US20110116408A1

US20110116408A1 - Substrate conveying device

Info

Publication number: US20110116408A1
Application number: US13/002,649
Authority: US
Inventors: Dong Cheol Kim; Min Seok Noh; Yeong Hyeon Kwon; Jin Sam Kwak; Sung Ho Moon; Seung Hee Han; Hyun Woo Lee
Original assignee: Individual
Current assignee: LG Electronics Inc
Priority date: 2008-07-08
Filing date: 2009-07-08
Publication date: 2011-05-19
Also published as: WO2010005239A3; WO2010005238A2; US20110110257A1; WO2010005239A2; US8531975B2; WO2010005238A3; US20110134759A1; WO2010005237A3; WO2010005237A2; CN102089998A

Abstract

A method for controlling uplink transmission power of a mobile station (MS) in a wireless communication system is provided. The method includes: obtaining a plurality of interference indicators indicating uplink interference from a base station (BS), wherein a full bandwidth is divided into a plurality of frequency partitions, and the plurality of interference indicators respectively correspond to the plurality of frequency partitions; determining an uplink transmission power level of a frequency partition corresponding to an interference indicator selected from the plurality of interference indicators on the basis of the selected interference indicator; and controlling the uplink transmission power on the basis of the uplink transmission power level. Accordingly, inter-cell interference can be reduced, and reliability of an MS located in a cell edge can be improved.

Description

TECHNICAL FIELD

The present invention relates to wireless communications, and more particularly, to a method for controlling uplink transmission power by a mobile station in a wireless communication system, and the mobile station using the method.

BACKGROUND ART

A wireless communication system needs to control uplink transmission power. This is to regulate a magnitude of a reception signal of a base station to a proper level. If transmission power is too weak in uplink transmission, the base station cannot receive a transmission signal of a mobile station. On the other hand, if the transmission power is too strong, the transmission signal of the mobile station may act as interference to a transmission signal of another mobile station, which increases battery consumption of the mobile station. When the magnitude of the reception signal is maintained to the proper level by controlling the uplink transmission power, unnecessary power consumption of the mobile station can be avoided, and a data transfer rate can be adaptively determined, thereby improving transmission efficiency.
The uplink transmission power control is roughly classified into two types, i.e., an open loop power control and a closed loop power control. The open loop power control predicts uplink signal attenuation by measuring or estimating downlink signal attenuation so as to compensate for uplink transmission power, and determines uplink power by considering an amount of a radio resource allocated to the mobile station or an attribute of data to be transmitted. The closed loop power control regulates transmission power through interworking between the base station and the mobile station by using feedback information on the transmission power control.
A fractional frequency reuse (FFR) is one of schemes for reducing inter-cell interference. The FFR uses a feature in which a mobile station located in a cell center and a mobile station located in a cell edge are differently affected by interference caused by a neighbor cell. The mobile station located in the cell center is not significantly affected by interference from a neighbor base station, but the mobile station located in the cell edge is significantly affected by the inference from the neighbor base station. In the FFR, the mobile station located in the cell center uses a frequency reuse of 1, and the mobile station located in the cell edge uses a frequency reuse greater than 1. When the frequency reuse is greater than 1, it implies that frequency overlapping does not occur in an edge between neighbor cells.
Accordingly, there is a need for a method capable of controlling uplink transmission power by a mobile station in a system using an FFR.

SUMMARY OF INVENTION

Technical Problem

The present invention provides a method and apparatus for controlling uplink transmission power for each frequency partition.
The present invention also provides a method and apparatus for providing interference information for uplink transmission power control.

Technical Solution

According to an aspect of the present invention, there is provided a method for controlling uplink transmission power of a mobile station (MS) in a wireless communication system. The method includes: obtaining a plurality of interference indicators indicating uplink interference from a base station (BS), wherein a full bandwidth is divided into a plurality of frequency partitions, and the plurality of interference indicators respectively correspond to the plurality of frequency partitions; determining an uplink transmission power level of a frequency partition corresponding to an interference indicator selected from the plurality of interference indicators on the basis of the selected interference indicator; and controlling the uplink transmission power on the basis of the uplink transmission power level.
In the aforementioned aspect of the present invention, the plurality of interference indicators may be obtained for each of uplink data and an uplink control signal, and the plurality of interference indicators may be determined according to a radio resource allocation type of each of the uplink data and the uplink control signal. In this case, the radio resource allocation type may be a type in which resources are allocated in contiguous resource allocation units in a frequency domain or a type in which resources are allocated in non-contiguous resource allocation units.
In addition, each of the plurality of frequency partitions may include a plurality of subband physical resource units (PRUs) and a plurality of miniband PRUs. The plurality of interference indicators may be broadcast from the BS.
In addition, the uplink transmission power control may be an open loop transmission power control.
According to another aspect of the present invention, there is provided an MS including: a radio frequency (RF) unit for transmitting/receiving a radio signal; and a processor coupled to the RF unit, wherein the processor is configured to: obtain a plurality of interference indicators indicating uplink interference from a BS, wherein a full bandwidth is divided into a plurality of frequency partitions, and the plurality of interference indicators respectively correspond to the plurality of frequency partitions; to determine an uplink transmission power level of a frequency partition corresponding to an interference indicator selected from the plurality of interference indicators on the basis of the selected interference indicator; and to control the uplink transmission power on the basis of the uplink transmission power level.

Advantageous Effects

According to the present invention, inter-cell interference can be reduced, and reliability of a mobile station located in a cell edge can be improved.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows an example of using a fractional frequency reuse (FFR).

FIG. 3 shows an example of radio resource allocation.

FIG. 4 shows an example of transmission power control in a hard FFR.

FIG. 5 shows an example of transmission power control in a soft FFR.

FIG. 6 is a flowchart showing an uplink transmission power control method according to an embodiment of the present invention.

FIG. 7 shows interference information according to another embodiment of the present invention.

FIG. 8 is a block diagram showing a wireless communication system for implementing an embodiment of the present invention.

MODE FOR INVENTION

FIG. 1 shows a wireless communication system.
Referring to FIG. 1, a wireless communication system 10 includes at least one base station (BS) 11. Respective BSs 11 provide communication services to specific geographical regions (generally referred to as cells) 15 a, 15 b, and 15 c. The cell can be divided into a plurality of regions, each of which is referred to as a sector. The BS 11 is generally a fixed station that communicates with a mobile station (MS) 12 and may be referred to as another terminology, such as an evolved node-B (eNB), a base transceiver system (BTS), an access point, an access network (AN), etc. The BS 11 can perform functions such as connectivity with the MS 12, management, control, resource allocation, etc.
The MS 12 may be fixed or mobile, and may be referred to as another terminology, such as a user equipment (UE), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device, an access terminal (AT), etc. Hereinafter, a downlink (DL) denotes communication from the BS 11 to the MS 12, and an uplink (UL) denotes communication from the MS 12 to the BS 11.
FIG. 2 shows an example of using a fractional frequency reuse (FFR). One cell C1 is divided into a center region 21 and three edge regions 22, 23, and 24. A full bandwidth of available frequencies in one cell is divided into four frequency partitions (FPs). The center region 21 uses a 4^thfrequency partition (i.e., F4). The three edge regions 22, 23, and 24 respectively use 1^st, 2^nd, and 3^rdfrequency partitions (i.e., FP1, FP2, and FP3). Contiguous cells use different FPs. That is, the edge region 22 of the cell C1 uses the F1, an edge region 32 of a cell C2 uses the F3, and an edge region 43 of a cell C3 uses the F2.
FIG. 3 shows an example of radio resource allocation. A physical resource unit (PRU) may be a basic physical unit of resource allocation. For example, one PRU may include P_sccontiguous subcarriers in a frequency domain and N_symcontiguous orthogonal frequency division multiple access (OFDMA) symbols in a time domain. For example, P_scmay be 18, and N_symmay be 6 or 7. The PRUs are divided into a subband and a miniband. The subband is a logical unit including a plurality of contiguous PRUs. Herein, one subband may include 4 contiguous PRUs. The miniband is a logical unit including at least one PRU. PRUs belonging to the subband are called subband PRUs (i.e., PRU_SB), and PRUs belonging to the miniband are called miniband PRUs (i.e., PRU_MB).
In this example, 24 PRUs indexed from 0 to 23 are mapped to 12 subband PRUs and 12 miniband PRUs (step S402). The 24 PRUs are grouped into sub-groups in a unit of 4 (i.e., corresponding to the number of PRUs belonging to the subband), and non-contiguous sub-groups are sequentially mapped to the subband and the miniband. Permutation may be performed on the miniband PRUs to shuffle locations of the miniband PRUs (step S403).
The subband PRUs and the miniband PRUs are divided for each frequency partition (step S404). Although it is shown herein that they are divided into two frequency partitions FP1 and FP2, the number of frequency partitions is not limited thereto. The frequency partition may be a logical frequency allocation unit divided in a full bandwidth of available frequencies. At least one frequency partition may be allocated to an MS. The frequency partition may include a plurality of logical PRUs, and may also include subband PRUs and miniband PRUs. The frequency partitions FP1 and FP2 may be used for other purposes, e.g., an FFR and/or a multicast and broadcast service (MBS).
The FFR includes a hard FFR and a soft FFR. In the hard FFR, a 2^ndfrequency partition is inactive if a 1^stfrequency partition is active. In the soft FFR, the 2^ndfrequency partition can be active even if the 1^stfrequency partition is active.
FIG. 4 shows an example of transmission power control in a hard FFR. MSs 1, 2, and 3 may belong to different sectors (or cells). In the MS 1, if a 1^stfrequency partition (i.e., F1) is active, 2^ndand 3^rdfrequency partitions (i.e., F2 and F3) are inactive. In this case, a 4^thfrequency partition (i.e., F4) may also be active in the MS 1. The F4 may be used in transmission of a control signal 500 for MSs located in an inner cell. Therefore, the MS 1 performs the transmission power control in the F1 and the F4.
In the MS 2, if the F2 is active, the F1 and the F3 are inactive. In this case, the F4 may also be active in the MS 2. The MS 2 performs transmission power control in the F2 and the F4.
Likewise, in the MS 3, if the F3 is active, the F1 and the F2 are inactive. In this case, the F4 may also be active in the MS 3. The MS 3 performs transmission power control in the F3 and the F4.
FIG. 5 shows an example of transmission power control in a soft FFR. MSs 1, 2, and 3 may belong to different sectors (or cells). In the MS 1, an F1 and an F4 may be active, and an F2 and an F3 may also be active. Therefore, the MS 1 performs transmission power control in the F1 to the F4. However transmission power of the F2 and the F3 has a maximum transmission power level lower than those of the F1 and F4 which can be regarded as primary frequency partitions. The same also apply to the MS 2 and the MS 3.
Since the frequency partitions can be used for different purposes such as an FFR, an MBS, etc., it is preferable to perform power control for each frequency partition.
FIG. 6 is a flowchart showing a UL transmission power control method according to an embodiment of the present invention. A BS estimates an interference indicator (i.e., a noise and interference level indicator (NI)) for each frequency partition by using signals received from neighbor cells (step S61). The BS sends the NI corresponding to each frequency partition to an MS (step S62). The NI may be broadcast through a broadcast channel. Alternatively, the NI may be unicast/multicast to an individual MS and/or a plurality of MSs with respect to allocated frequency partitions. The MS controls UL transmission power of a UL channel for each frequency partition (step S63). The MS transmits UL data through the UL channel (step S64).
In an open loop power control, UL transmission power for each frequency partition can be determined by the following equation.
P _i =L _i+SINR_Target,i +NI _i+OffsetMS_perMS+OffsetBS_perMS [Equation 1]
In Equation 1, P_idenotes a transmission power level of an i^thfrequency partition, L_idenotes an estimated UL propagation loss of the i^thfrequency partition, SINR_Target,idenotes a target UL signal-to-interference plus noise ratio (SINR) of the i^thfrequency partition, NI_idenotes an NI of the i^thfrequency partition, OffsetMS_perMSdenotes a correction term for MS-specific power offset, and OffsetBS_perMSdenotes a correction term for BS-specific power offset. L_ican be determined based on total power received on an active subcarrier of a preamble. SINR_Target,imay be determined based on a power control value received from the BS, or may be a predetermined value. The NI, may be information which is broadcast by the BS.
The NI denotes an interference level when UL transmission of MSs belonging to neighbor cells has an effect on an MS in a serving cell. Hereinafter, the NI indicates an estimated average power level of noise and interference, and is generally expressed by average power per subcarrier (i.e., dBm per subcarrier). However, the present invention is not limited thereto, and thus the NI can be expressed variously such as average power per frequency (dBm per Hz), average power per band (dBm per band), average power per subchannel (dBm per subchannel), etc. The NI may be determined to average power with respect to a sum of noise and interference per subcarrier, or the sum of the noise and interference may be normalized to noise. By the use of the NI given for each frequency partition, UL power control is possible for each frequency partition.
Although it is introduced in the above example that UL transmission power is obtained for each frequency partition by the MS, the BS may determine UL transmission power for each frequency partition. The BS may estimate an interference level for each frequency partition and may perform UL transmission power control for each frequency partition, thereby being able to decrease inter-cell interference.
FIG. 7 shows an NI according to another embodiment of the present invention.
In each FP, the NI may be given differently according to UL data and a UL control signal. The UL control signal may include at least one of a hybrid automatic repeat request (HARQ) acknowledgement (ACK)/negative-acknowledgement (NACK) signal, a ranging signal, a channel quality indicator (CQI), a sounding signal, and a precoding matrix index (PMI). The UL data may include user data. The UL control signal and the UL data may be transmitted simultaneously in a frequency partition. This implies that the UL control signal and the UL data can be transmitted on one OFDMA symbol.
The control signal generally does not use or cannot use an additional characteristic such as retransmission, link adaptation etc. Therefore, to increase reception throughput in transmission, more attention is required such as modulation, a coding rate, power allocation, etc. In addition, the control signal has a tendency to maintain a statistical characteristic by performing transmission only for a specific symbol and a specific frequency band among radio resources. The data and the control signal require different transmission power controls. Therefore, effective transmission power control is possible in such a manner that the NI is reported by a BS to an MS by dividing the NI into an NI 710 for the UL data and an NI 720 for the UL control signal in the frequency partition.
In addition thereto, the NI 710 for the UL data and the NI 720 for the UL control signal can be further sub-divided. For example, the NI may be given per distributed bands 711 and 721, per localized bands 712 and 722, and per average localized bands 713 and 723. The distributed band denotes a band in which a resource allocation unit (e.g., PRU) is allocated not-contiguously, and may correspond to a miniband for example. The localized band denotes a band in which a plurality of contiguous resource allocation units are allocated, and may correspond to a subband for example. The average localized band denotes an average NI for a plurality of subbands.
That is, the NI transmitted by the BS to the MS may be determined according to allocation of a radio resource used in transmission of the UL data and/or the UL control signal transmitted by the MS to the BS, for example, according to: 1) whether it is allocated to a distributed band or a localized band; 2) whether the UL data and the UL control signal are transmitted simultaneously by performing frequency division multiplexing (FDM) or are transmitted by using different time resources; and 3) which FP will be used to transmit the UL data and the UL control signal.
FIG. 8 is a block diagram showing a wireless communication system for implementing an embodiment of the present invention. A BS 50 includes a processor 51, a memory 53, and a radio frequency (RF) unit 52. The processor 51 estimates a plurality of interference indicators indicating UL interference. Layers of a radio interface protocol may be implemented by the processor 51. The memory 53 is coupled to the processor 51, and stores a variety of information for driving the processor 51. The RF unit 52 is coupled to the processor 51, and transmits and/or receives a radio signal.
An MS 60 includes a processor 61, a memory 62, and an RF unit 63. The processor 61 obtains a plurality of interference indicators indicating UL interference received through the RF unit 63, determines a UL transmission power level of a frequency partition corresponding to an interference indicator selected from the plurality of interference indicators on the basis of the selected interference indicator, and controls the UL transmission power on the basis of the UL transmission power level. Layers of a radio interference protocol may be implemented by the processor 61. The memory 62 is coupled to the processor 61, and stores a variety of information for driving the processor 61. The RF unit 63 is coupled to the processor 61, and transmits and/or receives a radio signal.
The processors 51 and 61 may include an application-specific integrated circuit (ASIC), a separate chipset, a logic circuit, and/or a data processing unit. The memories 52 and 62 may include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and/or other equivalent storage devices. The RF units 53 and 63 may include one or more antennas for transmitting and/or receiving a radio signal. When the embodiment of the present invention is implemented in software, the aforementioned methods can be implemented with a module (i.e., process, function, etc.) for performing the aforementioned functions. The module may be stored in the memories 52 and 62 and may be performed by the processors 51 and 61. The memories 52 and 62 may be located inside or outside the processors 51 and 61, and may be coupled to the processors 51 and 61 by using various well-known means.
Although a series of steps or blocks of a flowchart are described in a particular order when performing methods in the aforementioned exemplary system, the steps of the present invention are not limited thereto. Thus, some of these steps may be performed in a different order or may be concurrently performed. Those skilled in the art will understand that these steps of the flowchart are not exclusive, and that another step can be included therein or one or more steps can be omitted without having an effect on the scope of the present invention.
The aforementioned embodiments include various exemplary aspects. Although all possible combinations for representing the various aspects cannot be described, it will be understood by those skilled in the art that other combinations are also possible. Therefore, all replacements, modifications and changes should fall within the spirit and scope of the claims of the present invention.

Claims

1-12. (canceled)

13. A method for operating a mobile station (MS) in a wireless communication system using a specific frequency, the method comprising:

receiving a noise and interference level indicator (NI),

wherein the specific frequency includes a first frequency partition and a second frequency partition, and

wherein the NI includes a first noise and interference value for the first frequency partition and a second noise and interference value for the second frequency partition.

14. The method of claim 13,

wherein the specific frequency further includes a third frequency partition, and

wherein the NI further includes a third noise and interference value for the third frequency partition.

15. The method of claim 14,

wherein the specific frequency further includes a fourth frequency partition, and

wherein the NI further includes a fourth noise and interference value for the fourth frequency partition.

16. The method of claim 15,

wherein one of the first noise and interference value, the second noise and interference value, the third noise and interference value, and the fourth noise and interference value is for a control signal.

17. The method of claim 13, wherein at least one of the first noise and interference value and the second noise and interference value has a noise and interference value for each of uplink data and an uplink control signal.

18. The method of claim 13, wherein the NI is broadcasted from a base station (BS).

19. The method of claim 13, wherein the NI is for an open loop power control.

20. The method of claim 13, wherein uplink transmission power is determined based on the received NI according to the following equation:

P(dBm)=L+SINR_Target +NI+OffsetMS_perMS+OffsetBS_perMS

where P(dBm) is an uplink transmission power level (dBm) per subcarrier, L is an estimated average current uplink propagation loss value, SINR_Targetis a target uplink SINR value, NI is the aforementioned NI, OffsetMS_perMSis a correction term for MS-specific power offset regulated by the MS, and OffsetBS_perMSis a correction term for BS-specific power offset regulated by a BS.

21. The method of claim 20, further comprising transmitting an uplink signal on the basis of the uplink transmission power.

22. The method of claim 13, wherein the NI is an average power level of noise and interference per subcarrier estimated by a BS.

23. A method for operating a base station (BS) in a wireless communication system using a specific frequency, the method comprising:

transmitting a noise and interference level indicator (NI),

24. The method of claim 23,

25. The method of claim 24,

26. The method of claim 25, wherein one of the first noise and interference value, the second noise and interference value, the third noise and interference value, and the fourth noise and interference value is for a control signal.

27. The method of claim 23, wherein at least one of the first noise and interference value and the second noise and interference value has a noise and interference value for each of uplink data and an uplink control signal.

28. The method of claim 23, wherein the NI is broadcasted from the BS.

29. The method of claim 23, wherein the NI is for open loop power control.

30. The method of claim 23, wherein uplink transmission power is determined based on the transmitted NI according to the following equation:

P(dBm)=L+SINR_Target +NI+OffsetMS_perMS+OffsetBS_perMS

where P(dBm) is an uplink transmission power level (dBm) per subcarrier, L is an estimated average current uplink propagation loss value, SINR_Targetis a target uplink SINR value, NI is the aforementioned NI, OffsetMS_perMSis a correction term for MS-specific power offset regulated by a mobile station (MS), and OffsetBS_perMSis a correction term for BS-specific power offset regulated by the BS.

31. The method of claim 30, further comprising:

receiving an uplink signal on the basis of the uplink transmission power.

32. The method of claim 23, wherein the NI is an average power level of noise and interference per subcarrier estimated by the BS.