3G Media Gateway Software for GSM Transcoder

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3G Media Gateway Software for GSM Transcoder

• Author Mikko Mäkinen
• Supervisor Professor Raimo Kantola
• Instructor Lic.Sc. (Tech) Jyri Suvanen

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Contents of the presentation

• Objectives of the thesis
• Speech transcoding in mobile networks
• Role of TRAU (Transcoder and Rate Adaptation
  Unit) and MGW (Media Gateway) in GSM and 3G
  networks
• Digital Signal Processing (DSP) Hardware and
  Software (HW/SW)
• Comparing TRAU and MGW software
• Applying MGW software for TRAU environment
• Performance of the new software
• Conclusions

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Objectives of the thesis

• Problem
• Two separate network elements (TRAU and MGW) are
  handling basically the same task i.e. transcoding
  speech. However, their development has been
  relatively independent in Nokia up to this date.
• Methods
• Study the roles of the TRAU and the MGW unit in
  current and future network architectures
• Comparison of the MGW and the TRAU software
• Apply the MGW software in the TRAU hardware
  environment and implement needed software parts
• Feasibility performance study of the new
  software
• Thesis was carried out in Nokia Networks Signal
  Processing System unit

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Speech transcoding in mobile networks

• Radio frequencies are scarce and expensive
  resource
• Speech encoding saves radio channels remarkably
• Traditional PCM (64kbit/s) versus HR (5.6kbit/s),
  FR (13kbit/s), EFR(12.2kbit/s) and
  AMR-NR(4.75-12.2kbit/s)
• Exploitation of the statistical characteristics
  of the human speech
• Short term correlation linear prediction
• Long term correlation fundamental period of
  voiced sounds
• Hybrid coders combination of waveform coders
  and vocoders
• Compatible interconnections towards other
  wireless and wireline networks usually
  implemented with PCM

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Role of TRAU and MGW (1/3)

• MS Mobile Station
• BTS Base Transceiver Station
• BSC Base Station Controller
• TRAU Transcoding and Rate Adaptation Unit
• MSC Mobile Switching Station
• GMSC Gateway MSC
• VLR Visitor Location Register
• HLR Home Location Register
• AuC Authentication Centre
• EIR Equipment Identity Register
• PSTN Public Switched Telephone Network
• PLMN Public Land Mobile Network

• TRAU is a part of the GSM access network
• Handling FR/HR/EFR/AMR-NB to PCM conversion
• Most of its new markets in developing countries
  (plus capacity updates in developed countries)

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Role of TRAU and MGW (2/3)
RAN Radio Access Network GERAN GSM/EDGE
RAN UTRAN UMTS Terrestrial RAN CS Circuit
Switched PS Packet Switched RNC Radio Network
Controller SGSN Serving GPRS Support Node GGSN
Gateway GPRS Support Node MGW Media Gateway

• MGW is a part of the 3G core network (Release4)
• MGW handles only user plane traffic
• Placed behind TRAU if co-operated with the
  GSM/EDGE access network
• Handling data type conversion (IP/ATM/PCM) in
  addition to the media format conversion
• Under active product development (new features
  capacity updates)

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Role of TRAU and MGW (3/3)

• Problem Duplicate transcoders in 3G core/ GSM
  access network situation
• Expensive for the operator and multiple lossy
  transcodings decrease the speech quality
• Solution 1 Avoid tandem transcoding with
  end-to-end codec negotiation
• Tandem Free Operation (TFO) pack encoded bits
  inside 64kbit/s PCM stream, no bandwidth savings
• Transcoder Free Operation (TrFO) send encoded
  bits directly over an IP/ATM network, saves also
  bandwidth compared to 64kbit/s PCM
• Does not solve the problem of duplicate hardware
  units
• Solution 2 Remove separate TRAU-unit, implement
  Ater-interface in MGW
• Cost efficient
• Dynamic allocation of 2G/3G transcoding
  capabilities
• Unfortunately Ater-interface is proprietary and
  thus this solution works only in limited
  situations (access and core network from the same
  manufacturer)

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DSP HW/SW (1/2)

• Why to use specialized DSP hardware with
  processor specific Assembly code when commercial
  off-the shelf processors have higher clock rates,
  wider range of third party compilers/development
  tools/software/etc. and support for higher (more
  abstracted) programming languages (C/C/Java..)
  that are easily ported for new hardware
  environments?
• DSP processors are superior in certain
  application fields (price competitive and
  computationally demanding functions) due to their
  special characteristics
• Separate multiply-accumulate unit (e.g. for
  vector products)
• Multiple memory fetches within single clock cycle
• Fixed point arithmetic
• Special instruction sets
• Minimal and power consumption effective design
• Skilled Assembly programmer can beat modern
  C-compilers anytime in small, algorithm intensive
  tasks
• Tenfold margin is not extraordinary

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DSP HW/SW (2/2)

• However, modern transcoding units have new
  requirements for DSP SW
• Size of the software has explode
• Dynamic functionality, lots of control oriented
  tasks
• Shorter time-to-market cycles
• Rapid hardware updates to increase capacity
• It is not possible to design each new hardware
  from scratch and reprogram the whole software for
  the new hardware
• Use of common and modular hardware units
• Separation of the hardware dependent software
  from others
• Separation of the control oriented and the
  algorithm intensive pieces of software
• Use of higher languages (mostly C) whenever its
  possible
• Use of Assembly only when really needed!

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TRAU and MGW software comparison

• The development of these units have been
  relatively independent due to their distinct
  functions and different historical background
• However, today the functionality set of TRAU is
  almost an inclusive subset of the corresponding
  MGW functionality set. Moreover, the MGW software
  offers several additional services such as the
  wideband AMR codec.
• The whole TRAU software was originally written in
  Assembly although in later releases some C-code
  was added -gt simple and effective but nowadays
  unmanageable, error prone and stretched to its
  limits
• Not too optimized anymore, as the current version
  is only translated version of the previous
  release (optimized for a different processor)
• The MGW software has a more modern layered
  architecture (operating system, drivers,
  platform, application) making it flexible,
  modular and portable
• Even more detailed separation in application
  part, making it possible to for example outsource
  the development of standard speech codecs

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Applying MGW software for TRAU environment (1/2)

• Two similar products but both have distinct
  markets and hardware environments, although both
  units use the same DSP currently (Texas
  Instruments TNETV3010)
• However, Nokia could enhance its software
  development and maintenance processes by reusing
  the more modern MGW software in TRAU unit. This
  is possible, as also the Assembly code is
  portable between units due to the same
  processors.
• Minimum target same functionality and similar
  capacity
• Possible problems in external interfaces
• MGW SW has no support for direct serial port
  traffic that TRAU uses for all user traffic
• Operation Maintenance (OM) interface
  technically very different
• MGWs dynamic resource control vs. TRAUs static
  speech coding channels

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Applying MGW software for TRAU environment (2/2)

• Only few new modules
• However, lots of little changes and adjusting -gt
  fiddly and time consuming project
• Only basic call through functionality, OM
  interface ignored at this stage

• Simplified picture of the new Software

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Performance of the new Software

• Clear performance advantage compared to the old
  TRAU SW
• Greatest difference in actual speech codecs
  (translated versus native code)
• Possibility to even double the capacity!

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Conclusions

• Separate GSM transcoder unit have markets for
  years, although larger investments should be
  reconsidered thoroughly
• The MGW software has clear performance advantage
  -gt more handled channels per unit or less needed
  DSP hardware capacity
• Only minor changes needed for the new software -gt
  possible to develop in parallel with the main MGW
  software -gt only one software to maintain
• More flexible software for new features or other
  updates. AMR-WB is a possible newcomer for GSM
  networks in the future.
• Final product decisions not made yet, but used
  approach seems to be very promising
• Further study
• Implementation of the OM interface if green
  light shown
• Future of the AMR-WB codec (in GSM networks)

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• Thank You!
• Questions/Comments?