In parallel combinatory spread spectrum pcss system, the soft decision of qpsk modulation will make the superposed pseudonoise pn sequences lose its correlation, which leads to the failure of the demodulation. Qpskdemodulator creates a demodulator system object, h. The previous section of this workflow uses hard decision demodulation and hard decision viterbi decoding processes that map symbols to bits. This matlab function returns a column vector containing bits resulting from soft constellation demodulation of complex values in vector in. Specifies the use of hard decision, llr, or approximate llr during demodulation. Demodulation using oqpsk method matlab mathworks italia. Demodulated output bits, returned as a numeric column vector. Softdecision viterbi decoding with puncturing matlab central. A comparison of simulation results with theoretical results is also shown. All communications toolbox demodulator functions, system objects and blocks can demodulate binary data using either hard decisions or soft decisions. The top receiver performs hard decision demodulation in conjunction with a viterbi decoder that is set up to perform hard decision decoding.
If you are reading this reference page in the matlab help browser, click fixed point harddecision viterbi decoding and fixedpoint softdecision viterbi. To perform soft demodulation of the filtered oqpsk signal use the qamdemod function. For example, y stepobj,x and y objx perform equivalent operations. Demodulate qpskmodulated data simulink mathworks italia. Estimate ber for hard and soft decision viterbi decoding. The techniques of bit weighting, soft decision demodulation, and channel coding are compared for reducing or eliminating the effects of channel errors on compressed imagery. Estimate bit error rate ber performance for harddecision and. The probability that all constellation points occur are equally likely, so maximizing is equivalent to maximizing. Observe that the ber is only slightly degraded by using soft decision decoding instead of unquantized decoding. With llr demodulation, one can use the viterbi decoder either in the unquantized decoding mode or the soft decision decoding mode. The output out inherits its data type from the input in. Performs softdecison viterbi decoding with puncturing over an awgn channel using simulinkr.
Each element is the loglikelihood ratio for a received bit and the value is more likely to be 0 if the loglikelihood ratio is positive. The modulated signal passes through an additive white gaussian noise channel. You can specify additional namevalue pair arguments in any order. The source coding method used is the twodimensional discrete cosine transform of 16 by 16 blocks. Thus the soft decision decoding improves the decision making process by supplying additional reliability information calculated euclidean distance or calculated loglikelihood ratio for the same encoder and channel combination lets see the effect of replacing the hard decision block with a soft decision block. Soft decision demodulation how is soft decision demodulation abbreviated. This matlab function returns a demodulated signal, z, given quadrature amplitude modulation. Each demodulated symbol is mapped to a group of log 2 m bits, where the first bit represents the most significant bit msb and the last bit. Ber results for hard decision demodulation and llr demodulation with unquantized and soft decision decoding are plotted in red, blue, and black, respectively. This section of the workflow uses soft decision demodulation and soft decision viterbi decoding. N is the number of bits in the ldpc codeword before modulation. Hard decision mode results in the output containing the bit sequences corresponding to the closest constellation points to the input.
Extraction of bit planes in a grayscale image using matlab. Input x must be a scalar or a column vector with double or single precision data type. Starting in r2016b, instead of using the step method to perform the operation defined by the system object, you can call the object with arguments, as if it were a function. The soft bits are scaled with the variance of additive white gaussian noise awgn. How to calculate soft output for bpsk demodulator matlab. The default value corresponds to an snr of 100 db, assuming unit signal power. Extraction of bit planes in a grayscale image using matlab 07. Uses esno provided by the user for ldpc decoding, instead of estimating the esno from the received signal. Differential phase shift keying dpsk is a digital modulation schemethat uses bit patterns to change the phase of a wave as opposed to setting itto a new value. The top receiver performs hard decision demodulation in conjunction with a viterbi decoder that is set up to perform hard decision.
The ber performance improvement for qpsk modulation when using loglikelihood ratio llr instead of hard decision demodulation in a convolutionally coded communication link. The code of fsk modulation and demodulation has been developed using matlab according to conventional theory. Demodulate using qpsk method matlab mathworks united. Create qpsk equivalent signal to align inphase and quadrature. Matlab code for fsk modulation and demodulation file. The examples show its validity and the features of visualization, modularization, high. Soft decisions for dqpsk demodulation for the viterbi decoding of the convolutional codes conference paper in acoustics, speech, and signal processing, 1988. This argument contains bits resulting from soft constellation demodulation of complex values vector, in. The output vector length is twice as long as the number of input symbols. Use soft decision decoding to improve ber performance. On the receiver side of the lte system, i need to perform a soft demodulation 16qam and 64qam so i can feed real values to the turbo coder for decoding. Soft decisions for dqpsk demodulation for the viterbi. Demodulate using bpsk method matlab mathworks italia.
When you set this property to false, the object outputs a column vector of integer values with a length equal to the number of demodulated symbols. Qpskdemodulatorname,value creates a qpsk demodulator object, h, with each specified property set to the specified value. This parameter appears when you select bit from the output type dropdown list. This paper develops a brief method for 1d simulation of shb test using the software package matlab simulink. This criterion is called maximum a posteriori probability map. This model shows a system that includes convolutional coding and gmsk modulation. Use the qamdemod function to simulate soft decision output for oqpskmodulated signals. This is to be expected, because soft decisions enable the system to retain more information from the demodulation operation to use in the decoding operation. Algorithms are analyzed based on performance simulation in matlab and complexity analysis. Learn more about soft bit, bpsk, modulation, demodulation. The output values for loglikelihood ratio and approximate loglikelihood ratio decision types are. The number of rows in z is log 2 m times the number of rows in y. Iterative design workflow for communication systems.
Demapper will send hard decision 10 or soft decision 346bits as per ur design. As a result, the demodulator determines the changes in thephase of the received signal rather than the phase itself, making it easier toim. The llr values computed by the demodulator are multiplied by 1. Outputtype return value of qamdemod dimensions of output integer demodulated integer values from 0 to m 1z has the same dimensions as input y. Weighted soft decision of qpsk modulation in parallel. This object demodulates the input signal using the quadrature phase shift keying qpsk method. The theoretical description of qpsk modulation and demodulation are available in the book of communication system by simon haykin. All communications toolbox demodulator functions, system objects and blocks can demodulate binary data using either hard decisions or soft. I have looked for information about soft demodulation on the. For demodulation, we would want to maximize the probability that the bit was transmitted given we received i. Perform qpsk demodulation in soft decision mode for a noise variance of 0. Approximates the loglikelihood ratio of the channel output for ldpc decoding by considering only two points in the constellation nearest to the received signal during soft decision demodulation.
Matlab code for qpsk modulation and demodulation file. I am using turbo coding with soft decision decoding. In soft viterbi decoding we avoid demodulation, but immeadiarely try to find the estimate of the transmitted bits according to the minimum of euclidean distance. According to the characteristics of qpsk modulation, the superposed sequence is mapped to two sequences, and. Whereas a hard decision decoder operates on data that take on a fixed set of possible values typically 0 or 1 in a binary code, the inputs to a soft decision decoder may take on a whole range of values inbetween. Soft decision mode results in the output indicating the bit values using the sign ve for. The output values are integer representations of two bits and range from 0 to 3 when you set this property to true, the object outputs a binary column vector of bit values. A viterbi decoder that is set up for soft decision decoding processes these quantized values. Loglikelihood ratios, specified as an nby1 column vector containing the soft decision output from demodulation. Through preliminary research, several dvbs2 soft decision llr algorithms are investigated for different modulation schemes in order to decide which algorithm will be implemented in synthesizable hardware description language hdl.
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