WO2011028369A1

WO2011028369A1 - Uplink resource assignment in a wireless communication network

Info

Publication number: WO2011028369A1
Application number: PCT/US2010/044940
Authority: WO
Inventors: Dan Tayloe; James Chiang; Shalini Gulati
Original assignee: Motorola Mobility, Inc.
Priority date: 2009-09-02
Filing date: 2010-08-10
Publication date: 2011-03-10

Abstract

An apparatus and method for spectrally efficient uplink resource assignment in a wireless communication network includes a first step (200) of defining a share pool in a time slot for use in a spectrally efficient distribution of uplink resources. A next step (202) includes calculating a maximum carrier-to-interference ratio that a given user equipment (102) can generate when using its maximum power on a single uplink resource share. A next step (204) includes determining how many shares each user equipment (102) can support at a lowest rate modulation coding scheme. A next step (206) includes summing the number of shares that can be support at a lowest rate modulation coding scheme for all user equipment (102). A next step (208) includes assigning spectrally efficient uplink resources based upon the given user equipment fraction of shares that can be supported at a lowest rate modulation coding scheme compared to total sum of shares that can be supported at a lowest rate modulation coding scheme across all user equipment (102).

Description

UPLINK RESOURCE ASSIGNMENT IN A WIRELESS COMMUNICATION

NETWORK

FIELD OF THE INVENTION

The present invention relates generally to wireless radio communication and, in particular, to uplink resource assignment in a wireless communication network.

BACKGROUND OF THE INVENTION

In 4G communication systems, such as the Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX) communication systems, uplink data channel resources are allocated to user equipment as they are selected on the uplink. Uplink resource assignment is finished when all the uplink channel resources are assigned.

The 4G system operators have a range of operational expectations when it comes to resource assignment. On one end of the spectrum, some system operators may want to see the uplink data channel resources equally divided among the user equipment. This would give the users a "fair" share of the data channel resources. Other system operators may wish to see maximum system capacity and thus would want the data channel resources assigned among the user equipment in a way that gives maximum spectral efficiency among the user equipment. In either case, the existing allocation scheme for LTE or WiMAX does not accomplish either goal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims. However, other features of the invention will become more apparent and the invention will be best understood by referring to the following detailed description in conjunction with the accompanying drawings in which:

Figure 1 illustrates an example of a communication system in accordance with the present invention; and Figure 2 illustrates an example of a method in accordance with the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention provides an uplink allocation technique that strikes a balance between best spectral efficiency and resource fairness. In particular, the present invention takes the available uplink resources (i.e., Physical Resource Blocks or PRBs) and splits them by a system specified percentage between fairness shares and spectrally efficient shares for user equipment (UE). The actual percentage can be set by the communication network operator. The default could be to set aside a small percentage (10 to 15%) of the resources for spectral efficiency. However, the network operator may have a problem site that is heavily overloaded, and the network operator may chose for that particular site to increase the spectral efficiency percent (e.g., 50%) in order to get best RF users to complete communications faster and thus improve the site's total throughput at the expense of the throughput of poorer RF users.

Fairness shares (e.g., PRBs) are equally divided among the UEs. Fairness shares that one UE does not need are offered to other fairness share UEs or added to the spectrally efficient pool of shares.

Spectrally efficient shares are assigned to UEs based on an RF metric such as the maximum Carrier-to-interference ratio (C/I) a UE is capable of in the reverse link. A list of UEs is arranged in order of highest maximum C/I capability to lowest maximum C/I capability. Spectrally efficient shares are allocated to UEs with respect to their order on the list, as detailed below. If a UE cannot consume all of its shares of spectrally efficient resources, the left over resources (PRBs) are offered to the next UE in the list. Specifically, once selected, the users are tested one by one to see if they can make use of the uplink resources offered to them. If they cannot make use of all the resources, the excess is offered to the next user being tested in addition to the resources (fairness share) they were originally going to be offered. As a result, all UEs are provided a mixture of "fairness" and "spectrally efficient" PRBs depending on the fairness/spectrally efficient resource split and the Maximum C/I capability of each UE. The following description focuses on embodiments of the invention applicable to 4G communication systems such as LTE and WiMAX. For example, the present invention can be implemented for LTE evolved NodeBs (eNB). The present invention could also be applied to the WiMAX base stations. However, it will be appreciated that the invention is not limited to these applications but may be applied to many other cellular communication systems such as a 3 GPP (Third Generation Partnership Project) E-UTRA (Evolutionary UMTS Terrestrial Radio Access) standard, a 3GPP2 (Third Generation Partnership Project 2) Evolution communication system, a CDMA (Code Division Multiple Access) 2000 1XEV-DV communication system, a Wireless Local Area Network communication system as described by the Institute of Electrical and Electronics Engineers 802.xx standards, for example, the 802.1 la/HiperLAN2, 802.1 lg, 802.16, or 802.21 standards, or any of multiple other proposed ultra wideband communication systems. Therefore, as used herein the term eNB can also represent a base station, access point, NodeB, or other similar device, and the term user equipment can also represent a mobile station, subscriber station, access terminal, and the like.

Figure 1 shows a communication network in accordance with the present invention. An eNB 100 is serving one or more UE 102. During a communication time slot (i.e., uplink subframe or transmission time interval (TTI)), one or more UE will request 104 uplink access to the eNB. The processor 110 of the eNB allocates uplink resources (i.e., PRBs) in that communication time slot to these requesting UEs 102, in accordance with the present invention. The communication network defines how the uplink resources are split between a fairness share pool and spectrally efficient share pool, which is known to the eNB 100 and stored in memory 112. The portion of the fairness shares are divided equally by the eNB among the uplink-requesting UEs in that communication time slot. The processor 110 of the eNB then calculates how the spectrally efficient share pool is divided among the uplink-requesting UEs in that time slot. First, a calculation is made in the processor 110 of the maximum C/I a given UE could generate into the eNB if it used its maximum power on a single resource (such as a physical resource block or PRB). This is called the "Maximum C/I Capability" of that UE.

Second, the minimum supportable C/I for a lowest MCS rate PRB is used to determine by processor 110 how many of these lowest MCS rate PRBs each UE can support. This lowest MCS rate C/I is called "MCS 0 C/I." The number of MCS 0 C/I PRBs that can be supported is:

Maximum C/I Capability (dB)-(MCS 0 C/I (dB)) number of MCS 0 C/I PRBs = 10 ^~°

Third, the processor 110 sums up across all the UEs that are being given a spectrally efficient resource assignment at this period of time (i.e., LTE subframe or TTI) the total number of MCS 0 PRBs that can be supported across all users.

Fourth, the processor 1 10, through the transceiver 108, assigns 106 each UE his fraction of PRBs from the spectrally efficient PRB resource pool as calculated by his number of supported MCS 0 PRBs divided by the total MCS 0 PRBS across all the UEs assigned to this uplink subframe or TTI.

In practice, the present invention provides a mechanism for determining the most spectrally efficient assignment of resources to a group of uplink UEs. The above algorithm is based on the observation that maximum spectral efficiency occurs when all resources are assigned such that they all end up using the same modulation and coding scheme (MCS), i.e., all require the same uplink C/I or MCS. This is readily accomplished by calculating the "max C/I capability," or the C/I that the UE could generate if all power were concentrated on a single uplink resource (e.g., an LTE resource block). Next, break this up into a linear integer number per each UE. For LTE, the number of MCS 0 PRBs that the Max C/I could support is used. For example, MCS 0 = -7 dB C/I, UE #1 has Max C/I capability of 20 dB, UE #1 can then support:

20-(-7)

501 MCS 0 C/I PRBs = 10 ¹⁰ This linear number is summed across all UEs, and each UE is assigned the fraction of data resources (like LTE PRBs) corresponding to each UE's fraction of the total sum of the linear number across all UEs, as follows: assigned PRBs

(number of supported MCS 0 C/I PRBs) total number of PRBs ·

(total number of MCS 0 C/I PRBs)

Example

Assuming that there are a total of 40 PRBs available to be allocated to four UEs with Max C/I capabilities of 13 dB, 10 dB, 8 dB, and 5 dB C/Is, respectively. Assuming MCS 0 has a lowest supportable C/I of -7 dB:

13 dB corresponds to 100 MCS 0 C/I PRBs.

10 dB corresponds to 50 MCS 0 C/I PRBs.

8 dB corresponds to 32 MCS 0 C/I PRBs.

5 dB corresponds to 16 MCS 0 C/I PRBs.

Therefore, the sum across all UEs totals 198 MSC 0 PRBs. Breaking up the 40 available uplink PRBs is done as follows:

UE with 13 dB Max C/I would be assigned: 40* 100/198 = 20 PRBs

UE with 10 dB Max C/I would be assigned: 40*50/198 = 10 PRBs

UE with 8 dB Max C/I would be assigned: 40*32/198 = 6 PRBs

UE with 5 dB Max C/I would be assigned: 40* 16/198 = 3 PRBs

Due to round off error, this is 39 out of 40 PRBs. The extra PRB can be given to the best UE. All of these PRBs end up with roughly the same C/I requirements of 0 dB C/I per PRB after power splitting. For example, if one starts with a maximum power capability of 10 dB (from the second UE example above example) and splits this total power across 10 PRBs, the power per PRB is 10 dB - 10*logl0(10 PRBs) or 0 dB. If one starts with a maximum power capability of 8 dB (from the third UE example above) and split this total power across 6 PRBs, the power per PRB is 8 dB - 10*logl0(6 PRBs) or 0.22 dB.

The power per PRB for the four UEs above turn out to be:

UE with 13 dB: 13 - 10*logl0( 20 PRBS) = 0 dB

UE with 10 dB: 10 - 10*logl0( 10 PRBS) = 0 dB

UE with 8 dB: 8 - 10*logl0( 6 PRBS) = 0.22 dB

UE with 5 dB: 5 - 10*logl0( 3 PRBS) = 0.23 dB

For each of the examples given above, the power per PRB ends up to be about 0 db C/I. It should be noted that power computations (i.e., 10 to the Ν^Λ power) may take a significant amount of time and that these computations can be approximated using look up tables based up 1 dB incremental step over a range from -7 to +40 dB for example.

Figure 2 illustrates a method for spectrally efficient uplink resource assignment in a wireless communication network. The method includes a first step 200 of defining a pool of uplink resource shares in a time slot for use in a spectrally efficient distribution of uplink resources. Preferably, this is in addition to defining a pool of uplink resource shares in a time slot for use in fairness distribution of uplink resources, wherein the share pools for both the spectrally efficient distribution of uplink resources and the fairness distribution of uplink resources is divided among the total uplink resources for a time slot.

A next step 202 includes calculating a RF metric such for a given user equipment, such as calculating a maximum carrier-to-interference ratio (i.e., Maximum C/I capability) RF metric that a given user equipment can generate when using its maximum power on a single physical resource block in this time slot. Alternatively, the RF metric can be a Receive Signal Strength Indicator, Channel Quality Index, and the like. In one embodiment, this step includes arranging a list of UEs in order of highest maximum C/I capability to lowest maximum C/I capability. Preferably, this step calculates a linear equivalent of the RF metric.

A next step 204 includes determining how many shares each user equipment can support based upon the RF metric, such as determining physical resource blocks at a lowest rate modulation coding scheme in this time slot. In one embodiment, this step includes determining the minimum carrier-to-interference ratio that can be supported at the lowest rate modulation coding scheme (i.e., MCS 0 C/I) to provide a linear equivalent metric based on an uplink power RF metric. In particular, this step can determine how many PRBs each user could support if MCS 0 were used. This is a linear metric. Maximum Uplink C/I Capability is in dB which is a logarithmic metric. A power function (or a lookup table) can be used to convert from dB into how many MCS 0 PRBs can be supported. This lookup table could simply be a table in 1 dB steps from -7 dB to + 40 dB (48 entries total), each giving the number of MCS 0 PRBs that can be supported. However, for the purpose of this calculation, any linear metric will do. Simply converting dB into a linear number (0 dB = 1, 10 dB = 10, 20 dB = 100, 30 dB = 1000, 40 dB = 10000) in 1 dB steps from -7 to +40 would also be sufficient. However, since MCS 0 is roughly equivalent to - 7 dB, MCS 0 equivalents could be made to always be an integer value. Specifically, this step determines the number of MCS 0 C/I PRBs for the given UE as:

Maximum C/I Capability (dB)-(MCS 0 C/I (dB)) number of MCS 0 C/I PRBs = 10 ^~°

A next step 206 includes summing the number of uplink resource shares for all user equipment, such as the number of MCS 0 C/I PRBs for all UEs that are being given a spectrally efficient resource assignment at this time slot. For logarithmic RF metrics, it is preferred that linear equivalents of the RF metric are summed.

A next step 208 includes assigning spectrally efficient uplink resources based upon user equipment fraction of linear metric compared to total sum of linear metric across all user equipment. Specifically, each UE is assign his fraction of PRBs from the spectrally efficient PRB resource pool as calculated by his number of supported MCS 0 PRBs divided by the total MCS 0 PRBS across all the UEs assigned to this time slot, as follows: assigned PRBs

(number of supported MCS 0 C/I PRBs) total number of PRBs ·

(total number of MCS 0 C/I PRBs)

In addition, the pool of fairness share PRBs can be distributed substantially equally among UEs that have been given an uplink resource assignment for this period of time.

A next step 210 is using the assigned uplink resources by the UEs for up link communications. If any of the uplink resources are not used by a given user equipment in the time slot they can be offered to the next UE in the maximum C/I capability list. If the uplink resources are fairness shares, these shares can be distributed substantially equally among the UEs or can be offered as spectrally efficient shares to the next user in the maximum C/I capability list.

Claims

CLAIMS We claim:

1. A method for spectrally efficient uplink resource assignment in a wireless communication network, the method comprising the steps of:

defining (200) a pool of uplink resource shares in a time slot for use in a spectrally efficient distribution of uplink resources;

calculating (202) a RF metric for a given user equipment (102);

determining (204) how many uplink resource shares each user equipment (102) can support based upon the RF metric;

summing (206) the number of uplink resource shares for all user equipment (102);

assigning (208) spectrally efficient uplink resources based upon the given user equipment fraction of the pool of shares compared to total sum of shares across all user equipment (102); and

using (210) the assigned uplink resources by the user equipment for uplink communications.

2. The method of claim 1 wherein the uplink resource shares are physical resource blocks.

3. The method of claim 1 wherein the defining step includes defining a pool of uplink resource shares in a time slot for use in fairness distribution of uplink resources, wherein the share pools for both the spectrally efficient distribution of uplink resources and the fairness distribution of uplink resources is divided among the total uplink resources for a time slot.

4. The method of claim 3 wherein the assigning step includes distributing fairness shares substantially equally among all user equipment.

5. The method of claim 1 wherein the RF metric is a maximum carrier-to- interference ratio that a given user equipment can generate when using its maximum power on a single physical resource block.

6. The method of claim 5 wherein the calculating and determining steps utilize a linear equivalent of the RF metric.

7. The method of claim 5 wherein the calculating step includes arranging a list of user equipment in order of highest maximum C/I capability to lowest maximum C/I capability.

8. The method of claim 5 wherein the determining step includes determining the minimum carrier-to-interference ratio that can be supported at the lowest rate modulation coding scheme (MCS 0 C/I).

9. A method for spectrally efficient uplink resource assignment in a wireless communication network, the method comprising the steps of:

calculating (202) a maximum carrier-to-interference ratio that a given user equipment (102) can generate when using its maximum power on a single uplink resource share;

determining (204) how many uplink resource shares each user equipment (102) can support at a lowest rate modulation coding scheme;

summing (206) the number of uplink resource shares that can be support at a lowest rate modulation coding scheme for all user equipment (102);

assigning (208) spectrally efficient uplink resources based upon the given user equipment fraction of the pool of shares that can be supported at a lowest rate modulation coding scheme compared to total sum of shares that can be supported at a lowest rate modulation coding scheme across all user equipment (102); and

using (210) the assigned uplink resources by the user equipment for uplink communications. An evolved NodeB (100) for assigning spectrally efficient uplink resources in a wireless communication network, the evolved NodeB (100) comprising: a memory (112) operable to store a defined (200) pool of uplink resource shares in a time slot for use in a spectrally efficient distribution of uplink resources;

a processor (110) coupled to the memory (112), the processor (110) operable to calculate (202) a RF metric for a given user equipment (102), determine (204) how many uplink resource shares each user equipment (102) can support based upon the RF metric, sum (206) the number of uplink resource shares for all user equipment (102), and assign (208) spectrally efficient uplink resources based upon the given user equipment fraction of the pool of shares compared to total sum of shares across all user equipment (102); and

a transceiver (108) coupled to the processor (110), the transceiver (108) operable to provide the uplink assignments from the processor (110) to the user equipment (102) such that the user equipment (102) can use (210) the assigned uplink resources for uplink communications with the evolved NodeB (100).