WO1991009474A1 - Adjacent and co-channel interference avoidance - Google Patents

Adjacent and co-channel interference avoidance Download PDF

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Publication number
WO1991009474A1
WO1991009474A1 PCT/CA1990/000376 CA9000376W WO9109474A1 WO 1991009474 A1 WO1991009474 A1 WO 1991009474A1 CA 9000376 W CA9000376 W CA 9000376W WO 9109474 A1 WO9109474 A1 WO 9109474A1
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WO
WIPO (PCT)
Prior art keywords
channel
adjacent
message
cell controller
interference
Prior art date
Application number
PCT/CA1990/000376
Other languages
French (fr)
Inventor
Paul Solomon Meche
Eugenie Marie Chaplain
Original Assignee
Northern Telecom Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Northern Telecom Limited filed Critical Northern Telecom Limited
Priority to DE69008865T priority Critical patent/DE69008865T2/en
Priority to EP90915738A priority patent/EP0506665B1/en
Publication of WO1991009474A1 publication Critical patent/WO1991009474A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/20—Control channels or signalling for resource management
    • H04W72/29—Control channels or signalling for resource management between an access point and the access point controlling device

Definitions

  • This invention relates to mobile cellular systems, and more particularly to the avoidance of co-channel and adjacent channel interference.
  • a cellular radio signal is commonly affected by two types of interference: co-channel interference and adjacent channel interference.
  • co-channel interference interference is caused on a communication channel by a transmitter operating in the same frequency.
  • adjacent channel interference is caused when the extraneous power originating from a first assigned channel spills over into an adjacent channel.
  • the effects of co-channel and adjacent channel interference are two important constraints upon system performance where frequency re-use is important.
  • filters are used to reduce interference, narrow or tighter filters are generally more expensive. There is accordingly a need for a method of reducing the effects of co-channel and adjacent channel interference on a cellular system.
  • the present invention is a method which is used to enhance the quality of service by allocating only those channels that have a reduced likelihood of co-channel or adjacent channel interference.
  • This technique allows information to be provided to the operating company of drawbacks with the currently engineered RF environment.
  • an idle base station will scan for the presence of signal on its channel. It will also periodically scan for the presence of signal on channels adjacent to it. If a signal is present and is measured to be above a predetermined threshold, RSSI level, it is an indication that the base station is intercepting a signal from a mobile that is presently being served by another voice channel in the system.
  • this base station may interfere with the call that is already in progress on the current channel or a call that is in progress on an adjacent channel.
  • the base station will inform the controller when it detects a signal having an RSSI reading above the predefined threshold indicating that the possibility for co-channel and/or adjacent channel interference exists. It will also inform the controller when the detected RSSI reading has gone back below the predefined threshold indicating that the possibility for co-channel and/or adjacent channel interference has ceased. This information will be factored into the channel allocation algorithm in the cell controller. If an idle voice channel reports the possibility of co-channel or adjacent interference, it will not be chosen to process a call until all other voice channels that are not reporting interference are in use.
  • the voice channel When the voice channel reports that the possibility for co-channel or adjacent channel interference has ceased, it will be returned to its normal priority level to be selected to process a call. Since co-channel interference causes more serious degradation of the signal than adjacent channel interference, voice channels reporting adjacent channel interference will be selected before those reporting co-channel interference.
  • the cell controller can increment the corresponding operational measurement. These operational measurements can be checked by the operating company periodically to determine how their system is performing. If these are high, the operating company can consider the re-engineering of the RF environment.
  • Figures la and lb are flowcharts illustrating the monitoring algorithms for an assigned channel and its adjacent channels
  • Figures 2a to 2d are flowcharts illustrating the channel processing algorithms of the cell controller; and Figure 3 is a flowchart illustrating the channel priority allocating algorithm for the cell controller. Description of the Invention
  • a voice channel while in idle state, will be directed 10 to scan its assigned frequency, as shown in Fig. la, and the frequencies directly adjacent, as shown Fig. lb, to identify the existence of co-channel and adjacent interference respectively.
  • the RSSI reading for that channel is compared to a predetermined threshold.
  • Adjacent channels are scanned as described above and as shown in Figure lb.
  • incoming messages are monitored to determine whether the message is one of the following:
  • noise message a) from a co-channel (Fig. 2a) ; or b) from an adjacent channel (Fig. 2b) ;
  • a voice channel when not allocated to a user, can be in: a) an idle queue waiting to be allocated to a user; b) a co-channel interference queue, until the RSSI reading decreases below the specified threshold for the assigned channel; or c) an adjacent channel interference queue, until the RSSI reading for that adjacent channel decreases below the specified threshold.
  • an operational measurement is also incremented 50 when an adjacent noise message is received. If the voice channel is stored in the idle queue, an adjacent marker is set 51, the voice channel is removed 52 from the idle queue and it is added 53 to the adjacent channel interference queue. This voice channel will remain in the adjacent channel interference queue until the RSSI reading decreases below the threshold. If the voice channel is in the co-channel interference queue, an adjacent marker is set 54.
  • an idle message When an idle message is received, it indicates that the voice channel has an RSSI reading below the specified threshold and is being stored in an interference queue.
  • the adjacent marker is eset 60 and if the voice channel is on the adjacent channel interference queue, it is removed 61 from the adjacent channel interference queue and added 62 to the idle queue.
  • FIG. 3 illustrates the channel priority allocating algorithm 80. Selection priority will be given initially to voice channels on the idle queue, i.e. those that do not report the possibility of interference. Those channels will be removed 81 from the idle queue and provided 82 to the requestor. If no voice channels are available on the idle queue, then a voice channel will be selected from the adjacent channel interference queue, if any are available. This VCH will be removed 83 from the queue and provided 82 to the requestor. Finally, if the only remaining channels are in the co-channel interference queue, then one VCH will be removed 84 therefrom and provided 82 to the requestor.

Abstract

A method to enhance the quality of cellular radio service is disclosed. Only those channels that have a reduced likelihood of co-channel or adjacent channel interference are allocated. This technique, in addition, allows information to be provided to the operating company of drawbacks with the currently engineered RF environment. In particular, the base station will scan for RSSI readings on its channel and channels adjacent to it. If an RSSI measurement above a predetermined threshold is detected, it is assumed that the base station is intercepting a signal from a mobile that is presently being served by another voice channel on an adjacent cell. If this base station were selected to process a call, it may interfere with the call that is already in progress on the current channel or a call that is in progress on an adjacent channel. The base station will inform the controller when it detects an RSSI reading above the predefined threshold indicating that the possibility for co-channel and adjacent interference exists. It will also inform the controller when the detected RSSI reading has gone back below the predefined threshold indicating that the possibility for co-channel and adjacent interference has ceased. If an idle voice channel reports the possibility of co-channel or adjacent interference, it will not be chosen to process a call until all other voice channels that are not reporting interference are in use. When the voice channel reports that the possibility for co-channel or adjacent channel interference has ceased, it will be returned to its normal priority level to be selected to process a call.

Description

ADJACENT AND CO-CHANNEL INTERFERENCE AVOIDANCE Field of the Invention
This invention relates to mobile cellular systems, and more particularly to the avoidance of co-channel and adjacent channel interference.
Background of the Invention
A cellular radio signal is commonly affected by two types of interference: co-channel interference and adjacent channel interference. In the case of co-channel interference, interference is caused on a communication channel by a transmitter operating in the same frequency. Whereas, adjacent channel interference is caused when the extraneous power originating from a first assigned channel spills over into an adjacent channel. The effects of co-channel and adjacent channel interference are two important constraints upon system performance where frequency re-use is important. Although filters are used to reduce interference, narrow or tighter filters are generally more expensive. There is accordingly a need for a method of reducing the effects of co-channel and adjacent channel interference on a cellular system.
Summary of the Invention The present invention is a method which is used to enhance the quality of service by allocating only those channels that have a reduced likelihood of co-channel or adjacent channel interference. This technique, in addition, allows information to be provided to the operating company of drawbacks with the currently engineered RF environment. With the present invention, an idle base station will scan for the presence of signal on its channel. It will also periodically scan for the presence of signal on channels adjacent to it. If a signal is present and is measured to be above a predetermined threshold, RSSI level, it is an indication that the base station is intercepting a signal from a mobile that is presently being served by another voice channel in the system. If this base station were selected to process a call, it may interfere with the call that is already in progress on the current channel or a call that is in progress on an adjacent channel. The base station will inform the controller when it detects a signal having an RSSI reading above the predefined threshold indicating that the possibility for co-channel and/or adjacent channel interference exists. It will also inform the controller when the detected RSSI reading has gone back below the predefined threshold indicating that the possibility for co-channel and/or adjacent channel interference has ceased. This information will be factored into the channel allocation algorithm in the cell controller. If an idle voice channel reports the possibility of co-channel or adjacent interference, it will not be chosen to process a call until all other voice channels that are not reporting interference are in use. When the voice channel reports that the possibility for co-channel or adjacent channel interference has ceased, it will be returned to its normal priority level to be selected to process a call. Since co-channel interference causes more serious degradation of the signal than adjacent channel interference, voice channels reporting adjacent channel interference will be selected before those reporting co-channel interference. Each time a voice channel reports the possibility of interference, the cell controller can increment the corresponding operational measurement. These operational measurements can be checked by the operating company periodically to determine how their system is performing. If these are high, the operating company can consider the re-engineering of the RF environment.
Brief Description of the Drawings
Figures la and lb are flowcharts illustrating the monitoring algorithms for an assigned channel and its adjacent channels;
Figures 2a to 2d are flowcharts illustrating the channel processing algorithms of the cell controller; and Figure 3 is a flowchart illustrating the channel priority allocating algorithm for the cell controller. Description of the Invention
As shown in Figures la and lb, a voice channel (VCH) while in idle state, will be directed 10 to scan its assigned frequency, as shown in Fig. la, and the frequencies directly adjacent, as shown Fig. lb, to identify the existence of co-channel and adjacent interference respectively. The RSSI reading for that channel is compared to a predetermined threshold. a) If the reading is greater than or equal to that threshold 11a, and if a noise report has not previously been sent 12a for that channel, then a noise report 13 is sent to the cell controller; b) If the reading is greater than or equal to that threshold 11a, and if a noise report has already been reported 12b, then the VCH will scan 14 channels adjacent thereof; c) If the reading is less than the threshold lib, and if a noise report has not previously been reported 14a, then the VCH will scan 14 channels adjacent thereof; and d) If the reading is less than the threshold lib, and if a noise report has already been reported 15b, then an idle report is sent 16 to the cell controller.
Adjacent channels are scanned as described above and as shown in Figure lb.
At the cell controller 40, Fig. 2a, incoming messages are monitored to determine whether the message is one of the following:
1) noise message: a) from a co-channel (Fig. 2a) ; or b) from an adjacent channel (Fig. 2b) ;
2) an idle message: a) from a co-channel (Fig. 2d) ; or b) from an adjacent channel (Fig. 2c) . When the received message is a noise message from an assigned channel (Fig. 2a), i.e. indicating the possibility of co-channel interference, then an operational measurement is incremented 41. From these, the operating company can periodically verify the system's performance.
A voice channel, when not allocated to a user, can be in: a) an idle queue waiting to be allocated to a user; b) a co-channel interference queue, until the RSSI reading decreases below the specified threshold for the assigned channel; or c) an adjacent channel interference queue, until the RSSI reading for that adjacent channel decreases below the specified threshold.
In figure 2a, if the voice channel is stored in an idle queue, it is removed from the idle queue 42 and added 43 to an interference queue. This way, this channel will not be selected until all other channels are in use, (see Fig. 3) since it is likely to create co-channel interference. The specified channel will remain in the co-channel interference queue until the RSSI reading decreases below the threshold. If the voice channel is held on the adjacent channel interference queue, it is removed 44 from that queue and added 45 to the co-channel interference queue.
In figure 2b, an operational measurement is also incremented 50 when an adjacent noise message is received. If the voice channel is stored in the idle queue, an adjacent marker is set 51, the voice channel is removed 52 from the idle queue and it is added 53 to the adjacent channel interference queue. This voice channel will remain in the adjacent channel interference queue until the RSSI reading decreases below the threshold. If the voice channel is in the co-channel interference queue, an adjacent marker is set 54.
When an idle message is received, it indicates that the voice channel has an RSSI reading below the specified threshold and is being stored in an interference queue. In figure 2c, when an adjacent channel idle message is received, the adjacent marker is eset 60 and if the voice channel is on the adjacent channel interference queue, it is removed 61 from the adjacent channel interference queue and added 62 to the idle queue.
In figure 2d, when a co-channel idle message is received, if a voice channel is on the co-channel interference queue, it is removed therefrom 70. If the adjacent marker is set, the voice channel is added 71 to the adjacent interference queue. If there is no.adjacent marker, the voice channel is added 72 to the idle queue.
Since co-channel interference causes more serious degradation of the signal than adjacent channel interference, voice channels reporting the possibility of adjacent channel interference will be chosen to service mobiles before a voice channel reporting the possibility of co-channel interference. Figure 3 illustrates the channel priority allocating algorithm 80. Selection priority will be given initially to voice channels on the idle queue, i.e. those that do not report the possibility of interference. Those channels will be removed 81 from the idle queue and provided 82 to the requestor. If no voice channels are available on the idle queue, then a voice channel will be selected from the adjacent channel interference queue, if any are available. This VCH will be removed 83 from the queue and provided 82 to the requestor. Finally, if the only remaining channels are in the co-channel interference queue, then one VCH will be removed 84 therefrom and provided 82 to the requestor.

Claims

CLAIMS:
1. A method of avoiding co-channel interference, wherein channels are stored in an idle queue until allocated by a cell controller to a user, comprising the steps of: a) monitoring an assigned voice channel; b) measuring the RSSI level of said assigned channel; c) sending a co-channel idle voice message to said cell controller if the RSSI level is less than a threshold
Tl; d) sending a co-channel noise message to said cell controller if said RSSI level is greater than or equal said threshold Tl; e) receiving a message at said cell controller; and f) removing said assigned voice channel from the idle channel queue if said received message is a co-channel noise message from said assigned channel.
2. A method as defined in claim 1, further comprising the step of holding said removed voice channel in a co-channel interference queue until said RSSI level of said assigned channel is less than said threshold Tl.
3. A method as defined in claim 2, wherein said co-channel noise message is sent to said cell controller only if no previous co-channel noise messages were sent thereto.
4. A method as defined in claim 3, further comprising the step of incrementing operational measurements associated with said RSSI levels each time a co-channel noise message is received by said cell controller.
5. A method of avoiding adjacent channel interference, wherein the channels are stored in an idle queue until allocated by a cell controller to a user, comprising the steps of: a) monitoring channels adjacent an assigned voice channel; b) measuring the RSSI level of said adjacent channels; c) sending an adjacent idle voice message to said cell controller if the RSSI level is less than a threshold T2; d) sending an adjacent noise message to said cell controller if said RSSI level in one of said adjacent channels is greater than or equal said threshold T2; e) receiving a message at said cell controller; and f) removing said one of said adjacent channels from said idle channel queue if said received message is an adjacent noise message from said adjacent channel.
6. A method as defined in claim 5, further comprising the step of holding said removed adjacent channel in an adjacent channel interference queue until said RSSI level of said adjacent channel is less than said threshold T2.
7. A method as defined in claim 6, wherein said adjacent channel noise message is sent to said cell controller only if no previous adjacent channel noise messages were sent thereto.
8. A method as defined in claim 7, further comprising the step of incrementing operational measurements associated with said RSSI levels each time an adjacent channel noise message is received by said cell controller.
9. A method of avoiding co-channel and adjacent channel interference, said channels being stored in an idle queue until allocated by a cell controller to a user, comprising the steps of: a) monitoring an assigned voice channel; b) measuring the RSSI reading of said assigned channel; c) sending a co-channel idle voice message to said cell controller if the RSSI level is less than a threshold Tl; d) sending a co-channel noise message to said cell controller if said RSSI level is greater than or equal said threshold Tl; e) monitoring channels adjacent said assigned voice channel; f) measuring the RSSI level of said adjacent channels; g) sending an adjacent idle voice message to said cell controller if the RSSI level is less than said threshold T2; h) sending an adjacent noise message to said cell controller if said RSSI level in one of said adjacent channel is greater than or equal said threshold T2; i) receiving a message at said cell controller; j) removing said assigned voice channel from the idle channel queue if said received message is a co-channel noise message from said assigned channel; and k) removing said one of said adjacent channel from said idle channel queue if said received message is an adjacent noise message from said adjacent channel.
10. A method as defined in claim 8, further comprising the step of holding said removed assigned voice channel in a co-channel interference queue until said RSSI reading of said assigned channel is less than said threshold Tl.
11. A method as defined in claim 10, further comprising the step of holding said removed adjacent channel in an adjacent channel interference queue until said RSSI level of said adjacent channel is less than said threshold T2.
12. A method as defined in claim 10, wherein, if no voice channels are available from said idle VCH queue when a request for a voice channel is received by said cell controller, a voice channel from said adjacent interference queue will be selected before a voice channel from said co-channel interference queue is selected, so that co-channel interference is minimized.
13. A method as defined in claim 7, wherein said co-channel noise message is sent to said cell controller only if no previous co-channel noise messages were sent thereto.
14. A method as defined in claim 13, further comprising the step of incrementing operational measurement associated with said RSSI levels each time a co-channel noise message is received by said cell controller.
15. A method as defined in claim 7, wherein said adjacent channel noise message is sent to said cell controller only if no previous adjacent channel noise messages were sent thereto.
16. A method as defined in claim 15, further comprising the step of incrementing operational measurement associated with said RSSI levels each time an adjacent channel noise message is received by said cell controller.
PCT/CA1990/000376 1989-12-19 1990-11-07 Adjacent and co-channel interference avoidance WO1991009474A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
DE69008865T DE69008865T2 (en) 1989-12-19 1990-11-07 AVOID INTERFERENCE BETWEEN NEIGHBOR CHANNELS AND USED CHANNEL.
EP90915738A EP0506665B1 (en) 1989-12-19 1990-11-07 Adjacent and co-channel interference avoidance

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US07/452,341 US5148548A (en) 1989-12-19 1989-12-19 Method of monitoring cellular radio channels to avoid adjacent and co-channel interference
US452,341 1989-12-19

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WO1991009474A1 true WO1991009474A1 (en) 1991-06-27

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US (1) US5148548A (en)
EP (1) EP0506665B1 (en)
JP (1) JP2967237B2 (en)
AU (1) AU641444B2 (en)
CA (1) CA2059666C (en)
DE (1) DE69008865T2 (en)
WO (1) WO1991009474A1 (en)

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JPH05501036A (en) 1993-02-25
EP0506665B1 (en) 1994-05-11
AU641444B2 (en) 1993-09-23
DE69008865D1 (en) 1994-06-16
CA2059666C (en) 1998-12-01
CA2059666A1 (en) 1991-06-20
US5148548A (en) 1992-09-15
EP0506665A1 (en) 1992-10-07
AU6614490A (en) 1991-07-18
DE69008865T2 (en) 1994-08-18
JP2967237B2 (en) 1999-10-25

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