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PDSCH Bit Error Rate Curve Generation

This example shows how the LTE System Toolbox™ can be used to create Physical Downlink Shared Channel (PDSCH) Bit Error Rate (BER) curves under Additive White Gaussian Noise (AWGN) in a simple Graphical User Interface (GUI).

Introduction

hPDSCHBER.m provides a simple GUI to draw different BER curves for given SNR values and modulation schemes.

A random stream of bits the size of the desired transport block undergoes Downlink Shared Channel (DL-SCH) coding to rate match the transport block to the available PDSCH bits. Scrambling, modulation, precoding and layer mapping are then applied to form the complex PDSCH symbols. AWGN is added to these symbols after which channel decoding and demodulation are performed to recover the transport block. Using the recovered transport block a BER curve is plotted for a given range of SNR values.

hPDSCHBER; % Launch GUI

Parameters

The following GUI parameters are available:

  • TransportBlockSize - Size of transport block

  • AvailablePDSCHBits - Size of coded transport block after rate matching (codeword size)

  • Modulation - Modulation scheme, one of {'QPSK', '16QAM', '64QAM'}

  • SNRRange - Eb/No range in dB

  • RVSeq - Redundancy version indicators sequence

  • NTurboDecIts - Number of turbo decoder iteration cycles

  • OverlayGraphs - Holds the previous graphs when checked, thus overlays new curve on previously drawn curves

Altering the various input parameters will affect the shape of the BER curve in different ways. The ratio of values assigned to the transport block size and available PDSCH bits should fit the range of target turbo code rates defined by LTE (1/3, 1/2, 3/4). Furthermore the value assigned to the available PDSCH bits are governed by the modulation scheme selected, e.g. for 16QAM a value which is a multiple of 4 must be chosen. Higher symbol modulation orders are more sensitive to noise interference and thus will suffer degradation in performance when compared to lower symbol modulation orders schemes at similar SNR values. The redundancy version must come from the range {0,1,2,3}. It can be a single value or a vector of values from the defined set.

The GUI also provides control over the configuration of the number of turbo decoder iteration cycles to be used in the decoder algorithm. This helps to perform an extended performance analysis of turbo decoder algorithm under AWGN. To compare the effect of altering the various parameters, all the curves can be plotted onto the same graph by checking the OverlayGraphs check box.

Appendix

This example uses the following helper functions:

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