Method of packet scheduling, with improved delay performance, for wireless networks
First Claim
1. A method for scheduling queued packets for service by a wireless base station, wherein there is a queue of packets destined for each of a plurality of users, the method comprising:
- periodically identifying a queue having a largest weighted delay; and
scheduling the identified queue for service, during a scheduling interval, at the greatest transmission rate available for serving said queue;
wherein;
(a) each queue i has, at a given time t, a delay Wi(t) determined by one of the following;
the age of the oldest packet in said queue;
a total amount of data in said queue;
in a system in which service of said queue is regulated by a virtual queue that receives tokens at a constant rate, the age of the oldest token in the virtual queue;
or the number of tokens in a corresponding virtual queue; and
(b) at time t, the weighted delay of each queue i is expressed by
times Wi(t), or by
times an increasing function of Wi(t), wherein γ
i is a constant, and ci(t) is a weight coefficient that represents the transmission power required per unit data rate to transmit data, at time t, to the user whose destined queue is queue i.
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Abstract
A new scheduling discipline is disclosed for the forward link of a wireless network such as a CDMA network. The new discipline, which we denominate Modified LWDF (M-LWDF), resembles the known LWDF discipline in that only one queue is served at a time, and the queue to be served is that having the largest weighted delay. According to M-LWDF, the weighted delay of the i'"'"'th queue is defined as
wherein Wi(t) is a packet delay, a queue length, or an increasing function of packet delay or queue length for the i'"'"'th queue, ci(t) is a weight coefficient descriptive of channel conditions for the i'"'"'th user, and γi is a fixed constant that can be chosen arbitrarily. We have found that if any scheduling discipline can yield stable queues for a given traffic pattern of arriving packets, then M-LWDF can, even under changing channel conditions. Moreover, we have found that M-LWDF can provide favorable QoS in terms of delay bounds.
80 Citations
15 Claims
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1. A method for scheduling queued packets for service by a wireless base station, wherein there is a queue of packets destined for each of a plurality of users, the method comprising:
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periodically identifying a queue having a largest weighted delay; and
scheduling the identified queue for service, during a scheduling interval, at the greatest transmission rate available for serving said queue;
wherein;
(a) each queue i has, at a given time t, a delay Wi(t) determined by one of the following;
the age of the oldest packet in said queue;
a total amount of data in said queue;
in a system in which service of said queue is regulated by a virtual queue that receives tokens at a constant rate, the age of the oldest token in the virtual queue;
or the number of tokens in a corresponding virtual queue; and
(b) at time t, the weighted delay of each queue i is expressed by
times Wi(t), or by
times an increasing function of Wi(t), wherein γ
i is a constant, and ci(t) is a weight coefficient that represents the transmission power required per unit data rate to transmit data, at time t, to the user whose destined queue is queue i.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
each constant γ
i is proportional toTi is a specified delay threshold for queue i; and
δ
i is a specified maximum probability that the delay of queue i exceeds Ti.
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5. The method of claim 4, wherein each constant γ
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i is equal to
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i is equal to
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6. The method of claim 4, wherein each constant γ
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i is proportional to
wherein {overscore (c)}i represents a measured short-term average or short-term median value of the weight coefficient ci(t).
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i is proportional to
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7. The method of claim 6, wherein each constant γ
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i is equal to
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i is equal to
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8. The method of claim 1, wherein:
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the weighted delay of each queue i is expressed by
times an increasing function of Wi(t);
said increasing function has the form F( . . . ) and G( . . . ) are increasing functions;
ai is a positive scaling coefficient;
aiWi is a scaled delay of queue i; and
{overscore (aW)} is a scaled delay averaged over all queues.
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9. The method of claim 8, wherein each scaling coefficient ai is derived from a specified delay threshold Ti for queue i and a specified maximum probability δ
- i that the delay of queue i exceeds Ti.
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10. The method of claim 9, wherein each scaling coefficient ai is proportional to
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δ i T i .
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11. The method of claim 9, wherein each scaling coefficient ai is equal to
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δ i T i .
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12. The method of claim 9, wherein {overscore (aW)} is the mean value of aiWi over all queues i.
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13. The method of claim 8, wherein G ( . . . ) is a sub-linear function.
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14. The method of claim 13, wherein G({overscore (aW)}) is equal to {square root over ({overscore (aW)})}+b, b a positive constant.
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15. The method of claim 13, wherein
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( a i W i ( t ) G ( aW _ ) ) is equal to
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Specification