Patent Grant
10356716
This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/SE2014/050898, filed on Jul. 17, 2014, the disclosure and content of which is incorporated by reference herein in its entirety. The above-referenced PCT International Application was published in the English language as International Publication No. WO 2016/010467 A1 on Jan. 21, 2016.
The technology disclosed herein relates generally to the field of wireless networks, and in particular to resource scheduling in wireless networks.
Scheduling comprises assigning a communication resource to a particular communication device (denoted user equipment, UE, in the following) at a given time interval. The scheduling can be done in accordance with different packet scheduling schemes. For instance, a scheduler implementing a delay based scheduling (DBS) tries to maintain given delay thresholds for traffic flows by minimizing their packet queuing delay. A scheduler implementing a proportional fair may aim at providing a guaranteed data rate for the traffic flows.
Real-time applications, such as Voice over Internet Protocol (VoIP) and video telephony, have strict delay constraints and require that the packets are sent within a certain delay budget for keeping user satisfaction. Delay based scheduling used for conversational type of traffic such as Voice over Internet Protocol (VoIP) applications or conversational video bundles together multiple packets within a packet delay budget to one transmission in order to save resources (e.g. Physical Downlink Control Channel, PDCCH, resources in case of Long Term Evolution, LTE). For a mixed traffic scenario, comprising both delay critical traffic and delay tolerant traffic, an improved throughput for best effort traffic is thereby achieved without compromising the Quality of Service (QoS) of e.g. VoIP/conversational video applications.
A number of packets are thus bundled together before transmission. In delay based scheduling, for instance, a fixed packet bundling time is used to decide when to schedule a particular UE, and the packet delay budget stipulates for how long the oldest packet of a packet bundle can be held before transmission without the QoS being compromised. When the packet is older than the packet bundling time, the corresponding UE is scheduled with absolutely highest priority in order to meet the QoS requirement. This is done by adding an extra scheduling weight bonus (weight boost) on the scheduling weight of the packet bundle, thus giving the packet a higher priority.
In minimum bit rate proportional fair, the scheduling weight is computed based on instantaneous rate, which is a data rate that the UE could potentially get, and based on an average rate for the UE.
Within wireless networks, there are time domain restrictions that may be introduced for various purposes. The communication devices may for example be configured to use a discontinuous reception (DRX) mode in order to reduce energy consumption. Besides DRX, such time domain restrictions can be introduced by features/schemes such as for instance Almost Blank Subframe (ABS) and in enhanced Inter-Cell Interference Coordination (eICIC) schemes. These features are all valuable, e.g. saving energy of the limited energy source in the case of DRX and reducing interference in the case of eICIC, but such features may also pose difficulties in view of scheduling.
Taking the DRX as an example; in DRX a DRX cycle is used which comprises an “On Duration” during which the UE should monitor downlink channels and a “DRX sleep period” during which the UE does not receive downlink channels. The UE saves energy by turning off circuitry during the inactive DRX sleep periods. If the UE is in a DRX sleep period at a scheduled time then the bundled packet transmission is not allowed and a new scheduling time is determined. At this new scheduling time, the oldest packet may be older than the packet delay budget and therefore be lost. This problem could be overcome by adjusting the DRX cycle of the UE in view of the scheduling, but this would entail increased signaling in the network in reconfiguration of the UEs. Further, the UE would be in DRX sleep mode for a shorter period of time, which is disadvantageous in view of its battery consumption.
A minimum bit rate proportional fair scheduling may also encounter packet losses due to such future time restrictions. In particular, it may not be possible to guarantee a minimum bit rate for a UE being in a DRX sleep period.
The time restrictions posed by these features at a future time instance might thus cause packet losses when performing scheduling.
An object of the present disclosure is to solve or at least alleviate at least one of the above mentioned problems.
The object is according to a first aspect achieved by a method performed in a network element for scheduling a communication device of a wireless network. The method comprises estimating a scheduling metric of a first arrived packet at a future time instant t, taking into account time domain restrictions for the communication device that restricts a future scheduling occasion; determining whether the estimated scheduling metric at the future time instant t is within limits of the scheduling metric; calculating, for the case the estimated scheduling metric is within limits of the scheduling metric, a scheduling weight for a packet bundle comprising the first arrived packet and at least one more packet, and else calculating a scheduling weight for the first arrived packet for transmission of the first arrived packet without bundling; and scheduling the communication device according to determined scheduling weight.
The method enables improved service quality, e.g. in terms of reduced packet losses. The service quality can be improved without adding overhead to the battery consumption of the communication device. The method may automatically adapt packet, arrival time in view of e.g. a discontinuous reception mode and decide whether to bundle the packets or send them without bundling, while maintaining required quality of service for the communication device.
The object is according to a second aspect achieved by a network element for scheduling a communication device in a wireless network. The network element is configured to: estimate a scheduling metric of a first arrived packet at a future time instant, taking into account time domain restrictions for the communication device that restricts a future scheduling occasion; determine whether the estimated scheduling metric at the future time instant t is within limits of the scheduling metric; calculate, for the case the estimated scheduling metric is within limits of the scheduling metric, a scheduling weight for a packet bundle comprising the first arrived packet and at least one more packet, and else calculating a scheduling weight for the first arrived packet for transmission of the first arrived packet without bundling; and schedule the communication device according to determined scheduling weight.
The object is according to a third aspect achieved by a computer program for a network element for scheduling a communication device, the computer program comprising computer program code, which, when executed on a processor of the network element causes the network element to perform the method as above.
The object is according to a fourth aspect achieved by a computer program product comprising a computer program as above, and a computer readable means on which the computer program is stored.
The object is according to a fifth aspect achieved by network element comprising first means for estimating a scheduling metric of a first arrived packet at a future time instant, taking into account time domain restrictions for the communication device that restricts a future scheduling occasion; means for determining whether the estimated scheduling metric at the future time instant is within limits of the scheduling metric, means for calculating, for the case the estimated scheduling metric is within limits of the scheduling metric, a scheduling weight for a packet bundle comprising the first arrived packet and at least one more packet, and else calculating a scheduling weight for the first arrived packet for transmission of the first arrived packet without bundling; and means for scheduling the communication device according to determined scheduling weight.
Further features and advantages of the present disclosure will become clear upon reading the following description and the accompanying drawings.
In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description with unnecessary detail. Same reference numerals refer to same or similar elements throughout the description.
In the following, the shortcoming mentioned briefly under the Summary section is elaborated on.
In delay based scheduling, a fixed packet bundling time is used for awaiting and bundling a number of packets. The packet bundling time is used to decide when to schedule a particular UE. When the QoS requirement of a packet of the packet bundle is about to be violated, i.e. when the age of the oldest packet is longer than packet bundling time, the UE will be scheduled with the absolutely highest priority. This is done by adding an extra scheduling weight bonus (weight boost) on the scheduling weight of the packet bundle, thereby giving the packets a higher priority.
The above indicated weight function of delay based scheduling (DBS) is illustrated in
For example, VoIP TALK packets are sent with 20 ms period (i.e. one packet every 20 ms), and the TALK quality is considered to be good when a packet delay is smaller than certain time, e.g. 40 ms, which may be denoted VoIP delay tolerance limit. Based on that delay tolerance limit a scheduler packet delay budget (SPDB) is estimated and applied to a DBS weight algorithm in the scheduling.
The scheduling weight corresponds to the scheduling priority, and the UE's scheduling weight thus gets boosted, as described above, if the age of a packet bundle comprising a fixed number of packets is larger than the difference SPDB−Td, where Td is the expected transmission delay of a packet bundle counted from the time of the transmission thereof being scheduled to the time of the transmission being successfully received. That is:
Age of packet bundle=t_current−t_oldest
, wherein t_current stands for the point of time at which the scheduling weight was calculated for the UE, and t_oldest stands for the point of time when the first VoIP-packet of the packet bundle got identified in the scheduler.
If t_current>SPDB-Td+t_oldest, the scheduling weight is boosted by adding a weight bonus on the scheduling weight. This may for instance be done according to:
F=t_current>(SPDB−Td+t_oldest)?1:0
W=Age*WDBS+F*W_bonus;
That is, if t_current>(SPDB-Td+t_oldest) is true, the F=1, else F=0. Then a bonus weight W_bonus is added to the scheduling weight W accordingly, by multiplying it with 1 or 0.
The current scheduling scheme fails to consider e.g. the DRX impact to the delay sensitive packet. The DRX pattern of a UE is fixed, i.e. configured by Radio Resource Control (RRC) signaling, telling the UE when to enter sleep mode and when to be monitoring downlink channels.
VoIP packet is semi-static in that when the first packet arrives the consecutive packets arrive every 20 ms, but it is unknown when the first VoIP packet arrives. Bundling of the fixed number of VoIP packets without considering the configured DRX pattern of the UE will cause packet loss and QoS is sacrificed. In the DRX cycle that is configured for the UE, an active period denoted On Duration is configured during which the UE is active and monitors downlink channels. The remaining time of the DRX cycle, the UE can be inactive and turn off circuitry, thus saving battery.
This is a problem which may happen if there are any time domain restrictions introduced for any purpose. Besides DRX, and as mentioned earlier, such restriction may be introduced by features/schemes such as for instance Almost Blank Subframe (ABS) and in in enhanced Inter-Cell Interference Coordination (eICIC) schemes.
A problem of the current delay based scheduling as identified by the inventors of the present disclosure is that the delay budget SPDB is based on the current time tcurrent when the scheduling is performed and not on a future time instance when the bundled transmission is performed. Without taking into account possible time restrictions at the future time instance, the delay based scheduling might cause packet losses as is evident e.g. from the situation described with reference to
Other scheduling schemes besides the delay based scheduling also encounter difficulties due to such future time restrictions. In the minimum bit rate proportional fair scheduling for instance, such restrictions may lead to that a minimum bit rate cannot be guaranteed for a UE being in a DRX sleep period. This is described a bit more in the following.
In minimum bit rate proportional fair, the scheduling weight W is computed based on
wherein Rins tan tα is the instantaneous rate, e.g. bit rate, that the UE could currently get based on radio conditions estimated at the current time, a is a fraction of proportional fair ratio, and Ravg is the average rate of the UE at the current time. A minimum bit rate may be defined by an operator and be based on QoS requirement of the application and QoS Class Identifier (QCI). If the average rate Ravg is lower than the minimum bit rate, the UE will get a very high scheduling weight W so that the UE is scheduled immediately to fulfill the QoS requirement.
However, if the DRX sleep period is long, it may not be possible to guarantee minimum bit rate anymore. The average bit rate Ravg is computed at the current time and if the average bit rate at this time is larger than the minimum bit rate and if the UE is in bad radio condition, the UE will get low scheduling weight W according to the minimum bit rate proportional fair scheduling and will hence not be scheduled. The UE then waits for the next DRX on duration to transmit and the average bit rate will be much lower than the minimum bit rate. To schedule the UE at that time will make it impossible to fulfill the QoS requirement.
It is important to satisfy quality of service (QoS) requirements, whether it is in terms of keeping a delay budget or guaranteeing a received data rate, while at the same time allowing time constraints such as DRX or eICIC in order to reduce power consumption or reduce interference.
Briefly, in order to overcome the above problems, a scheduling is provided wherein knowledge about time domain restrictions introduced by different features, for example DRX, is used in the scheduling. It is predicted if transmission is possible at the transmit time of the bundled packets based on this knowledge. Depending on a predicted packet delay at future time instance, a scheduling weight is calculated, e.g. using the delay based scheduling weight function or minimum bit rate proportional fair scheduling. In case there is a time restriction in the future, the oldest packet might be transmitted without bundling. Thereby packet losses are reduced. The quality for these delay critical services can be improved by the present algorithm that involves for instance DRX cycle knowledge to calculate a UE scheduling priority.
In an embodiment, described next, DRX is used as the time restriction, restricting the possible scheduling occasions for the UE. Further, the concept of the present disclosure of introducing time restrictions in the packet scheduling is described in relation to and exemplified by delay based scheduling. It is however noted that other scheduling schemes may be used, e.g. proportional fair scheduling with a guaranteed minimum bit rate, and that the time restriction could be other than DRX.
It is assumed that packets can be identified as being either delay critical or delay non-critical. Such identification may for instance be made by identifying the packet as delay critical based on QoS class identifier in a packet header or other priority indicator. The length of DRX cycle, TDRX, is introduced in the scheduling algorithm when handling delay critical packets. An embodiment of an algorithm 20 according to the present disclosure is described with reference to
First, the age of the oldest packet at the current time t_current is computed, box 21.
The age Δt_0 of the oldest packet is defined as:
Δt_0=t_current−t_oldest;
, where t_oldest is the expected arrival time (or identified arrival time) of the oldest packet of a bundle of packets and t_current is the current time when scheduling is performed.
Next, still with reference to box 21, it is checked if the age Δt_0 of the oldest packet is smaller than or equal to the predefined packet delay budget (SPDB):
Is Δt_0<=SPDB?
If the age Δt_0 of the oldest packet is smaller than or equal to SPDB (box 24), then the age Δt_1 of the oldest packet at the next possible scheduling occasion is computed, box 25. The next possible scheduling occasion may for instance be the next DRX On Duration window if the UE is configured with a DRX cycle.
Δt_1=Δt_0+t_d
, where t_d is the time difference from the current time t_current to the next scheduling occasion, e.g. to the start of the next DRX On Duration window.
The DRX knowledge is thereby according to this embodiment introduced into the scheduler by using t_d. In other embodiments, other time restrictions that restrict the possible scheduling occasions are used instead or used in addition to DRX.
Scheduling packet delay budget (SPDB) is the delay budget that is used in order for the scheduling to fulfill the QoS requirement for a certain type of delay critical packets. The delay budget SPDB can be a parameter defined internally in a radio access node, e.g. evolved NodeB (eNB) for a scheduling of a packet in one wireless link direction link, that is, for uplink (from UE to eNB) or for downlink (from eNB to UE). A typical value may for instance be in the range 40 ms-50 ms. Such values are typically larger than the length of a DRX cycle.
If, at box 26, the age Δt_1 at the next possible scheduling occasion is larger than the SPDB, i.e. if Δt_1>SPDB, then the age Δt of the oldest packet is set equal to Δt_1 and scheduling weight is computed by using Δt_1 in the scheduling weight function and the oldest packet is scheduled and sent without bundling, as indicated in box 27.
If the age Δt_1 of the oldest packet is smaller than or equal to the SPDB, i.e. if Δt_1<=SPDB, then the age Δt of the oldest packet is instead set equal to Δt_0, and scheduling weight for the packet bundle is computed according to the delay based weight function using Δt_0 as indicated in box 28.
If in box 21 the age Δt_0 of the oldest packet is larger than delay budget (box 22), then the scheduling weight is again (as in box 28) calculated for the packet bundle according to the delay based weight function using Δt_0, as indicated in box 23.
The above exemplifying scheduling algorithm 20 for the case of delay based scheduling scheme can be summarized as follows:
Step 1: Compute the oldest packet age at the current time t_current:
Δt_0=t_current−t_oldest
Step 2: check if Δt_0 is smaller than the predefined packet delay budget (SPDB)
The wireless network 10 typically comprises various other network nodes, such as Mobility Management Entity (MME), or operation and maintenance (OM) nodes, packet data network gateways, mobility management entities, serving gateways etc. Such other network nodes are collectively and schematically illustrated at reference numeral 15 as Core network nodes.
The radio access node 12 may comprise a scheduler 14 for scheduling radio resources to the UEs 13 residing within its one or more coverage areas (also denoted cell(s)). The various embodiments of the scheduling algorithm according to the present disclosure may be implemented in such scheduler 14. However, it is noted that the scheduler 14 may be a standalone node, not integrated with the radio access node 12.
A method 30 is provided that may be performed in a network element 14 for scheduling a communication device 13 of a wireless network 10. The network element 14 may for instance comprise a scheduler of a radio access node 12 or be a standalone node. The method 30 comprises estimating 31 a scheduling metric of a first arrived packet at a future time instant t, taking into account time domain restrictions for the communication device 13 that restricts a future scheduling occasion. The scheduling metric may for instance be delay or bit rate.
The method 30 comprises determining 32 whether the estimated scheduling metric at the future time instant t is within limits of the scheduling metric. The limits of the scheduling metric may for instance be a delay budget or a minimum bit rate.
The method 30 comprises calculating 33, for the case the estimated scheduling metric is within limits of the scheduling metric, a scheduling weight for a packet bundle comprising the first arrived packet and at least one more packet, and else calculating a scheduling weight for the first arrived packet for transmission of the first arrived packet without bundling.
The method 30 comprises scheduling 34 the communication device 13 according to determined scheduling weight.
The method 30 is applicable to different scheduling schemes, for instance to delay based scheduling or to proportional fair scheduling with minimum guaranteed bit rate. The method 30 may thus predict the possibility of transmission of a packet bundle with maintained quality of service at a future transmit time based on knowledge of any time domain restrictions that might be introduced by different features such as for instance DRX or eICIC. Depending on the predicted packet delay at the future instant, the packet might be transmitted without bundling. This reduces the packet losses, in particular for delay based scheduling schemes, but also for other scheduling schemes.
In an embodiment, the limits of the scheduling metric comprise limits for meeting a quality of service of a traffic stream to which the first arrived packet belongs.
In an embodiment, the scheduling metric comprises a packet delay or a bit rate.
In different embodiments, the limits of the scheduling metric comprise a packet delay budget or a minimum bit rate.
In an embodiment, using delay based scheduling:
In a variation of the above embodiment:
In another variation of the above embodiment the determining 32 comprises determining that the first age, Δt_0, is larger than the packet delay budget and the calculating 33 comprises calculating a scheduling weight for the packet bundle comprising the first arrived packet and at least one more packet, for transmission of the packet bundle.
In an embodiment, the time domain restrictions for the communication device 13 comprises one or more of: configuration of discontinuous reception mode for the communication device 13, information about Almost Blank Subframe and information on enhanced Inter-Cell Interference Coordination schemes.
In an embodiment, the method 30 comprises, prior to the estimating 31 a scheduling metric, establishing that the packet comprises a delay critical packet.
The network element 14 comprises a processor 40 comprising any combination of one or more of a central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit etc. capable of executing software instructions stored in a memory 41, which can thus be a computer program product 41. The processor 40 can be configured to execute any of the various embodiments of the method as described for instance in relation to
In particular, a network element 14 is provided for scheduling a communication device 13 in a wireless network 10. The network element 14 is configured to:
The network element 14 may for instance be configured to perform the various steps by comprising a processor 40 and memory 41, the memory 41 containing instructions executable by the processor 40, whereby the network element 14 is operative to perform the various steps.
In an embodiment, the limits of the scheduling metric comprises limits for meeting a quality of service of a traffic stream to which the first arrived packet belongs.
In different embodiments, the scheduling metric comprises a packet delay or a bit rate.
In an embodiment, the limits of the scheduling metric comprise a packet delay budget or a minimum bit rate.
In an embodiment, the network element is configured to:
In a variation of the above embodiment, the network element is configured to:
In another variation of the above embodiment, the network element is configured to determine by determining that the first age, Δt_0, is larger than the packet delay budget and configured to calculate by calculating a scheduling weight for the packet bundle comprising the first arrived packet and at least one more packet, for transmission of the packet bundle.
In an embodiment, the time domain restrictions for the communication device 13 comprises one or more of: configuration of discontinuous reception mode for the communication device 13, information about Almost Blank Subframe and information on enhanced Inter-Cell Interference Coordination schemes.
In an embodiment, the network element is configured to, prior to the estimating a scheduling metric, establish that the packet comprises a delay critical packet.
Still with reference to
A data memory 43 may also be provided for reading and/or storing data during execution of software instructions in the processor 40. The data memory 43 may for instance be any combination of read and write memory (RAM) and read only memory (ROM).
The present disclosure also encompasses computer program 42 comprising computer program code for causing a network element 14 to perform the method for instance as described in relation to
The present disclosure also encompasses a computer program product 41 as above, and a computer readable means on which the computer program 42 is stored.
An example of an implementation using function modules/software modules is illustrated in
The network element 14 may comprise second means 52 for determining whether the estimated scheduling metric at the future time instant t is within limits of the scheduling metric. Such means may for example comprise processing circuitry adapted to perform this determining by using program code stored in a memory.
The network element 14 may comprise third means 53 for calculating, for the case the estimated scheduling metric is within limits of the scheduling metric, a scheduling weight for a packet bundle comprising the first arrived packet and at least one more packet, and else calculating a scheduling weight for the first arrived packet for transmission of the first arrived packet without bundling. Such means may for example comprise processing circuitry adapted to perform this calculating by using program code stored in a memory.
The network element 14 may comprise fourth means 54 for scheduling the communication device 13 according to determined scheduling weight. Such means may for example comprise processing circuitry adapted to perform this scheduling by using program code stored in a memory.
The network element 14 may comprise yet additional means (not illustrated in the
The function modules 51, 52, 53, 54 may be implemented using software instructions such as computer program executing in a processor and/or using hardware, such as application specific integrated circuits, field programmable gate arrays, discrete logical components etc.
The invention has mainly been described herein with reference to a few embodiments. However, as is appreciated by a person skilled in the art, other embodiments than the particular ones disclosed herein are equally possible within the scope of the invention, as defined by the appended patent claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2014/050898 | 7/17/2014 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/010467 | 1/21/2016 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/SE2014/050898 | Jul 2014 | US |
| Child | 15325990 | US |
