METHOD FOR SIGNAL TRANSMISSION IN WIRELESS SYSTEMS

TECHNICAL FIELD

When a plurality of terminals simultaneously use an acknowledgement/negative acknowledgement (ACK/NAK) channel in a wireless communication system, code divisi on multiplexing (CDM) may be used to allow for the plurality of terminals. In CDM, eac h of the plurality of terminals transmits a signal multiplied by a spreading code allocated thereto.

The present invention relates to code hopping for efficiently mitigating interferenc e among terminals in the same cell and between terminals of adjacent cells when each of a plurality of terminals uses a spreading code along a frequency axis and a spreadin g code along a time axis.

The present invention is derived from a research project partly supported by the I nformation Technology (IT) Research & Development (R&D) program of the Ministry of Information and Communication (MIC) and the Institute for Information Technology Adv ancement (IITA) [2005-S-404-13, Development of Radio Transmission Technology for 3G Evolution].

BACKGROUND ART The present invention relates to a method of transmitting an acknowledgement/n egative acknowledgement (ACK/NAK) signal by a terminal as a response to data receiv ed from a base station.

A receiver sends an ACK signal to a transmitter when the receiver is successful i n demodulating received data, and sends a NAK signal to the transmitter when the rece iver is unsuccessful in demodulating the received data. Each of the ACK/NACK signal is expressed as one bit per codeword. A plurality of terminals should be able to simul taneously transmit their ACK/NAK signals by using given time and frequency resources through multiplexing.

Multiplexing techniques are classified into frequency division multiplexing (FDM) and code division multiplexing (CDM). While FDM is a form of multiplexing where a pi urality of terminals use different time and frequency resources, CDM is a form of multipl exing where a plurality of terminals use the same time/frequency resources but transmit signals multiplied by orthogonal codes so as for a receiver to distinguish the plurality of

users.

In uplink, a Zadoff-Chu sequence is widely used because it has an ideal peak to average power ratio (PAPR). Such a Zadoff-Chu sequence achieves orthogonality bet ween terminals through cyclic delay without multiplying a signal by a specific code in a f requency domain.

A terminal transmits an uplink ACK/NAK signal to a base station to signify succe ssful or unsuccessful receipt of downlink data. The uplink ACK/NAK signal requires on e bit per codeword used to transmit the downlink data.

FIG. 1 illustrates time/frequency resources used by a terminal to transmit an upli nk ACK/NAK signal through a control channel in a 3 ^rd generation partnership projection long term evolution (3GPP LTE) system. Referring to FIG. 1 , resources used by one c ontrol channel are grouped into two separate resource blocks. Each of the two resour ce blocks includes N subcarriers along a frequency axis, and 7 orthogonal frequency di vision multiplexing (OFDM) symbols, which corresponds to one slot, along a time axis. One slot has a length of 0.5 ms.

In FIG. 1 , a plurality of terminals may commonly use one control channel. That is, one control channel may be shared by the plurality of terminals.

In this case, in order to distinguish the plurality of terminals using the same contr ol channel, a specific code sequence is allocated to each of the plurality of terminals. That is, each of the plurality of terminals forms and transmits a signal spread on a frequ ency axis and a time axis by using its own specific code.

FIG. 2 illustrates a code sequence and a symbol transmitted to each of N subcar riers in an ACKNAK channel occupying a resource block that includes the N subcarriers on a frequency axis and 7 OFDM symbols on a time axis. In FIG. 2, the resource bio ck corresponding to one slot described with reference to FIG. 1 occupies N subcarriers on a frequency axis and includes 7 symbol blocks BL #0 through #6 on a time axis.

When CDM is used in order to distinguish signals of a plurality of terminals, a sy mbol and a sequence may be mapped to each time/frequency resource as shown in Fl G. 2. In order to distinguish the plurality of terminals, a sequence is applied to each of the frequency axis and the time axis. In FIG. 2, a reference signal is used for channel estimation, and p re-determined signal is communicated between a terminal and a base station.

The base station estimates a channel by using a reference signal, and demodula

tes an ACK/NAK symbol transmitted by a control signal by using the estimated channel. Each time/frequency resource transmits a signal multiplied by two or three symbols.

That is, a time/frequency resource on which a reference signal is transmitted is o

btained by multiplying a frequency-axis sequence symbol ^y and a time-axis

sequence symbol * A time/frequency resource on which a control signal is transmitted is obtained by multiplying a frequency-axis sequence symbol

C " * (Jt) , a time-axis sequence symbol C ₁ - (/=0, 1 ,2,3) , and an ACK/NAK sy

mbol Q m

In FIG. 2, the frequency-axis sequence symbol C ^" * (Jt) is given by

where is the length of a Zadoff-Chu sequence applied to a k subcarrier on th e frequency axis. The small letter m is a primary index, and q is a cyclic delay index One sequence is applied to each of a reference signal and a control signal along the time axis. That is, a sequence applied to a control signal in FIG. 2 is expressed a

C C C C s . A sequence applied to a reference signal is expressed as

R ₀ , R i , i? 2

Currently, in 3GPP LTE, three reference signals per slot are used for an uplink A CK/NAK channel.

Also, in order to distinguish terminals, a Zadoff-Chu sequence along a frequency axis is used and a discrete Fourier transformation (DFT) vector, a Walsh-Hadamard se quence, or a Zadoff-Chu sequence along a time axis may be used.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates time/frequency resources used by a terminal to transmit an upli nk acknowledgement/negative acknowledgement (ACK/NAK) signal through a control c hannel in a 3 ^rd generation partnership projection long term evolution (3GPP LTE) syste m.

FIG. 2 illustrates a code sequence and a symbol transmitted to each of subcarrie rs in an ACK/NAK channel having the N subcarriers on a frequency axis and 7 orthogon al frequency division multiplexing (OFDM) symbols on a time axis.

FIG. 3 illustrates a slot structure of an ACK/NAK channel including 3 reference si gnals per slot, according to an embodiment of the present invention.

FIG. 4 illustrates a slot structure of an ACK/NAK channel including 3 reference si gnals per slot, according to another embodiment of the present invention.

FIG. 5 illustrates a slot structure of an ACK/NAK channel including 3 reference si gnals per slot, according to another embodiment of the present invention. FIG. 6 illustrates a frequency code hopping pattern of a terminal group including one or more terminals in a first slot, according to an embodiment of the present inventio n.

FIG. 7 illustrates a frequency code hopping pattern of a terminal group including one or more terminals in a second slot, according to an embodiment of the present inve ntion.

FIG. 8 illustrates a frequency code hopping pattern of a terminal group including one or more terminals in a first slot in the slot structure of FIG. 5, according to an embo diment of the present invention.

FIG. 9 illustrates a frequency code hopping pattern of a terminal group including one or more terminals in a second slot in the slot structure of FIG. 5, according to an e mbodiment of the present invention.

FIG. 10 is a block diagram of a terminal apparatus for mitigating interference bet ween terminals in a wireless communication system using a method of transmitting a si gnal, according to an embodiment of the present invention. FIG. 11 is a block diagram a base station employing a method of transmitting a s ignal, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL PROBLEM

In a wireless communication system, acknowledgement/negative acknowledgem ent (ACK/NAK) control information sent by a terminal to a base station in order to signif y that the terminal is successful or unsuccessful in demodulating data is transmitted an d received. In order to efficiently transmit and receive such ACK/NAK control informati on, the same ACK/NAK resources are used by a plurality of terminals, thereby causing i nterference between terminals in a cell or between terminals of adjacent cells. In orde r to mitigate the interference, there is a demand for efficient code hopping.

TECHNICAL SOLUTION

According to an aspect of the present invention, there is provided a method of for ming a signal in a wireless communication system in which a plurality of terminals com monly use time and frequency resources, the method comprising: allocating the same fr equency-axis sequence and different time-axis sequences to a plurality of terminals by using a resource index according to a first slot in the first slot; and allocating different fr equency-axis sequences and different time-axis sequences to the plurality of terminals by using a resource index according to a second slot in the second slot.

According to another aspect of the present invention, there is provided a method of forming a signal in a wireless communication system in which a plurality of terminals commonly use time and frequency resources, the method comprising: allocating the sa me frequency-axis sequence and different time-axis sequences to a plurality of terminal s by using a resource index according to a first slot in the first slot; and allocating differe nt frequency-axis sequences to the plurality of terminals by using a resource index acco rding to a second slot in the second slot. According to another aspect of the present invention, there is provided a method of forming a signal in a wireless communication system in which a plurality of terminals commonly use time and frequency resources, the method comprising: causing one or m ore terminals, which use the same frequency axis code and different time axis codes in a first slot, to constitute a terminal group for a reference signal symbol block; causing o ne or more terminals, which use the same frequency axis code and different time axis c odes in a first slot, to constitute a terminal group for a control signal symbol block, whic h is independent from the terminal group for the reference signal symbol block; causing the one or more terminals belonging to the same terminal group for the reference signal

symbol block in the first slot to belong to different terminal groups for a reference signa I symbol block in a second slot; and causing the one or more terminals belonging to the same terminal group for the control signal symbol block in the first slot to belong to diffe rent terminal groups for a control signal symbol block in a second slot. According to another aspect of the present invention, there is provided a method of forming a signal in a wireless communication system in which a plurality of terminals commonly use time and frequency resources, the method comprising: causing one or m ore terminals, which use the same frequency axis code and different time axis codes in a first symbol block, to constitute one terminal group on one frequency code; and causi ng the one terminal group to use a frequency axis code, which is different from the freq uency axis code used in the first symbol bock, in a second symbol block different from t he first symbol block in one slot.

According to another aspect of the present invention, there is provided a code ho pping method for reducing interference between terminals in a wireless communication system in which a plurality of terminals commonly use time and frequency resources, th e code hopping method comprising: causing one or more groups, which use the same f requency axis code and different time axis codes in a first slot, to constitute one termina I group; and, when a time axis code length is less than a slot length, changing a termina I group according to the time axis code length achieving orthogonality so that the one or more terminals belonging to the same terminal group in the first slot belong to different terminal groups in a second slot.

According to another aspect of the present invention, there is provided a terminal using code hopping in a wireless communication system, the terminal apparatus comp rising: a resource index receiving unit receiving a resource index that is changed accord ing to a change in a slot or a symbol block; a frequency-axis code sequence allocating unit determining a frequency-axis code sequence according to the received resource in dex and allocating the determined frequency-axis code sequence to a terminal; and a ti me-axis code sequence allocating unit determining a time-axis code sequence accordin g to the received resource index and allocating the determined time-axis code sequenc e to the terminal.

According to another aspect of the present invention, there is provided a base st ation using code hopping in a wireless communication system, the base station compris ing: a resource index transmitting unit transmitting a resource index that is changed ace

ording to a change in a slot or a symbol to terminals; a frequency-axis code sequence d etermining unit determining a frequency-axis code sequence according to the resource i ndex; and a time-axis code sequence determining unit determining a time-axis code se quence according to the resource index.

ADVANTAGEOUS EFFECTS

As described above, when acknowledgement/negative acknowledgement (ACK/

NAK) control information sent by a terminal to a base station in a wireless communicati on system is transmitted and received, the present invention can efficiently mitigate inte rference between terminals in a cell or between terminals of adjacent cells which is cau sed when a plurality of terminals use the same ACK/NAK resources.

MODE OF THE INVENTION

A code hopping method and apparatus for mitigating interference between termi nals in a wireless communication system according to the present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

Detailed explanation will not be given when it is determined that detailed explana tion about well-known functions and configurations of the present invention may dilute t he point of the present invention. Terms used hereinafter are used considering the fun ctions in the present invention and may be changed according to a user's or operator's i ntention or usual practice. Accordingly, the terms will be defined based on the entire c ontent of the description of the present invention.

In particular, the term "frequency axis code" or "frequency axis code index" used hereinafter is interchangeable with "cyclic shift" or "cyclic shift index", and the term "time axis code" or "time axis code index" used hereinafter is interchangeable with "orthogon al cover" or "orthogonal cover index".

FIGS. 3 through 5 illustrate slot structures of acknowledgement/negative acknowl edgement (ACK/NAK) channels, each slot structure including 3 reference signals per si ot, according to embodiments of the present invention.

Referring to FIGS. 3 through 5, one slot includes 3 reference signals and 4 contr ol signals.

When a plurality of terminals are used, a receiver should be able to receive and

distinguish reference signals transmitted by the plurality of terminals, and also should re ceive and distinguish control signals transmitted by the plurality of terminals.

In order to distinguish signals, code division multiplexing (CDM) using both frequ ency and time resources may be used as described above.

In CDM, a time-axis sequence is an orthogonal sequence. When the number of contin uous orthogonal frequency division multiplexing (OFDM) symbols along a time axis is

, a sequence length may be and sequences achieving orthogonality therebetween may be formed. When an i ^th sequence is expressed as a row vector

^f , orthogonality is given by

NA

G ₁ - ' G _j [C _{i 0} ,C _j i , ..., C J _N ^ ₁ ] - δj C _hk C _{j k} -N _t b _u V A=O

C hN _t -\

(2)

w _{here .}

Theoretically, since the total number of resources on a frequency axis is M and t here are 3 reference signals in FIGS. 3 through 5, Mx3 reference signals in total can be distinguished by CDM.

Since the total number of resources on the frequency axis is M and there are 4 c ontrol signals in FIGS. 3 through 5, Mx4 control signals can be distinguished by CDM.

However, since each terminal should transmit at least one reference signal in ord er for a base station to demodulate a control signal by using the reference signal, the to tal number of distinguishable terminals is Mx3. In this case, an orthogonal sequence h aving a spreading factor (SF) of 3 is used for the reference signals, and an orthogonal s equence having an SF of 4 is used for the control signals.

Code hopping for efficiently mitigating interference according to the present inve

ntion will now be explained. Code hopping is performed on both or each of a frequenc y axis code and a time axis code.

(1 ) Code Hopping on Symbol Block-by-Symbol Block Basis One frequency-axis code sequence and one time-axis code sequence are allocat ed to each terminal. It is assumed that a frequency axis code and a time axis code wh

ich are used by an i ^th terminal in a t ^th block of an s ^th slot are expressed as ' ³ ^ and

r , ^■ „

' , respectively. In a multiplexing structure, 3 or less terminals in one symbol bloc k use the same frequency axis code and different time axis codes that are transmitted t hrough a plurality of blocks. The present invention is not limited to the slot structures of FIGS. 3 through 5, an d the number of symbol blocks included in a slot may vary.

A Zadoff-Chu sequence of Equation 1 may be applied to a frequency axis code. However, the frequency axis code is not limited to the Zadoff-Chu sequence, and may use any sequence that achieves orthogonality. At this time, a frequency axis code, which is used by a plurality of terminals in the same cell, has the same primary index and different cyclic delay indices. However, te rminals belonging to different cells have different primary indices.

A frequency axis code used by each terminal may be changed according to a bio ck index "t". It is assumed that a frequency axis code used by an i ^th terminal for blocks belonging to an s ^th slot is expressed as

{ ? i _λ *=0 ^> ? i,,, ^/ =l ^> 4 _iλ t=2 ^> - ^> 4 ;^=7 > A time axis code may be express

f ^■ ed as *' ^s . If frequency axis codes used for a first symbol block by a j ^th terminal an d an i ^th terminal are the same, the same frequency axis code should be used for remain ing symbol blocks. That is, when

^q ^= ^{0^} SW= ⁰ _{, then} ^ ⁼ * (k=h2X..,6) _{shou|d be satjsfje} d. That is, frequency axis codes used by two terminals in all symbol blocks should be t

he same. Also i i,s k ⁷ ^ <ϊ

⁾ ,, if 4 ^J w,t=-* ¹ j^,s=,t'= ^" "k f , then

<7 i,s,t=k ≠ <lu _,t=k O= 1,2, 3, ..., 6) should be satisfied. That is, frequenc y axis codes used by two terminals in all symbol blocks in the same slot should be differ ent from each other. The aforementioned code hopping may be implemented as folio ws. For starters, a terminal group is defined as follows. One terminal group include s one or more terminals which use the same frequency axis and different orthogonal tim e axis codes. A plurality of terminals groups are generated on a frequency axis, and o ne frequency code hopping pattern corresponds to each of the plurality of terminal grou ps. Since the one or more terminals belonging to the same terminal group use the s ame frequency axis code even when blocks are changed, orthogonality on a time axis b etween the terminals can be maintained.

If the terminals constituting the same terminal group are changed as a symbol bl ock index is changed, orthogonality on a time axis between the terminals is broken, res ulting in interference between the terminals.

FIGS. 6 illustrate frequency code hopping patterns of terminal groups each inclu ding one or more terminals in a first slot and a second slot, respectively, according to e mbodiments of the present invention.

Referring to FIG. 6, a terminal #0, a terminal #6, and a terminal #12 constitute on e terminal group. A frequency axis code commonly allocated to the three terminals #0, #6, and #12 is changed as a symbol block is changed. Accordingly, code hopping is carried out on a symbol block-by-symbol block basis.

In other words, the terminals #0, #6, and #12 of the terminal group in a first symb ol block use the same frequency axis code but each terminal uses different time axis co de. In a second symbol block, the terminals #0, #6, and #12 of the terminal group use a new frequency axis code different from that in the first symbol block, thereby performi ng code hopping on a symbol block-by-symbol block basis. (2) Code Hopping on Slot-by-Slot Basis

Code hopping performed on a slot-by-slot basis will now be explained. An uplink ACK/NAK channel includes two slots. A plurality of terminal signals ar e introduced through an ACK/NAK channel in code division multiple access (CDMA). At this time, terminal speeds and powers are different from one another. A terminal gr

oup is formed for each slot, and terminals belonging to the same terminal group in a firs t slot belong to different terminal groups in a second slot in order to mitigate interferenc e between the terminals, thereby improving receiving performance.

Terminals in a terminal group are distinguishable by using different time axis cod es as described above. For example, a specific terminal in a terminal group may have a high speed or high power because of incomplete power control. Other terminals are interfered by this specific terminal. In particular, remaining terminals other than the sp ecific terminal in the same terminal group are most severely interfered by the specific te rminal. If constituent terminals of a terminal group are changed according to a slot such t hat terminals belonging to the same terminal group in a first slot belong to different term inal groups in a second slot, interference due to the specific terminal may be mitigated.

Code hopping performed on a slot-by-slot basis will now be explained with refere nee to FIGS. 6 and 7 in further detail.

Referring to FIG. 6, the terminals #0, #6, and #12 constitute one terminal group f or each symbol block in the first slot. The terminals #0, #6, and #12 constituting one te rminal group in FIG. 6 do not belong to the same terminal group in the second slot in Fl G. 7. Referring to FIG. 7, in the second slot, terminals #4, #10, and #0 constitute a ne w terminal group. The terminals #6 and #12 constituting the same terminal group toge ther with the terminal #0 in the first slot belong to different terminal groups in the second slot. For example, the terminal #6 constitutes a new terminal group in the second slot together with terminals that belong to different terminal groups in the first slot. The re arrangement of terminals is performed by determining a frequency axis code and a time axis code according to resource indices corresponding to each slot and changing termi nals constituting a terminal group. A method of changing a time axis code will be expl ained later in detail.

Accordingly, terminals belonging to the same terminal group in the first slot may not belong to the same terminal group in the second slot, and may constitute a new ter minal group together with other terminals.

The code hopping performed on the slot-by-slot basis can randomize and averag e interference between terminals. That is, since a terminal with high power in a first si

ot does not belong to the same terminal group in a second slot, interference can be miti gated.

The code hopping performed on the slot-by-slot basis may change a time axis co de allocated to each terminal when a terminal group is changed according to slots. Th at is, a time axis code allocated to the terminal #0 in FIG. 6 and a time axis code allocat ed to the terminal #0 in FIG. 7 may be different from each other.

FIGS. 8 and 9 illustrate frequency code hopping patterns of terminal groups each including one or more terminals in a first slot and a second slot, respectively, in the slo t structure C of FIG. 5, according to embodiments of the present invention. In this case, code hopping is independently performed for a reference signal sym bol block and a control signal symbol block. In FIGS. 8 and 9, it is assumed that a tim e axis code having a length of 4 is used for control signal symbol blocks #0, #1 , #5, and #6, whereas a time axis code having a length of 3 is used for reference signal symbol blocks #2, #3, and #4. A terminal group used in a control signal symbol block and a te rminal group used in a reference signal symbol block may be different from each other as shown in FIGS. 8 and 9.

A terminal group defined in the control signal symbol blocks #0, #1 , #5, and #6 in the first slot of FIG. 8 and a terminal group defined in the control signal symbol blocks #0, #1 , #5, and #6 in the second slot of FIG. 9 are different from each other. Terminal s constituting the same terminal group together with the terminal #0 in the first slot belo ng to terminal groups different from that of the terminal #0 in the second slot.

For example, while terminals #0, #6, and #12 constitute one terminal group in th e first slot of FIG. 8, terminals #4, #0, and #16 constitute one terminal group in the seco nd slot of FIG. 9. Accordingly, terminals constituting the same terminal group together with the terminal #0 in the first slot belong to terminal groups different from that of the te rminal #0 in the second slot.

A terminal group defined in the reference signal symbol blocks #2, #3, and #4 in the first slot of FIG. 8 is different from a terminal group defined in the reference signal s ymbol blocks #2, #3, and #4 in the second slot of FIG. 9. While terminals #0, #3, and #8 constitute a terminal group in the reference signal symbol block #2 in the first slot of FIG. 8, terminals #2, #0, and #13 constitute a terminal group in the reference signal sy mbol block #2 in the second slot of FIG. 9. That is, terminals constituting the same ter minal group together with the terminal #0 in the first slot belong to terminal groups from

that of the terminal #0 in the second slot.

When a terminal group is changed, a time axis code allocated to each terminal may be changed. A time axis code allocated to the terminal #0 in FIG. 8 and a time ax is code allocated to the terminal #0 in FIG. 9 may be different from each other. When a time axis code allocated to a terminal is changed whenever a terminal group is chang ed, interference caused by the use of a specific time axis code may be mitigated.

(3) Code Hopping Changing Terminal Group According to Time Axis Code Lengt h Basis When a time axis code length does not occupy one slot, a terminal group may be changed according to a time axis code length basis. A method of changing a termina I group according to a time axis code length basis in code hopping will now be explaine d.

In the frequency code hopping patterns of FIGS. 3 through 5, when a time axis c ode length is 2, one time axis code is transmitted in two control signal symbol blocks CO and C1 , and another time axis code is transmitted in remaining control signal symbol b locks C2 and C3.

In this case, a terminal group is changed every 2 control signal symbol blocks. When a time axis code having a length of 3 is applied to reference signal symbol blocks RO, R1 , and R2, a terminal group is not changed in the reference signal symbol blocks RO, R1 , and R2.

Whenever a terminal group is changed, a time axis code allocated to each termi nal may be changed. When a time axis code length of 2 is applied to the control signa I symbol blocks, CO, C1 , C2, and C3, 4 time axis codes are transmitted for one terminal.

That is, a time axis code applied to the control signal symbol blocks CO and C1 o f a first slot, a time axis code applied to the control signal symbol blocks C2 and C3 of t he first slot, a time axis code applied to the control symbol blocks CO and C1 of a secon d slot and a time axis applied to the control signal symbol blocks C2 and C3 of the seco nd slot are transmitted for one terminal. In this case, a terminal group is changed thre e times, and a time axis code used by each terminal is accordingly changed.

FIG. 10 is a block diagram of a terminal 1000 for mitigating interference between terminals in a wireless communication system using a method of transmitting a signal,

according to an embodiment of the present invention.

The terminal 1000 includes a resource index receiving unit 1010, a frequency-axi s code sequence allocating unit 1020, and a time-axis code sequence allocating unit 10 30. The resource index receiving unit 1010 receives a resource index according to a change in a slot or a symbol block. That is, a resource index is a basic value for deter mining a frequency-axis code sequence and a time-axis code sequence which are to be determined according to a change from a first slot to a second slot. A terminal receiv es a resource index from a base station. The terminal and the base station share a fre quency-axis code sequence and a time-axis code sequence allocated to the terminal on the basis of the resource index.

The frequency-axis code sequence allocating unit 1020 determines a frequency axis code to be used by a current slot on the basis of the resource index. The determ ined frequency axis code is allocated to a terminal. In code hopping performed on a s ymbol block-by-symbol block basis, a frequency axis code to be determined according t o a symbol block index that is changed whenever a symbol block is changed is determi ned and allocated to a terminal.

A plurality of terminals having the same frequency axis code in a first slot receive a new resource index in a second slot, and accordingly have a new frequency axis cod e. Also, a plurality of terminals belonging to one terminal group have a time axis code i n a second slot which is different from a time axis code in a first slot. Accordingly, ter minals belonging to the same terminal group in a first slot do not belong to the same ter minal group in a second slot, and constitute a new terminal group together with terminal s belonging to different terminal groups in the first slot. A terminal group may be chan ged on a symbol block-by-symbol block basis in this way.

The time-axis code sequence allocating unit 1030 calculates a time-axis code se quence to be allocated to terminals in a current slot or symbol block on the basis of the resource index that is changed according to the slot or the symbol block, and allocates t he calculated time-axis code sequence to the terminal. In order to identify terminals, a base station should know the information of a cod e sequence allocated to each terminal. As described above, the base station transmit s a resource index and shares a time-axis code sequence and a time-axis code sequen ce with each terminal by using the resource index. As a result, the base station knows

a frequency axis code and a time axis code of each terminal in a slot or symbol block. The base station knows from a resource index in a first slot that a plurality of ter minals have the same frequency axis code. The base station also knows from a resou rce index in a second slot that terminals belonging to the same terminal group in the firs t slot do not belong to the same terminal group, but have different frequency axis codes and belong to different terminal groups in the second slot. The base station should al so know that a time axis code may be changed according to a resource index in a slot. As described above, a time axis code allocated to terminals in a first slot is different fro m a time axis code allocated to the terminals in a second slot. A base station apparatus performing the aforesaid functions will now be explaine d.

FIG. 11 is a block diagram illustrating a base station 1100 employing a method o f transmitting a signal, according to an embodiment of the present invention.

Referring to FIG. 11 , the base station 1100 includes a resource index transmittin g unit 1110, a frequency-axis code sequence determining unit 1120, and a time-axis co de sequence determining unit 1130. The resource index transmitting unit 1110 transm its a resource index, which is changed according to a change in a slot or a symbol block , to terminals. The frequency-axis code sequence determining unit 1120 determines a frequency-axis code sequence according to the resource index. The time-axis code se quence determining unit 1130 determines a time-axis code sequence according to the r esource index.

Code hopping according to the present invention may be embodied as computer -readable codes on a computer-readable recording medium. The computer-readable r ecording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer-readable recording medium i nclude read-only memories (ROMs), random-access memories (RAMs), CD-ROMs, ma gnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet).

The computer-readable recording medium can also be distributed over network c oupled computer systems so that the compute readable code is stored and executed in a distributed fashion. Functional programs, codes, and code segments for embodying the present invention may be easily deducted by programmers in the art to which the pr esent invention belongs.

While the present invention has been particularly shown and described with refer ence to exemplary embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and detail may be made therein without departing fr om the spirit and scope of the present invention as defined by the following claims. Th e preferred embodiments should be considered in a descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detai led description of the invention but by the appended claims, and all differences within th e scope will be construed as being included in the present invention.