[Positioner] Measurement: fix recalculate_average()
Adds the attribute variance_size to handle the number of elements taken into account in the variance computation, instead of relying on ss_list.size(), which is a mistake in the case of recalculate_average().
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@ -117,6 +117,7 @@ void Measurement::clear()
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average_mw = 0 ;
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variance_mw = 0 ;
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variance_mw_m2 = 0 ;
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variance_size = 0 ;
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ap = NULL ;
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}
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@ -186,6 +187,7 @@ void Measurement::recalculate_average()
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average_mw = 0 ;
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variance_mw = 0 ;
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variance_mw_m2 = 0 ;
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variance_size = 0 ;
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for (map<pkt_id_t, ss_t>::const_iterator
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i = ss_list.begin() ; i != ss_list.end() ; ++i)
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@ -195,18 +197,21 @@ void Measurement::recalculate_average()
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void Measurement::update_average(ss_t ss_dbm)
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{
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++variance_size ;
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assert(variance_size <= ss_list.size()) ;
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// Convert the new SS in mW:
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float ss_mw = pow(10, static_cast<float>(ss_dbm) / 10.0) ;
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// Update the average:
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float delta = ss_mw - average_mw ;
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average_mw += delta / ss_list.size() ;
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average_mw += delta / variance_size ;
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average_dbm = 10.0 * log10(average_mw) ;
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// Update the variance:
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variance_mw_m2 += delta * (ss_mw - average_mw) ;
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if (ss_list.size() > 1)
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variance_mw = variance_mw_m2 / (ss_list.size() - 1) ;
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if (variance_size > 1)
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variance_mw = variance_mw_m2 / (variance_size - 1) ;
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}
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@ -225,6 +230,7 @@ Measurement& Measurement::operator=(const Measurement &m)
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average_mw = m.average_mw ;
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variance_mw = m.variance_mw ;
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variance_mw_m2 = m.variance_mw_m2 ;
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variance_size = m.variance_size ;
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return *this ;
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}
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@ -33,8 +33,10 @@ protected:
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float variance_mw ;
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private:
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/// Intermediate variable used to compute the variance
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/// Intermediate variable used to compute the variance (mW)
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float variance_mw_m2 ;
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/// Number of elements taken into account in the variance computation
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unsigned int variance_size ;
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protected:
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@ -54,12 +56,14 @@ protected:
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public:
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Measurement(const AccessPoint *_ap = NULL):
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ap(const_cast<AccessPoint*>(_ap)), average_dbm(0),
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average_mw(0), variance_mw(0), variance_mw_m2(0) {}
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average_mw(0), variance_mw(0), variance_mw_m2(0),
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variance_size(0) {}
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Measurement(const Measurement &source):
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ap(source.ap), ss_list(source.ss_list),
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average_dbm(source.average_dbm), average_mw(source.average_mw),
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variance_mw(source.variance_mw), variance_mw_m2(0) {}
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variance_mw(source.variance_mw), variance_mw_m2(0),
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variance_size(0) {}
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~Measurement(void) ;
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@ -73,7 +77,7 @@ public:
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float get_average_dbm() const ;
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/// Returns the variance of the SS list
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float get_variance_mw() const ;
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/// Returns the standard deviation of the SS list
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/// Returns the standard deviation of the SS list (mW)
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float get_std_deviation_mw() const ;
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/// Returns the number of SS in the SS list
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int get_nb_ss() const ;
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