1. OpenAirInterface Overview and Lab Session 1

2. OpenAir4G Tutorial (openair1, Feb 2012)
Provides open-source (hardware and software) wireless technology platforms
target innovation in air-interface technologies through experimentation
We rely on the help of
Publicly-funded research initiatives (ANR,ICT,CELTIC)
Direct contracts with industrial partners
Widespread collaboration with a network of partners using open-source development and tools
LINUX/RTAI based SW development for PCs
LEON3/GRLIB-based HW and eCos/MutexH-based SW development for FPGA targets
LINUX networking environment
Experimental Licenses from ARCEP (French Regulator) for medium-power outdoor network deployments
1.9 GHz TDD, 5 MHz channel bandwidth
2.6 GHz FDD (two channels), 20 MHz channel bandwidth
800 MHz FDD (two channels) : 10 MHz channel bandwidth
OpenAir4G Tutorial (openair1, Feb 2012)

3. OpenAirInterface Development Areas
OPENAIR3 : Wireless Networking
All-IP, Mobility Management, , Cellular/Mesh Routing Protocols, Mesh Topology Management, Multimodal Radio Resource Management
Cognitive Technologies Wideband RF, Agile Spectrum Management, Interference Management and Control,
Distributed/Collaborative techniques, Spectrum Sensing, Cognitive and Flexible Radio Architectures,
Ambient Networking
OPENAIR2: Medium-Access Protocols
Cellular topologies, single-frequency resource allocation, cross-layer wideband scheduling, Mesh topologies, distributed resource control
OPENAIR1: Baseband/PHY
Advanced PHY (LTE), Propagation Measurement and Modelling, Sensing and Localization Techniques, PHY Modeling Tools
OPENAIR0: Wireless Embedded System Design
Agile RF design, Reconfigurable High-end Transceiver
Architectures, FPGA prototyping, Simulation Methodologies,
Software development tools, low-power chip design
OpenAir4G Tutorial (openair1, Feb 2012)

4. Collaborative Web Tools
OpenAirInterface SVN Repositories
All development is available through SVN repository (openair4G) containing
OPENAIR0 (open-source real-time HW/SW)
OPENAIR1 (open-source real-time and offline SW)
OPENAIR2 (open-source real-time and offline SW)
OPENAIR3 (open-source Linux SW suite for cellular and MESH networks)
TARGETS : different top-level target designs (emulator, RTAI, etc.)
Partners can access and contribute to our development
OpenAirInterface TWIKI
A TWIKI site for quick access by partners to our development via a collaborative HOW-TO
Soon
Sourceforge distribution of stable code
OpenAir4G Tutorial (openair1, Feb 2012)

5. OpenAir4G Tutorial (openair1, Feb 2012)
Equipment and SW
OpenAir4G Tutorial (openair1, Feb 2012)

6. Prototype Equipment Timeline
Planned replacement
for CBMIMO1
ExpressMIMO2
AgileRF/Express MIMO
CBMIMOI – V1
CBMIMOI – V2
PLATON/RHODOS
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
Cellular, AdHoc and P2MP Topologies
FPGA SoC (Virtex 5)+ Interface for partner Processing Engines
Agile Tuning module (0.2 – 7 GHz)
Maximum Channel BW 20 MHz
OFDM(A)/WCDMA
AdHoc/Mesh and Cellular Topologies
FPGA-SoC (Virtex 2)
2x2 2 GHz, 5MHz channels
Cellular (towards LTE)
Cellular Systems
Pure Software Radio
WCDMA-TDD
All-IPv4/v6
OpenAir4G Tutorial (openair1, Feb 2012)

7. Software Roadmap OpenAirDAB OpenAir.11p OpenAir4G
OpenAirInterface (WIDENS/CHORIST)
WIRELESS3G4FREE
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
LTE compliant waveform
Mesh extensions from WIDENS/CHORIST
Partial 3GPP protocol stack (openair2)
AdHoc/Mesh and Cellular Topologies
In-house MIMO-OFDMA TDD waveform (WiMAX 2004 like)
Distributed Signal Processing and Mesh-Topology functions (L2.5 relaying)
TD-SCDMA SDR
IPv6 interconnect
No longer supported
OpenAir4G Tutorial (openair1, Feb 2012)

8. OpenAir4G Tutorial (openair1, Feb 2012)
CardBus MIMO 1
Current platform for application experimentation and test network deployments
5 MHz channel bandwidth MHz
PCMCIA-CardBus form-factor
2x2 MIMO-OFDMA, LTE waveform
Two-way communications
Full Software Radio under RTAI/Linux on x86 architectures
OpenAir4G Tutorial (openair1, Feb 2012)

9. Current CBMIMO1 V2 Designs
CBMIMO1 provides
A Leon3-based embedded processing engine on a Xilinx XC2V3000 FPGA
52 MHz processor speed
64 kByte embedded memory (16 Mbyte SDRAM not used currently)
DMA engine for PCI/CardBus burst transfers
AD9862 acquisition engine
LTE TDD/FDD framing (7.68 Ms/s)
LTE 5 MHz baseband filtering (TX)
Digital Frequency-correction
LTE FFT (TX, 512-point), regular cyclic-prefix processing (TX/RX) – 2009 firmware
Note: For LTE, limited to OFDMA transmission formats (i.e. no SC-FDMA, true SRS, etc.) and extended prefix mode
Generic SDR TX – 2011 firmware
No limitations for LTE, except dual-antenna TX on some PCI configurations (laptops)
Will not work properly in TX direction with off-the-shelf CardBus<->ExpressCard adapters because of insufficient upstream reads
RF control (gains, frequencies, timing of RF)
CBMIMO1 allows for 2x2 MIMO operation in either FDD (with external RF) or TDD
Embedded software handles LTE framing and transfers of signals to/from PC memory along with synchronization events for RTAI scheduling
PC configures CBMIMO1 with memory regions for signals and frame parameters on init and card does the rest
Special frame resynchronization for two-way operation is provided (timing drift adjustments)
OpenAir4G Tutorial (openair1, Feb 2012)

10. ExpressMIMO Baseband Prototyping Board
FPGA-based baseband platform
One Virtex 5 LX330, One Virtex 5 LX110T (PCIexpress)
4x AD9832 (dual 14-bit 128 Ms/s D/A, dual 12-bit 64 A/D 64Ms/s)
Up to 8x8 MIMO capacity with low-IF, 4x4 I/Q Baseband
Low-jitter clock generation for converters
128 Mbytes/133 MHz DDR (LX110T)
1-2 Gbytes DDR2 (LX330)
CompactFlash (SystemACE), JTAG Configuration
PCIexpress 8-way interconnect (4-way in practice)
LVDS expansion interface (daughter boards)
RF interface (micro-coax and parallel I/O for Microwire busses)
OpenAir4G Tutorial (openair1, Feb 2012)

11. ExpressMIMO SoC Target (cont’d)
OpenAir4G Tutorial (openair1, Feb 2012)

12. ExpressMIMO/ExpressMIMO2 Application Development
A software application (MODEM + MAC) is a C program running on a micro-controller (LEON3) with HW API for DSP
SW library is available (libembb), developped and maintained by LabSoC, TelecomParisTech (openair0)
Same approach as x86 SDR (CBMIMO1) but on an embedded system
More difficult to validate functionality -> Software models for HW required
Current testcases
DAB/DMB (MODEM implementation by TUM/BMW)
OpenAir.11p : full PHY and multicast/broadcast component of MAC
Dual-mode receiver (i.e. both MODEMS share the same HW, two threads in SW)
Next step
Port of OpenAir4G to ExpressMIMO
Training
Acropolis Winter School 2011 (OAI2)
OpenAir4G Tutorial (openair1, Feb 2012)

13. OpenAir4G Tutorial (openair1, Feb 2012)
ExpressMIMO2 Platform
Recall
CBMIMO1 platform : cheap, fixed band, 5 MHz channels, 3G EVM (RF) characteristics (2 bits/s/Hz limit), SDR/x86, good for networking experiments, many fabricated for EURECOM and partners
ExpressMIMO + AgileRF : very expensive, arbitrary band, 20 MHz channels, SDR/MPSoC, good for architecture exploration, few fabricated for internal use only
Objectives for new platform
Low-cost of CBMIMO1 (<2k€ for baseband board)
Networking experiments (tens of nodes)
As frequency agile as possible (for multimodal operation and CR/DSA experiments) but not total flexibility like AgileRF (low cost)
High performance RF (LTE compliant performance) for state-of-the-art MODEM design
Interconnection possibilities with high-power RF for basestation deployment
Optimize partition of x86 and FPGA DSP for rapid-prototyping
OpenAir4G Tutorial (openair1, Feb 2012)

14. OpenAir4G Tutorial (openair1, Feb 2012)
Elements
Baseband/RF engine (first prototypes imminent)
Spartan 6 LX150T FPGA (PCIexpress like ExpressMIMO)
Derived from Xilinx/Avnet evaluation board (but smaller, medium-sized PCIe format)
Used for FFT and Turbo/Viterbi decoders (key processing bottlenecks)
Control of RF and acquisition from converters
4 LIME Semiconductor zero-IF RF chipsets
TX, RX and A/D, D/A on single-chip (1.5cm x 1.5cm)
300 MHz – 3.8 GHz tuning bandwidth
FDD or TDD operation
LTE UE, RN RF compliance (EVM), even better (this is really good)
0 dBm output power
OpenAir4G Tutorial (openair1, Feb 2012)

15. OpenAir4G Tutorial (openair1, Feb 2012)
Elements
OpenAir4G Tutorial (openair1, Feb 2012)

16. OpenAir4G Tutorial (openair1, Feb 2012)
Elements PC
PC runs RTOS (RTAI) like CBMIMO1
MAC + remainder of PHY (low-complexity components)
Linux kernel network interface
Low-end x86, embedded x86
RF front-ends (PA/LNA, duplexing, filtering) – External boards developped by InsightSIP (local company)
Extra frequency transposition to go to 4-6 GHz
21 dBm PAs (5-6 GHz, 2 GHz, UHF)
FDD with standard Duplexer solution for 2 GHz
TDD with tunable filters (Hittite) and TX/RX switch for all other bands (focus on 3.5 GHz, 5-6 GHz, 1.9 GHz)
Existing EURECOM basestation front-ends (1.9 GHz, 2.6 GHz and UHF)
OpenAir4G Tutorial (openair1, Feb 2012)

17. OpenAir4G Tutorial (openair1, Feb 2012)
OpenAir4G MODEM
OpenAir4G Tutorial (openair1, Feb 2012)

18. OpenAir4G Tutorial (openair1, Feb 2012)
Purpose
Develop an open-source baseband implementation of a subset of LTE Release-8/9 on top of OpenAirInterface.org SW architecture and HW demonstrators
Goals
Representative of LTE access-stratum
Full compliance of LTE frame (normal and extended prefix)
Full Downlink shared channel compliance
Support for a subset of transmission modes (2x2 operation)
Modes 1,2,4,5,6 (Mode 3 to be studied for inclusion)
Support for up to 3 sectors in eNB
Useful for measurement campaigns
Useful as starting point for research-oriented extensions (to justifiably claim potential impact on LTE-A)
Provide realistic (and rapid) LTE simulation environment for PHY/MAC (OAI3 lab session)
OpenAir4G Tutorial (openair1, Feb 2012)

19. OpenAirLTE PHY/MAC Protocol Stack (partial 3GPP, openair1, openair2)
Linux networking device
(IPv4/IPv6, classification/routing
Services for DRB)
36-331
ASN.1 messages
Compliance
Subset of LTE-only
procedures
PDCP is an empty box
3GPP Compliance
Rel-9
3GPP Compliance
(v 8.6)
Openair1
3GPP Compliance (v8.6)
36-211,36-212,36-213
OpenAir4G Tutorial (openair1, Feb 2012)

20. Current Status (LTE/LTE-A)
PHY (36.211,36.212,36.213)
LTE softmodem for 5 MHz (1.5, too, but not completely functional yet)
Subset of , and specifications
Mode 1, Mode 2 and Mode 6 support
Enhanced-Mode 5 and Mode 4 under integration (SAMURAI)
Missing elements (the rest is largely supported)
User-selected feedback (not planned)
Modes 3,7 (not planned)
Rel-9/10 enhancements (Carrier Aggregation, Modes 8,9) under integration
MAC (36.321)
Full random-access procedure, Scheduling Request, Buffer Status Reporting
eNB scheduler is incomplete (to be built per application)
UE Power headroom under integration
RLC (36.322)
Complete UM/AM implementation, SRB interfaces with RRC for the moment
OpenAir4G Tutorial (openair1, Feb 2012)

21. OpenAir4G Tutorial (openair1, Feb 2012)
Current Status
PDCP (36.323)
Currently just provides DRB interface for linux networking device
No security and compressions features
New implementation under integration (PDCP headers, SRB interfaces, opensource ROHC integration)
RRC (36.331)
Two separate actions, RRC LITE and Cellular
LITE
is LTE only, with ASN.1 messages (asn1c C code generator) and subset of LTE RRC procedures (RRCConnectionRequest/Setup,ReconfigurationRequest)
Empty security context establishment will be added
Currently integrating measurement reporting and MobilityControlInfo (handover)
Extendable for Mesh networks (LOLA)
No SAE NAS support currently, but could be added …
Cellular
Inherits RRC from W3G4Free (IP/UMTS)
Automatic code generation using Esterel Studio
“hand”-compressed messages and research-oriented NAS extensions for IPv6 interconnect (QoS and mobility management)
OpenAir4G Tutorial (openair1, Feb 2012)

22. OpenAir4G Tutorial (openair1, Feb 2012)
OpenAir4G Lab Session 1
OpenAir4G Tutorial (openair1, Feb 2012)

23. OpenAir4G Tutorial (openair1, Feb 2012)
Objectives
Familiarization of OpenAir4G Development Environment through a simple example
Insertion of kernel modules for CBMIMO1/ExpressMIMO hardware
Control of HW with OCTAVE (signal acquisition)
Basic DSP example
LTE Initial synchronization
Control of HW with user-space C programs (signal acquisition) using OpenAir4G x86-based DSP
Basic principles of Real-time operation under RTAI with CBMIMO1
OpenAir4G Tutorial (openair1, Feb 2012)

24. OpenAir4G Tutorial (openair1, Feb 2012)
Directories
targets
Specific SW targets (SIMU,RTAI) for instantiating OpenAir4G components
openair1
Basic DSP routines for implementing subset of LTE specifications under x86 (36.211, , GPP specifications)
Channel simulation, sounding and PHY abstraction software,
openair2 (not for this lab session)
MAC/RLC/PDCP/RRC
openair3 (not for this lab session)
L3 IP-based Networking elements and applications
OpenAir4G Tutorial (openair1, Feb 2012)

25. Compiling and Loading the kernel modules
Start from $OPENAIR1_DIR
Kernel modules for CBMIMO1 and ExpressMIMO are made as
make oai_user.ko (ExpressMIMO)
make openair_rf_cbmimo1_softmodem.ko OPENAIR2=0 (CBMIMO1)
This creates one module (as well as other things …)
openair_rf.ko
Interfaces for openair1 running in user-space
PCI/PCIe driver for CBMIMO1/ExpressMIMO
RTAI threading interfaces
LINUX character device interfaces (open,close,ioctl,mmap)
OpenAir4G Tutorial (openair1, Feb 2012)

26. Compiling and Loading the kernel modules
Loading can be done with scripts found in $OPENAIR1_DIR
Try
make install_oai_user
Make install_cbmimo1_softmodem OPENAIR2=0
sudo (if not root) because insmod is needed (do cat start_rf.sh)
The module should now be attached to the kernel (do lsmod) and the leds on CBMIMO1 should be moving (ExpressMIMO nothing …)
Identifying the HW
To see that the HW is identified by Linux you can do lspci and you should see either
“European Space Agency …” which is the identifier for the GRLIB (Gaisler) embedded system in CBMIMO1
“Xilinx Corporation …” which is the identifier for the Xilinx PCIe endpoint on ExpressMIMO
To see that the HW is identified by the openair_rf driver do dmesg and you should see traces of one of the two cards
OpenAir4G Tutorial (openair1, Feb 2012)

27. PC Environment at this point
SW in the PC looks (looked!) like
Linux char device interface
for control / non-real-time
acquisition and generation
OpenAir4G Tutorial (openair1, Feb 2012)

28. PC Environment at this point
SW in the PC looks like
Linux char device interface
for control / non-real-time
acquisition and generation
LXRT (user-space real-time)
OpenAir4G Tutorial (openair1, Feb 2012)

29. User-space applications
Dialogue with driver through
open/close (access device through fileops)
ioctl : basic instructions to control HW / RTAI
mmap : access shared memory buffer (signals, measurement information, etc.)
Dialogue with RTAI threads through
RT-fifos (/dev/rtfXX)
Two methods
OCTAVE .oct files (like MATLAB .mex) with ioctl interfaces for OCTAVE users (note: GPIB .oct files available too using libgpib to control measurement equipment, e.g. signal generator, spectrum analyzer)
C/C++ programs
OpenAir4G Tutorial (openair1, Feb 2012)

30. Build an OCTAVE Application
The OCTAVE scripts and .oct files are in
cd $OPENAIR1_DIR/USERSPACE_TOOLS/OCTAVE/CBMIMO1_TOOLS
To compile the .cc to .oct files (note: octave-headers needs to be installed), do make oarf OPENAIR_LTE=1 (and make gpib if you want gpib)
Examine rx_spec.m as an example (or rx_spec_exmimo.m)
OpenAir4G Tutorial (openair1, Feb 2012)

31. OpenAir4G Tutorial (openair1, Feb 2012)
OCTAVE example
dual_tx=0;
oarf_config(0,1,dual_tx)
gpib_card=0; % first GPIB PCI card in the computer
gpib_device=28; % this is configured in the signal generator Utilities->System
cables_loss_dB = 6; % we need to account for the power loss
power_dBm = -95;
%gpib_send(gpib_card,gpib_device,['POW ' int2str(power_dBm+cables_loss_dB) 'dBm']);
%gpib_send(gpib_card,gpib_device,'OUTP:STAT ON'); % activate output
oarf_set_calibrated_rx_gain(0); % turns off the AGC
oarf_set_rx_gain(80,85,0,0);
oarf_set_rx_rfmode(0);
s=oarf_get_frame(0);
f = (7.68*(0:length(s(:,1))-1)/(length(s(:,1))))-3.84;
spec0 = 20*log10(abs(fftshift(fft(s(:,1)))));
spec1 = 20*log10(abs(fftshift(fft(s(:,2)))));
clf
plot(f',spec0,'r',f',spec1,'b')
axis([-3.84,3.84,40,160]);
%gpib_send(gpib_card,gpib_device,'OUTP:STAT OFF'); % activate output
legend('Antenna Port 0','Antenna Port 1');
grid
Init card (freq 0, tdd, 1 TX antenna)
If GPIB is used
RF configuration
Get 10ms of signal from RX chains
OpenAir4G Tutorial (openair1, Feb 2012)

32. LTE Initial Synch Example
Need a few basics in LTE DL Transmission (OFDM + QAM)
Frame formats
Synchronization signals
Primary Synchronization Signal (PSS)
Secondary Synchronization Signal (SSS)
Physical Broadcast Channel (PBCH)
Cell-specific Reference Signals (CSRS)
OpenAir4G Tutorial (openair1, Feb 2012)

33. OpenAir4G Tutorial (openair1, Feb 2012)
Resource blocks
LTE defines the notion of a resource block which represents the minimal scheduling resource for both uplink and downlink transmissions
A physical resource block(PRB) corresponds to 180 kHz of spectrum
OpenAir4G Tutorial (openair1, Feb 2012)

34. Common PRB Formats Typical IDFT size
Channel Bandwidth (MHz)
NRBDL/NRBUL
Typical IDFT size
Number of Non-Zero Sub-carriers (REs)
1.25 6
128 72 5 25
512
300 10 50
1024
600 15 75
1024 or 2048
900 20
100
2048
1200
PRBs are mapped onto contiguous OFDMA/SC-FDMA symbols in the time-domain (6 or 7)
Each PRB is chosen to be equivalent to 12 (15 kHz spacing) sub-carriers of an OFDMA symbol in the frequency-domain
A 7.5kHz spacing version exists with 24 carriers per sub (insufficiently specified)
Because of a common PRB size over different channel bandwidths, the system scales naturally over different bandwidths
UEs determines cell bandwidth during initial acquisition and can be any of above
OpenAir4G Tutorial (openair1, Feb 2012)

35. OFDMA/SC-FDMA Mapping
OFDMA/SC-FDMA Sub-carriers are termed “Resource Elements” (RE)
DC carrier (DL) and high-frequencies are nulled
Spectral shaping and DC rejection for Zero-IF receivers
Half the bandwidth loss w.r.t. WCDMA (22%)
Channel Bandwidth (MHz)
NRBDL/NRBUL
Bandwidth
Expansion
1.25 6 8% 5 25
11% 10 50 15 75 20
100
OpenAir4G Tutorial (openair1, Feb 2012)

36. Example: 300 REs, 25 RBs (5 MHz channel)
PRB13
PRB24
“Normal” Cyclic Prefix Mode
(7 symbols)
PRB23
PRB22
PRB21
PRB20
PRB19
PRB18
PRB17
PRB16
“Extended” Cyclic Prefix Mode
(6 symbols)
PRB15
PRB14
PRB13
PRB12
NRBDL/NRBUL
PRB12
PRB11
PRB10
PRB9
PRB8
PRB7
PRB6
PRB5
PRB4
PRB3
NSCRB
PRB2
PRB1
PRB0
PRB11
l=0
l=6
NULsymb /NULsymb
OpenAir4G Tutorial (openair1, Feb 2012)

37. OpenAir4G Tutorial (openair1, Feb 2012)
Sub-frame and Frame
One frame = Tf =307200Ts = 10ms
Tslot= 15360Ts=500ms 1 2 3 18 19
One subframe
71.3ms
71.9ms
Normal Prefix
4.69ms
5.2ms
Frequency
Domain
View
83ms
Extended Prefix
Time-domain
View
13.9ms
OpenAir4G Tutorial (openair1, Feb 2012)

38. LTE UE Synchronization Procedures
Cell Search comprises
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)
Cell ID NID(1) (0,…,167) and Frame type (FDD/TDD, Normal/Extended Prefix) determination from secondary synchronization reference signals
Demodulation of PBCH (using NIDCell= 3NID(1) + NID(2)) to receive basic system information during steady-state reception
NRBDL (cell bandwidth)
PHICH-config (to allow PDCCH demodulation, for system information)
Frame number (8 bits from payload, 2 bits from redundancy version)
Antenna configuration (1,2,4 from CRC mask)
OpenAir4G Tutorial (openair1, Feb 2012)

39. OpenAir4G Tutorial (openair1, Feb 2012)
Initial Timing/Frequency Acquisition (Synchronization Signals, FDD Normal CP)
10 ms
Subframe 0
Subframe 1
Subframe 4
Subframe 5
Subframe 9
Frequency
(PRBs)
Time
(symbols)
Primary(Y) and Secondary(B)
Synchronization Signals
(2nd half)
Primary (Y) and Secondary B)
Synchronization Signals
(first half)
PBCH
OpenAir4G Tutorial (openair1, Feb 2012)

40. Primary Synchronization
Zadoff-Chu root-of-unity sequence has excellent auto-correlation properties and is very tolerant to frequency-offsets
Autocorrelation sequence
Real component
(time-domain
u=25)
Imag component
(time-domain,
u=25)
OpenAir4G Tutorial (openair1, Feb 2012)

41. 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))
Threshold
d*u(-n) ↓M
()2
r(n)
Received
Frame
Decimating correlator + non-coherent thresholding
Primary Purpose: Determine start of frame
Alternate purposes: Channel estimation for SSS/PBCH and frequency offset estimation
Implemented as Zadoff-Chu sequence of length 62 REs around DC (i.e. same resource block as PBCH, but only 62 out of 72 REs)
OpenAir4G Tutorial (openair1, Feb 2012)

42. Secondary Synchronization
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
OpenAir4G Tutorial (openair1, Feb 2012)

43. 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)
OpenAir4G Tutorial (openair1, Feb 2012)

44. Secondary Synchronization RX
H*0 (k)
D*sss,0,n(k)
e2pjD/N
D=-3,…,3, N=8 S
Rsss,0(k), k=0,...,62 X X Re
H*5 (k)
D*sss,5,n(k) X
Rsss,5(k), k=0,...,62 X X
H*0 (k)=Dpss,0,u(k) Rpss,0*(k), k=0,...,62
H*5 (k)=Dpss,5,n(k) Rpss,5*(k), k=0,...,62
PSS-based channel estimates
OpenAir4G Tutorial (openair1, Feb 2012)

45. Building the PSS/SSS Part First
OCTAVE files for PSS generation can be found here
$OPENAIR1_DIR/PHY/LTE_REFSIG/primary_synch.m
OCTAVE files for SSS generation can be found here
$OPENAIR1_DIR/USERSPACE_TOOLS/OCTAVE/CBMIMO1_TOOLS/sss_gen.m
Start an editor and create a file based on rx_spec.m, in the same directory so you have the OpenAir4G .oct files
OpenAir4G Tutorial (openair1, Feb 2012)

46. OpenAir4G Tutorial (openair1, Feb 2012)
Steps
Correlate received signal with time-domain PSS sequence and square (use conv and abs)
Search for peaks (both) separated by samples ( Ms/s)
Do above SSS procedure according to 4 potential SSS positions (assume extended prefix and FDD)
FDD/Normal CP : SSS is (512+40) 552 samples before PSS
FDD/Extended CP: SSS is ( ) 640 samples before PSS
TDD/Normal CP: SSS is ( ) 1648 samples before PSS
TDD/Extended CP: SSS is ( ) 1920 samples before PSS
OpenAir4G Tutorial (openair1, Feb 2012)

47. OpenAir4G Tutorial (openair1, Feb 2012)
PBCH Detection
Detection of the PBCH requires the following steps
Generation of the cell-specific reference signals based on the cell ID derived from SSS detection
Performing channel estimation for the 4 symbols of the PBCH
Extracting the PBCH reference elements
Applying the conjugated channel estimates to the received reference elements
Channel decoding
OpenAir4G Tutorial (openair1, Feb 2012)

48. Cell-Specific Reference Signals
p={0},p={0,1}
p=0
p=0
p=0
p=1 (if active)
p=1
p=1 (if active)
OpenAir4G Tutorial (openair1, Feb 2012)

49. Cell-Specific Reference Signals
Pseudo-random QPSK OFDM symbols
Based on generic LTE Gold sequence
Different sequence for different cell IDs
Different in each symbol of sub-frame
Different in each sub-frame, but periodic across frames (10ms)
Evenly spaced in subframe to allow for simple and efficient least-squares interpolation-based receivers
Between REs in frequency-domain
Across symbols in time-domain
OpenAir4G Tutorial (openair1, Feb 2012)

50. Channel Estimation in LTE (simple)
Recall that receiver sees
Must get channel estimate for channel compensation
Estimation error
PRB1
PRB0
Interpolation
Extrapolation
Interpolation
Extrapolation
NO pilots here
OpenAir4G Tutorial (openair1, Feb 2012)

51. Channel Estimation in LTE (simple) – cont’d
The previous steps allow for determining the frequency response (MIMO) on symbols where the pilots are located
For the remaining symbols, we perform time-interleaving across adjacent symbols with pilots
OpenAir4G Tutorial (openair1, Feb 2012)

52. Performing the Channel Estimation and Channel Compensation
Use the supplied txsigF0.m file, which contains the transmit signal for the PBCH (normal prefix)
This is usually recomputed in the receiver (we will examine the C version later)
Extract reference symbols (symbols 7 and 11) and perform the time/frequency interpolation
Apply (channel compensation) the channel estimate to the received resource elements and plot the constellation of the output
H*0 (l,k)
RPBCH,0(l,k), k=0,...,72,
l=7,8,9,10 X
OpenAir4G Tutorial (openair1, Feb 2012)

53. OpenAir4G Tutorial (openair1, Feb 2012)
The rest …
The rest we cannot do in OCTAVE (unless we implement all the channel decoding functions), but need to go to the OpenAir4G C implementation for
Deinterleaving
Channel decoding
Descrambling
To see how this is done check out the following files
openair1/PHY/LTE_TRANSPORT/initial_sync.c
openair1/PHY/LTE_TRANSPORT/sss.c
openair1/PHY/LTE_TRANSPORT/pbch.c
OpenAir4G Tutorial (openair1, Feb 2012)

54. Towards real-time operation
Real-time operation depends on two things
FPGA firmware
RTAI interfaces
Here we describe the functionality of the 2011 firmware (2009 is too confusing)
OpenAir4G Tutorial (openair1, Feb 2012)

55. Acquisition (Card side)
A/D 1
A/D 2
D/A 1
D/A 2
Address
Control
Logic and
Interrupt
Generation
7.68 Mword/s B U F E R 1 B U F E R 2 B U F E R 3 B U F E R 4
AMBA Bus
(52 MHz/32bit)
52 Mword/s
(Peak)
Block Interrupt
Parameters
AMBA/PCI
Bridge
CardBus/PCI Bus
(33 MHz/32bit)
OpenAir4G Tutorial (openair1, Feb 2012)

56. OpenAir4G Tutorial (openair1, Feb 2012)
Acquisition (AMBA)
AMBA can burst at a peak rate of 52 MHz, very comfortable.
PCI DMA controller (GRPCI) on AMBA can’t do quite this but it’s close enough
Acquisition unit stores blocks (minimum 2) of a programmable size (<= 1Kbyte) and generates an interrupt to CPU at the end of each block. The CPU programs a 2 DMAs (one for each chain) AMBA->PCI (RX) or PCI->AMBA (TX)
TX and RX cannot occur at the same time (time-division duplex)
OpenAir4G Tutorial (openair1, Feb 2012)

57. OpenAir4G Tutorial (openair1, Feb 2012)
Acquisition (AMBA)
Input/Output
Block 0
Block 1
Block 2
Block 3
Block 0
AHB Interrupt
Data (AMBA)
RX/TX
Block 3/1
Block 0/2
Block 1/3
Block 2/0
Block 3/1
Data (PCI)
RX/TX
Block 3/1
Block 0/2
Block 1/3
Block 2/0
Block 3/1
Blocks are 480 samples of signal (62.5 ms)
A PCI interrupt is generated every slot (500 ms) to trigger RTAI
OpenAir4G Tutorial (openair1, Feb 2012)

58. OpenAir4G Tutorial (openair1, Feb 2012)
PC Memory View
PC signal memory time-scale
AMBA signal memory time-scale
62.5 ms
10 ms
OpenAir4G Tutorial (openair1, Feb 2012)

59. OpenAir4G Tutorial (openair1, Feb 2012)
RTAI end
RTAI receives an interrupt every slot
RT interrupt handler is served in less than 30 ms (can be measured!) with very high determinism
RT SW components (openair1/SCHED/sched_lte.c)
RT interrupt handler (slot_irq_handler())
Inner-modem thread (openair_thread())
Turbo-decoding thread (dlsch_thread()) (note: this is deactivated in most recent “stable” version, to be reactivated!)
OpenAir4G Tutorial (openair1, Feb 2012)

60. OpenAir4G Tutorial (openair1, Feb 2012)
Basic Ideas (for UE)
Slot_irq_handler is awoken every 500 us
Checks that interrupt source is CBMIMO1 (it can be sharing IRQ line with others …)
Does some bookkeeping (counters, etc.)
Schedule openair_thread to wake up via cond_signal to user-space thread
Returns
Openair thread (LXRT user-space)
Waits for signal to wakeup via pthread_cond_wait
Checks mode of transceiver (idle, get frame, sensing, steady-state)
Invokes inner-modem DSP processing, quick channel decoding (control information with turbo and convolutional code, PBCH, PDCCH, SI DLSCH, RA DLSCH) and schedules MAC layer processing
Decoding Thread
Invoked by openair_thread for high-throughput CRNTI DLSCH (later ULSCH) decoding (decoding time > 0.5ms)
Make use of multi-core CPUs to parallelize inner-MODEM and channel decoding (turbo-decoder) which operate on different time-scales
Multiple decoding threads will be considered in medium-term for higher throughput
OpenAir4G Tutorial (openair1, Feb 2012)

61. OpenAir4G Tutorial (openair1, Feb 2012)
Take a look at code
openair1/SCHED/sched_lte_fw2011.c
OpenAir4G Tutorial (openair1, Feb 2012)