diff --git a/srsapps/radio/include/srsapps/radio/radio.h b/srsapps/radio/include/srsapps/radio/radio.h
index 8a98ba44d..8f192a3a6 100644
--- a/srsapps/radio/include/srsapps/radio/radio.h
+++ b/srsapps/radio/include/srsapps/radio/radio.h
@@ -42,6 +42,7 @@ namespace srslte {
     public: 
       virtual void get_time(srslte_timestamp_t *now) = 0; 
       virtual bool tx(void *buffer, uint32_t nof_samples, srslte_timestamp_t tx_time) = 0;
+      virtual bool tx_end() = 0;
       virtual bool rx_now(void *buffer, uint32_t nof_samples, srslte_timestamp_t *rxd_time) = 0;
       virtual bool rx_at(void *buffer, uint32_t nof_samples, srslte_timestamp_t rx_time) = 0;
 
diff --git a/srsapps/radio/include/srsapps/radio/radio_uhd.h b/srsapps/radio/include/srsapps/radio/radio_uhd.h
index 22ae95756..e7b33e6e3 100644
--- a/srsapps/radio/include/srsapps/radio/radio_uhd.h
+++ b/srsapps/radio/include/srsapps/radio/radio_uhd.h
@@ -49,6 +49,7 @@ namespace srslte {
 
       void get_time(srslte_timestamp_t *now);
       bool tx(void *buffer, uint32_t nof_samples, srslte_timestamp_t tx_time);
+      bool tx_end();
       bool rx_now(void *buffer, uint32_t nof_samples, srslte_timestamp_t *rxd_time);
       bool rx_at(void *buffer, uint32_t nof_samples, srslte_timestamp_t rx_time);
 
@@ -72,7 +73,17 @@ namespace srslte {
       
     private:
       void *uhd; 
-      bool is_first;
+      
+      static const double lo_offset = 8e6; // LO offset (in Hz)      
+      static const double burst_settle_time = 0.4e-3; // Start of burst settle time (off->on RF transition time)      
+      const static uint32_t burst_settle_max_samples = 12288;  // 30.72 MHz is maximum frequency
+
+      srslte_timestamp_t end_of_burst_time; 
+      bool is_start_of_burst; 
+      uint32_t burst_settle_samples; 
+      double burst_settle_time_rounded; // settle time rounded to sample time
+      cf_t zeros[burst_settle_max_samples]; 
+      double cur_tx_srate;
   }; 
 }
 
diff --git a/srsapps/radio/src/radio_uhd.cc b/srsapps/radio/src/radio_uhd.cc
index 0ba16daf1..a5a0cd17a 100644
--- a/srsapps/radio/src/radio_uhd.cc
+++ b/srsapps/radio/src/radio_uhd.cc
@@ -28,7 +28,6 @@
 #include "srslte/srslte.h"
 #include "srsapps/radio/radio_uhd.h"
 
-
 namespace srslte {
 
 bool radio_uhd::init()
@@ -57,7 +56,6 @@ void radio_uhd::set_tx_rx_gain_offset(float offset) {
 
 bool radio_uhd::init_agc(char *args)
 {
-  is_first = true; 
   printf("Opening UHD device with threaded RX Gain control ...\n");
   if (cuhd_open_th(args, &uhd, true)) {
     fprintf(stderr, "Error opening uhd\n");
@@ -65,6 +63,11 @@ bool radio_uhd::init_agc(char *args)
   }
   cuhd_set_rx_gain(uhd, 40);
   cuhd_set_tx_gain(uhd, 40);
+
+  burst_settle_samples = 0; 
+  burst_settle_time_rounded = 0; 
+  is_start_of_burst = true; 
+
   return true;    
 }
 bool radio_uhd::rx_at(void* buffer, uint32_t nof_samples, srslte_timestamp_t rx_time)
@@ -88,14 +91,31 @@ void radio_uhd::get_time(srslte_timestamp_t *now) {
 
 bool radio_uhd::tx(void* buffer, uint32_t nof_samples, srslte_timestamp_t tx_time)
 {
-  if (cuhd_send_timed2(uhd, buffer, nof_samples, tx_time.full_secs, tx_time.frac_secs, is_first, false) > 0) {
-    is_first = false; 
+  if (is_start_of_burst) {
+    if (burst_settle_samples != 0) {
+      srslte_timestamp_t tx_time_pad; 
+      srslte_timestamp_copy(&tx_time_pad, &tx_time);
+      srslte_timestamp_sub(&tx_time_pad, 0, burst_settle_time_rounded); 
+      cuhd_send_timed2(uhd, zeros, burst_settle_samples, tx_time_pad.full_secs, tx_time_pad.frac_secs, true, false);
+    }        
+    is_start_of_burst = false; 
+    srslte_timestamp_copy(&end_of_burst_time, &tx_time);
+    srslte_timestamp_add(&end_of_burst_time, 0, nof_samples*cur_tx_srate); 
+  }
+  
+  if (cuhd_send_timed2(uhd, buffer, nof_samples, tx_time.full_secs, tx_time.frac_secs, false, false) > 0) {
     return true; 
   } else {
     return false; 
   }
 }
 
+bool radio_uhd::tx_end()
+{
+  cuhd_send_timed2(uhd, zeros, burst_settle_samples, end_of_burst_time.full_secs, end_of_burst_time.frac_secs, false, true);
+  is_start_of_burst = true; 
+}
+
 void radio_uhd::set_rx_freq(float freq)
 {
   cuhd_set_rx_freq(uhd, freq);
@@ -118,8 +138,7 @@ void radio_uhd::set_rx_srate(float srate)
 
 void radio_uhd::set_tx_freq(float freq)
 {
-  //cuhd_set_tx_freq(uhd, freq);
-  cuhd_set_tx_freq_offset(uhd, freq, 8e6);  
+  cuhd_set_tx_freq_offset(uhd, freq, lo_offset);  
 }
 
 void radio_uhd::set_tx_gain(float gain)
@@ -139,7 +158,13 @@ float radio_uhd::get_rx_gain()
 
 void radio_uhd::set_tx_srate(float srate)
 {
-  cuhd_set_tx_srate(uhd, srate);
+  cur_tx_srate = cuhd_set_tx_srate(uhd, srate);
+  burst_settle_samples = (uint32_t) (cur_tx_srate * burst_settle_time);
+  if (burst_settle_samples > burst_settle_max_samples) {
+    burst_settle_samples = burst_settle_max_samples;
+    fprintf(stderr, "Error setting TX srate %.1f MHz. Maximum frequency for zero prepadding is 30.72 MHz\n", srate*1e-6);
+  }
+  burst_settle_time_rounded = (double) burst_settle_samples/cur_tx_srate;
 }
 
 void radio_uhd::start_rx()
diff --git a/srsapps/ue/phy/include/srsapps/ue/phy/phy.h b/srsapps/ue/phy/include/srsapps/ue/phy/phy.h
index 45f862b8f..564a4da16 100644
--- a/srsapps/ue/phy/include/srsapps/ue/phy/phy.h
+++ b/srsapps/ue/phy/include/srsapps/ue/phy/phy.h
@@ -167,6 +167,8 @@ private:
   float        old_gain; 
   uint32_t     sr_tx_tti;
 
+  bool         is_first_of_burst; 
+  
 };
 
 } 
diff --git a/srsapps/ue/phy/include/srsapps/ue/phy/ul_buffer.h b/srsapps/ue/phy/include/srsapps/ue/phy/ul_buffer.h
index b08faecf7..615ce3151 100644
--- a/srsapps/ue/phy/include/srsapps/ue/phy/ul_buffer.h
+++ b/srsapps/ue/phy/include/srsapps/ue/phy/ul_buffer.h
@@ -59,11 +59,9 @@ namespace ue {
     bool     generate_data();   
     bool     generate_data(ul_sched_grant *pusch_grant, uint8_t *payload);   
     bool     generate_data(ul_sched_grant *pusch_grant, srslte_softbuffer_tx_t *softbuffer, uint8_t *payload);   
-    bool     send(radio* radio_handler, float time_adv_sec, float cfo, srslte_timestamp_t rx_time, bool normalize_amp);
     bool     send(radio* radio_handler, float time_adv_sec, float cfo, srslte_timestamp_t rx_time);
-    bool     send_zeros(radio* radio_handler, float time_adv_sec, srslte_timestamp_t rx_time);
     static const uint32_t tx_advance_sf = 1; // Number of subframes to advance transmission
-
+    static const bool normalize_amp = true; 
   private: 
     log               *log_h; 
     phy_params        *params_db; 
diff --git a/srsapps/ue/phy/src/phy.cc b/srsapps/ue/phy/src/phy.cc
index 313d260d5..3406633ea 100644
--- a/srsapps/ue/phy/src/phy.cc
+++ b/srsapps/ue/phy/src/phy.cc
@@ -74,6 +74,7 @@ bool phy::init_(srslte::radio* radio_handler_, srslte::ue::tti_sync* ttisync_, l
   dl_buffer_queue = new queue(6, sizeof(dl_buffer));
   do_agc = do_agc_;
   last_gain = 1e4; 
+  time_adv_sec = 0; 
   
   // Set default params  
   params_db.set_param(phy_params::CELLSEARCH_TIMEOUT_PSS_NFRAMES, 100);
@@ -143,8 +144,8 @@ bool phy::send_prach(uint32_t preamble_idx, int allowed_subframe, int target_pow
   if (phy_state == RXTX) {
     srslte_agc_lock(&ue_sync.agc, true);
     old_gain = radio_handler->get_tx_gain();
-    radio_handler->set_tx_gain(0);
-    Info("Stopped AGC. Set TX gain to %.1f dB\n", 0);
+    radio_handler->set_tx_gain(10);
+    Info("Stopped AGC. Set TX gain to %.1f dB\n", radio_handler->get_tx_gain());
     return prach_buffer.prepare_to_send(preamble_idx, allowed_subframe, target_power_dbm);
   } 
   return false; 
@@ -508,7 +509,8 @@ void phy::run_rx_tx_state()
         phy_state = IDLE; 
         break; 
       case 1:
-        is_sfn_synched = true; 
+        is_sfn_synched = true;
+        is_first_of_burst = true; 
         break;        
       case 0:
         break;        
@@ -520,7 +522,7 @@ void phy::run_rx_tx_state()
 
     bool tx_zeros = true; 
     
-    // Prepare transmission for the next tti 
+    // Advance transmission time for the next tti 
     srslte_timestamp_add(&last_rx_time, 0, 1e-3);
 
     // Generate scheduling request if we have to 
@@ -543,17 +545,15 @@ void phy::run_rx_tx_state()
         get_ul_buffer_adv(current_tti)->generate_data();
       }
       // And transmit
-      get_ul_buffer_adv(current_tti)->send(radio_handler, time_adv_sec, cfo, last_rx_time);      
+      get_ul_buffer_adv(current_tti)->send(radio_handler, time_adv_sec, cfo, last_rx_time);
+      is_first_of_burst = false; 
     } else {
-      // Transmit zeros to avoid transitions. 
-      // FIXME: This keeps the TX RF chain always on. Should transmit zeros only before a true transmission
-      get_ul_buffer_adv(current_tti)->send_zeros(radio_handler, time_adv_sec, last_rx_time);
+      if (!is_first_of_burst) {
+        radio_handler->tx_end();
+        is_first_of_burst = true; 
+      }
     }
     
-    
-      // send ul buffer if we have to 
-      // Generate PUCCH if no UL grant
-    
     // Receive alligned buffer for the current tti 
     get_dl_buffer(current_tti)->recv_ue_sync(&ue_sync, &last_rx_time);
 
diff --git a/srsapps/ue/phy/src/prach.cc b/srsapps/ue/phy/src/prach.cc
index 066d3174a..820283e1b 100644
--- a/srsapps/ue/phy/src/prach.cc
+++ b/srsapps/ue/phy/src/prach.cc
@@ -160,7 +160,6 @@ bool prach::send(radio *radio_handler, float cfo, srslte_timestamp_t rx_time)
     }
   }
   
-  // transmit
   radio_handler->tx(signal_buffer, len, tx_time);                
   Info("PRACH transmitted CFO: %f, preamble=%d, len=%d rx_time=%f, tx_time=%f, PeakAmplitude=%.2f\n", 
        cfo*15000, preamble_idx, len, rx_time.frac_secs, tx_time.frac_secs, max);
diff --git a/srsapps/ue/phy/src/ul_buffer.cc b/srsapps/ue/phy/src/ul_buffer.cc
index 7d55fa349..f7e039538 100644
--- a/srsapps/ue/phy/src/ul_buffer.cc
+++ b/srsapps/ue/phy/src/ul_buffer.cc
@@ -49,7 +49,7 @@ bool ul_buffer::init_cell(srslte_cell_t cell_, phy_params *params_db_, log *log_
   if (!srslte_ue_ul_init(&ue_ul, cell)) {  
     srslte_ue_ul_set_normalization(&ue_ul, false); 
     signal_buffer = (cf_t*) srslte_vec_malloc(sizeof(cf_t) * SRSLTE_SF_LEN_PRB(cell.nof_prb));
-    cell_initiated = signal_buffer?true:false;
+    cell_initiated = (signal_buffer)?true:false;
     srslte_ue_ul_set_cfo_enable(&ue_ul, false);
     bzero(&uci_data, sizeof(srslte_uci_data_t));
     uci_pending = false; 
@@ -218,21 +218,9 @@ bool ul_buffer::generate_data(ul_sched_grant *grant, srslte_softbuffer_tx_t *sof
 
 int nof_tx = 0; 
 
-bool ul_buffer::send_zeros(srslte::radio* radio_handler, float time_adv_sec, srslte_timestamp_t rx_time)
-{
-  bzero(signal_buffer, sizeof(cf_t)*SRSLTE_SF_LEN_PRB(cell.nof_prb));
-  send(radio_handler, time_adv_sec, 0, rx_time, false); 
-}
-
 bool ul_buffer::send(srslte::radio* radio_handler, float time_adv_sec, float cfo, srslte_timestamp_t rx_time)
-{
-  send(radio_handler, time_adv_sec, cfo, rx_time, true);
-}
-
-bool ul_buffer::send(srslte::radio* radio_handler, float time_adv_sec, float cfo, srslte_timestamp_t rx_time, bool normalize_amp)
-{
-  
-  // send packet through usrp 
+{  
+  // send packet next timeslot minus time advance
   srslte_timestamp_t tx_time; 
   srslte_timestamp_copy(&tx_time, &rx_time);
   srslte_timestamp_add(&tx_time, 0, tx_advance_sf*1e-3 - time_adv_sec); 
@@ -256,7 +244,7 @@ bool ul_buffer::send(srslte::radio* radio_handler, float time_adv_sec, float cfo
     srslte_vec_sc_prod_cfc(signal_buffer, 0.9/max, signal_buffer, SRSLTE_SF_LEN_PRB(cell.nof_prb));
   }
   
-  Info("TX CFO: %f, len=%d, rx_time= %.6f tx_time = %.6f TA: %.1f us PeakAmplitude=%.2f PKT#%d\n", 
+  Info("TX CFO: %f, len=%d, rx_time= %.6f tx_time = %.6f TA: %.1f PeakAmplitude=%.2f PKT#%d\n", 
         cfo*15000, SRSLTE_SF_LEN_PRB(cell.nof_prb),
         srslte_timestamp_real(&rx_time), 
         srslte_timestamp_real(&tx_time), time_adv_sec*1000000, max, nof_tx);
diff --git a/srslte/examples/usrp_txrx.c b/srslte/examples/usrp_txrx.c
index b0b79ad4e..f86ce4e26 100644
--- a/srslte/examples/usrp_txrx.c
+++ b/srslte/examples/usrp_txrx.c
@@ -98,6 +98,7 @@ int main(int argc, char **argv) {
   parse_args(argc, argv);
   
   uint32_t flen = srslte_sampling_freq_hz(nof_prb)/1000;
+  uint32_t nsamples_adv = 3000; 
 
   cf_t *rx_buffer = malloc(sizeof(cf_t)*flen*nof_frames);
   if (!rx_buffer) {
@@ -105,11 +106,13 @@ int main(int argc, char **argv) {
     exit(-1);
   }
 
-  cf_t *tx_buffer = malloc(sizeof(cf_t)*flen);
+  cf_t *tx_buffer = malloc(sizeof(cf_t)*(flen+nsamples_adv));
   if (!tx_buffer) {
     perror("malloc");
     exit(-1);
   }
+  bzero(tx_buffer, sizeof(cf_t)*(flen+nsamples_adv));
+  
   cf_t *zeros = calloc(sizeof(cf_t),flen);
   if (!zeros) {
     perror("calloc");
@@ -132,24 +135,28 @@ int main(int argc, char **argv) {
   cuhd_set_tx_freq_offset(uhd, uhd_freq, 8e6);  
   sleep(1);
   
-  srslte_vec_load_file(input_filename, tx_buffer, flen*sizeof(cf_t));
+  srslte_vec_load_file(input_filename, &tx_buffer[nsamples_adv], flen*sizeof(cf_t));
 
   srslte_timestamp_t tstamp; 
   
   cuhd_start_rx_stream(uhd);
   uint32_t nframe=0;
   
+  float burst_settle_time = (float) nsamples_adv/srslte_sampling_freq_hz(nof_prb);
+  
+  printf("timeadv=%f\n",burst_settle_time);
+
   while(nframe<nof_frames) {
     printf("Rx subframe %d\n", nframe);
     cuhd_recv_with_time(uhd, &rx_buffer[flen*nframe], flen, true, &tstamp.full_secs, &tstamp.frac_secs);
     nframe++;
     if (nframe==9 || nframe==8) {
-      srslte_timestamp_add(&tstamp, 0, 2e-3);
+      srslte_timestamp_add(&tstamp, 0, 2e-3-burst_settle_time);
       if (nframe==8) {
-        cuhd_send_timed2(uhd, zeros, flen, tstamp.full_secs, tstamp.frac_secs, true, false);      
+        //cuhd_send_timed2(uhd, zeros, flen, tstamp.full_secs, tstamp.frac_secs, true, false);      
         printf("Transmitting zeros\n");        
       } else {
-        cuhd_send_timed2(uhd, tx_buffer, flen, tstamp.full_secs, tstamp.frac_secs, false, true);      
+        cuhd_send_timed2(uhd, tx_buffer, flen+nsamples_adv, tstamp.full_secs, tstamp.frac_secs, true, true);      
         printf("Transmitting Signal\n");  
       }
     }
diff --git a/srslte/include/srslte/ue/ue_ul.h b/srslte/include/srslte/ue/ue_ul.h
index 7a38b113e..06efd70c4 100644
--- a/srslte/include/srslte/ue/ue_ul.h
+++ b/srslte/include/srslte/ue/ue_ul.h
@@ -149,4 +149,10 @@ SRSLTE_API void srslte_ue_ul_reset(srslte_ue_ul_t *q);
 SRSLTE_API void srslte_ue_ul_set_rnti(srslte_ue_ul_t *q, 
                                       uint16_t rnti);
 
+/* Other static functions for UL PHY procedures defined in 36.213 */
+
+SRSLTE_API int srslte_ue_ul_sr_config(uint32_t I_sr, 
+                                      uint32_t *sr_periodicity, 
+                                      uint32_t *sr_N_offset);
+
 #endif
diff --git a/srslte/lib/cuhd/src/cuhd_imp.cpp b/srslte/lib/cuhd/src/cuhd_imp.cpp
index 45305bf2a..259b9682f 100644
--- a/srslte/lib/cuhd/src/cuhd_imp.cpp
+++ b/srslte/lib/cuhd/src/cuhd_imp.cpp
@@ -162,7 +162,7 @@ int cuhd_open_(char *args, void **h, bool create_thread_gain, bool tx_gain_same_
 {
   cuhd_handler *handler = new cuhd_handler();
   std::string _args = std::string(args);
-  handler->usrp = uhd::usrp::multi_usrp::make(_args);// + ", master_clock_rate=30720000, num_recv_frames=512");
+  handler->usrp = uhd::usrp::multi_usrp::make(_args + ", master_clock_rate=30720000, num_recv_frames=512");
 
 //  handler->usrp = uhd::usrp::multi_usrp::make(_args + ", master_clock_rate=50000000" + ", num_recv_frames=512");
   handler->usrp->set_clock_source("internal");
diff --git a/srslte/lib/ue/src/ue_ul.c b/srslte/lib/ue/src/ue_ul.c
index 97ec24e35..982b386aa 100644
--- a/srslte/lib/ue/src/ue_ul.c
+++ b/srslte/lib/ue/src/ue_ul.c
@@ -374,6 +374,41 @@ int srslte_ue_ul_pusch_encode_cfg(srslte_ue_ul_t *q, srslte_pusch_cfg_t *cfg,
     ret = SRSLTE_SUCCESS; 
   } 
   
-  return ret; 
-  
-}
\ No newline at end of file
+  return ret;   
+}
+
+/* Obtains Scheduling Request channel assignment as defined in Table 10.1-5, 36.213 */
+int srslte_ue_ul_sr_config(uint32_t I_sr, uint32_t *sr_periodicity, uint32_t *sr_N_offset) {
+  if (sr_periodicity && sr_N_offset) {
+    if (I_sr < 5) {
+      *sr_periodicity = 5;
+      *sr_N_offset    = I_sr; 
+    } else if (I_sr < 15) {
+      *sr_periodicity = 10;
+      *sr_N_offset    = I_sr-5;     
+    } else if (I_sr < 35) {
+      *sr_periodicity = 20;
+      *sr_N_offset    = I_sr-15; 
+    } else if (I_sr < 75) {
+      *sr_periodicity = 40;
+      *sr_N_offset    = I_sr-35; 
+    } else if (I_sr < 155) {
+      *sr_periodicity = 80;
+      *sr_N_offset    = I_sr-75; 
+    } else if (I_sr < 157) {
+      *sr_periodicity = 2;
+      *sr_N_offset    = I_sr-155; 
+    } else if (I_sr == 157) {
+      *sr_periodicity = 1;
+      *sr_N_offset    = I_sr-157; 
+    } else {
+      return SRSLTE_ERROR;
+    }
+  } else {
+    return SRSLTE_ERROR_INVALID_INPUTS;
+  }
+  return SRSLTE_SUCCESS;
+}
+
+
+