Patent Publication Number: US-2009225704-A1

Title: Uplink tile index generation apparatus and a uplink subchannel allocation apparatus of an ofdma system

Description:
TECHNICAL FIELD 
     The present invention relates to an uplink subchannel allocation apparatus used in an orthogonal frequency division multiplexing access system, and more particularly to a tile index generation apparatus for allocating subchannels of a control channel and a diversity channel, a subchannel allocation apparatus for allocating subchannels of a diversity channel, and a subchannel allocation apparatus for allocating subchannels of an adaptive modulation coding (AMC) channel, which are used for an uplink of an orthogonal frequency division multiplexing access (OFDMA) system. 
     BACKGROUND ART 
     In the OFDMA scheme, subchannel and subcarrier allocation are performed so as to divide subscribers according to a state of the subcarriers. The subchannel and the subcarrier allocations are defined as a wireless access standard applied for an IEEE standard 802.16d Wireless MAN-OFDMA physical layer. 
     In the OFDMA scheme, a subchannel having a plurality of subcarriers is allocated to a subscriber for multiple accesses, and multi-subscriber stations transmit data through the allocated subchannel to a base station. 
     In this case, different subchannel and subcarrier allocation methods are used according to the respective base station cell IDs provided to the respective base station sectors. This prevents interference between the base stations and also enhances frequency allocation efficiency. In addition, uplink channels are divided into a control channel, a diversity channel, and an adaptive modulation coding (AMC) channel, each respectively having a different subchannel allocation method. 
     Korean Patent Application No. 2002-0009270 (Feb. 21, 2002) entitled “Pilot carrier allocation method in an orthogonal frequency division multiplexing access system” is incorporated herein by reference. 
     The above prior art discloses a scheduling method for allocating a pilot carrier so as to perform an OFDMA in an OFDM communication system. In more detail, when a plurality of subscribers simultaneously access a transmit port of the OFDM communication system, the subscribers share pilot carriers with a time interval, rather than the respective subscribers using different pilot carriers allocated for the respective using systems. Accordingly, the same phase error estimating performance as with the access of a single subscriber can be obtained when the number of pilot carriers to be allocated to a single subscriber is increased and simultaneously the plurality of subscribers can gain access. 
     Meanwhile, Korean Patent Application No. 2002-14334 (Mar. 16, 2002), entitled “Adaptive pilot carrier allocation method and apparatus in an orthogonal frequency division multiplexing access system” is incorporated herein by reference. 
     The prior art discloses a scheduling method for adaptively allocating a pilot carrier so as to perform an OFDMA in an OFDM communication system. In more detail, the number of pilot carriers that are allocated from a transmit port of the OFDM communication system to the respective systems is adaptively varied according to the state of a subchannel to which the respective pilot carriers are allocated. Accordingly, when the state of the accessed subchannel is good, the number of pilot carriers is reduced thereby minimizing power consumption of the subscriber, and when the state of the accessed subchannel is bad, a channel estimating performance can be preserved even though the power consumption is increased due to the increased number of pilot subcarriers. 
     Korean Patent Application No. 2003-7007962 (Jun. 13, 2003) entitled “A multi-carrier communication using a group-based subcarrier allocation” is incorporated herein by reference. 
     The prior art discloses a subcarrier selecting apparatus and method. In more detail, the same spectrum is used for a plurality of adjacent cells in the OFDMA so that intra-cell interference is adaptively allocated to the subcarriers, and also, the subcarriers are adaptively allocated to the subscribers in the OFDMA communication system so that respective subscribers can obtain a high channel gain. 
     However, the above prior art fails to optimize the definition of a subchannel allocation of an uplink control channel, a diversity channel, and an AMC channel to realize a real design. Accordingly, the prior art has a problem in that a large amount of subchannel allocation and operation must be performed corresponding to the base station cell IDs. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention has been made in an effort to provide a tile index generation apparatus and an uplink subchannel allocation apparatus having advantages of providing optimum designs for the uplink subchannel allocation in an OFDM scheme to a modulator of a subscriber station and a demodulator of a base station and having a simple structure and an enhanced transmission speed. 
     Technical Solution 
     An exemplary tile index generation apparatus for allocating subchannels of a control channel and a diversity channel in an uplink of an orthogonal frequency division multiplexing access scheme according to an embodiment of the present invention includes: 
     a first adder for adding lower-order bits of base station cell IDs to tile indexes, the tiles included in a subchannel; 
     a second adder for adding higher-order bits of the base station cell IDs to the tile index; 
     a modulo operator for modulo-operating the sum of the lower-order bits of the base station cell IDs and the tile indexes; 
     a first permutation circulator for circulating a first permutation of the output of the modulo operator; 
     a second permutation circulator for circulating a second permutation of the output of the second adder; 
     a third adder for adding higher-order bits of subchannel index numbers to the tile index; 
     an XOR circuit for selectively performing an exclusive XOR operation of the lower-order bits of the subchannel index numbers and the outputs of the first and second permutation circulators; 
     a plurality of fourth adders for selectively adding the outputs of the third adder, the outputs of the XOR circuit, and the lower-order bits of the subchannel index numbers; 
     and a shift register for selectively outputting tile indexes from the outputs of the XOR circuit and the outputs of the plurality of fourth adders based on the higher-order bits and lower-order bits of the base station cell IDs. 
     In addition, an exemplary subchannel allocation apparatus for allocating subchannels of a diversity channel in an uplink of an orthogonal frequency division multiplexing access scheme according to another embodiment of the present invention includes a first modulo operator for performing a modulo-N operation for a base station ID (c), an operation converter for storing N previously operated results corresponding to the output of the first modulo operator, a first adder for adding subcarriers (n) to the output of the operation converter, and a second modulo operator for performing a modulo-N operation for the outputs of the first adder and outputting a subcarrier index. 
     In addition, an exemplary subchannel allocation apparatus for allocating subchannels of an uplink adaptive modulation coding channel in an orthogonal frequency division multiplexing access scheme according to another embodiment of the present invention includes: 
     a first operation converter for outputting a predetermined value based on a range of input base station cell IDs; 
     a second operation converter for outputting a modulo operation value (per) by a scale (N), which is the range of input base station cell IDs; 
     a first adder for performing a per+j operation by adding a symbol (j) matched with the subcarrier to the modulo-N operation value (per); 
     a first modulo operator for performing the modulo-N operation for the outputs of the first adder; 
     a third operation converter for storing N predetermined operation values and outputting an output of the first modulo operator corresponding to one of the N predetermined operation values; 
     a second adder for adding the output of the first operation converter to the output of the third operation converter; 
     first and second function processors for outputting function values corresponding to the outputs of the second adder; and 
     a shift register for defining subcarrier indexes in the AMC channel by outputting the subcarrier index 0 when the first operation converter outputs 0, and outputting subcarrier indexes through the first and second function processors when the first operation converter does not output 0. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a tile configuration, the tile being a standard unit of a subchannel allocation of an OFDMA uplink control channel and a diversity channel 
         FIG. 2  is a block diagram showing a bin configuration, the bin being a standard unit of a subchannel allocation of an OFDMA uplink AMC channel. 
         FIG. 3  is a block diagram showing a tile index generator, the tile being a standard unit of a subchannel allocation of an OFDMA uplink control channel and a diversity channel according to an exemplary embodiment of the present invention. 
         FIG. 4  is a block diagram showing a subchannel allocation apparatus for allocating subchannels of an OFDMA uplink diversity channel according to an exemplary embodiment of the present invention. 
         FIG. 5  is a block diagram showing a subchannel allocation apparatus for allocating subchannels of an OFDMA uplink AMC channel according to an exemplary embodiment of the present invention. 
     
    
    
     MODE FOR THE INVENTION 
     Exemplary embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
     Hereinafter, a configuration and an operation of an uplink subchannel allocation apparatus of the OFDMA system according to an exemplary embodiment of the present invention is described with reference to the accompanying drawings. 
     First, an uplink subchannel allocation method disclosed in the above-noted 802.16d Wireless MAN-OFDMA PHY will be described. 
       FIG. 1  is a block diagram showing a tile configuration, the tile being a standard unit of a subchannel allocation of an OFDMA uplink control channel and a diversity channel. The control channel and the diversity channel basically have the shape of the tile shown in  FIG. 1 . 
     Referring to  FIG. 1 , in the case of an OFDMA uplink control channel, 6 tiles  100  form one subchannel. Each tile is composed of 3 consecutive subcarriers    3  consecutive symbols. Substantially, each of the 6 tiles  100  may include 8 resources M 0 , M 1 , M 2 , M 3 , M 4 , M 6 , and M 7 , and a pilot  110  having a tone 
     The 6 tiles may compose various subchannels according to Equation 1, which is called an uplink permutation formula. 
     
       
         
           
             
               
                 
                   
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     In Equation 1, tile (s, m) indicates an m-th tile index in the subchannel s, and it is given that S=s/16 and s′=smod16. Here, m is defined as the tile index in the subchannel. Since 6 tiles are used, m has values 0 to 5, and s indicates a subchannel index number and has values 0 to 47. 
     In addition, P1,c1(j) indicates a j-th element of a sequence obtained by left-rotating c1 times a basic permutation sequence P1. For example, P1 may become 1, 2, 4, 8, 3, 6, 12, 11, 5, 10, 7, 14, 15, 13, and 9. In addition, P2,c2(j) indicates a j-th element of a sequence obtained by left-rotating c2 times a basic permutation sequence P2. For example, P2 may become 1, 4, 3, 12, 5, 7, 15, 9, 2, 8, 6, 11, 10, 14, and 13. In addition, c1 is given as an (ID cell)mod16, and c2 is given as ID cell/16. 
     In Equation 1, operations in [ ] are performed on GF (16), and at GF (2n), and an addition becomes a binary XOR operation. For example, at GF (16), 13+4 becomes [(1101)2 XOR (0100)2]=(1001)2=9, wherein (xxxx)2 indicates a binary number format of xxxx. 
     Therefore, as above noted, the tiles are allocated to the subchannel and the control channel allocates the subcarriers to the respective tiles. 
     Meanwhile, the subchannel allocation of the diversity channel is performed by indexing the subcarrier included in the 6 tiles as follows. 
     First, at a first symbol, the subcarriers included in the tile are indexed in a low index order, and then, at second and third symbols, the subcarriers included in the tile are indexed in the same manner. At this time, the subcarrier indexes become 0 to 47. 
     After being indexed in this manner, data are really mapped with the respective subcarriers according to an order determined by Equation 2. 
     
       
     
     In Equation 2, n is given as [0, . . . , 47] and c is given as (ID cell)mod 48 . 
       FIG. 2  is a block diagram showing a bin configuration, the bin being a standard unit of a subchannel allocation of an OFDMA uplink AMC channel and having 9 consecutive subcarriers layered on the same symbol. 
     Referring to  FIG. 2 , the AMC subchannel is formed with the 9 consecutive bins  200  which exist on the same band. At this time, a pilot subcarrier  210  is placed at a predetermined position that is determined according to the positions of the one bin  200  and the one symbol. The AMC subchannel may be formed with the 6 consecutive bins that exist on the same band. 
     First, traffic subcarriers are indexed from 0 to 47 in the AMC subchannel. At this time, at a first bin, a first traffic subcarrier index is 0, and a next traffic subcarrier index is 1. At the first bin, all of the mode subcarriers are indexed in this manner. The subcarriers are increasingly indexed along an axis of the subcarriers and then an axis of the bins. 
     In addition, in a single subchannel, the 6 bins  200  are indexed from the lowest bin index in the first symbol to the highest bin index in the last symbol among the symbols included in the 6 bins  200 . 
     In the single subchannel, the bands are respectively indexed, that is, the bands are increasingly indexed along the bin direction and then increasingly indexed along the symbol axis at the end of the band. 
     At this time, among 48 symbols in which AMC subchannels are allocated, a j-th symbol is mapped with a (    
     −1)-th subcarrier, as in Equation 3. In Equation 3,
 
 
 
is a j-th element of a series
 
 
 
, and j is in the range 0 to 47.
 
     
       
         
           
             
               
                 
                   
                     
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     In Equation 3, 
         
indicates a j-th element of a signal series obtained by left-circulating
 
per
 
times a basic permutation
 
     P 0    
     . 
     In addition, the    
     is a basic permutation defined in GF (72) and is expressed in septenary format as 01, 22, 46, 52, 42, 41, 26, 50, 05, 33, 62, 43, 63, 65, 32, 40, 04, 11, 23, 61, 21, 24, 13, 60, 06, 55, 31, 25, 35, 36, 51, 20, 02, 44, 15, 34, 14, 12, 45, 30, 03, 66, 54, 16, 56, 53, 64, and 10. 
     In addition, it is given that 
         
and    
, and that
 
n mod m
 
indicates a remainder of n?m and    
indicates a maximum integer which is less than X.
 
     In Equation 3, a formula for obtaining    
     is defined in GF (72) and uses an operation on GF (72). That is, an addition on GF (72) performs a mod 7 operation for respective chippers. For example, in GF (72), it is given as (56)+(34)=(13), that is, a remainder 1 of (5+3)÷7 is added to a remainder 3 of (6+4)÷7 so that 13 is obtained. 
     Hereinafter, definitions for a subchannel allocation of an uplink control channel, a diversity channel, and an AMC channel expressed in Equations 1 to 3 according to an exemplary embodiment of the present invention will be described with reference to  FIG. 3  to  FIG. 5 . 
       FIG. 3  is a block diagram showing a tile index generator, the tile being a standard nit of a subchannel allocation of an OFDMA uplink control channel and a diversity channel according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , a tile index generator according to an exemplary embodiment of the present invention includes a first adder  310 , a second adder  320 , a modulo operator  330 , a first multiplier  340 , a P1 permutation circulator  350 , a P2 permutation circulator  360 , three XOR circuits, a third adder  370 , fourth to seventh adders  381 ,  382 ,  383 , and  384 , and a shift register  390 . 
     First, tiles, which are a standard unit of a subchannel of a control channel and a diversity channel, are indexed. The tiles are indexed by realizing Equation 1. 
     Referring to  FIG. 3 , base station cell IDs are expressed in the range of 0 to 127 by cutting a bit. That is, although the base station cell ID is expressed in a 7 bit format, the base station cell ID may have values 4 bit([3:0]) and 3 bit([6:4]) respectively cut by c1 and c2 of Equation 1. As a result, c1 has values 0 to 15 and c2 has values 0 to 7. In addition, the tile indexes in the subchannel are expressed in a 3 bit format having 0 to 5 as above noted. 
     Therefore, the first adder  310  adds the cut 4 bit([3:0]) base station cell IDs (c1) to the 3-bit tile indexes (m) and outputs 5-bit values. 
     The second adder  320  adds the cut 3 bit([6:4]) base station cell ID c2 to the 3-bit tile index (m) and outputs 4-bit values. 
     The first multiplier  340  multiplies the 3-bit tile index (m) in the subchannel by “11” expressed in a 2 bit format and generates 5-bit values. Thereafter, the 4 bit([3:0]) values are input to the third adder  370 . 
     In addition, the modulo operator  330  15-modulo operates the sum of c1 and m and outputs 4-bit values. This is because the P1 permutation circulator  350  has 15 elements. 
     In addition, the P2 permutation circulator  360  P2 permutation-circulates the sum of c2 and m. In this case, since the sum of c2 and m has values 0 to 12, the last elements  14  and  13  may be absent among elements of the P2 permutation. 
     In addition, the 6-bit subchannel index number (s), having values of 0 to 47, is respectively expressed in [5:4] and [3:0]. In this case, S has values 0 to 2 as 2-bit values expressed in the upper order of the subchannel (s) and s′ has values 0 to 15 as 4-bit values expressed in the lower order of each subchannel (s). 
     The third adder  370  operates 48m+16S. The 48m+16S are utilized while changed into 16(3m+S) 
     That is, the third adder  370  substantially calculates 3m+S, and the fourth adder  381  receives the 3m+S and expresses 16(3m+S) by multiplying the 3m+S by 16. In this case, the 16(3m+S) may be obtained by left-shifting the 3m+6 by 4 bits. That is, the 16(3m+S) may be obtained by inserting LSB “0000”. 
     The fourth adder  381  outputs c1=0 and c2=0, and performs 48m+16S+s′. 
     In addition, the fifth adder  382  adds XOR operation results of the output of the P1 permutation circulator  350  and s′ to the 48m+16S as Equation 1. At this time, c1 is not 0 and c2 is 0. 
     Likewise, all cases where c1 is 0 and c2 is not 0, or c1 is greater than 0 and c2 is less than 16 can be verified, and Equation 1 may be expressed by  FIG. 3 . 
     Ultimately, as shown in  FIG. 3 , the shift register  390  determines the tiles, which are the standard unit of the subchannel allocation of the uplink control channel and the diversity channel, in 9-bit indexes. 
     Meanwhile, the control channel may allocate the subcarriers appropriately to the subchannel indexes. However, the diversity channel must allocate the subcarriers as in Equation 2. 
       FIG. 4  is a block diagram showing a subchannel allocation apparatus for allocating subchannels of an OFDMA uplink diversity channel according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , a subchannel allocation apparatus for allocating subchannels of an OFDMA uplink diversity channel according to an exemplary embodiment of the present invention may include a first modulo operator  410 , an operation converter  420 , a first adder  430 , and a second modulo operator  440 . 
     In more detail, as shown in  FIG. 4 , Equation 2 
         
is realized when the first modulo operator  410  obtains c. That is, since the first modulo operator  410  modulo-48 operates the base station Cell IDs, the base station Cell IDs 0 to 47 have original values, the base station Cell IDs 48 to 95 respectively have the Cell ID-48, and the base station Cell IDs 96 to 127 respectively have the Cell ID-96.
 
     In addition, in Equation 2, the (n+23c)mod48 may be developed in ((n)mod48+23cmod48)mod48. Using these relations, the operation converter  420  firstly performs (23c)mod48. In this case, c has values 0 to 47, and also the (23c)mod48 has values 0 to 47. Accordingly, the operation converter  420  stores the previously operated values so that the operation converter  420  can output (23c)mod48 when c is input. 
     In addition, the first adder  430  adds subcarrier (n) to (23c)mod48, and the second modulo operator  440  performs Xmod48 and outputs the 6-bit subcarrier index so that Equation 2 may be realized. Accordingly, the subcarrier indexes are defined in the diversity subchannel using Equation 2, so that the subchannels can be allocated in the diversity channel. 
       FIG. 5  is a block diagram showing a subchannel allocation apparatus for allocating subchannels of an OFDMA uplink AMC channel according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , a subchannel allocation apparatus for allocating subchannels of an OFDMA uplink AMC channel according to an exemplary embodiment of the present invention may include a first operation converter  510 , a second operation converter  520 , a first adder  530 , a first modulo operator  540 , a third operation converter  550 , a second adder  560 , a first function processor  570 , a second function processor  580 , and a shift register  590 . 
     In more detail, the AMC channel is defined in Equation 3, the first operation converter  510  can express an off of Equation 3, and the second operation converter  520  can express a per of the second operation converter  520 . 
     That is, when the base station Cell IDs 0 to 127 are input, the first operation converter  510  outputs 0 for the base station Cell IDs 0 to 47, and outputs 1 for the base station Cell IDs 48 to 95, and outputs 3 for the base station Cell IDs 96 to 127. In addition, when the base station Cell IDs 0 to 127 are input, the second operation converter  520  outputs the original Cell IDs for the base station Cell IDs 0 to 47, and outputs Cell ID-48 for the base station Cell IDs 48 to 95, and outputs Cell ID-96 for the base station Cell IDs 96 to 127. Therefore, the off becomes 2-bit values having values 0 to 2 and the per has values 0 to 47. 
     In addition, the first adder  530  outputs 7-bit values by adding a symbol (j) matching with the subcarrier having values 0 to 47 to the per, that is, performing a per+j operation. Thereafter, the per+j left-shifts the P0 permutation. At this time, since the P0 permutation has 48 elements, the first modulo operator  540  performs a modulo-48 operation. 
     In addition, the third operation converter  550  can convert the 7-bit values to 6-bit values corresponding to the outputs of the first modulo operator  540 , since the third operation converter  550  has stored the previously operated GF (72). Thereafter, the second adder  560  adds the converted values to the off. 
     That is, when the off is given as 0 in Equation 3, the shift register  590  outputs 0 as the subcarrier index. When the off is not given as 0 in Equation 3, the shift register  590  outputs the subcarrier indexes through the operations of the first function processor  570  and the second function processor  580 . Accordingly, the subcarrier indexes are defined in the AMC channel, so that the subchannels of the AMC channel can be allocated. 
     Ultimately, optimum designs for the uplink subchannel allocation in the OFDM scheme according to an exemplary embodiment of the present invention can be provided to a modulator of a subscriber station and a demodulator of a base station. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     According to an exemplary embodiment of the present invention, the optimum designs for the uplink subchannel allocation in the OFDM scheme can be provided to a modulator of a subscriber station and a demodulator of a base station, and so the uplink subchannel allocation apparatus has a simple structure and an enhanced transmission speed.