Microsoft Word - km20020087.docin Mobile Wireless Communication


2 ……………….………….…………… 3
2.1 …………………………….……………. 3
2.2 ……………………..…….………….…….. 11
2.3 ……………………………...……….………….. 17
3 OFDM …………………………... 24
3.1 …………….……….. 24
3.2 OFDM …………………….………. 27
3.3 OFDM …………….………… 30
3.4 OFDM ………………………… 32
4 ………………… 34
4.1 OFDM ………………………….………. 34
4.2 OFDM …………………………………….………. 37
5 ……………………………………………………………… 39
……………………………………………………………………….. 40
BM : (branch metric)
i tc : t j
),( ikcm : m k i
ind , : n [ ]TnnT )1(, + i

tSM : t s
)(tp : Tt ≤≤0 1, 0

j tr : t j
)(trnm : n m
),( ikrnm : siT k FFT
iii
ABSTRACT
Recently the rapid growth of wireless voice subscribers, the growth of the internet and
the increasing use of portable computing devices suggest that wireless internet access will
rise rapidly over the next few years. Wireless internet is demanded to increase the channel
capacity and data rate. It is difficult to increase the channel capacity or reducing the
effective error rate in a multipaths fading channel.
To solve the above problems in wireless communications, Tarokh et al. introduced space
-time codes adopting a joint design of coding, modulation, and transmit diversity. Space-
time coding introduces temporal and spatial correlation into signals transmitted from
different antennas, in order to provide diversity at the receiver, and coding gain over an
uncoded system without sacrificing the bandwidth. The spatial-temporal structure of these
codes can be exploited to increase further the capacity of wireless systems with a relatively
simple receiver structure. Simulation results show that at the frame error rate of 110− the
32-state code with two receiver antennas gives about 3dB gain over the use of a 4 states and
two receiver antennas with the 32-state code give about 6 dB gain over the use of one
receiver antenna. It appears from the simulation results that the coding advantage obtained
by increasing the number of states and diversity gain obtained by increasing the number of
receive antenna.
This thesis also studies space-time codes applying orthogonal frequency division
multiplexing (OFDM) systems in wireless communication. In OFDM, the entire channel is
divided into many narrow parallel subchannels, thereby increasing the symbol duration and
reducing or eliminating the intersymbol interference (ISI) caused by the multipath
environments. At the frame error rate of 110− the 32-state code with space-time codes
applying OFDM gives about 7dB gain over the use of the 4-state code by simulation.
Therefore, space-time codes applying OFDM systems can be used for highly efficient data
transmission over mobile wireless channels.
1
1

.
.

(uplink) (downlink) (capacity) .
(cell site),
.

, .
AT&T Tarokh .
.


.

[1].
OFDM
(Orthogonal Frequency Division Multiplexing) .
,
(impulse noise)
(ISI ; Inter Symbol Interference)
,

. OFDM
2
, WLAN (Wireless Asynchronous Transfer Mode), WATM (Wireless Local Area
Network) . ,
, [8].
,
,
, .
OFDM .
3
2.1
2.1.1

.

. .
.
(time diversity)

. (frequency diversity)


. (space diversity)

.
.
3

.
.
(uplink) (downlink) (capacity)
. (cell site),
4
.
SNR
.

.
,
(multiuser detector) .

.
,
.
, ,
,
.

, .


.

[1].
2.1.2
(Space Time Coding) AT&T Tarokh
.
.

5
source sinkSTTC Decoder
Fig. 2-1. Space Time Coding System Model.
n , m
.
n
. pulse shaper . shaper
. t i ni ≤≤1
i i tc . n

T .
(rayleigh fading) (rician fading)
n .
1 sE .
mj ≤≤1
. t j
6
j t Ecr
1 , ηα (2.1)
t j tη 2
0E
.
ji,α i j .

[1]-[3].
n
n (in the space
domain) (in the time domain) .
MRRC (Maximal Ratio Receive Combining)
.
.
difference matrix distance matrix
.
difference matrix full rank .
, distance matrix
.
1)
ji,α ][ , jiE α
0.5 .
7
.
2 2
1 21
2 1
(maximum-likelihood receiver) n lll
nn eeeeeeeeee ΛΛΛΛ 21 2
2 2
1 21
2 1
,
)4/),(exp(
),,2,1,,,2,1,(
∑∑∑ = = =
2 )(),( α (2.3)
Gaussian tail function . ),,( ,,1 jnjj αα Λ=
,
*2 ),( (2.5)
nqp ≤≤ ,1 qppq xxA ⋅= , ),,,( 2211 p l
p l
),( ecA Hermite Unitary V DVecVA =*),(
D . V },,,{ 21 nvvv Λ A
nC orthonormal basis . D
A nii ,,2,1, Λ=λ .
),( ecB =
∑ =
*),( βλ (2.8)
, ji,α jiE ,α
),,,( ,,2,1 jnjj j EEEK ααα Λ= .
V Unitary },,,{ 21 nvvv Λ nC orthonormal basis
ji ,β 0.5 jK • iv
. jiK , = 2
, jiEβ = 2
i j vK . ji,β 0, ≥jiβ
(probability density function)
(independent rician distribution).
,,, jijijijijiji KIKp ββββ −−= (2.9)
0I (• ) 1 Bessel function .

− m
2 ,0 )4exp( βλ
. i j 0, =jiEα jiK , = 0 .
.
m
0λ (2.11)
r A rank , A rn − A rn −
. A rλλλ ,, 21 Λ
.
mr r r
1 21 ),,( λλλ Λ [1].
2)
The Rank Criterion : nm ),( ecB
c e full rank . ),( ecB
rank rm
.
The Determinant Criterion : rm
c e rr ×
10
),( ecA = ),( ecB ),(* ecB r th root
r ),( ecA rank . rank
. nm
c e ),( ecA
.
.
.
rm (2.13) .
( ) rm
m
j
r

.
The Rank Criterion : .
The Coding Advantage Criterion : rr × ),( ecA
),( ecΛ r ),( ecA rank .
c e ( ) rm
m
j
r
11
2.2
n m
(space time trellis code)
. (quasi-static fading) (flat fading)
.
2-3 4
.
0 . t
.
n ttt qqq Λ21 t i
),,2,1( niqi t Λ=
. 2-2 QPSK 8PSK
.
0
Fig. 2-2. QPSK and 8PSK constellations.
. ,
2 tx . ,
1 tx .
12
.

.
,
.
.

.
(delay diversity)
.
2-3 2-10 QPSK ,
4, 8, 16, 32 .
(2.16) (2.19) .
1a , 2a 3a , 4a , 5a , 6a , 7a
. QPSK
modulo 4 , 1 tx 2
tx
13
Fig. 2-3. Trellis diagram of the 4 states STTC.
4 (2.16) .
)()(2 12 2 tataxt +=
τ τ
QPSK Mapping
QPSK Mapping
2 tx
Fig. 2-4. Encoder block diagram of the 4 states STTC.
14
01 02 03
22 23 20 21
32 33 30 31
02 03 00 01
12 13 10 11
345 aaa
01 02 03
22 23 20 21
32 33 30 31
02 03 00 01
12 13 10 11
inpu t b its
sta te b its
transm itted sy m bols 2-5. 8
Fig. 2-5. Trellis diagram of the 8 states STTC.
8 (2.17) .
125125 2 )(222 aaaaaaxt ++=++=
τ τ
QPSK Mapping
QPSK Mapping
Fig. 2-6. Encoder block diagram of the 8 states STTC.
15
Fig. 2-7. Trellis diagram of the 16 states STTC.
16 (2.18) .
12361236 2 )(2222 aaaaaaaaxt +++=+++=
τ
Fig. 3-7. Encoder block diagram of the 16 states STTC.
0 0
0 1 0 2 0 3
1 2
2 0
3 2
1 1
2 1
3 3
1 2
2 2
3 0
1 3
2 3
3 1
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
1 0
3 0
1 1
3 1
1 2
3 2
1 3
3 3
2 2 2 3 2 0 2 1
0 0 0 1 0 2 0 3
1 2 1 1 1 2 1 3
2 0 2 1 2 2 2 3
0 2 0 3 0 0 0 1
1 0 1 1 1 2 1 3
2 2 2 3 2 0 2 1
3 0 3 1 3 2 3 3
in p u t b it s (a 2 , a 1 )s ta te b its a 4 a 3 a 4 a 3
a n t 1 a n t 2 tra n s m itte d s y m b o ls
0 0
0 1 0 2 0 3
1 2
2 0
3 2
1 1
2 1
3 3
1 2
2 2
3 0
1 3
2 3
3 1
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
1 0
3 0
1 1
3 1
1 2
3 2
1 3
3 3
2 2 2 3 2 0 2 1
0 0 0 1 0 2 0 3
1 2 1 1 1 2 1 3
2 0 2 1 2 2 2 3
0 2 0 3 0 0 0 1
1 0 1 1 1 2 1 3
2 2 2 3 2 0 2 1
3 0 3 1 3 2 3 3
in p u t b it s (a 2 , a 1 )s ta te b its a 4 a 3 a 4 a 3
a n t 1 a n t 2 tra n s m itte d s y m b o ls
16
state bits
transmitted symbols
34567 aaaaa
state bits
transmitted symbols 2-9. 32
Fig. 2-9. Trellis diagram of the 32 states STTC.
17
1362467 2 )(2 aaaaaaaxt ++++++=
τ QPSK
Fig. 2-10. Encoder block diagram of the 32 states STTC.
2.3
IMT-2000 3


.

,
.
g . g
kxxx ,,, 21 Λ .
n .
2g (3.11)
18
.
2g
xx (2.20)
b2 . 1
kb ksss ,,, 21 Λ . g
ki ,,2,1 Λ= ii sx = , ksss ,,, 21 Λ
c . g kxxx ,,, 21 Λ , c
kb n
. i tc c t i ,
ni ,,2,1 Λ= i tc pt ,,2,1 Λ= n,,2,1 Λ
. c i i
, c t t . c g
, g
. p k , pkR =
R . 21
[6],[7].
2.3.1
2-11

.
19
interference & noise
0n 1n
0 00
interference & noise
0n 1n
0 00
0s * 1s−
1s * 0s
2-11.
Fig. 2-11. The tow-branch transmit diversity scheme with one receiver.
,


.
.
.
0s 1s .
)( * 1s− *
0s
. * . 3-1
. 2-1 .
20
Table 2-1. The Encoding and Transmission Sequence
antenna 0 antenna 1
time t 0s 1s
0s
t )(0 th
)(1 th , (complex multiplicative distortion)
.
(2.21) .
0 0000 )()( θα jehTthth ==+=
1 0111 )()( θα jehTthth ==+= (2.21)
T . (2.22)
.
011000 )( nshshtrr ++==
1 * 01
* 101 )( nshshTtrr ++−=+= (2.22)
0r 1r t Tt + , 0n 1n
.
, 2-11
(combiner) (2.23) .
* 110
* 00
~ rhrhs +=
* 100
* 11
21
* 110
* 00
,
(2.25)
[5].
),~(),~( 0 2
0 2
2.3.2 M

.
M 2M
.
. M .
2-2.
Table 2-2. The definition of channels between the transmit and receive antennas.
Rx antenna 0 Rx antenna 1
Tx antenna 0 0h 2h
Tx antenna 1 1h 3h
2-3.
Table 2-3. The notation for the receive signals at the two receive antennas.
Rx antenna 0 Rx antenna 1
time t 0r 2r
time Tt + 1r 3r
22
2-12
. 2-1
. 2-2
2-3
.
Tx antenna0
Tx antenna1
Rx antenna1
Rx antenna0
Interference & noise
Interference & noise
2-12.
Fig. 2-12. The two-branch transmit diversity scheme with two receiver antenna.
0r = 01100 nshsh ++
1r = 1 * 01
2-12 (2.27)
.
0 ~s = *
332 * 2
2 0 )( nhnhnhnhs +−+−+++ αααα (2.28)
0s PSK (2.27) (2.28)
(decision criteria) .
),~()1( 0 222
3 2 2
),~()1( 0 222
3 2 2
2 0 kk ssds −−+++≤ αααα (2.29)
is ks (2.29) (2.30)
.
issd ),~( 0 2
kssd≤ ki ≠∀ (2.30)
0 ~s (2.30) is .
[5].
.
(BM ; Branch Metric) .
, ji,α ( ni ,,2,1 Λ= , mj ,,2,1 Λ= ) i tη
∑ =
j t Eqr
1 , ηα (3.1)
. )( 21 n ttt qqq Λ
. .
2
(PM ; Path Metric) .
t=0
. ,
trace
back .
,
1−+= tt PMBMPM (3.3)
. tPM t , BM
.
25
.
.
},,min{ 21 s tttS PMPMPMM
t Λ= (3.4)
tSM t s . 3.1
4, 8, 16, 32 .
0
0
1
2
3
PS
0
4
8
12
Fig. 3-1. Path signal of each states.
. 4
0=δ , 8 1=δ , 16 2=δ , 32 3=δ
26
4 )2(1
S Mt
M PSS +×=−
δ (3.5)
1−tS 1−t , tSM t ,
tSMPS t . tSMPS
2 bit 64 3bit 5bit
tSM ν ( = ν2 )
. (3.6) .
22 >>+<< ttS SM MPS δ (3.6)
trace back .
trace back , δ2
. ,
. (3.5)
. (3.5)
.
01
t=1 t=2 t=3 t=4 t=5 Sk
11 10 00 01 00
01 10 00 10 01 01
11 10 11 10 10 10
00 01 01 11 11 11
01 11 10 01
10 11 10 01
01
t=1 t=2 t=3 t=4 t=5 Sk
11 10 00 01 00
01 10 00 10 01 01
11 10 11 10 10 10
00 01 01 11 11 11
01 11 10 01
10 11 10 01
Fig. 3-2. Decoding process of 4 states.
27
00
t=1 t=2 t=3 t=4 t=5 Sk
11 10 10 01 000
00 01 10 11 10 001
10 00 11 10 11 010
11 00 01 11 00 011
01 10 11 00 11
11 10 10 01 01
10 11 10 11 01
11 10 11 10 00
010 110 100 010
10 10 00 10
PS4,K
PS5,K
PS6,K
PS7,K
100
101
110
111
00
t=1 t=2 t=3 t=4 t=5 Sk
11 10 10 01 000
00 01 10 11 10 001
10 00 11 10 11 010
11 00 01 11 00 011
01 10 11 00 11
11 10 10 01 01
10 11 10 11 01
11 10 11 10 00
010 110 100 010
10 10 00 10
Fig. 3-3. Decoding process of 8 states.
3.2 OFDM
(OFDM ; Orthogonal Frequency Division Modulation)
.
1960 ,
VLSI(Very
Large Scale Integration) 1980
.
,

,

. OFDM ,
WATM (Wireless Asynchronous Transfer Mode), WLAN (Wireless Local Area
28
Network) . , offset
, .
OFDM
π (3.7)
. N , C , T
OFDM , ind , n [ ]TnnT )1(, + i
, if i . )(tp
Tt ≤≤0 1, 0
. T ifi =
.
OFDM

. OFDM
OFDM
IFFT(Inverse Fast Fourier Transform). CP(cyclic prefix)
RF .
. 3-4 .
Data Encoder S/P IFFT CP P/S D/A
carrier
carrier
Fig. 3-4. Block diagram of OFDM System (Transmitter).
29
OFDM MCM(Multi-Carrier Modulation)
spacing 1/T . T .
9 OFDM 3-5
.




Fig. 3-5. Frequency spectrum of OFDM Signal.
1/T
(orthogonality)
. OFDM
, Ns
Ns
Ns . Ns
.
CP
. CP
. OFDM
25% CP . CP IFFT

[8].
OFDM
3-6 .
Fig. 3-6. Space time trellis code for OFDM.
n [ ]{ },,2,1:, Λ=kknb 2,1=i
[ ]{ }Kkknti ,,2,1:, Λ= .
OFDM . [ ]knt ,1 [ ]knt ,2
OFDM . FFT
. FFT
[ ] [ ] [ ] [ ]knwkntknHknr ji i
[ ] [ ] [ ]

≡


. (channel estimator)
. (3.8) FFT
BM , BM
[ ] [ ] [ ] 2 ,,,],[ kntknHknrknBM
)) −= (3.12)
. * . BM
[9],[10].
32
4.3 OFDM
OFDM .
Alamouti .
M od
ul at
Fig. 3-7. Space time block code for OFDM.

. , ,
. m k
i ),( ikcm )2,1( =m . m
)(tsm
33
)(),()( 0
1
0
π (3.13)
. ν . kf k
.
kff += (3.14)
of st OFDM
. sT += ss tT OFDM ,
. OFDM )(tg

>−< ≤≤−
)();()()( tnthstr nmmnm +∗= ττ (3.16)
. ∗ )(tn .
siT k FFT ),( ikrnm
dtetr t
ikr ss
. ),( ikrnm
[11].
34


,
. , OFDM
.

. 4-1 QPSK ,
, 130
. 32 16
. , (frame error rate) 110− 32 4
1.5dB .
4-2 QPSK ,
, 130
. 32, 16, 8
. , 110− 32 4
2.7dB .

.
35
0
9 10 11 12 13 14 15 16 17 18
Es/No
4-1. QPSK
Fig. 4-1. Performance of QPSK with one receive and tow transmit antenna.
-2.5
-2
-1.5
-1
-0.5
0
Es/No
4-2. QPSK
Fig. 4-2. Performance of QPSK with two receive and tow transmit antenna.
36
-7
-6
-5
-4
-3
-2
-1
0
Es/No
4-3
Fig. 4-3. Performance of space time block codes versus antenna number.
4-3 . BPSK QPSK
. p k
, R p k . 2
2 1 bit/s/Hz .
. (bit error rate) 510− BPSK
QPSK 3dB
.
. ,
.
37
Fig. 4-4. Performance of space time trellis code for OFDM.
4-4
OFDM . QPSK
, 32 16 . ,
110− 32 4 7dB
.
38
-7
-6
-5
-4
-3
-2
-1
0
Eb/No
Fig. 4-5. Performance of space time block code for OFDM.
4-5
OFDM . BPSK QPSK
OFDM . OFDM
64 SNR 32
, SNR
.
5

.
.
.

. , ,
.
,

,
4
32 3dB
.
,
OFDM

. OFDM
. OFDM
4 32 7dB
.


.
40

[1] Vabid Tarokh, Nambi Seshadri, A. R. Calderbank, “Space-Time Codes for High
Data Rate Wireless Communication: Performance Criterion and Code
Construction,” IEEE Transactions on Information Theory, Vol. 44, No. 2, pp. 744-
765, March 1998.
[2] N. Seshadri, V. Trarokh , A. R. Calder bank, “Space-Time Codes for High Data
Rate Wireless Communication: Code Construction,” IEEE Transactions on
Information Theory, Vol. 44, No. 2, pp. 637-641, 1998.
[3] Vahid Tarokh, Ayman Naguib, Nambi Seshardri, A. R. Calderbank, “Space-Time
Code for High Data Rate Wireless Communication: Performance Criteria in the
Presence of Channel Estimation Errors, Mobility, and Multiple Paths,” IEEE
Transaction on Communications, Vol. 47, No.2, pp. 199-207, February 1999.
[4] Ran Gozali, Brian D. Woerner, “Applying the Calderbank-Mazo Algorithm to
Space-Time Trellis Coding,” Proceedings of the 2000 IEEE Southeastion, pp.
309-314, April 2000.
[5] Siavash M. Alamouti, “A Simple Transmit Diversity Technique for Wireless
Communications,” IEEE Journal on Select Areas in Communications, Vol. 16, No.
8, pp. 1451-1458, Oct. 1998.
[6] Vabid Tarokh, Hamid Jafarkhani, A. R. Calderbank, “Space-Time Block Codes for
Wireless Communication: Performance Results,” IEEE Journal on Selected Areas
in Communications, Vol. 17, No. 3, pp. 451-460, March 1999.
[7] Vahid Tarokh, Hamid Jafarkhani, A. R. Calderbank, “Space-Time Block Codes
from Orthogonal Designs,” IEEE Transactions on Information Theory, Vol. 45,
No. 5, pp. 1456-1467, July 1999.
[8] , , “OFDM
”, , Vol.16, No. 10, pp. 24-41, October 1999.
[9] Dakshi Agrawal, Vahid Trarokh, Ayman Naguib, Nambi Seshadri “Space-Time
Coded OFDM for High Data-Rate Wireless Communication over Wideband
41
Channels,” in 48th IEEE Vehicular Technology Conference, Vol. 3, pp. 2232-2236,
May 1998.
[10] Ye Li, Nambirajan Seshadri, Sirikiat Ariyavisitakul, “Channel Estimation for
OFDM Systems with Transmitter Diversity in Mobile Wireless Channels,” IEEE
Journal on Selected Areas in Communications, Vol.17, No. 3, pp. 461-471, March
1999.
[11] Ye Li, Justin C. Chuang, Nelson R. Sollenberger, “Transmitter Diversity for
OFDM Systems and Its Impact on High-Rate Data Wireless Networks,” IEEE
Journal on Selected Areas in Communications, Vol.17, No. 7, pp. 1233-1243,
July 1999.
[12] Vahid Tarokh, Ayman Naquib, Nambi Seshafri, Fovert Calderbank, “Combined
Array Processing and Space-Time Coding,” IEEE Transactions on Information
Theory, Vol. 4, pp. 1121-1128, May 1999.
[13] Sumeet Sandhu, Robert W. Heath Jr., Arogyaswami Paulraj, “Space-Time Block
Codes versus Space-Time Trellis Codes,” Proceedings of the 2001 IEEE
International Conference on Communications Record, Vol. 4, pp.1132-1136,
June 2001.
[14] Vahid Tarokh, Ayman Naquib, Nambi Seshafri, Fovert Calderbank, “Space-Time
Codes for High Data Rate Wireless Communication: Performance Criteria in the
Presence of Channel Estimation Errors, Mobility, and Multiple Paths,” IEEE
Transactions on Communications, Vol. 47, No. 2, pp. 199-207, February 1999.
[15] Justin Chuang, Nelson Sollenberger, “Beyond 3G: Wideband Wireless Data
Access Based on OFDM and Dynamic Packet Assignment,” IEEE
Communications Magazine, pp. 78-87, July 2000.
[16] Paul H. Moose, “A Technique for Orthogonal Frequency Division Multiplexing
Frequency Offset Correction,” IEEE Transactions on Communications, Vol. 42,
No. 10, pp. 2908-2914, October 1994.
[17] Ayman F. Naguib, Namgi Seshafri, A.R. Calderbank, “Space-Time Coding and
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Processing Magazine, pp.76-92, May 2000.
42

2 . , . . , , , , , . , , , , , , , , , , , , . , , , , , , . , , , , . ,
, , . .

2
2.1
2.2
2.3
4
4.1 OFDM
4.2 OFDM
5