3Correlation in MIMO Occurs due to: 12 RBS=0.0,RMS=0.0 RBS=0.4,RMS=0.4 10 RBS=0.5,RMS=0.5 RBS=0.0,RMS=0.9 8 RBS=0.9,RMS=0.0 capacity (bps/Hz)• antenna location/spacing RBS=0.9,RMS=0.9 6 RBS=1.0,RMS=1.0• lack of scatterers 4• angular spread. 2 0 -10 -5 0 5 10 15 20 SNR (dB) Resulting in self-interference. Retransmissions and equalisation do notimprove the BER performance.
4Self-Interference MIMO only works when the channel is inlow 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 revert
5SINR Metric As the performance metric to determine thesubcarrier allocation. MMSE filter q= spatial layer Main spatial layer 2 Gk H k qq Es q ESINRk 2 2 2 Gk H k qj, j q Es Gk qq Gk qj, j q N Knowledge of self-interference k= subcarrier index
6DSA-SINR Involves sorting, comparing and simplearithmetic. Ranks users from lowest to highest SINR. Fairness: Allow poor users to have the next‘best’ subcarriers. Prevents users from sharing the samesubcarrier with the adjacent layer (interferer).
7System Model X1 Tx1 Rx1 H1 X1 With Index 1 Transmitter at Base Station OFDM H3 X1User 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
8Simulation Setup Nsub= 768, NFFT= 1024 for 16 users, 48subcarriers per user 3GPP-SCM ‘Urban Micro’: 1 Rms delay spread= 251 ns 0.9 0.8 0.7 Normalised power Excess delay= 1200 ns 0.6 0.5 0.4 0.3 2000 i.i.d Rayleigh 0.2 0.1 200 300 400 500 600 700 800 900 1000 Excess delay (ns) Six MCS schemes, consists of BPSK,QPSK, 16-QAM and 64-QAM with ½ or ¾coding rate
11Conclusions SINR with combination of DSA can minimise the effect of self-interference. Allocation improves as SNR increase. Future works: Consider different case of correlation scenarios, e.g. moderate, full correlation Apply adaptive MCS on the BS Tx antenna Study the effect of self-interference between STBC and SM