31
Wilson W. K. Thong (ASTRI), Fabrice Nabet, Haithem Bilel (TCL), Florian Kaltenberger, Raymond Knopp (Eurecom) OAI workshop 2017 BUPT, Beijing, April 27 th 2017 OAI UE overview
Wilson W. K. Thong (ASTRI), Fabrice Nabet, Haithem Bilel (TCL), Florian Kaltenberger,
Raymond Knopp (Eurecom)
OAI workshop 2017
BUPT, Beijing, April 27th 2017
OAI UE overview
Agenda
Overview of LTE UE Attach Procedure
OAI-UE Threading Structure & Timing
Walk through the OAI-UE Codes
2
Overview of LTE UE Attach Procedure
UE Power On Downlink synchronization (PSS/SSS/MIB, TS36.211) Listening broadcast information (TS36.331) PLMN Selection and Cell Selection (TS36.304)
During UE Attach (TS23.401) Random access and uplink synchronization (TS36.300) RRC connection setup (TS36.331) UE authentication (TS24.301) NAS security setup (TS24.301) RRC security setup (TS36.331)
UE capability enquiry (TS36.331) RRC connection reconfiguration (TS36.331)
EPS bearer establishment (TS24.301)
UE IP Address Allocated (TS24.301)
4
Overview : UE Attachment
7
Uplink Synchronized
Uplink unsynch
Random Access Succeeded
UE AuthenticatedNAS Integrity And Ciphering Configured
RRC Integrity And Ciphering Configured
IP Address AllocatedQoS negotiated
Radio Configured(PHY,MAC,RLC,SRB,DRB)
Attach SucceededDate TimeConfigured
UE eNB MME
Msg1: PRACH
Msg2: RAR
Msg3: RRC Connection Request
EMM Information : Time Zone and Time / Daylight Saving Time
RRC Connection Setup Complete
EMM Attach Request
EMM Authentication Response
NAS Security Mode Command
NAS Security Mode Complete
RRC Security Mode Command
RRC Security Mode Complete
Initial Context Setup Request
EMM Attach Accept
ESM PDN Connectivity Request
ESM Activate Default EPS Bearer Context Request
RRC UE Capability Information
RRC UE Capability Enquiry
UE Capability Info Indication
Msg4: RR Connection Setup
RRC Connection Reconfiguration
RRC Connection Reconfiguration Complete
EMM Attach Complete
ESM Activate Default EPS Bearer Context Accept
EMM Authentication Request
UL/DL Data UL/DL Data
Initial Context Setup Response
Progress A
chieved
Protocol M
essage Timing
OAI-UE Threading Structure
Two Parallelized threads are running on physical layer One Thread for Odd subframes processing, the second thread for Even subframes
processing Timing Constraint 2ms !!! Each Thread “UE_thread_RxNTxNp4” is responsible of :
downlink subframe decoding (#Subframe N) uplink subframe encoding (#Subframe N+4)
Three Cores are fully used for the whole PHY processing Core 0: Samples Acquisition / Core 1: Processing of Even Subframes / Core 2:
Processing of Odd Subframes
5MHz 10MHz 20MHz SISO MIMO
(2CWs) SISO MIMO
(2CWs) SISO MIMO
(2CWs) FFT 3 ~45 3
~45 3 ~45 5 70 5 ~70 8 ~112
ChanEst 10 40 10 40 5 20 25 100 11 45 50 200
Front End Processing
85
85 62 170 120 310
Pdcch Decoding
36 80 65 80 90 80
Pdsch Processing : Channel Scale/Channel Compensation
4 ~55 4 ~55 6 ~80 5 ~65 8 ~104 10 130
LLRs Computation
1 ~15
30 ~400 2 ~25
65 ~845 3 ~39 130 1690
Turbo Decoding 60 180 60 360 60 360 60 720 60 720 60 1440
Full Channel Decoding unscrambling/rate Matching/deinterleaving/turbo decoding
300 550 665 1296 1330 2600
Subframe Processing
450us < 2ms
1150us < 2ms
850us < 2ms
2456us !!! 1650us < 2ms
4810us !!!
OAI-UE Timing Measurement
OAI-UE Timing Measurement Critical Blocks: Channel Decoding (~2600 us)
Unscrambling Rate matching Deinterleaving Turbo Decoding
LLRs Computation (Mimo) (~1700 us)
Potential Optimization: SW Optimization:
Phy Processing Parallelization More efficient implementation
(AVX512 / AVX2) depending on GPP (Xeon Phi etc)
HW Optimization: Offload channel decoding on HW
accelerator Offload LLRs computation on HW
accelerator Estimation of time usage is needed
20MHz
Percentage
SISO MIMO SISO MIMO
Front End Processing
120 310 7,3% 6,5%
Pdcch Decoding 90 80 5,45% 1,66%
Pdsch Processing : Channel Scale/Channel Compensation
104 130 6,3% 2,7%
LLRs Computation
39 1690 2,36% 35,13%
Full Channel Decoding unscrambling/rate Matching/deinterleaving/turbo decoding
1330 2600 80,6% 54%
Subframe Decoding
1650 4810
Downlink Synchronization – Initial • To know where is subframe #0 Search PSS0..2 position Search SSS0..167 in 4 possibilities: Normal CP + FDD
Normal CP + TDD Extended CP + FDD Extended CP + TDD
14 Figure from: Figure 7.2 – 7.3 of “LTE – the UMTS long term evolution :
from theory to practice / Stefania Sesia, Issam Toufik, Matthew Baker. – 2nd ed.”
FDD TDD
Downlink Synchronization – Initial
• Check PBCH CRC to confirm if PSS/SSS is real • Re-synchronize USRP Rx timing
Related code location: initial_sync() in openair1/PHY/LTE_TRANSPORT/initial_sync.c, UE_thread() in targets/RT/USER/lte-ue.c
15
#3#0 #1 #2#7 #8 #9#4 #5 #6
1st capture start
rx offset
capture length = 10ms
(not used)
2nd capture start
capture length = rx offset
3rd capture start
#0 #1 #2 #3 #4 #5 #6 #7 #8 #9
capture length = 10ms
rx offset = 0
Downlink Synchronization – Continuous • Calculate IFFT(channel estimation) i.e. channel impulse response
(CIR) • Estimate time drift (rx_offset)from CIR peak • Correct the time drift by “time shifting”
Related code location: lte_adjust_synch()in openair1/PHY/LTE_ESTIMATION/lte_adjust_sync.c UE_thread() in targets/RT/USER/lte-ue.c
16
#1#0#9#1
#9 #0 #9
Actual frame start
OAI-UE frame start, estimate rx_offset
…...
rx_offset
overwrite by rx_offset
…...
OAI-UE frame start adjusted
…...
Actual frame start
#1#0
#0 #1
OAI-UE frame start, estimate rx_offset
Downlink Synchronization – Flow
17
• Estimate rx_offset in UE_thread_rx()
• Affect USRP read operation in UE_thread()
Listening Broadcast Information – SIB1
• PHY/MAC detects SI-RNTI DCI and PDSCH
• RRC parses the SIB1 information element
• Configure PHY/MAC accordingly
o TDD UL/DL
configuration
o Other SIBx scheduling information
18
Listening Broadcast Information – SIB1
• Overall timing diagram
19
slot 10 slot 11 slot 12 slot 13
0=l 6=l
subframe 5 subframe 6
……
slot 14 slot 15
subframe 7
0=l 6=l
slot_fep
pdcch
pdsch (1)
ue_decode_si
SI receiving
subframe 5
pdsch (2)
subframe 5
ue_scheduler
mac_rrc_data_ind
rrc_ue_task
TASK_MAC_UE →TASK_RRC_UERRC_MAC_BCCH_DATA_IND
TASK_RRC_UE→TASK_NAS_UENAS_CELL_SELECTION_CNF
nas_ue_task
UE
_thr
ead(
)U
E_t
hrea
d_rx
()rr
c_ue
_tas
k()
nas_
ue_t
ask(
)
PHY_var_UE_g
UE_mac_inst
RRC_mac_inst
Listening Broadcast Information – SIB1
20
slot 10 slot 11 slot 12
0=l 6=l
subframe 5 subframe
0=l 6=l
slot_fep
pdcch
pdsch (1)
ue decode si
subframe
pdsch (2)
ue scheduler
mac rrc data ind
UE_thread()
UE_thread_rx()
PHY_var_UE_g
UE mac inst
Detected SI-RNTI DCI
• PHY/MAC detects SI-RNTI DCI slot fep (front end processor) = FFT + channel estimation +
frequency offset estimation
Related code location: phy_procedures_UE_RX()in openair1/SCHED/phy_procedures_lte_ue.c
Listening Broadcast Information – SIB1
21
slot 10 slot 11 slot 12 slot 13
6=l
subframe 5 subframe 6
slot 14 slot 15
subframe 7
0=l 6=l
slot_fep
pdcch
pdsch (1)
ue_decode_si
SI receiving
subframe 5
pdsch (2)
subframe 5
ue_scheduler
mac_rrc_data_ind
rrc ue task
TASK_MAC_UE →TASK_RRC_UERRC_MAC_BCCH_DATA_IND
TASK RRC UE→TASK NAS UENAS CELL SELECTION CNF
nas ue task
()
UE_thread_rx()
Detected SI-RNTI PDSCH
• PHY/MAC detects SI-RNTI PDSCH pdsch (1) = RE demap + channel compensation + spatial
decode + QPSK demodulation pdsch (2) = unscrambling + Turbo decoding
Related code location: rx_pdsch()in openair1/PHY/LTE_TRANSPORT/dlsch_demodulation.c
Listening Broadcast Information – SIB1
22
slot_fep
pdcch
pdsch (1)
ue_decode_si
SI receiving
subframe 5
pdsch (2)
ue_scheduler
mac_rrc_data_ind
TASK_MAC_UE →TASK_RRC_UERRC_MAC_BCCH_DATA_IND
TASK_RRC_UE→TASK_NAS_UENAS_CELL_SELECTION_CNF
UE_thread_rx()
subframe 5
Parse SIB1Configure PHY/MAC
rrc_ue_task()
nas_ue_task()
rrc_ue_task
nas_ue_task
• RRC parses the SIB1 information element • Configure PHY/MAC accordingly
Related code location: decode_SIB1()in openair2/RRC/LITE/rrc_UE.c
LTE UE Synchronization Procedures
Cell Search comprises 1. Timing and frequency synchronization with the cell using the
primary synchronization reference signal. This also gives the Cell ID group NID
(2) (0,1,2) 2. Cell ID NID
(1) (0,…,166) and Frame type (FDD/TDD, Normal/Extended Prefix) determination from secondary synchronization reference signals
3. Demodulation of PBCH (using NIDCell= 3NID
(1) + NID(2)) to
receive basic system information during steady-state reception 1. NRB
DL (cell bandwidth)
2. PHICH-config (to allow PDCCH demodulation, for system information)
3. Frame number (8 bits from payload, 2 bits from redundancy version)
4. Antenna configuration (1,2,4 from CRC mask)
27/04/2017 24
Initial Timing/Frequency Acquisition (Synchronization Signals, FDD Normal CP)
27/04/2017
Subframe 0 Subframe 1 Subframe 4 Subframe 5 Subframe 9
Primary (Y) and Secondary B) Synchronization Signals
(first half)
PBCH Primary(Y) and Secondary(B)
Synchronization Signals (2nd half)
10 ms
Freq
uenc
y (P
RB
s)
Time (symbols)
25
Primary Synchronization Signal (PSS)
Zadoff-Chu root-of-unity sequence has excellent auto-correlation properties and is very tolerant to frequency-offsets
27/04/2017
Autocorrelation sequence
Real component (time-domain
u=25)
Imag component (time-domain,
u=25)
26
Primary Synchronization RX
Correlation of 3 primary sequences (d*u(-n)) with received signal. Each eNB (or sector) has different sequence => Reuse pattern of 3 for different eNB or sectors (NID
(2))
Primary Purpose: Determine start of frame
Alternate purposes: Channel estimation for SSS/PBCH and frequency offset estimation
27/04/2017 27
Secondary Synchronization Signal (SSS)
Purpose: determine frame type and cell ID NID(1)
Implemented as BPSK-modulated interleaved sequence of two length-31 binary m-sequences (m=31) with cyclic shifts m0 and m1. and scrambled by the two different scrambling sequences Results in 167 possible BPSK sequences for each of subframe 0 and 5
The receiver must perform correlations with all 167 sequences and find the most likely transmitted sequence. It can use the output of the primary sequence correlation as a rough channel estimate to improve detection probability
Position relative to PSS allows for frame type determination
27/04/2017 28
Secondary Synchronization RX
Hypothesis: one of 4 frame types TDD/FDD, normal/extended prefix => gives position in samples of SSS with respect to PSS detected in primary synchronization
Use channel estimate (partially coherent) from PSS and quantized uniform phase offset to compensate residual frequency offset (PSS/SSS not in same symbol) and amplitudes in SSS symbol
Correlate with 167 out of 167 * 3 sequences (167 per PSS NID(2)) of
length 62 in each of slots 0 and 10
Choose sequence which has highest coherent correlation
This has to be done with 2 different assumptions (subframe 0 or subframe 5 is first in RX buffer), or we just wait until we receive an RX frame in the correct order (i.e. when subframe 0 falls in the first 5 ms of the RX buffer)
27/04/2017
29
PBCH Detection
Detection of the PBCH requires the following steps 1. Generation of the cell-specific reference signals based
on the cell ID derived from SSS detection 2. Performing channel estimation for the 4 symbols of the
PBCH 3. Extracting the PBCH reference elements 4. Applying the conjugated channel estimates to the
received reference elements 5. Channel decoding
27/04/2017 31
Generic OFDM Receiver
BroadbandChannel
Estimates
Digital Baseband Inputs
I[n]
Q[n] Prefix
Extraction FFT
I[k]
Q[k] Channel Compen-
sation
Channel Estimation
Pilot extraction
I[k]
Q[k] LLR Unit
To timing (DAQ) and frequency
correction units, and I/Q imbalance
Channel Decoding
27/04/2017 32
Key linear processing operations which can be vectorized easily with SIMD
Inner-products (synchronization, projection operations)
Componentwise products (compensation/equalization, channel estimation)
FFT/IFFTs (OFDM TX/RX)
Peak search in vector (synchronization)
Vector addition, subtraction, energy, absolute value
27/04/2017 33
