Methods and systems for assigning channels in a power controlled time slotted wireless communications system

• US 20040171401A1
• Filed: 02/28/2003
• Published: 09/02/2004
• Est. Priority Date: 02/28/2003
• Status: Active Grant

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Balachandran, Krishna, Kang, Joseph H.
• Granted Patent: US 7,116,982 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H04M 2215/32 Involving wireless systems
• CPC Class Codes: H04W 24/10 Scheduling measurement reports ; Arrangements for measurement reports
• CPC Class Codes: H04W 4/24 Accounting or billing
• CPC Class Codes: H04W 52/287 when the channel is in stand-by
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 72/044 based on the type of the allocated resource
• CPC Class Codes: H04W 72/542 using measured or perceived quality

Abstract

Systems and methods for intelligently assigning a channel to a device being used by a mobile user in a power controlled, wireless communications system by minimizing the difference between a mobile user'"'"'s received signal power and the minimum received signal power of a current user on a candidate carrier frequency. Each carrier frequency within a cell is examined to determine whether it has at least one current user assigned to a channel and also has at least one unoccupied channel. For each carrier frequency that meets both of these requirements, a channel quality metric is obtained for each occupied channel. The carrier frequencies are pruned down to a subset of candidate carrier frequencies using the channel quality metrics. Finally, a channel within the set of candidate carrier frequencies is selected by computing a cost function based on the received signal power of the mobile user and the received signal power of each occupied channel.

Claims

1. A method for assigning a channel to a mobile user requesting a channel assignment in a wireless communications system after receiving a signal power measurement associated with the mobile user, the method comprising the steps of:

selecting at least one carrier frequency from a plurality of carrier frequencies, the at least one carrier frequency comprising at least one occupied and one unoccupied channel;

obtaining received signal power for the at least one occupied channel of the at least one carrier frequency; and

selecting a channel on at least one carrier frequency from a subset of candidate carrier frequencies by calculating a cost function based on a received signal power of the mobile user and a received signal power of at least one current user on at least one carrier frequency.

2. The method of claim 1, further comprising the steps of:

receiving a channel quality report comprising channel quality metrics for each channel occupied by a current user on each carrier frequency; and

creating the subset of candidate carrier frequencies based on channel quality metrics.

3. The method of claim 2, wherein the step of creating the subset of candidate carrier frequencies further comprises the steps of:

comparing each channel quality metric to a predetermined threshold channel quality metric value;

adding a carrier frequency to the subset of candidate carrier frequencies if each channel quality metric indicates better channel quality than that indicated by the predetermined threshold channel quality metric value; and

discarding a carrier frequency if at least one channel quality metric indicates worse channel quality than that indicated by the predetermined threshold channel quality metric value.

4. The method of claim 3, further comprising the steps of:

opening a new carrier frequency; and

assigning the mobile user to an unoccupied channel of the new carrier frequency if all of the carrier frequencies are discarded.

5. The method of claim 3, further comprising the step of assigning the mobile user to an unoccupied channel of a carrier frequency with at least one occupied channel if all of the carrier frequencies are discarded.

6. The method of claim 1, further comprising the step of creating the subset of candidate carrier frequencies using the steps of:

calculating a difference between the received signal power from the mobile user and a received signal power from a current user on a particular channel;

calculating a received signal power-to-interference (C/I) ratio;

comparing the calculated C/I ratio with a predetermined C/I ratio;

adding a carrier frequency to the subset of candidate carrier frequencies if the C/I ratio is greater than the predetermined C/I threshold value;

discarding a carrier frequency if the C/I ratio is less than the predetermined C/I threshold value; and

opening a new carrier frequency and assigning the mobile user to an unoccupied channel of the new carrier frequency if all of the carrier frequencies are discarded.

7. The method of claim 1, wherein the step of calculating the cost function, comprises:

for each candidate carrier frequency in the subset of candidate carrier frequencies, determining a channel with a minimum received power and calculating an absolute difference value between the received power from the mobile user and the minimum received power for the channel;

selecting a candidate carrier frequency that has a minimum absolute difference value; and

assigning the mobile user to an unoccupied channel of the selected candidate carrier frequency.

8. The method of claim 7, further comprising the steps of:

obtaining an average interference value for each candidate carrier frequency in the subset of candidate carrier frequencies;

adding an average interference value to the absolute difference between the received power from the mobile user and the minimum received power on a channel; and

selecting a candidate carrier frequency that has a minimum value.

9. The method of claim 1, wherein the step of calculating the cost function further comprises the steps of:

for each candidate carrier frequency, calculating an absolute difference between the received signal power of the mobile user and a received signal power for each occupied channel, raising each difference to the p^th power, summing these values over all occupied channels, and dividing the result by the number of occupied channels within the candidate carrier frequency; and

determining the candidate carrier frequency that has a minimum calculated value.

10. The method of claim 9, further comprising the steps of:

obtaining an average interference value for each candidate carrier frequency in the subset of candidate carrier frequencies;

for each candidate carrier frequency, calculating an absolute difference between the received signal power of the mobile user and a received signal power for each occupied channel, raising each difference to the p^th power, adding the average interference, summing these values over all occupied channels, and dividing the result by the number of occupied channels within the carrier frequency; and

selecting a candidate carrier frequency that has a minimum value.

11. The method of claim 1, wherein the step of calculating the cost function further comprises:

for each candidate carrier frequency in the subset of candidate carrier frequencies, determining a channel with a minimum received power and calculating an absolute difference between the received power from the mobile user and the minimum received power for the channel;

comparing the absolute difference to a predetermined threshold power value;

discarding a candidate carrier frequency if the absolute difference is greater than the predetermined threshold power value;

selecting a candidate carrier frequency that has a minimum absolute difference value from the remaining candidate carrier frequencies; and

assigning the mobile user to an unoccupied channel of the selected candidate carrier frequency.

12. The method of claim 1, further comprising the step of requesting a channel assignment, said step being triggered by an event selected from the list consisting of receiving a call setup request, intra-sector handover, inter-sector handover, detecting a change in received signal strengths on at least one carrier frequency, or detecting a change in average interference levels for at least one candidate carrier frequency.

13. A channel assignment unit (CAU) for assigning a channel to a mobile user within a wireless communications system, comprising:

a processor unit operable to;

obtain the received signal power for a mobile user requesting a channel assignment;

select at least one carrier frequency from a plurality of carrier frequencies, the at least one carrier frequency having at least one occupied and one unoccupied channel; and

select a channel on at least one candidate carrier frequency from a subset of candidate carrier frequencies by calculating a cost function based on the received signal power of the mobile user and the received signal power of at least one current user on at least one carrier frequency.

14. The CAU of claim 13, wherein the processor unit is further operable to:

receive a channel quality report for the at least one occupied channel assigned to a current user of the at least one selected carrier frequency, the channel quality report consisting of a received signal strength of the current user and a channel quality metric; and

create the subset of candidate carrier frequencies based on the channel quality metrics.

15. The CAU of claim 14, wherein the processor unit is further operable to create the subset of candidate carrier frequencies by:

comparing the channel quality metric to a predetermined threshold value;

adding a carrier frequency to the subset of candidate carrier frequencies if each channel quality metric indicates better channel quality than that indicated by, the predetermined threshold value; and

discarding a carrier frequency if at least one channel quality metric for the carrier frequency indicates worse channel quality than that indicated by the predetermined threshold value.

16. The CAU of claim 15, wherein the processor unit is further operable to:

open a new carrier frequency and assign the mobile user to an unoccupied channel of the new carrier frequency if all of the carrier frequencies are discarded.

17. The CAU of claim 15, wherein the processor unit is further operable to:

assign the mobile user to an unoccupied channel of a carrier frequency with at least one occupied channel if all of the carrier frequencies are discarded

18. The CAU of claim 13, wherein the processor unit is further operable to create the subset of candidate carrier frequencies using channel quality metrics by:

calculating a difference between the received signal power from the mobile user and a received signal power from a current user on a particular channel;

calculating a received signal power-to-interference (C/I) ratio by converting the channel quality metric to C/I, if applicable, and adding it to the computed signal power difference;

comparing the calculated C/I ratio with a predetermined C/I ratio;

adding a carrier frequency to the subset of candidate carrier frequencies if the C/I ratio is greater than the predetermined C/I threshold value;

discarding a carrier frequency if the C/I ratio is less than the predetermined C/I threshold value; and

opening a new carrier frequency and assigning the mobile user to an unoccupied channel of the new carrier frequency if all of the carrier frequencies are discarded.

19. The CAU of claim 13, wherein the processor unit is further operable to calculate the cost function by:

for each candidate carrier frequency in the subset of candidate carrier frequencies, determining a channel with a minimum received power and calculating an absolute difference value between the received power from the mobile user and the minimum received power for the channel;

selecting a candidate carrier frequency that has a minimum absolute difference value; and

assigning the mobile user to an unoccupied channel of the selected carrier frequency.

20. The CAU of claim 19, wherein the processor unit is further operable to:

obtain an average interference value for each candidate carrier frequency in the subset of candidate carrier frequencies;

add the average interference value to the absolute difference between the received power from the mobile user and the minimum received power of the channel; and

select a candidate carrier frequency that has a minimum value.

21. The CAU of claim 13, wherein the processor unit is further operable to calculate the cost function by:

for each candidate carrier frequency, calculating an absolute difference between the received signal power of the mobile user and a received signal power for each occupied channel, raising each difference to the p^th power, summing these values over all occupied channels, and dividing the result by the number of occupied channels within the candidate carrier frequency; and

determining a candidate carrier frequency that has a minimum calculated value.

22. The CAU of claim 13, wherein the processor unit is further operable to:

obtain an average interference value for each candidate carrier frequency in the subset of candidate carrier frequencies;

for each candidate carrier frequency, calculate the absolute difference between the received signal power of the mobile user and the received signal power for each occupied channel, raising each difference to the p^th power, adding an average interference, summing these values over all occupied channels, and dividing the result by the number of occupied channels within the candidate carrier frequency; and

select a candidate carrier frequency that has a minimum value.

23. The CAU of claim 13, wherein the processor unit is further operable to calculate the cost function by:

for each candidate carrier frequency in the subset of candidate carrier frequencies, determining a channel with the minimum received power and calculating an absolute difference value between the received power from the mobile user and the minimum received power for the channel;

comparing the absolute difference to a predetermined threshold power value;

discarding a candidate carrier frequency if the absolute difference is greater than the predetermined threshold power value;

selecting a candidate carrier frequency that has the minimum absolute difference value from the remaining candidate carrier frequencies; and

assigning the mobile user to an unoccupied channel of the selected carrier frequency

24. The CAU of claim 23, wherein the processor unit is further operable to:

detect an event selected from the list consisting essentially of a call setup request, an intra-sector handover, an inter-sector handover, a change in the received signal strengths on at least one carrier frequency, a change in the average interference levels for at least one carrier frequency, and a call departure signal; and

initiate the assignment of a channel to the mobile user upon detecting such an event.

25. A channel assignment unit (CAU) for assigning a channel to a mobile user within a wireless communications system, comprising:

means for obtaining the received signal power for the mobile user requesting a channel assignment;

means for selecting the carrier frequencies from a plurality of carrier frequencies, each carrier frequency having at least one occupied and one unoccupied channel;

means for selecting a channel on at least one candidate carrier frequency from a subset of candidate carrier frequencies by calculating a cost function based on the received signal power of the mobile user and a received signal power of at least one current user on at least one carrier frequency.

26. The CAU of claim 25, further comprising:

means for receiving a channel quality report for each occupied channel assigned to a current user of each selected carrier frequency, the channel quality report consisting of a received signal strength of the current user of the selected carrier frequency and channel quality metrics; and

means for creating the subset of candidate carrier frequencies based on the channel quality metrics.

27. The CAU of claim 26, wherein the means for creating the subset of candidate carrier frequencies comprises:

means for comparing each channel quality metric to a predetermined threshold value;

means for adding a carrier frequency to the subset of candidate carrier frequencies if each channel quality metric indicates better channel quality than that indicated by the predetermined threshold value; and

means for discarding a carrier frequency if at least one channel quality metric for the carrier frequency indicates worse channel quality than that indicated by the predetermined threshold value.

28. The CAU of claim 25, further comprising means for opening a new carrier frequency and assign the mobile user to an unoccupied channel of the new carrier frequency if all of the carrier frequencies are discarded.

29. The CAU of claim 25, further comprising means for assigning the mobile user to an unoccupied channel of a carrier frequency with at least one occupied channel if all of the carrier frequencies are discarded.

30. The CAU of claim 25;

wherein the means for selecting a subset of candidate carrier frequencies further comprises;

means for calculating a difference between the received signal power from the mobile user and a received signal power from a current user on a particular channel;

means for calculating a received signal power-to-interference (C/I) ratio by converting the channel quality metric to C/I, if applicable, and adding it to the computed signal power difference;

means for comparing the calculated C/I ratio with a predetermined C/I ratio;

means for adding a carrier frequency to the subset of candidate carrier frequencies if the C/I ratio is greater than the predetermined C/I threshold value;

means for discarding a carrier frequency if the C/I ratio is less than the predetermined C/I threshold value; and

means for opening a new carrier frequency and assign the mobile user to an unoccupied channel of the new carrier frequency if all of the carrier frequencies are discarded.

31. The CAU of claim 25, further comprising means for calculating the cost function, said means comprising:

means for determining a channel with a minimum received power and calculating an absolute difference value between the received power from the mobile user and the minimum received power for the channel for each candidate carrier frequency in the subset of candidate carrier frequencies;

means for selecting a candidate carrier frequency that has a minimum absolute difference value; and

means for assigning the mobile user to an unoccupied channel of the selected carrier frequency.

32. The CAU of claim 31, further comprising:

means for obtaining an average interference value for each candidate carrier frequency in the subset of candidate carrier frequencies;

means for adding the average interference value to the absolute difference between the received power from the mobile user and the minimum received power of the channel; and

means for selecting a candidate carrier frequency that has a minimum value.

33. The CAU of claim 25, further comprising:

means for calculating an absolute difference between the received signal power of the mobile user and a received signal power for each occupied channel, raising each difference to the p^th power, summing these values over all occupied channels, and dividing the result by the number of occupied channels within the candidate carrier frequency for each frequency; and

means for selecting a candidate carrier frequency that has a minimum calculated value.

34. The CAU of claim 25, further comprising means for calculating the cost function, said means comprising:

means for obtaining an average interference value for each candidate carrier frequency in the subset of candidate carrier frequencies;

for each candidate carrier frequency, means for calculating the absolute difference between the received signal power of the mobile user and the received signal power for each occupied channel, raising each difference to the p^th power, adding an average interference, summing these values over all occupied channels, and dividing the result by the number of occupied channels within the candidate carrier frequency; and

means for selecting a candidate carrier frequency that has a minimum value.

35. The CAU of claim 33, wherein the means for calculating the absolute difference further comprises:

for each candidate carrier frequency in the subset of candidate carrier frequencies, means for determining a channel with the minimum received power and calculating an absolute difference value between the received power from the mobile user and the minimum received power for the channel;

means for comparing the absolute difference to a predetermined threshold power value;

means for discarding a candidate carrier frequency if the absolute difference is greater than the predetermined threshold power value;

means for selecting a candidate carrier frequency that has the minimum absolute difference value from the remaining candidate carrier frequencies; and

means for assigning the mobile user to an unoccupied channel of the selected carrier frequency