UPLINK TRANSMISSION POWER CONTROL METHOD IN A WIRELESS COMMUNICATION SYSTEM
Provided is an uplink transmission power control method in a wireless communication system. Said method includes preferentially determining the transmission power of an uplink control channel, and determining the transmission power of an uplink data channel within the difference between the maximum transmittable power of a terminal and the transmission power of the uplink control channel, wherein the transmission of the uplink control signal through the uplink control channel and the transmission of the uplink data through the uplink data channel are performed at the same time using wireless resources different from one another. The present invention preferentially allocates the transmission power required for the transmission of an uplink control channel, and allocates residual power to an uplink data channel, thereby improving the effectiveness of power allocation when an uplink control signal and an uplink data signal are transmitted at the same time using physical resources different from one another.
The present invention relates to wireless communications, and more particularly, to a method of controlling uplink transmission power when an uplink control signal and an uplink data signal are simultaneously transmitted by using different radio resources in an 802.16m system.
BACKGROUND ARTThe institute of electrical and electronics engineers (IEEE) 802.16e standard was adopted in 2007 as a sixth standard for international mobile telecommunication (IMT)-2000 in the name of ‘WMAN-OFDMA TDD’ by the ITU-radio communication sector (ITU-R) which is one of sectors of the international telecommunication union (ITU). An IMT-advanced system has been prepared by the ITU-R as a next generation (i.e., 4th generation) mobile communication standard following the IMT-2000. It was determined by the IEEE 802.16 working group (WG) to conduct the 802.16m project for the purpose of creating an amendment standard of the existing IEEE 802.16e as a standard for the IMT-advanced system. As can be seen in the purpose above, the 802.16m standard has two aspects, that is, continuity from the past (i.e., the amendment of the existing 802.16e standard) and continuity to the future (i.e., the standard for the next generation IMT-advanced system). Therefore, the 802.16m standard needs to satisfy all requirements for the IMT-advanced system while maintaining compatibility with a mobile WiMAX system conforming to the 802.16e standard.
An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference (ISI) with a low complexity is taken into consideration as one of next generation wireless communication systems. In the OFDM, a serially input data symbol is converted into N parallel data symbols, and is then transmitted by being carried on each of separated N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, and an interval of a transmitted symbol is increased, thereby minimizing inter-symbol interference. In a system using the OFDM as a modulation scheme, orthogonal frequency division multiple access (OFDMA) is a multiple access scheme in which multiple access is achieved by independently providing some of available subcarriers to a plurality of users. In the OFDMA, frequency resources (i.e., subcarriers) are provided to the respective users, and the respective frequency resources do not overlap with one another in general since they are independently provided to the plurality of users. Consequently, the frequency resources are allocated to the respective users in a mutually exclusive manner. In an OFDMA system, frequency diversity for multiple users can be obtained by using frequency selective scheduling, and subcarriers can be allocated variously according to a permutation rule for the subcarriers.
In the 802.16m system, when a user equipment (UE) transmits an uplink signal to a base station (BS), an uplink control channel for transmitting a control signal and an uplink data channel for transmitting data can be physically divided, and the uplink control signal and the uplink data can be simultaneously transmitted by using one symbol. Transmission power of the uplink control channel and the uplink data channel can be determined by using formulas.
Meanwhile, maximum transmissible power that can be allocated by the UE for uplink transmission is predetermined in general according to a bandwidth assigned to the UE. Therefore, if a sum of the transmission power of the uplink control channel and the transmission power of the uplink data channel (herein, the transmission power is determined by the formulas) is greater than the maximum transmissible power, uplink transmission cannot be achieved properly since power required for uplink transmission is not enough. In particular, if the power allocated to the uplink control channel is not enough, a big problem may occur in operating the wireless communication system.
Accordingly, there is a need for a method for effective power allocation when an uplink control signal and uplink data are simultaneously transmitted by using different physical regions.
DISCLOSURE Technical ProblemThe present invention provides a method of controlling uplink transmission power when a control signal and a data signal are simultaneously transmitted by using different uplink physical resources in an 802.16m system.
Technical SolutionIn an aspect, a method of controlling uplink transmission power in a wireless communication system is provided. The method include determining preferentially transmission power of an uplink control channel, and determining transmission power of an uplink data channel within a difference between maximum transmissible power of a user equipment and the transmission power of the uplink control channel, wherein an uplink control signal transmitted through the uplink control channel and uplink data transmitted through the uplink data channel are simultaneously transmitted by using different radio resources. The transmission power of the uplink control channel may be determined by a power control equation, and the transmission power of the uplink control channel may be determined by the predetermined transmission power level. The transmission power of the uplink data channel may be determined by a power control equation, and the transmission power of the uplink data channel may be determined by a predetermined transmission power level.
Also, the uplink control channel and the uplink data channel may belong to different regions divided according to a frequency. A region to which the uplink control channel belongs may be a common region of a cell. A region to which the uplink data channel belongs may be one of a part of the common region remaining after the uplink control channel is allocated, an active region, and an inactive region.
In another aspect, a user equipment (UE) in a wireless communication system is provided. The UE include a data processor for processing an uplink control signal and uplink data, a power controller for controlling a power resource to be allocated to an uplink control channel and an uplink data channel, and a radio frequency (RF) unit for transmitting the uplink control signal through the uplink control channel and for transmitting the uplink data through the uplink data channel, wherein the power controller determines preferentially transmission power of an uplink control channel, and determines transmission power of an uplink data channel within a difference between maximum transmissible power of a user equipment and the transmission power of the uplink control channel.
Advantageous EffectsAccording to the present invention, power required to transmit an uplink control channel is preferentially allocated and the remaining power is allocated to an uplink data channel. Therefore, mutual interference can be effectively controlled when an uplink control signal and an uplink data signal are simultaneously transmitted by using different physical resources, and power can be effectively allocated.
an FFR.
to a power control formula.
maximum transmission power level.
using a hard FFR.
when using a hard FFR.
This technique can be used in an uplink or a downlink. In general, the downlink denotes communication from the BS 11 to the UE 12, and the uplink denotes communication from the UE 12 to the BS 11. In the downlink, a transmitter may be a part of the BS 11, and a receiver may be a part of the UE 12. In the uplink, the transmitter may be a part of the UE 12, and the receiver may be a part of the BS 11.
Referring to
The preamble is used between a BS and a UE for initial synchronization, cell search, and frequency-offset and channel estimation. The FCH includes information on a length of a DL-MAP message and a coding scheme of the DL-MAP.
The DL-MAP is a region for transmitting the DL-MAP message. The DL-MAP message defines access to a DL channel. This implies that the DL-MAP message defines indication and/or control information for the DL channel. The DL-MAP message includes a configuration change count of a downlink channel descriptor (DCD) and a BS identifier (ID). The DCD describes a DL burst profile applied to a current MAP. The DL burst profile indicates characteristics of a DL physical channel. The DCD is periodically transmitted by the BS by using a DCD message.
The UL-MAP is a region for transmitting a UL-MAP message. The UL-MAP message defines access to a UL channel. This implies that the UL-MAP message defines indication and/or control information for the UL channel. The UL-MAP message includes a configuration change count of an uplink channel descriptor (UCD) and also includes an effective start time of UL allocation defined by the UL-MAP. The UCD describes a UL burst profile. The UL burst profile indicates characteristics of a UL physical channel and is periodically transmitted by the BS by using a UCD message.
The DL burst is a region for transmitting data transmitted by the BS to the UE. The UL burst is a region for transmitting data transmitted by the UE to the BS.
A UL control signal and UL data are transmitted in a UL subframe. For this, a UL control channel and a UL data channel are allocated. Examples of the UL control channel include a fast feedback channel (FFBCH), a bandwidth request channel (BRCH), an HARQ feedback channel (HFBCH), a sounding channel, a ranging channel, etc. The FFBCH is a channel for UL transmission faster than normal UL data. The BRCH is a channel for requesting radio resources for transmitting UL data or control signals to be transmitted by the UE. The HFBCH is a channel for transmitting an acknowledgment (ACK)/non-acknowledgment (NACK) signal in response to data transmission. The sounding channel is a channel for UL closed-loop multiple-in multiple-out (MIMO) transmission and UL scheduling. The ranging channel is a channel for UL synchronization. By using the aforementioned various control channels, control information such as ACK/NACK, a channel quality indicator (CQI), a precoding matrix index (PMI), etc., can be transmitted.
For transmission of the UL control signal and the UL data, there is a need to allocate power required for the UL control channel and the UL data channel. In general, a transmission power level of the UL control channel and the UL data channel can be calculated by Equation 1 and Equation 2. Hereinafter, a formula having a format of Equation 1 or Equation 2 is called a power control formula.
PPSD
PPSD
In Equation 1 above, PPSD
In Equation 2 above, PPSD
The transmission power allocated to the UL control channel and the UL data channel can be obtained by using the values PPSD—ctrl and PPSD
Ptotal
Ptotal
In Equation 3 and Equation 4 above, Mt denotes the number of streams. BW denotes a size of a bandwidth assigned for transmission of each UE.
Hereinafter, a UL transmission power control method proposed in the present invention will be described.
Maximum transmissible power PMax of a UE has a different value for each system. The UE has to determine a transmission power level of each channel in a range not exceeding a limited Pmax. If a sum of Ptotal
PMax−Ptotal
That is, transmission power allocated to a UL data channel has to be less than a value obtained by subtracting transmission power preferentially allocated to the UL control channel from maximum transmission power of the UE. The proposed invention will be described hereinafter on the premise that a power resource is preferentially allocated to the UL control channel as expressed in Equation 5 above.
First, the UL transmission power control method will be described in case of not using a fractional frequency reuse (FFR). The FFR implies the use of an assigned bandwidth by splitting the bandwidth by using different reuse factors. The FFR can be used when separate radio resources belonging to different regions are intended to be used for a particular purpose. For example, in order to increase throughput in a cell edge in one cell, a part of the bandwidth may be allocated to a cell edge portion by splitting the bandwidth.
In step S100, a temporary transmission power level of a UL control channel is calculated. The temporary transmission power level of the UL control channel can be calculated by the power control formula of Equation 1 above.
In step S110, a transmission power level of the UL control channel is determined. This can be expressed by Equation 6 below.
Pctrl=min(PPSD
In Equation 6 above, PPSD
In step S120, a temporary transmission power level of a UL data channel is calculated. The temporary transmission power level of the UL data channel can be calculated by the power control formula of Equation 2 above.
In step S130, a transmission power level of the UL data channel is determined by using the value Pctrl. This can be expressed by Equation 7 below.
Pdata=min(PPSD
In Equation 7 above, PPSD
Alternatively, the transmission power level of each channel may be determined by using a pre-fixed transmission power level. In this case, the transmission power level may be always determined to be greater than or equal to the fixed transmission power level in a place where many reception requests exist such as a hot spot, or the transmission power level may be always determined to be less than or equal to the fixed transmission power level in order to decrease interference to a neighbor cell.
In step S200, a temporary transmission power level of a first region is calculated. The temporary transmission power level of the first region can be calculated by the power control formula.
In step S210, a transmission power level of the first region is determined. This can be expressed by Equation 8 below.
Pregion1=min(PPSD
In Equation 8 above, PPSD
When the first region corresponds to the UL control channel, the first region can be divided into a plurality of regions. Each of the plurality of regions can transmit a different control signal such as CQI, ACK/NACK, etc. In this case, priorities can be assigned according to an importance level of the control signal transmitted in each region, and the transmission power level can be preferentially determined according to an order of the priorities. For example, if the CQI is the most important among the control signals, a transmission power level may be determined preferentially for a region in which the CQI is transmitted in the UL control channel. Regarding the remaining control signals, the transmission power level may be determined from the remaining power resources other than a power resource allocated to the region in which the CQI is transmitted.
In step S220, a temporary transmission power level of a second region is calculated. The temporary transmission power level of the second region can be calculated by a power control formula.
In step S230, a transmission power level of the second region is determined. This can be expressed by Equation 9 below.
Pregion2=min(PPSD
In Equation 9 above, PPSD
When a radio resource is divided for three or more regions, the aforementioned process may be repeated to determine a transmission power level of each region. The method is applicable when a resource of a specific region is limitedly used. However, since a maximum transmission power level is determined and used for all resource regions, there is a demerit in that a power resource cannot be additionally allocated to a portion which requires more power resources.
In the determining of the transmission power level of the second region, the maximum transmission power level of the second region may be not used. Instead, by using a difference between a maximum transmissible power level of a UE and the transmission power level of the first region, the transmission power level of the second region may be determined. This can be expressed by Equation 10 below.
Pregion2=min(PPSD
In Equation 10 above, PPSD
When the radio resource is divided for three or more regions, the aforementioned process may be repeated to determine the transmission power level of each region. In this case, Equation 10 may be applied to a region which requires a fixed maximum transmission power level, so that power required for each region is effectively allocated.
Hereinafter, a UL transmission power control method in case of using an FFR will be described.
The FFR has two types, i.e., a hard FFR and a soft FFR. The hard FFR uses only the active region without using the inactive region. The soft FFR uses the inactive region as well, by allocating a specific resource to the inactive region. Since the hard FFR does not use a certain part of resources, resource utilization is low, but tends to decrease inter-frequency interference to that extent. Since the soft FFR uses a full band, resource utilization is high, but requires a method of effectively using the inactive region.
Referring to
In step S400, a temporary transmission power level of a UL control channel is determined. The temporary transmission power level of the UL control channel can be calculated by the power control formula of Equation 1 above.
In step S410, transmission power of the UL control channel is determined. This can be expressed by Equation 11 below.
Pctrl=min(Ptotal,PPSD
In Equation 11 above, Ptotal total denotes maximum transmissible power of a UE, and PPSD
In step S420, a transmission power level of a UL data channel is determined by using the value Pctrl. This can be expressed by Equation 12 below.
In Equation 12 above, Ptotal total denotes maximum transmissible power of the UE, and Pctrl denotes transmission power of the UL control channel. BW denotes a bandwidth assigned to the UL data channel. The transmission power level PPSD
When the power resource is allocated to the UL control channel as shown in the aforementioned embodiment, the transmission power level of the UL control channel may be determined by using the power control formula as described above, or the power resource may be allocated to the UL control channel by predetermining a maximum transmission power level and the remaining power may be allocated to the UL data channel. In addition, when using the hard FFR, an inactive region has a relatively less effect on the UL control channel, and thus a maximum transmission power level of the UL data channel itself may be predetermined and a power resource may be allocated according to the maximum transmission power level irrespective of the transmission power level of the UL control channel.
In step S500, the same maximum transmissible power level is assigned to a UL control channel and a UL data channel. This can be determined by dividing maximum transmission power of a UE by a bandwidth of a region in which a resource is allocated.
In step S510, a transmission power level of each of the UL control channel and the UL data channel is determined on the basis of the maximum transmissible power level. In this case, each channel may determine a required transmission power level by using a power control parameter designated for each channel and a common power control parameter which is common in all regions.
In step S520, if the required transmission power level of the UL data channel exceeds the maximum transmissible power level, a remaining power resource is allocated to the UL data channel by comparing the maximum transmissible power level of the UL control channel and the transmission power level. In this case, the remaining power resource may be allocated in a range satisfying the required transmission power level of the UL data channel, or the remaining power resource of the UL control channel may be entirely allocated to the UL data channel irrespective of the required transmission power level.
Even in a case where the required transmission power level of the UL control channel exceeds the maximum transmissible power level, the process of step S520 can be applied. Meanwhile, a plurality of control channels may be allocated. In this case, priorities of the channels may be determined according to a UL control signal contained the UL control channel, and the required transmission power of the UL control channel may be decreased by ignoring some of information having a low priority.
The required transmission power levels of both of the UL control channel and the UL data channel may exceed the maximum transmissible power level. In this case, transmission may be performed with the maximum transmissible power level, or a power resource of a channel having a low priority may be allocated to a channel having a high priority by determining the priorities of the control signal and data.
When using a soft FFR, allocation of a power resource is required for an inactive region. In this case, the transmission power level of the UL control channel may be determined by using a power control formula, and the transmission power level of the inactive region may be determined to the predetermined transmission power level. Alternatively, the transmission power level of the UL control channel may be determined to the predetermined transmission power level, and the transmission power level of the inactive region may also be determined by predetermining the maximum transmissible power level.
The present invention can be implemented using hardware, software, or a combination of them. In the hardware implementations, the present invention can be implemented using an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), a Programmable Logic Device (PLD), a Field Programmable Gate Array (FPGA), a processor, a controller, a microprocessor, other electronic unit, or a combination of them, which is designed to perform the above-described functions. In the software implementations, the present invention can be implemented using a module performing the above functions. The software can be stored in a memory unit and executed by a processor. The memory unit or the processor can use various means which are well known to those skilled in the art.
What has been described above includes examples of the various aspects. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the various aspects, but one of ordinary skill in the art may recognize that many further combinations and permutations are possible. Accordingly, the subject specification is intended to embrace all such alternations, modifications and variations that fall within the spirit and scope of the appended claims.
Claims
1. A method of controlling uplink transmission power in a wireless communication system, the method comprising:
- determining preferentially transmission power of an uplink control channel; and
- determining transmission power of an uplink data channel within a difference between maximum transmissible power of a user equipment and the transmission power of the uplink control channel,
- wherein an uplink control signal transmitted through the uplink control channel and uplink data transmitted through the uplink data channel are simultaneously transmitted by using different radio resources.
2. The method of claim 1, wherein the transmission power of the uplink control channel is determined by the equation:
- Pctrl=min(PPSD—total,PPSD—ctrl)
- where Pctrl is to-be-determined transmission power of the uplink control channel, PPSD—total is a predetermined maximum transmissible power level of the user equipment, and PPSD—ctrl is a temporary transmission power level of the uplink control channel.
3. The method of claim 2, wherein the temporary transmission power level of the uplink control channel is determined by the equation:
- PPSD—ctrl(dBm)=L+SINRTarget—ctrl+NI+OffsetAMSperAMS+OffsetABSperAMS
- where PPSD—ctrl is the to-be-determined temporary transmission power level of the uplink control channel, L is an average estimation value of an uplink propagation loss, SINRTarget—ctrl is a target signal-to-interference plus noise ratio (SINR) value of the uplink control channel received by a base station, noise and interference (NI) is an average estimation value between noise and an interference level, and OffsetAMSperAMS and OffsetABSperAMS are offset values controlled respectively by the user equipment and the base station.
4. The method of claim 1, wherein the transmission power of the uplink control channel is determined by the predetermined transmission power level.
5. The method of claim 4, wherein the transmission power of the uplink control channel is determined to a smaller value between the predetermined transmission power level and a transmission power level calculated by a power control formula.
6. The method of claim 4,
- wherein the uplink control channel is divided into a plurality of regions, and
- wherein the transmission power level is preferentially determined for a region having a high priority by assigning priorities to the plurality of regions.
7. The method of claim 1, wherein the transmission power of the uplink data channel is determined by the equation:
- Pdata=min(PPSD—total−Pctrl,PPSD—data),
- where Pdata is to-be-determined transmission power of the uplink data channel, PPSD—total is a maximum transmissible power level of the user equipment, Pctrl is transmission power of the uplink control channel, and PPSD—data is a temporary transmission power level of the uplink data channel.
8. The method of claim 7, wherein the temporary transmission power level of the uplink data channel is determined by the equation:
- PPSD—data(dBm)=L+SINRTarget—data+NI+OffsetAMSperAMS+OffsetABSperAMS
- where PPSD—data is a to-be-determined temporary transmission power level of the uplink data channel, L is an average estimation value of an uplink propagation loss, SINRTarget—data is a target SINR value of the uplink data channel received by a base station, NI is an average estimation value between noise and an interference level, and OffsetAMSperAMS and OffsetABSperAMS are offset values controlled respectively by the user equipment and the base station.
9. The method of claim 1, wherein the transmission power of the uplink data channel is determined by a predetermined transmission power level.
10. The method of claim 9, wherein the transmission power of the uplink data channel is determined to a smaller value between the predetermined transmission power level and a transmission power level calculated by a power control formula.
11. The method of claim 1, wherein the uplink control channel and the uplink data channel belong to different regions divided according to a frequency.
12. The method of claim 11, wherein a region to which the uplink control channel belongs is a common region of a cell.
13. The method of claim 12, wherein a region to which the uplink data channel belongs is any one of a part of the common region remaining after the uplink control channel is allocated, an active region, and an inactive region.
14. A user equipment in a wireless communication system, comprising:
- a data processor for processing an uplink control signal and uplink data;
- a power controller for controlling a power resource to be allocated to an uplink control channel and an uplink data channel; and
- a radio frequency (RF) unit for transmitting the uplink control signal through the uplink control channel and for transmitting the uplink data through the uplink data channel,
- wherein the power controller determines preferentially transmission power of an uplink control channel, and determines transmission power of an uplink data channel within a difference between maximum transmissible power of a user equipment and the transmission power of the uplink control channel.
Type: Application
Filed: Jul 8, 2009
Publication Date: May 12, 2011
Inventors: Dong Cheol Kim (Anyang-si), Min Seok Noh (Anyang-si), Yeong Hyeon Kwon (Anyang-si), Jin Sam Kwak (Anyang-si), Sung Ho Moon (Anyang-si), Seung Hee Han (Anyang-si), Hyun Woo Lee (Anyang-si)
Application Number: 12/996,974
International Classification: H04W 52/00 (20090101);