Full duplex MAC 기술 -...

한국통신학회 차세대 초저지연/고효율 무선접속기술 워크샵

Full duplex MAC 기술

2016. 07. 14.

Jae-Hyun Kim

[email protected]

Wireless Internet aNd Network Engineering Research Lab.

http://winner.ajou.ac.kr

School of Electrical and Computer Engineering

Ajou University, Korea

Contents

LTE MAC protocol

Full duplex technology

LTE 적용예시

Full duplex 구현시고려사항

2

LTE MAC protocol

3

Control Plane Protocol Overview

4

Non-access stratum PLMN selection

Tracking area update

Paging

Authentication

EPS bearer establishment, modification and release

• Access stratum control plane

– radio-specific functionalities

– The AS interacts with the NAS (upper layers)

RRC: Radio Resource Control PDCP: Packet Data Convergence Protocol

RLC: Radio Link Control PLMN: Public Land Mobile Network EPS: Evolved Packet System

eNB

PHY

UE

PHY

MAC

RLC

MAC

MME

RLC

NAS NAS

RRC RRC

PDCP PDCP

PHY

MAC

IP

S1-AP

SCTP

PHY

MAC

IP

S1-AP

SCTP

LTE-Uu(radio interface)

S1-MME(logical interface)

DRB Establishment : Signaling Radio Bearers

5

An EPS bearer is mapped (1-to-1) to a DRB

A DRB is mapped (1-to-1) to a DTCH logical channel

All logical channels are mapped (n-to-1) to the DL-SCH or UL-SCH

DL-SCH or UL-SCH are mapped (1-to-1) to the corresponding PDSCH or PUSCH

EPS Bearer Service Architecture

6

EPS bearer / E-RAB is established when the UE connects to a PDN

Default bearer

remains established throughout the lifetime of the PDN connection

Dedicated bearer

Any additional EPS bearer/E-RAB that is established to the same PDN is referred to as a dedicated bearer.

P-GWS-GW Peer

Entity

UE eNB

EPS Bearer

Radio Bearer S1 Bearer

End-to-end Service

External Bearer

Radio S5/S8

Internet

S1

E-UTRAN EPC

Gi

E-RAB S5/S8 Bearer

3GPP TS 36.300 V11.6.0 “E-UTRA and E-UTRAN; Overall description”, June, 2013

Summary of Control Plane

7

1

3

2 4 5

67 9

8 EMM- Registered

Overview of User Plane Protocol

8

PDCP layer

Process RRC messages in the control plane and IP messages in the user plane

Header compression

Security

reordering and retransmission during handover

PDCP : Packet Data Convergence Protocol RLC: Radio Link Control

MAC: Medium Access Control HARQ : Hybrid Automatic Repeat Request

QoS : Quality of Service

RLC layer

Segmentation and reassembly

ARQ

Reordering for HARQ

MAC layer

Multiplexing of data from different radio bearer

Achieve QoS for each radio bearer

Report the eNodeB to the buffer size for uplink

S5/S8a

eNB

LTE-Uu

UE

Application

IP

PDCP

L1

MAC

RLC

S1-U

PDCP

L1

MAC

RLC

GTP-U

L1

L2

UDP/IP

S-GW

GTP-U

L1

L2

UDP/IP

GTP-U

L1

L2

UDP/IP

P-GW

IP

GTP-U

L1

L2

UDP/IP

SGi

Servers PDN

Application

IP

PDCP overview

9

Functions Header compression/

decompression of user plane data

Security Ciphering and deciphering for

user plane and control plane data Integrity protection and

verification for control plane data

Handover support In-sequence delivery and

reordering of upper layer PDUs at handover

Lossless handover for user plane data mapped on RLC Acknowledge Mode (AM)

Discard for timeout user plane data

* 3GPP TS 36.323 v11.2.0: “Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP)

specification”(Release 11), April, 2013

RLC Overview

Radio Link Control(RLC) Located between RRC/PDCP and MAC

Error correction through ARQ

Segmentation/Concatenation/Reassembly of RLC SDUs

3 transfer modes

TM (Transfer Mode)

• Only used for RRC messages which do not need RLC configuration

• through BCCH, DL/UL CCCH and PCCH

UM (Unacknowledged Mode)

• Utilized by delay-sensitive and error-tolerant real-time applications

• through DL/UL DTCH, MCCH or MTCH

AM (Acknowledged Mode)

• Utilized by error-sensitive and delay-tolerant non-real-time applications

• through DL/UL DCCH or DL/UL DTCH

10

SDU: Service Data Unit BCCH: Broadcast Control Channel CCCH: Common Control ChannelPCCH: Paging Control Channel DTCH: Dedicated Traffic Channel MCCH: Multicast Control ChannelMTCH: Multicast Traffic Channel DCCH: Dedicated Control Channel

MAC overview

11

Random

Access Control

PCCH BCCH CCCH DCCH DTCH MAC-control

Upper layers

PCH BCH DL-SCH UL-SCH RACH

Lower layer

(De-) Multiplexing

Logical Channel Prioritization (UL only)

HARQ

Control

MCCH MTCH

MCH

De Multiplexing

Transport channel name Direction Acronym

Broadcast Channel Downlink BCH

Downlink Shared Channel Downlink DL-SCH

Paging Channel Downlink PCH

Multicast Channel Downlink MCH

Uplink Shared Channel Uplink UL-SCH

Random Access Channel Uplink RACH

Logical channel name Type Acronym

Broadcast Control Channel Control BCCH

Paging Control Channel Control PCCH

Common Control Channel Control CCCH

Dedicated Control Channel Control DCCH

Multicast Control Channel Control MCCH

Dedicated Traffic Channel Traffic DTCH

Multicast Traffic Channel Traffic MTCH

Functions Channel Mapping

Building MAC PDU

Random access

Scheduling

Power saving by Discontinuous Reception(DRX)

Error correction through HARQ

Multiplexing / Demultiplexing

Transport Format Selection

Priority handling

Logical Channel prioritization

Random Access(RA) Procedure

Purpose RA is performed when UE didn’t assigned resource for data transmission

Contention based Perform when eNB doesn’t know the presence of UE or UE have data to transmit

while UE lost timing information

Examples• Initial access from RRC_IDLE

• RRC Connection Re-establishment procedure

• UL data arrival during RRC_CONNECTED requiring random access procedure» E.g. when UL synchronisation status is "non-synchronised" or there are no PUCCH resources for

SR available

Non-contention based Perform when eNB know the incoming of UE or eNB have data to transmit while

UE lost timing information

Examples• Handover

• For positioning purpose during RRC_CONNECTED requiring RA

• DL data arrival during RRC_CONNECTED requiring random access procedure» E.g. when UL synchronisation status is “non-synchronised”

12

Random Access Procedure- Contention based(1)

13

(0) Selection of preamble : select a preamble in preamble groups

Preambles for contention based access

(2 groups, select a group by message size)

Total 64 preambles(spreading codes) in each cell

Preambles for

contention-free access

(1) Preamble Transmission on RACH

• Set transmission power : according to DL estimation on RSRP

• Power ramping : increase transmission power by number of retrials

(2) RA Response (PDCCH tagged with RA-RNTI + PDSCH)

• Send response for a UE if single preamble is detected

• This message includes UL resource grant, timing alignment

information for sending third message

• Assign a temporary ID for UE(TC-RNTI)

• RSRP : Reference Signal Received Power

• RA-RNTI : Random Access Radio Network Temporary Identifier•TC-RNTI : Temporary Cell Radio Network Temporary Identifier

• No RA Response for UE Backoff Back to Selection of preamble

Random Access Procedure- Contention based(2)

14

(3) First PUSCH TX – Includes TC/C-RNTI

• Conveys actual random access procedure message

• If multiple UEs selected same RACH and preamble in (1), collision occurs

• No collision eNB detects one C-RNTI and get message from PUSCH

• UE considers as success, and TC-RNTI is promoted to C-RNTI

• If (3) is collided No arrival of Contention Resolution for UE

Backoff Back to Selection of preamble

(4) Contention Resolution on DL

Random Access Procedure- Non-Contention based

15

(0) RA Preamble Assignment

(1) RA Preamble

(2) RA Response

• eNB assigns to UE a non-contention Random Access Preamble

before RA(ex> before handover)

• Transmits non-contention RA Preamble

• Conveys at least timing alignment information and initial UL grant for

handover, timing alignment information for DL data arrival, RA-

preamble identifier

Data Transmission after RA- Downlink Scheduling(1) Dynamic Scheduling

Signal and transmit data without periodicity

Signaling is required at each transmission

16

Signaling for dynamic

scheduled data

PDCCH

DL-SCH

•PDCCH(Physical Downlink Control Channel)

•DL-SCH(Downlink Shared Channel)

Subframe

Subframe 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6

Data Transmission after RA- Downlink Scheduling(2) Semi-persistent scheduling

Schedule periodical transmission

Only the one signaling at first transmission is required

Reduce signaling overhead

Scheduling periodicity is configured by RRC

17

PDCCH

DL-SCH

Signaling for semi-persistent data

(example : period = 4)

No additional signalling for semi-

persistent scheduled data

Subframe 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6

Data Transmission after RA- Uplink Scheduling Procedure

eNodeB notifies the TX slot which can be used by UE for uplink transmission

UE sends data through UL-SCH and activates HARQ process

HARQ mechanism : Stop-and-Wait

eNodeB signals transmission result by HARQ ACK/NACK to UE

For NACK, eNodeB schedule for retransmission through PDCCH

18

Tx in 5

Txin 7

Tx in 7

ULData

PDCCH

UL-SCH

ACK NACKPHICH

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6

ULData

7

ULData

N=4 N=4UE Response eNB Response

Subframe

• Example for N=4 : UE/eNB response after 4 subframe

•PDCCH(Physical Downlink Control Channel)

•UL-SCH(Uplink Shared Channel)

•PHICH(Physical HARQ Indicator Channel)

Wireless Packet Scheduling Algorithm

Features of Scheduling Algorithms for Wireless Network Each user experience different transmission speed

Channel environment differ by randomly through time

Bursty error occurs

User’s channel capacity changes by fading

Require to estimate channel environment

19

• Additional Slides

Signaling for Resource Allocation

For resource allocation, eNodeB requires…

Channel Quality Information(frequency specific)

Traffic information(volume and priority, queue status

Signaling tradeoff Data rate ↔ Overhead

CQI measurement DL : through the feedback of CQIs by UEs

UL : by Sounding Reference Signals(SRS) transmitted by UE to estimate ch. quality

Frequency of the CQI reports is configurable

Reduce overhead ↔ Accuracy

Information about queue status DL : directly available at eNB

UL : specific reporting mechanism

20


Scheduling Algorithms

Opportunistic algorithm / High Rate User First (HRUF)

Simplest algorithm considering wireless channel

Optimizing the total throughput

Assign resources to user with best CQI

Fairness problem occurs

If the an user with best channel continuously generates traffic, then other users cannot be assigned wireless resource

Other users cannot transmit their traffic Fairness and QoS are not assured

21

max ( )it

( )it : Maximum transmission rate of user i



Fair algorithmsMinimize UE latency

Ex. Min-Max : Maximizes the minimum allocated rate

Total Throughput reduced

22

max min{ ( )}i

it



Proportional Fair Share Scheduling (PFSS) AlgorithmMaximize Throughput with some degree of fairness

Algorithm Basically, schedule UE when its instantaneous channel quality is

high relative to its own average channel

Reduce priority of UE by volume of received traffic increase fairness

23

( )max

ˆ ( )

i

i

t

t

1 ( -1)( ) 1- ( -1)

e e

served rate in slot tt t

T T

Te : Estimation interval

m : resource block

f : subframe

2( ) log 1 ( , )i kt SNR m f

Large Te tends to maximize the total average throughput

Small Te tends to maximize fairness


Full duplex Technology

24


Self interference cancellation(SIC) Key technology to implement full duplex communication

At least -110dB cancellation is required

Self interference

Interference from transmitting signal to receiving signal

25

Tx Rx

Transmitting Signal Receiving Signal

SelfInterference


Self interference cancellation(SIC) Key technology to implement full duplex communication

At least -110dB cancellation is required

Self interference

Interference from transmitting signal to receiving signal

26

Tx Rx

Transmitting Signal Receiving Signal

XSelf Interference

Cancellation


Feature On the same time and frequency resource

Up to 2x throughput improvement

Referred as Simultaneous Transmit and Receive (STR)

27

OO

O

O

<Full Duplex>

OX

OX

<Half Duplex>

Technical issues of full duplex MAC protocols

Distributed vs Centralized Distributed (Contra Flow [1])

Contention based full duplex MAC protocol

Primary receiver starts the secondary transmission

• Based on past success ratio of each dual-link

Problems and issues

• Inefficient asymmetric dual-link, fairness, busy tone

28[1] N. Singh, D. Gunawardena, A. Proutiere, B. Radunović, H. V. Balan and P. Key, “Efficient and Fair MAC for Wireless Networks

with Self-interference Cancellation,” in Proc. WiOpt 2011, May 2011

Sender #1

A

Receiver #2

B

Receiver #1

A

B C

D

Sender #1

Receiver #1 Receiver #2

<Symmetric dual link>

<Asymmetric dual links>

PACKET TX TO C

PACKET TX TO B

DIFS

Node A

Node B

2 1 0

B/TONE

t=0 tend

time

Node C

ACK1

PACKET RCD FROM A ACK2

ACK2

PACKET RCD FROM B ACK1

<Successful dual link transmissions>

B

A

D

C

F

E

<3-link network with fairness issues>


Distributed vs Centralized Centralized ( Janus [2] [3] )

Scheduling based full duplex MAC protocol

• AP collects data size, interference level from each station for scheduling the transmissions

Problems and issues

• Amount of data, which AP should handle would be increased

• Scheduling time is needed before transmit data

29[2] J. Y. Kim, O. Mashayekhi, H. Qu, M. Kazadiieva, P. Levis, “Janus: A Novel MAC Protocol for Full Duplex Radio,” CSTR 2013-

02 7/23/13 2013

[3] P. Levis, Stanford University, IEEE 11-13/1421r1 “STR Radios and STR Media Access,” November 2013


Residual self interference (RSI) [4] [5] Insufficient cancellation level of self interference

Imperfect sensing caused by RSI

• False alarm and miss detection problem

» False alarm : transmitter sensed busy when the channel is idle

» Miss detection : transmitter sensed idle when the channel is busy

30[4] Y. Liao and L. Song, ”Full-Duplex MAC Protocol Design and Analysis,” IEEE Communications Letters, VOL. 19, NO.7, July, 2015

[5] L. Song, Y. Liao, K. Bial, L.Song and Z. Han ”Cross-Layer Protocol Design for CSMA/CA in Full-Duplex WiFi networks,” IEEE

Communications Letters, VOL. 20, NO.4, April, 2016


Residual self interference (RSI) Protocol design

31


32

Residual self interference (RSI) Simulation results


Backward comparability Coexistence of half duplex and full duplex devices

Must be considered for transition period

Asymmetrical-Duplex [6] Network with full duplex AP and half duplex stations

Support efficient coexistence between half duplex clients and the full duplex AP

Considers capture effects

AP uses SIR map when choosing downlink transmission

Tradeoff between fairness and throughput

• Nearest station is always the best choice to improve throughput

33[6] A. Tang and X. Wang, ”A-Duplex: Medium Access Control for Efficient Coexistence Between Full-Duplex and Half-Duplex

Communications,” IEEE Transactions on Wireless Communications, Vol. 14, NO. 10, October, 2015


Asymmetrical-Duplex First case

AP-shorter

• Client A first transmits RTS frame to the AP

• The AP replies a CTS frame to client A and then transmits the packet to client B immediately

• Client A transmits packet to the AP after preamble time

34


Asymmetrical-Duplex Second case

AP-longer

• Client A first transmits RTS frame to the AP

• The AP replies a CTS frame to client A and then transmits the packet to client B immediately

• Client A delays its transmission for enough time such that two transmissions finish simultaneously

35


Asymmetrical-Duplex Third case

No dual links

• This case is same with half duplex

Fourth case

AP acquires the channel

• The AP transmits data packet without RTS/CTS exchange

36


Asymmetrical-Duplex Performance analysis and simulation results

A-Duplex improves throughput by 23% and 24% over 802.11 DCF with RTS/CTS 5 clients and 40 clients, respectively.

It improves throughput by 24% and 54% over 802.11 DCF with out RTS/CTS 5 clients and 40 clients, respectively.

37

LTE 적용 예시

38

Uplink / Downlink 공유

FDD 방식 FDD 방식의 경우 Uplink와 downlink의 주파수 영역이 다름

Self interference cancellation을 통해 간섭 제거

Uplink와 downlink 같은 주파수 영역 사용 가능

39

Uplink (10MHz)

Downlink (10MHz)

Uplink (20MHz)

Downlink (20MHz)

Uplink DownlinkFrequency ~ ~10Mhz 10MHz

Uplink / Downlink Uplink / DownlinkFrequency ~ ~10Mhz 10MHz

Uplink / Downlink 공유

TDD 방식 TDD 방식의 경우 Uplink와 downlink의 전송 시간이 다름

Self interference cancellation을 통해 간섭 제거

Uplink와 downlink 채널 동시에 사용 가능

40

Uplink DownlinkTime

Uplink

Downlink

Uplink / Downlink Uplink / DownlinkTime

Uplink

Downlink

Uplink

Downlink

Relay

기존 Relay 순서 및 resource block allocation

41

DonoreNodeB RN UE

BD AD

AUBU

Resource block

4개사용

Relay

Full duplex 적용 가능 시

42

DonoreNodeB RN UE

Resource block

2개사용

BD/AD

BU/AU

DonoreNodeB RN UE

Resource block

2개사용

BD/BU

AD/AU

D2D communication

Advantage of D2D Reduce cellular network loads

Improve a bandwidth efficiency via spatial reuse

Reduce power consumptions of mobile devices

Increase cell coverage

43

Full duplex 구현 시 고려사항

44


Transmission power 세기 Transmission power가 너무 강하면 self interference cancellation이

완벽하게 되지 않음

Residual self interference 발생

순차적인 전송 시 gain을 얻기 힘듦 Ex) LTE RRC Connection 과정 등

Msg 1 수신 후 Msg 2 전송

Msg 2 수신 후 Msg 3 전송

45

Msg 1

Msg 2

Msg 3


Interference 범위 증가 Hidden/Exposed node problem 발생 가능성 증가

적절한 full duplex pair를 찾는 것이 중요

46

Half duplex interference 범위

Full duplex interference 범위


Backward compatibility Legacy device와 호환 필요

47

FD

HDHD

HD

HDHD

Full duplex AP

Half duplex station

FD

HDFD

FD

HDHD

Full duplex AP

Full duplex, Half duplex station

FD

FDFD

FD

FDFD

Full duplex AP

Full duplex station

Thank you !

Q & A

48

Retransmission – HARQ (1/5)

Downlink : Asynchronous adaptive HARQ Asynchronous

Retransmission with additional explicit signaling to indicate the HARQ process number to the receiver

Adaptive HARQ

Modulation and coding scheme(MCS), resource allocation can be changed

Non-adaptive HARQ : retransmit with previous MCS and resource

49

Sig.

Data

PDCCH

DL-SCH

ACK or

NACK

PUCCHor

PUSCH

Sig.

New/ReTxData

Retransmission – HARQ (2/5)

Uplink : Synchronous Non-adaptive/adaptive HARQ Uplink : Synchronous HARQ

Synchronous

• Retransmission occur at predefined times relative to the initial transmission to reduce control signaling

50

Grant

Data

PDCCH

UL-SCH

Grant

New/ReTxData

PHICHACK /NACK

HARQ

feedback seen

by the UE

PDCCH

seen by

the UE

UE behaviour

ACK

or NACK

New

Transmission

New transmission according

to PDCCH

ACK

or NACK

Retrans-

mission

Retransmission according to

PDCCH(adaptive retransmission)

ACK None

No (re)transmission

PDCCH is required to resume

Retransmissions

NACK None Non-adaptive retransmission

Power Saving/Fast Wake-up –Discontinuous Reception(DRX)

51

CELL_DCH

CELL_FACH

CELL_PCHURA_PCH

IDLE_MODE

TX delay

Power Consumption

High Transition Delay(2~3sec) Lex> click after web page view

to reduce battery consumption

state changesex> during web page reading

Power saving in UMTS Through the state change from CELL_DCH to IDLE_MODE

Fast recovering to CELL_DCH takes undesired delay

•DCH (Dedicated Channel)

•FACH (Forward access channel)

•PCH (Cell Paging channel)

•URA_PCH (URA Paging channel).

Power Saving/Fast Wake-up –Discontinuous Reception(DRX)

52

RRC_CONNECTED

RRC_IDLE

• DRX UE only listens at certain Intervals

• DRX reduced battery consumption

• DRX resume transfer even quicker

• DRX reduced signaling

Power Saving in LTE/LTE-Advanced : Discontinuous Reception(DRX)

Power saving with maintaining connected states

When need power saving

Change to DRX mode while maintain RRC_CONNECTED state

UE can fast wake-up, because it maintain connectivity with eNodeB

Power Saving/Fast Wake-up –Discontinuous Reception (DRX) UE does not monitor the downlink channels during

such DRX period HARQ Round Trip Time (RTT)

Short cycle, Long cycle Wake-up and check downlink during “on duration” only

By two timer, control wake-up interval(=short DRX cycle and long DRX cycle)

53

①

③

Activate

Inactivity timer

Activate

Short DRX Cycle Timer

④

② ⑤

⑥ enter short DRX mode enter long DRX mode

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