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EspañolPROPORTIONALLY FAIR
(Redirected from Proportionally Fair)
In a 'proportionally fair' scheduling algorithm, the data flows are assigned a data rate that is inversively proportional to its "cost" in terms of resource consumption. For example, a cell phone that is at far distance from the base station will usually achieve lower data rate than one that is close to the base station.
'Proportionally fair scheduling' can be achieved by means of weighted fair queuing (WFQ), by setting the scheduling weights for data flow to , where the cost is the amount of consumed resources per data bit. For instance:
★ In CDMA spread spectrum cellular networks, the cost may be the required energy per bit in the transmit power control (the increased interference level).
★ In wireless communication with link adaptation, the cost may be the required time to transmit a certain number of bits using the modulation and error coding scheme that this required.
★ In wireless networks with fast Dynamic Channel Allocation, the cost may be the number of nearby base station sites that can not use the same frequency channel simultaneously, in view to avoid co-channel interference.
A 'proportionally fair' scheduling algorithm schedules the channel for the station that has the maximum of the priority function , where denotes the data rate potentially achievable for the station at the present moment (in the present time slot), is the average data rate of this station. The time and station indexes are omitted for convenience. Parameters and tune the fairness of the scheduler, that is, is it fair to all stations giving them equal bandwidth or is the scheduler maximizing the throughput of the channel. If and , then the scheduler becomes a round-robin scheduler that is very fair to all stations. If and then the scheduler is called Maximum C/I scheduler, that maximizes the throughput of the channel while stations with low (that are far away, probably) are disadvantaged.
In a 'proportionally fair' scheduling algorithm, the data flows are assigned a data rate that is inversively proportional to its "cost" in terms of resource consumption. For example, a cell phone that is at far distance from the base station will usually achieve lower data rate than one that is close to the base station.
'Proportionally fair scheduling' can be achieved by means of weighted fair queuing (WFQ), by setting the scheduling weights for data flow to , where the cost is the amount of consumed resources per data bit. For instance:
★ In CDMA spread spectrum cellular networks, the cost may be the required energy per bit in the transmit power control (the increased interference level).
★ In wireless communication with link adaptation, the cost may be the required time to transmit a certain number of bits using the modulation and error coding scheme that this required.
★ In wireless networks with fast Dynamic Channel Allocation, the cost may be the number of nearby base station sites that can not use the same frequency channel simultaneously, in view to avoid co-channel interference.
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Alternative definition
A 'proportionally fair' scheduling algorithm schedules the channel for the station that has the maximum of the priority function , where denotes the data rate potentially achievable for the station at the present moment (in the present time slot), is the average data rate of this station. The time and station indexes are omitted for convenience. Parameters and tune the fairness of the scheduler, that is, is it fair to all stations giving them equal bandwidth or is the scheduler maximizing the throughput of the channel. If and , then the scheduler becomes a round-robin scheduler that is very fair to all stations. If and then the scheduler is called Maximum C/I scheduler, that maximizes the throughput of the channel while stations with low (that are far away, probably) are disadvantaged.
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