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OpenAirInterface Overview and Lab Session 1

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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 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 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)

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