Abstract:
A method and apparatus for hopping of a Code Division Multiple Access (CDMA) control segment that carries control information in an Orthogonal Frequency Division Multiple Access (OFDMA) packet data mobile communication system are provided, in which a number of CDMA control segment hopping zones, each CDMA control segment hopping zone representing a frequency area for CDMA control segment hopping, is determined according to a total number of available tiles in the system and a number of tiles per CDMA control segment, each tile including a predetermined number of subcarriers, or according to a total number of available subcarriers in the system and a number of subcarriers per CDMA control segment. Start points of the hopping zones are determined using the number of the hopping zones, and the control information is transmitted or received in the CDMA control segment through hopping of the CDMA control segment over the hopping zones using the start points.

Description:
PRIORITY 
     This application claims priority under 35 U.S.C. §119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Oct. 25, 2006 and assigned Serial No. 2006-104235, the entire disclosure of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a method and apparatus for transmitting uplink control information in a mobile communication system. More particularly, the present invention relates to a method and apparatus for hopping of a Code Division Multiple Access (CDMA) segment carrying control information in CDMA in an Orthogonal Frequency Division Access (OFDMA) packet data mobile communication system. 
     2. Description of the Related Art 
       FIG. 1  is a block diagram of a transmitter  100  for transmitting control information  102  in a conventional OFDMA uplink system. The control information can be a Channel Quality Indicator (CQI), an access probe, or a Multiple-Input Multiple-Output (MIMO) beamforming index. 
     Referring to  FIG. 1 , a Walsh code mapper  104  maps the control information  102  to a predetermined Walsh code and a chip repeater  106  repeats the chips of the mapped control information. After I/Q mapping in an I/Q mapper  108 , a scrambler  110  scrambles the I/Q-mapped control information. An output A  112  is the result from processing the uplink control information  102  in the components  104  to  110 . The output A  112  is transmitted in a method described in  FIG. 2 . 
       FIG. 2  illustrates a conventional method for transmitting the output A  112  illustrated in  FIG. 1  on a physical channel. That is, after Walsh code mapping, chip repetition, I/Q mapping, and scrambling, the output A  112  is transmitted in the method illustrated in  FIG. 2 . 
     Referring to  FIG. 2 , the vertical axis represents frequency and the horizontal axis represents time. Each smaller rectangle  200  represents a tile. In general, one tile is defined by 16 successive subcarriers and 8 successive OFDMA symbols. The tile definition varies according to system configuration. For example, if a system has 480 available subcarriers, there are 30 tiles, each tile having 16 subcarriers (480=30×16). 
     The total frequency band of the system is usually divided into a plurality of subbands, as illustrated in  FIG. 2 . The subbands are used for frequency selective scheduling or other purposes. In  FIG. 2 , 6 subbands, Subband  0  to Subband  5  exist. Each larger square  202  represents a CDMA control segment. The CDMA control segment includes a plurality of tiles and a plurality of OFDM symbols. The square  202  is called a CDMA segment because the output A  112  is mapped to the square  202 , for transmission. The CDMA control segment  202  frequency hops over time as illustrated in  FIG. 2  to achieve maximum channel and interference diversity. The CDMA control segment  202  hops on a subband basis. This hopping rule is preferable when the size of the CDMA control segment  202  is equal to that of a subband. 
       FIG. 3  illustrates a phenomenon that appears when a CDMA control segment hops on a subband basis, in the case where the CDMA control segment differs from a subband in size. 
     Referring to  FIG. 3 , it is noted that CDMA control segments are overlapped with one another over a large area along the frequency axis, which is not preferred in terms of maximization of channel and interference diversity. In general, the CDMA control segment size is determined by the size of the control information  102  and the subband size is determined by a frequency selective scheduling gain. Therefore, the CDMA control segment size is different from the subband size. 
     SUMMARY OF THE INVENTION 
     An aspect of exemplary embodiments of the present invention is to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide an apparatus and method for setting an efficient CDMA control segment hopping rule and transmitting/receiving control information according to the CDMA control segment hopping rule, if a CDMA control segment size is different from a subband size in transmitting uplink control information in CDMA in an OFDMA system. 
     In accordance with an aspect of exemplary embodiments of the present invention, there is provided a method for CDMA control segment hopping, wherein the control segment carries control information in an OFDMA packet data mobile communication system, in which the number of CDMA control segment hopping zones, each CDMA control segment hopping zone representing a frequency area for CDMA control segment hopping is determined according to a total number of available tiles in the system and a number of tiles per CDMA control segment, each tile including a predetermined number of subcarriers, or according to a total number of available subcarriers in the system and a number of subcarriers per CDMA control segment, start points of the CDMA control segment hopping zones are determined using a number of the CDMA control segment hopping zones, and the control information is transmitted or received in the CDMA control segment through CDMA control segment hopping over the CDMA control segment hopping zones using the start points. 
     In accordance with another aspect of exemplary embodiments of the present invention, there is provided an apparatus for CDMA control segment hopping, wherein the control segment carries control information in an OFDMA packet data mobile communication system, in which a hopping zone decider determines the number of CDMA control segment hopping zones, each CDMA control segment hopping zone representing a frequency area for CDMA control segment hopping, according to a total number of available tiles in the system and a number of tiles per CDMA control segment, each tile including a predetermined number of subcarriers, or according to a total number of available subcarriers in the system and a number of subcarriers per CDMA control segment, and determines start points of the CDMA control segment hopping zones using a number of the CDMA control segment hopping zones, and a device transmits or receives the control information in the CDMA control segment through CDMA control segment hopping over the CDMA control segment hopping zones using the start points. 
     In accordance with a further aspect of exemplary embodiments of the present invention, there is provided a method for CDMA control segment hopping, wherein the CDMA control segment carries control information in an OFDMA packet data mobile communication system, in which a start point corresponding to each hopping time is read from a memory that pre-stores start points of CDMA control segment hopping zones, the start points of CDMA control segment hopping zones being determined according to a total number of available subcarriers in the system and a number of subcarriers per CDMA control segment, and the control information is transmitted or received in a CDMA control segment hopping zone corresponding to the read start point. 
     In accordance with still another aspect of exemplary embodiments of the present invention, there is provided an apparatus for CDMA control segment hopping, wherein the CDMA control segment carries control information in an OFDMA packet data mobile communication system, in which a memory stores start points of CDMA control segment hopping zones, the start points of CDMA control segment hopping zones being determined according to a total number of available subcarriers in the system and a number of subcarriers per CDMA control segment, a hopping zone decider reads a start point corresponding to a hopping time from among the stored start points of the memory, and a device transmits or receives the control information in a CDMA control segment hopping zone corresponding to the read start point. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a transmitter for transmitting control information  102  in a conventional OFDMA uplink system; 
         FIG. 2  illustrates a conventional method for transmitting the control information illustrated in  FIG. 1  on a physical channel; 
         FIG. 3  illustrates a phenomenon that appears when a CDMA control segment hops on a subband basis, in the case where the CDMA control segment differs from a subband in size; 
         FIG. 4  illustrates a CDMA control segment hopping method according to an exemplary embodiment of the present invention; 
         FIG. 5  is a block diagram of a Mobile Station (MS) transmitter for transmitting a CDMA control segment according to an exemplary embodiment of the present invention; and 
         FIG. 6  is a block diagram of a Base Station (BS) receiver for receiving a CDMA control segment according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of exemplary embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
     The features of the present invention are summarized as follows. 
     An exemplary embodiment of the present invention provides a CDMA control segment hopping rule that is specified as follows. 
     (1) The number of CDMA control segment hopping zones is determined according to the total number of tiles available to the system and a CDMA control segment size (i.e. the number of tiles per CDMA control segment). 
     (2) The start point of each hopping zone is determined on a tile basis using the number of the hopping zones according to a predetermined rule. If the end of a hopping zone including the last tile is outside the total system frequency band, as many tiles of the hopping zone as outside the total system frequency band are pushed inward so that the hopping zone falls into the system frequency band. 
     (3) One of the start points of the CDMA control segment zones is selected using a PN sequence at each hopping time, for frequency hopping of a CDMA control segment to which control information is mapped. 
     Another exemplary embodiment of the present invention provides a CDMA control segment hopping rule that is specified as follows. 
     (1) The start positions of hopping zones are calculated according to the total number of available subcarriers in the system and the total number of subcarriers per CDMA control segment. These start positions are stored beforehand in a memory. Then, a start point corresponding to a hopping time is read from the memory. 
     (2) Control information is carried in the hopping zone that starts at the read start point. 
     Equation (1a) and Equation (1b) describe the afore-stated rule of determining the number CDMA control segment hopping zones. 
                   ⌈         number   ⁢           ⁢   of   ⁢           ⁢   tiles   ⁢           ⁢   in   ⁢           ⁢   entire   ⁢           ⁢   BW     ⁢               number   ⁢           ⁢   of   ⁢           ⁢   tiles   ⁢           ⁢   in   ⁢           ⁢   a   ⁢           ⁢   CDMA   ⁢           ⁢   segment       ⌉           (     1   ⁢           ⁢   a     )               
where number of tiles in entire BW denotes the total number of tiles that can be defined with a total bandwidth (i.e. the total number of tiles available for transmission of control information in the OFDM system) and number of tiles in a CDMA segment denotes the number of tiles per CDMA segment. ┌x┐ represents the minimum integer greater than or equal to x.
 
                   ⌈       number   ⁢           ⁢   of   ⁢           ⁢   useful   ⁢           ⁢   subcarriers   ⁢           ⁢   in   ⁢           ⁢   entire   ⁢           ⁢   BW       number   ⁢           ⁢   of   ⁢           ⁢   subcarriers   ⁢           ⁢   in   ⁢           ⁢   a   ⁢           ⁢   CDMA   ⁢           ⁢   segment       ⌉           (     1   ⁢           ⁢   b     )               
where number of useful subcarriers in entire BW denotes the total number of subcarriers that can be defined with the total bandwidth (i.e. the total number of subcarriers available for transmission of control information in the OFDM system) and number of subcarriers in a CDMA segment denotes the number of subcarriers per CDMA segment. ┌x┐ represents the minimum integer greater than or equal to x.
 
     With the number of CDMA control segment hopping zones computed by Equation (1a), the start of each hopping zone is determined as follows. 
                     ⌊         number   ⁢           ⁢   of   ⁢           ⁢   tiles   ⁢           ⁢   in   ⁢           ⁢   entire   ⁢           ⁢   BW       number   ⁢           ⁢   of   ⁢           ⁢   hopping   ⁢           ⁢   zones       ·   k     ⌋     ,     
     ⁢     k   =   0     ,   …   ⁢           ,       number   ⁢           ⁢   of   ⁢           ⁢   hopping   ⁢           ⁢   zones     -   l             (   2   )               
where number of tiles in entire BW denotes the total number of tiles that can be defined with a total bandwidth (i.e. the total number of tiles available for transmission of control information in the OFDM system) and number of hopping zones denotes the number of CDMA control segment hopping zones. └x┘ represents the maximum integer less than or equal to x. The start of a hopping zone computed by Equation (2) is a tile index. If Equation (2) results ‘3’, the hopping zone starts from tile 3.
 
     An example for the CDMA control segment hopping rule based on Equation (1a) and Equation (2) will now be given. If number of tiles in entire BW is 30 and number of tiles in a CDMA segment is 8, the number of CDMA control segment hopping zones is 4 according to Equation (1a). If Equation (1b) is computed instead of Equation (1a), the number of subcarriers substitutes for the number of tiles. 
     According to Equation (2), the start points of the CDMA control segment hopping zones are given as tile indexes 0, 7, 15, and 22. Thereafter, at each hopping time, one of the four start points is selected by a predetermined randomization method, for example, by use of a predetermined PN sequence and control information is transmitted by CDMA control segment hopping in the CDMA control segment hopping zone with the selected start point. 
       FIG. 4  illustrates a CDMA control segment hopping method according to an exemplary embodiment of the present invention. In the illustrated case of  FIG. 4 , the total number of tiles in the system is 30 (tile index 0 to tile index 29) and 8 tiles are included in each CDMA control segment. Thus, the hopping zones start from tile indexes 0, 7, 15 and 22, respectively. It is noted from  FIG. 4  that a CDMA control segment hops in the hopping zones based on the start points. 
     Referring to  FIG. 4 , for number of tiles in entire BW=30 and number of tiles in a CDMA segment=8, four CDMA control segment hopping zones are created according to Equation (1a). Computation of Equation (2) using the number of CDMA control segment hopping zones tells that their start points are tiles  410   a  to  410   d  (tile index 0, tile index 7, tile index 15, and tile index 22). 
     Considering one tile includes a plurality of subcarriers, it is obvious that Equation (1a) and Equation (2) are also computable by substituting subcarriers for tiles. 
       FIG. 5  is a block diagram of an MS transmitter  500  for transmitting a CDMA control segment according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , a Walsh code mapper  502  maps control information  501  to a Walsh code according to a predetermined mapping rule. A chip repeater  503  repeats the chips of the mapped control information in a predetermined method, an I/Q mapper  504  maps the chip-repeated control information to I and Q signals, and a scrambler  505  scrambles the I/Q-mapped signal. 
     The output of the scrambler  505  is mapped to a CDMA control segment  400  in  FIG. 4  under the control of a hopping zone decider  507 . The hopping zone decider  507  selects one of the start points of hopping zones computed using information  508  indicating the total number of available tiles, the number of tiles per CDMA control segment, and a time index corresponding to a hopping time for deciding a hopping sequence. This means that the hopping zone decider  507  selects one of the four start points according to the time index corresponding to the hopping time since each hopping occurs at one of the start points, time indexes 0, 7, 15 and 22. As stated before, the start points of the hopping zones can be computed on a subcarrier basis rather than on a tile basis. The hopping zone decider  507  can be incorporated into a controller (not shown). 
     Therefore, the CDMA control segment can be transmitted in a hopping zone corresponding to the selected start point. 
     That is, in accordance with an exemplary embodiment of the present invention, the hopping zone decider  507  determines the number of hopping zones each representing a frequency band in which a CDMA control segment hops, according to the total number of available tiles in the system and the number of tiles per CDMA segment. Then, the hopping zone decider  507  calculates the start points of the hopping zones based on the number of the hopping zones. 
     In accordance with another exemplary embodiment of the present invention, a memory  511  pre-stores the number of hopping zones each representing a frequency band in which a CDMA control segment hops, which is determined according to the total number of available subcarriers in the system and the number of subcarriers per CDMA segment. Then, the hopping zone decider  507  reads a start point corresponding to each hopping time from the memory according to a predetermined rule such as a hopping sequence. Then a subcarrier mapper  506  maps the control information to the subcarriers of a hopping zone corresponding to the read start point. 
     The selection of a start point from among the start points stored in the memory  511  can be considered in two ways. 
     One of the ways that a start point can be selected is that the hopping zone decider  507  reads the pre-stored start points from the memory  511  and selects one of the start points at each hopping time according to a predetermined rule and the subcarrier mapper  506  transmits control information according to the selected start point. 
     The other way is that the hopping zone decider  507  reads one start point corresponding to a current hopping time among the pre-stored start points from the memory  511  and the subcarrier mapper  506  transmits control information according to the read start point. 
     The output of the subcarrier mapper  506  is processed in an OFDM symbol configurer  509  by Fast Fourier Transform (FFT) and a Cyclic Prefix (CP) addition and then transmitted as Transmission (Tx) data  510 . 
     In  FIG. 5 , a Walsh code mapper  502 , a chip repeater  503 , an I/Q mapper  504 , a scrambler  505 , a subcarrier mapper  506  and an OFDM symbol configurer  509  are called transmitting device. 
       FIG. 6  is a block diagram of a BS receiver  600  for receiving a CDMA control segment according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , a CP remover  601  removes a CP from a Received (Rx) signal  611 . An Inverse Fast Fourier Transform (IFFT) processor  602  converts the CP-free signal to a time signal. A subcarrier demapper  603  demaps subcarriers from the time signal in the reverse order of the subcarrier mapping in the subcarrier mapper  506  illustrated in  FIG. 5  under the control of a hopping zone decider  604 . 
     The hopping zone decider  604  functions to select one of the start points of hopping zones computed using information  605  indicating the total number of available tiles, the number of tiles per CDMA control segment, and a time index corresponding to a hopping time for deciding a hopping sequence. The information  605  is identical to the information  508  input to the transmitter  500  of  FIG. 5 . The same hopping rule as used in the transmitter  500  is applied in selecting the start point. 
     That is, in accordance with an exemplary embodiment of the present invention, the hopping zone decider  604  determines the number of hopping zones, each representing a frequency band in which a CDMA control segment hops, according to the total number of available tiles in the system and the number of tiles per CDMA segment. Then, the hopping zone decider  604  calculates the start points of the hopping zones based on the number of the hopping zones. 
     In accordance with another exemplary embodiment of the present invention, a memory  612  pre-stores the number of hopping zones each representing a frequency band in which a CDMA control segment hops, which is determined according to the total number of available subcarriers in the system and the number of subcarriers per CDMA segment. Then, the hopping zone decider  604  reads a start point corresponding to each hopping time from the memory according to a predetermined rule such as a hopping sequence. Then the subcarrier demapper  603  extracts the control information from the subcarriers of a hopping zone corresponding to the read start point. 
     The selection of a start point from among the start points stored in the memory  612  can be considered in two ways. 
     One of them is that the hopping zone decider  604  reads the pre-stored start points from the memory  612  and selects one of the start points at each hopping time according to a predetermined rule and the subcarrier demapper  603  extracts control information according to the selected start point. 
     The other way is that the hopping zone decider  604  reads one start point corresponding to a current hopping time among the pre-stored start points from the memory  612  and the subcarrier demapper  603  extracts control information according to the read start point. 
     The subcarrier demapper  603  outputs a frequency signal with as many tiles as included in a CDMA control segment, counted from the start point that the hopping zone decider  604  indicates. Therefore, the receiver  600  receives control information in a CDMA control segment transmitted in a CDMA control segment hopping zone corresponding to a predetermined frequency area. 
     The demapped signal from the subcarrier demapper  603  is descrambled in a predetermined method by a descrambler  606  and I/Q-demapped by an I/Q demapper  607 . The I/Q demapped signal is combined as many times as chip repetitions performed in the chip repeater  503  of  FIG. 5  by a combiner  608 . The combined signal is provided to a Walsh code decider  609  and control information  610  is output according to decision of the Walsh code decider  609 . 
     In  FIG. 6 , a CP remover  601 , an IFFT  602 , a subcarrier demapper  603 , a descrambler  606 , an I/Q demapper  607 , a combiner  608  and a Walsh code decider  609  are called receiving device. 
     As is apparent from the above description, the present invention provides an efficient hopping rule for a CDMA control segment, when uplink control information is transmitted in CDMA with a CDMA control segment size different from a subband size in an uplink OFDMA system. Therefore, channel and interference diversity effects are maximized according to the hopping rule and thus uplink performance is significantly improved. 
     While the invention has been shown and described with reference to certain exemplary embodiments of the present invention thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents.