1. IEEE 802.16 OFDMA PHY Wen-bin Lin g925629@oz.nthu.edu.tw 08-09-2006

2. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Convolutional Turbo Codes 8.4.9.2.3 CTC encoder –Use a double binary Circular Recursive systematic convolutional code –Can be used for supported hybrid ARQ (HARQ) –The encoder is fed by blocks of k bits or N couples k: multiple of 8 N: multiple of 4 Advantage of the code –Better convergence –Better performance, especially low SNR and high data rate –Circular state transition property eliminates the need for tail ending data and hence achieving higher data rate

3. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 CTC Encoder First, we feed the bits to be encoded to A and B The encoding bits are separate into six sub-block, and send into the sub-block interleaver Finally, according to the request data rate, combine the punctured sub-block into a sub-frame 1/3 CTC encoder Puncturing block Interleaver A B

4. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 1/3 CTC Encoder Feedback branch: 0xB, 1+D+D 3 Y parity: 0xD, 1+D 2 +D 3 W parity: 0x9, 1+D 3

5. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 CTC Interleaver The interleaver requires the parameters P 0, P 1, P 2, P 3 –Parameters are shown in table 326, and 327 for HARQ Two steps interleaver –Switch alternate couples For time index is odd, swap (A, B) as (B, A) Let the resulting sequence be u 1 –The function P(j) provide the address of the sequence form step 1 for j = 0:N-1 –switch j mod 4 –case 0: P(j) = (P 0 *j + 1) modN –... Let the resulting sequence be u 2, where u 2 (j) = u 1 (P(j))

6. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 CTC Initialization The state of the encoder is denoted S Initialization step –Encode the sequence in natural order with S = 0, the final state is S0 N-1 –According to N and S0 N-1 to look up table to determine S c1 –Encode the sequence in interleaved order with S = 0, the final state is S0 N-1 –According to N and S0 N-1 to look up table to determine S c2

7. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Subpacket Generation In order to achieve various coding rate, puncturing is introduced to the mother code

8. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Subblock Interleaving The six subblocks are interleaved seperately A “symbol” based interleaving Symbols are written in to an array at address 0~N-1, and read out in a permuted order with address AD i Determine AD i –Determine interleaving parameter according Table 329 –Initial I and k to 0 –Calculate a tentative address T k –If T k is less than N, AD i = T k, otherwise discard T k –Repeat untill all address are generated

9. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Grouping and Selection Symbol grouping –Subblock A and B are not multiplexed –Y 1 and Y 2 are multiplexed by one Y 1 symbol follow a Y 2 symbol –W 1 and W 2 are multiplexed by one W 1 symbol follow a W 2 symbol Symbol selection –The puncturing block is referred as symbols selection in the view point of subpacket generation –Symbols in subpacket are formed by selecting specified sequences of symbols from CTC encoder output –Select by the formula

10. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 A Simulation Result In 802.16d

11. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Automatic Repeat Request Introduction of ARQ –Messages are encoded with error detection code –If there is any error during transmission, a retransmission is issued There are three conventional types of ARQ –Stop-and-wait ARQ –Go-back-N ARQ –Selective-repeat ARQ Introduction to hybrid-ARQ –Type I HARQ Using a simultaneous error correction and detection code Transmit / retransmit whole codeword –Type II HARQ The parity check bits for error correction are sent when they are needed Retransmit different parity check bits may introduce diversity gain

12. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Stop-and-Wait ARQ Simplest ARQ procedure The transmitter sends a codeword to the receiver and wait a response –Acknowledgement (ACK): transmits next message –Negative Acknowledgement (NACK): retransmits current message In-efficient because of the idle time

13. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Go-Back-N ARQ Transmission continuously until NACK is received –Transmitter does not wait for ACK after sending codeword –A retransmission length N is identical to round trip delay –N-1 codewords followed are also retransmitted Receiver sends at least N NACKs whether the codeword is correct or not

14. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Selective-Repeat ARQ Transmission continuously until NACK is received –Only retransmits messages with NACK A buffer must be provided in the receiver –Store error free codewords following a message in error –May cause buffer overflow

15. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 HARQ (1/3) 8.4.15 802.16e support 3 optional HARQs –Chase combining for all coding schemes Retransmission according to AI_SN filed CRC16-CCITT is appended to MAC data after padding Mobile station may support –Incremental redundancy for convolutional code Similar to Chase HARQ An SPID filed is supplied to indicate the puncture pattern SS, MS may support –Incremental redundancy (IR) for convolutional turbo code (CTC)

16. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 HARQ (2/3) CRC16-CCITT check –Polynomial = 0x1021 –Initial value = 0xffff Basically stop-and-wait protocol (retransmission) –NACK signal receiving –ACK is not received within the duration of “HARQ ACK Delay for UL/DL burst”, which are specified in DCD message

17. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 C 15 C 14 C 13 C 12 C 11 C 10 C9C9 C8C8 C7C7 C6C6 C5C5 C4C4 C3C3 C2C2 C1C1 C1C1 C0C0 inputs HARQ (3/3) CRC CCITT16 generator CxCx 1-bit shift register 2-in, 1-out XOR Polynomial = 0x1021 initial = 0xffff Cycles = Length (M) + Length (P) - 1

18. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 UL ACK Channel (1/2) 8.4.5.4.13 Provides feedback for Downlink HARQ –One ACK channel occupies half subchannel by three OFDMA symbols 3 pieces of 4x3 uplink tile in the case of PUSC 3 pieces of ex3 uplink tile in the case of optional PUSC –1 for NACK, while 0 for ACK (ACK encoding) If 0, than transmit vector 0,0,0 on ACK channel If 1, than transmit vector 4,7,2 on ACK channel ACK Channel –Orthogonal modulated with QPSK symbol –Even and odd half subchannel

19. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 UL ACK Channel (2/2)

20. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 CC Supported HARQ Chase HARQ, 8.4.9.2.1.1 Incremental HARQ –For each transmission, the coded block is not the same –Different puncture patterns are used to create HARQ packets identified by SPID –Combination is performed at receiver SPID –SPID = 0, puncture pattern us the same as the mandatory one –SPID = 1, the left cyclic shift of the one from SPID = 0

21. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 CTC Support HARQ Chase HARQ, 8.4.9.2.3.5 IR HARQ –Define special channel coding procedure –Modulation is chosen by some parameters Number of encoding bits Number of allocated slots Padding CRC addition FregmentationRandomization CTC encoding

22. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Padding & CRC The basic channel coding unit is MAC PDUs If the length of MAC PDU is not include in allowed set, ‘1’s are padded at the end of MAC PDU Padding until the smallest allowed length not less than the length of MAC PDU 16 bits CRC-CCITT defined in ITU-R Recommendation X.25 The packet size shall belong to set

23. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Fragmentation & Randomization If the size after padding and CRC encoding is lager than 4800 bits, fragmentation is needed Encoding separately by block of 4800 bits and concatenated as the same order before modulation The allowed number of the bits in and encoder packet The randomization is performed on each encoder packet –1+X 14 +X 15 generator polynomial –Preamble are not randomized –Initial value: [LSB] 0 1 1 0 1 1 1 0 0 0 1 0 1 0 1 [MSB]

24. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Modulation Order The randomized codeword is than modulated according to number of bits to be encoded (N EP ) and allocated slots (N SCH ) The N EP is encoded by 4-bits in HARQ MAP, every N EP has its associated encoded N SCH

25. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 AMC 8.4.6.3 A BS may change from distributed subcarrier permutation to adjacent subcarrier permutation –From non-AAS to AAS-enables traffic –Return distributed permutation at the beginning of a new DL subframe –The pilot and data subcarriers are assigned fixed positions Bin Structure –A set of nine contiguous subcarriers –8 data and 1 pilot carriers –Basic allocation unit in DL/UL

26. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 AMC AMC allocation can be made by two mechanisms –Subchannel index reference in DL / UL MAP A slot is defined as N bines by M symbols NxM = 6, N = 2 and M = 3 –Subchannel allocation in a band using HARQ map A group of 4 rows of bins is called a band A slot consists of 6 contiguous bins in a band 48 A band

27. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Symbol Allocation Numbering the traffic subcarrier in a slot –From 0~47 –Subcarrier first, then the bin The j-th symbol in a slot is mapped onto the -th subcarrier per PermBase mod 48 off, an element of GF(7 2 )

28. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Transmitter Requirements Power level control –Monotonic power level control of 45 dB minimum –1 dB minimum step size Spectral flatness –Absolute difference between adjacent subcarriers < 0.1 dB –Average energy of constellation –Power at DC subcarrier shall not exceed -15 dB relative to total transmitted power Constellation error –Relative constellation RMS error, averaged over subcarriers, frames, and packets shall not exceed specified values

29. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Receiver Requirement Receiver sensitivity –The BER measured after FEC(CC-1/2) must < 10 -6 –Using standardized packets –Using AWGN channel

30. Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Channel Rejection Measured by setting transmitting power 3dB larger than the minimum receiver sensitivity Adjacent channel rejection –Conforming OFDMA signal –At least 11 dB power above than desired signal when 16-QAM-3/4 –At least 4 dB power above than desired signal when 64-QAM-2/3 Non-adjacent rejection –Any channel other than adjacent channel or co-channel –At least 30 dB power above than desired signal when 16-QAM-3/4 –At least 23 dB power above than desired signal when 64-QAM-2/3 BER < 10 -6