Technical Presentation at Columbia University WiBro– A Mobile WiMAX System, and Radio Resource Management Sept 20, 2006 Byeong Gi Lee Seoul National University.
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Technical Presentation at Columbia University WiBro– A Mobile WiMAX System, and Radio Resource Management Sept 20, 2006 Byeong Gi Lee Seoul National University ICT Snapshot - Services Penetration of high-speed Internet (4Q 2005) 152M 30% 52M USA Denmark Belgium Japan Netherland Canada Taiwan Korea 39% 19M 43% 25M 73% 0 20 40 60 80 Seoul National University, BG Lee, Sept. 2006 2 ICT Snapshot - Devices Mobile phone market share 25% (4Q, 2005) 31% 7% 6% 13% 18% Seoul National University, BG Lee, Sept. 2006 Nokia Motorola Samsung Sony Ericsson LG Others 3 Wireless Internet in Korea Wireless Internet Subscribers 1 (Source KT) Wireless Internet Subscribers 45 40 96% 97% 27M 94% 25 20 39M 33M 35 30 38M 78% 2001 2003 15 2005 2008 10 5 0 Mobile Phone Subscribers2005 2001 2003 2006.7 Wireless Internet Subscribers Seoul National University, BG Lee, Sept. 2006 4 Wireless Internet in Korea 2 Wireless Internet Sales (wrt Total Sales) 6.7 billion USD 3.7 billion 35.7% 2 billion 19.8% 0.5 billion 11.6% 4.6% 2001 2003 2005 Seoul National University, BG Lee, Sept. 2006 2008 5 Part 1. WiBro: A Mobile WiMAX System Seoul National University, BG Lee, Sept. 2006 6 What is WiBro? WiBro (Wireless + Broadband) Harmonization with Mobile WiMAX Based on IEEE 802.16e Standard - An OFDMA based Profile of IEEE 802.16e Standard Mobility IP Vehicle speed (60 km/h, 120 km/h) Compatible with Good performance while on the move Diverse terminal types (PC/PMP/PDA/Phones etc) Internet world Broadband 1Mbps per user Broadband uploading capability Seoul National University, BG Lee, Sept. 2006 7 WiBro on the Evolution Paths to 4G 1995 2000 2005 2010+ 4G Fast 3G 2G 1G (IMT2000) (Digital) (Analog) WiBro Slow 802.11b 2.4 GHz WLAN PAN 5 GHz WLAN 5 GHz WLAN 802.11a/g ~ 14.4 kbps 144 kbps 384 kbps 802.11n 50 Mbps 200 Mbps Seoul National University, BG Lee, Sept. 2006 1Gbps 8 WiBro on the Evolution Paths to 4G 2000~2002 2003~2004 2Mbps/2Mbps WCDMA Cellular Based (3GPP, 3GPP2) 153kbps/ 307kbps EV-DO 153kbps/2.4Mbps 2005~2006 2Mbps/14.4Mbps 30Mbps WCDMA(R5) HSDPA WCDMA(R6) HSUPA 1.8Mbps/3.1Mbps EV-DO Rev. A cdma2000 1x 2008~2010 1.8Mbps/4.9Mbps* 3G LTE HSOPA EV-DO Rev. B EV-DO Rev. C 4G Internet Based (IEEE) 11Mbps 54Mbps 802.11b 802.11a/g 6Mbps/18.4Mbps 100Mbps WiBro WiBro-2 75Mbps(Fixed) 802.16a/b/d Harmonization 802.16e Seoul National University, BG Lee, Sept. 2006 9 IEEE 802.16 Standardization IEEE 802.16 (~2001) PHY and MAC standard for fixed wireless users with LOS (10~66GHz) IEEE 802.16a (~Apr. 2003) For fixed wireless users with NLOS (2~11GHz) Three PHY structures: SC, OFDM, OFDMA IEEE 802.16c (~Jan. 2003) System profile for interoperability (10~66GHz) IEEE 802.16d (Rev approval, June 2004) Consolidated standard of .16, .16a, and .16c IEEE 802.16e (WG ballot, June 2004) 802.16d-based amendment for mobility Seoul National University, BG Lee, Sept. 2006 10 Standards – 802.16 vs. WiBro IEEE 802.16 and WiBro WiBro Mobility (Handoff & Sleep mode) 802.16 e MAC 802.16 d SC OFDM OFDMA Scalable OFDMA, MIMO, LDPC, Seoul National University, BG Lee, Sept. 2006 11 WiBro Requirements Major System Parameters Radio Access Requirement Duplexing TDD Frequency Reuse Factor 1 Multiple Access OFDMA Mobility ≤ 60 [Km/h] Channel BW 10 [MHz] Service Coverage ≤ 1 [Km] Spectral Efficiency [bps/Hz/cell(sect.)] Max. DL / UL = 6 / 2 Aver. DL / UL = 2 / 1 Handoff ≤ 150 [ms] Throughput (per user) Max. DL / UL = 3 / 1 [Mbps] Min.DL/UL = 512/128 [Kbps] Seoul National University, BG Lee, Sept. 2006 12 Cellular vs. WiBro vs. WLAN WiBro Cellular Cellular WLAN Metro Zone (2G, 3G) WiBro WLAN AP Hot Spot AP AP AP Indoor Seoul National University, BG Lee, Sept. 2006 13 WiBro Network Architecture NMS : Network Management System CMS : Contents Management System PMS : Product Management System VCC : Voice Call Continuity MSC : Mobile Switching Center IMS : IP Multimedia Subsystem RAS : Radio Access Station ACR : Access Control Router AAA : Authentication, Authorization and Accounting PSTN BTS BSC Toll MSC CDMA WiBro Trunk Gatew VCC ay PMS CMS IMS Server Farm RAS ACR Edge Core Router Router (Portal, VOD, etc) AAA Back End Platform A Server Mediation Billing WiFi Internet AP Edge Router Gateway Core Router Seoul National University, BG Lee, Sept. 2006 14 WiBro System by Samsung Electronics Access Control Router Radio Access Station Seoul National University, BG Lee, Sept. 2006 15 WiBro System Functions RAS MIP FA Function Scheduling MAC PDU Processing MAC ARQ Control Packet Header Suppression Air Link ACR Handoff Packet Classification Handoff Control (relay) Packet Forwarding Security Management Session Control Core Network Traffic Interface Connection Control Signaling Plane Mobility Management User Traffic Plane Physical Layer Seoul National University, BG Lee, Sept. 2006 16 Deployment of WiBro Services Trials (’05~’06) Commercial services (’06) KT, SKT in Korea Service trial and commercial service TVA in Brasil Cooperation in progress with various operators and vendors in Mobile WiMax Forum Seoul National University, BG Lee, Sept. 2006 17 Commercial WiBro Service BunDang Area Located 20km South of Seoul Population: 450,000 Area: 70 Km2 by KT 22 Radio Access Stations RAS Repeater Seoul National University, BG Lee, Sept. 2006 18 WiBro PHY - Features High spectral efficiency support TDD Minimize guard band 10MHz BW/OFDMA Minimize multi-path interference High modulation order (QPSK, 16QAM, 64QAM) & enhanced channel coding (convolutional turbo code) Full coverage support Cellular operation with frequency reuse factor 1 High spectral efficiency & easy cell planning Minimize interference using diversity subchannel Compensate low SINR at cell edge using low rate coding Fast handover with mobile IP Seoul National University, BG Lee, Sept. 2006 19 WiBro PHY – Features (cont’d) Performance enhancement considering mobility H-ARQ FEC and ARQ Band selection AMC & diversity subchannel For slowly moving users: allocate band selection AMC subchannels which have high channel quality For fast moving users: allocate diversity subchannels Support mobility Short OFDM symbol Pilot structure supporting channel estimation while moving Support fast access during handover Short frame length Non-contention based control channel access Seoul National University, BG Lee, Sept. 2006 20 WiBro PHY – Features (cont’d) Flexible resource allocation TDD: asymmetric DL / UL allocation Subchannel-level multiuser scheduling Power saving mechanisms Sleep mode Idle mode Advanced optional features Smart antenna support Space-time code/Spatial multiplexing support Seoul National University, BG Lee, Sept. 2006 21 WiBro PHY – OFDMA Basic Concept of OFDM Orthogonal Frequency Division Multiplexing : Advanced FDM Divide into N orthogonal subcarriers Transmit N symbols in N subcarriers respectively Reconstruct N symbols using orthogonality FDM: Use separated subcarriers (A, C, E) OFDM : Use overlapped orthogonal subcarriers (A,B,C,D,E) Seoul National University, BG Lee, Sept. 2006 22 WiBro PHY – OFDMA (cont’d) One Big Stream Huge bunch of small streams Long Symbol Period Robust to multipath fading ( Small guard time overhead) Huge bunch + Orthogonality Robust to narrowband interference Efficient use of radio spectrum Appropriate for Broadband System 1Mbps Stream (Ts : 1us) 10 X 100 Kbps (Ts : 10 us) 1us delayed path signal Narrowband interference Strong Candidate for the Next-Generation Wireless Access Seoul National University, BG Lee, Sept. 2006 23 WiBro PHY – System Parameters Parameter Value Duplex TDD Multiple Access OFDMA System Bandwidth 10 MHz Sampling frequency 10 MHz Number of used tones 864 out of 1,024 Number of data tones 768 Number of pilot tones 96 Tone spacing 9.765625 kHz Signal bandwidth 8.447 MHz Ratio of cyclic prefix time to basic OFDM symbol time Basic OFDMA symbol time 1/8 102.4 ms 12.8 ms Cyclic prefix time 115.2 ms OFDMA symbol time TDD frame length 5 ms Number of symbols in a frame Seoul National University, BG Lee, Sept. 2006 42 24 WiBro PHY – Subchannel DL-Diversity subchannel (FUSC, full usage) IDcell-based permutation Distributed data subcarriers in a symbol Seoul National University, BG Lee, Sept. 2006 25 WiBro MAC – Features Flexible BW allocation On frame basis Flexible QoS provisioning UGS, rtPS, nrtPS, BE Efficient MAC PDU construction Variable size MAC PDU Fragmentation, packing, concatenation Support header suppression Energy-saving Sleep & idle mode Handover Hard & soft handover Multicast and Broadcast Services Security support Seoul National University, BG Lee, Sept. 2006 26 WiBro MAC – Frame Structure Frame structure Management messages (GMH & CRC) DL-MAP, UL-MAP Burst profile Uplink control channel (CQI, ACK, ranging) DOWNLINK GMH UPLINK GMH DL-MAP IE UL-MAP IE DL-MAP IE UL-MAP IE DL-MAP IE UL-MAP IE DL-MAP IE UL-MAP IE Burst #3 CRC UL-MAP UL Burst #1 Burst #1 UL Burst #2 ACK CH Burst #2 CRC DL-MAP CQICH CDMA Ranging Seoul National University, BG Lee, Sept. 2006 UL Burst #3 27 WiBro Evolution Issues Scalability 10/20/40MHz TDD, 10/20 MHz FDD Throughput enhancement MU-MIMO, LDPC Mobility improvement Up to ~300Km/h Spectral efficiency increase Up to ~10b/s/Hz/cell Control overhead minimization Multi-hop relay Backward compatibility Seoul National University, BG Lee, Sept. 2006 28 Comparison of WiBro, HSPA, and EVDO EVDO Rev B (3-carrier) HSDPA HSPA Parameter 1xEVDO Rev A WiBro (2x2) Duplex FDD FDD FDD FDD TDD Occupied spectrum 2.5 MHZ 10 MHz 10 MHz 10 MHz 10 MHz DL 1.25 MHZ 5 MHz 5 MHz 5 MHz UL 1.25 MHZ 5 MHz 5 MHz 5 MHz DL 3.1 Mbps 14.7 MHz 14 Mbps 14 Mbps 46 Mbps UL 1.8 Mbps 5.4 MHz 2.0 Mbps 5.8 Mbps 14 Mbps DL 0.85 bps/HZ 0.93 bps/Hz 0.78 bps/Hz 0.78 bps/Hz 1.93 bps/Hz UL 0.36 bps/Hz 0.28 bps/Hz 0.14 bps/Hz 0.30 bps/Hz 0.88 bps/Hz Channel BW Peak data rate Spectral efficiency Net information throughput per channel/sector 10 MHz DL 1.06 Mbps 4.65 Mbps 3.91 Mbps 3.91 Mbps 14.1 Mbps UL 0.45 Mbps 1.38 Mbps 0.70 Mbps 1.50 Mbps 2.19 Mbps Seoul National University, BG Lee, Sept. 2006 29 WiBro Services Personal • Integrated Messaging Service - SMS/MMS, Group Messaging - Instant Messaging/Chatting • Mobile Blog IP Telephony • VoIP, Video Telephony • PTA - PTT (Push to talk- 1:N telephony) - PTD (Push to Data - Send data during PTT) - Web Blog + Mobile • Telematics - PTV (Push to Video - 1:N Video telephony) - Traffic Information, Location Search, etc. Internet Entertainments • AOD/MOD, VOD • Web Service - E-mail, Internet Browsing • Information On Demand - Personalized Information Service • Streaming Broadcasting • 3D/Interactive Game • M-Commerce Seoul National University, BG Lee, Sept. 2006 30 Part 2. Radio Resource Management for Next-Generation Broadband Wireless Communications Seoul National University, BG Lee, Sept. 2006 31 Radio Resource Radio Resource Something to allocate to each service traffic in order to provide the requested service Categories of Resources Bandwidth (time, frequency) Transmission power Transmit/receive antenna Buffer space, MAC address, … Three Fundamental Radio Resources Seoul National University, BG Lee, Sept. 2006 32 Radio Resource (cont’d) Limitations in Using Radio Resources Bandwidth: Absolutely limited, License fee Transmission power: Available operation range of amplifier, Mitigation of interference, Lifetime of battery-powered devices Antenna: Difficulty in deployment, Operation complexity Should utilize radio resources efficiently. Need efficient radio resource management techniques. Seoul National University, BG Lee, Sept. 2006 33 Radio Resource Management (cont’d) Why Important? Limited Radio Resources Service Requirements QoS Provisioning Radio Resource Management Communication Environments High System Efficiency Plays a key role for efficiency enhancement for next-generation wireless communications Seoul National University, BG Lee, Sept. 2006 34 Radio Resource Management Radio Resource Management Determines the amount of each resource to allocate to each service traffic In general RRM problem is formulated as a constrained optimization. Problem Objective: Maximization of the system efficiency Under constraints on: Amount of available resources User performances (strongly related to QoS requirements) Seoul National University, BG Lee, Sept. 2006 35 Radio Resource Management (cont’d) Composition of RRM Admission control Scheduling Channel adaptation; power and rate control MAC state management etc. Selected Issues in RRM 1. 2. 3. 4. Opportunistic scheduling RRM for OFDM Antenna management Inter-cell resource management Seoul National University, BG Lee, Sept. 2006 36 Opportunistic Scheduling 1 Time-Varying Nature of Wireless Channels Fading due to constructive and destructive interference among multiple signal paths Seoul National University, BG Lee, Sept. 2006 37 Opportunistic Scheduling 2 Fading is viewed as a Source of Unreliability For delay-sensitive traffics (e.g. voice) Should be compensated by using more resources Power control, antenna diversity, … Fading may be viewed as a Source of Opportunity Change of the viewpoint For delay-tolerable traffics (e.g. best effort data) Transmit only when the channel quality is near its peak Can help to save resources Can increase the system capacity Opportunistic Scheduling Seoul National University, BG Lee, Sept. 2006 38 Opportunistic Scheduling 3 Communications in Shared Channels If the constituent users have independent channel statistics, Schedule the user whose channel quality is near its peak Can increase of the capacity by multiuser diversity gain Seoul National University, BG Lee, Sept. 2006 39 Opportunistic Scheduling 4 User Performance in Multiuser Scheduling Most researches focused on the “fairness” among the users with different average channel quality In terms of the served time or the throughput ratio Fairness criterion is not directly related to the service requirement; it only provides relative differences among the users (e.g. [Liu01, Borst01, Vis02]) QoS Provisioning with Multiuser Diversity Prediction of the required amount of resources Determination of the fairness criterion according to the predicted results Admission control for infeasible requirements CDF-based scheduling [Park05] → A predictable opportunistic scheduler Seoul National University, BG Lee, Sept. 2006 40 Opportunistic Scheduling 5 CDF-based Scheduling Algorithm [Park05] Uses the CDF of each user’s channel quality as the scheduling metric Exact calculation of user performance becomes possible Seoul National University, BG Lee, Sept. 2006 41 RRM for OFDM 1 OFDM in view of RRM High degree of flexibility in resource allocations Two-dimensional degree of freedom Subcarrier (bandwidth) Transmission power Exploits the multiuser diversity in frequency domain Becomes an opportunistic scheduling problem equipped with power allocation for multiple parallel channels Seoul National University, BG Lee, Sept. 2006 42 RRM for OFDM 2 Subcarrier Allocation Straightforward extension of single-channel case possible Main source of performance gain Transmission Power Allocation Intra-user allocation Power distribution among subcarriers allocated to a specific user Inter-user allocation Power distribution among different users Users with weak channel prefer the transmission power; users with strong channel prefer the subcarrier About 10~20% additional gain is observed in several papers [Song05, Shen05, Seo06] Seoul National University, BG Lee, Sept. 2006 43 RRM for OFDM 3 Performance Comparison Non-opportunistic subcarrier allocation Opportunistic subcarrier allocation Opportunistic subcarrier allocation with asymptotically optimal power allocation - Single cell OFDMA - Proportional fair throughput Seoul National University, BG Lee, Sept. 2006 44 RRM for OFDM 4 Issues in RRM for OFDM Feedback overhead in OFDM Channel state information of all the subcarriers are needed. How to reduce this feedback overhead? Service convergence Each service type has its own optimal allocation strategy (e.g. scheduling metric). How can integrate different strategies in a single OFDM system? Computational complexity Interactive relation between the subcarrier and transmission power allocation Iterative determination High complexity Equal power allocation Performance loss Seoul National University, BG Lee, Sept. 2006 45 Antenna Management 1 MIMO Technique Multiple Input Multiple Output Use of multiple transmit/receive antenna Diversity, beamforming, spatial multiplexing, space division multiple access (SDMA) One of the key technologies for high spectral efficiency Tx Data MIMO Encoder Tx Rx Tx Rx Tx Rx MIMO Decoder Seoul National University, BG Lee, Sept. 2006 Rx Data 46 Antenna Management 2 Diversity Makes individual point-to-point links reliable All the antennas transmit the same information Fading of each antenna is averaged The number of independent copies diversity order Multiplexing Splits the information stream into several parallel substream Each antenna transmits different substream Proper signal processing such as BLAST is needed Increases the transmission rate of the link Seoul National University, BG Lee, Sept. 2006 47 Antenna Management 3 Beamforming Steers the transmission beam to a specific direction Improves the SNR of users in the direction while reducing interference to others How to Apply These Techniques? Tradeoff relation among different antenna techniques What is the optimal combination of the above three schemes? Different answers for different services and environments (e.g. dependent on delay requirement, rank of channel matrix, channel coding scheme and HARQ, …) A guideline is needed for switching the techniques. A hybridization can improve the performance. Seoul National University, BG Lee, Sept. 2006 48 Antenna Management 4 Switching between diversity and multiplexing [Heath05] 2*2 MIMO Fixed tx rate; 4 bits/symbol Diversity, multiplexing, optimal selection of them Seoul National University, BG Lee, Sept. 2006 49 Antenna Management 5 Hybridization of beamforming and diversity [Kwon] 6 tx, 1 rx antenna N: number of antenna groups Beamforming in each group Diversity among different groups Seoul National University, BG Lee, Sept. 2006 50 Inter-cell Resource Management 1 Intra-Cell RM - Scheduling Power and rate control Admission control MAC state control considering power saving, … Inter-Cell RM - Inter-cell interference management - Frequency reuse factor adjustment - Inter-cell load balancing Decentralized Coordination - Minimized inter-cell coordination - Signaling protocol via the backbone network Autonomous RM - No coordination - Implicit signaling via interference measurement Seoul National University, BG Lee, Sept. 2006 51 Inter-cell Resource Management 2 Illustration of cell and pseudo-cell Seoul National University, BG Lee, Sept. 2006 52 Inter-cell Resource Management 3 Necessity of Inter-cell RM Severe inter-cell interference to users at the cell boundary in OFDM systems Cell planning? Not a suitable solution when considering the “plug-and-access” concept of all-IP networks Practical difficulties in cell planning because of different size and shape of each cell Requirement on Inter-cell RM Distributed operation: No hierarchical structure in all-IP networks Load balancing: Adjust the amount of the used resources Reduce the ICI of a heavily loaded cell Seoul National University, BG Lee, Sept. 2006 53 Inter-cell Resource Management 4 Decentralized Coordination [Kwon04] Pseudo cell structure; group of dominant interfering sectors Inter-cell RM with coordination only within each pseudo cell → limited signaling Autonomous RM [Kwon05] Inter-cell RM without any explicit signaling Implicit signaling via interference measurement Interpret the increment of ICI as a request of more resources Multi-cell iterative water-filling with price adaptation Seoul National University, BG Lee, Sept. 2006 54 Inter-cell Resource Management 5 Signaling structure Coordinated RM Autonomous RM Coordinating Function Power update Power allocation information BS Channel & load informaion BS BS No signaling BS BS MS MS Parameter broadcast BS Channel informaion Channel informaion MS MS Seoul National University, BG Lee, Sept. 2006 55 Inter-cell Resource Management 6 Performance comparison Seoul National University, BG Lee, Sept. 2006 56 Summary – Advanced RRM Radio Resource Management Plays the key role in the next-generation wireless communications System efficiency and QoS provisioning Current Issues in RRM Opportunistic scheduling RRM for OFDM Antenna management Inter-cell resource management Many interesting and important RRM problems yet to be solved for the efficiencyenhancement of next-generation wireless communications. Seoul National University, BG Lee, Sept. 2006 57 Selected References [Liu01] X. Liu et. al., "Opportunistic transmission scheduling with resource-sharing constraints in wireless networks," IEEE J-SAC, Oct. 2001. [Borst01] S. Borst et. al., "Dynamic rate control algorithms for HDR throughput optimization," IEEE INFOCOM 2001. [Vis02] P. Viswanath et. al., "Opportunistic beamforming using dumb antennas," IEEE T-COM, June 2002. [Park05] D. Park, et. al., "Wireless packet scheduling based on the cumulative distribution function of user transmission rates," IEEE TCOM, Nov. 2005. [And01] M. Andrews et. al., "Providing quality of service over a shared wireless link," IEEE Commun. Mgz., Feb. 2001. [Seo05] H. Seo, et. al., "Capacity region of multiuser shared channel when available transmission power is time-varying," IEEE ICC 2005. [Song05] G. Song, et. al., "Cross-layer optimization for OFDM wireless networks -- Part I & II," IEEE T-WCOM, Mar. 2005. [Shen05] Z. Shen, et. al., "Adaptive resource allocation in multiuser OFDM systems with proportional rate constraints," IEEE T-WCOM, Nov. 2005. Seoul National University, BG Lee, Sept. 2006 58 Selected References [Seo06] H. Seo, et. al. "Proportional-fair power allocation with CDFbased scheduling for fair and efficient multiuser OFDM systems," IEEE T-WCOM, May 2006. [Heath05] R. W. Heath, "Switching between diversity and multiplexing in MIMO systems," IEEE T-COM, June 2005. [Vis05] H. Viswanathan et. al., "Rate schedulnig in multiple antenna downlink wireless systems," IEEE T-COM, Apr. 2005. [Hwang05] S.-S. Hwang et. al., "Multi-beam multiplexing using multiuser diversity and random beams in wireless systems," IEEE ICC 2005. [Kwon04] H. Kwon et. al., "Low-overhead resource allocation with load balancing in multi-cell OFDMA systems," IEEE VTC 2005-Spring. [Kwon05] H. Kwon et. al., "Distributed resource allocation through noncooperative game approach in multi-cell OFDMA systems," IEEE ICC 2006. Seoul National University, BG Lee, Sept. 2006 59