makinen_051206(1)

3G Media Gateway Software for GSM transcoderAuthor: Mikko Mäkinen
© 2006 NOKIA * [email protected] 1.12.2006
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
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 Network’s Signal Processing System unit
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
MS – Mobile Station
MSC – Mobile Switching Station
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)
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)
RAN – Radio Access Network
MGW – Media Gateway
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)
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
Skilled Assembly programmer can beat modern C-compilers anytime in small, algorithm intensive tasks
Tenfold margin is not extraordinary
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!
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 -> 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
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 (O&M) interface technically very different
MGW’s dynamic resource control vs. TRAU’s static speech coding channels
Simplified picture of the new Software
Only few new modules
However, lots of little changes and adjusting -> fiddly and time consuming project
Only basic call through functionality, O&M interface ignored at this stage
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!
Conclusions
Separate GSM transcoder unit have markets for years, although larger investments should be reconsidered thoroughly
The MGW software has clear performance advantage -> more handled channels per unit or less needed DSP hardware capacity
Only minor changes needed for the new software -> possible to develop in parallel with the main MGW software -> 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 O&M interface if green light shown
Future of the AMR-WB codec (in GSM networks)
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makinen_051206(1)