1. Measuring LTE sensitivity with a single resource block (RB) located in the middle of the channel can degrade sensitivity. This is because control channels like the primary synchronization signal (PSS), secondary synchronization signal (SSS) and physical broadcast channel (PBCH) are also located in the middle, making decoding more difficult.
2. With a single middle RB, the coding rate needs to be twice as high on subframe 0 compared to other subframes to achieve the same block error rate. This requires at least 3dB higher signal-to-noise ratio (SNR).
3. Testing sensitivity with few RBs near the channel center can also degrade sensitivity slightly due to interference from the in-band
3. LTE Frame Structures
1 Radio Frame = 10 Subframe1 Subframe = 1 TTI = 1 ms = 2 time slot
1 time slot = 0.5 ms = 7 OFDM symbols = 1 RB 時間x軸 = 2048 × 7 + 160 + 144 × 6 = 15360 Ts
1st CP = 5.2 μs = 160 Ts other six CP = 4.7 μs = 144 Ts
1 OFDM symbol = 66.7 μs = 2048 TsBW = 20 MHz(use 30.72MHz sampling rate)
取樣點時長 = 1/30.72MHz = 32.5 ns
Def: LTE最小時間單位最小時間單位最小時間單位最小時間單位 Ts = 32.5 ns
目前無法顯示此圖像。
(2:2)
(1:3)
(UL : DL)
#0 & #5一定是DL subframe
#1一定是Special subframe
#2一定是UL subframe
3
36.211 defined:
TDD 7種 subframe組合
Special subframe Special subframe
Downlink Pilot Time Slot
36.211 defined:
TDD 9種 special subframe組合
常見(3:9:2), (9:3:2), (10:2:2)
代表(DL:GP:UL)
2 time slots = 14 OFDM symbols
4. 4https://www.mathworks.com/help/lte/ug/synchronization-signals-pss-and-sss.html
Primary Synchronization Signal (PSS)
• PSS is based on a frequency-domain Zadoff-
Chu sequence.
Zadoff-Chu Sequences
• ZC sequences are a construction of Frank-
Zadoff sequences defined by D. C. Chu.
• These codes have the useful property of
having zero cyclic autocorrelation at all
nonzero lags.
• When used as a synchronization code, the
correlation between the ideal sequence
and a received sequence is greatest when
the lag is zero.
• When there is any lag between the two
sequences, the correlation is zero.
72 sub-cars
31 sub-cars 31 sub-cars5 sub-cars 5 sub-cars
PSS/SSS
SSS
SSS
5. 5
Physical Broadcast Channel (PBCH)
Purpose: Carriers BCH Master Information Block(MIB)
• System bandwidth
• System frame number
• Antenna information
Transmission
• Time: First 4 symbols in subframe 0 and slot 1
• Frequency: Middle 1.08 MHz (6 RBs)
• Allows UE to quickly decode PBCH after decoding PSS and SSS
TTI = 40 ms
• Transmitted in four bursts at a very low data rate
• CRC check uniquely determines 40 ms PBCH TTI boundary
BCH is QPSK-modulated
slot 0 slot 1
subframe 0
LTE PBCH的開銷
slot 1
#0~#3
6. 6
Physical Broadcast Channel (PBCH)
PBCH is downlink only channel.
It occupies 72 subcarriers belong to first 4 OFDMA symbols of second slot of every 10ms radio frame.
Pls. note that reference signal(RS) resource elements(REs) are excluded from the PBCH allocation.
Hence PBCH will occupy about (72 x 4) - 48 = 240 REs. PS. 2nd slot每個RB有2個RS, so 2 × 6RBs × 4 Frames = 48
As PBCH uses QPSK modulation, it leads to about 480 bits per 240 REs.
1 RB1 OFDM
symbol
1 subcarrier
1 RE = 1 OFDM symbol × 1 subcarrier
1RB = 7 OFDM symbols(normal CP) × 12 subcarriers
http://www.rfwireless-world.com/Terminology/LTE-PBCH-Physical-Broadcast-Channel.html
10. 10
Q: Measuring LTE sensitivity with 1 RB located at the center of the channel sensitivity also degrade ?
(問題同上頁問題同上頁問題同上頁問題同上頁All LTE band sensitivity will be degraded with 1RB @ middle RB location).
另一種解釋
A:
• Subframe0 should be set to MCS = 1 and subframe5 should be omitted.
• The PDSCH with 1 RB allocated on subframe0 has more than twice the coding rate of PDSCH with 1
RB allocation on subframes other than 0 and 5. (subframe0的PDSCH在1RB @ middle RB location需
要2倍的coding rate 跟 subframe0 and subframe5以外的1RB PDSCH coding rate比起來的話).
• Therefore, the SNR needed to achieve the same BLER (block error rate) is more than 3 dB higher for
subframe0. (subframe0 1RB coding rate~1 幾乎沒有糾錯碼,為了達到相同的BLER, subframe0 1RB
SNR勢必要是原本subframe0的2倍以上, 降才能有相同的BER(假設#碼誤相同)).
• For this reason the coding rate is reduced for subframe0 and subframe5 is omitted during this test. If
these settings are not used potentially 3 dB degradation in sensitivity could be seen during this test.
other subframe 1RB subframe0 1RB
MCS 1 1
PDSCH coding rate 1/2 1/2 (假設)
sensitivity 爛3dB
other subframe 1RB subframe0 1RB
1 1
1/2 2/2 (假設)
same same
12. 12
Q: When testing with low numbers of RBs near the center of the channel bandwidth, LTE sensitivity
be degraded ?
A:
• The IM2 product can begin to desense the receiver.
• Few RBs where are located near the center of the channel.
• Because the IM2 product is in the same location.
• There can be a slight degradation in sensitivity.
• Ex: SVLTE B4+BC0 Tx cause IM2 product in BC0 Rx.
Band_Allocation_Overlap_and_IM2_IM3_Freq_Calculator 判斷一下