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Reference (Cha 11 and 12):

LTE for 4G mobile broadband [electron ic resource] : air interface technologies and performance /Farooq Khan

Material can be access through ebook via the HKU library:

http://library.hku.hk/search~S6?/aKhan+Farooq/akhan+farooq/1%2C1%2C2%2CB/frameset&FF=akhan+farooq&2%2C%2C2

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Channel coding schemes in the LTE system

1/3 Turbo codes for large data packets Tail biting Convolutional code (1/3) for

control packets

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Transport channel processing for DL-SCH, PCH and MCH:

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Transport channel processing for BCH and DCI:

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Codeblock segmentation and CRC Attachment:

A transport block is segmented to C code blocks of equal length (max CB size 6144 bits) Two cyclic generator polynomials gCRC24A(D) and gCRC24B(D) are used to generate transport

block CRC and codeblock CRC respectively which give better TB error miss rate

performance:

e.g.

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Turbo Coding (1/3) :

Compose of two identical recursive systematic convolutional (RSC) codes with parallelconcatenation. Input to the second RSC is interleaved using an internal turbo code QPP

interleaver which allows parallel access to the memory bank by multiple processors without

contention during decoding and thus enable high speed parallel decoding.

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Quadratic permutation polynomial (QPP) interleaver memory access

contention free during parallel decoding

e.g. Addresses for four processors assuming QPP interleaver using:

(i) = 3 i + 10 i2 mod 40

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Tail-Biting Convolutional Code

- normally adding tail bits to ensure encoder ends in all-zero state to ensure encoder beginsand ends in a known state for better decoding performance

- disadvantage is increased overheads and a waste of transmit power- tail biting ensures final state of a convolution encoder is the same as initial state by

initializing the shift register state with the last bits of the information block

- tail biting can reduce overheads at the expense of increase in decoding complexity andslight performance degradation

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Circular-Buffer Rate Matching for Turbo Code

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Subblock interleaving is achieved by (1) writing row-wise in arectangular matrix with 32 columns, (2) applying matrix

columns permutations using bit-reversal-order e.g. for column j

= 3 [00011], P(j) = 24 [11000], where the bits in binary notation

are reversed, (3) reading from the matrix column-wise

Parity subblocks are interlaced to guarantee equal amount of parity 1 and 2 bits aretransmitted in response to hybrid ARQ NACK.

During incremental redundancy based ARQ procedure, different redundancy version (RV)of the codeword is transmitted. Each RV has a fixed starting point.

A rate matching (RM) algorithms punctures or repeats the bits of a mother codeword togenerate a requested number of bits according to a desired code rate.

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Circular-Buffer Rate Matching for Convolutional Code:

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N-channel stop-and-wait (SAW) protocol in LTE

N-channel SAW protocol is a multi-channel variant of SAW protocol and has the samebenefits as selective repeat protocol (SAR) that the sending process can continuously send

a number of packets while avoiding duplicate transmissions.

Each channel operates like a simple stop-and-wait protocol. When transmitter is waiting for acknowledgment on one SAW channel, it can start

transmission on the remaining SAW channels.

The number of channels required for continuous transmission depends upon the round-triptime (RTT), which is defined as the period from the time a packet is sent to the time when

ACK or NACK is received at the transmitter.

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A single-bit ACK/NACK indication is required on each SAW channel because the timingof ACK/NACK relative to the packet transmission is pre-determined and fixed. This avoids

sending the packet sequence number in the ACK/NACK.

The maximum buffering required for N-channel SAW is Npackets.