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Wireless ATM 에서의 무선 액세스 기술

W IRELESS I NFORMATION S YSTEM E NGINEERING L ABORATORY. Wireless ATM 에서의 무선 액세스 기술. Presented at HSN ‘98. 1998. 2. 13. 고려대학교 전기  전자  전파공학부 강 충 구. High-Speed Multimedia Application. Wireless ATM History. ETSI STC RES 10: HIPERLAN/1 => HIPERLAN/2 (5.2GHz, ATM-based).

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Wireless ATM 에서의 무선 액세스 기술

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  1. WIRELESS INFORMATION SYSTEM ENGINEERING LABORATORY Wireless ATM에서의 무선 액세스 기술 Presented at HSN ‘98 1998. 2. 13. 고려대학교전기전자전파공학부 강 충 구

  2. High-Speed Multimedia Application Wireless ATM History • ETSI STC RES 10: HIPERLAN/1 => HIPERLAN/2 (5.2GHz, ATM-based) • United States (1) Petition to reallocate a block of unused spectrum at 5.2GHz in US - NII from Apple - SUPERNet from WINForum (“Shared Unlicensed Personal Radio Network”) (2) NPRM (Notice of Proposed Rule Making) from FCC • Frequency Characteristics at 5.2GHz - Fading rate is almost 120 times greater Short Packet • Wireless ATM Working Group in ATM Forum (1996/8)

  3. 무선 ATM 프로토타입 시스팀 구현 사례

  4. 표준화 동향 - ACTS: Advanced Communications Technologies and Services - RES10: Radio Equipment and System 10 - UMTS: Universal Mobile Telephone System - TTC: Telecommunications Technical Committee - MMAC-PC: Multimedia Mobile Access Communication - Promotion Council

  5. Reference Architecture - Application Scenario

  6. Wireless ATM terminal User Service Q.2931 User Service AAL SAAL ATM multiplexer Q.2931 M-Ctrl ATM AAL SAAL ATM terminal ATM multiplexer ATM ATM PHY W-LLC User Service ATM W-MAC PHY Q.2931 PHY W-PHY PHY PHY PHY PHY AAL SAAL Base station ATM User Service M-Ctrl PHY Q.2931 Q.2931 M-Ctrl SAAL AAL SAAL ATM ATM W-LLC ATM W-LLC W-MAC PHY W-MAC PHY W-PHY User Service W-PHY PHY Q.293 1 AAL SAAL ATM User Service Q.2931 M-Ctrl PHY AAL SAAL ATM ATM W-LLC W-MAC PHY PHY W-PHY Wireless Access Layers for W-ATM • 유선 ATM 망에서의 다중화 형태 • 무선 ATM 망에서의 다중화 형태 (1) Mobile = Distributed Queue (2) Channel = Unreliable Bit Pipe

  7. W-ATM Access Architecture (1) • Integrated Access vs. Modular Access MT: Mobile Terminal RP: Radio Port AP: Access Point EMAS: End-user Mobility supporting ATM switch - EMAS-E: Entry switch - EMAS-N: Network switch APCP: Access Point Control Protocol - Integrated Access: No AP involved - Modular Access: AP as virtual multiplexer

  8. (MAC address, VPI) VPI W-ATM Access Architecture (2) • Access Point (AP) as Virtual Multiplexer - MAC address uniquely identifies a logical port in the multiplexer:

  9. ATM Terminal Mobile ATM Terminal Base Station Controller User Service User Service M-Ctrl M-Ctrl Q.2931 Q.2931 Q.2931 AAL SAAL SAAL AAL SAAL ATM ATM ATM M-LLC M-LLC PHY PHY M-MAC M-MAC M-PHY M-PHY Wireless Channel VCC end-point ATM Network User plane End-to-End Connection over W-ATM • Protocol Stacks for a Full Integration of Mobile ATM Terminals to a Fixed ATM Network

  10. Physical Layer (1) • 5GHz Requirements • (from WATM-WG ‘Baseline Text for Wireless ATM specification’)

  11. ; fading rate ; AFD ; maximum doppler frequency Physical Layer (2) • Frequency Characteristics at 5.2GHz - Fading rate can be almost 120 times greater It is essential to use the short packet - Fading characteristics w.r.t. velocity & frequency band

  12. Time Slot W-ATM Header W-ATM Trailer GT ATM Cell GT 25 Mbps channel 64 kbps channel t t t t Physical Layer (3) • Channel Efficiency in High-Speed Wireless TDMA System - How to improve the channel efficiency in high-speed wireless system?

  13. Physical Layer (4) • Physical Layer Implementation for Broadband Wireless System • Standardization - No specific activities in W-ATM WG for the physical layer

  14. TDMA Frame ATM Cell ATM Cell ATM Cell DFT Frame 15+64 Static Frame 79 DFT Frame 15+64 DFT Frame 15+64 DFT Frame 15+64 DFT Frame 15+64 DFT Frame 15+64 DFT Frame 15+64 10.87 us Physical Layer (5) • MCM System for 155Mbps Transmission: Example - Data Rate: 39 Mbps - Symbol Rate: (64+15) symbols / 10.87 us = 58.14 Msymbols/sec - Bandwidth Requirement: 70 MHz (< 20% roll-off factor) - Allowed Delay Spread: < 258 ns

  15. Control Plane User Plane ATM Adatation Layer Wireless Control ATM Layer Data Link Control Medium Access Control Radio Physical Layer Mobility “M” Specification Radio Access “R” Specification Error Control for Wireless ATM (1) • Error Control Architecture (1) Forward Error Correction Coding - Header Protection - Payload Protection (2) Interleaving - Channel Interleaver - ATM Cell Interleaver (3) Data Link ARQ - Go Back N - Selective Repeat Request

  16. Error Control for Wireless ATM (2) • Forward Error Correction (FEC) Scheme: Single-Level FEC Scheme Concatenated Coding: Convolutional Code + Reed-Solomon Code - BER vs. CLR - Performance of Concatenated Coding

  17. Error Control for Wireless ATM (3) • Forward Error Correction (FEC) Scheme: Dual-level FEC Scheme Header Protection: HEC (40,32) => FEC (28,16) (24 dB gain at CLR of 10-4, 75% increase in BW) ATM Payload Protection: Variable Rate Error Control => Shortened Code ( n - l , k - l ) - Performance of Dual-level FEC Scheme

  18. Wireless ATM Cell Structure • MAC Frame and W-ATM cells - Example 1: - Example 2:

  19. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Fading Channel 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Error Control for Wireless ATM (4) • Interleaving: to randomize channel burst errors (2) ATM Cell Interleaver (1) Channel Interleaver Interleaved Sequence: [1,8,15,22,2,9,16,23, .....] Received Sequence: [1,8,15,22,2,9,16,23, .....] Deinterleaved Sequence: [1,2,3,4,5,6,7,8,9,.....,14,15, 16,.....,21,22,23,......,27,28]

  20. Error Control for Wireless ATM (5) • Data Link ARQ - Go Back N vs. Selective Repeat Request: BER to required for efficiency of 80% (30-cell packet) - BT >> 1 & or large BER => Selective Repeat Request - Throughput efficiency of Go Back N vs. BER • ARQ Protocol Parameters - Retransmission time out - Window Size - Tx & Rx Buffer Size - ARQ Protocol Frame Length • ARQ Protocol for Wireless ATM Example: ASR-ARQ Protocol proposed for MBS - Multiple ARQ instances => one ARQ instance per VC - Delayed cell discarded - Overhead equivalent to TCP/IP over AAL5

  21. Wireless MAC Layer • The MAC protocol is the pivot between the ATM world and the wireless world - Provides means to share the wireless channel among mobile terminals with varying data rates and QoS requirements

  22. Wireless ATM terminal User Service ATM multiplexer Q.2931 M-Ctrl AAL SAAL ATM ATM W-LLC W-MAC PHY PHY W-PHY Base station User Service M-Ctrl Q.2931 Q.2931 M-Ctrl SAAL AAL SAAL ATM ATM W-LLC ATM W-LLC W-MAC PHY W-MAC PHY W-PHY W-PHY PHY User Service Q.2931 M-Ctrl AAL SAAL ATM ATM W-LLC W-MAC PHY PHY W-PHY W-ATM MAC as a Distributed ATM Switch • HFC Networks • W-ATM Networks

  23. 무선 ATM에서의 매체접근제어 요구 사항 • 무선 ATM 매체 접근 제어 방식이 기존 방식이 무엇이 다른가? - 다양한 서비스 트래픽을 어떻게 통합된 접속 구조에서 수용할 것인가?

  24. 무선 ATM에서의 매체접근제어 요구 사항 • 5GHz Requirements • (from WATM-WG ‘Baseline Text for Wireless ATM specification’)

  25. Access Control Protocol Options • Different types of services may be best served • by different access control protocol choices

  26. 무선 ATM 매체 접근 제어 모델 • Generic MAC Model • Scheduler - responsible for dynamic slot assignment - based upon the static and dynamic parameters

  27. Packet Reservation Multiple Access (PRMA) • PRMA: Reservation ALOHA for Microcellular Environment • - real-time transmission constraint for packet voice • - voice activity detection for throughput improvement • Operational Concept of PRMA (1) A MT a with a new talkspurt to transmit sends the first packet on the first available time slot which is permitted for MT a with a probability p. (2) If the first packet is transmitted successfully, BS reserves the slot P to the MT a. (3) If the first packet collides, the MT a retransmits on the next available and permitted slot. Frame BS R R MT P R Reservation Indicated BS MT

  28. Integrated PRMA (I-PRMA) • Integration of Voice & Data • I-PRMA Frame Structure TDMA Frame (T sec.) Frame Overhead Request Slots Data only Voice Slots 1 2 3 ............... Nv 1 2 3 ...... Nr Sync & Overhead Guard Time Sync & Overhead Guard Time Guard Time Guard Time Request Data (User ID’s) Voice Data

  29. Dynamic Slot Assignment (1) • Dynamic Slot Assignment (DSA) • - Proposed for RACE MBS (Mobile Broadband System) • Frame structure • Flow Chart for DSA Protocol • Scheduling parameters - Static parameters (call setup parameters) : mean bit rate, peak bit rate (QoS) - Dynamic parameters : waiting period of the cell in a queue, current queue length

  30. Dynamic Slot Assignment (2) • Strategies to minimize the contention (1) Periodically broadcasting state parameters ( e.g. Setting probability of transmission according to the current load of RACH ) (2) Increasing density of RACH ( e.g. Using subslots ) (3) Inserting sufficient RACH by calculating priority for RACH • Slot assignment strategies in BS Reservation Mode Contention Mode

  31. DSA++ • Disadvantages of DSA (1) BS point of view - Difficult to perform power control (2) MT point of view - Difficult to implement a power saving mode - Difficult to find a channel for fast and seamless handovers Downlink Signalling Burst • Downlink signalling scheme of DSA++

  32. DQRUMA • Distributed Queue Reservation Update Multiple Access for BAHAMA (AT&T Bell Lab.) • Uplink & Downlink Structure • Block Diagram of DQRUMA

  33. Wireless ATM MAC Example (1) • MEDIAN - ATTD (Adaptive Time Division Duplexing) • ATDD frame & extended cell structure • Adaptive PRMA (Packet Reservation Multiple Access)

  34. Variable Length Time Frame ..... FH Down Up Contention ..... Variable Boundary Variable Boundary Variable Boundary Time Radio turn-around Broadcast Reservation based Contention based From AP to MT From MT to AP MASCARA (Mobile Access Scheme based on Contention And Reservation for ATM) Wireless ATM MAC Example (2) • MAC time frame structure • MPDU & Cell Train Concept

  35. 무선 ATM 매체 접근 제어 구현 사례 비교

  36. 프레임 구조 (1) • MDR-TDMA (Multi-service Dynamic Reservation TDMA) Protocol in WATMnet

  37. 프레임 구조 (2) • Pilot-Assisted MAC - “Adaptive MAC Protocol in Harsh Fading and Interference” (Acampora ’97)

  38. Preamble (16 octets) Control (2 octets) Address (6 octets) Header (4 octets) Payload (48 octets) CRC (2 octets) Guard (2 octets) 프레임 구조 (3) • MAC Frame proposed by Fujitsu (ATM Forum/97-0783) - Multiple types of MAC frames to enhance the wireless efficiency (1) Frame Type 1: low-bandwidth type of traffic (e.g., voice traffic) (2) Frame Type 2: high-bandwidth type of traffic (e.g., IP traffic) Payload (48 octets) CRC (2 octets) Guard (2 octets) Preamble (16 octets) Control (2 octets) Address (6 octets) Header (4 octets) Payload (48 octets) Example: Type-1 Frame = 80 octets (48 octet payload + 32 octet overhead) Type-2 Frame with 6 cells = 320 octets (48 x 6 octet payload + 32 octet overhead) - Efficiency vs. Frame Type

  39. 슬롯 할당 방식 (1) • 무선 구간에서의 통계적 다중화 구현이 가능한가? • 트래픽별 슬롯 할당 방안

  40. 슬롯 할당 방식 (2) • 슬롯 할당 방식의 구현 요구 사항

  41. Movable Boundary Request Slots CBR Slots VBR Slots + Data Slots 1 2 3 ....... Nv Nv+1 ....................................... Nt Reservation Minislots (Slotted ALOHA) TDMA Frame 슬롯 할당 방식의 예 • Estimation-Prorated Slot Assignment for VBR traffic (in WATMnet) WATM Cell Mobile Terminal (1) Down-link Estimation: (2) Up-link Estimation Out-of-band Control: Estimated by the mobile terminal In-band Control: Estimated by the base station

  42. 결 론 • 물리 계층 - 고속 무선 전송 기술 (> 25 Mbps) - Multi-carrier Modulation Modem • 매체 접근 제어 계층 - 동적 예약(Dynamic Reservation) TDMA/TDD - 트래픽 클래스 별 QoS 보장을 위한 스케쥴링 알고리즘 - 프레임 구조 (전력 효율성,대역 효율성, 페이딩, Dynamic Parameters) • 데이터 링크 계층 - 셀 헤더(Header) 보호를 위한 오류 정정 부호화(FEC) - 무선 셀에 대한 오류 정정 부호화 및 재전송 프로토콜(ARQ) - 무선 셀 및 프레임 구조의 최적화

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