Specific Systems Cellular. Part 1 #12

Transcription

1 Specific Systems Cellular Part 1 #12 Victor S. Frost Dan F. Servey Distinguished Professor Electrical Engineering and Computer Science University of Kansas 2335 Irving Hill Dr. Lawrence, Kansas Phone: (785) FAX:(785) frost@eecs.ku.edu All material copyright 2006 Victor S. Frost, All Rights Reserved #12 1 Outline Part 1 Basic components 3G Overview of W-CDMA/UMTS HSPDA Part 2 EV-DO overview Case study: Mitigating scheduler-induced starvation in 3G wireless networks #12 2

2 Cellular Network: Physical Topology Base station Transmits to users on forward channels Receives from users on reverse channels Mobile Switching Center Controls connection setup within cells & to telephone network HLR VLR EIR AC BSS MSC BSS STP PSTN SS7 Mobile Stations Internet Wireline terminal AC = authentication center BSS = base station subsystem EIR = equipment identity register HLR = home location register MSC = mobile switching center PSTN = public switched telephone network STP = signal transfer point VLR = visitor location register Modified from: Leon-Garcia & Widjaja: Communication Networks #12 3 Components Mobile stations (MS) Transmit/Receive over the air interface Signaling User information Voice Internet Video Will set up multiple channels for communication Signaling/Control Set up and maintain calls Establish relationship between mobile unit and nearest BS User voice/data channels traffic channels #12 4

3 Components Base station (BS) Transmit/Receive over the air interface to multiple mobile stations Terminates radio signals Packages information for transport to a controller (MSC) for routing Sends information to Mobile Switching Center #12 5 Components Mobile Switching Center (MSC) Connects to many BSs Performs call set up Provides routing functions Typically associated with voice calls Sometines called Mobile Telecommunications Switching Office (MST0) Home location register (HLR) Wireless service provider (WSP) maintains a database Subscriber personal information, e.g., phone number, mobile identification number, electronic serial number (ESN) of phone Service Profile Current location of subscriber One HLR may serve several MSCs Visitor location register (VLR) Data base containing temporary information of subscribers For subscribers away from home service area VRL information retrieved from the HLR #12 6

4 Process Registration Turn on cell phone BS continually transmit signals on control channels Cell phone scans for strongest signal Cell phone decodes control signal to determine System Id Initial Tx power setting Radio channels to use for further communications Cell phone registers with network Note as the MS moves it may need to cancel registration in old area and re-register in new area #12 7 Process Mobile Call Initiation To make a call the mobile keys the phone # and hits send Phone # transmitted over preselected control channel The BS relays information to the MSC MSC looks into the control message to get the # and processes the call, i.e., does the routing #12 8

5 Process Call initiation to mobile Call routed to home MSC MSC checks HLR to determine location of subscriber MSC has current visiting MSC stored in the HLR Home MSC communicates with the visiting MSC to rout the call The MSC sends a paging message to the paging message to BS The BS then send the paging message on to the subscriber on an assigned control (paging) channel #12 9 Process Call accepted MS sees the paging signal and responds to the BS The BS send response to the MSC The MSC sets up the call to the BS The MSC also assigns a air interface channel for the BS to use for the call The MS communicates of the assigned channel Here the call is between two mobiles The communications is monitored for the ongoing call #12 10

6 Handoff (or handover) MS continually scans for control signals of BS Knowledge of the results of scans is used by MSC, e.g., power of control signal drops below some threshold Upon that event the MSC will initiate a handoff procedure Handoff procedures can be implemented transparent to the users, no interruption The handoff procedure tells the MS to use a specific channel to communicate with the new BS Process #12 11 Process Handoffs Hard: communications with old BS is terminated and a new communications to a new BS is established Soft: Soft: mobile station temporarily connected to more than one base station simultaneously Softer: mobile station temporarily connected to more than one sector of the same base station simultaneously Soft-softer: mobile station temporarily connected to more than one sector of the same base station and more than one base station simultaneously Provides diversity Occurs at boundaries of sectors/cells #12 12

7 Other Functions Call blocking if all traffic channels busy Call termination when user hangs up Call drop when BS cannot maintain required signal strength #12 13 Other Functions Power control CDMA Purpose Removes near-far effect. Mitigates fading, i.e., compensates changes in propagation conditions. In the system level decrease interference from other users increase capacity of the system Uplink Power control in uplink must make signal powers from different users nearly equal at the BS in order to maximize the total capacity in the cell. Downlink In downlink the power control must keep the signal at minimal required level in order to decrease the interference to users in other cells. #12 14

8 Other Functions Power control CDMA Types Open loop Set initial power for MS Each MS sets power based on individual measurements Coarse scale Closed loop BS knows receive power from each MS BS can tell each MS to set its power to achieve system goals. Fast power control can mitigate fast fading Three steps: Transmission Measurement Feedback # G 1G: Analog Cellular Phones. Needs a modem. 9.6 kbps max. 2G: Digital Cellular Phones. No modem required kbps max. 2.5G: General Packet Radio Service (GPRS) 144kbps. Data only. 3G: Future high-speed data with Voice. 64 kbps to 2 Mbps. W-CDMA/UMTS (Universal Mobile Telecommunications System CDMA2000 #12 16

9 Organizations 3GPP 3 rd Generation Partnership Project. 3GPP is responsible for writing and maintaining the UMTS specifications American National Standards Institute (ANSI) CDMA2000 Internet Engineering Task Force (IETF) Modified from: # G- Advantages 3G phones: The promise Improved digital voice communications Larger Bandwidth Higher Data rate Greater subscriber capacity Fast packet-based data services like , short message service (SMS), and Internet access at broadband speeds. Most carriers also expect consumers to want: location services interactive gaming streaming video home monitoring and control and who knows what else, while being fully mobile anywhere in the world. Modified from: #12 18

10 3G Capabilities Voice quality comparable to the public switched telephone network 144 Kbps- user in high-speed motor vehicles 384 Kbps- pedestrians standing or moving slowly over small areas Up to 2 Mbps- fixed applications like office use Symmetrical/asymmetrical data transmission rates Support for both packet switched and circuit switched data services like Internet Protocol (IP) traffic and real time video Modified from: #12 19 Technologies 3G is superior to the other digital standards like:- GSM (Global System for Mobile) communications standard used worldwide And IS-136 TDMA standard used primarily in North America. IS-95 CDMA systems 3G Technologies:- WCDMA or UMTS-FDD (Universal Mobile Telecommunications System - Frequency Division Duplex)---Direct Sequence Spread Spectrum CDMA2000-1x-EvDO/EvDV---Multi carrier UMTS TDD (Time Division Duplex) or TD-SCDMA (Time Division - Synchronous Code Division Multiple Access) ---Time Code CDMA2000 and WCDMA or UMTS-FDD have similar architectures Modified from: #12 20

11 Evolution Paths cdmaone IS-95A cdmaone IS-95B Cdma2000 1X Cdma2000 1xEV-DO TDMA IS-41 Core Network Cdma2000 1xEV-DV EDGE WCDMA GSM GPRS GSM Map Core Network 2G 2.5G 3G Modified from: #12 21 WCDMA Spectrum 1920 MHz 1980 MHz (uplink) 2110 MHz 2170 MHz (downlink) or 1850 MHz 1910 MHz (uplink) 1930 MHz 1990 MHz (downlink) Channel Spacing 5 Mhz WCDMA is connected to the FDD Phy and the associated protocols Focus here UTRAN-Universal Terrestrial Radio Access Network- is associated with the WCDMA radio Access Network UMTS refers to the whole network #12 22

12 UMTS-FDD / WCDMA Wideband Direct Sequence Code Division Multiple Access Does not assign a specific frequency to each user. Instead every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence Ref: #12 23 WCDMA Parameters Channel B.W Forward RF Channel Structure Chip Rate Frame Length No. of slots/frame No. of chips/slot Power Control Uplink Spreading Factor Downlink Spreading Factor 5 MHz Direct Spread 3.84 Mcps 10 ms (38400 chips) chips (Max bits) Open and fast close loop (1.6 KHz) 4 to to 512 #12 24

13 Spreading Operation Spreading means increasing the signal bandwidth Strictly speaking, spreading includes two operations: Channelisation (increases signal bandwidth) using orthogonal codes Scrambling (does not affect the signal bandwidth) using pseudo noise codes #12 25 Codes Usage Channellization Code UL: Separation of physical data and control channels from same UE DL: Separation of different users within one cell Scrambling Code UL: Separation of terminals DL: Separation of cells/sectors Length No. of codes Code Family Increase B.W? UL:4-256 chips DL:4-512 chips No. of codes under one scrambling code= SF Orthogonal Variable Spreading Factor YES chips UL: Several million DL: 512 Long 10ms code: Gold code Short code: Extended S(2) code Family NO #12 26

14 UMTS Architecture External Networks Core Network Access Network Cell site User Equipment Modified from: M. D. Yacoub, Wireless Technology, Protocols, Standards, and Techniques, CRC Press, 2002 #12 27 UMTS Architecture From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/lecture-5%206%20slides%20per%20page.pdf #12 28

15 UMTS Architecture User equipment-ue UMTS Subscriber Identity Module USIM Mobile Equipment- cell phone UMTS Terrestrial Radio Access Network Radio Network Subsystem Node B- BS Transceiver Rate adaptation Radio resource management Power control #12 29 UMTS Architecture Radio Network Controller RNC Radio access control Connection control Load, congestion and admission control Code allocation Core Network MSC VLR HLR Gateway MSC GMSC Supports circuit switched connections Serving GRPS Support Node SGPRS Logical interface to UTRAN for packet transport» Session management» Logical link management Gateway GPRS Support Node GGSN Supports packet switched transport This is an IP router #12 30

16 UMTS Protocol Architecture -User Plane FP= Framing Protocol GTP-U= GPRS Tunneling Protocol-User PDCP =Packet Data convergence Protocol From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/lecture-5%206%20slides%20per%20page.pdf #12 31 UMTS Protocol Stack Radio Resource Control-RRC Broadcast/mulitcast control- BMC Packet Data convergence Protocol- PDCP Header compression Modified from: M. D. Yacoub, Wireless Technology, Protocols, Standards, and Techniques, CRC Press, 2002 #12 32

17 Packet SAR Modified from: M. D. Yacoub, Wireless Technology, Protocols, Standards, and Techniques, CRC Press, 2002 #12 33 Physical Layer The physical layer offers information transfer services to the MAC layer. These services are denoted as Transport channels (TrCh s). There are also Physical channels. Physical layer comprises following functions: Various handover functions Error detection and report to higher layers Multiplexing of transport channels Mapping of transport channels to physical channels Fast Close loop Power control Frequency and Time Synchronization Other responsibilities associated with transmitting and receiving signals over the wireless media. Measurements SIR Tx power, Frame error rate, etc Physical channel is assigned a specific code #12 34

18 Physical Layer From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/lecture-5%206%20slides%20per%20page.pdf #12 35 Transport & Physical Channels Transport Channel (UL/DL) Dedicated Channel DCH (UL) Random Access Channel RACH (UL) Common packet channel CPCH (DL) Broadcast channel BCH (DL) Forward access channel FACH (DL) Paging channel PCH (DL) Downlink shared channel DSCH Signaling physical channels Physical Channel Dedicated Physical Data Channel DPDCH Dedicated Physical Control Channel DPCCH Physical random access channel PRACH Physical common packet channel PCPCH Primary common control physical channel P- CCPCH Secondary common control physical channel S- CCPCH Physical downlink shared channel PDSCH Synchronization channel SCH Common pilot channel CPICH Acquisition indication channel AICH Paging indication channel PICH CPCH Status indication channel CSICH Collision detection/channel assignment indicator channel CD/CA-ICH #12 36

19 UMTS FDD frame structure From: Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/lecture-5%206%20slides%20per%20page.pdf #12 37 MAC Layer The MAC layer offers data transfer to RLC and higher layers. The MAC layer comprises the following functions: Selection of appropriate Transport Format (TF), basically bit rate, within a predefined set, per information unit delivered to the physical layer Service multiplexing on RACH, FACH, and dedicated channels Priority handling between data flows of one user as well as between data flows from several users the latter being achieved by means of dynamic scheduling Access control on RACH Address control on RACH and FACH Contention resolution on RACH Traffic volume measurements #12 38

20 RRC Layer The RRC layer offers the core network the following services: General control service, which is used as an information broadcast service Notification service, which is used for paging and notification of a selected UEs Dedicated control service, which is used for establishment/release of a connection and transfer of messages using the connection. The RRC layer comprises the following functions: Broadcasting information from network to all UEs Radio resource handling (e.g., code allocation, handover, admission control, and measurement reporting/control) QoS Control UE measurement reporting and control of the reporting Power Control, Encryption and Integrity protection #12 39 RLC Layer The RLC layer offers the following services to the higher layers: Layer 2 connection establishment/release Transparent data transfer, i.e., no protocol overhead is appended to the information unit received from the higher layer Assured and un assured data transfer The RLC layer comprises the following functions: Segmentation and assembly Transfer of user data Error correction by means of retransmission optimized for the WCDMA physical layer Sequence integrity-in sequence delivery (used by at least the control plane) Duplicate detection Flow control Ciphering Encryption of user and signaling traffic over air interface SIM provides key information Terminates at the RNC #12 40

21 RLC Layer-Modes Transparent-TM No header attached SAR SDU discard Delete SDU if not sent before timer expires Used for Voice Some signaling Unacknowledged (UM) Header with Seq number SAR Pad SDU discard Provides some reliability Acknowledged Mode (AM) Siding window-arq Selective repeat #12 41 RLC Layer From, Juan J. Alcaraz, Fernando Cerdan, and Joan García-Haro, Optimizing TCP and RLC Interaction in the UMTS Radio Access Network, IEEE Network March/April 2006 #12 42

22 UE-Call states Designed to Take advantage of bursty nature of data Save battery power Maintains logical session and tracks mobility when appropriate Releases dedicated resources to increase overall capacity Put UE to sleep the UE #12 43 UE-Call states From: #12 44

23 UE-Call states Idle mode No active session UE monitors Paging CH Sleeps between paging cycles From: #12 45 UE-Call states CELL_DCH state (Dedicated) A dedicated physical channel is allocated to the UE in uplink and downlink. The UE is known on cell level Dedicated transport channels, downlink and uplink (TDD) shared transport channels, and a combination of these transport channels can be used by the UE. Call types Circuit Switched always in this state Packet Switched in this state if transferring large volume of data Modified rom: #12 46

24 UE-Call states CELL_FACH state (Forward Access Ch) No dedicated physical channel is allocated to the UE. The UE continuously monitors a FACH in the downlink. The UE is assigned a default common or shared transport channel in the uplink (e.g. RACH) that it can use anytime according to the access procedure for that transport channel. The position of the UE is known by UTRAN on cell level according to the cell where the UE last made a cell update. Radio not put to sleep For packet switched sessions Modified rom: #12 47 Random Access RACH will carry SMS Short bursts of data in absence of dedicated channel UE sends a request on the RACH upstream Request uses a code (1 of 16 signature) from a predefined set- Access Services Class If Node B can demodulate and accepts the request then it sends a ACK downstream on the Acquisition Indicator Channel (AICH) for that signature UE Receives the ACK and waits three access slots and transmits data and control information #12 48

25 Random Access If request initially fails no ACK UE selects new code Increases the power and retransmits That is the UE persist in trying to transmit for a while UE gives up and then backoffs if: Runs out of codes or Runs out of power or Node B tells it to go away with a NACK #12 49 Packet Access-Concept At low loads use CELL_FACH state and transmit over RACH At high loads assign dedicated resources (channels) for packet transmission-cell-dch state #12 50

26 UE-Call states CELL_PCH state (Paging Ch) No dedicated physical channel is allocated to the UE. The UE selects a PCH with the algorithm, and uses DRX for monitoring the selected PCH via an associated PICH. No uplink activity is possible. Sleep between pages A logical session is still up The position of the UE is known by UTRAN on cell level according to the cell where the UE last made a cell update in CELL_FACH state. DRX= Discontinuous reception. The time between the transmission of successive paging indicator messages is the DRX cycle length. The DRX mode saves power. Modified rom: #12 51 UE-Call states URA_PCH State No dedicated channel is allocated to the UE. The UE selects a PCH with the algorithm, and uses DRX for monitoring the selected PCH via an associated PICH. No uplink activity is possible. The location of the UE is known on UTRAN Registration area (URA) level according to the URA assigned to the UE during the last URA update in CELL_FACH state. Similar to CELL_PCH state only location known at the URA level URA covers multiple cells Modified rom: #12 52

27 Power Control-PC Fast Closed Loop PC Inner Loop PC Feedback information. Uplink PC is used for near-far problem. Downlink PC is to ensure that there is enough power for mobiles at the cell edge. Two special cases for fast closed loop PC: Soft handover:- how to react to multiple power control commands from several sources. At the mobile, a power down command has higher priority over power up command. Compressed mode:- Large step size is used after a compressed frame to allow the power level to converge more quickly to the correct value after the break. #12 53 Power Control Open loop PC No feedback information. Make a rough estimate of the path loss by means of a downlink beacon signal. Provide a coarse initial power setting of the mobile at the beginning of a connection. Apply only prior to initiating the transmission on RACH or CPCH. #12 54

28 Packet Access in WCDMA Packet allocations performed in the RNC by the packet scheduler (PS) Time, code or power Bit rates Holding times Channel selection PS allocates traffic to specific channels Common Delectated RNC can decide when and how to send packets based on type of packet traffic, Conversational class -> real-time connection, performed between human users, really low delay, nearly symmetric, e.g., speech Streaming class -> real-time connection, transferring data as a steady and continuous, low delay, asymmetric, e.g., video Interactive class -> non-real-time packet data, response requested from other end-user, reasonable round-trip delay, e.g., Web browsing Background class -> non-real-time packet data, no immediate action expected, less sensitive to delivery time, e.g., RNC can assign a packet to a specific channel Modified from: P. Chong, #12 55 Packet Access in WCDMA Common channels - RACH in the uplink and FACH in the downlink One or few RACH or FACH per sector Low setup time No feedback channel -> no fast closed loop power control, no soft handover, use fixed power Poor link-level radio performance and generated more interference Suitable for small data amounts Common packet channels - CPCH in the uplink Bit rate can be high Support fast power control Suitable for small or medium data amounts Dedicated Channel - DCH in the uplink and downlink Use fast power control and soft handover Better link-level radio performance and less interference Longer setup time Up to 2 Mbps Suitable for large data amounts Not suitable for bursty data In case of changing bit rate in the downlink, the downlink orthogonal code is reserved according to maximum bit rate. From: P. Chong, #12 56

29 Packet Access in WCDMA In WCDMA packet scheduling algorithms can be done in two ways, in a time or code division manner. Time division scheduling one user is allocated a channel at a time (10 ms frame) all available capacity can be allocated to that user high data rate for a short period of time increase more users, each user has to wait longer Advantages of time division scheduling high bit rate required less energy per bit less interference shorter delay due to high bit rate Disadvantages high unused physical resources due to short transmission time and relatively long set up and release time high variations in the interference levels due to high bit rate and bursty traffic limited uplink range of high bit rate due to mobile s limited transmission power From: P. Chong, #12 57 Packet Access in WCDMA Code division scheduling many users are allocated the channels simultaneously the capacity is shared with all users low data rate for a long period of time increase more users, each user s bit rate is decreased Advantages resources are in full usage due to longer transmission time small variation in interference level longer uplink range due to lower bit rate Disadvantages longer transmission delay due to low bit rate high interference due to high energy per bit low total throughput From: P. Chong, #12 58

30 Packet Access in WCDMA Time division is normally used with shared channels and code division is normally used with dedicated channels. From: P. Chong, #12 59 Packet Access in WCDMA Transmission Power-based Scheduling The bit rate allocated to each packet data users could be based on required transmission power Users close to the BS requires less transmission power and can get a higher bit rate, whereas users at the cell edge could get lower bit rate Advantages minimize the average power sent per bit less interference increase the throughput Disadvantages accurate power estimation unfair resource allocation From: P. Chong, #12 60

31 HSDPA & Enhance Uplink HSDPA = High Speed Downlink Packet Access From: Stefan Parkvall, Eva Englund, Magnus Lundevall, and Johan Torsner, Evolving 3G Mobile Systems: Broadband and Broadcast Services in WCDMA, IEEE Communications Magazine, February 2006 #12 61 HSDPA & Enhance Uplink Remember it is better (more efficient) to have a large number of users sharing a single server This lead to a desire to have fast allocation of shared resources Downlink resources Transmit power (interference to other cells) Channelization code Uplink resources Interference at the BS Other fast mechanisms Fast scheduling Fast ARQ (hybrid ARQ) (this is in addition to the RLC AM) To be fast mechanisms must be close to the air interface HSDPA but the mechanisms in BS (Node B) not at the RNC #12 62

32 HSDPA & Enhance Uplink UTRAN Architecture with HSDPA and enhanced uplink From: Stefan Parkvall, Eva Englund, Magnus Lundevall, and Johan Torsner, Evolving 3G Mobile Systems: Broadband and Broadcast Services in WCDMA, IEEE Communications Magazine, February 2006 #12 63 HSDPA & Enhance Uplink Changes Removed Variable spreading factor Fast power control Added shorter radio frame enable quick response to changes new high-speed downlink channels High-speed Shared Channel HS-DSCH High-speed Shared Control Channel HS-SCCH High-speed Dedicated Phy Control Channel HS-DPCCH use of 16 QAM modulation in addition to QPSK modulation fixed spreading factor code multiplexing combined with time multiplexing fast link adaptation using adaptive modulation and coding (AMC) use of hybrid automatic-repeat-request (HARQ) incremental redundancy medium access control (MAC) scheduling function moved to Node-B (WCDMA packet scheduling was done in the RNC) From: Agilent, Applications note: Concepts of High Speed Downlink Packet Access: Bringing Increased Throughput and Efficiency to W-CDMA #12 64

33 HSDPA & Enhance Uplink Gain in Performance From: WCDMA Evolved: High Speed Downlink Packet Access Mechanisms and Capabilities, Alexander Wang #12 65 HSDPA Shared transmission mechanism Definition of a new channel High-speed downlink shared channel (HS-DSCH) The HS-DSCH is dynamically used to transmit to individual users Supports link adaptation, hybrid ARQ and scheduling Always associated with a DPCH Never in soft handover Fixed spread factor Mapped to one or several channelization codes An associated control channel is also defined High Speed- shared control channel (HS-SCCH) #12 66

34 HSDPA New frame structure Five subframes/w-cdma frame User data can be assigned on a subframe basis System can adjust in 2ms Each subframe is a transmission time interval (TTI) = 2ms * *From: Agilent, Applications note: Concepts of High Speed Downlink Packet Access: Bringing Increased Throughput and Efficiency to W-CDMA #12 67 HSDPA HS-DSCH structure both Code sharing and TDM Spread Factor = 16 fixed 15 different spreading codes UE can send on multiple codes in a TTI A difference with W-CDMA is that the shared resource is also in the time domain 10 out of 16 codes used by one user From: Stefan Parkvall, Eva Englund, Magnus Lundevall, and Johan Torsner, Evolving 3G Mobile Systems: Broadband and Broadcast Services in WCDMA, IEEE Communications Magazine, February 2006 #12 68

35 HSDPA Another view * Spreading Code *From: Agilent, Applications note: Concepts of High Speed Downlink Packet Access: Bringing Increased Throughput and Efficiency to W-CDMA #12 69 HSDPA Link Adaptation Remember the fast power control is commonly used to: Maintain constant Energy/Noise ratio Reduce effect of fading This is suitable for constant bit rate transmissions Here bit rate can change introducing delay, delay is ok Changing bit rate can also maintain constant Energy/Noise while keeping the tx power constant The is called link rate adaptation * Notes: Resources spectrum, time, power, here total BW used In DS total power limited my interference to other cells *From: WCDMA Evolved: High Speed Downlink Packet Access Mechanisms and Capabilities, Alexander Wang #12 70

36 HSDPA Bit rate changed by using QPSK (2 bits per symbol time) Or 16 QAM (4 bits per symbol time) Modulation selected every 2 ms Number of codes assigned selected every 2 ms (Bit rate/code) * # codes = bit rate Theoretical maximum Largest transport block = 27,952 bits in 2ms = 13.9Mb/s consumes most of cell s resources for one user 1 2 Mb/s closer to achievable under real conditions #12 71 HSDPA To assign a modulation and bit rate/code the BS (Node B) needs some link quality feed back from the UE Each UE regularly transmits Channel Quality Indicator (CQI) to the BS CQI comes from a CIR measurement and current Spreading Factor Configurable Can be every 2 ms CQI (0-30) each mapping into a modulation, SF, etc. Note the better UE s can ask for higher CQI s, e.g., a UE with interference suppression #12 72

37 HSDPA Scheduling The scheduler decides which user should get access to each TTI CQI provides input into a Scheduler Proportional Fair (PF) Scheduler can be used Implementation Specific #12 73 HSDPA Hybrid ARQ (HARQ) Uses incremental redundancy (IR) Note when UE close the BS the number of spreading codes limits rate not power, so likely receive first transmission At greater distances move from BS see more errors, IR will require additional transmission but not many. HARQ only retransmit upon an ACK or NACK #12 74

38 HSDPA From: Mohamad Assaad, Zeghlache Djamal TCP Performance Over UMTS-HSDPA Systems, CRC Press, 2007 #12 75 HSDPA Key concepts Shared Channel Transmission (via codes) Higher Order Modulation Short Transmission Time Interval (2 ms) Fast Hybrid ARQ with Soft Combining Fast Link Adaptation Fast Radio Channel Dependent Scheduling HSDPA has a theoretical maximum of 14 Mb/s. #12 76

39 Enhance Uplink (HSUPA) Enhanced dedicated channel (E-DCH) Needs power control for near-far problem so no higher order modulation can not trade off data rate for E/N Shared resource is CDMA interference at the BS (Node B) desire to maintain a target interference level at Node B Interference a fuction of UE SF data rate (higer rate more interference) UE transmission time HSUPA has a theoretical maximum of 5.76 Mb/s. #12 77 Enhance Uplink (HSUPA) A scheduler is used to control When each UE transmits What rate each UE transmits at Goal of the scheduler is to assign resource to those UEs with data to send BS (Node B) sends scheduling grants There are two types of grants: The Absolute Grants provide an absolute limitation of the maximum amount of UL resources the UE may use; The Relative Grants increase or decrease the resource limitation compared to the previously used value; #12 78

40 Enhance Uplink (HSUPA) Method 1 UE sends scheduling requests with Available Tx power UE buffer state Priority of buffered data (to provide QoS) BS knows via signaling Instantaneous interference level All requests»buffer size» Priority of waiting traffic Then determines which grants to sent #12 79 Enhance Uplink (HSUPA) Method 2 UE send a Happy Bit every 2 ms Node B sends a grant in the form of a proportion of power that maybe sent on the uplink This corresponds to a maximum date rate Adapted from: Nick Hallam-Baker, Challenges of the Evolving 3G Technology, #12 80

41 Enhance Uplink (HSUPA) This resource allocation scheme more efficient for bursty traffic allowing more liberal connection admission control. HARQ is also used on the uplink #12 81 References #12 Attar, R., et al., Evolution of cdma2000 cellular networks: multicarrier EV-DO. Communications Magazine, IEEE, (3): p Bhushan, N., et al., CDMA2000 1xEV-DO revision a: a physical layer and MAC layer overview. Communications Magazine, IEEE, (2): p Ekstrom, H., et al., Technical solutions for the 3G long-term evolution. Communications Magazine, IEEE, (3): p Guangyi, L., et al., Evolution map from TD-SCDMA to FuTURE B3G TDD. Communications Magazine, IEEE, (3): p Parkvall, S., et al., Evolving 3G mobile systems: broadband and broadcast services in WCDMA. Communications Magazine, IEEE, (2): p Sanjiv Nanda, K.B., Sarath Kumar,, Adaptation Techniques in Wireless Packet Data Services. IEEE Communications Magazine, 2000(1): p Sarikaya, B., Packet mode in wireless networks: overview of transition to third generation. Communications Magazine, IEEE, (9): p Yavuz, M., et al., VoIP over cdma2000 1xEV-DO revision A. Communications Magazine, IEEE, (2): p #12 82

42 References #12 Leon-Garcia & Widjaja: Communication Networks, McGraw Hill, pt M. D. Yacoub, Wireless Technology, Protocols, Standards, and Techniques, CRC Press, 2002 Geert Heijenk, wwwhome.cs.utwente.nl/~heijenk/mwn/slides/lecture- 5%206%20slides%20per%20page.pdf Juan J. Alcaraz, Fernando Cerdan, and Joan García-Haro, Optimizing TCP and RLC Interaction in the UMTS Radio Access Network, IEEE Network March/April P. Chong, Agilent, Applications note: Concepts of High Speed Downlink Packet Access: Bringing Increased Throughput and Efficiency to W-CDMA #12 83 References #12 Alexander Wang, WCDMA Evolved: High Speed Downlink Packet Access Mechanisms and Capabilities, Mohamad Assaad, Zeghlache Djamal TCP Performance Over UMTS-Hsdpa Systems, CRC Press, 2007 HSUPA Enhanced Uplink DCH(HSUPA), Nick Hallam-Baker, Challenges of the Evolving 3G Technology, 6/0406challenges.asp #12 84