1 RB sensitivity at middle RBs poor than other RBs
5 likes1,842 views
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
1 RB sensitivity at middle RBs poor than other RBs
- 1. 1RB Sensitivity at Middle RBs Poor Than Other RBs ? Jay Chang 1
- 2. 2 實際量測值實際量測值實際量測值實際量測值 All LTE band Sensitivity will be degraded with 1RB @ middle RB location. WHY ?
- 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
- 7. 7 在資料傳輸過程中, 每個subframe上都有用戶使用的數據輸出. 所以各個信道的消息都由subframe上的各個time slot攜帶, 攜帶消息越多, 傳輸中可能引起的 丟幀(包)數目就越多, 誤碼(包)率就越大, 實際過程中sensitivity也就會越差. 以#0 subframe為例, 當DL(用戶數據)分配在#0 subframe中間的RB時, PSS、SSS、PBCH(控制信 息)映射在#0 subframe的中間位置; 因此, 在這種測量條件下, 解碼就會很困難 與full RB條件下相比, 部分RB條件對PSS、SSS、PBCH解碼影響很大. 在full RB條件下, 對測量結果的影響很小. 因為subframe分配在全資源塊範圍內, 與部分RB相比, 有很多使用者資料, 因此, 影響較小. http://dhagle.in/LTE
- 8. 8 先接受這個觀念 各個信道的消息都由subframe上的各個time slot攜帶 攜帶消息越多, 傳輸中可能引起的丟幀(包)數目就越多, 碼誤率就越大, 實際過程中sensitivity也就 會越差. 以#0 subframe為例 當DL(用戶數據)分配在#0 subframe中間的RB(10M為例PRB22-PRB27)時 PSS、SSS、PBCH映射在#0 subframe的中間位置, 因此, 在這種測量條件下, 解碼就會很困難(因為 有用戶數據 + PSS同步碼 + SSS輔助同步碼 + PBCH廣播信道盲檢) 這麼多一拖拉庫的擾碼等著UE作解調, 那妳現在攜帶消息全塞在中間的RB, 丟包多, 碼誤率大, sensitivity差.
- 9. 9 實際量測值實際量測值實際量測值實際量測值 All LTE band Sensitivity will be degraded with 1RB @ middle RB location.
- 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
- 13. 13 Thank you for your attention