Post on 06-May-2018
Communications Engineering Lab (CEL)Univ.-Prof. Dr.rer.nat. Friedrich K. Jondral
A LTE Receiver Framework Implementation inGNU Radio
Johannes Demel, Sebastian Koslowski, Friedrich K. Jondral
KIT – University of the State of Baden-Wuerttemberg and
National Laboratory of the Helmholtz Association
www.kit.edu
Contents
LTE air interface overviewBasic system parameters
Project roadmapImplementation
Implementation overviewSynchronizationOFDM operationPhysical channel decodingTest with recorded data
Performance results
Conclusion
2 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
LTE overview
Air interface basics (downlink)
OFDM signal (15 kHz subcarrierbandwidth)different modes possible
variable bandwidth (up to 20 MHz)MIMO capabilites (up to 4x4)
6 physical channels3 transport channels3 control information channels
resourceblock (RB)
time
frequency
pilot
reserved
3 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Roadmap
Taskssynchronization
time, frequency, frame timing
OFDM operationradio channel estimation,equalization
demodulationSTBC, FECphysical channel demultiplexing
extract system parameterscell IDMIMO configurationsystem bandwidth
Implementation goals
modular block-based structure
separate handling of data andcontrol information
use stream- and event-basedprocessing
4 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Implementation overview
Receiver framework components at work: Example flowgraph with MIB decoding
synchronization
OFDM operation
5 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Synchronization
cyclic prefix (CP)-based synchronization
recover coarse symbol timing n̂0
calculate sliding window correlation with fixed lag of NFFT
n̂0 = arg maxn|γ(n)| , γ(n) =
n+NCP−1∑m=n
r(m) r∗(m − NFFT)
stream tagstags indicate symbol start
6 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Synchronization
primary synchronization symbol (PSS) detection
recover fine symbol timing and half-frame timing
extract cell ID number NID2 from PSSstream tags
indicate half-frame startpropagate cell ID number NID2
6 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Synchronization
frequency offset detection and correction
recover fractional frequency offsethalf-frame timing needed
different CP-lengths within each slot
6 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Synchronization
secondary synchronization symbol (SSS) detectionrecover frame timingextract cell ID group NID1
receive NID2 tagcalculate cell ID NID = 3 ∗ NID1 + NID2
message portpublish NID for dynamic block configuration
stream tagsindicate frame start
6 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
OFDM operation
inverse OFDM operation
remove cyclic prefix
compute FFTextract subcarriers of interest
complexity reduction
channel estimation
get pilot positions
calculate channel coefficients
linearly interpolation
output data stream andchannel estimates for antennaport 0 and 1
7 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Implementation overview
Receiver framework components at work: Example flowgraph with MIB decoding
synchronization
OFDM operation
8 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Decode PBCH
MIMO configuration still unknown at this pointtrail & error: different configurations interleaved in output
inverse Alamouti Operation
deinterleave layers
demodulation: PBCH always uses QPSKdescrambling
scrambling sequence depends on NID
9 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Decode BCH
BCH is transmitted on PBCH
Deinterleaving (block-based)Viterbi decoder
hierarchical blockparameterized GNU Radio Viterbi decoder
Calculate CRCCRC checksum depends on MIMO configurationCRC match indicates number of TX antennas
10 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Implementation overview
Receiver framework components at work: Example flowgraph with MIB decoding
synchronization
OFDM operation
11 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Test with recorded data
IQ baseband samples asinput
recorded using aUSRP N210
flowgraph outputfixed parameters
MIMO: 2x1RB: 50 equals10 MHzPHICH parameters
system frame number
decoding rate 97.8%
tests indicate real timecapabilities
12 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Effect of sample rate on performance
varying sample rateFFT-length depends onsample rate
relative performance changeslower sample rate
less multiplicationssmaller correlationsequencessmaller FFT-length
Sync
hron
izat
ion
OFDM
Deco
de P
BCH
Deco
de B
CH
MIB
106
107
108
109
1010
Inst
ruct
ion
Fetc
h
Instruction Fetch per blockFFT-length
2048512
13 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Effect of computed resource blocks onperformance
varying number of RBsFFT-length always 2048number of RBs limited byFFT-length
channel estimation is morecomplex
great increase of powerconsumption in OFDM part
Sync
hron
izat
ion
OFDM
Deco
de P
BCH
Deco
de B
CH
MIB
105
106
107
108
109
1010
Inst
ruct
ion
Fetc
h
Instruction Fetch per blocknumber of RBs
1006
14 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
Conclusion
LTE overviewintroduction to our GNU Radio LTE receiver
synchronization, OFDM operation, PBCH extractionexample output
performance analysisdifferent parameters
possibilitiesDetect LTE cells with parameters
What’s nextextend flowgraph with additional channels and uplink
source code available at github.com/kit-cel/gr-lte
15 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL
The End
Thanks for your attention!gr-lte source code available at github.com/kit-cel/gr-lte
16 A LTE Receiver Framework Implementation in GNU RadioJohannes Demel, Sebastian Koslowski, Friedrich K. Jondral
Communications Engineering LabUniv.-Prof. Dr.rer.nat. Friedrich K. Jondral CELCEL