Method and apparatus for downlink joint detection in a communication system

1. A ZF (Zero Forcing) joint detection apparatus used for a downlink receiver, comprising:

a channel estimator for estimating a channel impulse response of a multipath fading channel of a received signal;

a channel equalizer including means for estimating a transmission signal ŝ j− by performing channel compensation and removing multipath interference by a deconvolution technique based on the estimated channel impulse response h of the received signal r j , represented by the following equation:

s

^

j

=

r

j

h

1

,

for

⁢

⁢

j

=

1

;

s

^

j

=

1

h

1

⁢

{

r

j

-

∑

i

=

2

J

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⁢

h

i

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s

^

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-

i

+

1

}

,

for

⁢

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j

=

2

,

3

,

…

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,

W

;

and

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^

j

=

1

h

1

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{

r

j

-

∑

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=

2

W

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⁢

h

i

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s

^

j

-

i

+

1

}

,

for

⁢

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j

=

W

+

1

,

W

+

2

,

…

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,

NQ

,

wherein N, Q, and W are positive integers respectively representing, a length of a data sequence, a length of a spreading sequence, and a length of a channel impulse response; and

a user detector for receiving the transmission signal from the channel equalizer and for detecting a symbol-level data sequence transmitted by a specific user.

2. The apparatus as claimed in claim 1 , wherein the user detector adetects the symbol-level data sequence transmitted by the specific user by despreading the transmission signal estimated by the channel equalizer with a spreading code for the specific user and a scrambling code.

3. A ZF (Zero Forcing) joint detection apparatus in a downlink receiver, for detecting a data sequence transmitted by a specific user, in a CDMA (Code Division Multiple Access) communication system in which there are K users, a length of a data sequence is N, a length of a spreading sequence is Q, and a length of a channel impulse response is W, the apparatus comprising:

a channel estimator for estimating the channel impulse response of a multipath fading channel of a received signal;

a channel equalizer for estimating a chip-level transmission signal ŝ j by performing channel compensation and removing multipath interference by a deconvolution technique based on the estimated channel impulse response h of the received signal r j , represented by the following equation:

s

^

j

=

r

j

h

1

,

for

⁢

⁢

j

=

1

;

s

^

j

=

1

h

1

⁢

{

r

j

-

∑

i

=

2

j

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⁢

h

i

⁢

s

^

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-

i

+

1

}

,

for j=2, 3, . . . , W; and

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^

j

=

1

h

1

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{

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j

-

∑

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=

2

W

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h

i

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s

^

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-

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+

1

}

,

for j=W+1, W+2, . . . , NQ,

wherein K, N, Q, and W are positive integers; and

a user detector for receiving the chip-level transmission signal ŝ j estimated by the channel equalizer and detecting a symbol-level data sequence transmitted by the specific user.

4. The apparatus as claimed in claim 3 , wherein the user detector detects the symbol-level data sequence transmitted by the specific user by despreading the chip-level transmission signal ŝ j estimated by the channel equalizer with a spreading code for the specific user and a scrambling code.

5. A ZF (Zero Forcing) joint detection method for a downlink receiver, comprising the steps of:

estimating a channel impulse response of a multipath fading channel of a received signal;

estimating a transmission signal ŝ j by performing channel compensation and removing multipath interference by a deconvolution technique based on the estimated channel impulse response h of the received signal r j , represented by the following eciuation:

s

^

j

=

r

j

h

1

,

for

⁢

⁢

j

=

1

;

s

^

j

=

1

h

1

⁢

{

r

j

-

∑

i

=

2

J

⁢

⁢

h

i

⁢

s

^

J

-

i

+

1

}

,

for

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j

=

2

,

3

,

…

⁢

,

W

;

and

s

^

j

=

1

h

1

⁢

{

r

j

-

∑

i

=

2

W

⁢

⁢

h

i

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s

^

j

-

i

+

1

}

,

for

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j

=

W

+

1

,

W

+

2

,

…

⁢

,

NQ

,

wherein N, Q, and W are positive integers respectively representing, a length of a data sequence, a length of a spreading sequence, and a length of a channel impulse response; and

detecting a symbol-level data sequence transmitted by a specific user by using the estimated transmission signal.

6. The method as claimed in claim 5 , wherein the step of detecting the symbol-level data sequence transmitted by the specific user is performed by despreading the estimated transmission signal with a spreading code for the specific user and a scrambling code.

7. A ZF (Zero Forcing) joint detection method in a downlink receiver, for detecting a data sequence from a specific user, in a CDMA (Code Division Multiple Access) communication system in which there are K users, a length of a data sequence is N, a length of a spreading sequence is Q, and a length of a channel impulse response is W, the method comprising the steps of:

estimating a channel impulse response of a multipath fading channel of a received signal;

performing channel compensation and removing multipath interference based on the estimated channel impulse response h of the received signal r j using a deconvolution technique;

estimating a first sequence of a chip-level transmission signal ŝ j in accordance with

s

^

j

=

r

j

h

1

,

for

⁢

⁢

j

=

1

;

estimating second to W th sequences of the estimated chip-level transmission signal ŝ j in accordance with

s

^

j

=

1

h

1

⁢

{

r

j

-

∑

i

=

2

j

⁢

⁢

h

i

⁢

s

^

j

-

i

+

1

}

,

for j=2, 3, . . . , W;

estimating (W+1) th to (NQ) th sequences of the estimated chip-level transmission signal ŝ j in accordance with

s

^

j

=

1

h

1

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{

r

j

-

∑

i

=

2

W

⁢

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h

i

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s

^

j

-

i

+

1

}

,

for j=W+1, W+2, . . . , NQ,

wherein K, N, Q and W are positive integers; and

detecting a symbol-level data sequence transmitted by the specific user by using at least one of the sequences of the estimated chip-level transmission signal.

8. The method as claimed in claim 7 , wherein the step of detecting the symbol-level data sequence transmitted by the specific user is performed by despreading the estimated at least one of the sequences of the chip-level transmission signal with a spreading code for the specific user and a scrambling code.