applicable. "N/A" indicates that the issue has not been resolved.
Date Added - The date the issue was added to the document (not the reported date).
MT Viterbi decoder fails when bits are not aligned correctly
Consider a rate 1/2 Viterbi decoder. This decoder expects the same two bits that result out of a single bit fed to the encoder. If the decoder is given the first bit from the current code word and second bit from the next code word, that is, the coded bitstream is not aligned to the info bit stream, the Viterbi decoder fails to decode correctly.
Workaround: Align the coded bits appropriately before feeding to the MT Convolutional Decode VI.
OQPSK BER using MT PSK demodulation is suboptimal at SNR <15 dB
The BER computed from the bits returned by the Offset option in the MT Demodulate PSK VI deviates significantly from the theoretical BER curve at SNR less than 15 dB or at low excess bandwidth (for example, when the pulse-shaping filter used is Raised Cosine/Root Raised Cosine, and the value of the filter rolloff coefficient is less than 0.3).
MT RS Symbol Decode VI returns incorrect data if number of errors exceeds (n-k)/2
Reed Solomon decoders can correct the input symbol stream only if the number of symbol errors is less than or equal to (n-k)/2. However, in the MT Reed Solomon Symbol Decode VI, if there are more than (n-k)/2 symbol errors in the input codeword, new errors may be introduced in the decoded information symbols.
If the number of bits at the input of the MT RS Symbol Encoder (Normal) is less than k*bits/symbol, no error is returned, but the output array is empty
If the number of bits to the MT RS Symbol Encoder (Normal) is less than k*bits/symbol, no error is returned, but the output array is empty.
Workaround: Explicitely check for the size of the input to the encoder.
Need to relink deprecated VIs/subVIs for applications built with NI Modulation Toolkit 4.2.1 or earlier
If an application built with NI Modulation Toolkit 4.2.1 or earlier uses deprecated VIs or subVIs from previous versions of the NI Modulation Toolkit, and you upgrade to NI Modulation Toolkit 4.3, the application may not find the deprecated VIs/subVIs, even though the VIs are present on the disk.
Workaround: Specify the new paths to the deprecated VIs/subVIs.
Upgrading the NI Modulation Toolkit from a previous installation
Upgrading to Modulation Toolkit 4.3 for LabVIEW from a previous installation may lead to the installation of the Modulation Toolkit files to versions of LabVIEW that are not present on the system, in addition to versions of LabVIEW present on the system. This happens only if any of the following standard-specific toolkits are installed on the system:
NI GPS Simulation Toolkit for LabVIEW
NI WLAN Measurement Suite
NI Measurement Suite for Fixed WiMAX
NI Measurement Suite for Mobile WiMAX
Workaround: Uninstall the standard-specific toolkits and upgrade to the latest version of NI Modulation Toolkit for LabVIEW. Install the standard-specific toolkits after upgrading the NI Modulation Toolkit.
Setting the 3D Eye Graph default acceleration
The Use 3D acceleration option for the 3D eye control is set to OFF by default for widest compatibility. If your computer has a hardware accelerator, you can improve the performance of the graph by changing this setting. To change this setting, right-click the 3D eye control, select CWGraph3DÂ»Properties, and select the Use 3D acceleration option. You can also change this setting in examples that use the 3D eye control.
Demod/Bit Recovery VIs may show degraded BER performance if data is fed in chunks
For demodulating continuously or for demodulating a large input data, the NI Modulation Toolkit Demodulator/Bit Recovery VIs may need to run multiple times in a loop with the input data fed in chunks. In this case, the reset parameter must be TRUE in the first call and FALSE in the subsequent calls to the VI. However, in such cases, the recovered bits may not be error free in the subsequent calls, even at very high SNR values.
Workaround: Divide the input data into overlapping chunks and feed each chunk to the demodulator/bit recovery VI, with the reset parameter set to TRUE. Delete the appropriate number of bits at the beginning of each demodulated chunk of bits.
Demodulation VIs show degraded BER performance at SNR < 15dB
Some digital demodulation VIs, such as the MT Demodulate PSK, MT Demodulate QAM, MT Demodulate CPM, and MT Demodulate MSK VIs may exhibit BER performance that significantly deviates from the theoretical BER curves at SNR values less than 15 dB.
Reported Version: 4.3
Resolved Version: N/A
Contact NI regarding this document or issues in the document. If you contact NI in regards to a specific issue, reference the ID number given in the document. The ID number contains the current issue ID number as well as the legacy ID number (use the current ID number when contacting NI). You can contact us through any of the normal support channels including phone, email, or the discussion forums. Visit the NI Website to contact us. Also contact us if you find a workaround for an issue that is not listed in the document.