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Baseband Signal Processing Framework Baseband Signal Processing Framework for the OsmocomBB GSM Protocol Stack Harald Krll, Christian Benkeser, Stefan Zwicky, Benjamin Weber, Qiuting Huang Integrated Systems Laboratory, ETH Zurich d S b i h

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Baseband Signal Processing Framework Baseband Signal Processing Framework for the OsmocomBB GSM Protocol Stack

Harald Kröll, Christian Benkeser, Stefan Zwicky,

d S b i h

Benjamin Weber, Qiuting Huang

June 27, 2012

Integrated Systems Laboratory, ETH Zurich

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Outline

d d

  • Introduction into GSM and OsmocomBB
  • Framework and interface
  • Testbed architecture and setup
  • Conclusion

Integrated Systems Laboratory

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GSM and Open Source

  • Facts
  • Most ubiquitous cellular standard
  • 5 billion subscribers (2010)
  • Phones on the market since 1992
  • Very few baseband vendors
  • Open Source in GSM
  • OpenBTS (since 2007/08)
  • AirProbe (since 2007)
  • OpenBSC (since 2008)
  • OsmocomBB (since 2010)
  • …

Integrated Systems Laboratory

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GSM and OsmocomBB

  • GSM Protocol Layers, simplified overview
  • Relationship to OSI protocol

layers

  • Influences from various

specifications (GERAN/UTRAN) (GERAN/UTRAN)

Integrated Systems Laboratory

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GSM and OsmocomBB

  • GSM Layers, various protocols
  • Influences from
  • A/Gb (pre release 5

(p terminals)

  • Iu (release 5 terminals,

UMTS interface)

Integrated Systems Laboratory

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GSM and OsmocomBB

  • OsmocomBB
  • Open Source GSM Baseband

software

  • Implementation of L2/L3 in C

running on a host PC

  • Low cost feature phones

used as L1

  • “Limited” PHY support
  • Interfacing of baseband

( TI’ C l ) processors (e.g. TI’s Calypso)

Integrated Systems Laboratory

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Architecture of a Feature Phone

  • Baseband processor / modem processor (Qualcomm pat.)
  • Computationally intensive tasks in accelerator blocks

Integrated Systems Laboratory

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OsmocomBB Setup

  • Baseband and protocol stack

Data link layer, Network Layer Physical layer

Integrated Systems Laboratory

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OsmocomBB Setup

  • Baseband and protocol stack

Data link layer, Network Layer Physical layer

Support of an ubiquitous pp q scientific computer language like GNU/Octave or Matlab is missing

Integrated Systems Laboratory

is missing

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Prospects of running a complete GSM stack

  • New approaches during PHY development

Si l ti f PHY t th ith L2/L3

  • Simulation of PHY together with L2/L3
  • Interaction between PHY and higher layers
  • PHY development: controlling debugging visualization
  • PHY development: controlling, debugging, visualization
  • Reporting of measurement data to display of phone
  • En‐/disabling specific PHY functions from user interface
  • En‐/disabling specific PHY functions from user interface
  • Hybrid ARQ schemes, incremental redundancy (IR)
  • Interaction between channel decoding and MAC layer
  • Interaction between channel decoding and MAC layer
  • Improved average throughput evaluation
  • A flexible interface between L1 and upper layers allows

A flexible interface between L1 and upper layers allows crossing layer boundaries

Integrated Systems Laboratory

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Interface between L1 and L2

  • No standardized interface specified
  • 3GPP foresees primitive messages
  • Request (REQ), confirm (CONF) and indication (IND)
  • L1CTL from OsmocomBB
  • Message examples

Functionality L1CTL messages Reset PHY L1CTL_RESET_REQ L1CTL_RESET_CONF Power Measurement L1CTL_PM_REQ L1CTL PM CONF L1CTL_PM_CONF Synchronization L1CTL_FBSB_REQ L1CTL FBSB CONF

Integrated Systems Laboratory

_ _

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Proposed Signal Processing Framework

  • Goals
  • Map complete PHY to Matlab
  • L1CTL interface to simplify operation with OsmocomBB

Integrated Systems Laboratory

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Framework Overview

  • mobile: OsmocomBB application running L2/L3
  • phyconnect: Interface to connect mobile to Matlab via

unix socket and memory mapped file

  • phydev: PHY implementation in Matlab
  • Primitives: signal processing blocks
  • L1 controller, TPU, handles: event scheduling, controlling

Integrated Systems Laboratory

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phyconnect: Interfacing OsmocomBB & Matlab

  • Interfacing mobile (C) and phydev (Matlab)
  • Matlab inter‐process communication
  • TCP/IP socket
  • Memory mapped file
  • MEX function
  • Requirements
  • Fast and simple
  • Non blocking operation
  • Best option: memory mapped file

Integrated Systems Laboratory

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phydev: A PHY realization in Matlab for GSM

  • L1 Controller
  • Dispatch L1CTL messages
  • TPU
  • GSM counters, FSM according to standard
  • handles
  • Controllers of receiver blocks, call and evaluate primitives

Integrated Systems Laboratory

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phydev: A PHY realization in Matlab for GSM

  • primitives
  • Signal processing blocks
  • Operate on a defined amount of I/Q samples
  • auxiliaries
  • Basic RF transceiver operations, e.g. gain settings,

tune_DCXO()

Integrated Systems Laboratory

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L1 Controller & TPU

  • Timebase counters

(QN BN TN FN) (QN,BN,TN,FN)

  • FSM for a MS according to

3GPP TR 44.004 3GPP TR 44.004

  • Sample accurate operation
  • Each primitive gets the number

Each primitive gets the number

  • f samples it operates on as an

argument

  • Synchronization between

input samples and called i i i primitives

Integrated Systems Laboratory

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primitives: Signal Processing Blocks

  • Operations on RX baseband samples e.g.
  • Frequency burst detection FB_det()
  • Carrier Frequency offset estimation FB_est()
  • Normal Burst demodulation NB_demod()

Integrated Systems Laboratory

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primitives: Signal Processing Blocks

  • Operations on RX baseband samples e.g.
  • Frequency burst detection FB_det()
  • Detection of a complex sinusoid

Integrated Systems Laboratory

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primitives: Signal Processing Blocks

  • Operations on RX baseband samples e.g.
  • Carrier Frequency offset estimation FB_est()
  • Correlation based estimator

b l f f

  • Accuracy below 0.1 ppm of carrier frequency

Integrated Systems Laboratory

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primitives: Signal Processing Blocks

  • Operations on RX baseband samples e.g.
  • Normal Burst demodulation NB_demod()
  • Least squares channel estimator

h l h l f l

  • Channel shortening linear filter
  • Reduced State Sequence Estimator

Integrated Systems Laboratory

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Exemplary Processing of a L1CTL Message

  • Synchronization procedure: L1CTL_FBSB_REQ message

Integrated Systems Laboratory

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Testbed Setup

  • OpenBTS as base station, wireshark for visualization
  • Over the air interface
  • State‐of‐the art multiband RF transceiver

Integrated Systems Laboratory

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Wireshark output, GSM system information

  • GSM state: camping on any cell

Integrated Systems Laboratory

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Conclusion

  • Running a complete GSM stack is fruitful for PHY

l ith d l t algorithm development

  • There is a growing interest in PHY operations, also by SDR

d i i and open source communicites

  • We have shown OsmocomBB can be interfaced to PHY

i l i f k simulation framework

Integrated Systems Laboratory

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Conclusion

  • Running a complete GSM stack is fruitful for PHY

l ith d l t algorithm development

  • There is a growing interest in PHY operations, also by SDR

d i i and open source communicites

  • We have shown OsmocomBB can be interfaced to PHY

i l i f k simulation framework

Thank you for your attention!

Integrated Systems Laboratory