Determining fractional frequency reuse power levels for downlink transmissions

An example method is provided in one example embodiment and includes receiving at least one relative interference statistic from each of a plurality of cells, the at least one relative interference statistic associated with a relative interference of downlink transmission from the cell to a plurality of user equipment devices associated with the cell. The method further includes determining a power level for each of one or more resources within a fractional frequency reuse portion of a frequency spectrum based upon the at least one relative interference statistic received from each of the plurality of cells, and determining a power level for a reuse one portion of the frequency spectrum based upon the determined power level for each of the one or more resources within the fractional frequency reuse portion of the frequency spectrum.

TECHNICAL FIELD

This disclosure relates in general to the field of communications and, more particularly, to determining fractional frequency reuse power levels for downlink transmissions.

BACKGROUND

Long Term Evolution (LTE) networks often employ fractional frequency reuse (FFR) schemes in order to optimally allocate frequencies within a cellular network. FFR partitions a cell's (e.g. an LTE eNodeB) bandwidth among user equipment within the network such that cell-edge users of adjacent cells do not interfere with each other and interference received by cell interior users is reduced. The use of FFR in a cellular network is a tradeoff between improvement in rate and coverage for cell edge users, and sum network throughput and spectral efficiency for the network.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

A method according to one embodiment includes receiving at least one relative interference statistic from each of a plurality of cells, the at least one relative interference statistic associated with a relative interference of downlink transmission from the cell to a plurality of user equipment devices associated with the cell. The method further includes determining a power level for each of one or more resources within a fractional frequency reuse portion of a frequency spectrum based upon the at least one relative interference statistic received from each of the plurality of cells, and determining a power level for a reuse one portion of the frequency spectrum based upon the determined power level for each of the one or more resources within the fractional frequency reuse portion of the frequency spectrum.

In a particular embodiment, receiving the at least one relative interference statistic includes: receiving a total number of user equipment devices connected to each of the plurality of cells; receiving a total number of user equipment devices for each cell satisfying a first condition in which a neighboring cell Reference Signal Received Power (RSRP) value is at least equal a serving cell RSRP value plus a predetermined minimum relative interference value; and receiving relative RSRP values for each cell satisfying the first condition.

In still another particular embodiment, determining a power level for each of the one or more resources within the fractional frequency reuse portion includes: ordering the user equipment devices in each of the plurality of cells decreasing order of their relative RSRP values; computing signal-to-interference-plus-noise ratio (SINR) values for each of the user equipment devices based on the received relative RSRP values; discarding the user equipment devices having an SINR value below a predetermined percentile value; and determining a power level value of at least one resource within the fractional frequency reuse portion of a frequency spectrum based upon a predetermined selection criterion utilizing the non-discarded UEs within the predetermined percentile.

In another particular embodiment, the method further includes determining a power level value of a resource within a reuse one portion of the frequency spectrum based upon the determined power level of the at least one resource within the fractional frequency reuse portion. In still another embodiment, the method further includes ordering a set of user equipment device and interfering cell pairs in decreasing order of relative RSRP from an interfering cell with respect to a serving cell; determining the pairs from the set with a serving cell RSRP less than a interfering cell RSRP plus a predetermined threshold value; discarding user equipment devices from the set with a highest of a predetermined percentile of RSRP for neighboring cells; and determining a power level value of at least one resource within the fractional frequency reuse portion of the frequency spectrum based upon a predetermined selection criterion utilizing the non-discarded UEs within the predetermined percentile.

In another particular embodiment, receiving the at least one relative interference statistic includes: receiving relative Reference Signal Received Power (RSRP) values from each of the plurality of cells, wherein the relative RSRP values are ordered in descending order of a number of user equipment devices associated with the cell having a maximum value of relative interference such that the strongest interfering cell RSRP is equal to at least a serving cell RSRP plus a predetermined relative interference value, ordering the cells in descending order of the number of neighbors of the cells within a predetermined percentile, and determining relative power levels for each of one or more resources within a fractional frequency reuse portion of a frequency spectrum chosen such that when a particular cell transmits at a first power level and neighboring cells transmit at a second power level, a resulting interference is lowered to a predetermined threshold level below a serving cell power for cells within the predetermined percentile.

In another particular embodiment, the method further includes determining a power level value of the at least one resource within the fractional frequency reuse portion of the frequency spectrum based upon the relative power levels. In still another particular embodiment, the method further includes determining a power level value of a resource within a reuse one portion of the frequency spectrum based upon the determined power level of the at least one resource within the fractional frequency reuse portion.

One or more non-transitory tangible media according to one embodiment includes code for execution and when executed by a processor operable to perform operations comprising: receiving at least one relative interference statistic from each of a plurality of cells, the at least one relative interference statistic associated with a relative interference of downlink transmission from the cell to a plurality of user equipment devices associated with the cell; determining a power level for each of one or more resources within a fractional frequency reuse portion of a frequency spectrum based upon the at least one relative interference statistic received from each of the plurality of cells; and determining a power level for a reuse one portion of the frequency spectrum based upon the determined power level for each of the one or more resources within the fractional frequency reuse portion of the frequency spectrum.

An apparatus according to one embodiment includes a memory element configured to store data, a processor operable to execute instructions associated with the data, and at least one module. The at least one module is configured to: receive at least one relative interference statistic from each of a plurality of cells, the at least one relative interference statistic associated with a relative interference of downlink transmission from the cell to a plurality of user equipment devices associated with the cell, determine a power level for each of one or more resources within a fractional frequency reuse portion of a frequency spectrum based upon the at least one relative interference statistic received from each of the plurality of cells, and determine a power level for a reuse one portion of the frequency spectrum based upon the determined power level for each of the one or more resources within the fractional frequency reuse portion of the frequency spectrum.

Example Embodiments

Referring now toFIG. 1,FIG. 1is a simplified block diagram of a communication system10for resource allocation in a fractional frequency reuse (FFR) cellular network in accordance with one embodiment of the present disclosure. Communication system10ofFIG. 1includes a first cell (Cell1)12ahaving a first coverage area14a, a second cell (Cell2)12bhaving a second coverage area14b, and a third cell (Cell3)12chaving a third coverage area14c. In accordance with one or more embodiments, first cell12a, second cell12b, and third cell12care each a long term evolution (LTE) evolved Node B (eNodeB). In other embodiments, first cell12a, second cell12b, and third cell12cmay be any suitable base station. First coverage area14a, second coverage area14b, and third coverage area14care representative of a geographic area for which first cell12a, second cell12b, and third cell12c, respectively, can effectively provide service to a user equipment device therein.

First cell12aincludes a first user equipment (UE) device16aand a second user equipment (UE) device16blocated within first coverage area14aand served by first cell12a. Second cell12bincludes a third user equipment (UE) device16cand a fourth user equipment (UE) device16dlocated within second coverage area14band served by second cell12b. Third cell12cincludes a fifth user equipment (UE) device16eand a sixth user equipment (UE) device16flocated within third coverage area14cand served by third cell12c. In one or more embodiments, first cell12a, second cell12b, and third cell12callocate resources within their respective coverage areas14a-14cusing fractional frequency reuse (FFR) as will be further described herein.

In at least one embodiment, each of first UE16a, second UE16b, third UE16c, fourth UE16d, fifth UE16e, and sixth UE16fis a mobile device having the ability to communicate with and handover between one or more of first cell12a, second cell12b, and third cell12cusing one or more mobile wireless connections. In accordance with various embodiments, one or more of UEs16a-16fmay include a computer (e.g., notebook computer, laptop, tablet computer or device), a tablet, a cell phone, a personal digital assistant (PDA), a smartphone, or any other suitable device having the capability to communicate using wireless access technologies with one or more of first cell12a, second cell12b, and third cell12c.

In the embodiment illustrated inFIG. 1, first cell12a, second cell12b, and third cell12care in communication with one another. Communication system10further includes a server18in communication with each of first cell12a, second cell12b, and third cell12c. In one or more embodiments, server18is located in an evolved packet core (EPC) network which may include one or more of a serving GPRS support node (SGSN)/mobile management entity (MME), a home subscriber server (HSS), a serving gateway (SGW), a packet data network (PDN) gateway (PGW), a policy and charging rules function (PCRF), and one or more packet networks. In accordance with various embodiments, server18is configured to receive feedback from each of first cell12a, second cell12b, and third cell12c, and determine how resources should be allocated between first cell12a, second cell12b, and third cell12cbased upon the feedback. In one or more embodiments, server18is further configured to provide resource allocation parameters to first cell12a, second cell12b, and third cell12c. In one or more embodiments, the resource allocation parameters provided to first cell12a, second cell12b, and third cell12care used to optimize resources allocated among first cell12a, second cell12b, and third cell12cused to serve the UEs within their respective coverage areas14a-14c. In particular embodiments, the resource allocation parameters include parameters related to allocation of fractional frequency reuse (FFR) resources.

Before detailing some of the operational aspects ofFIG. 1, it is important to understand different scenarios involving location of user equipment in a mobile network. The following foundation is offered earnestly for teaching purposes only and, therefore should not be construed in any way to limit the broad teachings of the present disclosure. The basic idea of FFR is to partition the cell's bandwidth so that (i) cell-edge users of adjacent cells do not interfere with each other and (ii) interference received by (and created by) cell interior users is reduced, while (iii) using more total spectrum than classical frequency reuse. The use of FFR in cellular network is a tradeoff between improvement in rate and coverage for cell edge users, and sum network throughput and spectral efficiency. FFR is a compromise between hard and soft frequency reuse. Hard frequency reuse splits the system bandwidth into a number of distinct sub bands according to a chosen reuse factor and allows neighbor cells to transmit on different sub bands. FFR splits the given bandwidth into an inner and outer portions. FFR allocates an inner portion to the UEs located near to the eNodeB in terms of path loss with reduced power applying frequency reuse factor of one, i.e. the inner portion is completely reused by all eNodeBs. For the UEs close to the cell edge, a fraction of the outer portion of the bandwidth is dedicated with a frequency reuse factor greater than one. With soft frequency reuse the overall bandwidth is shared by all eNodeBs (i.e., a reuse factor of one is applied) but for the transmission on each sub-carrier, the eNBs are restricted to a particular power bound.

There are two common FFR models: strict FFR and Soft Frequency Reuse (SFR). Strict FFR is a modification of the traditional frequency reuse in which exterior frequency subbands are not shared with the inner frequency bands. Soft Frequency Reuse (SFR) employs the same cell-edge bandwidth partitioning strategy as Strict FFR, but the interior UEs are allowed to share subbands with edge UEs in other cells. Accordingly, shared subbands by interior UEs users are transmitted at lower power levels than for the cell edge UEs. SFR is more bandwidth efficient than strict FFR, but results in more interference to both cell-interior and edge UEs.

FIGS. 2A-2Billustrate an example of bandwidth allocation using fractional frequency reuse for a number of cells. In the example ofFIGS. 2A-2B, seven cells are arranged in a hexagonal configuration200with Cell1in the center and surround by Cells2-7numbered in a clockwise pattern in which strict FFR for reuse3is employed at cell edge UEs. In the example illustrated inFIGS. 2A-2Ba power allocation scheme250is shown in which the inner portion of each of cells1-8is allocated a first frequency portion of the total frequency bandwidth at a particular power level P1. The edges of cell1are allocated a second portion of the total bandwidth at a power level P2, the edges of cells2,4, and6are allocated a third portion of the total bandwidth at a power level P3, and the edges of cells3,5, and7area allocated a fourth portion of the total bandwidth at a power level P4.

Referring now toFIG. 3,FIG. 3is a simplified diagram of an example of resource block power allocation300for communication system10ofFIG. 1in accordance with one embodiment. To overcome the effect of multipath fading problem present in Universal Mobile Telecommunications System (UMTS), LTE uses Orthogonal Frequency Division Multiplexing (OFDM) for downlink from the base station to the UE to transmit the data over many narrow band carriers of 180 KHz each instead of spreading one signal over the complete 5 MHz career bandwidth. Accordingly, OFDM uses a large number of narrow sub-carriers for multi-carrier transmission to carry data. Orthogonal frequency-division multiplexing (OFDM), is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method and meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. The basic LTE downlink physical resource can be seen as a time-frequency grid in which the OFDM symbols are grouped into resource blocks. In LTE, the resource blocks have a total size of 180 kHz in the frequency domain and 0.5 ms in the time domain. A resource element (RE) is the smallest defined unit which consists of one OFDM sub-carrier during one OFDM symbol interval. Each resource block (RB) consists of 12·7=84 resource elements in case of normal cyclic prefix (72 for extended CP). Each UE is allocated a number of the resource blocks in the time frequency grid. The more resource blocks a UE is allocated, and the higher the modulation used in the resource elements, the higher the bit-rate. Which resource blocks and how many the UE is allocated at a given point in time depends upon frequency and time scheduling mechanisms.

FIG. 3illustrates frequency domain power variation across multiple cells to mitigate interference between the cells. In the reuse portion there are a number of resource blocks (RBs) in which all the cells on the downlink use the same amount of transmit power per RB. As described above, a RB is an allocated portion of time and frequency spectrum used for downlink transmission from the cell to one or more UEs. If there was no interference, management in every cell would transmit at the same power across all the resources, and the interference a UE would experience on the downlink would be same across frequency from all of the cells if they were all fully loaded.

In the embodiment ofFIG. 3, three different power levels (P1, P2, and P3) for resource blocks (RBs) are illustrated in which P3>=P1>P2. In the illustrated embodiment, P1is the power level used by all cells in the reuse one portion of the spectrum. In the reuse one portion every cell reuses that portion of the spectrum and uses the same transmission power across the spectrum. In the FFR portion of the spectrum, a given cell transmits at a higher power on the P1portion of the FFR, and lowers its power per RB on the rest of the RBs in that part of the frequency, which is P2. If a given cell increases its power P1in the FFR portion of the spectrum, then a neighboring cell will reduce its power in the same portion but will have a higher power of transmission on P2. Accordingly in the FFR portion, one cell may increase its power on one part of the FFR spectrum and neighboring cells may reduce their power on the same part of the FFR spectrum. Typically, the FFR portion is used to serve mobiles UEs located close to a coverage area between, for example, within the coverage area14aof cell1(12a) but close to the coverage area14bof cell2(12b). The cost is that the number of resources to serve UEs are reduced because the opposite must be performed on the other part of the spectrum. However, UE's at the boundary of two cells will still gain an increase in performance because the signal-to-noise ratio (SNR) increases even though resources are reduced. Accordingly, the net change in capacity is positive for UEs near the edge of a cell.

One or more embodiments described herein are directed to determining a number of resource blocks (RBs) to be allocated in a reuse one portion and a number of resource blocks (RBs) to be allocated in the fractional frequency resource (FFR) portion for a given set of power levels based upon information collected from the cells in a centralized manner. In one example allocation, if more UEs are located near a cell edge, it is desired to allocate more resources in the FFR portion. In another example allocation, if more of the UEs are close to the cells that serve them, it is desired to allocate more resources in the reuse one portion.

Referring again toFIG. 1, in one embodiment each of cells12a-12ccollect information obtained from one or more UEs, such as path loss or interference information, and provide feedback regarding the collected information to server18. In at least one embodiment, server18then computes resource allocation parameters including one or more of the fraction of resources (e.g., RBs) in the FFR portion and the fraction of resources in which a cell can expect higher signal-to-interference-plus-noise ratio (SINR) in the FFR portion of the spectrum, and sends the resource allocation parameters to each of cells12a-12c. Upon receiving the fraction of resources allocated to the FFR portion, each of the cells12a-12bcan determine the number of resources allocated to each of the FFR portion and the reuse portion. Based upon the received resource allocation parameters, neighboring cells12a-12cthen exchange information with one another to determine the power allocation for specific resources in which a cell will set a higher or lower power allocation for each RB. In a particular embodiment, the determination of whether each RB should increase or decrease power is determined through an X2 message exchange between cells12a-12c. In particular embodiments, the power allocation for each RB is measured as the power spectral density (PSD) for each RB. Accordingly, for a given set of power levels in the neighboring cell and the serving cell, the spectral density that can be supported for each UE on each set of RBs is determined.

In one or more embodiments, the parameter ρffrrepresents the fraction of RBs in the FFR portion of the spectrum and is determined by server18based upon given power levels and cell feedback. Referring again to the example ofFIG. 3, for power levels P1, P2, and P3such that P3>=P1>P2, a parameter ρedgerepresents the fraction of RBs with power P3. The parameter ρlow,interfrepresents the fraction of RBs in which a cell transmits power P1but neighboring cell transmits at power P2.

In one or more embodiments, each of cells12a-12creceive performance metrics from each UE connected to it related to downlink power and feeds back the performance metrics to server18. Based upon the received performance metrics, server18computes the fraction of RBs in the FFR portion of the spectrum, ρFFR, and provides resource allocation parameters including an indication of the computed fraction of RBs in the FFR portion to each of cells12a-12c. Cells12a-12cmay then exchange messages amongst themselves to determine how specific resources should be allocated to each of cells12a-12c, such as specific power allocation within the reuse one and FFR portions, based upon the indication of the computed fraction of RBs in the FFR portion.

Referring now toFIG. 4,FIG. 4is a simplified flow diagram400illustrating example operations associated with server18in one example embodiment of communication system10. In402, server18receives one or more performance metrics from each of cells12a-12c. In one or more embodiments, the performance metrics are associated with downlink transmission from each of cells12a-12cto one or more user equipment devices associated with each cell12a-12c. In one or more embodiments, each of cells12a-12creceive one or more performance metrics from each UE connected to it related to downlink power and sends the performance metrics to server18. In other embodiments, each of cells12a-12creceives the one or more performance metrics from each UE connected to it, computes an effective rate representative of the overall throughput performance of all UEs associated with the particular cell for different values of ρFFR, and each of cells12a-12csends the computed effective rate to server18.

In404, server18determines the fraction of resources for allocation within the fractional frequency resource portion of the frequency spectrum, ρFFR, based upon the received one or more performance metrics as further described herein.

In one embodiment, the performance metrics received by each of cells12a-12care provided to server18, and server18performs substantially all the computations required to determine the value of ρFFRbased upon the received performance metric. In a particular embodiment, the performance metrics that each of the cells12-12cfeeds back to server18includes the spectral efficiencies and/or average modulation and coding scheme (MCS) for each UE on (a) reuse one RBs, (b) FFR RBs with PSD P1, (c) FFR RBs with PSD P2, and (d) reuse 1 RBs with PSD P3. Server18then computes the value of ρFFRusing the received spectral efficiencies and/or average MCS metrics. In a particular embodiment, server18computes the value of ρFFRby solving a utility maximization resource allocation function across cells12a-12cto allocate fractions of reuse one and FFR RBs to the UEs.

In another embodiment, the performance metrics are received by each of cells12a-12c, and each of cells12a-12ccalculates an effective rate representative of the overall throughput performance of all UEs associated with the particular cell for different values of ρFFR. Each of cells12a-12cthen send the effective rate to server18. In particular embodiments, the calculation of the effective rate by each of cells12a-12cmay include solving a utility function. Examples of effective rate computation that may be performed by each of cells12a-12cin one or more embodiments include calculating a geometric mean of UE throughputs corresponding to a sum log utility, and calculating an inverse utility function of a sum of utilities of UE throughputs in the cell. In one or more embodiments, the utility function used to compute the effective rate may be configured by server18and/or may be specific to each of cells12a-12c.

In particular embodiments, the effective rate is computed for each cell through solving a low complexity optimization function problem for a given value of ρFFRand assuming other parameters are known. In solving the problem, an assumption is made that a ρlow,interfscales linearly with ρFFR. In one or more embodiments, the scaling constant is determined by server18based upon the number of neighbors of each cell in the network. The optimization problem is performed over the numbers (αj(i)) of four types of RBs assigned to a UE i based on downlink power and reuse pattern. In one or more embodiments, the utility function U (r(i)) is a concave, monotone increasing function of r(i) so that U−1(.) is well defined. Example values of αj(i) corresponding to the example ofFIG. 3are as follows:

In order to solve the optimization problem the following function is optimized over α:
Max.ΣiU(r(i))
s.t. r(i)=α3(i)R3(i)+α2(i)R2(i)+α1,reuse(i)R1,reuse(i)+α1,FFR(i)R1,FFR(i)

Rj(i) are average spectral efficiencies provided by link adaptation for UE i

The effective rate is U−1(ΣiU(r*(i))

The above optimization problem is to maximize a sum of concave function subject to linear constraints. In accordance with various embodiments, standard efficient computational methods can be used to exploit structure and compute an approximate solution.

α is the fraction of the resources that the UE allocated in that portion of the spectrum. Accordingly, the rate r(i) that a UE is allocated over time is a weighted average of the spectral efficiency across different portions. Upon solving the above problem, server18can determine the value of ρFFR.

In another embodiment, instead of solving an optimization problem to calculate ρFFR, an outer loop adaptation may be used to calculate ρFFR. In accordance with this embodiment, an initial value of ρFFRis selected, and then ρFFRis adapted in a closed loop manner based on feedback. In accordance with such an embodiment, a target threshold value for a performance metric, such as MCS or SINR, is selected for downlink transmissions to a UE. This target threshold value presents a tradeoff (in terms of spectral efficiency) between serving cell interior UEs at lower SINR and serving cell edge UEs at higher SINR. Each cell12a-12cfeeds back, to server18, the number of UEs served by the particular cell that have a performance measure metric (e.g., SINR and/or MCS) in reuse one below the target threshold value on reuse one RBs, and the total number of UEs served by the particular cell. Server18then determines an initial value of ρFFR. The initial value of ρFFRis chosen to be the fraction of total RBs where the fraction correspond to the ratio of UEs across the network with the performance metric (e.g., MCS and/or SINR) below the target threshold value to the total UEs in the network.

After the initial value of ρFFRis chosen, ρFFRis adapted according to further feedback from cells12a-12c. For each UE served by a particular cell, the particular cell computes a median value for a block error rate (BLER) threshold (e.g., 10%) on P1RBs in reuse one spectrum via link adaptation prediction, and a fraction of high SINR RBs allocated to the UE. Each of cells12a-12cfeeds back the fraction of high SINR RBs allocated to UEs that have a value of the performance metric (SINR and/or MCS) in the reuse one part of the spectrum to be higher than the target threshold value. In the adaptation loop, ρFFRis adapted such that a predefined percentile of downlink transmission to the UEs occur at a predefined performance metric threshold. In a particular embodiment, ρFFRis increased if the predefined percentile (e.g. 90%) of the UEs among all cells12a-12chave a performance metric that is below a predetermined threshold (e.g., SINR and/or MCS threshold). Conversely, ρFFRis reduced if the predefined percentile (e.g. 90%) of the UEs among all cells12a-12chave a performance metric that is above the predefined threshold.

In step406, upon determining an updated value of ρFFR, server18determines the fraction of resources for allocation within the reuse one portion of the frequency spectrum based upon the determined fraction of resources for allocation within the fractional frequency reuse portion of the frequency spectrum (ρFFR). In a particular embodiment, upon determining the value of ρFFR, server18may determine the fraction of resources for allocation within the reuse one portion of the frequency spectrum by the equation 1-ρFFR.

In408, server18sends resource allocation parameters including an indication of the fraction of resources for allocation within the fractional frequency reuse portion of the frequency spectrum (ρFFR) and an indication of the fraction of resources for allocation within the reuse one portion of the frequency spectrum to cells12a-12c. Based upon this received information, cells12a-12ccommunicate with one another in order to determine the specific resources allocated to each of cells12a-12c. In particular embodiments, cells12a-12cmay communicate with one another via X2 messaging in order to determine the specific resource allocation among the FFR and reuse one portion used by each of cells12a-12c. Accordingly, if many UEs which would obtain performance metrics (e.g. SINR and/or MCS) above the target threshold value in the reuse one portion but those UE keep getting allocations in the FFR portion, then the number of RBs in the FFR portion may be reduced to prevent wasting of resources in the network. If many UEs are scheduled in the reuse one portion, but the obtainable performance metrics (SINR and/or MCS) fall below the target threshold values, there are too few FFR resources and the number of resources in the FFR portion may be increased in response.

Flow400then ends. It should be understood that in various embodiment that flow400may be repeated on a continuous basis upon receiving updated performance metrics from cells12a-12cso that the resource allocation between the FFR portion and the reuse one portion of the spectrum may be adapted according to changing conditions within network10.

Referring now toFIG. 5,FIG. 5is a simplified flow diagram500illustrating example operations associated with cell12ain one example embodiment of communication system10. In the embodiment ofFIG. 5, cell12ais configured to compute an effective rate based upon performance metrics received from one or more UEs connected to cell12asuch as UE16aand UE16b, and feed back the effective rate to server18as previously discussed herein. In502, cell12areceives performance metrics from each of UE16aand UE16brelated to downlink power performance between cell12aand each of UE16aand UE16b.

In504, cell12acomputes an effective rate for cell12abased upon the received performance metrics received from each of UE16aand UE16b. As previously discussed, In particular embodiments the calculation of the effective rate by cell12amay include solving a utility function based upon the received performance metrics.

In506, cell12asends the computed effective rate for cell12ato server18. Based upon the computed effective rate received from cell12a, server18may determine the fraction of resources for allocation within the fractional frequency resource portion of the frequency spectrum, ρFFR, based upon the received effective rate information as well as the fraction of resources for allocation within the reuse one portion of the frequency spectrum. Server18may then send resource allocation parameters including an indication of the fraction of resources for allocation within the fractional frequency reuse portion of the frequency spectrum (ρFFR) and an indication of the fraction of resources for allocation within the reuse one portion of the frequency spectrum to cell12a.

In508, cell12areceives the resource allocation parameters from server18. Cell12amay then communicate with cells12b-12cto determine the specific allocation of FFR resources and reuse one resources between cells12a-12cbased upon the received resource allocation parameters. Flow500then ends.

Other embodiments are directed to choosing power levels for fractional frequency reuse in the downlink between a cell and UE. In one or more embodiments, UE statistics are used to select power levels for each of the resources in the FFR portion of the spectrum.

FIG. 6is a simplified diagram of an example of resource block power allocation600for communication system ofFIG. 1in accordance with another embodiment. In the embodiment ofFIG. 6, three different power levels (P1, P2, and P4) for resource blocks (RBs) are illustrated in which P4>P2where both P1and P2are power per RB (e.g., PSD). In the illustrated embodiment, P1is the power level used by all cells in the reuse one portion of the spectrum. In the FFR portion of the spectrum, three RBs are illustrated in which two RBs have a power level of P2and one RB has a power level of P4. As previously described, the parameter ρFFRrepresents the fraction of RBs in the FFR portion of the spectrum. The parameter ρlow_interfrepresents the fraction of RBs in which a cell transmits power at power level P4but a neighboring cell transmits at power level P2. In accordance with various embodiments, server18is configured to determine values of ρlow,interfand power per RB for P1, P2, and P4for a given value of ρFFRbased upon feedback received from cells as will be further described herein.

Referring now toFIG. 7,FIG. 7is a simplified flow diagram700illustrating example operations associated with downlink inter-cell interference management in one example embodiment of communication system10. In702, server18receives downlink relative interference statistics associated with the UEs served be each of cells12a-cells12c. In one example, server18receives downlink relative interference statistics associated with UEs16a-16bfrom cell12a, receives downlink relative interference statistics associated with UEs16c-16dfrom cell12b, and receives downlink relative interference statistics associated with UEs16e-16ffrom cell12c.

In accordance with particular embodiments, each of cells12a-12cdetermines relative Reference Signal Received Power (RSRP) values for each UE served by the particular cell and determines either UE specific downlink relative interference statistics or cell specific downlink relative interference statistics from the RSRP values. In an embodiment in which each of cells12a-12csends back UE specific feedback, each of cells12a-12csends back downlink relative interference values as the downlink relative interference statistics for each UE served by the particular cell to server18as will be further described herein. In an embodiment in which each of cells12a-12csends back cell specific feedback, each cell12a-12cdetermines downlink relative interference statistics for the particular cell from the relative interference values received from each UE and sends the downlink relative interference statistics to server18as will be further described herein.

In704, server18determines a power level for each resource (e.g., resource block (RB)) within the FFR portion of the spectrum based upon the received downlink relative interference statistics received from each of cells12a-12cas further described herein. In a particular embodiment, server18determines the power level per RB for P4, P2, and P1based upon the received downlink relative interference statistics. In706, server18determines the value of ρlow_interfrepresentative of a fraction of RBs where a particular cell transmits at a first FFR power level (e.g., P4) but a neighboring cell transmits at a second FFR power level (e.g. P2). In a particular embodiment, ρlow_interfis set to ρFFR/Nmaxin which Nmaxdenotes the maximum sum of neighbors of a cell in the network and ρFFRis equal to the fraction of RBs within the FFR portion of the spectrum. Flow700then ends.

Referring now toFIG. 8,FIG. 8illustrates a simplified flow diagram800illustrating example operations associated with downlink inter-cell interference management using UE specific feedback in accordance with one embodiment. In802, server18receives, from each of cells12a-12c, an indication of the total number of UEs connected to the particular cell. In804, server18receives, from each of cells12a-12c, an indication of the total number of UEs for which the neighboring cell RSRP is at least equal to the serving cell RSRP plus a minimum relative interference value, minRelativeInterf. In806, server18receives, from each of cells12a-12c, a relative RSRP value from each of the UEs satisfying the above condition in which the neighboring cell RSRP is at least equal to the serving cell RSRP+minRelativeInterf.

In808, server18orders the UEs in all cells in decreasing order of their RSRP when the serving cell and the interfering cells all transmit at the same power. In810, server18computes SINRs for each of the UEs based on the received relative RSRP values. In812, server18discards the UEs having an SINR value below a predetermined percentile (e.g., the 5th percentile). In814, server18sets the power level of the highest power level FFR resource block (e.g., P4) to a predetermined value assuming uniform distribution of maximum cell power across the frequency spectrum.

In816, server18determines a value of the lowest power level FFR resource block (e.g., P2) based upon a predetermined selection criterion utilizing the non-discarded UEs within the predetermined percentile (e.g., the 5th percentile). A first criterion according to a particular embodiment considers the value of P2at the strongest neighboring cell such that when it transmits at power P2per RB and the serving cell transmits at power P4RB, the RSRP from the neighboring cell is less than or equal to the serving cell RSRP minus a predetermined threshold value Δ (e.g., 6 dB). A second criterion according to a particular embodiment considers the neighboring cells for which RSRP is greater than or equal to the RSRP of the serving cell plus a predetermined threshold value Δ (e.g., 6 dB). A power per RB P2is computed such that when all neighboring cells according to the first criterion transmit at power P2per RB but the serving cell transmits at power P4per RB, the expected SINR at the UE is above a minimum SINR threshold.

In818, server18determines the maximum number of neighbors of a cell in the network (Nmax) that satisfy the predetermined selection criterion focusing on the UEs which were not discarded. In a particular embodiment, the number of neighbors of a cell Nmaxis equal to those that satisfy the first criterion or the second criterion for at least one UE in the cell. In820, server18determines ρlow_interf=ρFFR/Nmax. In822, server18determines the reuse one power level value (e.g., P1) based upon one or more of the determined FFR power level values (e.g., P4or P2). In one embodiment, the reuse one power level value (P1) is set to the highest power level FFR resource block (e.g., P4) and the relative value of P2previously determined is used. P1and P2are selected such that the total power for the cells add up to the maximum transmit power for the cell. In another embodiment, the reuse one power level value (P1) is set to the lowest power level FFR resource block (e.g., P2). The flow800then ends.

Referring now toFIG. 9,FIG. 9illustrates a simplified flow diagram900illustrating example operations associated with downlink inter-cell interference management using UE specific feedback in accordance with another embodiment. In902, server18receives, from each of cells12a-12c, an indication of the total number of UEs connected to the particular cell. In904, server18receives, from each of cells12a-12c, an indication of the total number of UEs for which the neighboring cell RSRP is at least equal to the serving cell RSRP plus a minimum relative interference value, minRelativeInterf. In906, server18receives, from each of cells12a-12c, a relative RSRP value from each of the UEs satisfying the above condition in which the neighboring cell RSRP is at least equal to the serving cell RSRP+minRelativeInterf.

In908, server18orders UE and interfering cell pairs in decreasing order of relative RSRP from interfering cell with respect to the serving cell. In910, server18determines the pairs from the set with a serving cell RSRP less than a interfering cell RSRP+a predetermined threshold value Δ. In912, server18discards UEs with a highest predetermined percentile (e.g., 5th percentile) of RSRP for neighboring cells. In914, server18determines the number of neighbors of a cell, Nmax, equal to the maximum over the UEs associated with the cell satisfying the criterion that the serving cell RSRP is less than the interfering cell RSRP plus a predetermined threshold value Δ. In916, server18determines ρlow_interf=ρFFR/Nmax.

In918, server18sets the power level of the highest power level FFR resource block (e.g., P4) to a predetermined value assuming uniform distribution of maximum cell power across the frequency spectrum. In920, server18determines a value of the lowest power level FFR resource block (e.g., P2) based upon a predetermined selection criterion utilizing the non-discarded UEs within the predetermined percentile. A first criterion according to a particular embodiment considers the value of P2at the strongest neighboring cell such that when it transmits at power P2per RB and the serving cell transmits at power P4RB, the RSRP from the neighboring cell is less than or equal to the serving cell RSRP minus a predetermined threshold value Δ (e.g., 6 dB). A second criterion according to a particular embodiment considers the neighboring cells for which RSRP is greater than or equal to the RSRP of the serving cell plus a predetermined threshold value Δ (e.g., 6 dB). A power per RB P2is computed such that when all neighboring cells according to the first criterion transmit at power P2per RB but the serving cell transmits at power P4per RB, the expected SINR at the UE is above a minimum SINR threshold.

In922, server18determines the reuse one power level value (e.g., P1) based upon one or more of the determined FFR power level values (e.g., P4or P2). In one embodiment, the reuse one power level value (P1) is set to the highest power level FFR resource block (e.g., P4) and the relative value of P2previously determined is used. P1and P2are selected such that the total power for the cells add up to the maximum transmit power for the cell. In another embodiment, the reuse one power level value (P1) is set to the lowest power level FFR resource block (e.g., P2). The flow900then ends.

Referring now toFIG. 10,FIG. 10illustrates a simplified flow diagram1000illustrating example operations associated with downlink inter-cell interference management using cell specific feedback in accordance with another embodiment. In1002, server18receives ordered values of relative RSRP from each of cells12a-12cas follows: The first value corresponds to the maximum among UEs associated with the cell having a maximum value of relative interference (relativeInterf) such that the strongest interfering cell RSRP is equal to at least the serving cell RSRP+relativeInterf. The corresponding neighboring cell is denoted as C1. The second value corresponds the maximum among UEs associated with the cell having a maximum value of relative interference (relativeInterf) such that the strong interfering cell, other than C1, RSRP is equal to at least the serving cell RSRP+relativeInterf. Additional values for all neighboring cells such that the neighboring cell RSRP is at least serving cell RSRP+a minimum relative interference (minRelativeInterf) at a minimum of one UE associated with the serving cell.

In1004, server18orders the cells in terms of the number of neighbors. In1006, server18determines a predetermined percentile (e.g., 80th percentile) of the ordered cells in terms of number of neighbors. This corresponds to the number of neighbors of a cell Nmax. In1008, server18creates a list of (cell, relativeInterf) pairs of FFR power levels (P4, P2) chosen such that when a given cell transmits at P4per RB and neighboring cells transmit at P2per RB, then for a predetermined percentage of pairs (e.g., 80%), the resulting interference is lowered to a predetermined threshold below serving cell power. This determines the relative values for the FFR power levels (P2, P4).

In1010, server18determines actual values of the FFR power levels (P2, P4) from the relative values. In1012, server18determines ρlow_interf=ρFFR/Nmax. In1014, server18determines the reuse one power level value (e.g., P1) based upon one or more of the determined FFR power level values (e.g., P4or P2). In one embodiment, the reuse one power level value (P1) is set to the highest power level FFR resource block (e.g., P4) and the relative value of P2previously determined is used. P1and P2are selected such that the total power for the cells add up to the maximum transmit power for the cell. In another embodiment, the reuse one power level value (P1) is set to the lowest power level FFR resource block (e.g., P2). The flow1000then ends.

Referring now toFIG. 11,FIG. 11is a simplified block diagram of a communication system1100for selecting cells for downlink inter-cell interference coordination (ICIC) in accordance with one embodiment of the present disclosure. Communication system1100ofFIG. 11includes a first cell (Cell1)12ahaving a first coverage area14a, and a second cell (Cell2)12bhaving a second coverage area14b. In accordance with one or more embodiments, first cell12aand second cell12bare each a long term evolution (LTE) evolved Node B (eNodeB). In other embodiments, first cell12aand second cell12bmay be any suitable base station such as a femtocell. First coverage area14aand second coverage area14bare representative of a geographic area for which first cell12aand second cell12b, respectively, can effectively provide service to a user equipment device therein.

First cell12aincludes a first user equipment (UE) device16alocated within the interior of first coverage area14aand served by first cell12a. Second cell12bincludes second user equipment (UE) device16blocated near the edge of the second coverage area and third user equipment (UE) device16clocated within second coverage area14band served by second cell12b. In the embodiment illustrated inFIG. 11, first cell12aand second cell12bare in communication with one another. In one or more embodiments, first cell12aand second cell12ballocate resources within their respective coverage areas14a-14busing a frequency domain inter-cell interference coordination (ICIC) framework in which interference is managed through Fractional Frequency Reuse (FFR). In particular embodiments, it is assumed that that all cells that participate in the ICIC scheme have the same fraction of resources in reuse one portion of the spectrum and the FFR portion of the spectrum.

Various embodiments are directed selecting a subset of cells in the network that should participate in inter-cell interference coordination (ICIC) while all other cells may transmit at the same power (e.g., PSD) on all resource blocks (RBs) in the frequency spectrum. When a FFR scheme is implemented, if a particular cell does have not any interfering cells there is no reason for the particular cell to reduce power on any of the resource blocks (RBs). It is desirable to perform interference management only on the subset of cells experiencing interference from other cells in order to maximize network capacity. Accordingly, a cell which does not cause significant interference to UEs in neighboring cells does not have to lower power on any RBs. In addition, cells which participate in ICIC and have UEs which suffer from interference can obtain more resources at higher SINR without loss of performance in cells which do no cause interference.

FIG. 12is a simplified diagram of an example of resource block power allocation for the communication system1100ofFIG. 11in accordance with one embodiment. In the embodiment ofFIG. 12, three different power levels (P1, P2, and P3) for resource blocks (RBs) are illustrated in which P3>P1>P2where P1, P2, and P3are power per RB (e.g., PSD). In the illustrated embodiment, the reuse one fraction of resources is lowered in order to server interference limited users. In the reuse one portion of the spectrum, two RBs are illustrated in which P1and P3are power levels used by cells. In the FFR portion of the spectrum, three RBs are illustrated in which two RBs have a power level of P2and one RB has a power level of P1. The parameter ρFFRrepresents the fraction of RBs in the FFR portion of the spectrum. The parameter ρedgerepresents the fraction of RBs with power P3. The parameter ρlow_interfrepresents the fraction of RBs in which a cell transmits power at power level P1but a neighboring cell transmits at power level P2. In one or more embodiments, it is assumed that P1≧Pmax/NRBwhere Pmaxrepresents total power of the cell, and NRBrepresents the total of RBs used by the cell.

Referring again toFIG. 11, first UE16acan obtain a high SINR on RBs on which first cell12atransmits at power P1and second cell12btransmits at power P1. Hence, second cell12bdoes not need to reduce its power per RB to P2on any RB to allow first cell12ato serve first UE16a. In general, if first cell12adoes not serve a UE on the edge of the coverage areas of first cell12aand second cell12b, second cell12bdoes not need to reduce power on any RB for first cell12ato serve cell edge UEs. It should be noted that the converse may not be true. For example, in the illustrated example second UE12bis on the edge of coverage areas of first cell12aand second cell12b, and is served by second cell12b.

In accordance with one or more embodiments, a particular cell should participate in interference coordination if either of the following is true: 1) at least one of the UEs of the cells suffers from high interference from a neighboring cell; or 2) a given cell causes high interference to a UE of a neighboring cell. In various embodiments, a process of distributed interference management is provided in which a cell which is non-interfering does not reduce its power on any RBs and a cell which is non-interfered does not request its neighboring cells to reduce power levels on any RBs.

In determining whether a particular cell is a non-interfering cell, it is assumed that a given cell transmits with power per RB of P1. A cell is considered to be non-interfering if there is no neighboring cell such that when the neighboring cell also transmits with power per RB of P1, any UE connected to that cell receives the signal from the given cell at a power less than equal to the signal from its own serving cell minus a fixed threshold value. In one or more embodiments, the criterion may be evaluated on the basis or RSRP measurements. In particular embodiments, a cell is non-interfering if the following is true of all neighboring cells: RSRP from a given cell is less than the RSRP for a neighboring cell minus the fixed threshold value as measure at any UE associated with the neighboring cell. In particular embodiments, to determine whether the cell is non-interfering requires inputs from multiple neighboring cells in LTE.

In determining whether a particular cell is a non-interfered cell, it is assumed that a given cell transmits with power per RB of P1. A cell is considered to be non-interfered if there is no neighboring cell such that when the neighboring cell also transmits with power per RB of P1, any UE connected with the given cell receives the signal from the given cell at a power greater than equal to the signal from the neighboring cell plus a fixed threshold value. In one or more embodiments, the criterion may be evaluated on the basis or RSRP measurements. In a particular embodiment, a cell is non-interfered if the following is true of all neighboring cells: RSRP from the given cell is greater than the RSRP for the neighboring cell plus the fixed threshold value as measured at any UE associated with the given cell. In particular embodiments, whether a cell is non-interfered can be evaluated locally at the eNB in LTE networks.

In a distributed interference management scheme according to one or more embodiments, in a first component when a particular cell A is non-interfering to a given cell B, then the given cell B indicates to cell A that it has no cell edge UEs. In a second component, when no neighboring cell indicates to cell B that it has cell edge UEs, then cell B does not reduce power to P2on any RB. In such a case, cell B can distribute power across the RBs in any manner, as long as the power constraint corresponding to power per RB P1, P3are obeyed on appropriate RBs. In a third component of a cell is non-interfered, it does not indicate to any neighboring cell that it has cell edge UEs.

In some embodiments, ICIC is performed among cells using X2 messages such as using relative narrow-band transmit power (RNTP) messages between the cells. RNTP messages include a bit-mapping of resource blocks (RB) in which a bit corresponding to a particular RB is either given a value of one or zero. An ICIC scheme is assumed through which resources with power levels P1and P2are determined in a distributed manner through the exchange of RNTP messages. In a particular embodiment, if a bit for a given RB is set within a RNTP message it represents an indication that the cell will use transmission per RB of P1. However, if the bit is not set within the RNTP message is represents an indication that the cell will use transmission per RB of P2. If a cell is non-interfering to a given cell, the RNTP message from the given cell to that cell contains all zeros for the FFR RBs. A cell which receives no RNTP message or only RNTP messages from neighboring cells with all zeros for FFR RBs does not need to lower its power on any RBs. If a cell is a non-interfered cell, then it only sends RNTP message with all zeros to its neighboring cells. This cell may be required to reduce power on certain RBs on the basis of RNTP messages received from other cells.

Referring now toFIG. 13,FIG. 13illustrates a simplified flow diagram1300illustrating example operations associated with selecting cells for downlink inter-cell interference coordination (ICIC) in accordance with one embodiment of the present disclosure. In1302, a particular cell, such as first cell12a, receives a first message from one or more neighboring cells, such as second cell12bindicative of whether the cell is non-interfering to the neighboring cell(s). In one or more embodiments, a cell is considered to be non-interfering if there is no neighboring cell such that when the neighboring cell also transmits with power per RB P1, any of one or more UEs (e.g., UE16band/or UE16c) connected to second cell12breceives the signal from the cell at a power less than equal to the signal from its own serving cell (e.g., second cell12b) minus a fixed threshold. In one or more embodiments, the criterion that the neighboring cell uses to determine whether a given cell is an interfering cell includes an evaluation on the basis of RSRP measurements such that RSRP from a given cell is less than the RSRP for the neighboring cell minus the fixed predetermined threshold as measured at any UE associated with the neighboring cell. In one or more embodiments, when the cell is non-interfering to a neighboring cell, the neighboring cell indicates to the cell that it has no cell edge UEs connected to it.

In a particular embodiment, if a cell is non-interfering to a neighbor cell, the RNTP message from the neighbor cell contains all zero bits values for the FFR RBs. A cell which receives no RNTP message or only RNTP messages from neighboring cells with all zero bit values for FFR RBs, does not need to lower its power on any RBs.

In1304, the cell determines whether the cell is a non-interfering cell to neighboring cells based upon the received first message. In1306, if the first message is indicative of the cell being a non-interfering cell the flow continues to1308. In1308, the cell maintains the current power level on all downlink resource blocks and flow continues to1312. Accordingly, the cell is selected to not participate in ICIC. For example, in a particular embodiment when no neighboring cell indicates that it has cell edge UEs, the cell does not reduce power to P2on any RB and can distribute power across the RBs in any manner, as long as the power constraint corresponding to power RB P1, P3are obeyed on appropriate RBs. In1306, if the first message is indicated of the cell being an interfering cell the flow continues to1310. In1310, the cell reduces power on one or more downlink resource blocks through participation in ICIC and the flow continues to1312.

In1312, the cell determines if the cell is non-interfered by one or more neighboring cells. In one or more embodiments, the cell determines that the cell is non-interfered by one or more neighboring cells if when the neighboring cell also transmits with power per RB P1, any UE connected with the cell receives the signal from the cell at a power greater than equal to the signal from the neighboring cell plus a fixed threshold. In particular embodiments, the criterion can be evaluated on the basis of RSRP measurements such that a cell is non-interfered if for all neighboring cells RSRP from the cell is greater than the RSRP for the neighboring cell plus a fixed threshold as measured at any UE associated with the cell. In1314, if the cell determines that it is non-interfered by neighboring cells the flow continues to1316. In1316, the cell sends a message to the neighboring cell(s) indicative that the cell is non-interfered by neighboring cell(s). In a particular embodiment, if a cell is a non-interfered cell, the cell sends RNTP messages with all zero bit values to its neighboring cells. In response to receiving the message indicative that the cell is non-interfered, one or more of the neighboring cells may maintain its current power levels on all downlink RBs and not participate in an ICIC scheme. The flow then returns to1302.

In1314, if the cell determines that it is interfered by neighboring cells the flow continues to1318. In1318, the cell sends a message to the neighboring cell(s) indicative that the cell is interfered by the neighboring cell(s). In response to receiving the message indicative that the cell is interfered by the neighboring cell, the neighboring cell may reduce the power levels on one or more downlink RBs, such as FFR RBs, and thus be selected for participation in the ICIC scheme. The flow then returns to1302.

Accordingly, in a particular embodiment for a cell that is not causing interference to any of the neighboring cells even when transmitting at P1, all RBs can have power level P1. If a cell is not receiving interference from any of the neighboring cells, then all power levels in the RBs can be P2because it doesn't need to boost it's power to UEs at a cell edge.

Other embodiments are directed to user equipment (UE) power level selection for downlink. It should be understood that in an LTE system the power level at which a particular UE is served on the downlink by a cell cannot vary arbitrarily from one subframe to another because the UE needs to know the ratio of the reference signal power which is constant across all of the bandwidth to the data signal power in order to perform decoding optimally. Considering downlink transmission modes in which a UE demodulates using Cell Specific Reference Signals (CRS) received from the cell, the UE is signaled the ratio of CRS energy per resource element (EPRE) to the data (e.g., Physical Downlink Shared Channel (PDSCH) EPRE via radio resource control (RRC) protocol signaling. In order to change the PDSCH EPRE, the UE needs to be informed via RRC signaling a few subframes in advance of the change. The CRS EPRE is typically kept constant over long periods of time. Hence, a serving cell needs to compute the PDSCH EPRE per UE in a semi-static matter in which cell edge UEs have the highest PDSCH EPRE and the cell interior UEs have lower PDSCH EPRE.

FIG. 14is a simplified diagram of an example of resource block power allocation1400for the communication system10ofFIG. 1in accordance with one embodiment. In the embodiment ofFIG. 14, three different power levels (P1, P2, and P4) for resource blocks (RBs) are illustrated in which P4>P2>P1where P1, P2, and P4are power per RB (e.g., PSD). In the reuse one portion of the spectrum, one RB is illustrated in which P1is the power levels used by cells. In the FFR portion of the spectrum, three RBs are illustrated in which two RBs have a power level of P1and one RB has a power level of P4.

The power level of downlink data transmission will typically vary across the frequency spectrum. For example, if it is desired to schedule a particular UE in a portion of the spectrum having a power level P1and a few subframes later schedule the UE in a portion of the spectrum having power level P4, a control message is sent at power level P1indicating that the cell is going to change the data power level with respect to the reference to some different value. Accordingly, it is necessary for the cell to periodically determine which set of UEs will be scheduled at each of the power levels of the spectrum. In accordance with particular embodiments, for the subset of RBs in the reuse one portion of the spectrum all cells use the same transmission power per RB, P1, for reuse one RBs. For the subset of RBs in the FFR portion of the spectrum, on RBs with power per RB P4, neighboring cells lower their power per RB to P2<P4such that a given cell's UEs attain higher SINR.

In various embodiments, given a choice of power levels for the UEs and the knowledge of interference levels in different portions of the spectrum, the cell determines the power level that each UE should be scheduled at. In particular embodiments, a cell computes PDSCH EPRE for each UE based on the 1) number of resource blocks (RBs) that the cell can use to transmit at a given EPRE (e.g., due to interference considerations, power constraints, etc.), and 2) estimated spectral efficiency (e.g, based on MCS for 90 BLER on first transmission) at a given PDSCH EPRE and on each RB in the frequency domain on the downlink. The interference and channel to the UE may vary across different RBs. In particular embodiments, estimation of MCS is through an LTE Link Adaption Algorithm.

In one embodiment, a case is considered in which two PDSCH EPREs, P1>P2, are allowed in which the set of UEs to be used for each EPRE are computed. In other embodiments, the case is generalized in which multiple (N) EPREs, P1> . . . >PNare allowed in which the set of UEs to be used for each of the N EPREs are computed. In both cases, classification of UEs is based upon a threshold policy based upon the average wideband channel quality between the cell (e.g., eNB) and the UE in which a threshold is computed based on throughput performance of all UEs in the cell. Based upon whether a particular UE exceeds the threshold value, the particular UE may be classified by identifying a particular UE as either a cell interior UE which can tolerate a higher amount of interference or a cell edge UE which may have a low tolerance to interference. Based upon the classification, the power levels for the RBs in the frequency spectrum are calculated and assigned to the respective RBs.

In one or more embodiments, downlink transmission power level for multiple UEs in a cell are determined based on the overall throughput performance of all UEs in the cell. In one or more particular embodiments, a power level is chosen for a particular UE from a plurality of power levels on different RBs in the cell such that the average spectral efficiency of UEs with higher power level and lower interference is higher than the average spectral efficiency if the particular UE shared resources with other UEs that are served by RBs with lower power level and higher interference. In accordance with one or more embodiments, power levels of UEs are adapted as one or more of the UEs' channel conditions change. In particular embodiments, a hysteresis tolerance may be used for adaptation such that one or more UEs' power levels are changed if in addition to the criterion described above, the average throughput in the cell will improve by a predetermined amount, such as a percentage (e.g., five percent (5%)), if such a power level change is performed.

FIG. 15is a simplified diagram of an example of resource block power allocation1500for cell interior UEs for the communication system10ofFIG. 1in accordance with one embodiment. In the embodiment ofFIG. 15, two different power levels (P1, and P2) for resource blocks (RBs) are illustrated in which P2>P1where P1and P2are power per RB (e.g., PSD). In the reuse one portion of the spectrum, one RB is illustrated in which P1is the power level used by cells. In the FFR portion of the spectrum, three RBs are illustrated in which two RBs have a power level of P2and one RB has a power level of P1. In accordance with one or more embodiments, power level P1is kept fixed in the reuse one portion of the spectrum and a determination is made regarding wither a particular UE located in an interior portion of the cell coverage area will be assigned an RB having a power level of P1or a RB having a power level of P2within the FFR portion of the spectrum.

Referring now toFIG. 16,FIG. 16illustrates a simplified flow diagram1600illustrating example operations associated with determining downlink transmission power levels for interior cell UEs in accordance with one embodiment. In accordance with one or more embodiments of the flow1600ofFIG. 16, cell interior UEs are served at a lower power and higher interference than all other UEs in the cell. In1602, a cell12receives an indication of an average signal power on the downlink connection between the cell and a particular UE for each of N UEs connected to the cell. In1604, the cell12receives an indication of an average interference measurement on the downlink connection between the cell and a particular UE for each UE connected to the cell. In1606, the cell computes an average spectral efficiency for each UE based upon the average signal power and average interference. In a particular embodiment, the average spectral efficiency is computed as a function of the average signal power divided by the average interference for each cell. In one or more embodiments, the average spectral efficiency is a representative of an overall throughput performance of the UE.

In1608, UE1. . . UENare ordered in decreasing order of the computed spectral efficiency for each UE. In1610, an iterative procedure for determining downlink power levels for the UEs is initiated by setting an index value i equal to a value of 1. In1612, the cell determines whether a particular UEimeets a condition for being assigned a power level of P2. In one embodiment, the condition for UEibeing assigned a power level P2is if the particular UEireceives a higher throughput rate when it shares resources with UE1, . . . , UEi−1with power level P2than when the UEiis scheduled on resources with power level P1. In particular embodiments, equal resource/proportional fair scheduling of resources is used to maximize total throughput while at the same time allowing all users at least a minimal level of service. Further conditions for UEibeing assigned a power level P2may include if the reduction in utility of rates for UE1, . . . , UEi−1is less than the increase in utility of rate for UEi, and UE1. . . UENhave enough traffic to consume all RBs with power P1.

If UEimeets the condition for being assigned power level P2, the flow continues to1614. In1614, UEiis assigned power level P2and the flow continues to1618. If UEidoes not meet the condition for being assigned power level P2, the flow continues to1616. In1616, UEiis assigned power level P1and the flow continues to1618. In1618, the cell determines whether the index value i=N. If the index value i is not equal to N, the flow continues to1620in which the index i is incremented by 1 (i=i+1). After1620, the flow returns to1612in which the next UE is evaluated for determining whether it meets the condition to be assigned power level P2. If the index value i is equal to N, the flow returns to1602such that the assignment of power levels for the interior UEs may be performed on a periodic basis in order to adapt to changing conditions within the network.

FIG. 17is a simplified diagram of an example of resource block power allocation1700for cell edge UEs for the communication system10ofFIG. 1in accordance with one embodiment. In the embodiment ofFIG. 17, two different power levels (P1, and P4) for resource blocks (RBs) are illustrated in which P4>P1where P1and P4are power per RB (e.g., PSD). In the reuse one portion of the spectrum, one RB is illustrated in which P1is the power level used by cells. In the FFR portion of the spectrum, three RBs are illustrated in which two RBs have a power level of P1and one RB has a power level of P4. In accordance with one or more embodiments, power level P1is kept fixed in the reuse one portion of the spectrum and a determination is made regarding wither a particular UE located at an edge portion of the cell coverage area will be assigned an RB having a power level of P4or a RB having a power level of P1within the FFR portion of the spectrum.

Referring now toFIG. 18,FIG. 18illustrates a simplified flow diagram1800illustrating example operations associated with determining downlink transmission power levels for cell edge UEs in accordance with one embodiment. In the embodiment ofFIG. 18, the flow includes identifying cell edge UEs that have low tolerance to interference and involves a tradeoff between assigning a UE to an RB with higher SINR and giving a UE a larger number of RBs as RBs with higher SINR are limited. In accordance with one or more embodiments of the flow1800ofFIG. 18, cell edge UEs are served at a higher power and lower interference than all other UEs in the cell. In1802, a cell12receives an indication of the average of signal power on the downlink connection between the cell and a particular UE for each of N UEs connected to the cell. In1804, the cell12receives an indication of an average interference measurement on the downlink connection between the cell and a particular UE for each UE connected to the cell. In a particular embodiment, the average interference measurement is a signal-to-interference-plus-noise ratio (SINR) measurement. In1806, the cell computes an average spectral efficiency for each UE based upon the average signal power and average interference. In a particular embodiment, the average spectral efficiency is computed by dividing the average signal power by the average interference for each cell.

In1808, UE1. . . UENare ordered in increasing order of the reuse one SINR. In particular embodiments, the reuse one SINR is the estimated SINR when all cells transmit at the same power per RB. In1810, an iterative procedure for determining downlink power levels is initiated by setting an index value i equal to a value of 1. In1812, UE1with the lowest SINR in reuse one is assigned power level P4, with P4>P1. In1814, the index i is incremented by 1 (i=i+1). In1816, the cell determines whether a particular UEimeets a condition for being assigned a power level of P4. In one embodiment, the condition for UEibeing assigned a power level P4is if the estimated rate when assigned all RBs with power level P4divided by i is greater than the average spectral efficiency on RBs with power P1multiplied by the total RBs with power P1divided by (N−i+1).

If UEimeets the condition for being assigned power level P4, the flow continues to1818. In1818, UEiis assigned power level P4and the flow continues to1822. If UEidoes not meet the condition for being assigned power level P4, the flow continues to1820. In1820, UEiis assigned power level P1and the flow continues to1822. In1822, the cell determines whether the index value i=N. If the index value i is not equal to N, the flow returns to1814in which the index i is incremented by 1 (i=i+1). After1814, the flow returns to1816in which the next UE is evaluated for determining whether it meets the condition to be assigned power level P4. If the index value i is equal to N, the flow returns to1802such that the assignment of power levels for the cell edge UEs may be performed on a periodic basis in order to adapt to changing conditions within the network.

Although the embodiments described inFIGS. 15-18are described with respect to two possible power levels for a particular UE, in other embodiments the principles described herein may be applied to more than two power levels. In accordance with one embodiment in which multiple power levels are available for a UE, a procedure for assigning power levels may include beginning with an RB/power level corresponding to highest SINR. Assuming that frequency bands/RBs are ordered as a function of SINR (e.g., based on RSRP computations and not accounting for frequency selective fading) is the same for all UEs, the procedure described inFIG. 18may be applied for this frequency band assuming that RBs with lower SINR are equally distributed among all UEs. The procedure may then be repeated for the next highest power level to fix the allocation of UEs to a power level. The process may then be repeated until all available power levels have been assigned.

In accordance with one or more embodiments, the principles described herein may be used for UE transmission power level adaptation in order adapt the power allocation to UEs due to UE mobility. In particular embodiments, a hysteresis effect can be used in order to avoid frequency changes in power levels such that one or more UEs' power levels are changed only if in addition to the criterion described above, the average throughput in the cell improves by a predetermined percentage (e.g., five percent (5%)) if such a power level is performed.

Referring now toFIG. 19,FIG. 19illustrates an embodiment of a cell12a-12cof communication system10ofFIG. 1. Cell12a-12cincludes one or more processor(s)1902, a memory element1904, a radio access module1906, and a resource allocation module1908. Processor(s)1902is configured to execute various tasks of cell12a-12cas described herein and memory element1904is configured to store data associated with cell12a-12c. Radio access module506is configured to wirelessly communication with one or more of UEs16a-16f. Resource allocation module1908is configured to perform the operations associated with determining allocation of network resources to UEs16a-16fas described herein.

Referring now toFIG. 20,FIG. 20illustrates an embodiment of server18of communication system10ofFIG. 1. Server18includes one or more processor(s)2002, a memory element2004, and a resource allocation module2006. Processor(s)2002is configured to execute various tasks of server18as described herein and memory element2004is configured to store data associated with server18. Resource allocation module2006is configured to perform the operations associated with determining allocation of network resources to cells12a-12cand/or UEs16a-16fas described herein.

In regards to the internal structure associated with communication system10and communication system1100, each of UEs16a-16f, cells12a-12c, and server18can include memory elements for storing information to be used in achieving the operations, as outlined herein. Additionally, each of these devices may include a processor that can execute software or an algorithm to perform the activities as discussed in this Specification. These devices may further keep information in any suitable memory element [random access memory (RAM), read only memory (ROM), an erasable programmable read only memory (EPROM), an electrically erasable programmable ROM (EEPROM), etc.], software, hardware, or in any other suitable component, device, element, or object where appropriate and based on particular needs. Any of the memory items discussed herein should be construed as being encompassed within the broad term ‘memory element.’ The information being tracked or sent to UEs16a-16f, cells12a-12c, and server18could be provided in any database, register, control list, cache, or storage structure: all of which can be referenced at any suitable timeframe. Any such storage options may be included within the broad term ‘memory element’ as used herein in this Specification. Similarly, any of the potential processing elements, modules, and machines described in this Specification should be construed as being encompassed within the broad term ‘processor.’ Each of the network elements and mobile nodes can also include suitable interfaces for receiving, transmitting, and/or otherwise communicating data or information in a network environment.

Although the present disclosure has been described in detail with reference to particular arrangements and configurations, these example configurations and arrangements may be changed significantly without departing from the scope of the present disclosure. For example, although the present disclosure has been described with reference to particular communication exchanges involving certain network access, and signaling protocols, communication system10and/or communication system1100may be applicable to other exchanges, routing protocols, or routed protocols in which in order to provide hand-in access to a network. Moreover, although communication system10and communication system1100have been illustrated with reference to particular elements and operations that facilitate the communication process, these elements and operations may be replaced by any suitable architecture or process that achieves the intended functionality of communication system10and/or communication system1100.