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ttsou, 02/19/2016 10:47 PM


= OsmoTRX =

OsmoTRX is a software-defined radio transceiver that implements the Layer 1 physical layer of a BTS comprising the following 3GPP specifications: * TS 05.01 "Physical layer on the radio path" * TS 05.02 "Multiplexing and Multiple Access on the Radio Path" * TS 05.04 "Modulation" * TS 05.10 "Radio subsystem synchronization"

OsmoTRX is based on the OpenBTS transceiver, but setup to operate independently with the purpose of using with non-OpenBTS software and projects. Currently there are numerous features contained in OsmoTRX that extend the functionality of the OpenBTS transceiver. These features include enhanced support for embedded platforms - notably ARM - and dual channel diversity support for the Fairwaves UmTRX. Most of these features will eventually be merged into mainline OpenBTS, but primary development will occur on OsmoTRX.

Features Intel SSE Support
  • SSE3
  • SSE4.1

On Intel processors, OsmoTRX makes heavy use of the Streaming SIMD Extensions (SSE) instruction set. Accelerated operations include pulse shape filtering, resampling, sequence correlation, and many other signal processing operations. SSE3 is the minimum requirement for accelerated use. SSE3 is present in the majority of Intel processors since later versions of the Pentium 4 architecture and is also present on low power Atom processors.

ARM NEON Support
  • NEON
  • NEON-VFPv4

OsmoTRX runs on a variety of ARM processors with and without NEON coprocessors. Like SSE on Intel processors, NEON provides acceleration with SIMD vectorized instructions. Tested popular architectures include ARM11 (Raspberry Pi), Cortex-A8 (BeagleBoard), and Cortex-A15 (ArndaleBoard). These platforms include no NEON coprocessor, standard NEON, and NEON-VFPv4 respectively. The latter NEON variation, VFPv4, provides additional fused-multiply-accumulate (FMA) instructions useful for many DSP operations. NEON optimization must be used enabled at built time.

Dual Channel (UmTRX only)

Two dual channel modes are available: standard dual channel mode and diversity. In standard dual channel mode, each RF
path of the dual channel device - currently only UmTRX - supports a different ARFCN. Each path operates independently a
nd operates similarly to two separate devices. GSM channel capacity in this mode is doubled.

Dual Channel Diversity (UmTRX only)

Diversity mode is similar to the standard dual channel mode except each antenna supports both ARFCN channels. In this case, the receiver sample bandwidth is widened to handle both ARFCN's and subsequently converted and demultiplexed into separate sample streams. Each GSM receive path is fed dual signals, where antenna selection diversity is performed by taking the stronger signal on a burst-by-burst basis. The limitations are increased CPU utilization and that ARFCN spacing is restricted (currently at 400 kHz) by the receiver sampling bandwidth. Setting the ARFCN spacing beyond the sampling limit will disable the diversity path.

Low Phase Error Modulator

The default GSM downlink signal is configured for low distortion using a linearized GMSK modulator. The implementation is based on a two pulse Laurent approximation of continuous phase modulated (CPM) signals. On capable devices, the signal measures with very low phase error and passes industry specturm mask specifications.

Hardware support Fairwaves
UmTRX
Ettus Research
USRP1
USRP2
B100
B110
B200
B210
N200
N210
E100
E110
Embedded Platform Support

OsmoTRX has been tested on the following embedded platforms.

Platform Processor SIMD/FPU
BeagleBoard-xM ARM Cortex-A8 NEON
ArndaleBoard ARM Cortex-A15 NEON-VFPv4
RaspberryPi ARMv6k VFP
Shuttle PC Intel Atom D2550 SSE3
Ettus E100 ARM Cortex-A8 NEON
Benchmarks

{{{
[+] Testing: GSM xCCH (non-recursive, flushed, not punctured)
[.] Input length : ret = 224 exp = 224 -> OK
[.] Output length : ret = 456 exp = 456 -> OK
[.] Pre computed vector checks:
[..] Encoding: OK
[..] Decoding base:
[..] Decoding SIMD:
[..] Code N 2
[..] Code K 5
OK
[.] Random vector checks:
[.] Testing baseline:
[..] Encoding / Decoding 10000 cycles:
[.] Elapsed time........................ 0.395893 secs
[.] Rate................................ 11.518264 Mbps
[.] Testing SIMD:
[..] Encoding / Decoding 10000 cycles:
[.] Elapsed time........................ 0.047606 secs
[.] Rate................................ 95.786245 Mbps
[.] Speedup............................. 8.316032

[+] Testing: GSM TCH/AFS 7.95 (recursive, flushed, punctured)
[.] Input length : ret = 165 exp = 165 -> OK
[.] Output length : ret = 448 exp = 448 -> OK
[.] Pre computed vector checks:
[..] Encoding: OK
[..] Decoding base:
[..] Decoding SIMD:
[..] Code N 3
[..] Code K 7
OK
[.] Random vector checks:
[.] Testing baseline:
[..] Encoding / Decoding 10000 cycles:
[.] Elapsed time........................ 1.435066 secs
[.] Rate................................ 3.121808 Mbps
[.] Testing SIMD:
[..] Encoding / Decoding 10000 cycles:
[.] Elapsed time........................ 0.073524 secs
[.] Rate................................ 60.932485 Mbps
[.] Speedup............................. 19.518334
}}}

Status GPRS support Source code

The source code is available from git.osmocom.org (module osmo-trx).

Public read-only access is available via
git clone git://git.osmocom.org/osmo-trx
You can browse it via cgit: http://cgit.osmocom.org/cgit/osmo-trx/

Configuration and Build

The only package dependency is the Universal Hardware Driver (UHD).

{{{
$ ./configure
$ make
$ sudo make install
}}}

Running

{{{
$ osmo-trx -h
linux; GNU C++ version 4.8.1 20130603 (Red Hat 4.8.1-1); Boost_105300; UHD_003.005.004-140-gfb32ed16

Options:
-h This text
-a UHD device args
-l Logging level (EMERG, ALERT, CRT, ERR, WARNING, NOTICE, INFO, DEBUG)
-i IP address of GSM core
-p Base port number
-d Enable dual channel diversity receiver
-x Enable external 10 MHz reference
-s Samples-per-symbol (1 or 4)
-c Number of ARFCN channels (default=1)
}}}

{{{
$ osmo-trx -a "addr=192.168.10.2"
linux; GNU C++ version 4.8.1 20130603 (Red Hat 4.8.1-1); Boost_105300; UHD_003.004.000-b14cde5

Config Settings
Log Level............... INFO
Device args............. addr=192.168.10.2
TRX Base Port........... 5700
TRX Address............. 127.0.0.1
Channels................ 1
Samples-per-Symbol...... 4
External Reference...... Disabled
Diversity............... Disabled

-- Opening a UmTRX device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes
-- Setting UmTRX 4 SPS
-- Transceiver active with 1 channel(s)
}}}

Authors

OsmoTRX is currently developed and maintained by Thomas Tsou. The original code is derived from the OpenBTS project, which was developed by David Burgess and Harvind Samra at Range Networks.

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