WO2005104589A1

WO2005104589A1 - Transmitter and receiver for multicarrier system and subcarrier assignment method thereof

Info

Publication number: WO2005104589A1
Application number: PCT/KR2004/003470
Authority: WO
Inventors: Dong-Seung Kwon; Seong-Rag Kim; In-Kyeong Choi; Choong-Il Yeh; Seong-Chul Cho; Yu-Ro Lee
Original assignee: Electronics And Telecommunications Research Institute; Samsung Electronics Co., Ltd.; Kt Corporation; Sk Telecom Co., Ltd.; Ktfreetel Co., Ltd.; Hanaro Telecom, Inc.; Oh, Jong-Ee
Priority date: 2004-04-23
Filing date: 2004-12-27
Publication date: 2005-11-03
Also published as: KR20050102852A

Abstract

Disclosed is a subcarrier assignment method in a multicarrier communication system, e.g. an OFDM communication system. A frequency bandwidth is divided into a plurality of groups having a predetermined number of contiguous subcarriers, a (pn-1, 1, pn-1) Reed-Solomon code on the Galois Field (pn) to which identifiers are added according to primitive elements is used, a subcarrier is selected from each group to generate a subchannel, and the generated subchannel is assigned to a base station user. Accordingly, the subcarrier assignment method provides easy cell planning even when using a considerably short Reed-Solomon sequence. The frequency diversity effect is provided to the base station user, and the Reed-Solomon sequence for averaging adjacent cell interference is generated to increase the number of identifiable base stations.

Description

Description TRANSMITTER AND RECEIVER FOR MULTICARRIER SYSTEM AND SUBCARRIER ASSIGNMENT METHOD THEREOF Technical Field

[1] The present invention relates to a subcarrier assignor and method thereof in a rαil- ticarrier system. More specifically, the present invention relates to a subcarrier assignor and method thereof in a m lticarrier system for using the (p -1, 1, p -1) Reed- Solomon (R-S) code defined on the Galois Field GF (pⁿ) and increasing performance of distinguishing base stations. Background Art

[2] The orthogonal frequency division miltiplexing (OFDM) schemes based on mul- ticarriers have been actively studied for high-speed data rate methods in the wired/ wireless communication. Application of single carriers to high-speed data transmission with a short symbol period in radio communication with multipath fading generates nxich inter-symbol interference (TSI) and substantially increases complexity at a receiver, and the multicarrier method maintains data rates and extends the symbol period for each subcarrier by as many as the number of subcarriers to thereby appropriately process frequency-selective fading channels caused by imltipaths by using an equalizer with a single tap.

[3] The OFDM, one of π-ulticarrier systems, divides an available frequency bandwidth into a plurality of sub-bands, assigns orthogonal carriers in a superimposed manner with respect to each sub-band's carrier frequency, and transmit the assigned orthogonal carriers, and hence, increases frequency usage efficiency, and the method for a transmitter and a receiver to modulate and demodulate the carriers is realized by using the inverse fast Fourier transform (IFFT) and the fast Fourier transform (FFT).

[4] In general, the milticarrier system assigns subcarriers and distingashes base stations by using the Latin square sequence, the Latin cube sequence, the Latin hypercube sequence, and the R-S sequence. PCT international publication number WO 02/09455 A2 entitled "System and method for cellular communications" discloses a conventional multicarrier system using the R-S sequence. Therein, 0 is added to the R- S code with the length of (p-1) defined on the GF (p) to generate a sequence with the length of p, and a sequence generated by adding a cyclic shift of the sequence and a predetermined offset thereto is used to assign subcarriers to users. The usage of the sequence with the length of p enables distingάshing of p base stations where p is a prime number.

[5] For example, the R-S sequence made by using the primitive element of 2 on the GF (13) is given as { 1,2,4,8,3,6,12,11,9,5,10,7}, and an addition of 0 to the sequence produces {0,1,2,4,8,3,6,12,11,9,5,10,7} with the length of 13. Cyclic shifts of the sequence generate thirteen sequences shown in FIG. 1, and an addition of an offset to the each of thirteen sequences of FIG. 1 generates thirteen different sequences. FIG. 2 shows the addition of offsets to the sequence of {0,1,2,4,8,3,6,12,11,9,5,10,7} with the length of 13, which is a summation on the GF (13).

[6] The conventional milticarrier system uses the above-generated 13 x 13 sequence to disting sh base stations and differently assign subcarriers for respective users. That is, the sequences caused by thirteen cyclic shifts are used to distingdsh base stations, thirteen sequences caused by offsets added to the sequences assigned to the base stations are used to distingdsh base station users, and on the contrary, the thirteen sequences according to the offsets are used to distingdsh base stations, and the sequences according to thirteen cyclic shifts are used to distingdsh base station users.

[7] However, the conventional R-S sequence based milticarrier system has a difficulty in cell planning when the length of p is not long. Disclosure of Invention Technical Problem

[8] It is an advantage of the present invention to provide a subcarrier assignor and a method thereof in a milticarrier system for providing easy cell planning while using a sequence that is not long. Technical Solution

[9] To achieve the advantage, a method for assigning subcarriers to a plurality of base station users in a milticarrier system is provided.

[10] In one aspect of the present invention, a method for assigning subcarriers to a base station users in a milticarrier communication system, comprises: (a) dividing a frequency bandwidth into a plurality of groups having a predetermined number of contigαis subcarriers; (b) using a Reed-Solomon (R-S) code on the Galois Field (GF(p )) to which identifiers are added according to primitive elements, and generating a subchannel by selecting a subcarrier from each divided group, p being a prime number, and n being a positive integer; and (c) assigning the generated subchannel to the base station user.

[11] In (b), no addition of 0 is generated to the Reed-Solomon code with the length of (p ⁿ-l) defined on the GF(p").

[12] The step of (b) comprises: (b-1) using a (p -l, 1, p -1) R-S code on the GF(p ) and generating a different R-S sequence to each base station; and (b-2) generating a subchannel based on the generated sequence, and (p -2) different primitive elements are generated by the (p"-l, 1, p"-l) R-S code on the GF(p").

[13] The step of (b-1) comprises: using a predetermined primitive element on the GF(p ), and generating a first R-S sequence with the length of (p -1); cyclically shifting the first R-S sequence to generate a second R-S sequence; and adding an offset to the second R-S sequence to generate a third R-S sequence. In addition, the step of (b-1) may comprise: using a predetermined primitive element on the GF(p"), and generating a first R-S sequence with the length of (p -1); adding an offset to the first R-S sequence to generate a second R-S sequence; and cyclically shifting the second R-S sequence to generate a third R-S sequence.

[14] The second R-S sequence is used to identify the base stations, and the third R-S sequence is used to identify the subchannels.

[15] In another aspect of the present invention, a transmitter for transmitting data to a receiver through a subchannel assigned to a base station user in a milticarrier communication system, comprises: a sequence generator and assignor for using primitive elements of a Reed-Solomon (R-S) code on a Galois Field GF(p ), generating a different sequence with the length of (p"-l) for each base station, and assigning the subcarrier to the base station user based on the generated sequence; a tone assignor for designating a physical position of the subcarrier assigned according to the generated sequence, and assigning the subchannel to the base station user; and a mapper for performing mapping for modulating the assigned subcarrier according to a predetermined modulation method.

[16] The sequence generator and assignor cyclically shifts the sequence with the length of (p -1) to generate a first R-S sequence, and adds an offset to the generated first R-S sequence to generate a second R-S sequence, and in addition, the sequence generator and assignor may add an offset to the generated sequence with the length of (p -1) to generate a first R-S sequence, and cyclically shift the first R-S sequence to generate a second R-S sequence.

[17] In still another aspect of the present invention, a receiver for receiving data from a transmitter through a subchannel allocated to the base station user in a milticarrier communication system, comprises: a sequence generator and assignor for using primitive elements of a Reed-Solomon (R-S) code on a Galois Field GF(p"), generating a different sequence with the length of (p -1) for each base station, and assigning the subcarrier to the base station user based on the generated sequence; a tone identifier for identifying the subcarrier assigned to the user corresponding to the generated subcarrier; and a mapper for receiving the data from the transmitter, performing mapping for demodulation corresponding to the modulation executed by the transmitter, mapping the subcarrier from the tone identifier, and providing the assigned data to the user.

[18] The sequence generator and assignor cyclically shifts the sequence with the length of (p -1) to generate a first R-S sequence, and adds an offset to the generated first R-S sequence to generate a second R-S sequence, and in addition, the sequence generator and assignor may add an offset to the generated sequence with the length of (p -1) to generate a first R-S sequence, and cyclically shift the first R-S sequence to generate a second R-S sequence. Brief Description of the Drawings

[19] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention:

[20] FIG. 1 shows a sequence generated by assignment of subcarriers in a conventional multicarrier system;

[21] FIG. 2 shows a sequence of FIG. 1 to which an offset is added;

[22] FIG. 3 shows a block diagram of a transmitter and a receiver of a milticarrier system according to an exemplary embodiment of the present invention; ₃ [23] FIG. 4 shows a sequence generated by using primitive elements on a GF (2 ) according to an exemplary embodiment of the present invention;

[24] FIG. 5 shows a sequence generated by cyclically shifting the sequence generated by ₃ using the primitive element of 2 on the GF (2 ) of FIG. 4; and

[25] FIG. 6 shows a sequence generated by adding an offset to the sequence of FIG. 5 Best Mode for Carrying Out the Invention

[26] In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive. To clarify the present invention, parts which are not described in the specification are omitted, and parts for which same descriptions are provided have the same reference numerals.

[27] A milticarrier system according to an exemplary embodiment of the present invention will be described.

[28] In general, the milticarrier system uses broadband frequencies. When a subscriber spreads subcarriers over the whole band, the subscriber obtains a frequency diversity effect and expects an interference averaging effect by randomizing the adjacent cell interference. In order to achieve the effects, the milticarrier system divides the total frequency bandwidth into groups of contigαis subcarriers, and generates a subchannel by selecting one subcarrier from each group and combining the selected subcarriers. The subchannel is assigned to the subscriber. For example, when it is assumed that a frequency bandwidth has 130 subcarriers, the milticarrier system combines thirteen contigαis subcarriers into a group to generate ten groups, and selects one subcarrier from each of ten groups to generate ten subchannels each of which has ten subcarriers over the frequency bandwidth, and assigns the generated subchannels to the subscriber.

[29] In this instance, the method for selecting one subcarrier from each group having clusters of subcarriers and generating a subchannel can be represented as a sequence. Elements of the sequence indicate locations of subcarriers selected from the groups. That is, the first element of the sequence is a position of the subcarrier selected from the first group, and the second element of the sequence is a position of the subcarrier selected from the second group.

[30] An OFDM system, one of multicarrier systems, according to an exemplary embodiment will be described with reference to FIG. 3.

[31] FIG. 3 shows a block diagram of a transmitter and a receiver of a milticarrier system according to an exemplary embodiment of the present invention.

[32] As shown, the transmitter 100 includes a sequence generator and assignor 110, a tone assignor 120, and a mapper 13Q

[33] The sequence generator and assignor 110 assigns a sequence according to base stations, modifies the sequence, and assigns the sequence to the user. In this instance, the sequence generator and assignor 110 uses the (p -1, 1, p -1) R-S code on the GF (p ) to generate a different sequence for each base station.

[34] The tone assignor 120 assigns a subchannel for designating a physical position of a subcarrier to the user of the base station according to the sequence generated by the sequence generator and assignor 110 so that specific tones are designated and assigned to the users of base stations covering the frequency bandwidth.

[35] The mapper 130 modulates data according to a modulation method defined by the data rates to map the data to the assigned subcarrier. In this instance, the modulation method supports the IEEE 802.1 la data formats including 1-bit BPSK, 2-bit QPSK, 4-bit 16QAM, and 6-bit 64QAM transmittable per period. That is, the mapper 130 performs IFFT on the modulated data, loads the IFFT-ed data on different subcarriers having orthogonality on the frequency domain, and transmits the same to a receiver 200 of the OFDM system through the subchannel assigned to the user of the base station.

[36] The receiver 200 in the OFDM system includes a sequence generator and assignor 210, a tone identifier 220, and a mapper 23Q

[37] The sequence generator and assignor 210 assigns a sequence according to base stations, modifies the sequence, and assigns the sequence to the user. In this instance, the sequence generator and assignor 210 uses the (p -1, 1, p -1) R-S code on the GF (p ) to generate a different sequence for each base station. The sequence generator and assignor 210 performs the same -unctions as those performed by the sequence generator and assignor 11Q Therefore, the receiver 200 obtains information on the varied base station and user when the transmitter 100 does not transmit the information on the varied base station and user each time the base station and the user are varied.

[38] The tone identifier 220 identifies the subcarrier assigned to the user of a base station according to the generated subcarrier.

[39] The mapper 230 receives the data in the frequency bandwidth from the transmitter of the milticarrier system to demodulate the data corresponding to the modulation method, maps the subcarrier identified by the tone identifier from the received data, and receives the data assigned to the user of the base station.

[40] As to the GF(p) and GF(p ), the GF is an algebraic field that has a finite number of members to allow addition, subtraction, miltiplication, and division where p is a number of elements. The Galois Field is given only when p is a prime number or a square of a prime number, and the operation of GF(p) corresponds to the operation of mod n.

[41] When the GF(p) is extended to the GF(p ), the GF(p ) has p elements. In particular, GF(2 ) has 2 elements and an extended field of the GF(2) with the elements of 0 and 1. Each GF(2") includes a zero element, a unit element, a primitive element, and at least one irreducible polynomial of G(x) = x + g x + g x + ... + g x + g . The m-l m-2 1 0 primitive element of otis the root of the irreducible polynomial G(x) and generates all the elements without 0 of GF(2").

[42] In the exemplary embodiment, it is allowed for the R-S code to extend the GF(p) to the GF(p") and generate the sequence with the length of (p"-l) without addition of 0, and increase a sequence identification number according to the primitive elements.

[43] A subcarrier assignment operation by the transmitter 100 and the receiver 200 of the milticarrier system will be described with reference to FTGs. 4 to 6. The sequence generator and assignors 110 and 210 of the transmitter 100 and the receiver 200 perform the same subcarrier assignment operation, but they perform different processes when having assigned the subcarriers. In detail, the transmitter 100 modulates data, maps the modulated data on the subcarriers, and transmits the mapped data to the receiver 200, and the receiver 200 receives the data and maps the user's subcarriers. The subcarrier assignment operation will now be described. ₃ [44] FIG. 4 shows a sequence generated by using primitive elements on the GF (2 ), FIG. 5 shows a sequence generated by cyclically shifting the sequence generated by ₃ using the primitive element of 2 on the GF (2 ) of FIG. 4, and FIG. 6 shows a sequence generated by adding an offset to the sequence of FIG. 5

[45] When p is defined to be a prime number and n is a positive integer, the sequence generator and assignors 110 and 210 use the (p"-l, 1, p"-l) R-S code defined on the GF(p ) to generate a sequence with the length of (p -1), and then generate (p -1) codewords except the codeword of 0 according to the respective primitive elements on the GF(p ) where (p -2) primitive elements are given on the GF(p ). No description on the (p -1, 1, p -1) R-S code defined on the GF(p ) will be provided since it is well known to a person skilled in the art.

[46] Also, the sequence generator and assignors 110 and 210 control the distance between the codewords to be (p"-l) according to the (p"-l, 1, p"-l) R-S code, and cyclically shifts one codeword according to cyclic codes of the R-S code, to generate residual codewords.

[47] In detail, when p is given to be 2 and n is given to be 3, the primitive elements on 3 3 the GF(2 ) are provided to be 2, 4, 3, 6, 7, and 5, a total of (2 -2) primitive elements. The sequence generator and assignors 110 and 210 use the primitive element of 2 on ₃ the GF(2 ) to generate the sequence of { 1,2,4,3,6,7,5 }, use the primitive element of 4 ₃ on the GF(2 ) to generate the sequence of { 1,4,6,5,2,3,7}, and use the primitive ₃ element of 3 on the GF(2 ) to generate the sequence of { 1,3,5,4,7,2,6}, and hence, six sequences are generated according to the primitive elements of 2, 4, 3, 6, 7, and 5 The ₃ six sequences caused by the primitive elements on the GF(2 ) are illustrated in FIG. 4.

[48] The sequence generator and assignors 110 and 210 generate seven sequences according to the cyclic shift of the sequence of { 1,2,4,3,6,7,5 } out of six sequences shown in FIG. 4. In a like manner, the sequence generator and assignors 110 and 210 generate seven sequences according to the cyclic shift of the sequence of { 1,4,6,5,2,3,7}, and generate seven sequences according to the cyclic shift of the sequence of { 1,3,5,4,7,2,6}. As a result, (6 x 7) (generated from ((p -2) x (p -1)) sequences are generated. The sequence generated by the cyclic shift of the sequence of { 1,2,4,3,6,7,5} is shown in FIG. 5

[49] The sequence generator and assignors 110 and 210 add an offset to the seven sequences shown in FIG. 5 to generate eight sequences for each sequence. The eight sequences generated by adding a predetermined offset to the sequence of { 1,2,4,3,6,7,5} are shown in FIG. 6, and thereby, (7 x 8) (generated from ((p -1) x p ) sequences are generated. ₃ [50] That is, the sequence generator and assignors generate (2 -1) sequences for each 3 3 primitive element on the GF(2 ) in the (2 -2) primitive elements according to the cyclic ₃ shift, and adds an offset for the generated sequences to generate 2 sequences. 3 3 Therefore, (2 -2) x (2 -1) base stations are identified when the sequences generated by 3 3 addition of an offset are used in order to identify subchannels, and (2 -2) x (2 ) base stations are identified when the sequences generated by the cyclic shift are used in order to identify subchannels.

[51] Accordingly, when the (p -1, 1, p -1) R-S code defined on the GF(p ) is used, (2 -2) x (2 -1) base stations are identifiable by an addition of an offset, and (2 -2) x (2 ) base stations are identifiable by the cyclic shift. The addition operation on the GF(2") is easily implemented in a hardwired manner by using the XOR operation.

[52] The number of identifiable sequences is increased by adding identifiers according to the primitive elements of the (p -1, 1, p -1) R-S code defined on the GF(p ), and the sequences are easily generated by obtaining the primitive elements, the cyclic shift, and the offset.

[53] The subcarrier assignment Junction by the transmitter and the receiver of the π-ulticarrier system can be realized into a program to be stored in computer readable recording media (a CD-ROM, a RAM, a floppy disk, an HDD, and an optical disc.)

[54] While this invention has been described in connection with what is presently considered to be the most practical and prefened embodiment, 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.

[55] According to the present invention, the frequency diversity effect is provided to the base station user, and the Reed-Solomon sequence for averaging the adjacent cell interference is generated to increase the number of identifiable base station. Also, the sequences used by the base stations are generated when the primitive elements, the cyclic shift, and the offset are given.

[56]

[57]

Claims

[1] A method for assigning subcarriers to base station users in a milticarrier communication system, comprising: (a) dividing a frequency bandwidth into a plurality of groups having a predetermined number of contigαis subcarriers; (b) using a Reed-Solomon (R-S) code on a Galois Field (GF(p )) to which identifiers are added according to primitive elements, and generating a subchannel by selecting a subcarrier from each group, p being a prime number, and n being a positive integer; and (c) assigning the generated subchannel to the base station user.

[2] The method of claim 1, wherein no addition of 0 is generated to the Reed- Solomon code with the length of (p"-l) defined on the GF(p") in (b).

[3] The method of claim 1, wherein (b) comprises: (b-1) using a (p"-l, 1, p°-l) R-S code on the GF(p") and generating a different R- S sequence to each base station; and (b-2) generating a subchannel based on the generated sequences.

[4] The method of claim 3, wherein (p"-2) different primitive elements are generated by the (p"-l, 1, p"-l) R-S code on the GF(p").

[5] The method of claim 3, wherein (b-1) comprises: using a predetermined primitive element on the GF(p ) and generating a first R-S sequence with the length of (p -1); cyclically shifting the first R-S sequence to generate a second R-S sequence; and adding an offset to the second R-S sequence to generate a third R-S sequence.

[6] The method of claim 3, wherein (b-1) comprises: using a predetermined primitive element on the GF(p ) and generating a first R-S sequence with the length of (p -1); adding an offset to the first R-S sequence to generate a second R-S sequence; and cyclically shifting the second R-S sequence to generate a third R-S sequence.

[7] The method of claim 5 or 6, wherein the second R-S sequence is used to identify the base stations.

[8] The method of claim 5 or 6, wherein the third R-S sequence is used to identify the subchannels.

[9] A transmitter for transmitting data to a receiver through a subchannel assigned to a base station user in a π-ulticarrier communication system, comprising: a sequence generator and assignor for using primitive elements of a Reed- Solomon (R-S) code on a Galois Field GF(p ), generating a different sequence with the length of (p -1) for each base station, and assigning the subcarrier to the base station user based on the generated sequence; a tone assignor for designating a physical position of the subcarrier assigned according to the generated sequence, and assigning the subchannel to the base station user; and a mapper for performing mapping for modulating the assigned subcarrier according to a predetermined modulation method.

[10] The transmitter of claim 9, wherein the sequence generator and assignor cyclically shifts the sequence with the length of (p"-l) to generate a first R-S sequence, and adds an offset to the generated first R-S sequence to generate a second R-S sequence.

[11] The transmitter of claim 9, wherein the sequence generator and assignor adds an offset to the generated sequence with the length of (p -1) to generate a first R-S sequence, and cyclically shifts the first R-S sequence to generate a second R-S sequence.

[12] The transmitter of claim 10 or 11, wherein the first R-S sequence is used to identify the base stations, and the second R-S sequence is used to identify the base station users.

[13] A receiver for receiving data from a transmitter through a subchannel allocated to a base station user in a milticarrier comminication system, comprising: a sequence generator and assignor for using primitive elements of a Reed- Solomon (R-S) code on a Galois Field GF(p"), generating a different sequence with the length of (p -1) for each base station, and assigning the subcarrier to the base station user based on the generated sequence; a tone identifier for identifying the subcarrier assigned to the user conesponding to the generated subcarrier; and a mapper for receiving the data from the transmitter, performing mapping for demodulation conesponding to the modulation executed by the transmitter, mapping the subcarrier from the tone identifier, and providing the assigned data to the user.

[14] The receiver of claim 13, wherein the sequence generator and assignor cyclically shifts the sequence with the length of (p"-l) to generate a first R-S sequence, and adds an offset to the generated first R-S sequence to generate a second R-S sequence. [15] The receiver of claim 13, wherein the sequence generator and assignor adds an offset to the generated sequence with the length of (p -1) to generate a first R-S sequence, and cyclically shifts the first R-S sequence to generate a second R-S sequence. [16] The receiver of claim 14 or 15, wherein the first R-S sequence is used to identify the base stations, and the second R-S sequence is used to identify the base station users.