Send a packet between phones without BSS?

[rodarima at gmail.com]

Hello.

In my phone specs says that it support: UMTS/HSDPA/HSUPA (850, 900, 1900, 2100 
MHz).

At the wikipedia, I can read:


		Uplink			Downlink
GSM-850 	824.2 – 849.2		869.2 - 894.2

GSM 900: ------------------------------------------------

P-GSM 900 	890,0 - 915,0		935,0 - 960,0
E-GSM 900	880,0 - 890,0		925,0 - 935,0
R-GSM 900	876,0 - 880,0		921,0 - 925,0

GSM1900: ------------------------------------------------

GSM 1900	1850,0 - 1910,0		1930,0 - 1990,0



More clearly(?):
			       MHZ                 1111111111
           88888888888888888888999999999999999999990000000000
           00112233445566778899001122334455667788990123456789
 BAND:     05050505050505050505050505050505050505050505050505
GSM-850  : -----^^^^^----vvvvvv------------------------------
P-GSM 900: ------------------^^^^^^---vvvvvv-----------------
E-GSM 900: ----------------^^^------vvv----------------------
R-GSM 900: ---------------^^-------vv------------------------

(^) means uplink, (v) downlink.

Posible overlap between bands:

SRC Band       From    To         DST Band  Hole size
P-GSM 900 ----(890.0 - 894.2)---> GSM-850 |  4.2 MHZ
E-GSM 900 ----(880.0 - 894.2)---> GSM-850 | 14.2 MHZ
R-GSM 900 ----(876.0 - 880.0)---> GSM-850 |  4.0 MHZ

Can a phone, with a modified baseband firmware, transmit data to another phone 
directly, without BSS? Or are there any hardware limitation?

From https://gnuradio.org/redmine/attachments/115/all_gsm_channels_arfcn.txt

Source channel:
Channel: 0;	Band: EGSM-900	Uplink: 890 MHz,	Downlink: 935 MHz
Channel: 1;	Band: GSM-900	Uplink: 890.2 MHz,	Downlink: 935.2 MHz
...
Channel: 20;	Band: GSM-900	Uplink: 894 MHz,	Downlink: 939 MHz
Channel: 21;	Band: GSM-900	Uplink: 894.2 MHz,	Downlink: 939.2 MHz

Destination channel:
Channel: 232;	Band: GSM-850	Uplink: 845 MHz,	Downlink: 890 MHz
Channel: 233;	Band: GSM-850	Uplink: 845.2 MHz,	Downlink: 890.2 MHz
...
Channel: 250;	Band: GSM-850	Uplink: 848.6 MHz,	Downlink: 893.6 MHz
Channel: 251;	Band: GSM-850	Uplink: 848.8 MHz,	Downlink: 893.8 MHz

For example using a phone on channel 0 (GSM-900 band) to send a packet to a 
phone on channel 232 (GSM-850 band), using 890 MHz common frecuency.

I could't get any useful info about that.

Greetings.
Rodrigo.
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