The present invention relates to methods and arrangements in a communication network system, in particular to an arrangement allowing for controlling an uplink data rate as well as a method for such control.
Load control and scheduling are two key functions to manage the radio resources in wideband code division multiple access (WCDMA) systems. The scheduler distributes the radio resource among user equipments (UEs) while the load control estimates the available scheduling headroom that the scheduler may use. This is illustrated in
In the uplink, the common radio resource shared among the user terminals is the total amount of tolerable interference, which is defined as the average interference over all the antennae. A relative measure of total interference is rise over thermal (ROT), i.e. the total interference relative to thermal noise.
Load factor represents the portion of uplink interference that a certain channel of a certain user terminal generates, which is defined as the interference due to the channel of that user terminal divided by the total interference. The total load factor of different channels equals to the sum of load factors due to different channels.
The uplink load control estimates the resource utilization in terms of cell load generated by different type of traffic and channels of each cell based on measurements, such as, rise over thermal and CIR; the load control also regulates the maximum available scheduling headroom that the scheduler can use to schedule user equipments for transmitting data in the cell.
The scheduler distributes the available scheduling headroom among the user equipments which have data to transmit, either one at a time, time division multiplexing (TDM) scheme, or several at a time, code division multiplexing (CDM) scheme. The scheduler determines when a certain user equipment is allowed to transmit and at what maximum data rate. In the existing scheduling framework, two scheduling grants, absolute grants and relative grants are used to control data transmission limit of each user equipment. The data transmission limit is expressed in terms of the maximum E-TFC. The E-TFC for different data rate is formulated by power offset between the enhanced dedicated physical data channel (E-DPDCH) and dedicated physical control channel (DPCCH), as shown in equation (1):
pwroffgrant
wherein:
The scheduler signals the scheduled user equipment with the maximum E-TFC or the maximum power offset via scheduling grant. To determine the scheduling grants, the uplink load generated by each scheduled user equipment needs to be estimated.
The uplink load may be estimated based on carrier-to-interference ratio (CIR) measurements. Suppose user k has N uplink channels, the load generated by the user equipment can be calculated by equation (2):
wherein:
The load parameters are system parameters selected by the radio network controller (RNC).
In the existing solution the scheduler controls the user equipment data rate by limiting the maximum E-TFC. To estimate the maximum E-TFC for a user equipment, the load generated by each user equipment in the cell needs to be estimated. There are several problems for EUL scheduler to estimate the load in the previously known systems:
The inaccuracy in the load estimation causes large oscillations in the actual cell load or rise over thermal; To ensure stability of the system, a large load margin is introduced to prevent the instability. However, it is difficult to configure the load margin for all different scenarios. A conservative large load margin may result in inefficiently utilization of resource while a small load margin may cause large oscillations in rise over thermal, both have negative impact on the system throughput.
The addressed problems may be mitigated by:
However, for all the schemes a precondition to achieve evident performance gain (both increased throughput and decreased rise over thermal oscillation) is that system delay is small and scheduling as well as load estimation are performed sufficiently frequently (especially when with high target rise over thermal). This is because with large system delay the load may vary a lot from the time when the EUL scheduler determines the power offset (E-TFC) that can be granted to the time when the granted E-TFC is used by the user equipment. This may lead to distinct load estimation error at the time the grant is used by the user equipment, even though the load is accurately estimated at the time the EUL scheduler issues the grants. Thus, the benefits of these schemes are decreased.
On the other hand, decreasing system delay is not an easy task when signaling procedure is involved, and more frequent execution of scheduling implies higher signaling overhead, especially for the third alternative addressed above, where two power control loops are needed.
Accordingly, one objective with embodiments of the present invention is to provide methods and arrangements in a communication network node of controlling an uplink data rate between a user equipment and a communication network node, which are communicating with each other on uplink and downlink data channels over a radio interface, whereby an available scheduling headroom is distributed by a scheduler between user equipments which are to be scheduled.
According to a first aspect of embodiments of the present invention this objective is achieved through a method in a communication network node as defined in the characterizing portion of claim 1, which specifies that the uplink data rate is controlled by the step of sending a scheduling grant signalling comprising a granted headroom to said user equipment, based on which said user equipment is able to select a transport format combination.
According to a second aspect of embodiments of the present invention this objective is achieved through a method in a user equipment as defined in the characterizing portion of claim 5, which specifies that the uplink data rate is controlled by the steps of: receiving a scheduling grant signalling comprising a granted headroom from said communication network node; and, selecting a transport format combination based on said received scheduling grant.
According to a third aspect of embodiments of the present invention this objective is achieved through a communication network node as defined in the characterizing portion of claim 8, which specifies that the uplink data rate is controlled by a communication network node that comprises a transmitting unit arranged to send a scheduling grant signalling comprising a granted headroom to said user equipment, based on which said user equipment is able to select a transport format combination.
According to a fourth aspect of embodiments of the present invention this objective is achieved through a user equipment as defined in the characterizing portion of claim 12, which specifies that the uplink data rate is controlled by a user equipment that comprises: a receiving unit arranged to receive a scheduling grant signalling comprising a granted headroom from said communication network node; and, a processing unit arranged to select a transport format combination based on said received scheduling grant.
Further embodiments are listed in the dependent claims.
Thanks to the provision of methods and arrangements, which change the scheduling grant to be scheduled power or interference headroom of UE, and move scheduling headroom to E-TFC mapping to UE side, the uplink performance is improved without increasing the system overhead. At the network side the load control & EUL scheduler can be performed at a relatively low rate. At the UE side the scheduling headroom to E-TFC mapping can be performed fairly fast.
Still other objects and features of embodiments of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.
For a better understanding, reference is made to the following drawings and preferred embodiments of the invention. In the drawings, wherein like reference characters denote similar elements throughout the several views:
According to a preferred embodiment of the present invention, the communication system is herein described as an HSPA communication system. The skilled person, however, realizes that the inventive method and arrangement works very well on other communications systems as well, such as CDMA2000. The user equipments 18 may be mobile stations such as mobile telephones (“cellular” telephones) and laptop computers with mobile termination and thus may be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with the RAN.
The core idea of this invention is to change the scheduling grant to be scheduled power or interference headroom of UE, and move the mapping between the headroom and E-TFC to the user equipment side. The invention includes that:
This is illustrated in
When comparing embodiments of the present invention with prior arts, the main difference is the scheduling grant. The proposed scheduling grant is power or interference headroom, instead of power offset or E-TFC. To be more explicit, the follow alternatives may be considered as the scheduling grant:
The proposed scheduling grant directly reflects to what extent the radio resource is utilized, and thus provides the possibility to more effectively keep the radio resource usage at the desired level. Moreover, by controlling only the average resource usage the uplink load control and EUL scheduling may be performed at a relatively slow rate and system delay is not a critical issue.
Another difference between embodiments of the present invention and prior art, is that the mapping between the scheduling headroom and E-TFC is moved from the network system side to the user equipment side. The existing E-TFC selection algorithm is modified to take the granted headroom into consideration, which is further described below.
With Tx power based scheduling grant
P
total=min(Tmax,Pmax) (4)
P
total
=P
DPCCH•(1+ΔE-DPDCH+ΔE-DPCCH) (5)
ΔE-DPDCHmax=min(Tmax,Pmax)/PDPCCH−ΔE-DPCCH−1 (6)
With (averaged) Rx power based scheduling grant
P
total=min(Rmax/gs,Pmax) (7)
ΔE-DPDCHmax=min(Rmax,gs,Pmax)/PDPCCH−ΔE-DPCCH−1 (8)
The power based load estimation is adopted in the scheduling headroom to E-TFC mapping which makes load estimation more accurate at the time the maximum supportable E-DPDCH to DPCCH power offset and the E-TFC to adopt are determined. Besides, at UE side the scheduling headroom to E-TFC mapping may be made fairly fast (every 2 ms TTI) with minor delay since the maximum supportable E-DPDCH to DPCCH power offset is determined by the UE itself and no signaling process is involved. This evidently decreases the load estimation error at the time the UE transmits with the selected E-TFC. Thus, the uplink performance is evidently improved.
It is shown clearly in the diagrams that the proposed solution increases the uplink capacity (
According to a general embodiment of the present invention a procedure in a communication network node of controlling an uplink data rate between a user equipment and said communication network node, which are communicating with each other on uplink and downlink data channels over a radio interface, as shown in
According to some embodiments, said scheduling grant is an upper limit of a receive power contribution of said user equipment.
According to some embodiments, said scheduling grant is an upper limit of a transmit power contribution of said user equipment determined by the steps of:
According to some embodiments, said scheduling grant is a portion of rise over thermal.
According to some embodiments, said step of distributing an available scheduling headroom between user equipments comprises the step of distributing the available scheduling headroom equally between said user equipments.
According to a general embodiment of the present invention a procedure in a user equipment of controlling an uplink data rate between a user equipment and said communication network node, which are communicating with each other on uplink and downlink data channels over a radio interface, as shown in
According to some embodiments, said step of selecting a transport format combination with a transmit power based scheduling grant, further comprises the steps of:
According to some embodiments, said step of selecting a transport format combination with a received power based scheduling grant, further comprises the steps of:
The Node B 15 comprises a transmitting unit 82 including a radio transmitter. The Node B 15 further comprises a receiving unit 81 including a receiver. The transmitter 82 is transmitting data to a receiver 87 of the user equipment 18 over a radio interface on the downlink channel 16. The receiver 81 is receiving data from the user equipment 18 on the uplink channel 17. Node B 15 further comprises an uplink load control unit 83 arranged to provide a scheduler 84, also comprised in Node B 15, with a total scheduling headroom of a cell. The scheduler 84 is arranged to distribute the available scheduling headroom between user equipments 18 which are to be scheduled. The transmitting unit 82 is arranged to send a scheduling grant signalling comprising a granted headroom to said user equipment 18, based on which said user equipment 18 is able to select a transport format combination.
According to some embodiments, said scheduling grant is an upper limit of a receive power contribution of said user equipment 18.
According to some embodiments, said scheduler 84 is further arranged to determine said scheduling grant being an upper limit of a transmit power contribution of said user equipment 18 by performing the steps of:
According to some embodiments, said scheduling grant is a portion of rise over thermal.
According to some embodiments, said scheduler 84 is arranged to distribute the available scheduling headroom equally between said user equipments 18.
The user equipment 18 comprises a transmitting unit 86 including a radio transmitter. The radio transmitter 86 is arranged to transmit data packets to the receiver 81 of the Node B 15 over the radio interface on the uplink channel 17. The UE 18 further comprises a receiving unit 87 including a receiver. The receiver 87 is arranged to receive data packets transmitted from the transmitter 82 of the Node B 15 on the downlink channel 16. The receiving unit 87 is further arranged to receive a scheduling grant signalling comprising a granted headroom from said communication network node. The UE 18 further comprises a processing unit 85 arranged to select a transport format combination based on said received scheduling grant.
According to some embodiments, said processing unit 85 is arranged to select a transport format combination with a transmit power based scheduling grant, by performing the steps of:
According to some embodiments, said processing unit 85 is arranged to select a transport format combination with a received power based scheduling grant, by performing the steps of:
As has been described above, the embodiments of the present invention is advantageous over prior art. Some of these advantages are that load estimation error due to either inaccurate load estimation during the EUL scheduler procedure or large system delay in scheduling headroom to E-TFC mapping is avoided; the need to have fast load control and scheduler operation at system side is mitigated; there is no increase in signalling overhead; increased throughput (with fast E-TFC selection at UE side) is obtained; decreased rise over thermal oscillation and less high rise over thermal peaks are obtained; and, it is easy to implement in existing systems.
Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
Expressions such as “including”, “comprising”, “incorporating”, “consisting of”, “have”, “is” used to describe and claim embodiments of the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural and vice versa.
Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/SE09/51209 | 10/23/2009 | WO | 00 | 4/13/2012 |