Jae-Hyun Kim

Transcription

1 한국통신학회차세대초저지연 / 고효율무선접속기술워크샵 Full duplex MAC 기술 Jae-Hyun Kim jkim@ajou.ac.kr Wireless Internet and Network Engineering Research Lab. School of Electrical and Computer Engineering Ajou University, Korea

2 Contents LTE MAC protocol Full duplex technology LTE 적용예시 Full duplex 구현시고려사항 2

3 LTE MAC protocol 3

4 Control Plane Protocol Overview UE NAS enb S1-MME(logical interface) MME NAS RRC RRC S1-AP S1-AP PDCP PDCP SCTP SCTP RLC RLC IP IP MAC MAC MAC MAC PHY PHY PHY PHY LTE-Uu (radio interface) 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 4

5 DRB Establishment : Signaling Radio Bearers 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 5

6 EPS Bearer Service Architecture 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. E-UTRAN EPC Internet UE enb S-GW P-GW Peer Entity End-to-end Service EPS Bearer External Bearer E-RAB S5/S8 Bearer Radio Bearer S1 Bearer Radio S1 S5/S8 Gi 3GPP TS V E-UTRA and E-UTRAN; Overall description, June,

7 Summary of Control Plane EMM- Registered 7

8 Overview of User Plane Protocol PDCP layer Process RRC messages in the control plane and IP messages in the user plane Header compression Security reordering and retransmission during handover 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 UE Servers PDN Application P-GW Application IP PDCP enb PDCP GTP-U S-GW GTP-U GTP-U IP GTP-U IP RLC RLC UDP/IP UDP/IP UDP/IP UDP/IP MAC MAC L2 L2 L2 L2 L1 L1 L1 L1 L1 L1 LTE-Uu S1-U S5/S8a SGi PDCP : Packet Data Convergence Protocol MAC: Medium Access Control QoS : Quality of Service RLC: Radio Link Control HARQ : Hybrid Automatic Repeat Request 8

9 PDCP overview 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 v11.2.0: Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification (Release 11), April,

10 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 SDU: Service Data Unit BCCH: Broadcast Control Channel CCCH: Common Control Channel PCCH: Paging Control Channel DTCH: Dedicated Traffic Channel MCCH: Multicast Control Channel MTCH: Multicast Traffic Channel DCCH: Dedicated Control Channel 10

11 MAC overview 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 Upper layers PCCH MCCH MTCH BCCH CCCH DCCH DTCH MAC-control De Multiplexing Logical Channel Prioritization (UL only) HARQ (De-) Multiplexing Random Access Control Control PCH MCH BCH DL-SCH UL-SCH 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 Lower layer 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 11

12 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

13 Random Access Procedure - Contention based(1) (0) Selection of preamble : select a preamble in preamble groups Preambles for contention based access (2 groups, select a group by message size) Preambles for contention-free access Total 64 preambles(spreading codes) in each cell (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) No RA Response for UE Backoff Back to Selection of preamble RSRP : Reference Signal Received Power TC-RNTI : Temporary Cell Radio Network Temporary Identifier RA-RNTI : Random Access Radio Network Temporary Identifier 13

14 Random Access Procedure - Contention based(2) (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 (4) Contention Resolution on DL 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 14

15 Random Access Procedure - Non-Contention based (0) RA Preamble Assignment enb assigns to UE a non-contention Random Access Preamble before RA(ex> before handover) (1) RA Preamble Transmits non-contention RA Preamble (2) RA Response Conveys at least timing alignment information and initial UL grant for handover, timing alignment information for DL data arrival, RApreamble identifier 15

16 Data Transmission after RA - Downlink Scheduling(1) Dynamic Scheduling Signal and transmit data without periodicity Signaling is required at each transmission Signaling for dynamic scheduled data Subframe PDCCH DL-SCH Subframe PDCCH(Physical Downlink Control Channel) DL-SCH(Downlink Shared Channel) 16

17 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 Signaling for semi-persistent data (example : period = 4) No additional signalling for semipersistent scheduled data Subframe PDCCH DL-SCH 17

18 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 Example for N=4 : UE/eNB response after 4 subframe Subframe PDCCH Tx Tx Tx in 5 in 7 in 7 7 UL-SCH UL Data UL Data UL Data PHICH ACK NACK N=4 N=4 UE Response enb Response PDCCH(Physical Downlink Control Channel) UL-SCH(Uplink Shared Channel) PHICH(Physical HARQ Indicator Channel) 18

19 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 Additional Slides 19

20 Signaling for Resource Allocation For resource allocation, enodeb requires Channel Quality Information(frequency specific) Traffic information(volume and priority, queue status Additional Slides 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

21 Scheduling Algorithms Additional Slides 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 max i ( t) () t i : Maximum transmission rate of user i 21

22 Scheduling Algorithms Fair algorithms Minimize UE latency Ex. Min-Max : Maximizes the minimum allocated rate Total Throughput reduced max min{ ( t)} i i Additional Slides 22

23 Scheduling Algorithms Proportional Fair Share Scheduling (PFSS) Algorithm Maximize 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 i () t max ˆ i () t 1 served rate in slot ( t -1) ( t) 1- ( t-1) Te Te T e : Estimation interval m : resource block 2 ( t) log 1 SNR ( m, f ) i f : subframe Additional Slides k Large T e tends to maximize the total average throughput Small T e tends to maximize fairness 23

24 Full duplex Technology 24

25 Full duplex technology 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 Transmitting Signal Receiving Signal Self Interference Tx Rx 25

26 Full duplex technology 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 Transmitting Signal X Self Interference Cancellation Receiving Signal Tx Rx 26

27 Full duplex technology Feature On the same time and frequency resource Up to 2x throughput improvement Referred as Simultaneous Transmit and Receive (STR) O X O O O X O O <Half Duplex> <Full Duplex> 27

28 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 Sender #1 Receiver #1 A B DIFS t=0 t end D Receiver #2 <Symmetric dual link> B D F Node A PACKET TX TO B B/TONE time B C Node B PACKET TX TO C PACKET RCD FROM A ACK1 ACK2 A Receiver #1 Receiver #2 A C E Node C PACKET RCD FROM B ACK1 ACK2 Sender #1 <Asymmetric dual links> <3-link network with fairness issues> <Successful dual link transmissions> [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

29 Technical issues of full duplex MAC protocols 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 [2] J. Y. Kim, O. Mashayekhi, H. Qu, M. Kazadiieva, P. Levis, Janus: A Novel MAC Protocol for Full Duplex Radio, CSTR /23/ [3] P. Levis, Stanford University, IEEE 11-13/1421r1 STR Radios and STR Media Access, November

30 Technical issues of full duplex MAC protocols 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 [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,

31 Technical issues of full duplex MAC protocols Residual self interference (RSI) Protocol design 31

32 Technical issues of full duplex MAC protocols Residual self interference (RSI) Simulation results 32

33 Technical issues of full duplex MAC protocols 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 [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,

34 Technical issues of full duplex MAC protocols 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

35 Technical issues of full duplex MAC protocols 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

36 Technical issues of full duplex MAC protocols 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

37 Technical issues of full duplex MAC protocols Asymmetrical-Duplex Performance analysis and simulation results A-Duplex improves throughput by 23% and 24% over DCF with RTS/CTS 5 clients and 40 clients, respectively. It improves throughput by 24% and 54% over DCF with out RTS/CTS 5 clients and 40 clients, respectively. 37

38 LTE 적용예시 38

39 Uplink / Downlink 공유 FDD 방식 FDD 방식의경우 Uplink 와 downlink 의주파수영역이다름 Uplink (10MHz) ~ Downlink (10MHz) Frequency Uplink 10Mhz ~ Downlink 10MHz Self interference cancellation 을통해간섭제거 Uplink 와 downlink 같은주파수영역사용가능 Uplink (20MHz) Downlink (20MHz) Frequency Uplink / Downlink 10Mhz Uplink / Downlink 10MHz 39

40 Uplink / Downlink 공유 TDD 방식 TDD 방식의경우 Uplink 와 downlink 의전송시간이다름 Uplink Downlink Time Uplink Downlink Self interference cancellation 을통해간섭제거 Uplink 와 downlink 채널동시에사용가능 Uplink Uplink Time Downlink Uplink / Downlink Downlink Uplink / Downlink 40

41 Relay 기존 Relay 순서및 resource block allocation BD AD BU AU Donor enodeb RN UE Resource block 4 개사용 41

42 Relay Full duplex 적용가능시 BD/ BU AD/ AU Donor enodeb RN UE Resource block 2 개사용 BD/ AD BU/ AU Donor enodeb RN UE Resource block 2 개사용 42

43 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

44 Full duplex 구현시고려사항 44

45 Full duplex 구현시고려사항 Transmission power 세기 Transmission power 가너무강하면 self interference cancellation 이완벽하게되지않음 Residual self interference 발생 순차적인전송시 gain 을얻기힘듦 Ex) LTE RRC Connection 과정등 Msg 1 수신후 Msg 2 전송 Msg 2 수신후 Msg 3 전송 Msg 1 Msg 2 Msg 3 45

46 Full duplex 구현시고려사항 Interference 범위증가 Hidden/Exposed node problem 발생가능성증가 적절한 full duplex pair 를찾는것이중요 Half duplex interference 범위 Full duplex interference 범위 46

47 Full duplex 구현시고려사항 Backward compatibility Legacy device 와호환필요 HD HD HD FD HD FD HD HD Full duplex AP Half duplex station HD FD FD HD Full duplex AP Full duplex, Half duplex station FD FD FD FD FD FD Full duplex AP Full duplex station 47

48 Thank you! Q & A 48

49 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 PDCCH Sig. Sig. DL-SCH Data New/ ReTx Data PUCCH or PUSCH ACK or NACK 49

50 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 HARQ feedback seen by the UE ACK or NACK ACK or NACK ACK PDCCH seen by the UE New Transmission Retransmission None UE behaviour New transmission according to PDCCH Retransmission according to PDCCH(adaptive retransmission) No (re)transmission PDCCH is required to resume Retransmissions NACK None Non-adaptive retransmission PHICH ACK / NACK PDCCH Grant Grant UL-SCH Data New/ ReTx Data 50

51 Power Saving/Fast Wake-up Discontinuous Reception(DRX) Power saving in UMTS Through the state change from CELL_DCH to IDLE_MODE Fast recovering to CELL_DCH takes undesired delay Power Consumption CELL_DCH High Transition Delay(2~3sec) L ex> click after web page view to reduce battery consumption state changes ex> during web page reading CELL_FACH CELL_PCH URA_PCH IDLE_MODE DCH (Dedicated Channel) FACH (Forward access channel) PCH (Cell Paging channel) URA_PCH (URA Paging channel). TX delay 51

52 Power Saving/Fast Wake-up Discontinuous Reception(DRX) 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 RRC_CONNECTED DRX UE only listens at certain Intervals DRX reduced battery consumption DRX resume transfer even quicker DRX reduced signaling RRC_IDLE 52

53 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) 1 4 enter short DRX mode 6 enter long DRX mode 3 2 Activate Inactivity timer 5 Activate Short DRX Cycle Timer 53