Scanning radio receiver for a wireless communication system

• US 6,453,156 B1
• Filed: 09/24/1998
• Issued: 09/17/2002
• Est. Priority Date: 09/24/1998
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Center, Stephen Douglas, Wallstedt, Yngve Kenneth
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): GELIN, JEAN ALLAND
• Application Number:
  US09/160,130
• Time in Patent Office: 1,454 Days
• Field of Search: 455/67.1, 455/63, 455/67.6, 455/502, 455/509, 455/512, 455/513, 455/522, 455/71, 455/423, 455/450, 455/422, 455/434, 455/436, 455/438, 455/439, 455/442, 455/446, 455/115, 455/126, 455/20, 455/21, 455/226.3, 455/23, 455/42, 455/421, 455/161.1, 455/161.3, 375/343, 375/245, 375/340, 375/346, 370/331, 370/332, 370/336, 370/356, 370/342
• US Class Current: 455/161.3
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 17/391 Modelling the propagation channel
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

A method for use in a receiver in a time division multiple access (TDMA) wireless communication system to determine whether a channel is occupied and whether the transmitter occupying the channel is internal or external to the system. The method comprises the steps of receiving a signal, on a channel determining that the channel is unoccupied when the signal strength of the channel signal is below a threshold, determining that the transmitter is internal to the system when the received signal is highly correlated to a signal that is known to contain the proper predefined field.

Claims

1. A method for use in a wireless communication system having a plurality of internal transmitters transmitting on a plurality of channels, for determining whether a signal on a channel is being transmitted by a transmitter internal to the system, the signal having a predefined field, said method comprising:

receiving the signal being transmitted by a transmitter on a channel;

determining a degree of correlation between the predefined field in the signal and a model of a predefined field of a signal transmitted by a transmitter synchronized to the system; and

determining that the transmitter of the signal is internal to the system if the degree of correlation is high.

2. The method of claim 1 wherein the step of determining the degree of correlation includes determining the degree of correlation between the predefined field in the signal over a predefined frequency range and a model of a predefined field of a signal transmitted by a transmitter synchronized to the system.

3. The method of claim 1 wherein the step of determining the degree of correlation includes determining the degree of correlation between the predefined field in the signal over a predefined time offset and a model of a predefined field of a signal transmitted by a transmitter synchronized to the system.

4. The method of claim 1 wherein the step of determining the degree of correlation includes determining the degree of correlation between the predefined field in the signal over a predefined frequency range and a predefined time offset and a model of a predefined field of a signal transmitted by a transmitter synchronized to the system.

5. A method of claim 1 further including the step of determining a signal strength of the signal and wherein the step of determining that the transmitter of the signal is internal to the system also includes determining that the signal strength is above a threshold.

6. The method of claim 1 wherein the step of determining a degree of correlation comprises comparing a phase angle of the signal to a model of a phase angle of the predefined field of a signal transmitted by a transmitter synchronized to the system.

7. The method of claim 6 wherein each channel comprises a frequency and a timeslot on the frequency and the predefined field comprises a predefined location in the timeslot and wherein the step of determining a degree of correlation comprises comparing a phase angle at the predefined location of the signal'"'"'s timeslot to a model of a phase angle of the predefined field of a signal transmitted by a transmitter synchronized to the system.

8. A scanning radio receiver for use in a wireless telephone system to measure a signal'"'"'s strength and determine whether the signal'"'"'s transmitter is internal or external to the system, said signal having a plurality of timeslots each having a predefined field, said scanning receiver comprising:

a variable frequency tuner having a tunable receiver to receive a timeslot of a signal on one of a plurality of frequencies and having means for measuring the signal'"'"'s strength and means for changing the frequency of the signal to an intermediate frequency;

a quantitizer configured to sample the signal strength measurement and to quantitize each sample of the signal strength;

a sampling device configured to sample the intermediate frequency signal and to derive a phase of the signal in each sample;

a memory containing a stored list of phases and signal strengths of samples of the predefined field; and

a comparator configured to determine whether the signal'"'"'s transmitter is internal or external to the system by determining whether the predefined field is present in the signal, said comparator including means for comparing the signal phase and the signal strength of a predetermined plurality of signal samples from the timeslot of the signal to the stored list of signal phases and signal strengths of the predefined field, wherein the transmitter of the signal is internal to the system if the phase of the signal is sufficiently similar to the stored list of signal phases.

9. A scanning radio receiver in accordance with claim 8 wherein said comparator is further configured to convert the phase angle and signal strength of the predetermined plurality of signal samples to complex IQ representation and wherein said stored list of mathematical representations and signal strengths of the unique synchronization words comprise complex IQ representations, said comparator being configured to correlate the complex IQ representation of the signal to the complex IQ representations of the predefined field to determine whether the predefined field is present in the signal based upon the degree of correlation of the two signal representations.

10. A scanning radio receiver in accordance with claim 9 wherein said comparator is further configured to add a phase angle offset to each of the plurality of samples.

11. A scanning radio receiver in accordance with claim 10 wherein said comparator is configured to repeatedly compare the complex IQ representation of said plurality of signal samples to the predefined field a plurality of times, using a different phase angle offset each repetition.

12. A scanning radio in accordance with claim 8 wherein said samples of said signal comprise a plurality of symbols, said predefined field comprises a group of adjacent symbols, and said comparator being further configured to start said correlation at a predetermined time prior to the expected start of the adjacent symbols.

13. A scanning radio in accordance with claim 8 wherein said samples of said signal comprise a plurality of symbols, said predefined field comprises a group of adjacent symbols, and said comparator being further configured to repeatedly correlate starting at a different one of said samples on each repetition.

14. A scanning radio in accordance with claim 13 wherein said comparator only converts a portion of said sampled symbols in the vicinity of said synchronization word in said time slot.

15. A scanning radio in accordance with claim 8 wherein said comparator reports that a transmitter is internal to the system if the correlation exceeds a predetermined threshold.

16. A method for use in a scanning radio receiver for determining source and strength of a signal on a predefined frequency, said method comprising:

tuning to the predefined frequency;

converting a signal on the predefined frequency to an intermediate frequency;

determining a signal strength for the signal;

determining a phase of the signal at the intermediate frequency;

comparing the phase of the signal to an expected phase of a synchronization word; and

reporting the signal strength and the result of said comparison.

17. A method in accordance with claim 16 wherein the step of determining a phase of the signal at the intermediate frequency comprising sampling the signal and determining a phase angle for each sample.

18. A method in accordance with claim 17 further including the step of converting the signal strength and phase angle for each sample to a complex mathematical notation, and the step of comparing comprises comparing the complex mathematical notation of the plurality of symbols to a complex mathematical notation of the expected synchronization word.

19. A method in accordance with claim 18 wherein the step of comparing further includes adding a phase angle offset to each sample to allow for frequency drift of the signal.

20. A method in accordance with claim 18 wherein the step of comparing further includes adding a one of consecutive range of phase angle offsets to each sample to allow for frequency drift of the signal, and comparing the complex mathematical notation to the complex mathematical notation of the expected synchronization word signal, adding a different one of said range of offsets to each sample and comparing again.

21. A method in accordance with claim 16 wherein said expected synchronization word in said signal comprises an adjacent group of symbols, and said step of comparing comprises starting with a group of symbols within a predetermined number of symbols from the expected location of the expected synchronization word, and repeatedly comparing the complex mathematical notation of the signal to the expected synchronization word signal, starting with a different sequential symbol each time.

22. A scanning receiver for use in a wireless telephone system to measure a signal'"'"'s strength and to determine whether the signal'"'"'s transmitter is synchronized to the system, said signal including a plurality of timeslots comprising a plurality of encoded symbols, each of said plurality of timeslots having a synchronization word comprising a predefined plurality of encoded symbols, said scanning receiver comprising:

means for measuring the signal strength of the signal;

means for determining the phase of the predefined plurality of encoded symbols; and

means for correlating said phase of the symbols of the signal with the phase of an expected synchronization word to determine whether the transmitter is synchronized to the system.

23. A method for use in a wireless communications system for determining whether a signal received on a predefined frequency was transmitted by a transmitter synchronized to said system, said method comprising:

tuning to said predefined frequency;

converting said signal on said predefined frequency to an intermediate frequency;

determining a signal strength for said signal;

determining a phase of said signal at said intermediate frequency;

comparing said phase of said signal to an expected phase of a synchronization word; and

determining based on said signal strength and said comparison, whether said signal was transmitted by a transmitter synchronized to said system.