NGMC Enabling Technologies

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NGMC Enabling Technologies

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Contents

• Unified MIMO
• Pilot Swapping/Sharing for Uplink OFDMA
• MAP Transmission for Relay
• Rate Compatible B-LDPC Codes
• IR-HARQ based on B-LDPC
• Effective Paging Mechanism
• Flexible Network Architecture

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Contents

• UL Synchronization (RACH)
• Cell Search
• Cyclic Delay Diversity (CDD)
• Variable Time-Frequency Selectivity Controller
• Closed Loop Tx. Diversity with codebook
• Adaptive MIMO-HARQ
• LDPC codes supporting IR
• LDPC Puncturing Algorithm
• LDPC codes decoding Algorithms
• LDPC codes combined with higher order modulation
• Constellation Rearrangement for HARQ in MIMO-OFDM

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Unified MIMO

• Same transmitter shape Common FB format for
  OL/CL-MIMO
• Can be adaptively adjusted by different scenario
  and user class
• Support flexible MIMO mode change
• Multiuser diversity and/or optimal
  diversity-multiplexing gain can be achieved

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Pilot sharing/swapping

• Pilot swapping/ sharing for uplink OFDMA
• Limited uplink pilot should be shared by multiple
  users in the uplink OFDMA ? high level of pilot
  overhead
• By swapping or sharing some pilot subcarriers at
  the edge of adjacent bands, increase effective
  number of pilot subcarriers
• Channel interpolation error can be reduced
  without increasing the pilot overhead

- Pilot swapping
- Pilot sharing
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MAP transmission for relay

• MAP transmission method for the decode and
  forward relay
• Each relay has dedicated MAP message with
  different MCS level
• Broadcast the position and MCS level of each MAP
  message with high reliability
• Reduce the MAP message overhead and the
  complexity of the relay

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Rate Compatible LDPC Codes
unpunctured node

• Rate Compatible B-LDPC Codes
• 0-Step Recoverable (0-SR) node
• Unpunctured variable node
• 1-Step Recoverable (1-SR) node
• 1-SR node has at least one neighbor check node
  (called survived check node) whose neighbor
  variable nodes are all unpunctured except for
  itself
• Can be recovered after 1 iteration
• k-Step Recoverable (k-SR) node
• k-SR node has at least one survived check node
  that has at least one (k-1)-SR node and m-SR
  nodes (0 m k-1).
• Can be recovered after k-iteration
• Classification based on k-SR node

punctured node
1 step recoverable (1SR) node



survived check (SC) node
k step recoverable (kSR) node



Bi-partite Graph Showing 1-SR k-SR node
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HARQ with B-LDPC Codes

• IR-HARQ based on B-LDPC
• IR-HARQ Scheme
• Channel adaptive and efficient in terms of
  Throughput
• Puncturing or Extension method
• IR-HARQ based on B-LDPC
• Rate compatible codes design
• for LDPC with high granularity
• Design of Shuffling pattern
• Block-wise
• Bit-wise
• High order modulation
• Circular buffer

Block diagram for IR-HARQ with B-LDPC
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Paging Mechanism

• Effective paging period determination
• Determining based on information about residual
  battery capacity of a mobile station
• The more residual battery capacity that a MS has,
  the frequent pages that it executes.

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Flexible Network Architecture

• X-tier Network Architecture supporting both
  1-tier and 2-tier structure

• 2-tier node
• (C-Plane Functionality)
• Location management
• Handover control
• Authentication
• Paging control
• Etc.

• 1-tier node
• (U-Plane Functionality)
• Packet classification
• Header compression
• ARQ
• Service flow management
• Etc.

C-Plane (2-tier)
2 tier node
C-RRM server
U-Plane (1-tier)
Internet
Subnet 1
1 tier node
1 tier node
Subnet 2
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RACH Design

• Random access channel (RACH)
• Uplink synchronization and request channel
• Design of RACH
• RACH structure, Preamble Design, Message
  Conveying, RACH access procedure
• Preamble
• Robust to timing offset, Easy to detect
• Message conveying
• Inform access purpose, whos who, parameters, etc

RACH structure
Preamble structure
Signature-base message mixing
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Sequence for Cell Search

• Requirements of sequence for cell search
• Good auto correlation property
• Low level for cross correlation value
• Low PAPR after IFFT in time domain for OFDM
  systems
• Many available cell IDs
• Sequence satisfying above requirements
• CAZAC sequence
• GCL sequence, Zadoff-Chu CAZAC sequence
• Increasing number of cell IDs
• Delayed CAZAC sequence

CAZAC Constant Amplitude Zero Auto
Correlation GCL Generalized Chirp Like
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CDD (PSD) 1/2

• Cyclic delay diversity (Phase shift diversity)
• Convert space diversity into frequency diversity
• Encoding/decoding complexity is much smaller than
  that of the STC
• Similar to SISO at the receiver (Rate-1 case)
• Can be used for both open-loop and closed-loop
• Large cyclic delay for open-loop (frequency
  diversity gain)
• Small cyclic delay for closed-loop (frequency
  scheduling gain)

PSD (frequency domain)
CDD (time domain)
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CDD (PSD) 2/2

• Simulation results

lt2Tx, 2Rxgt
lt2Tx, 1Rxgt
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Variable Time-Frequency Selectivity Controller

• VTFSC in MIMO-OFDM

• Simultaneously Control for channel selectivity on
  the Time-Freq. domain
• Transformation cyclic delay, cyclic phase for
  OFDM Symbol and subcarrier
• Channel response and impulse function manipulated
  by the VTFSC

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Closed-loop with codebook1/2

• Configuration
• Common codebook in BS and MS
• Low feedback overhead required

• 1 or 2bit codebook
• sign of correlation between transmit antennas

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Closed-loop with codebook 2/2

• Simulation results
• QPSK, correlation0.7

Time correlation
Feedback delay

• Codebook size 8
• (3bit feedback overhead)
• Proposed scheme
• (1bit feedback overhead)

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Adaptive MIMO-HARQ1/2

• MIMO-HARQ
• HARQ scheme using MIMO
• Configure retransmission packet as STBC with
  initial transmission packet
• Obtain antenna diversity gain in HARQ rather than
  time diversity
• The most efficient under low mobility while
  identical performance with simple chase combining
  scheme under high mobility
• Adaptive operation
• Given channel, select the best retransmission
  packet format
• Combination of MIMO-HARQ and closed-loop with
  codebook
• 2bit Feedback signaling
• ACK
• NACK with ALT1
• NACK with ALT2
• NACK with ALT3

BS

NACK with ALT3
NACK with ALT1
ACK
NACK with ALT2
ACK
MS
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Adaptive MIMO-HARQ 2/2

• Simulation
• Convolutional code ½, QPSK, 3 tx and 3 rx system

Figure 1. Packet error rate after retransmission
in Ped_A(3km/h) with delay20ms
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LDPC Codes supporting HARQ IR

• Multi-code rate with one mother matrix
• Easy to encode HARQ-IR support
• Parity bits are generated successively
• Any code rate is supported by using the part of H
  matrix
• A retransmission needed, the encoder continues to
  generate additional required parity bits from the
  last parity bits of the previous transmission.

x, Hd
p
r code rate nb size of column mb size of row
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LDPC Puncturing Algorithm1/2
Effect of punctured node
Variable node
Check node
Punctured nodes in bipartite graph
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LDPC Puncturing Algorithm2/2
Puncturing using grouping random puncturing
Simulation 1
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Approximated Log-BP algorithm

• Check node update process
• Bottle neck of the log-BP algorithm

Approximation of ln(cosh(x)) ln(cosh(x)) F
x - ln2 x - 0.6875, x gt
1.375 0.5x , 1.375 x
? 0.68750.1011(2) 1.3751.0110(2)
Approximated ln(cosh(x))
Simulation results
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Channel Codes Combined with High order Modulation

• Each coded bit which is encoded by the H matrix
  of LDPC code has different error probability
  according to the column weight in H matrix.
• Each bit position of M-ary QAM signal
  constellation has different error probability.
• With the combination of these two
  characteristics, we enhanced the channel coding
  performance
• Allocate more reliable encoded data bits to the
  bit position that is less vulnerable to errors.
• Allocate less reliable encoded data bits to the
  bit position that s more vulnerable to errors.

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Constellation Rearrangement for HARQ in MIMO-OFDM
1/2

• New Constellation Rearrangement
• Mapping rule considering spatial multiplexing
• Maximize MCSED (Minimum Combined Square Euclidean
  Distance)

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Constellation Rearrangement for HARQ in MIMO-OFDM
2/2

• UE 150km/h, Max Retrans. 2

• Simulation result 30km/h