Abstract:
A channel normally used to transmit acknowledgement of successful signal receipt and an indication of unsuccessful signal receipt is adopted to transmit power control information from a base station to a mobile station. The power control information can be encoded as a binary code where each value of the code is indicated by an acknowledgement or non-acknowledgement signal.

Description:
FIELD 
       [0001]    The subject matter disclosed herein relates generally to techniques to control power level of signals transmitted by a mobile station. 
       RELATED ART 
       [0002]    Orthogonal FDM (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) are common multiple access technique used in broadband wireless networks. Uplink power control is an extremely important part of OFDM and OFDMA systems for controlling the transmit power level. Uplink power control seeks to optimize the link performance and terminal battery power life while reducing inter-base station uplink co-channel interference. Uplink power control methods can be categorized generally as Open Loop Power Control (OLPC) and Closed Loop Power Control (CLPC). OLPC offers an advantage of low signaling overhead but has low accuracy of control of transmitter power. CLPC offers an advantage of high accuracy control of transmitter power but has high signaling overhead. 
         [0003]    “DRAFT Standard for Local and metropolitan area networks—Part 16: Air Interface for Broadband Wireless Access Systems”, by IEEE 802.16 (2008) describes an example CLPC power control mechanism in which transmitter power level is controlled by an offset signaled by a base station expressed as following formula: 
         [0000]        P   new   =P   last +( C/N   new   −C/N   last )−(10 log 10 ( R   new )−10 log 10 ( R   last ))+offset 
         [0000]    The base station transmits the offset information to a mobile station using a Fast Power Control (FPC) Message, Power Control Information Elements (IE), and RNG-RSP for periodic ranging. However, transmitting the offset information using CLPC introduces high signaling overhead. 
         [0004]    It is desirable to have a mobile station power control mechanism that can support rapid and accurate changes in power level with lower signaling overhead. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the drawings and in which like reference numerals refer to similar elements. 
           [0006]      FIG. 1  depicts a system in which a base station communicates with a mobile station, in accordance with an embodiment. 
           [0007]      FIG. 2  depicts a power control information setup process that is initiated by a base station, in accordance with an embodiment. 
           [0008]      FIG. 3  depicts a power control information setup process that is initiated by a mobile station, in accordance with an embodiment. 
           [0009]      FIG. 4  depicts an example in which a base station controls the uplink data transmission power level of a mobile station, in accordance with an embodiment. 
           [0010]      FIGS. 5A and 5B  depict processes in which a respective base station and mobile station initiate release of use of acknowledge channels to communicate power control information, in accordance with various embodiments. 
       
    
    
     DETAILED DESCRIPTION  
       [0011]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase “in one embodiment” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in one or more embodiments. 
         [0012]    Embodiments of the invention may be used in a variety of applications. Some embodiments of the invention may be used in conjunction with various devices and systems, for example, a transmitter, a receiver, a transceiver, a transmitter-receiver, a wireless communication station, a wireless communication device, a wireless Access Point (AP), a modem, a wireless modem, a Personal Computer (PC), a desktop computer, a mobile computer, a laptop computer, a notebook computer, a tablet computer, a server computer, a handheld computer, a handheld device, a Personal Digital Assistant (PDA) device, a handheld PDA device, a network, a wireless network, a Local Area Network (LAN), a Wireless LAN (WLAN), a Metropolitan Area Network (MAN), a Wireless MAN (WMAN), a Wide Area Network (WAN), a Wireless WAN (WWAN), devices and/or networks operating in accordance with existing IEEE 802.11, 802.11a, 802.11b, 802.11e, 802.11g, 802.11h, 802.11i, 802.11n, 802.16, 802.16d, 802.16e, 802.16m, or 3GPP standards and/or future versions and/or derivatives and/or Long Term Evolution (LTE) of the above standards, a Personal Area Network (PAN), a Wireless PAN (WPAN), units and/or devices which are part of the above WLAN and/or PAN and/or WPAN networks, one way and/or two-way radio communication systems, cellular radio-telephone communication systems, a cellular telephone, a wireless telephone, a Personal Communication Systems (PCS) device, a PDA device which incorporates a wireless communication device, a Multiple Input Multiple Output (MIMO) transceiver or device, a Single Input Multiple Output (SIMO) transceiver or device, a Multiple Input Single Output (MISO) transceiver or device, a Multi Receiver Chain (MRC) transceiver or device, a transceiver or device having “smart antenna” technology or multiple antenna technology, or the like. Some embodiments of the invention may be used in conjunction with one or more types of wireless communication signals and/or systems, for example, Radio Frequency (RF), Infra Red (IR), Frequency-Division Multiplexing (FDM), Orthogonal FDM (OFDM), Orthogonal Frequency Division Multiple Access (OFDMA), Time-Division Multiplexing (TDM), Time-Division Multiple Access (TDMA), Extended TDMA (E-TDMA), General Packet Radio Service (GPRS), Extended GPRS, Code-Division Multiple Access (CDMA), Wideband CDMA (WCDMA), CDMA 2000, Multi-Carrier Modulation (MDM), Discrete Multi-Tone (DMT), Bluetooth (RTM), ZigBee (TM), or the like. Embodiments of the invention may be used in various other apparatuses, devices, systems and/or networks. IEEE 802.11x may refer to any existing IEEE 802.11 specification, including but not limited to 802.11a, 802.11b, 802.11e, 802.11g, 802.11h, 802.11i, and 802.11n. 
         [0013]    Hybrid automatic repeat-request (HARQ) streams are described in IEEE 802.16 (2005) and 3GPP LTE (2008). HARQ is a link adaptation technique where link layer acknowledgements are used for re-transmission decisions at the physical layer. For each burst transmitted in a link, a receiver may or may not receive the burst properly. If the burst is received properly, an acknowledged (ACK) message is returned. However, if the burst is not received properly, a not-acknowledged (NACK) message is returned. Upon receipt of an ACK message, further data bursts can be sent. Upon receipt of a NACK message, a retry attempt can be made to resend the same burst information. Some embodiments include using existing HARQ feedback ACK/NACK channel for power control techniques. After establishing that a base station and mobile station are to use ACK/NACK channels to communicate power control information, a base station encodes a power control signal as ACK or NACK signals and transmits the ACK or NACK signals to the mobile station. The mobile station decodes the ACK or NACK signals to determine the desired power level. Some embodiments provide rapid power control with relatively low control signal overhead. Some embodiments can be used when a mobile station suffers fast channel variations such as when the mobile station is moving at high speed. Techniques can be applied to next generation OFDM or OFDMA-based wireless broadband technologies and related products, such as, but not limited to, IEEE 802.16e (2008), 802.16m (2008), 3GPP LTE (2008), and 3GPP UMB (2008). 
         [0014]      FIG. 1  depicts an example of a wireless communication system that includes a base station  10  that communicates with a mobile station  20 , in accordance with an embodiment. In various embodiments, base station  10  uses one or more downlink (DL) ACK channels to transmit commands to mobile station  20  to adjust transmitted power level of signals from mobile station  20 . In various embodiments, a pair of DL ACK Channels (DLACKCH) provides a downlink Power Control Channel (DLPCCH) to support fast uplink closed loop power control. In some embodiments, one or more bits of information can be transmitted using the DLPCCH to adjust power transmitted from mobile station  20 . A bit can be transmitted by an ACK or NACK signal in each of the DL ACK channels. Accordingly, a bit of information can be transmitted over each DL ACK channel to control transmitter power of mobile station  20 . In other embodiments, parameters other than mobile station transmitter power may be controlled using ACK channels. For example, the ACK channels can be used to provide the feedback for DL Hybrid ARQ, as described at section 8.4.16.3 (UL ACK Channel) of IEEE 802.16 (2008). 
         [0015]    Base station  10  may transmit signals to mobile station  20  to establish use of DL ACK channels to control transmitted power level. In some embodiments, base station  10  may set up or remove use of DL ACK channels with mobile station  20  to control power level using MAC messages (e.g., PMC_REQ/PMC_RSP). In addition, MAC messages can be used to establish a default power level increment. MAC messages are described for example in IEEE 802.16 (2005). 
         [0016]    Techniques may (1) have minor signaling overhead, compared to other existing CLPC mechanisms, (2) may provide the possibility for the system to implement fast and accurate link power adaptation in the case of fast channel variations (such as a fast moving mobile station), and (3) may provide more accurate power control, thereby providing high data rates for users. 
         [0017]    The following table provides an example of information mapping between control bits and two DLACK channels (A and B) transmitted to a mobile station. However, other numbers of ACK channels can be used. 
         [0000]                                                                                            Control bit value                    0x00   0x01   0x02   0x03                            DLACK channel A   ACK   ACK   NACK   NACK           DLACK channel B   ACK   NACK   ACK   NACK                        
Accordingly, to transmit a 00 value, DLACK channels A and B carry ACK signals. To transmit a 01 value, DLACK channel A carries an ACK signal but channel B carries a NACK signal. To transmit a 10 value, DLACK channel A carries a NACK signal but channel B carries an ACK signal. To transmit a 11 value, DLACK channels A and B carry NACK signals.
 
         [0018]    The following provides an example of power correction values associated with control bit values. 
         [0000]                                            Control bit               values   Power correction value                           0x00   −Offset_Step           0x01   0 dB           0x02   +Offset_Step           0x03   +2 * Offset_Step                        
Offset_Step may be set to 0.5 dB as a default value and then changed for each mobile station using a MAC message (e.g., POC_REQ/POC_RSP).
 
         [0019]      FIG. 2  depicts a process in which a base station establishes uses of downlink ACK channels to transmit power control information to a mobile station, in accordance with an embodiment. At  201 , the base station transmits a DLPCCH setup request message to a selected mobile station. The base station may use a MAC message to transmit the DLPCCH setup request message. For example, contents of the setup request message can include the fields in the following table. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Field 
                 Concise Description 
               
               
                   
                   
               
             
             
               
                   
                 Message_Type_Indication 
                 Value indicates the type of 
               
               
                   
                   
                 message. 
               
               
                   
                 CID 
                 The value indicates the 
               
               
                   
                   
                 Connection Identifier. Can 
               
               
                   
                   
                 be used to indicate the 
               
               
                   
                   
                 mobile station. 
               
               
                   
                 Type/length/value (TLV) 
                 TLV is described in section 
               
               
                   
                 Encoded Information 
                 11 of IEEE 802.16 (2008). 
               
               
                   
                   
               
             
          
         
       
     
         [0020]    At  202 , after correctly receiving the DLPCCH setup request message, the mobile station transmits a DLPCCH setup response message to the base station to accept or reject the DLPCCH setup process. For example, the mobile station could decide to reject use of DLPCCH based on lack of capacity by the mobile station. For example, a mobile station may decide to reject use of DLPCCH because the mobile station cannot support the fast power changing due to its power amplifier design. An example setup response message can include the fields in the following table. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Field 
                 Concise Description 
               
               
                   
                   
               
             
             
               
                   
                 Message_Type_Indication 
                 Indicates the type of 
               
               
                   
                   
                 message 
               
               
                   
                 Answer 
                 Indicates mobile station 
               
               
                   
                   
                 accepts or rejects the 
               
               
                   
                   
                 setup process. 
               
               
                   
                 TLV Encoded Information 
                 TLV is described in IEEE 
               
               
                   
                   
                 802.16 (2008) 
               
               
                   
                   
               
             
          
         
       
     
         [0021]    At  203 , after the base station receives the DLPCCH setup response message from the mobile station, if the mobile station accepts the DLPCCH setup, the base station transmits the DLPCCH assignment message to the mobile station. The DLPCCH assignment message may indicate which DLACK channels are used to transmit power control information. The DLPCCH assignment message may be transmitted using a MAC message. However, if the mobile station rejects the DLPCCH setup at  202 , the process stops. 
         [0022]    At  204 , if the mobile station correctly receives the DLPCCH assignment message from the base station, the mobile station transmits a DLPCCH assignment acknowledge message to the base station to finish the setup process. The DLPCCH assignment acknowledge message may be transmitted in a MAC message. An example assignment acknowledge message can include the fields in the following table. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Field 
                 Concise Description 
               
               
                   
                   
               
             
             
               
                   
                 Message_Type_Indication 
                 Indicates the type of message 
               
               
                   
                 Resource Location 
                 Indicates assigned location of 
               
               
                   
                   
                 DLPCCH values. These 
               
               
                   
                   
                 locations are two 8 bits indices 
               
               
                   
                   
                 of used DLACKCH. 
               
               
                   
                 TLV Encoded Information 
                 TLV is described in IEEE 
               
               
                   
                   
                 802.16 (2008). 
               
               
                   
                   
               
             
          
         
       
     
         [0023]      FIG. 3  depicts a DLPCCH setup process that is initiated by a mobile station, in accordance with an embodiment. At  301 , the mobile station transmits a DLPCCH Setup Request Message to the base station to initiate use of DLACK channels to communicate power control information. Contents of the setup request message may be similar to those described earlier with regard to  FIG. 2 . 
         [0024]    At  302 , the base station makes the decision to accept or reject the request based on current resources and mobile station priority. If the base station accepts the DLPCCH setup request from the mobile station, the base station transmits a DLPCCH setup response message along with a DLPCCH assignment message to the mobile station. If the base station rejects the DLPCCH setup request from the mobile station, the base station transmits a DLPCCH setup response message to the mobile station without a DLPCCH assignment message. The DLPCCH assignment message may indicate which DLACK channels are used to transmit power control information. Contents of the setup response message may be similar to those described earlier with regard to  FIG. 2 . 
         [0025]    At  303 , after correctly receiving the DLPCCH setup response message from the base station, the mobile station may transmit the DLPCCH assignment acknowledge message to the base station to complete initialization. Contents of the assignment acknowledge message may be similar to those described earlier with regard to  FIG. 2 . 
         [0026]      FIG. 4  depicts an example process in which a base station controls the uplink data transmission power level of a mobile station, in accordance with an embodiment. Process  400  may take place after DLACK channels have been established to control transmitter power level. At  401 , the mobile station transmits data to the base station. The data may be transmitted during a CLPC period. In response, the base station measures the uplink power level and decide the appropriate transmitter power level of the mobile station. At  402 , the base station transmits power level control information to the mobile station using the established DLACK channels. At  403 , the mobile station may adjust the uplink transmit power level based on the indications in the power control information transmitted at  402 . 
         [0027]      FIGS. 5A and 5B  depict processes in which a respective base station and mobile station initiate release of use of DLPCCH, in accordance with various embodiments. In  501  of  FIG. 5A , a base station initiates the release by transmitting a DLPCCH release request message to the mobile station. Example contents of the release request message can include the fields in the following table. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Field 
                 Concise Description 
               
               
                   
                   
               
             
             
               
                   
                 Message_Type_Indication 
                 Indicates the type of message 
               
               
                   
                   
                 as being a release request 
               
               
                   
                   
                 message. 
               
               
                   
                 TLV Encoded Information 
                 TLV is described in IEEE 
               
               
                   
                   
                 802.16 (2008) 
               
               
                   
                   
               
             
          
         
       
     
         [0028]    At  502 , after the message has been correctly received, the mobile station transmits DLPCCH Release Acknowledge Message to the base station to finish the MAC messages process. Example contents of the release acknowledge message may be as follows. 
         [0000]                                            Field   Concise Description                           Message_Type_Indication   Indicates the type of message               as a release acknowledge               message.           TLV Encoded Information   TLV is described in IEEE               802.16 (2008)                        
The PHY resources of the base station and mobile station occupied by the utilized DLACK channels will be released. PHY resources that are released can be assigned to one or more other mobile stations. For example, when fast power control is requested, a PHY resource, for example as defined in section 8.4.16.3 UL ACK Channel of IEEE 802.16 (2008), can be assigned.
 
         [0029]    In  551  of  FIG. 5B , a mobile station initiates release of use of DLPCCH by transmitting the DLPCCH release request message to the base station. At  552 , after the message has been correctly received, the base station transmits the DLPCCH release acknowledge message to the mobile station to finish the MAC messages process. The PHY resources of the base station and mobile station occupied by the utilized DLACK channels will be released. PHY resources that are released can be assigned to one or more other mobile stations. For example, when fast power control is requested, a PHY resource, for example as defined in section 8.4.16.3 UL ACK Channel of IEEE 802.16 (2008), can be assigned. 
         [0030]    Embodiments of the present invention may be provided, for example, as a computer program product which may include one or more machine-readable media having stored thereon machine-executable instructions that, when executed by one or more machines such as a computer, network of computers, or other electronic devices, may result in the one or more machines carrying out operations in accordance with embodiments of the present invention. A machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs (Compact Disc-Read Only Memories), and magneto-optical disks, ROMs (Read Only Memories), RAMs (Random Access Memories), EPROMs (Erasable Programmable Read Only Memories), EEPROMs (Electrically Erasable Programmable Read Only Memories), magnetic or optical cards, flash memory, or other type of media/machine-readable medium suitable for storing machine-executable instructions. 
         [0031]    The drawings and the forgoing description gave examples of the present invention. Although depicted as a number of disparate functional items, those skilled in the art will appreciate that one or more of such elements may well be combined into single functional elements. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of the present invention, however, is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of the invention is at least as broad as given by the following claims.