KR20090107030A - Reverse link power control - Google Patents

Abstract

In one embodiment, a reverse link transmission power for a user equipment is determined (S90) based on a first path loss and a second path loss. The first path loss is path loss between a serving station and the user equipment, and the serving station serves the communication needs of the user equipment. The second path loss is path loss between a neighboring station and the user equipment, and the neighboring station neighbors the serving station.

Description

REVERSE LINK POWER CONTROL}

Exemplary embodiments of the invention relate generally to reverse link power control in a wireless communication network.

A cellular communication network generally includes various communication nodes coupled by wireless and wired connections and accessed through different types of communication channels. Each communication node includes a protocol stack for processing data transmitted and received over communication channels. The operation and configuration of the various communication nodes differ depending on the type of communication system and are often referred to by different names. Such communication systems include, for example, a Code Division Multiple Access 2000 (CDMA2000) system and a Universal Mobile Telecommunications System (UMTS).

UMTS is a wireless data communication and telephone standard that describes a set of protocol standards. UMTS describes protocol standards for voice and data transmission between a base station (BS) or Node B and mobile or user equipment (UE). UMTS systems typically include multiple radio network controllers (RNCs). RNC in a UMTS network provides functions equivalent to base station controller (BSC) functions in GSM / GPRS networks. However, RNCs manage handovers autonomously, for example, without involving mobile switching centers (MSCs) and Serving General Packet Radio Service (GPRS) support nodes (SGSNs). Have other abilities, including doing so. Node B is responsible for air interface processing and some radio resource management functions. Node B in UMTS networks provides functions equivalent to a base station transceiver (BTS) in GSM / GPRS networks. Node Bs are typically physically co-located with existing GSM base station transceivers to reduce the cost of UMTS implementation and to minimize planning consent restrictions.

1 illustrates a conventional communication system 100 operating in accordance with UMTS protocols. Referring to FIG. 1, communication system 100 may include a number of Node Bs, such as Node Bs 120, 122, and 124, each with UEs 105 and 110 in their respective coverage areas. Serve communication requests of the same UEs. Node B may serve a coverage area called a cell, and the cell may be divided into a number of sectors. For ease of explanation, the term cell may mean the entire coverage area served by Node B or a single sector of Node B. The communication from the Node B to the UE is called forward link or downlink. The communication from the UE to the Node B is called a reverse link or uplink.

Node Bs are connected to an RNC, such as RNCs 130 and 132, and the RNCs are connected to MSC / SGSN 140. The RNC handles specific call and data processing functions, such as managing handovers autonomously that do not involve MSCs and SGSNs, as described above. MSC / SGSN 140 routes calls and / or data to other elements in the network (eg, RNCs 130/132 and Node Bs 120/122/124) or to an external network. It deals with doing Others shown in FIG. 1 are conventional interfaces Uu, Iub, Iur and Iu between these elements.

 A fractional power control scheme has been proposed for controlling mobile or UE transmit power on the reverse link of the 3GPP LTE standard. This open loop fragment power control technique proposes setting the UE transmit power spectral density so that fragments of path loss (including shadowing) can be compensated. That is, the UE transmit power spectral density TxPSD_dBm can be established as follows:

TxPSD_dBm = min (Max_TxPSD_dBm, Target_SINR_dB + PathLoss_dB + UL_Interference_dBm) (1)

Where Max_TxPSD_dBm is the maximum UE transmit power spectral density (power per tone), which is a function of the UE power rating and the allocated transmit bandwidth (eg, 21 dBm UE power allocated to a single resource unit of 12 subcarriers) Rating will have a maximum transmit power per tone of 10.21 dBm);

UL_Interference_dBm is the reverse or uplink interference measured by Node B serving the UE (typically, this Node B determines this as the total received energy minus the energy received from the UEs served by Node B) For example, reported to the UE via a control channel;

PathLoss_dB is the path loss between Node B and the UE;

Target_SINR_dB is the target signal-to-noise ratio (SINR) per antenna per tone. The fractional power control scheme available in this text sets the target SINR to be a function of path loss for the serving cell as follows:

Target_SINR_dB = A + (B -1) * (PathLoss_dB) (2)

Where A and B are design parameters. Ignoring the Max_TxPSD_dBm limit in [Equation 1], the UE transmit power spectral density is given as follows.

TxPSD_dBm = A + B * PathLoss_dB + UL_Interference_dBm (3)

Note that if B = 0, there is no compensation for transmission and power loss for all UEs with the same transmit power spectral density (maximum power possible), which leads to high interference levels and poor cell edge performance. If B = 1, then this is a conventional slow power control in which path loss is fully compensated and all UEs are received with the same SINR. This leads to poor spectral efficiency. By setting 0 <B <1, only a fraction of the path loss is compensated, which provides flexibility in balancing cell edge performance and spectral efficiency.

As mentioned above, at least one problem with open loop fragment power control is that the UE does not directly consider the amount of interference that the UE will generate in the neighbor cell / sector. At least one embodiment of the present invention uses the level of interference that the UE will generate in neighboring cells / sectors in determining the transmit power spectral density for the UE. Thus, it includes the benefit of smaller dispersion, higher throughput and / or the like in the interference distribution.

In one embodiment, the reverse link transmit power for the user equipment is determined based on the first path loss and the second path loss. The first path loss is a path loss between the serving station and the user equipment, which serving communication requests of the user equipment. The second path loss is a path loss between the neighboring station and the user equipment and the neighboring station is neighboring the serving station.

In another embodiment, the user equipment measures downlink power received from the serving station. The serving station serves communication requests of the user equipment. The user equipment also measures downlink power received from neighboring stations. The neighboring station is neighboring the serving station. The user equipment determines the reverse link transmit power based on the measured downlink power received from the serving station and the measured downlink power received from the neighboring station.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood from the detailed description given below and only the examples given herein, with like reference numerals designating corresponding parts in the various figures.

1 illustrates a conventional communication system 100 operating in accordance with UMTS protocols.

2 illustrates an example where a UE may cause interference in a neighboring cell.

3 shows a graph of path loss versus target SINR for first and second exemplary sets of disturbance parameters and process parameters.

4 illustrates a flowchart of a process performed by a UE in determining a transmit power spectral density in accordance with an embodiment of the present invention.

FIG. 5 illustrates the performance of power control schemes for hypotheses listed in Table 1 and provided as average cell throughput versus cell edge rate (defined as 5% CDF user throughput).

Exemplary embodiments of the invention will be described with respect to the UMTS system shown in FIG. However, it will be appreciated that the present invention is not limited to this system or UMTS systems.

As mentioned above, one problem with open loop fragment power is that the UE does not directly consider the amount of interference that the UE will generate in neighboring cells / sectors. For example, FIG. 2 shows an example where a UE may cause interference in neighboring cells / sectors (hereinafter collectively referred to as cells). In FIG. 2, UE T1 is served by Node B1 and causes interference to Node B2. However, if UE T1 has strong shadow fading at Node B2, then it should be allowed to transmit higher transmit power spectral density than when UE T1 has a small shadow fading at Node B2. Another example is the case of non-homogeneous deployment where node B2 has a much larger cell radius, in which case UE T1 should be allowed to transmit at higher power levels.

 According to one embodiment of the invention, the open loop fragment power control method can be modified as follows: The target SINR is a function of the path loss difference between the serving cell / serving node B and the strongest neighbor cell / neighbor node B. Can be set. For example, one embodiment determines this modified target SINR, Modified_Target_SINR_dB, as follows:

Modified_Target_SINR_dB = min (A + B * (PathLoss_Diff_dB), Max_Target_SINR_dB) (4)

Here, PathLoss_Diff_dB is the difference in path loss (including shadowing) between the strongest neighbor Node B and the current serving Node B. This measurement can easily be made by determining the ratio of received downlink pilot power measurements as follows:

PathLoss_Diff_dB = 10 * log ₁₀ (DL_Rx_PilotPower_ServingCell / DL_Rx_PilotPower_StrongestNeighborCell) (5)

Where DL_Rx_PilotPower_ServingCell is the downlink pilot power received from the serving Node B, and DL_Rx_PilotPower_StrongestNeighborCell is the downlink pilot power received from the strongest neighbor Node B. The amount in parentheses is simply referred to as downlink pilot power ratio (PPR). In Equation 4, the disturbance parameter A specifies the target SINR at the "cell edge" (ie, when PathLoss_Diff_dB = 0). Positive slope parameter B specifies how quickly the target SINR increases as the UE moves inside the cell, thus controlling the fairness of the power control scheme. Max_Target_SINR_dB is the maximum allowable target SINR.

3 shows a graph of path loss versus target SINR for the first and second exemplary sets of disturbance parameter A and process parameter B. FIG. In particular, FIG. 3 is an example where the target SINR increases as the path loss between the serving cell and the strongest non-serving cell increases (ie, as the UE moves inside the cell). . 3 includes a first curve expressed in diamonds when the disturbance parameter is -5 and the process parameter is 0.5, and a second curve represented by squares when the disturbance parameter is -5 and the process parameter is 0.7. As shown, larger values of process parameter B are more aggressive in increasing the target SINR for high geometry users.

4 shows a flow chart of the processing performed by the UE in determining the transmit power spectral density level, which will also be referred to as reverse link power. As shown, at step S10, the UE measures the downlink pilot power received from the current serving station (eg, Node B currently processing communication requests of the UE). Often this is expressed as measuring downlink pilot power received from the serving sector or cell. This measurement can be made every 100ms to 200ms and the received pilot power will be averaged over this interval to average the effects of fast fading. Thereafter, in step S20, the UE receives downlink pilot power received from any other neighboring station in the reception range (eg, Node Bs having a coverage area (cell or sector) adjacent to the serving Node B). Measure Often this is expressed as measuring downlink pilot power received from neighboring sectors or cells. This measurement can be made every 100ms to 200ms and the received pilot power will be averaged over this interval to average the effects of fast fading.

In step S30, the UE determines whether any neighboring stations have been detected in step S20. If not detected, in step S40, the UE sets the modified target SINR to the maximum allowed value (see step S70). However, if the neighboring station is detected in step S20, the UE determines in step S50 the strongest non-serving neighbor as having the highest received downlink pilot power detected in step S20. In step S60, the UE calculates the pilot power ratio (PPR) as the received downlink pilot power from the serving sector divided by the received downlink pilot power from the strongest non-serving sector. The UE then determines the path loss difference in dB scale as PathLoss_Diff_dB = 10 * log 10 (PPR).

The serving station broadcasts fragment power control parameters A, B, uplink interference and Max_Target_SINR_dB on the broadcast channel, allowing all UEs being served by this station to decode the parameters. Thus, in step S70, the UE obtains these values. However, it will be appreciated that obtaining these values may occur prior to or concurrent with any step of the processing.

Then, in step S80, the UE calculates the modified target SINR according to [Equation 5].

Following step S40 or step S80, the UE, in step S90, uses transmit target spectral density as follows according to [Equation 1] using the modified target SINR as shown in [Equation 6]. Determine:

Tx_PSD_dBm = min (Max_Tx_PSD_dBm, Modified_Target_SINR_dB + PathLoss_dB + UL_Interference_dBm) (6)

Where PathLoss_dB is the measured path loss for the serving station as shown in [Equation 1].

Using the system simulation assumptions listed in Table 1 below, simulating the behavior of fractional power control using only path loss (as in [Equation 1]) and pilot power ratio measurement (as in [Equation 6]). It became. For fractional power control schemes, a range of values for B was chosen to show the tradeoff between cell throughput and cell edge rates. For each value of B, A was chosen to obtain a median IoT (interference through heat) operating point of 4.5 dB. Indeed, the desired IoT operating point may be dictated by link budget requirements of reverse link control channels. In both cases of fractional power control, a maximum target SINR of 25 dB was used.

System simulation assumptions parameter home Transmission bandwidth 5 MHz FDD Cellular layout Hexagonal grid, 19 cell sites, 3 sectors per site Distance between sites 2500 meters Losses (cable loss, body loss, etc.) 7 dB Distance-dependent path loss COST 231 HATA Model L = 139.6 + 35.7log ₁₀ (.R), K in kilometers Log Regular Shadowing Similar to UMTS 30.03, B 1.4.1.4 Shadowing Standard Deviation 8 dB Shadowing Correlation Distance 50 m Shadowing Correlation Between cells 0.5 Between sectors 1.0 Antenna pattern (horizontal) (for 3-sector cell sites with fixed antenna patterns) Cadrain antenna pattern, 65 degree beamwidth, 17.1 dBi antenna gain Carrier Frequency / Bandwidth 1.9 GHz / 5 MHz Channel model GSM TU, 3km / hr Total BS TX Power (Ptotal) 43 dBm UE power rating 21 dBm (125 mW) Intercell Interference Modeling Explicit modeling (all cells occupied by UEs) Antenna bore-sight points facing the plane of the cell (for 3-sector sites with fixed antenna patterns)

Users dropped evenly across cells

Minimum distance between UE and cell > = 35 meters MCS Levels in the Scheduler QPSK R = 1/8, 1/4, 1/3, 1/2, 2/3, 3/4 16 QAM R = 1/2, 2/3, 3/4, 7/8 HARQ 8Tx maximum, target 20% BLER HARQ RTT = 5ms number of HARQ treatments for first Tx = 10 Reuse method Reuse-1, Fragment Frequency Reuse or No Interference Avoidance Applied Number of UEs per cell 10 Traffic model Pool buffer Scheduling Method Proportional Fair, 500 ms time constant. Scheduling selects frequency based on uplink CQI pilot, only local subcarrier assignments are used without any frequency hopping. Channel estimation model Non-ideal, assume one-shot channel estimation for TTI (= 1 ms) Modeled L1 / L2 Control Signaling none Link to system mapping Effective code rate method Open Loop Fractional Power Control Assumptions Ideal measurement of path loss (including shadowing)

5 shows the performance of the power control schemes for the assumptions listed in Table 1 and provided as average cell throughput versus cell edge rate (defined as 5% CDF user throughput). Note that the performance of fractional power control is significantly improved by using the difference in path loss from the serving cell to the strongest neighbor cell as compared to using only the path loss for the serving cell alone. That is, for a given cell edge rate, higher cell throughput can be obtained; Or for a given cell throughput, a higher cell edge rate can be obtained.

Open loop fractional power control using the path loss difference between the serving cell and the strongest neighbor cell provides significantly improved performance compared to using the path loss from the serving cell alone.

As such, while the invention has been described, it will be apparent that the same may be modified in many ways. For example, parameters A and B can be fixed, set by the system operator, updated by the system operator, and changed based on factors such as load, time of day. Can be adapted. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.

Claims (10)

In the reverse link power control method: Determining a reverse link transmit power for the user equipment based on the first path loss and the second path loss (S90), wherein the first path loss is between a serving station and the user equipment; Is a path loss of the serving station, the serving station serves communication requests of the user equipment, the second path loss is a path loss between a neighboring station and the user equipment, and the neighboring station is neighboring the serving station, Reverse link power control method. The method of claim 1, Measuring downlink power received from a plurality of neighboring stations (S20); And Determining (S50) one of the plurality of neighboring stations with the maximum received downlink power, And wherein the second path loss is between the neighboring station having the maximum received downlink power and the user equipment. The method of claim 1, Measuring down link power received from the serving station (S10); Measuring downlink power received from the neighboring station (S20); And Determining a path loss difference between the first path loss and the second path loss based on the measured downlink power received from the serving station and the measured downlink power received from the neighboring station ( S60), And determining the reverse link transmission power based on the determined path loss difference. The method of claim 3, wherein Determining the path loss difference based on the measured downlink power received from the serving station divided by the measured downlink power received from the neighboring station. Way. The method of claim 4, wherein And the neighboring station is a neighboring station with the maximum received downlink power at the user equipment. The method of claim 4, wherein Determining a target signal-to-noise ratio (SINR) for the user equipment based on the determined path loss difference (S80), And the determining the reverse link transmit power determines the reverse link transmit power based on the determined target SINR. The method of claim 6, The target SINR determining step determines the target SINR based on the determined path loss difference, a first parameter and a second parameter, wherein the first parameter is a desired target SINR at an edge of a coverage area of the serving station. And the second parameter specifies how quickly the target SINR increases as the user equipment moves toward the interior of the coverage area. The method of claim 7, wherein The target SINR determining step determines the target SINR as follows: Goal SINR = min (A + B * (PathLoss_Diff), Max_Target_SINR) Wherein the PathLoss_Diff is the path loss difference, A is the first parameter, B is the second parameter, and Max_Target_SINR is the maximum target SINR. The method of claim 8, The determining the reverse link transmit power may determine the reverse link transmit power as follows: Reverse link transmit power = min (max transmit power, target SINR + first path loss + UL_interference) Wherein the UL_interference is uplink interference at the serving station. The method of claim 6, And determining the reverse link transmit power based on the path loss difference and uplink interference at the serving station.

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