multi-rtl-sdr-calibration README

======================= By a enthusiast putaoshu@msn.com putaoshu@gmail.com of Software Defined Radio.

Try to process/calibrate multiple rtl-sdr dongles simultaneously.

Different dongles IQ samples are sent through different rtl_tcp instances. (rtl_tcp is a utility offered with rtl-sdr package: https://github.com/steve-m/librtlsdr.git)

Currently, it is only tested in Ubuntu Linux (12.04 LTS) You may try it in more diverse platform.

My initial purpose is performing in-fly calibration for multiple dongles according to some pre-known signals (GSM, ADS-B?) to let them work together coherently.

An ideal scheme may be that we should generate a very narrow band and very week signal in (or just located at the edge of) target working band of dongles, and perform the software in-fly calibration in background (or driver level). This would be user friendly.

I know it is far from final state currently, and many things are not clear yet (See TODO).

But please join me if you also think this is a good idea. Please see TODO firstly.

======================= News:

1. Now gsm_sync_demod.m can correct sampling and carrier error for multiple dongles, and display sampling phase difference (at 8X oversampling) for two dongles after sampling and carrier correction.

Don't forget to use multi_rtl_sdr_gsm_FCCH_scanner.m to find out strongest GSM broadcasting carrier in your location and set it to "freq" in gsm_sync_demod.m

2. I am trying to demodulate information in SCH and BCCH to help aligning further. See gsm_sync_demod.m

Usage

Assume that you have rtl-sdr worked correctly. (See http://sdr.osmocom.org/trac/wiki/rtl-sdr)

Quick demo after you plug dongle to your computer. (You may try more than one dongle on your computer.)

Assume that you have two dongles there, open two shell and run

rtl_tcp -p 1234 -d 0

rtl_tcp -p 1235 -d 1

in two shells respectively.

Then run matlab script: gsm_sync_demod.m/multi_rtl_sdr_split_scanner.m/multi_rtl_sdr_diversity_scanner.m/multi_rtl_sdr_gsm_FCCH_scanner.m to see how to use two dongles to scan a band simultaneously.

(See README_for_scanner.txt and README_for_gsm_scanner.txt for detail of "side products" -- spectrum scanner and FCCH scanner.)

If you only have one dongle, don't forget to change num_dongle from 2 to 1 in those scripts.

You may also define any other band according to your interests. Just modify start_freq, end_freq, etc., parameters in the scripts.

Detail usage example/explanation:

In matlab, I receive and process TCP streams like this:

tcp_obj0 = tcpip('127.0.0.1', 1234); % for dongle 0
tcp_obj1 = tcpip('127.0.0.1', 1235); % for dongle 1

fread_len = 8192;
set(tcp_obj0, 'InputBufferSize', fread_len);
set(tcp_obj0, 'Timeout', 1);
set(tcp_obj1, 'InputBufferSize', fread_len);
set(tcp_obj1, 'Timeout', 1);

fopen(tcp_obj0);
fopen(tcp_obj1);
while 1
    [a0, real_count0] = fread(tcp_obj0, fread_len, 'uint8');
    [a1, real_count1] = fread(tcp_obj1, fread_len, 'uint8');
    if real_count0~=fread_len || real_count1~=fread_len
      disp(num2str([fread_len, real_count0, real_count1]));
        continue;
    end

    %process samples from two dongles in varable "a0" and "a1"
    ....
end

See detail in script gsm_sync_demod.m/multi_rtl_sdr_split_scanner.m/multi_rtl_sdr_diversity_scanner.m/multi_rtl_sdr_gsm_FCCH_scanner.m

I also give some little tool scripts to set dongle's frequency, gain, etc.

Please see: set_gain_tcp.m, set_rate_tcp.m, set_freq_tcp.m.

Contributing

multi-rtl-sdr-calibration was started during the end of 2013 in my spare time.

You are welcome to send pull requests in order to improve the project.

See TODO list included in the source distribution first (If you want).