Specific Systems Wi-Max IEEE 802.16 #11 Victor S. Frost Dan F. Servey Distinguished Professor Electrical Engineering and Computer Science University of Kansas 2335 Irving Hill Dr. Lawrence, Kansas 66045 Phone: (785) 864-4833 FAX:(785) 864-7789 e-mail: frost@eecs.ku.edu http://www.ittc.ku.edu/ All material copyright 2006 Victor S. Frost, All Rights Reserved #11 1 Aug. 2005

Outline Motivation for IEEE 802.16 Applications Services and QoS Architecture Initialization Phy Layer MAC Packet formats Access protocol QoS support Evolution #11 2

Motivation for IEEE 802.16 Provide all aspect of a wireless MAN Alternative access technology in competition with, cable, fiber and DSL Higher carrier frequencies (10 to 66 GHz) to support higher data rates Expectations Cost Lower installation cost Higher equipment cost Reduced deployment time Ubiquitous coverage #11 3

From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: Overview of IEEE 802.16 Point-to-Multipoint Metropolitan Area Network Connection-oriented Supports difficult user environments High bandwidth, hundreds of users per channel Continuous and burst traffic – Very efficient use of spectrum Balances between stability of contentionless and efficiency of contention-based operation Flexible QoS offerings Supports multiple 802.16 PHYs Protocol-Independent core (ATM, IP, Ethernet, …) From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 4

IEEE 206.16 Protocol Architecture Convergence layer: Maps upper layer packets into MAC frames May fragment to gain efficiency Protocol-Independent core Modified from: W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition #11 5

From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 6

Services Support multiple services, e.g., TDM Voice VoIP Digital TV IP Bridged LAN Backhaul: Cell tower to switch replacing costly land lines #11 7

QoS Requirements From: W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition #11 8

IEEE 802.16 System Reference Points * Assumptions The subscriber stations (SS) are fixed Base stations are fixed (later version may allow mobility, i.e., IEEE 802.16e) High data rates in BOTH upstream and downstream directions Base station maybe heavily loaded Needs to be spectral efficient * From: W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition #11 9

Connections IEEE 802.16 MAC is connection-oriented. Provides Each service mapped to a connection A mechanism for requesting bandwidth, associating QoS and traffic parameters, transporting Routing data to the appropriate convergence sublayer, Other actions associated with the contractual terms of the service. Connection ID (CID)16 bit field Like virtual circuits Each SS has a standard 48 bit MAC address Equipment ID #11 10

Initialization Channel Acquisition SS scans its frequency list to find an operating channel (may be configured with a specific BS ID to look for) The SS synchronizes to the downstream transmission by detecting the periodic frame preamble The downstream periodically transmits its modulation and FEC schemes using Downlink Channel Descriptor (DCD) and Uplink Channel Descriptor (UCD) messages DCD and UDC are transmitted most robust (least efficient burst profile) #11 11

Initialization Ranging MAP messages are used to define the usage of channel DL-MAP downlink MAP UL-MAP uplink MAP SS scans the UP-MAP for opportunities to send a ranging messages SS selects a ranging time slot using a truncated exponential backoff algorithm (like in DOCSIS) Send ranging message (RNG-REQ message) with minimum power If no response increase power and tx again Success of the ranging message at the BS allows for the BS to send the SS Time synchronization information Power adjustment information Basic Channel ID (CID) Primary Management CID SS reports to BS PHY capabilities and BS can accept or deny any capability The above process is repeated to maintain the radio link (Radio link control-RLC) #11 12

Initialization SS Authentication and Registration IP connectivity Determine if SS can join the network If authorized then SS registers with the network IP connectivity Uses DHCP to get IP address And address of TFTP server to to obtain configuration files. #11 13

Initialization Connection set up Privacy and Security Associations Service flows define unidirectional transport Each service flow is mapped to a CID on a specific MAC address Service flows usually are set up by the BS during initialization, like permanent virtual circuits (PVCs) CID can be setup on demand, like a switched virtual circuit (SVCs) using a signaling protocol. Initially each SS sets up three management connections in each directsion Basic for short time critical MAC and RLC messages Primary for larger delay insensitive messages, eg., for authentication Secondary for management, SNMP, TFTP, and DHCP Privacy and Security Associations #11 14

Summary Initialization From: Govindan Nair, et. al., “IEEE 802.16 Medium Access Control and Service Provisioning”, Intel Technology Journal, Volume 08 Issue 03, August 20, 2004 ISSN 1535-864X #11 15

RLC Adaptation As Part of the MAC the RLC continues to adapt the uplink and downlink burst profiles to trade: Robustness Efficiency BS controls all burst profiles Control of uplink burst profile BS receives uplink messages BS can measure uplink quality BS specifies burst profile when granting access #11 16

RLC Adaptation Control of downlink burst profile SS receives downlink transmissions SS measures downlink quality Problem: SS must communicate appropriate burst profile to BS Note SS is required to receive more robust segments of the downlink transmission in addition to the negotiated burst profile Change messages must get through and acknowledged #11 17

RLC Adaptation Transition to a more robust burst profile. Transition to a less robust burst profile. From: Carl Eklund,, et., al., “IEEE Standard 802.16:A Technical Overview of the WirelessMAN™ Air Interface for Broadband Wireless Access,” IEEE Communications Magazine • June 2002 #11 18

Physical Layer Summary Designation Applicability MAC Duplexing WirelessMAN-SC 10-66 GHz Licensed Basic TDD, FDD, HFDD 2-11 GHz Licensed Basic, (ARQ), (STC), (AAS) TDD, FDD WirelessMAN-OFDM 2-11 GHz License-exempt Basic, (ARQ), (STC), (DFS), (MSH), (AAS) TDD WirelessMAN-OFDMA AAS= Adpative Antenna System STC= Space time coding MSH= Mesh DFS = Dynamic Frequency Selection #11 19

Physical Layer Upstream transmission Downstream Channel Bandwidth TDD or FDD Demand Assignment Multiple Access Downstream Continuous mode Burst mode Capability to dynamically change modulation and FEC Channel Bandwidth 20 or 25 MHz (US) 28 MHz (Europe) Frames 0.5, 1 or 2 ms Adaptive burst profile; changing modulation FEC #11 20

General Downlink Frame Structure DL MAP contains the changes in burst profile, i.e., modulation and FEC Downlink data is transmitted to each SS according to a negotiated burst profile Data is transmitted in the TDM part in order of decreasing robustness There maybe a mixture of burst profiles that vary frame to frame SS listen to all parts of the downlink frame they are capable or receiving * Downlink Interval Usage Code (DIUC) indicates burst profile * From: Carl Eklund,, et., al., “IEEE Standard 802.16:A Technical Overview of the WirelessMAN™ Air Interface for Broadband Wireless Access,” IEEE Communications Magazine • June 2002 #11 21 Aug. 2005

Downlink transmissions Two kinds of bursts: TDM and TDMA All bursts are identified by a DIUC Downlink Interval Usage Code TDMA bursts have resync preamble allows for more flexible scheduling Each terminal listens to all bursts at its operational IUC, or at a more robust one, except when told to transmit Each burst may contain data for several terminals SS must recognize the PDUs with known CIDs DL-MAP message signals downlink usage From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 22

Downlink Channel Descriptor Used for advertising downlink burst profiles Burst profile of DL broadcast channel is well known All others are acquired Burst profiles can be changed on the fly without interrupting the service Not intended as 'super-adaptive' modulation Establishes association between DIUC and actual PHY parameters From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 23

General Uplink Frame Structure UL-MAP grants BW to specific SS SS transmit bursts as defined in the UIUC SS tx their assigned allocations in the UIUC Uplink subframe uses DOCSIS like contention for transmission in contention slots Burst profiles can be changed dynamically SS transition gap are guard times * Uplink Interval Usage Code (UIUC) indicates burst profile * From: Carl Eklund,, et., al., “IEEE Standard 802.16:A Technical Overview of the WirelessMAN™ Air Interface for Broadband Wireless Access,” IEEE Communications Magazine • June 2002 #11 24 Aug. 2005

Uplink Transmissions Uplink Invited transmissions Transmissions in contention slots Bandwidth requests Contention resolved using truncated exponential backoff Transmissions in initial ranging slots RNG-REQ Bursts defined by UIUCs Transmissions allocated by the UL-MAP message All transmissions have synchronization preamble Ideally, all data from a single SS is concatenated into a single PHY burst a single PHY burst From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 25

Uplink Channel Descriptor Defines uplink burst profiles Sent regularly All Uplink Burst profiles are acquired Burst profiles can be changed on the fly Establishes association between UIUC and actual PHY parameters From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 26

From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: Uplink MAP Message UL-MAP message defines usage of the uplink Contains the "grants" Grants addressed to the SS Time given in mini-slots unit of uplink bandwidth allocation 2m physical slots in 10-66 GHz PHY, Time expressed as arrival time at BS From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 27

Uplink scheduling Uplink direction uses a schedule to allocate uplink capacity Uses a request-grant mechanism Specification of sechduling service is established at connection set up time. Scheduling services are based on DOCSIS #11 28

Class of uplink services Unsolicited Grant Service Real time Polling Service Non real time Polling Service Best Effort Like DOCSIS More later…. #11 29

PHY Frame-TDD example #11 30

MAC overview Uses Demand Assigned Multiple Access (DAMA) TDMA BS controls allocations of uplink bandwidth Unit of allocation is a mini-slot SS requests transmission opportunities on the uplink for a specific number of minislots on a contention basis Collisions on request messages are resolved using truncated binary exponential backoff algorithm BS collects requests and sends schedules on the downlink via an allocation map #11 31

From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: MAC PDU Transmission MAC PDUs are transmitted in PHY bursts A single PHY burst can contain multiple Concatenated Concatenated MAC MAC The PHY burst can contain multiple FEC blocks MAC PDUs may span FEC block boundaries The convergence layer between the MAC and the PHY allows for capturing the start of the next MAC PDU in case of erroneous FEC blocks From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 32

From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: MAC PDU Transmission PDU = Data exchanged between peer entities SDU = Data exchanged between adjunct layers From: R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf #11 33

MAC Frame Format MAC header formats Header format drives functionality * MAC header formats Generic downlink Generic uplink Bandwidth request Header format drives functionality Caution: details of fields have changed * From: W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition #11 34

Generic downlink header * EC-Encryption control EKS-Encryption control sequence, vector of key HT-Header type generic or bw req ARQ-indictor for link ARQ. IF ARQ the 2 bytes at start of frame use for ARQ process FC-Fragment control FSN- Fragment seq # HCS-Header check sequence. Only covers header * From: W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition #11 35

Generic uplink header Added 8 bit grant management field- three types USG SI-Slip indicator, reports to BS that SS’s queue is backlogged so BS can take action to resolve PM-Poll me Grants per interval # grants required by connection Piggy-pack request number of bytes requested USG with activity detection Can switch to USG when there is activity Suited for VoIP with speech detection UGS-AD starts as rtPS flow Detects VoIP do BW req to go to UGS Upon end of VoIP use BW req with 0 Bytes to go back to rtPS flow Piggyback request (because not use separate bw request message) * From: W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition #11 36

Bandwidth request header * 15 bits used to request transmissions of a number of bytes * From: W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition #11 37

Services Unsolicited grant service (UGS) Transport fixed data periodically No explicit BW requests Limit on jitter = one frame time Provides guarantees on throughput, latency, jitter Not allowed to use random access opportunities Targeted for T1/E1 over ATM ATM CBR Buffer build up Not expected for CBR, but Grants may be lost Clock skew between the 802.16 net and the backbone may Result backlog at SS To recover use the poll-me and slit indicators #11 38

Services Real-time polling service-rtPS Target services that are bursty but offers periodic dedicated request opportunities to meet real-time requirements. Does not use contention process to request bandwidth, used explicit MAC message Variable packet size Requests imply increased latency and overhead Suitable for VoIP with silence detection MPEG Video This is like rt-VBR ATM Provides guarantee on throughput Little less focus on latency. #11 39

Services Non-real-time Polling Services (nrtPS) Best Effort Provides guarantee on throughput, Suitable for non real time services that have variable data size, e. g., e-mail. Like rt-polling except but polls are less frequently Allowed to use contention requests May use Grant Management sub-header to request BW New request can be piggybacked with each new request can be piggybacked with each transmitted PDU Best Effort Provides no guarantees Can request bandwidth using contention or explicit processes #11 40

Classes of SS An SS can have one for more connections Grant per connection (GPC) class Bandwidth is granted explicitly for each connection SS needs to track each connection thus more complex Less flexible Less scaleable, more state to track Less efficient, because not as much sharing #11 41

Classes of SS Grant per SS (GPSS) Grants given to all connections on an SS as an aggregate GPSS SS needs to manage all the traffic thus the QoS for different applications Can react more quickly to changes #11 42

Protocols for grants Grants can be lost because: Errors cause the BS not to receive request Errors cause the grant involved in collision Errors cause the SS not to receive grant Bandwidth not provided because: Not enough available downstream bandwidth GPSS stole the bandwidth for other purpose #11 43

Protocols for grants How to deal with lost grants or unsatisfied grants? ARQ like protocol  not used because takes too much time A self correcting protocol is used. Note requests are usually incremental that is a change from current allocation. Set timer suitable for QoS If timer fires, SS requests again But the perception of current allocated BW at the BS may not track right because an incremental request is lost Solution: Occasionally send aggregate bandwidth requirement of SS, resets perception of current allocated BW to SS #11 44

References Eklund, C., et al., IEEE standard 802.16: a technical overview of the WirelessMAN air interface for broadband wireless access. Communications Magazine, IEEE, 2002. 40(6): p. 98-107. Ghosh, A., et al., Broadband wireless access with WiMax/802.16: current performance benchmarks and future potential. Communications Magazine, IEEE, 2005. 43(2): p. 129-136. Nair, G., et al., IEEE 802.16 Medium Access Control and Service Provisioning. Intel Technology Journal, 2004. 08(03): p. 213-228. Ramachandran, S., C.W. Bostian, and S.F. Midkiff, Performance evaluation of IEEE 802.16 for broadband wireless access. R. Marks, “The 802.16 WirelessMAN WirelessMAN MAC: MAC: It’s Done, but What Is It?” www.ieee802.org/16/docs/01/80216-01_58r1.pdf W. Stallings Wireless Communications and Networks, Prentice Hall, Second Edition, 2005 #11 45

References #11 46