OpenBTS: Kalibrasi

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Sumber: http://gnuradio.org/redmine/wiki/1/OpenBTSClockCalibration


Jika kita tidak mempunyai peralatan lab yang baik dan kita ingin mengetahui akurasi clock USRP, kita dapat menggunakan aplikasi Kalibrator (Copyright (c) 2009 Joshua Lackey, Alexander Chemeris). Tentunya kita tidak mungkin memperoleh hasil yang baik seperti hi-tech lab, tapi cukup lah untuk mengetahui error kalibrasi clock yang ada.

Download

Download dari 

http://thre.at/kalibrate/kal-v0.4.1.tar.bz2
git clone https://github.com/ttsou/kalibrate-uhd kalibrate-uhd

Compile

cp kal-v0.4.1.tar.bz2 /usr/local/src/
cd /usr/local/src
tar jxvf kal-v0.4.1.tar.bz2 
cd /usr/local/src/kal-v0.4.1
./bootstrap && CXXFLAGS='-W -Wall -O3' ./configure && make

Menjalankan

cd /usr/local/src/kal-v0.4.1/src/
./kal -h

Hasil 

kalibrate v0.4.1, Copyright (c) 2010, Joshua Lackey

Usage:
	GSM Base Station Scan:
		kal <-s band indicator> [options]

	Clock Offset Calculation:
		kal <-f frequency | -c channel> [options]

Where options are:
	-s	band to scan (GSM850, GSM900, EGSM, DCS, PCS) 
	-f	frequency of nearby GSM base station
	-c	channel of nearby GSM base station
	-b	band indicator (GSM850, GSM900, EGSM, DCS, PCS)
	-R	side A (0) or B (1), defaults to B
	-A	antenna TX/RX (0) or RX2 (1), defaults to RX2
	-g	gain as % of range, defaults to 45%
	-F	FPGA master clock frequency, defaults to 52MHz
	-v	verbose
	-D	enable debug messages
	-h	help

Scanning 1800

Menjalankan 

cd /usr/local/src/kal-v0.4.1/src/
./kal -s 1800 -F 64000000 -b DCS

Hasil 

kal: Scanning for DCS-1800 base stations.
DCS-1800:
 	chan: 513 (1805.4MHz + 14.952kHz)	power: 5336.89 
	chan: 514 (1805.6MHz + 14.954kHz)	power: 1927.35
	chan: 517 (1806.2MHz + 14.952kHz)	power: 3715.71
	chan: 518 (1806.4MHz + 14.983kHz)	power: 1717.65
	chan: 519 (1806.6MHz + 14.969kHz)	power: 5159.38
	chan: 520 (1806.8MHz + 14.951kHz)	power: 2017.03
	chan: 542 (1811.2MHz + 15.092kHz)	power: 4554.77
	chan: 544 (1811.6MHz + 15.084kHz)	power: 3730.97
	chan: 569 (1816.6MHz + 15.181kHz)	power: 6196.37
	chan: 570 (1816.8MHz + 15.172kHz)	power: 1924.81
	chan: 613 (1825.4MHz + 15.237kHz)	power: 15746.19
	chan: 614 (1825.6MHz + 15.242kHz)	power: 6683.53
	chan: 616 (1826.0MHz + 15.260kHz)	power: 12953.63
	chan: 617 (1826.2MHz + 15.248kHz)	power: 4816.39
	chan: 620 (1826.8MHz + 15.224kHz)	power: 4274.58
	chan: 625 (1827.8MHz + 15.268kHz)	power: 3613.13
	chan: 626 (1828.0MHz + 15.313kHz)	power: 1926.56
	chan: 627 (1828.2MHz + 15.274kHz)	power: 3536.15
	chan: 628 (1828.4MHz + 15.267kHz)	power: 2346.39
	chan: 629 (1828.6MHz + 15.288kHz)	power: 7923.44
 	chan: 632 (1829.2MHz + 15.316kHz)	power: 5417.85
 	chan: 633 (1829.4MHz + 15.312kHz)	power: 2652.96
   	chan: 689 (1840.6MHz + 15.602kHz)	power: 3734.25
 	chan: 692 (1841.2MHz + 15.587kHz)	power: 11674.51
	chan: 693 (1841.4MHz + 15.586kHz)	power: 5294.69

Scanning 900

Untuk Clock 64MHz Menjalankan 

cd /usr/local/src/kal-v0.4.1/src/
./kal -s 900 -F 64000000 -b GSM900

Untuk Clock 52MHz Menjalankan 

cd /usr/local/src/kal-v0.4.1/src/
./kal -s 900 -F 52000000 -b GSM900 -vv

Hasil 

FPGA clock : 52000000
Decimation : 192
Sample rate: 270833.343750
kal: Scanning for GSM-900 base stations.
channel detect threshold: 9458.928125
GSM-900:
	chan: 36 (942.2MHz + 423Hz)	power: 194131.34 
	chan: 37 (942.4MHz + 428Hz)	power: 50474.90
	chan: 38 (942.6MHz + 412Hz)	power: 50189.51
	chan: 39 (942.8MHz + 397Hz)	power: 14175.00
	chan: 40 (943.0MHz + 483Hz)	power: 38742.63
	chan: 41 (943.2MHz + 510Hz)	power: 50648.68
	chan: 61 (947.2MHz + 503Hz)	power: 73085.29
	chan: 62 (947.4MHz + 490Hz)	power: 18121.82
	chan: 66 (948.2MHz + 512Hz)	power: 16138.32
	chan: 68 (948.6MHz + 491Hz)	power: 18167.35
	chan: 113 (957.6MHz + 548Hz)	power: 24349.49
	chan: 114 (957.8MHz + 493Hz)	power: 11841.20
	chan: 115 (958.0MHz + 520Hz)	power: 20344.80
	chan: 119 (958.8MHz + 505Hz)	power: 31772.62
	chan: 120 (959.0MHz + 535Hz)	power: 10510.76
	chan: 123 (959.6MHz + 565Hz)	power: 18004.66

Scanning 850

Menjalankan 

cd /usr/local/src/kal-v0.4.1/src/
./kal -s 850 -F 64000000

Hasil

Scanning Channel

Menjalankan 

cd /usr/local/src/kal-v0.4.1/src/
./kal -c 513 -F 64000000 -b DCS

Hasil 

kal: Calculating clock frequency offset.
Using DCS-1800 channel 513 (1805.4MHz)
average		[min, max]	(range, stddev)
+ 17.109kHz		[17087, 17136]	(50, 14.080007)
overruns: 0
not found: 0


Kalkulasi Kalibrasi

Misalnya kita menggunakan BTS pada channel 47 untuk kalibrasi 

./kal -F 52000000 -c 47

Hasil 

kal: Calculating clock frequency offset.
Using GSM-900 channel 47 (944.4MHz)
average		[min, max]	(range, stddev)
+ 501Hz		[479, 524]	(45, 13.227342)
overruns: 0
not found: 0


Misalnya kita menggunakan BTS pada channel 61 untuk kalibrasi 

./kal -F 52000000 -c 61

Hasil 

kal: Calculating clock frequency offset.
Using GSM-900 channel 61 (947.2MHz)
average		[min, max]	(range, stddev)
+ 494Hz		[481, 504]	(23, 6.454695)
overruns: 0
not found: 0


Proses Kalibrasi

Ukur

Gunakan Kalibrate untuk mengukur offset frekuensi, misalnya pada channel 52 

./kal -f 945400000

Misalnya hasilnya adalah 

kal: Calculating clock frequency offset.
Using GSM-900 channel 52 (945.4MHz)
average		[min, max]	(range, stddev)
+ 498Hz		[429, 555]	(126, 32.384548)
overruns: 0
not found: 165

Hitung Offset

Hitung dengan asumsi

  • Frekuensi Clock 20MHz
  • Kanal 52 atau frekuensi 945.4MHz
  • Offset hasil pengukuran + 500Hz

Maka clock 20MHz harus di offset sebesar 

-500Hz/945.4MHz*20MHz=-10.6 Hz

Tepatnya menjadi 

19,999,990 Hz

Set Ulang ClockTamer

Set ulang OSC pada ClockTamer menggunakan 

sudo screen /dev/ttyACM0 115200,cs8,-ixon,-ixoff

Beberapa pilihan setting 

SET,,OSC,19999991
SET,,OSC,19999990
SET,,OSC,19999989
STE

Scan Ulang Frekuensi

Hasilnya harus lebih baik 

cd /usr/local/src/kal-v0.4.1/src
./kal -s 900 -F 52000000 -b GSM900 -vv

Semoga hasilnya memperoleh offset yang lebih baik, seperti 

FPGA clock : 52000000
Decimation : 192
Sample rate: 270833.343750
kal: Scanning for GSM-900 base stations.
channel detect threshold: 9212.598092
GSM-900:
	chan: 35 (942.0MHz -   1Hz)	power: 58221.58 
	chan: 36 (942.2MHz -  15Hz)	power: 277657.07
	chan: 37 (942.4MHz -  16Hz)	power: 69884.02
	chan: 38 (942.6MHz -  39Hz)	power: 51768.26
	chan: 39 (942.8MHz -  57Hz)	power: 14338.21
	chan: 40 (943.0MHz +  22Hz)	power: 39493.83
	chan: 41 (943.2MHz +  46Hz)	power: 51872.61
	chan: 61 (947.2MHz +  74Hz)	power: 52471.92
	chan: 62 (947.4MHz +  54Hz)	power: 12957.55
	chan: 66 (948.2MHz +  46Hz)	power: 15464.87
	chan: 72 (949.4MHz - 35.394kHz)	power: 11784.47
	chan: 109 (956.8MHz +  19Hz)	power: 18475.41
	chan: 113 (957.6MHz +  42Hz)	power: 17960.76
	chan: 114 (957.8MHz +  46Hz)	power: 11643.24
	chan: 119 (958.8MHz +  16Hz)	power: 28815.53
	chan: 120 (959.0MHz +  36Hz)	power: 9772.22
	chan: 123 (959.6MHz +  36Hz)	power: 16534.37

Referensi

Pranala Menarik

Persiapan

OpenBTS 2.6

OpenBTS 2.8

Ettus E110

Lain Lain

Catatan Legal dan Pendukung

Catatan Sejarah

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