Constellation Rearrangement for IEEE802.16m

IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number:

IEEE S802.16m-08/807Date Submitted:

2008-7-15Source:

Hyungho Park, HanGuy Cho, Sungho Moon Voice: +82-31-450-1934

LG Electronic Inc. E-mail:hyunghopark@lge.com, hgcho@lge.com, LG R&D Complex, 533 Hogye-1dong, msungho@lge.com Dongan-gu, Anyang, 431-749, Korea*<http://standards.ieee.org/faqs/affiliationFAQ.html>

Venue: Macau, China

Re : IEEE 802.16m-08/024 – Call for Contributions on Hybrid ARQ (PHY aspects)

Base Contribution: IEEE C802.16m-08/807Purpose: To be discussed and adopted by TGm for 802.16m SDD

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• HARQ mode for HARQ PHY structureHARQ mode for HARQ PHY structure– Both Chase HARQ and IR HARQ has been considered in IEEE802.16m

– Chase HARQ can achieve power gain with low complexity, however it has performance loss as compared with IR HARQ operation.

– For IR HARQ, the structure which is combined with the process of Partial IR and Full IR would be considered in 16m over retransmissions. Although higher coding gain may be achieved, its buffering overhead lay burden on a receiver side with decreasing mother code rate.

• Conventional CoRe Conventional CoRe – High cost effective solution for enhancement of 16m HARQ

• High additional HARQ gain regardless of MS’s mobility

• Low implementation complexity

– Unequal bit error probability• In case of high modulation order, the symbol has different bit reliabilities such as MSB, SB (64

QAM), and LSB. These kinds of bit reliability difference result in performance degradation in course of channel decoding

Constellation Rearrangement [1]Constellation Rearrangement [1]

– CoRe related Bitwise operations• Swapping operation: Averaging out the difference of bit reliability between component bits

(MSB, SB, LSB) within signal constellation.• Inversion operation: Averaging out the difference of bit reliability candidate component bits

• Considerations on enhancement of CoRe for IEEE802.16mConsiderations on enhancement of CoRe for IEEE802.16m– High modulation order supportHigh modulation order support

• Higher order modulated symbol has a larger potential gain from constellation rearrangement due to its increased number of component bits for bitwise rearrangement (up to 64 QAM)

– Both Chase and IR HARQ supportBoth Chase and IR HARQ support• The performance of IR HARQ can be also improved by CoRe in the way that recursive

systematic or parity bits adopt the bitwise operations such as swapping and inversion in order to average the reliability of coded bits

– Incorporation of Multiple Antenna configurationIncorporation of Multiple Antenna configuration• MIMO related LLR combing is not straightforward because the symbols transmitted from each

antenna interfere with each other. As the number of retransmission is increased, the interference is further aggravated in course of LLR combing.

Constellation Rearrangement [2]Constellation Rearrangement [2]

Constellation Rearrangement [3]Constellation Rearrangement [3]

• Proposed Constellation Rearrangement Proposed Constellation Rearrangement

– Horizontal bitwise mappingHorizontal bitwise mapping• Swapping operation exchanges component bits (i1, q1, i2, q2) on signal constellation in order to

average the difference of bit error probabilities. • Inversion operation averages out error probabilities of candidate component bits by taking

inversion of the corresponding bits on signal constellation – Vertical bitwise mappingVertical bitwise mapping

• perform to exchange component bits between transmit antennas for averaging the channel difference.

Mapper

Mapper

Bitwise Mapping

Ant. 11q 2q

1i 1q 2i 2q

1i 1q 2i 2q

2i

1i1q 2q 2i

1i

Initial transmisionFirst retransmission

Horizontal bitwise mapping

Vertical bitw

ise mapping

IFFT

IFFTAnt. N

Constellation Rearrangement [4]Constellation Rearrangement [4]

• Example of proposed CoRe for 16 QAM Example of proposed CoRe for 16 QAM

– 11stst retransmission retransmission• Horizontal bitwise mapping: swapping bit reliability between MSB and LSB• Vertical bitwise mapping : exchanging to average spatial channel difference between MSBs

– 22ndnd retransmission retransmission• Horizontal bitwise mapping: inversion of LSBs for averaging out the difference of bit

reliabilities between candidate component bits(10, 11, 01, 00) • Vertical bitwise mapping: exchanging to average spatial channel difference between LSBs

2i 1i 1i 1q 2i 2q

1i 1q 2i 2q

1q

2q2i 1i 1q

2q

Initial transmision

Swapping between MSB and LSB

2i 1i 1q

2q2i 1i 1q

2q

Horizontal bitwise mappingVertical bitwise mapping

Averaging spatial channel difference

First retransmission

Inversion of each LSB

Horizontal bitwise mappingVertical bitwise mapping

Averaging spatial channel difference

Second retransmission

1i 1q 2i 2q

1i 1q 2i 2q

1i 1q 2i 2q

1i 1q 2i 2q

Tx 1

Tx 2

Performance comparison [1]Performance comparison [1]

• Comparison of proposed CoRe and 16e Chase/IR HARQ Comparison of proposed CoRe and 16e Chase/IR HARQ

– Proposed CoRe obtains approximately 2~3dB FER gain over 16e Chase HARQ regardless of MS’s mobility

– Proposed CoRe shows little improvement in link performance gain over 16e CTC-IR HARQ

Performance gain(10% FER)

CoRe over Chase (30 km)

CoRe over Chase (120 km)

CoRe over IR, (30km)

CoRe over IR (120 km)

Nre = 1 1.7 dB 1.9 dB 0.30 dB 0.35 dB

Nre = 2 2.1 dB 2.2 dB 0.15 dB 0.15 dB

Nre = 3 2.8 dB 3.1 dB 0.47 dB 0.47 dBNre:Maximum number of retransmission

Performance comparison [2]Performance comparison [2]

• Simulation Parameters Simulation Parameters

Parameters Assumption

Bandwidth 10 MHz

Number of subcarrier 1024

Frame length 5ms

Channel estimation Perfect

Channel code CTC 1/2

Modulation 16 QAM

MIMO configuration Tx: 2, Rx:2

Resource allocation PUSC

Channel model VEH A

MS mobility 30km/h, 120km/h

Receiver type Linear MMSE

Maximum number of retransmission 1, 2, 3

Retransmission latency 10ms

Performance comparison [3]Performance comparison [3]

• Chase HARQ w/ CoRe vs 16e Chase HARQ Chase HARQ w/ CoRe vs 16e Chase HARQ

Performance comparison [4]Performance comparison [4]

• Chase HARQ w/ CoRe vs 16e IR HARQ Chase HARQ w/ CoRe vs 16e IR HARQ

Text Proposal for 802.16m SDD [1]

x.x HARQ mode

x.x.x. Constellation Rearrangement Constellation rearrangement considering both horizontal and vertical bitwise mapping shall be

adopted for IEEE 802.16m.

x.x.x.1. Horizontal bitwise mapping Horizontal bitwise mapping changes the bit position and its value on signal constellation in

order to get temporal diversity gain during retransmissions through the following operations. A specific mapping rule is FFS.

x.x.x.2 Vertical bitwise mapping Vertical bitwise mapping perform to exchange components bits between transmit antennas for

averaging the channel difference. A specific bitwise mapping rule is FFS

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