chest_dl: subframe averaging with previous

srslte/include/srslte/ch_estimation/chest_dl.h

@@ -63,6 +63,7 @@ typedef struct {
   srslte_refsignal_cs_t csr_signal;
   cf_t *pilot_estimates;
   cf_t *pilot_estimates_average; 
+  cf_t *pilot_average_last; 
   cf_t *pilot_recv_signal; 
   cf_t *tmp_noise; 
   
@@ -73,6 +74,9 @@ typedef struct {
   uint32_t smooth_filter_len; 
   float smooth_filter[SRSLTE_CHEST_MAX_SMOOTH_FIL_LEN];
 
+  float time_ema_coeff; 
+  bool  average_subframe; 
+  
   srslte_interp_linsrslte_vec_t srslte_interp_linvec; 
   srslte_interp_lin_t srslte_interp_lin; 
   
@@ -102,6 +106,12 @@ SRSLTE_API void srslte_chest_dl_set_smooth_filter(srslte_chest_dl_t *q,
 SRSLTE_API void srslte_chest_dl_set_smooth_filter3_coeff(srslte_chest_dl_t* q, 
                                                          float w); 
 
+SRSLTE_API void srslte_chest_dl_set_time_ema_coeff(srslte_chest_dl_t *q, 
+                                                   float t); 
+
+SRSLTE_API void srslte_chest_dl_set_average_subframe(srslte_chest_dl_t *q, 
+                                                     bool enable); 
+
 SRSLTE_API void srslte_chest_dl_set_noise_alg(srslte_chest_dl_t *q, 
                                               srslte_chest_dl_noise_alg_t noise_estimation_alg); 
 

srslte/lib/ch_estimation/chest_dl.c

@@ -39,32 +39,8 @@
 #include "srslte/utils/vector.h"
 #include "srslte/utils/convolution.h"
 
-#define AVERAGE_SUBFRAME
+#define DEFAULT_FILTER_LEN       3
-
+#define DEFAULT_TIME_EMA_COEFF   0.9
-//#define DEFAULT_FILTER_LEN 3
-
-#ifdef DEFAULT_FILTER_LEN 
-static void set_default_filter(srslte_chest_dl_t *q, int filter_len) {
-  
-  float fil[SRSLTE_CHEST_DL_MAX_SMOOTH_FIL_LEN]; 
-
-  for (int i=0;i<filter_len/2;i++) {
-    fil[i] = i+1;
-    fil[i+filter_len/2+1]=filter_len/2-i;
-  }
-  fil[filter_len/2]=filter_len/2+1;
-  
-  float s=0;
-  for (int i=0;i<filter_len;i++) {
-    s+=fil[i];
-  }
-  for (int i=0;i<filter_len;i++) {
-    fil[i]/=s;
-  }
-
-  srslte_chest_dl_set_smooth_filter(q, fil, filter_len);
-}
-#endif
 
 /** 3GPP LTE Downlink channel estimator and equalizer. 
  * Estimates the channel in the resource elements transmitting references and interpolates for the rest
@@ -104,6 +80,11 @@ int srslte_chest_dl_init(srslte_chest_dl_t *q, srslte_cell_t cell)
       perror("malloc");
       goto clean_exit;
     }      
+    q->pilot_average_last = srslte_vec_malloc(sizeof(cf_t) * 2 * cell.nof_prb);
+    if (!q->pilot_average_last) {
+      perror("malloc");
+      goto clean_exit;
+    }      
     q->pilot_recv_signal = srslte_vec_malloc(sizeof(cf_t) * SRSLTE_REFSIGNAL_MAX_NUM_SF(cell.nof_prb));
     if (!q->pilot_recv_signal) {
       perror("malloc");
@@ -127,7 +108,14 @@ int srslte_chest_dl_init(srslte_chest_dl_t *q, srslte_cell_t cell)
     
     q->noise_alg = SRSLTE_NOISE_ALG_REFS; 
     
-    q->smooth_filter_len = 3; 
+    q->time_ema_coeff = 1.0; 
+#ifdef DEFAULT_TIME_EMA_COEFF
+    q->time_ema_coeff = DEFAULT_TIME_EMA_COEFF;
+#endif
+    
+    q->average_subframe = true; 
+    
+    q->smooth_filter_len = DEFAULT_FILTER_LEN; 
     srslte_chest_dl_set_smooth_filter3_coeff(q, 0.1);
     
     q->cell = cell; 
@@ -158,6 +146,9 @@ void srslte_chest_dl_free(srslte_chest_dl_t *q)
   if (q->pilot_estimates_average) {
     free(q->pilot_estimates_average);
   }      
+  if (q->pilot_average_last) {
+    free(q->pilot_average_last);
+  }      
   if (q->pilot_recv_signal) {
     free(q->pilot_recv_signal);
   }
@@ -233,7 +224,7 @@ static float estimate_noise_empty_sc(srslte_chest_dl_t *q, cf_t *input) {
 static void interpolate_pilots(srslte_chest_dl_t *q, cf_t *pilot_estimates, cf_t *ce, uint32_t port_id) 
 {
     
-#ifdef AVERAGE_SUBFRAME
+  if (q->average_subframe) {
     // Interpolate symbol 0 in the frequency domain  
     uint32_t fidx_offset = srslte_refsignal_cs_fidx(q->cell, 0, port_id, 0);    
     srslte_interp_linear_offset(&q->srslte_interp_lin, pilot_estimates,
@@ -243,7 +234,7 @@ static void interpolate_pilots(srslte_chest_dl_t *q, cf_t *pilot_estimates, cf_t
     for (int l=1;l<2*SRSLTE_CP_NSYMB(q->cell.cp);l++) {
       memcpy(&ce[l*q->cell.nof_prb*SRSLTE_NRE], ce, q->cell.nof_prb*SRSLTE_NRE*sizeof(cf_t));
     }
-#else
+  } else {
     uint32_t l=0; 
     uint32_t nsymbols = srslte_refsignal_cs_nof_symbols(port_id); 
 
@@ -278,7 +269,7 @@ static void interpolate_pilots(srslte_chest_dl_t *q, cf_t *pilot_estimates, cf_t
         srslte_interp_linear_vector(&q->srslte_interp_linvec, &cesymb(1), &cesymb(7), &cesymb(8), 6, 4);
       }    
     }
-#endif
+  }
 }
 
 void srslte_chest_dl_set_smooth_filter(srslte_chest_dl_t *q, float *filter, uint32_t filter_len) {
@@ -307,21 +298,36 @@ void srslte_chest_dl_set_smooth_filter3_coeff(srslte_chest_dl_t* q, float w)
   q->smooth_filter[1] = 1-2*w; 
 }
 
+void srslte_chest_dl_set_time_ema_coeff(srslte_chest_dl_t *q, float t) {
+  if (t > 0.0 && t <= 1.0) {
+    q->time_ema_coeff = t; 
+  }
+}
+
+void srslte_chest_dl_set_average_subframe(srslte_chest_dl_t *q, bool enable) {
+  q->average_subframe = enable; 
+}
+
 static void average_pilots(srslte_chest_dl_t *q, cf_t *input, cf_t *output, uint32_t port_id) {
   uint32_t nsymbols = srslte_refsignal_cs_nof_symbols(port_id); 
   uint32_t nref = 2*q->cell.nof_prb;
 
   memcpy(output, input, nref*sizeof(cf_t));
   for (int l=1;l<nsymbols;l++) {
-#ifdef AVERAGE_SUBFRAME
+    if (q->average_subframe) {
       srslte_vec_sum_ccc(output, &input[l*nref], output, nref);  
-#else  
+    } else {
       srslte_conv_same_cf(&input[l*nref], q->smooth_filter, &output[l*nref], nref, q->smooth_filter_len);    
-#endif
     }
-#ifdef AVERAGE_SUBFRAME
+  }
-  srslte_vec_sc_prod_cfc(output, (float) 1.0/nsymbols, output, nref);
+  if (q->average_subframe) {
-#endif
+    srslte_vec_sc_prod_cfc(output, (float) q->time_ema_coeff/nsymbols, output, nref);
+    if (q->time_ema_coeff < 1.0) {
+      srslte_vec_sc_prod_cfc(q->pilot_average_last, 1-q->time_ema_coeff, q->pilot_average_last, nref);
+      srslte_vec_sum_ccc(q->pilot_average_last, output, output, nref);
+      memcpy(q->pilot_average_last, output, nref*sizeof(cf_t));
+    }
+  }
 }
 
 float srslte_chest_dl_rssi(srslte_chest_dl_t *q, cf_t *input, uint32_t port_id) {