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A 3-Dimensional Joint Interleaver for 802.11n MIMO Systems

A 3-Dimensional Joint Interleaver for 802.11n MIMO Systems. Jeng-Hong Chen (jhchen2@winbond.com) Pansop Kim (pkim@winbond.com) Winbond Wireless Design Center Torrance, CA, USA September 2004. Simulation Parameters (based on 11a). 2X2, 2X3, 2X4, 3X2, 3X3, 3X4, 4X2, 4X3, 4X4 antennas

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A 3-Dimensional Joint Interleaver for 802.11n MIMO Systems

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  1. A 3-Dimensional Joint Interleaver for 802.11n MIMO Systems Jeng-Hong Chen (jhchen2@winbond.com) Pansop Kim (pkim@winbond.com) Winbond Wireless Design Center Torrance, CA, USA September 2004 Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  2. Simulation Parameters (based on 11a) • 2X2, 2X3, 2X4, 3X2, 3X3, 3X4, 4X2, 4X3, 4X4 antennas • 11n Channel B, D, E and 11g uncorrelated exponential channel • OFDM based on 11a: 64-pt FFT (only 48 data sub-carriers) • 10% PER over 1000 simulated packets • 1000 un-coded bytes per packet • Perfect CSI, Perfect AFC, AGC, ACQ • No pulse shaping filter, no ADC/DAC • CC rates=1/3,1/2, 2/3,3/4,7/8 from ½ CC code (K=7) with puncturing/repetition • BPSK, QPSK, 16QAM, 64QAM • Interleaver defined in 11a and joint interleaver • 6, 8, 12, 18, 24, 36, 48, 63 Mbps per transmit antenna • MMSE Receiver Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  3. System Models PART-III: Coding Rates & MIMO Tables PART-I: Joint 3D Space-Frequency-Time Interleaver PART-II: Circulation Transmittion (1) OFDM Symbol Based Circulation (2) Sub-carrier Based Circulation Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  4. Challenges of MIMO Interleaver Design • L=Number of OFDM symbols from FEC outputs • NI=Number of OFDM symbols per 3D Joint Interleaver • NOFDM= Number of OFDM symbols are transmitting at the same time • M=Number of transmitter antennas (M NOFDM) • NCBPS=Number of coded bits per OFDM symbol • Nsub=Number of data sub-carriers per OFDM symbol • NBPSC=Number of coded bits per sub-carrier • Example: L=18, NI =6, NOFDM =2, M=3, and Nsub=48 (see next page) • How to choose an appropriate interleaver size, NI, for a MIMO system? • How to transmit NOFDM (M) OFDM symbols at the same time from M TX Ant.? • How to interleave total NI*NCBPS coded bits from FEC outputs and map into • NI*Nsub sub-carriers (frequency domain) and various NBPSC for different QAM • M TX antennas (spatial domain) and • NI total OFDM symbols and NOFDM at the same time? Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  5. Example: L=18, NI =6, NOFDM =2, M=3, and Nsub =48 18 OFDM 6 OFDM 6 OFDM 6 OFDM ? Uncoded bits 1 OFDM Time=t9 t8 t7 t6 t5 t4 t3 t2 t1 ? Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  6. PART-I: 3D Joint Interleaver Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  7. Transmitting Total L OFDM Symbols from M TX Antennas Coded bits has L OFDM symbols NI OFDM symbols NI OFDM symbols MIMO Circulation To M TX Antennas • Properties of a MIMO OFDM System: • Diversities include space (antennas),frequency (sub-carrier),and transmission in times • Adjacent coded bits from FEC are highly correlated within dfree bits • Same sub-carrier (frequency domain) from different antennas are correlated • The correlation between adjacent sub-carriers are strongly correlated especially if rms of delay spreading is small. • Purpose of 3D Joint interleaver (Part-II) and Circulation Transmission (Part-III) • Adjacent FEC coded bits are transmitted from nonadjacent sub-carriers and different TX antennas A(k) B(j) 1D output bit stream 1D input bit stream 1-to-1 mapping Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  8. 11a Interleaver 11a Interleaver A(K) B(j) • Two-step permutation • First permutation • To ensure that adjacent coded bits are mapped onto nonadjacent subcarriers • Three subcarrier separations between consecutive coded bits • Example: NBPSC=1, NCBPSC=48 Reading order (index of j) Writing order (index of k) • Second permutation (Only applied to 16QAM and 64QAM) • To ensure that adjacent coded bits are mapped alternately onto less and more significant subcarriers Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  9. Parallel 11a Interleavers (A1) • Example: NI=4 ,NBPSC=1, NCBPS=48 • Adjacent bits (ex, A(0), A(1), A(2) and A(3)) are assigned to the same TX antenna. • Performance is worse if low correlations between Tx antennas and small delay spread. Coded bits from FEC outputs Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  10. Parallel 11a Interleavers (A2) • Example: NI=4 ,NBPSC=1, NCBPS=48 • Adjacent bits (ex, A(0), A(1), A(2) and A(3)) are assigned to the same subcarrier. • Performance is worse if high correlations between Tx antennas and large delay spread. Coded bits from FEC outputs Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  11. 2D Joint 11a interleaver • Example: NI=4 ,NBPSC=1, NCBPS=48 • First Permutation (the number of rows is NI times.) Writing order (index of k) Reading Order (index of j) • Second Permutation • The same as the 11 a interleaver • Only apply to 16QAM and 64QAM Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  12. 2D Joint 11a Interleaver (B1) • Example: NI=4 ,NBPSC=1, NCBPS=48 • Adjacent bits (ex, A(0), A(4),A(8), and A(12).) are assigned to the same subcarrier, • Performance is worse if high correlations between Tx antennas and large delay spread. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  13. 2D Joint 11a Interleaver (B2) • Example: NI=4, NBPSC=1, NCBPS=48 • Adjacent bits (ex, A(0), A(1), A(2),.. and A(15)) are assigned to the same TX ant. • Performance is worse if low correlations between Tx antennas and small delay spread. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  14. Proposed 3D Joint Interleaver • Purposes • Backward compatible with 11a interleaver and preserve all good properties • To separate consecutive bits by 3*NBPSC or 3 sub-carriers. • To assign consecutive bits to different OFDM symbols • Example: NI=4, NBPSC=1, NCBPS=48 • Rotating the output bits of 2D 11a Joint Interleaver (B2) to different OFDM symbol Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  15. Indexing of Proposed 3D Joint Interleaver k: the index of coded bit before the first permutation i: the index after the first and before the second permutation j: the index after the second permutation, just prior to modulation mapping • First permutation rule where • Second permutation rule where • This interleaver can be easily implemented with 3D block memory Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  16. Input/Output Indexing (BPSK, NI=4, NCBPS=48) Input Index A(k) adjacent FEC coded bits Output Index B(j) different OFDM symbols adjacent 3 sub-carrriers different OFDM symbols Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  17. Generalized 3D Joint Interleaver NI =width of 3D interleaver=number of OFDM symbols Ncolumn=length of 3D interleaver=number of columns Nrow=NCBPS/Ncolumn=height of 3D interleaver=number of rows NSCPC=NCBPS/Nrow=number of subcarriers in one column NCBPS= Nrow Ncolumn=number of bits per OFDM symbol NSC = NSCPR Ncolumn=number of subcarriers per OFDM symbol Guaranteed separation of consecutive coded bits is NSCPC subcarriers. Guaranteed separation of coded bits in consecutive subcarriers is (NINcolumn) bits • First permutation rule where • Second permutation rule where Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  18. Generalized 3D Joint Interleaver NI bits Input Index A(k) Nrow bits NSC (subcarriers)= NSCPR Ncolumn NCBPS (bits)= Nrow Ncolumn Ncolumn bits NSCPC=Nrow/NBPSC Sub-carriers Output Index B(j) • Applicable to all numbers of TX antennas, e.g., NI=1,2,3,4,5,… • Applicable to all QAM modulations, e.g., NBPSC=1(BPSK),2(QPSK),4(16QAM), 6(64QAM),8,… • Applicable to both 20MHz and 40 MHz bandwidth • EX: NSC=48 (11a),54,96,108,114, or other numbers of subcarriers • EX: Ncolumn=6, 16 (11a),18 or other numbers of bits per column • Choose Ncolumnconsecutive coded bits has NSCPR=NSC/Noolumn subcarriers separation • EX: BW=40MHz, NSC=108, Ncolumn=18, NSCPR=6 subcarriers separation Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  19. 3D Joint Interleaver vs. Parallel 11a Interleaver (A2) • Channel D, half lambda, 2X2 SMX • 3D Joint interleaver performs better as expected. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  20. 3D Joint interleaver vs. 2D Joint 11a Interleaver (B1) • Channel B, half lambda, 2(4)X2 CSMX • 3D Joint Interleaver performs better. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  21. Input/Output Indexing (QPSK, NI=4, NCBPS=96) Input Index A(k) Output Index B(j) Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  22. Input/Output Indexing (16QAM, NI=4, NCBPS=192) Input Index A(k) Output Index B(j) 2nd Permutation Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  23. Input/Output Indexing (64 QAM, NI=4, NCBPS=288) Input Index A(k) Output Index B(j) 2nd Permutation Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  24. TGn Sync Interleaver (IEEE 802.11-04/889r0) • Ex. 20 MHz, NBPSC=1, NI=4, NCBPS=48, Ncolumn=16 • Note: NSS=4in the definition of above document. • Adjacent bits (ex. A(0), A(1), …, A(11)) are not evenly distributed over all subcarriers • Adjacent bits (ex. A(3),A(6),A(9),A(12)) are assigned to the same subcarrier. • Winbond proposed 3D Joint Interleaver, NBPSC=1, NI=4, NCBPS=48, Ncolumn=16 Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  25. WWiSE Interleaver (IEEE 11-04-0886-00-000n) • Ex. 20 MHz, NBPSC=1, NI=4, NCBPS=54 • Note: NCBPS=216, NSS=NI,IDEPTH=Ncolumn in the definition of above document. • Adjacent bits (ex. A(0), A(1), …, A(11)) are not evenly distributed over subcarriers. • Some adjacent bits (ex. A(21), A(27)) are on the same subcarrier. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  26. WWiSE Interleaver (IEEE 11-04-0886-00-000n) • Note: Equation (14) in the above doc. has been changed from to to shift Dn subcarriers for NBPSC=1,2,4 and 6. • Winbond proposed 3D Joint Interleaver, NBPSC=1, NI=4, NCBPS=54, Ncolumn=18 Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  27. PART-II: Circulation Transmission Transmission Options: Circular Spatial Multiplexing (CSMX) Circular Space-Time Alamouti (CALA) Circulation Options: (C) OFDM Symbol Based Circulation (S_BC) (D) Sub-carrier Based Circulation (Sub_BC) NOTE: The same proposed 3D Joint Interleaver is applied for all above options. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  28. Why Circulation? • Circulation is one simple way to achieve all available diversities including space, frequency, and time. When Circulation? • Always. Especially when transmitting NOFDM (M) at the same time from M TX antennas. How Circulation? • Together with proposed 3D Joint Interleaver to explore all available diversities Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  29. Transmission Options (A) Circular Spatial Multiplexing (CSMX) Transmitting NOFDM (M) OFDM Symbols from M TX Antennas High throughputs if high SNR (B) Circular of Space-Time Alamouti Code (CALA) Simple to encode and decode Can be easily modified to be compatible with 11a/g Circular Alamouti is applied if more than two transmit antennas Circulation bases on two OFDM symbols to preserve orthogonality Definition:NOFDM (M)denotes a MIMO system transmits NOFDM OFDM symbols at the same time from M TX antennas Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  30. Circulation Options for CSMX Systems • (C) OFDM symbol-based circulation (S_BC) • Only NOFDM IFFTs are required • Only NOFDM TX Ant. are transmitting at the same time • (D) Subcarrier-based circulation (Sub_BC) • M IFFTs are required • All M TX Ant. are transmitting at the same time • Smaller size of interleaver than S_BC • Smaller processing delay than S_BC Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  31. Circulation Options for CALA Systems (NOFDM=2) • (C) OFDM symbol-based circulation (S_BC) • Only 2 IFFTs are required • Only 2 TX Ant. are transmitting at the same time • (D) Subcarrier-based circulation (Sub_BC) • M IFFTs are required • All M TX Ant. are transmitting at the same time • Smaller size of interleaver than S_BC • Smaller processing delay than S_BC Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  32. Example of a 2 (3) CSMX System Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  33. Example of a 2 (3) CALA System Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  34. Interleaver Outputs Before Circulation Transmission • S-BC (Ex. NI=6, NOFDM=2, M=3) (C) S_BC • Sub-BC (Ex. NI=2, NOFDM=2, M=3) (D) Sub_BC Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  35. Circulation Patterns for CSMX NPattern= =Number of circulation patterns for both S_BC and Sub_BC NI=NOFDMX NPattern for CSMX systems with S_BC NI=NOFDM for CSMX systems with Sub_BC NOTE: Bigger NI implies bigger HW size and longer decoding delay Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  36. Circulation Patterns for CALA NPattern= = Number of circulation patterns for both S_BC and Sub_BC NI=NOFDM x NPattern for CALA systems with S_BC NI=NOFDM for CALA systems with Sub_BC NOTE: Bigger NI implies bigger HW size and longer decoding delay Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  37. Sub-carrier mapping for Sub-BC Example: 2(3) MIMO System CSMX with Sub_BC Coded bits from FEC outputs 11a/g sub-carrier intrerleaving with 3-sub-carrier separation Circulation subcarriers Into all TX antennas Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  38. Example: 2(3) MIMO System CSMX with Sub_BC Coded bits from FEC outputs Adjacent bits have 3-subcarrier separations and circulate into M TX antennas. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  39. Example: 2(3) MIMO CSMX System with S_BC Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  40. Sub-BC and S-BC in 11n Channel B • Two schemes have similar performances. The interleaver size and decoding delay for Sub_BC is much smaller than S_BC. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  41. Sub-BC and S-BC in 11n Channel D • Two schemes have similar performances. The interleaver size and decoding delay for Sub_BC is much smaller than S_BC. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  42. RF and BB Related Issues • RF Total TX Power for 2(3) MIMO Systems • Assuming max power of each subcarrier is p, • Total power of OFDM symbol based circulation = 48 * p * 2 = P • Total power of modulated symbol based circulation= 32 * p * 3 = P • Power per antenna is P/2 for S_BC and P/3 for (Sub_BC) • Baseband (BB) hardware requires • Two IFFT/FFT for S_BC and Three for Sub_BC • NOTE: Bigger NI implies bigger HW size and longer decoding delay • Example: 2(4) CSMX requires NI=12 for S_BC and NI=2 for Sub_BC • If the power consumption of more active TX antennas at RF and more active IFFT/FFT at BB are acceptable, Sub_BC is recommended with minimal decoding delay and interleaver size. Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  43. Backward Compatibility with 11a/g • The proposed 3D Joint Intereleaver is backward compatible to the standardized 11g/11a 2D interleaver • If NI=1, the 3D joint interleaver becomes a 2D 11a/g interleaver • The 3D joint based on 3-subcarrier separation is backward compatible to 11a/g interleaver for all 8 11a data rates • Same 2nd permutation as 11a • Both proposed circulation options (C) S_BC and (D) Sub_BC are backward compatible with 11a interleaver • No circulation (Npattern=1) for option (C) S_B Circulation • The 3-subcarrier separation of consecutive mapped data of option (D) Sub_BC is the same as the 11a interleaver Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  44. High Throughput Requirement for 11n • The proposed 3D Joint Intereleaver can be implemented into a general MIMO systems with M TX antenna • The proposed 3D Joint interleaver supports all 8 data rates in 11a • Tables up to 4x4 MIMO systems are shown in this proposal. For a NOFDM (M) MIMO system with MNOFDM=1,2,…,6,… Size of proposed 3D Joint Interleaver=NI= NOFDM x Example: M=4, data rate of a 4(4) CSMX system is Mx54=216 Mbps The proposed interleaver is a 4x16x18 3D interleaver (NI=4) • For a general NOFDM (M) MIMO system, the proposed 3D Joint interleaver can support data rates up to Mx54 Mbps in 20MHz bandwidth, M is any integer Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  45. Conclusions • Proposed 3D Joint Interleaver which intereleaves adjacent FEC coded bits into all available diversities in space, frequency, and time is recommended. • Proposed 3D Joint Interleaver is backward compatible with 11a/g standard interleaver. • Proposed OFDM symbol based circulation and sub-carrier based circulation can be applied in all MIMO mode with arbitrary TX antennas, and transmission schemes (CSMX,CALA). • Proposed S_BC and Sub_BC is backward compatible to 11a/g. • Proposed Sub_BC with minimal decoding delay is recommended Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  46. PART-III: Coding Rates Selection and MIMO Tables Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  47. Code rate selection • 11a selection • 6, 9, 12, 18, 24, 36, 48, 54 Mbps • Two problems • 9 Mbps (BPSK, 3/4) performs bad. • 48 and 54 Mbps is only 6 Mbps difference. • Suggestion • Introducing new low code rate • Rate 1/3 is generated by repetition of the rate 1/2 coded bits (next page) • 9 Mbps (BPSK, 3/4)  8Mbps (QPSK, 1/3) • Introducing new puncturing to increase the max. rate. • 7/8 by puncturing pattern (1111010, 1000101) • 54 Mbps  63 Mbps Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  48. Generate Rate 1/3 from Rate 1/2 64 coded bits • To decrease the coding rate from 1/2 to 1/3 • Two possible ways • New optimal code: (133, 145, 175) dfree=15 • New Viterbi decoder is required  Not recommended • By repetition every other coded bit: dfree=15 • Same Viterbi decoder (mother code rate=½) can be used • Repetition method is used for simulations Rate=1/2 Rate=1/3 Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  49. Code rate selection • Consistent decrease the rates (24% - 33%) by introducing 7/8 rate • 9 Mbps is replaced by 8 Mbps. 15 12 12 6 6 4 2 Jeng-Hong Chen, Pansop Kim, Winbond Electronics

  50. Code rate selection • Channel D, half lambda • New selection of rates provides more smooth curves, higher data rate Jeng-Hong Chen, Pansop Kim, Winbond Electronics

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