Added frequency shift to fft to support SC-FDMA

lte/phy/include/liblte/phy/common/fft.h

@@ -37,7 +37,7 @@
 #include "liblte/phy/common/phy_common.h"
 #include "liblte/phy/utils/dft.h"
 
-//#define LTE_FFT_NORMALIZE
+#define LTE_FFT_NORMALIZE
 
 typedef _Complex float cf_t; /* this is only a shortcut */
 
@@ -51,6 +51,9 @@ typedef struct LIBLTE_API{
   uint32_t slot_sz;
   lte_cp_t cp;
   cf_t *tmp; // for removing zero padding
+  
+  bool freq_shift;
+  cf_t *shift_buffer; 
 }lte_fft_t;
 
 LIBLTE_API int lte_fft_init(lte_fft_t *q, 
@@ -81,4 +84,7 @@ LIBLTE_API void lte_ifft_run_sf(lte_fft_t *q,
                                 cf_t *input, 
                                 cf_t *output);
 
+LIBLTE_API int lte_fft_set_freq_shift(lte_fft_t *q, 
+                                      float freq_shift); 
+
 #endif

lte/phy/lib/common/src/fft.c

@@ -28,6 +28,8 @@
 #include <string.h>
 #include <strings.h>
 #include <stdlib.h>
+#include <complex.h>
+#include <math.h>
 
 #include "liblte/phy/common/phy_common.h"
 #include "liblte/phy/utils/dft.h"
@@ -54,13 +56,11 @@ int lte_fft_init_(lte_fft_t *q, lte_cp_t cp, uint32_t nof_prb, dft_dir_t dir) {
 
   dft_plan_set_mirror(&q->fft_plan, true);
   dft_plan_set_dc(&q->fft_plan, true);
-#ifdef LTE_FFT_NORMALIZE
-  dft_plan_set_norm(&q->fft_plan, true);
-#endif
 
   q->symbol_sz = (uint32_t) symbol_sz;
   q->nof_symbols = CP_NSYMB(cp);
   q->cp = cp;
+  q->freq_shift = false;
   q->nof_re = nof_prb * RE_X_RB;
   q->nof_guards = ((symbol_sz - q->nof_re) / 2);
   q->slot_sz = SLOT_LEN(symbol_sz);
@@ -77,6 +77,9 @@ void lte_fft_free_(lte_fft_t *q) {
   if (q->tmp) {
     free(q->tmp);
   }
+  if (q->shift_buffer) {
+    free(q->shift_buffer);
+  }
   bzero(q, sizeof(lte_fft_t));
 }
 
@@ -106,6 +109,35 @@ int lte_ifft_init(lte_fft_t *q, lte_cp_t cp, uint32_t nof_prb) {
   return ret;
 }
 
+/* Shifts the signal after the iFFT or before the FFT. 
+ * Freq_shift is relative to inter-carrier spacing.
+ * Caution: This function shall not be called during run-time 
+ */
+int lte_fft_set_freq_shift(lte_fft_t *q, float freq_shift) {
+  q->shift_buffer = vec_malloc(sizeof(cf_t) * SF_LEN(q->symbol_sz));
+  if (!q->shift_buffer) {
+    perror("malloc");
+    return -1; 
+  }
+  cf_t *ptr = q->shift_buffer;
+  for (uint32_t n=0;n<2;n++) {
+    for (uint32_t i=0;i<q->nof_symbols;i++) {
+      uint32_t cplen = CP_ISNORM(q->cp)?CP_NORM(i, q->symbol_sz):CP_EXT(q->symbol_sz);
+      for (uint32_t t=0;t<q->symbol_sz+cplen;t++) {
+        ptr[t] = cexpf(I*2*M_PI*((float) t-(float)cplen)*freq_shift/q->symbol_sz);
+      }
+      ptr += q->symbol_sz+cplen;
+    }    
+  }
+  
+  /* Disable DC carrier addition */
+  dft_plan_set_dc(&q->fft_plan, false);  
+ 
+  q->freq_shift = true;
+  
+  return LIBLTE_SUCCESS;
+}
+
 void lte_ifft_free(lte_fft_t *q) {
   lte_fft_free_(q);
 }
@@ -126,6 +158,9 @@ void lte_fft_run_slot(lte_fft_t *q, cf_t *input, cf_t *output) {
 
 void lte_fft_run_sf(lte_fft_t *q, cf_t *input, cf_t *output) {
   uint32_t n; 
+  if (q->freq_shift) {
+    vec_prod_ccc(input, q->shift_buffer, input, 2*q->slot_sz);
+  }
   for (n=0;n<2;n++) {
     lte_fft_run_slot(q, &input[n*q->slot_sz], &output[n*q->nof_re*q->nof_symbols]);
   }
@@ -152,4 +187,10 @@ void lte_ifft_run_sf(lte_fft_t *q, cf_t *input, cf_t *output) {
   for (n=0;n<2;n++) {
     lte_ifft_run_slot(q, &input[n*q->nof_re*q->nof_symbols], &output[n*q->slot_sz]);
   }
+  if (q->freq_shift) {
+    vec_prod_ccc(output, q->shift_buffer, output, 2*q->slot_sz);
+  }
+#ifdef LTE_FFT_NORMALIZE
+  vec_sc_prod_cfc(output, (float) 1.0/sqrtf(q->symbol_sz),output,2*q->slot_sz);
+#endif
 }

lte/phy/lib/phch/test/pusch_encode_test_mex.c

@@ -193,16 +193,27 @@ void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
     }
   }
 
+  cf_t *scfdma = vec_malloc(sizeof(cf_t) * SF_LEN_PRB(cell.nof_prb));
+  bzero(scfdma, sizeof(cf_t) * SF_LEN_PRB(cell.nof_prb));
+  lte_fft_t fft; 
+  lte_ifft_init(&fft, CPNORM, cell.nof_prb);
+  lte_fft_set_freq_shift(&fft, 0.5);
+  lte_ifft_run_sf(&fft, sf_symbols, scfdma);
+  
   if (nlhs >= 1) {
-    mexutils_write_cf(sf_symbols, &plhs[0], nof_re, 1);  
+    mexutils_write_cf(scfdma, &plhs[0], SF_LEN_PRB(cell.nof_prb), 1);  
   }
   if (nlhs >= 2) {
-    mexutils_write_cf(pusch.pusch_z, &plhs[1], harq_process.nof_re, 1);  
+    mexutils_write_cf(sf_symbols, &plhs[1], nof_re, 1);  
+  }
+  if (nlhs >= 3) {
+    mexutils_write_cf(pusch.pusch_z, &plhs[2], harq_process.nof_re, 1);  
   }
   pusch_free(&pusch);  
   free(trblkin);
   free(uci_data.uci_cqi);
   free(sf_symbols);
+  free(scfdma);
   
   return;
 }

lte/phy/lib/phch/test/pusch_test.c

@@ -230,6 +230,14 @@ int main(int argc, char **argv) {
     }
   }
   
+  
+  cf_t *scfdma = vec_malloc(sizeof(cf_t) * SF_LEN_PRB(cell.nof_prb));
+  bzero(scfdma, sizeof(cf_t) * SF_LEN_PRB(cell.nof_prb));
+  lte_fft_t fft; 
+  lte_ifft_init(&fft, CPNORM, cell.nof_prb);
+  lte_fft_set_freq_shift(&fft, 0.5);
+  lte_ifft_run_sf(&fft, sf_symbols, scfdma);
+  
   gettimeofday(&t[1], NULL);
   //int r = pusch_decode(&pusch, slot_symbols[0], ce, 0, data, subframe, &harq_process, rv);
   int r = 0; 

matlab/tests/pusch_test.m

@@ -1,5 +1,5 @@
 clear 
-ueConfig=struct('NCellID',3,'NULRB',6,'NSubframe',0,'RNTI',1,'CyclicPrefixUL','Normal','NTxAnts',1);
+ueConfig=struct('NCellID',3,'NULRB',25,'NSubframe',0,'RNTI',1,'CyclicPrefixUL','Normal','NTxAnts',1);
 puschConfig=struct('NLayers',1,'OrthCover','Off','PRBSet',[0 1]','Modulation','QPSK','RV',0,'Shortened',0);
 
 addpath('../../debug/lte/phy/lib/phch/test')
@@ -43,8 +43,10 @@ for i=1:length(TBs)
                                 idx=ltePUSCHIndices(ueConfig,puschConfig);
                                 subframe_mat = lteULResourceGrid(ueConfig);
                                 subframe_mat(idx)=cw_mat;
-                                [subframe_lib, cwlib]=liblte_pusch_encode(ueConfig,puschConfig,trblkin,ones(1,cqilen(c)),ri_bit,ack_bit);
-                                err=mean(abs(subframe_mat(:)-subframe_lib));
+                                waveform = lteSCFDMAModulate(ueConfig,subframe_mat,0);
+                               
+                                [waveform_lib, subframe_lib, cwlib]=liblte_pusch_encode(ueConfig,puschConfig,trblkin,ones(1,cqilen(c)),ri_bit,ack_bit);
+                                err=mean(abs(waveform-waveform_lib));
                                 if (err > 10^-6)
                                   disp(err)    
                                   error('Error!');

matlab/tests/test_scfdma.m

@@ -0,0 +1,26 @@
+clear
+ue = struct('NULRB',6,'NDLRB',6);
+d = lteULResourceGridSize(ue);
+rgrid = complex(rand(d)-0.5,rand(d)-0.5);
+waveform = lteSCFDMAModulate(ue,rgrid,0);
+
+wave = [];
+freq_correct=[];
+for i=1:14
+    symbol = ifft(ifftshift([zeros(28,1); rgrid(:,i); zeros(28,1)]),128);
+    if (i==1 || i==8)
+        cp_len=10;
+    else
+        cp_len=9;
+    end
+    symbol_cp=[symbol((128-cp_len+1):128); symbol(1:128)];
+    freq_correct=[freq_correct; exp(1i*pi*(-cp_len:127)'/128)];    
+    wave = [wave; symbol_cp];
+end
+
+wave=wave.*freq_correct;
+
+%wave=transpose(wave);
+%plot(1:138,fftshift(fft(waveform(1:138))),1:138,fftshift(fft(wave(1:138))))
+plot(abs(wave(1:138)-waveform(1:138)))
+mean(abs(wave-waveform))