Over-The-Air Testing of Diversity and MIMO Capable Terminals
Mimo Diversity
Transcript of Mimo Diversity
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 1
Spatial Diversity
Tutorial ─ MIMO Communications with Applications to (B)3G and 4G Systems
Markku Juntti, Tadashi Matsumoto & Juha Ylitalo
Contents1. Introduction to diversity techniques2. Receive diversity3. Transmit diversity and space–time coding4. Transmit diversity in 3G systems5. Summary and Conclusions
References
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 2
1. Introduction to Diversity Techniques
• “Diversity” = “state of being varied, variety” [Oxford Advanced Learner’s Dictionary].
• The basic concept of diversity: transmit the signal via several independent diversity branches to get independent signal replicas via– time diversity– frequency diversity– space diversity– polarization diversity.
High probability: all signals not fade simultaneously.High probability: the deepest fades can be avoided.Protection against fading.
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 3
Diversity Domains
• Time diversity• Frequency diversity
– multicarrier communications– multipath diversity in spread spectrum communications.
• Spatial diversity– antenna diversity– macroscopic diversity via soft handovers
• Polarization diversity
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 4
Time Diversity
• Repetition after time delays.• Usually achieved by coding and interleaving.
DelayRX
Output
TX
Scatterer(s)Signal to be transmitted
DelayCombinerT
T
bi
Time
bi
Bandwidth expansion required.
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 5
Frequency Diversity
TX (f1 )Scatterer(s)
Signal to be transmitted
Bandwidth expansion required.
Multipath diversity
TX (fN)
+
Output
Combiner
Rx (f1 )
Rx (fN)
TXScatterer(s)
Signal to be transmitted
Path 1(Delay t1)
Path N (Delay tN)
Path combiner- Equalizer- Rake
Outputt1
t2
tN
t=0
Amplitude
No explicit bandwidth expansion.
Frequency Selective Fading
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 6
Space Diversity
Receive antenna diversity
Receiver/combinerTransmitter
(TX)
Scatterer(s)Signal to be transmitted
Macroscopic diversity
Output
BS1BS2
Combiner/splitter Output/input
Cell 2
Cell 1
Soft handover
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 7
Capacity Implications
• Does diversity increase capacity?• Ergodic capacity:
– Codeword length ∞ infinite time-diversity.Diversity cannot increase the ergodic capacity.
– However, it can improve the error performance or error exponent.
• Outage capacity is improved by diversity, since the diversity decreases the probability of outage.
.as,0maxe, ∞→→ nP( )
( ),;max YXICxp
=
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 8
2. Receive Diversity
• Receive diversity: several independent observations of the signal (one data bit) are combined at the receiver.– Applicable to all diversity domains:
• time• frequency• space.
• Combining techniques:– selection combining (SC)– equal gain combining (EGC)– maximum ratio combining (MRC).
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 9
Receive Antenna Diversity
CombinerTransmitter(TX)
Scatterer(s)Signal to be transmitted
• Collects more energy antenna gain.– Independent noise and/or interference processes in
different antennae signal–to–noise ratio (SNR) and/orsignal–to–interference–plus–noise ratio (SINR) gain.
• Observes several independent fading processesdiversity gain.
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 10
Selection Combining
Output
SnifferMax (|zF1|,|zF2|, ...,|zFN|)
rN=zFNs + AWGNN
r1=zF1s + AWGN1
Control
s = transmitted signalri = received signal on the i-th branchzFi = fading complex envelope
on the i-th branch
PDF of instantaneuos SNR:Select the best availabale signal. ( ) .exp1exp 1M-)}
Γγ(-){
Γγ(
ΓMγp −−=
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 11
Equal Gain Combining
r1=zF1s + AWGN1
rN=zFNs + AWGNN
s = transmitted signalri = received signal on the i-th branchzFi = fading complex envelope
on the i-th branchOutput
zF1/|zF1|*
zFN/|zFN|*
Sr = Σ|zFi|s + Σ zFi/|zFi|AWGNi
ii*
Phase rotation (carrier synchronization) and summing.
PDF of instantaneuos SNR(closed form not known, approximation):
( ) M
M-MM-
Γγ
)!M-(Mγp
11
122
=
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 12
Maximum Ratio Combining
r1=zF1s + AWGN1
rN=zFNs + AWGNN
s = transmitted signalri = received signal on the i-th branchzFi = fading complex envelope
on the i-th branchzF1* S
zFN*
r = Σ|zFi|s + Σ zFiAWGNiii
2 *
Phase rotation and weighting before summing SNR maximizationoptimal in Gaussian noise.
PDF of instantaneuos SNR:
( ) )Γγ(
Γγ
)!(M-γp M
M-−= exp
11 1
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 13
3. Transmit Diversity and Space–Time Coding
• Transmit diversity: one data bit is transmitted via several independent (spatial) channels.– The conventional diversity techniques in time and
frequency domains could be classified also to this class.
• No bandwidth expansion.
zF1*
zFN*
Rx
zF1s
zFNsOutput
s(n)
Open-loop TX diversity
Closed-loop TX
no CSI at the transmitter
diversityCSI at the
transmitter
Signal to betransmitted
Feedback: zF1 , ... , zFN
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 14
Early Solutions: Delay and Waveform Diversity
Equalizer
zF1s(n-1)
zF2s(n)
Delay diversity• No BW expansion.• Frequency–flat frequency–selective.
Spatial diversity into ”path” diversity .
Delays(n)
Encoder
zF1s(n)
Waveform×zF2 s(n)
Narrowband waveform
Decoder
s(n)
s(n)
Waveform diversity• BW expansion.• slow fast.
Spatial diversity into ”path” diversity.
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 15
Trellis Representation of Delay Diversity
Si: X0Y0 X1Y1 X2Y2 X3Y3
Sj If current state is Si, the input symbol is ”j”, (j = 0 ... 3)
Antenna #1 transmits Xj and antenna #2 transmits Yj, and the next state is Sj.
S0 Example: The current state is S0, and the input sequence is (10, 01, 11, 00, 01, ...).The corresponding QPSK symbol sequence is (2, 1, 3, 0, 1, ...).
The transmitted symbol sequences in delay diversity:
Antenna 1: 0, 2, 1, 3, 0, 1, ... Antenna 2: 2, 1, 3, 0, 1, ...
00 01 02 03
S1 10 11 12 13
20 21 22 23S2
30 31 32 33S301
2 3
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 16
Space–Time Trellis Codes
Allow more general and flexibe allocation of transmitted sequences space–time trellis codes (STTrC).
Example: The input sequence is (10, 01, 11, 00, 01, ...) QPSK symbol sequence (2, 1, 3, 0, 1, ...).
The transmitted symbol sequences in delay diversity:
Antenna 1: 0, 1, 2, 3, 0, 1, ...Antenna 2: 2, 1, 3, 0, 1, ...
S0 00 01 02 03
20 21 22 23S1
10 11 12 13S2
30 31 32 33S3
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 17
Alamouti scheme (2×2 Space–Time Block Coding)
∑=
+=L
jjjjj rrS
1
22111
** aa
∑=
+-=L
jjjjj rrS
1
12212
** aa
S1 S2
S2
STTD encoder
S1
-S2* S1
*
1*2
21
11jjjj nSSr +-= aa2*
12
212
jjjj nSSr ++= aa
2×2 space–time block coding (STBC) = Alamouti scheme• No BW expansion.• Simple MRC at the receiver.• Open–loop method.
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 18
Space–Time Block Coding
STBC can be generalized to arbitrary numbers of TX and RX antennae.• No optimal unique code design exists.• Both real and complex designs exist.• An example code:
(s1, -s2 , -s3, -s4 , s1*, -s2* , -s3*, -s4 *)(s2, s1 , s4, -s3 , s2*, s1* , s4*, -s3 *)(s3, -s4 , s1, s2 , s3*, -s4* , s1*, s2 *)(s4, s3 , -s2, s1 , s4*, s3* , -s2*, s1 *)
(s1, s2 , s3, s4 )
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 19
Closed–Loop Schemes
• Use transmitter channel state information (CSI) to weigh the transmission to optimize performance.– Typically SINR maximization in the receiver.
• Usually imperfect TX-CSI.– Often quantized feedback from RX to TX.
W2
W1
TX RX
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 20
4. Transmit diversity in 3G systems
• Applied due to the fact that UE has only 1 antenna– Robustness against fading
• Open loop mode, STTD (Alamouti scheme)• Closed loop modes 1 & 2• Time-switched TX diversity applied to sync. channel
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 21
Open Loop Transmit Diversity, STTDOpen Loop Transmit Diversity, STTD• Space-Time (Block Coded) Transmit Diversity (STTD) for WCDMA
– space-time coding over two symbols simple detection at the terminal
• Can be used in all physical channels except in SCH
∑=
+=L
jjjjj rrS
1
22111
** αα
∑=
+−=L
jjjjj rrS
1
12212
** ααDetectionat terminal,integrationover L paths
Detectionat terminal,integrationover L paths
1*2
21
11jjjj nSSr +−= αα2*
12
212
jjjj nSSr ++= αα
Rx signals for timeinstants 1 & 2,j = path indexα = channel coeff.
Rx signals for timeinstants 1 & 2,j = path indexα = channel coeff.
Channelencoder
Data Interleaver
MUX
Pilot
TPC
TFCI
STTD encoder
STTD encoder
STTD encoder
STTD encoder
Spreading &scrambling
Ant. 2
Ant. 1
S1 S2
S2
STTD encoder
S1
-S2* S1
*
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 22
• UE measures relative phase (and power) of two pilot (Primary CPICH) signalsFSM=f(∆φ,P1,P2)
P-CPICH1
Terminalmeasurement
Terminalmeasurement
P-CPICH2
• UE sends adjustment command to BS, feedback signalingmessage (FSM)
• FSM applied on DPCH to antenna signal #2 phasing, and (mode2 only) amplitude weighting (0.2/0.8) for both antenna signals
Closed Loop Transmit Diversity ModesClosed Loop Transmit Diversity Modes
DPCH (ampl(t))
DPCH (φ(t),ampl(t))
Phase (andampl.) adj.for antenna
signal #2
Phase (andampl.) adj.for antenna
signal #2
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 23
Link performance: Average Tx diversity gain
Link performance: Average Tx diversity gain
Average Ic/Ior gain in single link performance
0.01.02.03.04.0
3km/hPed.A
3km/h 50km/hVeh.A
120km/h
Channel type and UE speed
Gai
n [d
B]
STTDCL mode1
Gain in relative Tx power (Ic/Ior)= user/total Tx power, G = 3dB
Gain in relative Tx power (Ic/Ior)= user/total Tx power, G = 3dB
Average = through different data rates (12.2 - 144kbps)
Average = through different data rates (12.2 - 144kbps)
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 24
5. Summary and Conclusions
• Diversity has to be applied in one form or another• Receive diversity desirable vs. TX diversity• Channel state information (CSI) very beneficial• Multi-user diversity employing CSI can be achieved
through scheduling (e.g. HSDPA in 3GPP)
MIMO Communications with Applications to (B)3G and 4G Systems ─ Spatial Diversity
© M. Juntti et al., University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 25
References1. T. M. Cover & J. A. Thomas, Elements of Information Theory. John Wiley &
Sons, 1991. ISBN: 0-471-06259-6
2. S. M. Alamouti, “A simple transmit diversity technique for wireless communications,” IEEE J. Select. Areas Commun.,vol. 16, no. 8, pp. 1451–1458, Oct. 1998.
3. J.G. Proakis, Digital Communications, 3rd edition. McGraw-Hill, New York, 1995. ISBN 0-07-051726-6
4. M. Shwartz, W. Bennett and S. Stein, Communication Systems and Techniques.McGraw Hill, New York, 1966
5. V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space-time block codes from orthogonal designs,” IEEE Trans.Inform. Theory, vol. 45, no. 5, pp. 1456–1467, 1999.
6. V. Tarokh, N. Seshadri, and A. R. Calderbank, “Space-time codes for high data rate wireless communication:Performance criterion and code construction,”IEEE Trans. Inform. Theory, vol. 44, no. 2, pp. 744–765, Mar. 1998.
7. A. Wittneben, New bandwidth efficient transmit antenna modulation diversity scheme for linear digital modulation. In: Proceedings of the IEEE International Conference on Communications ICC'93, May 23-26, 1993, Geneva, Switzerland, pp. 1630-1634.