This document discusses cell reference signals (RS) in LTE networks. It describes how cell RS are used for cell search and acquisition, downlink channel estimation, and channel quality measurements. It then provides technical details on: - The frequency and time spacing of downlink RS - The pseudo-random sequence generation process used to calculate cell RS values - How the calculated cell RS values are mapped to resource elements for transmission

1. Cell Reference Signal and
Mapping
Yanuar T. Aditya N.

2. Cell Reference Signal are used for…
• Cell search and initial acquisition
• Downlink channel estimation at the UE
• Downlink channel quality measurements

3. Cell Search

4. 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

5. Screenshot #1
CELL ID = 0 ; B/W = 10 MHz

6. Screenshot #2
CELL ID = 1 ; B/W = 10 MHz

7. Screenshot #3
CELL ID = 6 ; B/W = 10 MHz

8. 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

9. 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

10. …more
• m_seq2 denoted by (need cinit)
for length=1:31
m_seq2[length] = c_init mod 2
c_init = c_init / 2

11. 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]
}
}

12. 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);
}
}

13. Mapping

14. …more

15. 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]]
}
}

16. Result

17. Q & A