R. Nordin, S. Armour, J.P. McGeehan, “Dynamic subcarrier allocation with ESINR metric in correlated SM-OFDMA”, Proceedings of 2010 6th Conference on Wireless Advanced (WiAD), pp.1-5, June 2010

1. Dynamic Subcarrier Allocation
with ESINR Metric in
Correlated SM-OFDMA
Wireless Advanced 2010
Rosdiadee Nordin, Prof. Joe McGeehan & Dr. Simon
University of Bristol
Centre for Communications Research

2. Presentation Outline
 Self-interference
 DSA-ESINR
 Simulation Parameters
 Results & Analysis
 Conclusion
Centre for Communications Research

3. 3
Correlation in MIMO
 Correlation occurs due to:
 antenna location/spacing
 lack of scatterers
 angular spread.
 Resulting in self-interference.
 Retransmissions and equalisation do not
improve the BER performance.

4. 4
Self-Interference
 MIMO only works when the channel is in
low correlation.
In practice:
h’
s0 h’ r0
r0=r1=h’(s0+s1)
BS h’ MS
Scenario: all spatial layers
`
h’ are fully correlated
s1 r1
Mathematically:
If h’ coefficients are correlated, then [H] is
[S] =[H]-1[R] ill-conditioned matrix and difficult to invert

5. 5
ESINR Metric
 Is the performance metric to determine the
subcarrier allocation.
MMSE filter
q= spatial layer Main spatial layer
Gk H k qq
2
Es
q

 N
ESINR k
Gk H k qj, j  q
2 2 2
E s  Gk qq
 Gk qj, j  q
Knowledge of
self-interference
k= subcarrier index

6. 6
DSA-ESINR
 Involves sorting, comparing and simple
arithmetic.
 Ranks users from lowest to highest ESINR.
 Fairness: Allow poor users to have the next
‘best’ subcarriers.
 Prevents users from sharing the same
subcarrier with the adjacent layer (interferer).

7. 7
System Model X1 Tx1 Rx1
H1
X1 With Index 1
Transmitter at Base Station OFDM H3
X1
User k Input With Index 2
Data Scrambling/ FEC/ Symbol Serial to Parallel& DSA
H2 Rx2
X1X2 Puncturing/ Interleaving Mapping Spatial Multiplexing mapping X2 Tx2
With Index 3
H4
X2 X2 OFDM
With Index 4
Uplink process Index 1 2 3 4
Downlink process Index 4
ESINR and channel
Index 1 DSA
Index 2
} DSA-ESINR gain feedback from
other users
Scheme
Index 3
Index 2
Index 3 Index 1
Index 4 } DSA-Scheme 1
ESINR1
ESINR2
[ H3 ]
[ H4 ]
ESINR
calculation
Receiver at Mobile Station k [ H1 H3 ] [ H2 H4 ]
S1 Y1 DSA
OFDM
User k Deinterleaving/ S1 S2 Parallel to MMSE [ H1 H3 ] Demapping
Symbol
Output Depuncturing/ Viterbi Serial& De- Linear
Demapping
Data Decoding/ Descrambling Multiplexing Detection Y2 DSA
S2
[ H2 H4 ] Demapping OFDM

8. 8
Compared against…
 Maximum Gain Sort-Swap (MGSS):
 Sort subcarriers pairs by metric of total
perceived gain.
 Swap subcarriers between users.
 Two parts: initial allocation and iteration.
 ESINR metric is used to improve the
allocation process.

9. 9
Simulation Setup
 Simulated under BPSK, ½ rate based on V-
BLAST (2×2).
 Nsub= 768, NFFT= 1024 for 16 users, 48
subcarriers per user. 1
0.9
3GPP-SCM ‘Urban Micro’: 0.8
0.7
• RMS delay spread= 251 ns
Normalised power
0.6
• Excess delay= 1200 ns
0.5
0.4
• 2000 i.i.d Rayleigh 0.3
0.2
0.1
200 300 400 500 600 700 800 900 1000
Excess delay (ns)

10. 10
Correlation Model
 Kronecker product, RMIMO=RMSRBS
 Uncorrelated = ideal channel environment
 Fully correlated = worst case, i.e. dominated
by self-interference
Correlation Modes RBS RMS
Uncorrelated 0.00 0.00
Fully Correlated 0.99 0.99

11. 11
Example of Spatial Correlation
RMIMO= 0.00 (uncorrelated) RMIMO= 0.85
10
10
5
5
0
0
-5
Transmit Power (dB)
-5
Transmit Power (dB)
-10 -10
-15 -15
-20 -20
-25 h -25 h11
11
h h12
-30 12 -30
h h21
21
-35 -35
h
22 h22
-40
0 100 200 300 400 500 600 700 -40
0 100 200 300 400 500 600 700
Subcarrier
Subcarrier
10
5
Transmit power (dB)
0
RMIMO= 0.99
-5
h11
-10 h12
h21
h22
-15
0 100 200 300 400 500 600 700
Subcarrier

12. 12
BER Performance
0 0
10 10
-1
10 -1
10
-2
10
-2
10
-3
BER
BER
10
-3
10
-4
10
-4
-5 MGSS-ESINR 10 MGSS-ESINR
10
MGSS-ChG MGSS-ChG
DSA-ESINR DSA-ESINR
DSA-ChG DSA-ChG
-6 -5
10 10
-10 0 10 20 30 -10 0 10 20 30
SNR(dB) SNR(dB)
Uncorrelated channel Fully correlated channel

13. 13
Allocated Subcarriers 10
0
Channel Gain (dB)
-10
-20
-30 Source
Interferer
ESINR Metric
-40 DSA-ESINR
DSA-ChG
DSA-ChG (Interferer)
-50
0 100 200 300 400 500 600 700
Subcarrier
Uncorrelated channel

14. 14
Allocated Subcarriers10
5
Channel Gain (dB)
0
-5
Source
Interferer
-10 ESINR Metric
DSA-ESINR
DSA-ChG
DSA-ChG (Interferer)
-15
0 100 200 300 400 500 600 700
Subcarrier
Fully correlated channel

15. 15
Effective Correlation
1
1
0.8
0.8
0.6
0.6
0.4
0.4
Effective Correlation
Effective Correlation
0.2
0.2
0
0
-0.2
-0.2
-0.4 -0.4
-0.6 DSA-ESINR -0.6 DSA-ESINR
MGSS-ESINR
MGSS-ESINR
-0.8 h &h -0.8 h11&h22
11 12
DSA-ChG DSA-ChG
-1 -1
1 11 21 1 11 21
SNR (dB) SNR (dB)
Uncorrelated channel Fully correlated channel

16. 16
Pdf distribution at SNR= 0 dB
3 2.5
DSA-ChG DSA-ESINR
DSA-ESINR MGSS-ESINR
MGSS-ESINR DSA-ChG
2.5
h11&h12 2
p(correlation coefficient)
p(correlation coefficient)
2
1.5
1.5
1
1
0.5
0.5
0 0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
correlation coefficient correlation coefficient
Uncorrelated channel Fully correlated channel

17. 17
Pdf distribution across SNR
1.8 2
SNR= 10 dB SNR= 10 dB
1.6 SNR= 20 dB 1.8 SNR= 20 dB
SNR= 30 dB SNR= 30 dB
1.4 1.6
p(correlation coefficient)
1.4
p(correlation coefficient)
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0 0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
correlation coefficient correlation coefficient
DSA-ESINR MGSS-ESINR

18. 18
Conclusions
 ESINR with a combination of DSA can minimise
the effect of self-interference.
 Outperforms other forms of suboptimal
allocation by 3 dB at BER=10-3 and known as
MGSS .
 Allocation improves as SNR increase.

19. Thank You!
Centre for Communications Research