Cell Reference Signal and Mapping

Yanuar T. Aditya N.

Cell Reference Signal are used for…

• Cell search and initial acquisition• Downlink channel estimation at the UE• Downlink channel quality measurements

Cell Search

Downlink RS (Reference Signals)

• Transmitted by each antenna (currently using single antenna)– Freq. domain spacing is 6 subcarrier– Time domain spacing is 4 OFDM symbols

Screenshot #1

CELL ID = 0 ; B/W = 10 MHz

Screenshot #2

CELL ID = 1 ; B/W = 10 MHz

Screenshot #3

CELL ID = 6 ; B/W = 10 MHz

Cell RS Equation

• Shall be transmitted in all downlink subframes• Shall be transmitted in one or several antennas

for number_of_slot=1:20 for ofdm_symbol=1:7 calculate rofdm_symbol,number_of_slot(m)

m = 0,1,…,2*N_RB - 1

Pseudo-Random Sequence Generator

• Initialized with

• Then, initialize the the Gold-Sequence m_seq1 and m_seq2. Each has 31-bit length.

for length=1:31 if length=1 m_seq1[length] = 1 else m_seq1[length] = 0

…more

• m_seq2 denoted by (need cinit)

for length=1:31 m_seq2[length] = c_init mod 2 c_init = c_init / 2

So far…

for length=1:31{ if length=1 m_seq1[length] = 1 else m_seq1[length] = 0}

for number_of_slot=1:20 for ofdm_symbol=1:7 { calc_c_init() for length=1:31 { m_seq2[length] = c_init mod 2 c_init = c_init / 2 } calc_pseudo_rand() calc_cell_RS() }

calc_pseudo_rand(){ for n=1:M_pn+Nc { m_seq1[n+31]=m_seq1[n+3]^m_seq1[n] m_seq2[n+31]=m_seq2[n+3]^m_seq2[n+2]^m_seq2[n+1]^m_seq2[n]

} for n=1:M_pn { pseudo_rand[n]=m_seq1[n+Nc]^m_seq2[n+Nc] }}

The cell RS value

…init m_seq1

for number_of_slot=1:20 for ofdm_symbol=1:7 { …init c_init …init m_seq2 …calc_pseudo_rand()

for m_index=1:N_RB*2 { out_signal[number_of_slot][ofdm_symbol][m_index].re = (1-2*pseudo_rand_seq[2*m_index])/SQRT_2; out_signal[number_of_slot][ofdm_symbol][m_index].im =

((1-2*pseudo_rand_seq[2*m_index+1])/SQRT_2); } }

Mapping

• We have to map the cell_RS which occupied m = 2 * N_RB on 12 * N_RB subcarriers per OFDM symbols.

• OFDM symbol wise, only selected symbol will be filled with cell_RS according to

…more

• v define the position in the freq domain (subcarrier) for the different RS

• vshift given by

Poured into code

for num_sub=1:2*N_RB /* 1 to 100 on 10 MHz */ for ofdm_sym=1:7 { if antenna_port == 0 || antenna_port == 1 { check_v01_value() slot[6 * num_sub + (v + v_shift)][ofdm_symb] = cell_RS[l][num_sub] } else if antenna_port == 2 || antenna_port == 3 { check_v23_value() slot[6 * num_sub + (v + v_shift)][ofdm_symb] = cell_RS[l][num_sub]] } }

Result

Q & A