USRP experiment2: GSM scanning

Abstract:

主要用USRP1的FFT功能来检测周边的BTS。

 

Introduction：

现在软件无线电非常热，open source and open hardware可以进行SDR的开发。利用GNURADIO可以加强对GSM进行学习和了解，可以用FFT找出附近的BTS。

 

Hardware ：

ThinkPad T61 一台

USRP1

DBSRX daughterboard (covers 800MHz – 2.4GHz)

Software:

Linux OS: Ubuntu 11.04

GNURADIO 3.4.1

 

related material:

 

频段	名称	信道号	上行(MHz)	下行(MHz)	其他
GSM 850	GSM 850	128 - 251	824,0 - 849,0	869,0 - 894,0	美国, 南美洲国家和 亚洲部分国家。
GSM 900	P-GSM 900	1-124	890,0 - 915,0	935,0 - 960,0	GSM最先实现的频段，也是使用最广的频段。
	E-GSM 900	975 - 1023	880,0 - 890,0	925,0 - 935,0	900M扩展频段
	R-GSM 900	n/a	876,0 - 880,0	921,0 - 925,0	铁路GSM（GSM-R），为铁路调度通信系统开发的特殊版本。
GSM1800	GSM 1800	512 - 885	1710,0 - 1785,0	1805,0 - 1880,0	适用于对信道容量需求大的市场，应用范围仅次于900M。
GSM1900	GSM 1900	512 - 810	1850,0 - 1910,0	1930,0 - 1990,0	主要用于美洲国家，由于有频率重叠，与1800M系统不兼容。

Steps:

 

First :

Enter gnuradio/gr-utils/src/python

Second:

Typed “./usrp_fft.py –R B –d 8 –g 32 –f 940M”

Third :

You will see the next result

Note: -R means “select USRP Rx side A or B”

-d means “set FPGA decimation rate to DECIM”, if you want to observe 8MHz wide band of spectrum, you set this at 8. Because it can be calculated by sample_rate / DECIM.  E.g. 64M/8 = 8MHz.

We observe 8MHz wide band of spectrum centered at 940MHz, in which we find several BTSs, each one transmitting in a 200KHz wide channel.

Ps: There are too many BTSs in mainland. Of course mainland has more people than other countries. However, we are always in radiation. Oops !

And we use other usrp1 to transmit data at 942MHz. Then we observe the 942MHz at received usrp1 FFT. You will see the power arising at 942MHz.

It proves that usrp can scan the BTSs using FFT method. And not all of the channels are used in every area, some of them are reserved to be used in neighboring cells(we see them as lower strength signals), or simply there is no need for more BTSs to operate in a specific population area.

Reporter: Nick Chan

                             2011-9-10

 

attached GSM channel frequency: http://caremind.homerictech.com/arfcn.php

 

ARFCN	FREQUENCE
1	935.2
2	935.4
3	935.6
4	935.8
5	936
6	936.2
7	936.4
8	936.6
9	936.8
10	937
11	937.2
12	937.4
13	937.6
14	937.8
15	938
16	938.2
17	938.4
18	938.6
19	938.8
20	939
21	939.2
22	939.4
23	939.6
24	939.8
25	940
26	940.2
27	940.4
28	940.6
29	940.8
30	941
31	941.2
32	941.4
33	941.6
34	941.8
35	942
36	942.2
37	942.4
38	942.6
39	942.8
40	943
41	943.2
42	943.4
43	943.6
44	943.8
45	944
46	944.2
47	944.4
48	944.6
49	944.8
50	945
51	945.2
52	945.4
53	945.6
54	945.8
55	946
56	946.2
57	946.4
58	946.6
59	946.8
60	947
61	947.2
62	947.4
63	947.6
64	947.8
65	948
66	948.2
67	948.4
68	948.6
69	948.8
70	949
71	949.2
72	949.4
73	949.6
74	949.8
75	950
76	950.2
77	950.4
78	950.6
79	950.8
80	951
81	951.2
82	951.4
83	951.6
84	951.8
85	952
86	952.2
87	952.4
88	952.6
89	952.8
90	953
91	953.2
92	953.4
93	953.6
94	953.8
95	954
96	954.2
97	954.4
98	954.6
99	954.8
100	955
101	955.2
102	955.4
103	955.6
104	955.8
105	956
106	956.2
107	956.4
108	956.6
109	956.8
110	957
111	957.2
112	957.4
113	957.6
114	957.8
115	958
116	958.2
117	958.4
118	958.6
119	958.8
120	959
121	959.2
122	959.4
123	959.6
124	959.8