2005-04-08 Assigned to LUCENT TECHNOLOGIES INC. reassignment LUCENT TECHNOLOGIES INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: LEE, JUNG-AH, RAO, ANIL M.
2011-06-20 Assigned to ALCATEL-LUCENT USA INC. reassignment ALCATEL-LUCENT USA INC. MERGER (SEE DOCUMENT FOR DETAILS). Assignors: LUCENT TECHNOLOGIES INC.
2011-06-23 Assigned to ALCATEL LUCENT reassignment ALCATEL LUCENT ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ALCATEL-LUCENT USA INC.
In an embodiment of the method, an estimated use of an uplink resource by prioritized users, if transmission rates for the prioritized users are granted, is determined. The transmission rates are then granted if the estimated use of the uplink resource is less than or equal to an available amount of the uplink resource. Otherwise, the granting of transmission rates of the prioritized users is controlled in order of lower priority prioritized users to higher priority prioritized users until the estimated use of the uplink resource by the prioritized users falls within the available amount of the uplink resource for the channel.
FIG. 1 illustrates a portion of a UMTS wireless communication network. As shown, user equipment (UE) wirelessly communicates with a Node-B serving the communication needs of a geographic area (often referred to as a cell or collection of cells). The UE may be a mobile phone, wireless equipped PDA, wireless equipped laptop, etc. The Node-B is often referred to as a base station in other communication standards. The Node-Bs communicate with a radio network controller (RNC). The RNC routes, for example, data between Node-Bs or on to another communication network such as the internet.
Communication from a Node-B to a UE is referred to as downlink or forward link communication, and communication from a UE to a Node-B is referred to as uplink or reverse link communication. In the uplink, various communication channels may exist.
In the UMTS uplink, a EDCH (Enhanced Dedicated Channel) is used to provide high-speed scheduled data service. In the EDCH, a distributed scheduling approach is taken where scheduling decisions are made at each Node-B and communicated to the UEs. A Node-B scheduler allocates the TFI (transport format indication) or TFC (transport format combination) that a UE can use, based on the available rise-over-thermal (RoT) target of a cell. Two types of rate scheduling approaches are supported in UMTS. In relative rate scheduling, a UE sends a 3 stage rate request relative to its current rate, based on its power limit and buffer status. The Node-B scheduler makes scheduling decisions and sends a relative rate grant (RG) message. In absolute rate scheduling, each UE reports its power limit and buffer status to the Node-B. The Node-B determines the allowed peak transmission rates and sends either the peak TFI or the peak traffic-to-pilotratio (TPR) that a UE can use for EDCH communication.
The 3GPP contributions "Reference Node-B scheduler for EUL," TSGR1#35(03)1246, 3GPP TSG RAN WG1, Qualcomm, Lisbon, Portugal, November 2003., and "Description of EUL scheduler," TSGR1 Rel-6 Ad-hoc(04)0698, 3GPP TSG RAN WG1, Samsung, Cannes, France, June 2004., describe scheduling algorithms based on a greedy filling of available RoT. These scheduling methods compute a priority function based on the requested rate and the average rate of the UEs. The scheduler grants the right to transmit starting from the highest priority UE or user, then, successively to the lower priority users. However, this method may penalize high-priority users, when the available RoT is smaller than what is required to support all the users rate requests.
The present invention provides a scheduling method that maximizes the likelihood that a user's (e.g., a UE's) requested rate is granted, without penalizing high-priority users. The scheduler processes users starting from the lowest priority. The method supports both relative and absolute rate scheduling. The method is easy to implement and the computational complexity is particularly low, when the cell load is small.
In an embodiment of the method, an estimated use of an uplink resource by prioritized users, if transmission rates for the prioritized users are granted, is determined. The transmission rates are then granted if the estimated use of the uplink resource is less than or equal to an available amount of the uplink resource. Otherwise, the granting of transmission rates of the prioritized users is controlled in order of lower priority prioritized users to higher priority prioritized users until the estimated use of the uplink resource by the prioritized users falls within the available amount of the uplink resource for the channel. The uplink resource may be load, rise-over-thermal, etc.
FIG. 2 illustrates a flow chart of a method of controlling transmission rates according to an embodiment of the present invention.
First, an embodiment of a relative rate scheduling method according to the present invention will be described. This will be followed by a description of an absolute rate scheduling method embodiment of the present invention.
In relative rate scheduling, a UE sends a 1 bit rate request (RR) signal to a Node-B. The Node-B makes scheduling decisions based on, for example, target loading. While this embodiment will be described using the example of load as the uplink resource for basing scheduling decisions, it will be appreciated that other uplink resources such as rise-over-thermal (RoT) may be used for basing scheduling decisions.
The available loading that can be allocated to the EDCH is computed. Then, a hypothetical or estimated loading is computed assuming all EDCH rate requests are granted. If the estimated loading exceeds the available loading, EDCH TFI is reduced starting from the lower priority user until the loading condition is met. Once the loading condition is met, rate requests for the remaining higher priority users are granted. This scheduling method will now be described in greater detail below.
where Tc is a time constant.
where the RSSI is computed every scheduling period as the slot-rate RSSI averaged over a period of the scheduling interval, and Pth is the well-known, measurable quantity, thermal noise power.
where Ec/Io is the received energy per chip to total received power, (βe/βc)2 is the transmit power ratio for EDCH, and Nmulticode is the number of multicodes used.
The last summation is for all on-going HARQ retransmissions of EDCH users.
Here, RG stands for relative rate grant.
8. Grant all users rate requests if estimated load is less than or equal to the available load. If ηj hyp≦nj available, the scheduler grants all users' rate requests.
9. Determine granted rates in reverse priority order If estimated load is greater than the available load. If ηj hyp>nj available, the scheduler begins selectively reducing the rates of the users starting from the lowest priority user. After each rate reduction, the scheduler updates the estimated load in light of the rate reduction. When the estimated load becomes less than or equal to the available load, the scheduler discontinues the rate reduction process and grants the requested rates of the remaining higher priority users. This rate reduction process will now be described in detail with reference to the flow chart illustrated in FIG. 2.
As shown, in step S10, processing starts with the lowest priority user. Then, in step S12, the scheduler determines if the rate request for this user is a step down request. If so, the rate request is granted in step S14, and processing proceeds to step S26.
If, in step S12, the scheduler determines that the rate request is not a step down, then in step S16, the scheduler determines if the rate request is a no change request. If so, then processing proceeds to step S14 where the scheduler assigns a rate grant of step down. Namely, if the UE requests to transmit at the same rate as the previous transmission, the scheduler decreases the transmission rate. Processing then proceeds to step S26.
If, in step S16, the scheduler determines that the rate request is not a no change request, then the rate request is a step up request. In step S18, the scheduler treats the rate request as a no change request, and in step S20 determines a new possible estimated load assuming the rate request is a no change request. Subsequently, in step S22, the scheduler determines if the new possible estimated load is less than or equal to the available load. If so, then the scheduler assigns a rate grant of no change. Namely, if the UE requests to transmit at higher rate than the previous transmission, the scheduler assigns the same transmission rate as the previous transmission. Processing then proceeds to step S26. However, if in step S22, the scheduler determines that the new possible estimated load is greater than the available load, then processing proceeds to step S14 where the scheduler assigns a rate grant of step down. Processing then proceeds to step S26.
In step S26, the scheduler updates the estimated load based on the rate granted to the UE under consideration. The scheduler then determines if the updated, estimated load is less than or equal to the available load in step S28. If so, then the scheduler grants the rate requests of all high priority users and processing ends. However, if the estimated load is still greater than the available load in step S28, then in step S32, the scheduler determines if a next higher priority user exists or not. If not, then processing ends. If a next higher priority user exists, then processing returns to step S12 for the next higher priority user.
In absolute rate scheduling, a UE sends scheduling information such as available power and queue size to the Node-B. The Node-B scheduler estimates the required maximum TFC for each UE. The scheduler then determines a maximum TFC allowed for each UE similar to the relative rate scheduling embodiment described above. This absolute rate scheduling methodology will be now described in more detail.
1. Calculate required rate: The Node-B determines a UE's required rate based on the UE's buffer status and power limits. For example, the required rate may be determined as in Eq. (1). In a special case, the required rate may be characterized as in equation (2). Namely, with respect to equation (2), if the Node B determines a required rate that is greater than the previous transmission rate for the UE, the required rate is characterized as a step up request; if the Node-B determines the required rate is the same as the previous transmission rate for the UE, the required rate is characterized as a no change request; and if the Node-B determines the required rate is less than the previous transmission rate for the UE, the required rate is characterized as a step down request.
2. Calculate available loading and hypothetical (or estimated) loading. The available and estimated loading may be determined in the same manner as described above in steps 5 and 7 for relative rate scheduling.
4. Grant all users rate requests. If ηj hyp≦nj available, the scheduler grants all users' rate requests.
5. Determine granted rates in reverse priority order. If ηj hyp>nj available, the scheduler selectively reduces the rates for users starting from the lowest priority user. After each rate reduction, the scheduler updates the estimated load in light of the rate reduction. When the estimated load becomes less than or equal to the available load, the scheduler discontinues the rate reduction process and grants the requested rates of the remaining higher priority users. For example, based on the characterization of the rate requests in step 1, the scheduler may employ the rate reduction process of FIG. 2 described in detail above.
When reducing the requested rate in step S14, the scheduler can step down rates by a fixed decrement as in relative rate scheduling, or the scheduler may aggressively step down a user's rate all the way down to an autonomous set rate (e.g., a minimum set rate). It will also be appreciated that other methodologies for determining the amount to step down the transmission rate may be used without departing from the present invention.
The invention being thus described, it will be obvious that the same may be varied in many ways. For example, while the embodiments described above concerned the EDCH in a UMTS wireless communication system, the present invention is not limited in application to this channel or a UMTS system. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.
granting transmission rates, at a network node, in order of lower priority prioritized users to higher priority prioritized users until an estimated use of an uplink resource by the prioritized users falls within an available amount of the uplink resource for the channel, the estimated use being based on determined transmission rates for the prioritized users, the priority of a particular user being determined based on a requested rate of the particular user and an average allocated rate of the particular user, the granting retaining the first priority order of the users.
2. The method of claim 1, wherein the granting step selectively reduces the determined transmission rate of the prioritized users in order of lower priority prioritized users to higher priority prioritized users until the estimated use of the uplink resource by the prioritized users falls within the available amount of the uplink resource to obtain the granted transmission rates.
3. The method of claim 2, wherein the granting step selectively reduces the determined transmission rate by a fixed decrement amount.
4. The method of claim 2, wherein the granting step selectively reduces the determined transmission rate to a minimum transmission rate.
5. The method of claim 1, wherein the granting step controls the granted transmission rate of at least one prioritized user based on the determined transmission rate and a previous granted transmission rate.
6. The method of claim 5, wherein the granting step decreases the determined transmission rate of the prioritized user to obtain the granted transmission rate when the determined transmission rate is unchanged from the previous granted transmission rate.
setting the granted transmission rate of the prioritized user to the previous granted transmission rate if the determining step determines that the maintaining results in the estimated use of the uplink resource falling within the available amount of the uplink resource.
decreasing the determined transmission rate to obtain the granted transmission rate if the determining step determines that the maintaining does not result in the estimated use of the uplink resource falling within the available amount of the uplink resource.
9. The method of claim 8, wherein the decreasing step decreases the determined transmission rate by a fixed decrement value.
10. The method of claim 8, wherein the decreasing step decreases the determined transmission rate to a minimum transmission rate.
11. The method of claim 5, wherein the granting step sets the granted transmission rate to the determined transmission rate if the determined transmission rate is less than the previous granted transmission rate.
12. The method of claim 1, wherein once the estimated use of the uplink resource falls within the available amount of the uplink resource, the granting step sets the granted transmission rates of the remaining prioritized users equal to the determined transmission rates for the remaining prioritized users.
the granting step is performed if the estimated use of the uplink resource exceeds the available amount of the uplink resource.
14. The method of claim 1, wherein the determined transmission rate is determined based on a relative rate request received from the user.
15. The method of claim 1, wherein the determined transmission rate is an absolute rate determined based on operating parameters received from the user.
16. The method of claim 1, wherein the wireless communication system is a UMTS system, and the channel is an enhanced dedicated channel.
granting the transmission rates, at the network node, in order of lower priority prioritized users to higher priority prioritized users, if the estimated use of the uplink resource is less than or equal to an available amount of the uplink resource, the granting retaining the first priority order, the priority of a particular user being determined based on a requested rate of the particular user and an average allocated rate of the particular user.
determining the available amount of the uplink resource.
determining the transmission rates for the prioritized users.
"Description of EUL scheduler," TSGRI Rel-6 Ad-hoc (04)0698, 3GPP TSG RAN WGI, Samsung, Cannes, France, Jun. 2004.
"Reference Node-B Scheduler for EUL," TSGRI #35 (03)1246, 3GPP TSG RAN WGI, Qualcomm, Lisbon, Portugal, Nov. 2003.
3GPP TR 25.896 Version 2.0.0, Feasibility study for enhanced uplink for UTRA FDD. Third Generation Partnership Project, Mar. 2004.
ES2292492T3 (en) 2008-03-16 Method for asigancion power for a downlink communication system division multiple access-code.