phy: add warning when choosing higher 3/4 sampling

common/utils/nr/nr_common.c

@@ -874,6 +874,7 @@ void get_samplerate_and_bw(int mu,
     switch(n_rb) {
     case 270:
       if (threequarter_fs) {
+        warn_higher_threequarter_fs(n_rb, mu);
         *sample_rate=92.16e6;
         *samples_per_frame = 921600;
         *tx_bw = 50e6;
@@ -973,6 +974,7 @@ void get_samplerate_and_bw(int mu,
 
     case 273:
       if (threequarter_fs) {
+        warn_higher_threequarter_fs(n_rb, mu);
         *sample_rate=184.32e6;
         *samples_per_frame = 1843200;
         *tx_bw = 100e6;

common/utils/nr/nr_common.h

@@ -37,6 +37,7 @@
 #include <stdlib.h>
 #include "assertions.h"
 #include "common/utils/utils.h"
+#include "common/utils/LOG/log.h"
 
 #define MAX_SI_GROUPS 3
 #define NR_MAX_PDSCH_TBS 3824
@@ -272,6 +273,19 @@ static __attribute__((always_inline)) inline int count_bits64_with_mask(uint64_t
   return count_bits64(v & mask);
 }
 
+static inline void warn_higher_threequarter_fs(const int n_rb, const int mu)
+{
+  LOG_W(PHY,
+        "3/4 sampling is not possible for current PRB size: %d and numerology: %d.\n "
+        "So 6/4 sampling is chosen to support x3xx type USRPs.\n "
+        "Note that this sampling rate increases fronthaul traffic, FFT buffer size and processing time by a factor of two compared "
+        "to 3/4 sampling rate.\n "
+        "Some PRACH configuration might not be supported with 6/4 FFT size.\n "
+        "Consider reducing the PRB size that would fit within the FFT size of 3/4 sampling\n",
+        n_rb,
+        mu);
+}
+
 uint64_t reverse_bits(uint64_t in, int n_bits);
 void reverse_bits_u8(uint8_t const* in, size_t sz, uint8_t* out);