In the hard decsion case, if I receive [0,1] say, then the metric compared to [0,0] is 1. Suppose I received [0.9,1.1] in the soft decision case. Is the metric compared to [0,1]... (0.9)^2 + (1.1)^2 ??? or 0.9 + 1.1 ????? Note: 0.9 is the correlation for a symbol 0 Note: 1.1 is the correlation for a symbol 1 Both correlations have been calculated by Quadrature Receiver (nocoherent detection)

# Viterbi Metric for a BFSK

Started by ●February 16, 2007

Reply by ●February 16, 20072007-02-16

On Feb 16, 9:53 am, "JAlbertoDJ" <nietoro...@yahoo.es> wrote:> In the hard decsion case, if I receive [0,1] say, then the metric > compared to [0,0] is 1. Suppose I received [0.9,1.1] in the soft > decision case. Is the metric compared to [0,1]... > > (0.9)^2 + (1.1)^2 ??? or 0.9 + 1.1 ?????Soft decoders are typically designed to use Euclidean distance as the metric; therefore it is correct to square each difference component. Therefore, the metric for [0.9, 1.1] vs. [0, 1] is: (0.9 - 0)^2 + (1.1 - 1)^2 -- Oli

Reply by ●February 16, 20072007-02-16

JAlbertoDJ wrote:> In the hard decsion case, if I receive [0,1] say, then the metric > compared to [0,0] is 1.It depends. Suppose I received [0.9,1.1] in the soft> decision case. Is the metric compared to [0,1]... > > (0.9)^2 + (1.1)^2 ??? or 0.9 + 1.1 ?????It depends.> > Note: 0.9 is the correlation for a symbol 0 > Note: 1.1 is the correlation for a symbol 1 > > Both correlations have been calculated by Quadrature Receiver (nocoherent > detection)The metric is the generalized distance between the reference vectors and the received vector. It depends on what signal vectors corresponds to [0,1], [0,0] and such. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com

Reply by ●February 16, 20072007-02-16

Oli Charlesworth wrote:> > Soft decoders are typically designed to use Euclidean distance as the > metric; therefore it is correct to square each difference component.No, this is not a correct statement. It depends on what is the channel and what are the signals. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com

Reply by ●February 18, 20072007-02-18

On Feb 16, 6:45 am, Vladimir Vassilevsky <antispam_bo...@hotmail.com> wrote:> Oli Charlesworth wrote: > > > Soft decoders are typically designed to use Euclidean distance as the > > metric; therefore it is correct to square each difference component. > > No, this is not a correct statement. > It depends on what is the channel and what are the signals. > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.comFor the AWGN channel, the soft decoder uses the Euclidean distance as the metric. To reduce the complexity, only the cross-correlation between the received signal and the modulation constellation is used. For the BPSK system, (0,1) is mapped to (1, -1).