| Title of Invention | A CHANNEL SPREADING DEVICE FOR A BASE STATION DEVICE IN A CODE DIVISION MULTIPLE ACCESS COMMUNICATION SYSTEM |
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| Abstract | Disclosed is a channel spreading device for a base station device in a CDMA communication system for spreading input symbols using a first quasi-orthogonal code having a first length or channel spreading the input symbols using a second quasi-orthogonal code having a second length which is a multiple of the first length. The device comprises a spreading code generator for generating the second quasi-orthogonal code; a channel spreader for providing a plurality of durations by dividing a duration of the second quasi-orthogonal code by said multiple of the length of the first quasi-orthogonal code, and spreading channel coded symbols with the quasi-orthogonal codes divided to have a length corresponding to the divided durations so as to spread the symbols identical in number to said multiple of the first quasi-orthogonal code duration at the duration of the second quasi-orthogonal; and a PN spreader for spreading the channel spread signal with a PN code. |
| Full Text | DEVICE AND METHOD FOR SPREADING CHANNELS IN MOBILE COMMUNICATION SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a channel spreading device for a base station device in a code division multiple access comnunication system 1. Field of the Invention The present invention relates generally to a device and method for spreading channels in a CDMA communication system, and in particular, to a channel communication device and method for a CDMA communication system having different spreading rates. 2. Description of the Related Art In order to increase channel capacity, a CDMA (Code Division Multiple Access) communication system spreads channels using orthogonal codes. For example, a forward link of an IMT-2000 system performs channel spreading using orthogonal codes. An example of an orthogonal code that is typically used is a Walsh code. The number of available orthogonal codes is determined depending upon a modulation method and a minimum data rate. However, in the proposed IMT-2000 CDMA system, the channels assigned to the users will increase in number in order to improve system performance. To this end, the future CDMA system includes a plurality of common channels and dedicated channels, and assigns the channels to the mobile stations, thereby increasing channel capacity. However, even in the proposed IMT-2000 CDMA system, an increase in the utilization of the channels limits the number of available orthogonal codes. Further, the reduced number of available Walsh orthogonal codes limits the increase in channel capacity. In an effort to solve this problem, there is proposed a method for using quasi-orthogonal codes for channel spreading codes which have a minimum interference with the orthogonal codes and have a variable data rate. In the IMT-2000 system, a lx system uses a spreading code group having a spreading code rate 1, and a 3x system uses a spreading code group having a -3- spreading code rate 3. In this case, the lx system has spreading codes with a maximum length of 128 as shown in FIG. 1A, and spreads code symbols by selecting a spreading code corresponding to a designated spreading code index. Further, the 3x system includes spreading codes with a maximum length of 256 as shown in FIG. IB, and spreads the code symbols by selecting a spreading code corresponding to a designated spreading code index. Referring now to FIG. 2, there is shown the channel characteristics at a frequency band of a multi-carrier mobile communication system. The lx system uses a single carrier whose channel band is 1.25MHz, and the 3x system uses 3 carriers, each distributed to a different channel band and having a combined channel band of 3.75MHz. A unique orthogonal code is assigned to each carrier. When the lx system is overlaid with the 3x system as shown in FIG. 2, it is not possible to guarantee a correlation property between a spreading code of length 128 using a mask function at a spreading rate 1 and a spreading code of length 128 using a mask function at a spreading rate 3, at each 1.25MHz band. Therefore, interference may increase between a user using the mask function at the spreading rate lx and another user using the mask function at the spreading rate 3x. A problem concerning the correlation property will be described with reference to FIG. 3. FIG. 3 is a diagram for explaining the mutual interference between a user of the lx system using a quasi-orthogonal code and a user of the 3x system using an orthogonal code. In FIG. 3, T1 denotes the number of chips into which the quasi-orthogonal code user of the lx system spreads one symbol, and T2 denotes the number of chip's into which the orthogonal code user of the 3x system spreads one symbol. Interference that the quasi-orthogonal code (Qm+WjJ user of the lx system, experiences from the orthogonal code (Wj) user of the 3x system can be given by the equation: That is, the interference satisfies an upper limit formula of the correlation for -4- the quasi-orthogonal code. Therefore, in this case, there is no serious matter. FIG. 4 is a diagram for explaining mutual interference between channels each using quasi-orthogonal codes of different lengths. In FIG. 4, lx denotes a user using a quasi-orthogonal code of length 128 and 3x denotes a user using a quasi-orthogonal code of length 256. In this case, interference that the quasi-orthogonal code (Qm+Wk) user of the lx system experiences from the quasi-orthogonal code (Qn+Wk) user of the 3x system does not satisfy the upper limit formula, as shown in Equation (2) below: In this case, the mutual interference between the channels increases. Therefore, when using the quasi-orthogonal codes of spreading code groups having different lengths, the mobile communication system stores the spreading codes of different lengths, and thus increases the hardware complexity. Further, using the spreading codes having different spreading rates deteriorates the interference property between two users thereby causing performance degradation SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a communication device and method for a CDMA communication system wherein a base station device spreads and despreads channel signals using spreading codes having the same length as those of mobile stations having different spreading rates. It is another object of the present invention to provide a communication device and method for a CDMA communication system wherein a mobile station spreads and despreads channel signals using spreading codes having the same length as those of base stations having different spreading rates. To achieve the above objects, there is provided a channel spreading device -5- for a base station device in a CDMA communication system for spreading input symbols using a first quasi-orthogonal code having a first length or channel spreading the input symbols using a second quasi-orthogonal code having a second length which is a multiple of the first length. The device comprises a spreading code generator for generating the second quasi-orthogonal code; a channel spreader for providing a plurality of durations by dividing a duration of the second quasi-orthogonal code by the multiple of the length of the first quasi-orthogonal code, and spreading channel coded symbols with the quasi-orthogonal codes having the plurality of durations described above; and a PN spreader for spreading the channel spread signal with a PN code. The spreading code generator comprises a controller for generating a mask index and a Walsh code index corresponding to a received index for generating the second quasi-orthogonal code; a mask generator for generating a mask of the second quasi-orthogonal code corresponding to the mask index; a Walsh code generator for generating a Walsh code corresponding to the Walsh code index; and a circuit for mixing the mask of the second quasi-orthogonal code with the Walsh code to generate the second quasi-orthogonal code to use as the spreading code. When the length of the second quasi-orthogonal code is 2 times the length of the first quasi-orthogonal code, the channel spreader spreads, at a spreading rate of the first quasi-orthogonal code, one symbol with a first half-period chip signal of the second quasi-orthogonal code output from the spreading code generator and another symbol with a second half-period chip signal of the second quasi-orthogonal code, whereby two symbols are spread at a duration of one spreading code. BRIEF DESCRIPTION OF THE.DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: FIGS. 1A and IB are diagrams for explaining the relationship between lx and 3x mobile communication systems with respect to code symbols and spreading codes; FIG. 2 is a diagram for explaining the channel band relationship between the lx and 3x mobile communication systems; -6- FIG. 3 is a diagram for explaining mutual interference between a channel using a quasi-orthogonal code and a channel using an orthogonal code, the codes having different lengths, in a mobile communication system; FIG. 4 is a diagram for explaining mutual interference between channels using quasi-orthogonal codes of different lengths in a mobile communication system; FIG. 5 is a diagram for explaining a method for channel spreading symbols of different lengths using spreading codes of the same length according to an embodiment of the present invention, in a mobile communication system; FIG. 6 is a diagram for explaining mutual interference between channels when symbols of different lengths are channel spread using quasi-orthogonal codes of the same length in a mobile communication system; FIG. 7 is a block diagram illustrating a spreading device for a transmitter in a Ix mobile communication system according to an embodiment of the present invention; FIG. 8 is a block diagram illustrating a spreading device for a transmitter in a 3x mobile communication system according to an embodiment of the present invention; FIG. 9 is a block diagram illustrating a despreading device for a receiver in the lx mobile communication system according to an embodiment of the present invention; and FIG. 10 is a block diagram illustrating a despreading device for a receiver in the 3x mobile communication system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. In the following description, the term "orthogonal spreading" will be used interchangeably with the terms "channel spreading", "short code spreading", "spreading" and "PN spreading". Further, the term "spreading codes of the same length" refers to a set of quasi-orthogonal codes having the same length. In addition, the term "spreading code" refers to a Walsh orthogonal code or quasi-orthogonal code. -7- Although an exemplary embodiment of the present invention will be described with reference to a spreading and despreading operation of an IMT-2000 base station and mobile station in which a lx system and a 3x system use the same spreading codes, it is also possible to apply the invention to the systems using different data rates. That is, the embodiment of the present invention will be described with reference to the case where a base station spreads channel signals using spreading codes of the same length and transmits the spread channel signals to mobile stations having different spreading rates, and the mobile stations then despread the transmitted spread channel signals. Alternatively, the invention can be equally applied to the case where a mobile station spreads channel signals using spreading codes of the same length and transmits the spread channel signals to base stations having different spreading rates, and the base stations then despread the transmitted spread channel signals, In the embodiment, the lx system and the 3x system share the spreading codes. It is possible to reduce the hardware complexity by allowing several Nx systems to share quasi-orthogonal sequences of the longest length. In addition, when the several Nx systems are used and each system uses spreading codes of the same length, it is possible to reduce interference between the users at the lx 1.25MHz band. Referring to FIG. 5, there, is shown a diagram for explaining an operation of channel spreading symbols of different lengths using the spreading codes of the same length according to an embodiment of the present invention. FIG. 5 shows a method for using the spreading codes, when an Nx system using spreading codes of length A and a Mx system using spreading codes of length B (where A>B) share the spreading codes of length A. More specifically, FIG. 5 shows a case where a lx system using spreading codes of maximum length 128 and a 3x system using spreading codes of maximum length 256 share the spreading codes of length 256, by way of example. In this manner, it is possible to solve the problems that occur when using the spreading codes in the prior art. FIG. 6 is a diagram for explaining the mutual interference between the lx system using the quasi-orthogonal codes and the 3x system using the quasi-orthogonal codes. In FIG. 6, Tj denotes the number of chips into which the quasi-orthogonal code user of the lx system spreads one symbol, and T2 denotes the -8- number of chips into which the quasi-orthogonal code user of the 3x system spreads one symbol. Referring to FIG. 6, interference that the quasi-orthogonal code (Qm+Wk) user of the Ix system experiences from the quasi-orthogonal code (Qm+Wj) user of the 3x system can be given by the equation; That is, since the interference is 0, there is no interference. Therefore, it is possible to solve the interference problem of the prior art Therefore, in the embodiment, it is possible to reduce the mutual interference between the users while decreasing the hardware complexity by allowing several Nx systems to share the spreading codes. Tables 1 and 2 below show quasi-orthogonal sequences of length 128 for use in the Ix system and quasi-orthogonal sequences of length 256 for use in the 3x system, by way of example. The Ix system and the 3x system can share either masks of length 128 shown in Table 1 or masks of length 256 shown in Table 2. [Table 1 ] | Function Masking Function (Hex) 1 ; 17dbbd71e8db427117dbbd71e8db4271 2 72824ebebebl7d7272824ebebebl7d72 3 2dee87bb8744d2ee2dee87bb8744d2ee [Table 2] Function Masking Function (Hex) 00000000000000000000000000000000 00000000000000000000000000000000 1 77MM77774bb48887bb447878bbbb78 -9- 77b44b88774b4b77784444788744bb78 2 7e4ddbe817244d7ed41871bd428el8d4 d4e77142bd8ee7d47eb2dbl7e824b27e 3 417214d87dbl281beb274172d7e47dbl b!7de4d78dbed8141b28bl7d27eb8dbe When the lx system and 3x system share the spreading codes of length 256, the 3x system, which originally uses the spreading codes of length 256, has the existing structure. Therefore, in the embodiment, a description will be made regarding only the structure of the lx system when using the spreading codes of length 256, in which a spreading factor is assumed to be 128 which is the highest one in the lx system. A. Embodiment of Transmitter In the transmitter described below, it is assumed that the lx system spreads one symbol into 128 chip length and the 3x system spreads one symbol into 256 chip length. Further, it is assumed that the lx system and the 3x system share the spreading codes of length 256. Referring now to FIG. 7, there is shown a structure of a lx system transmitter. A channel coder 700 codes an input signal into symbol data and an interleaver 705 interleaves the coded symbols output from channel coder 700. The coded symbols interleaved by the interleaver 705 are provided to a long code scrambler 710. A long code generator 715 generates a long code for scrambling the interleaved channel signal. Thus, the long code scrambler 710 spreads the interleaved symbols with the long code. An exclusive OR gate is typically used for the long code scrambler 710, and in this case, the long code scrambler 710 exclusively ORs the channel coded signal and the long code to generate scrambled symbols. The scrambled symbols are provided to a channel spreader (or orthogonal modulator) 720 after separation into I-component symbols and Q-component symbols. At the same time, a spreading code index k indicating a channel assigned to the user is input to a spreading code generator 740. As stated above, a Walsh code or a quasi-orthogonal code is typically used for the spreading code. With regard to 10 operation of the spreading code generator 740, upon receipt of the spreading code index k, an index controller 742 outputs a mask index and a Walsh orthogonal code index corresponding to the received spreading code index k. Here, the mask refers to a mask for a quasi-orthogonal code. Upon receipt of the mask index, a mask generator 744 accesses a mask of length 256 corresponding to the input mask index from a mask table. At the same time, upon receipt of the Walsh orthogonal code index output from the index controller 742, a Walsh orthogonal code generator 746 accesses an Walsh orthogonal code of length 256 corresponding to the received Walsh orthogonal code index from a Walsh orthogonal code table. An adder 748 then adds the quasi-orthogonal code mask of length 256 output from the mask generator 744 and the Walsh orthogonal code of length 256 chips output from the Walsh orthogonal code generator 746, to generate a quasi-orthogonal code. The generated quasi-orthogonal code is used as a spreading code corresponding to the spreading code index k, and this spreading code is provided to the channel spreader 720. Here, when no mask index is provided to the mask generator 744 (i.e., a mask index value=0), the mask generator 744 outputs no quasi-orthogonal code mask. In this case, the spreading code output from the adder 748 becomes the Walsh orthogonal code. The generated spreading codes of length 256 are input to the channel spreader 720 along with the long code spread symbols (i.e., the symbols scrambled with the long code). At this point, the one symbol is spread with the spreading codes of the specific number of chips (256/2n, l -11- spreading code generator 740 of FIG. 7. Referring now to FIG. 8, there is shown a structure of a multi-carrier 3x system transmitter. Upon receipt of an input signal, a channel coder 800 codes the input signal into symbol data, and an interleaver 805 interleaves the coded symbols. The symbols interleaved by the interleaver 805 are provided to a long code scrambler 810, and a long code generator 815 generates a long code for scrambling the symbols. The long code scrambler 810 then spreads the interleaved symbols with the long code to scramble the symbols. The scrambled symbols are demultiplexed into three groups by a demultiplexer 880 and then provided to channel spreaders 820, 822 and 824 after separation into I components and Q components. Here, the scrambled symbols are demultiplexed into three groups in order to transmit the channel signal using three carriers of the 3x system. Upon receipt of a spreading code index kl indicating a channel assigned to the user, the spreading code generator 840 generates a spreading code of length 256 corresponding to the received spreading code index kl. Upon receipt of the demultiplexed signals, channel spreader 820 spreads the scrambled symbols with the spreading code. At this point, the channel spreader 820 spreads one symbol with the specific number of chips (256/2", 0 12 after frequency up-conversion. In FIGS. 7 and 8, the lx system uses the spreading code of chip length 128 and the 3x system uses the spreading code of chip length 256, as shown in FIG. 4. When the quasi-orthogonal code is used for the spreading code, channel interference may occur between the lx system and the 3x system. In this case, in the lx system, the spreading code generator generates the spreading code of 256-chip length, and the channel spreader spreads one symbol with the 128 first half chips and spreads another symbol with the 128 second half chips, as shown in FIG. 5. Therefore, the channel spreader of the lx system channel spreads two symbols at one-spreading code duration. Further, in the 3x system, the spreading code generator also generates the spreading code of 256-chip length and the channel spreader spreads one symbol at 256-chip spreading code duration, as shown in FIG. 5. Herein, although the 3x system is a multi-carrier system, the invention can be equally applied to the case where the 3x system is a single-carrier system. In this case, the 3x system has the same channel structure as the lx system and the chip rate becomes 3 times higher. B. Embodiment of Receiver Referring now to FIG. 9, there is shown a receiver for the lx system. A PN despreader 930 receives input spread signals and a PN code generator 950 generates a PN code at 1.2288Mcps. The PN despreader 930 PN despreads the received spread signals with the PN code output from the PN code generator 950 on a chip unit basis. The PN desprcad signals are provided to a channel despreader 920. At this point, upon receipt of a spreading code index k indicating a channel assigned to the user, a spreading code generator 940 generates a spreading code of maximum length 256 corresponding to the received spreading code index k in the same manner as the spreading code generator 740 of FIG. 7. The channel despreader 920 then despreads the PN despread symbols with the spreading code of the specific number of chips (256/2n, l -13- long code descrambler 910 descrambles the despread signals with a long code output from a long code generator 915. The descrambled signals are deinterleaved by a deinterleaver 905 and then decoded by a channel decoder 900. Referring now to FIG. 10, there is shown the structure of a receiver for the multi-carrier 3x system. A PN despreader 130 receives input spread signals, and a PN code generator 150 generates a PN code at a chip rate of 1.2288Mcps. The PN despreader 130 then PN despreads the received spread signals with the PN code. The PN despread signals are applied to a channel despreader 120, and a spreading code generator 140 generates a spreading code of maximum length 256 corresponding to a spreading code index kl indicating a channel assigned to the user. The channel despreader 120 then channel despreads the PN despread signals with the spreading code. At this point, the channel despreader 120 despreads the PN despread symbols with the spreading code of the specific number of chips (256/2", 0 The novel spreading device for a CDMA communication system enables two users having different spreading rates to use the same spreading code, thereby - 14- reducing the hardware complexity. Further, the spreading device can improve the interference property between two users having the different spreading rates, when the two users are overlapped with each other. While the invention has been shown and described with reference to a certain preferred embodiment 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 invention as defined by the appended claims. -15- We claim: 1. A channel spreading device for a base station device in 3 CDMA (Code Division Multiple Access) communication system for spreading input symbols using a second quasi-orthogonal code having a length which is a multiple of a first quasi-orthogonal code having a certain length, the device comprising a spreading code generator (740, S40-844) for generating a second quasi-orthogonal code; a channel spreader (720, 820-824) for providing a plural ity of durations by di viding a duration of the second quasi-orthogonal code fay said multiple of the length of the first quasi-orthogonal code, and spreading channel coded symbols with the quasi-orthogonal codes having said plurality of durations; and a PH (Pseudo Noise) spreader f730, 330-834) for spreading the channel spread signal with a PN code. 2. The channel spreading device as claimed in claim 1, wherein the spreading code generator comprises: a controller (724) for generating a mask index; and B Walsh code index corresponding to a received spreading code inde>: for generating the second quasi-orthogonal code; a mask generator (744) for generating a mask of the second quasi-orthogonal code corresponding to the mask index{ - 16 - a Walsh code generator (746) for generating a Walsh code corresponding to thp Walsh code index 5 and a circuit (748) for mixing the mask of the second quasi-orthogonal code with the Walsh code to generate the second quasi-orthogonal code for use as the spreading code. 3. The channel spreading device as claimed in claim 1, wherein the channel spreader spreads two symbols at a spreading rate of the first quasi-orthogonal code, when the length of the second quasi-orthogonal code is 2 times the length of the first quasi-orthogonal code, whereby one symbol is spread wi th a first half-period chip signal of the second quasi-orthogonal code and another symbol is spread with a second half-period chip signal of the second quasi-orthogonal code. 4. A channel spreading method for a base station device in a CDMA communication system for spreading input symbols using a ssecond quasi-orthogonal code having a length which is a multiple of a first quasi-orthogonal code having a certain length, the method comprising the steps ofs generating a second quasi-orthogonal code having a second length which is a multiple of the first length; and - 17 - providing a plurality of durations by dividing a duration of the second quasi-orthogonal code by said multiple of the length of the first quasi-orthogonal code, and spreading channel coded symbols with the quasi-orthogonal codes having said plurality of durations. 5. The channel spreading method as claimed in claim 4, wherein the spreading code generating step comprises the steps of; generating a mask index and a Walsh code index corresponding to a received spreading code index for generating the second quasi-orthogonal code; generating a mast: of the second quasi-orthogonal code corresponding to the mask index; generating a Walsh code corresponding to the Walsh code index; and mixing the mask of the second quasi-orthogonal code with the Walsh code to generate the second quasi-orthogonal code for use as the spreading code. 6. The channel spreading method 3S claimed in claim 4, wherein when the length of the second quasi-orthogonal code is 2 times the length of the first quasi-orthogonal code, the channel - 18 - spreader spreads, at a spreading rate of the first quasi - orthogonal code, one symbol with a first half-period chip signal of the second quasi-orthogonal code and another symbol with a second half-period chip signal of the second quasi-orthogonal code, whereby two symbols are spread at a during of one spreading code . 7. A channel despreading device for a mobi le station device in a CDMA communication system for deepreading input symbols using a second quasi-orthogonal code having a length which is a multiple of a first quasi-orthogonal code having a certain length, the device comprising: a PN despreader (930, 130, 134) for mixing a received signal with a PN code to generate PN despread signal; a spreading code generator (940, 140, 144) for generating a second quasi-orthogonal code; and a channel despreader (920, 120, 124) for providing a plurality of durations by dividing a duration of the second quasi-orthogonal code by said multiple of length of the first quasi-orthogonal code, and despreading channel coded symbols with the quasi-orthogonal codes having said plurali ty of durations. 8. A channel spreading method for a mobile station device in a CDMA communication system for spreading input symbols using a second quasi-orthogonal code having a length which is a - 19 - multiple of a first quasi-orthogonal code having a certain 1ength, the method comprising the steps of; mining a received signal with a PN code to generate a PN despread signal; generating a second quasi-orthogonal code having a second length which is a multiple of the first length; and providing a plurality of durations by dividing e duration of the second quasi-orthogonal code by said multiple of the length of the first quasi-orthogonal code, and despreading channel coded symbols with the quasi-orthogonal codes having said plurality of durations. Disclosed is a channel spreading device for a base station device in a CDMA communication system for spreading input symbols using a first quasi-orthogonal code having a first length or channel spreading the input symbols using a second quasi-orthogonal code having a second length which is a multiple of the first length. The device comprises a spreading code generator for generating the second quasi-orthogonal code; a channel spreader for providing a plurality of durations by dividing a duration of the second quasi-orthogonal code by said multiple of the length of the first quasi-orthogonal code, and spreading channel coded symbols with the quasi-orthogonal codes divided to have a length corresponding to the divided durations so as to spread the symbols identical in number to said multiple of the first quasi-orthogonal code duration at the duration of the second quasi-orthogonal; and a PN spreader for spreading the channel spread signal with a PN code. |
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| Patent Number | 202479 | |||||||||||||||
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| Indian Patent Application Number | IN/PCT/2000/00276/KOL | |||||||||||||||
| PG Journal Number | 08/2007 | |||||||||||||||
| Publication Date | 23-Feb-2007 | |||||||||||||||
| Grant Date | 23-Feb-2007 | |||||||||||||||
| Date of Filing | 29-Aug-2000 | |||||||||||||||
| Name of Patentee | SAMSUNG ELECTRONICS CO. LTD. | |||||||||||||||
| Applicant Address | 416, MEETDAN-DONG PALDAL-GU, SUWON-SHI 442-370 KYUNGKI-DO REPUBLIC OF KOREA | |||||||||||||||
Inventors:
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| PCT International Classification Number | H 04 B 7/216 | |||||||||||||||
| PCT International Application Number | PCT/KR99/00835 | |||||||||||||||
| PCT International Filing date | 1999-12-29 | |||||||||||||||
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