Enhanced methods of cellular environment detection when interoperating with timed interfers
Techniques for performing analysis of a cellular telephone signaling environment in the presence of interferers. The techniques do the analysis by employing a receiver to listen to the cellular environment during holes in the interference. The holes have a timing which differs from that used by the cellular telephone signaling environment and will thus over time overlap with structures of interest in the cellular telephone environment. The holes may be smaller than the structure of interest. The signals which the receiver hears in the holes are analyzed and combined to reproduce the structure. The combination may involve statistical methods and weighted decoding. The analysis obtains information which permits surgical attacks on individual wireless devices which are in the traffic state. Example applications of the techniques are given for the GSM and CDMA cellular telephone standards.
1. A method of obtaining information about a repeated structure in a signal which is generated according to the Global System for Mobile Communications (GSM) standard and which represents a sequence of symbols, the repeated structure having a first timing in the signal and the method being performed in apparatus including a receiver and a signal analyzer and comprising the steps performed in the apparatus of:
receiving the signal for a set of discrete periods in the receiver, the periods in the set having a second timing such that over a plurality of repetitions of the repeated structure in the signal, the entire repeated structure is received in the receiver, wherein, the set of discrete periods is made up of periods during which the signal is not being interfered with by an interferer;
converting the signal as received in each of the discrete periods in the set into symbols; and
analyzing the symbols in the analyzer to obtain the information about the repeated structure.
2. The method set forth in claim 1 further comprising the step performed in the receiver of:
determining the set of discrete periods from the interferer's behavior.
3. The method set forth in claim 1 wherein:
the apparatus is operating in cooperation with the interferer.
4. The method set forth in claim 3 wherein the method further comprises the step of:
providing the obtained information about the repeated structure to the interferer.
5. The method set forth in claim 3 wherein the method further comprises the step of:
obtaining a specification of the set of discrete periods from the cooperating interferer.
6. The method set forth in claim 3 wherein:
the receiver determines the set of discrete periods during which the cooperating interferer does not interfere with the signal.
7. The method set forth in claim 6 wherein:
the receiver determines the set of discrete periods according to the kind of information to be obtained and/or the speed with which the information is to be obtained.
8. The method set forth in claim 1 wherein:
in the analyzing, the symbols from a plurality of the discrete periods are combined using a statistical method.
9. A method of obtaining information about a repeated structure in a signal which is generated according to a standard and which represents a sequence of symbols, the repeated structure having a first timing in the signal and the method being performed in apparatus including a receiver and a signal analyzer and comprising the steps performed in the apparatus of:
receiving the signal for a set of discrete periods in the receiver, the periods in the set having a second timing such that over a plurality of repetitions of the repeated structure in the signal, the entire repeated structure is received in the receiver;
converting the signal as received in each of the discrete periods in the set into symbols; and
analyzing the symbols in the analyzer to obtain the information about the repeated structure, wherein:
the repeated structure is a frame which includes another repeated structure which contains timing information about the frame; and
the method includes the steps performed in the analyzer of:
obtaining the timing information from the second repeated structure in the set of digital representations; and
using the timing information to determine a location of a further repeated structure in the frame.
10. The method set forth in claim 9 wherein the method includes the steps performed in the analyzer of:
using the determined location to locate a representation of the further structure in the set of digital representations; and
obtaining further information about the frame from the located representation.
11. A method of obtaining information about a repeated structure in a signal which is generated according to a standard and which represents a sequence of symbols, the repeated structure having a first timing in the signal and the method being performed in apparatus including a receiver and a signal analyzer and comprising the steps performed in the apparatus of:
receiving the signal for a set of discrete periods in the receiver, the periods in the set having a second timing such that over a plurality of repetitions of the repeated structure in the signal, the entire repeated structure is received in the receiver;
converting the signal as received in each of the discrete periods in the set into symbols; and
analyzing the symbols in the analyzer to obtain the information about the repeated structure, wherein:
the repeated structure is a frame which has a substructure; and
a discrete period in the set thereof is too short to receive a portion of the signal that contains an entire substructure.
12. The method set forth in claim 11 wherein:
in the step of analyzing, a plurality of the discrete periods that contain portions of the substructure are combined using a statistical method.
13. The method set forth in claim 12 wherein:
in the step of analyzing, the symbols are further combined using soft decoding techniques which employ results of the statistical method.
14. The method set forth in claim 11 wherein
the substructure includes an error detection code; and
the method further includes the step of:
using the substructure's error detection code to determine whether a result of the combination is correct.
15. The method set forth in claim 14 wherein:
the error detection code includes error correction information; and
the method further includes the step of:
using the error correction information to reduce the number of possible combinations of the symbols.