Basics, Network Entry Procedures, and Bandwidth Request/Grand Mechanism for IEEE Std. 802.16

1
Basics, Network Entry Procedures, and Bandwidth
Request/Grand Mechanism for IEEE Std. 802.16

• Chen-Nien Tsai
• Institute of Computer Science and Information
  Engineering
• National Taipei University of Technology
• 2007.10.8

2
Outline

• A Brief Introduction to IEEE Std. 802.16.
• Overview of IEEE 802.16
• MAC/PHY Basics
• Network Entry and Initialization
• Bandwidth Request/Grand Mechanism
• Summary

3
Introduction to IEEE Std. 802.16

• The central aim of IEEE 802.16 technology is to
  support broadband access.
• Providing service at a rate of at least 1.544
  Mbps. (ITU definition)
• Broadband Wireless Access (BWA)
• Broadband extension of the wireless access
  concept.
• Wireless Broadband Access
• A wireless implementation of broadband access
  concepts.

4
Introduction to IEEE Std. 802.16

• IEEE Std. 802.16 is called the wirelessMAN
  standard for wireless metropolitan area networks.
  
• Supports networks that are about the size of a
  city.
• Not limited to urban applications.
• Some of the most likely applications are in rural
  areas.
• Replace last-mile.

5
Wireless Technologies
6
IEEE 802.16 Project Timeline
1999 2000 2001 2002 2003 2004
2005 2006 2007 2008
IEEE Std 802.16-2001 IEEE Std 802.16a IEEE Std
802.16c IEEE Std 802.16-2004 IEEE Std
802.16-2004/Cor1 IEEE P802.16-2004/Cor2 IEEE
P802.16Rev2 IEEE Std 802.16e (mobile) IEEE Std
802.16f (MIB) IEEE P802.16g (management) IEEE
P802.16h (coexistence mechanism) IEEE P802.16i
(management) IEEE P802.16j (multihop relay) IEEE
Std 802.16k-2007 IEEE P802.16m IEEE Std
802.16/Conf01 IEEE Std 802.16/Conf02 IEEE Std
802.16/Conf03 IEEE Std 802.16/Conf04 IEEE Std
802.16.2-2001 IEEE Std 802.16.2-2004
Completed
In progress
Superseded Standards
7
IEEE Standard Styles

• Amendment
• contains new material to be incorporated into an
  existing IEEE standard.
• Designated by a lowercase letter after the
  primary standard number.
• 802.16c, 802.16a. (amendment to 802.16-2001)
• Corrigendum
• allows corrections but prohibits new features.
• 802.16-2004/Cor1, 802.16-2004/Cor2.

8
IEEE Standard Styles

• Revision
• Base standard and its published amendments are
  editorially merged.
• 802.16-2004 (802.16-REVd), including 802.16-2001,
  802.16c, 802.16a.
• 802.16Rev2 (under development)

9
Overview of IEEE 802.16
10
IEEE 802.16

• Scope
• Specifies the air interface of fixed BWA systems.
• Including the medium access control (MAC) layer
  and multiple physical (PHY) layer specifications.
• Purpose
• Enables rapid worldwide deployment of
  cost-effective BWA products.
• Facilitates competition in broadband access by
  providing alternatives to wireline broadband
  access.

11
Basic Network Architecture
Wireless link
Core network
Wired link
Users
Base Station (BS)
SS
Subscribe Station (SS)
SS
12
BS and SS

• Base station (BS)
• A generalized equipment set providing
  connectivity, management, and control of the SS.
• Subscribed station (SS)
• A generalized equipment set providing
  connectivity between subscriber equipment and a
  BS.

13
Typical Deployment Scenarios
Mesh Node
14
Reference Model
15
Service-Specific Convergence Sublayer

• Functions
• Classification.
• Header suppression.
• Two CS specified
• ATM CS.
• Packet CS.

16
MAC Common Part Sublayer

• Functions
• System access.
• Bandwidth allocation.
• Call admission
• Connection management.
• Two operation modes
• Point-to-multipoint (PMP)
• Mesh

17
Security Sublayer

• Functions
• Authentication
• Secure key exchange
• Encryption

18
Physical Layer

• Four PHY specified
• WirelessMAN-SC PHY
• WirelessMAN-SCa PHY
• WirelessMAN-OFDM PHY
• WirelessMAN-OFDMA PHY

19
Physical Layer

• For 10-66 GHz (IEEE 802.16-2001)
• WirelessMAN-SC PHY
• Single-carrier modulation.
• For 2-11 GHz (IEEE 802.16a)
• WirelessMAN-SCa PHY
• Single-carrier modulation

20
Physical Layer

• For 2-11 GHz (IEEE 802.16a)
• WirelessMAN-OFDM PHY
• 256-carrier OFDM (orthogonal-frequency division
  multiplexing)
• Multiple access is provided through TDMA
  (time-division multiple access).
• WirelessMAN-OFDMA PHY
• 2048-carrier OFDM.
• Multiple access is provided by assigning a subset
  of the carriers to an individual receiver.

21
MAC/PHY Basics
22
MAC Support of PHY

• Several duplexing techniques are supported by the
  MAC.
• Time division duplexing (TDD)
• UL and DL transmission occur at different times
  and usually share the same frequency.
• Frequency division duplexing (FDD)
• UL and DL channels are located on separate
  frequencies.
• Full duplex
• Half duplex
• FDD or TDD?

23
Framing

• Each frame has a DL subframe and UL subframe.
• DL subframe begins with information necessary for
  frame synchronization and control.
• In the TDD case, the DL subframe comes first,
  followed by the UL subframe.
• In the FDD case, UL transmission occur
  concurrently with the DL frame.

24
TDD Frame Structure
PS (Physical slot) a unit of time for allocating
bandwidth. Rate symbol rate for SC and SCa PHY,
nominal sampling frequency for OFDM and OFDMA PHY.
25
FDD Bandwidth Allocation
26
TDD Downlink Subframe
Burst profile for DIUC 0 is well-known
Downlink Interval Usage Code is a code
identifying a particular burst profile
BW allocation and other channel information for
DL/UL
synchronization
27
Downlink transmission

• Preamble
• Synchronization and equalization.
• Frame control
• DL-MAP
• How and when the DL data are transmitted.
• UL-MAP
• How and when the UL data are transmitted.
• DCD/UCD
• Channel description for UL/DL

28
TDD Uplink Subframe
29
Uplink Transmission

• Three classes of bursts may be transmitted in a
  UL subframe
• Contention opportunities for initial ranging.
• Contention opportunities for BW requests.
• Contention-free periods assigned by BS to
  individual SSs.

30
Connections and Addressing

• Each SS has a unique 48-bit MAC address.
• It is used only during the initial ranging
  process or authentication process.
• Not carried in every MPDU.
• How to identify src. and dest.? ? CID
• 802.16 MAC is connection-oriented.
• Connection is a unidirectional mapping between BS
  and SS MAC peers.
• A connection identifier (CID) is a 16-bit value
  that identifies a connection.
• A maximum of 65535 connections are supported for
  each DL and UL.

31
Connection Types

• Basic connection
• Assigned to each SS after successful ranging.
• To transport delay-intolerant basic MAC messages.
• Identify the SS for managing per-SS functions.
  (BW grants in UL-MAP)
• Primary management connection
• Assigned to each SS after successful ranging.
• To transport delay-tolerant basic MAC messages.

32
Connection Types

• Secondary management connection
• Assigned to each managed SS during the
  registration process.
• To transport higher layer management messages
  (SNMP, TFTP, and DHCP).
• Transport connection
• Created and changed by Dynamic Service series
  messages (DSA, DSD, and DSC).
• To transport user data.

33
MAC Management Messages
34
Connection Identifiers

• Initial Ranging CID.
• Basic CID.
• Primary Management CID.
• Secondary Management CID.
• Transport CID.
• AAS Initial Ranging CID.
• Multicast Polling CID.
• Padding CID.
• Broadcast CID.

35
Well-known Addresses and Identifiers
m is the maximum possible number of SSs that can
be supported
36
MAC Headers

• Stand-alone MAC header
• 6 bytes.
• The smallest possible information unit that can
  be transported between two nodes. (with the
  exception of HARQ MAPs)
• None of the stand-alone headers can be used to
  encapsulate any payload.
• It is a misnomer to call them headers.
• BW request header and signaling header (defined
  in other std.) are stand-alone MAC headers.

37
BW Request Header Format
000 incremental BR 001 aggregate BR
Bandwidth request in bytes
Encryption Control
Header Check Sequence
38
MAC Headers

• Generic MAC header
• Followed by the optional variable-size payload.
• Payload may consist of
• MAC subheaders
• Management messages
• Special payload
• Padding

39
Generic MAC Header Format
CRC Indictor
Subheader type
Encryption Key Sequence
Header Check Sequence
40
MAC Subheaders

• For generic MAC header only

Type
Packing and Fragmentation subheaders are mutually
exclusive.
Mesh subheader
ARQ Feedback payload
Extended Type Indicate whether the Packing or Fragmentation Subheaders is extended.
Fragmentation subheader
Packing subheader
Downlink FAST-FEEDBACK allocation subheader Uplink Grant Management subheader
41
Network Entry and Initialization

• Once the SS has powered up, it begins the network
  entry and initialization process. After
  completing the steps of the process, the SS has
  all the addresses and parameters it need to
  communicate with the rest of the network.

42
Network Entry and Initialization

• The procedures for entering and registering a new
  SS or a new node to the network.
• The procedures described here apply only to PMP
  mode.

43
Phases

• Scanning and synchronization to the DL
• Obtain transmit parameters
• Initial ranging
• SS basic capability negotiation
• SS authorization and key exchange
• Registration
• Establish IP connectivity
• Establish time of day
• Transfer operational parameters
• Establish provisioned connections

Optional
44
Scanning and synchronization to the DL

• Achieve PHY synchronization
• Scan the possible channels of the downlink
  frequency band of operation until it finds a
  valid downlink signal.
• Then try to acquire the channel control
  parameters for the DL and the UL.
• How?

45
Obtain Transmit Parameters (1/4)

• Achieve MAC synchronization.
• The SS achieves MAC synchronization once it has
  received at least one DL-MAP message.
• Obtain downlink parameters
• Retrieve parameters from the DCD messages.
• DCD messages contain
• Frame duration, TTG size, RTG size, downlink
  center frequency, BS ID, and more.
• Downlink burst profiles.

46
Obtain Transmit Parameters (2/4)

• SS want to know when BS broadcasts channel
  parameters.
• SS can know it from DL-MAP.
• Note that DL-MAP is encoded with well-known
  parameters.
• SS want to know the downlink channel parameters.
• SS can know it from Downlink Channel Descriptor
  (DCD) Message.

47
Obtain Transmit Parameters (3/4)

• Obtain uplink parameters
• Retrieve parameters from the UCD messages.
• UCD messages contain
• Uplink center frequency, bandwidth request
  opportunity size, ranging request opportunity
  size, and other PHY specific parameters.
• Uplink burst profiles.
• Receive the UL-MAP
• So that SS can perform initial ranging.
• Initial ranging opportunities.

48
Obtain Transmit Parameters (4/4)

• Now SS know downlink channel parameters, then it
  want to know uplink channel parameters.
• SS can know it from Uplink Channel Descriptor
  (UCD) Message.
• The next question is when SS can send requests to
  perform following procedures.
• SS can know it from UL-MAP

49
Message Flows
BS
SS
Wireless channel
Send DL/UL-MAP
SS power on
Send UCD/DCD
Power on sequence complete
Send DL/UL-MAP
Send DL/UL-MAP
Send DCD
Establish PHY synchronization Wait for UCD
Send DL/UL-MAP
Obtain parameters for UL channel
Send UCD
Extract slot info for uplink Wait for
transmission opportunity to perform ranging
Send DL/UL-MAP
Send DL/UL-MAP
Start ranging process
50
Initial Ranging (1/3)

• What is ranging?
• Ranging is the process of acquiring the correct
  timing offset and power adjustments.
• RNG-REQ/RNG-RSP messages.
• Two types of ranging
• Initial ranging allow SS to join the network.
• Periodic ranging allow SS to adjust transmission
  parameters and maintain the quality of RF
  communication link.

51
Initial Ranging (2/3)

• Initial Ranging accomplishes the following
• The time advance of SS transmissions is adjusted
  to make the SS appear collocated with the BS.
• The transmission power of the SS is adjusted for
  optimal reception at the BS.
• The SS is allocated its Basic and Primary
  Management CIDs.

52
Initial Ranging (3/3)

• If two SS send there RNG-REQ in the same slot
  (opportunity)
• Collision.
• Call for Contention Resolution Algorithm.
• Binary exponential backoff is specified in the
  spec.

53
Basic Capability Negotiation

• SS informs BS of its basic capabilities by
  transmitting an SBC-REQ message with its
  capabilities set to on.
• BS responds with an SBC-RSP message with the
  intersection of SSs and BSs capabilities set to
  on.
• Capabilities includes
• Bandwidth allocation support, max. transmit
  power, current transmit power, modulation type
  support, and more.

54
Authorization and Key Exchange

• Perform authorization and key exchange
  procedures.
• Details are skipped.

55
Registration

• The process by which SS is allowed entry into the
  network.
• SS sends a REG-REQ message to BS.
• BS responds with a REG-RSP message.
• The SS is allocated its Secondary management CID
  if the SS is managed.
• Also negotiate the version of IP and the QoS
  parameters for the secondary management
  connection.

56
Establish IP connectivity

• SS and BS shall negotiate IP version during
  REG-REQ/RSP exchange if the SS is managed.
• After registration, SS shall invoke DHCP
  mechanisms in order to obtain an IP address and
  any other parameters needed to establish IP
  connectivity.

57
Establish Time of Day

• That the SS and BS have the current date and time
  is required for time-stamping logged events by
  the management system.
• The protocol by which the time of day shall be
  retrieved is defined in IETF RFC 868 (Time
  protocol).

58
Transfer Operation Parameters

• If the SS has a configuration file, the name is
  indicated in DHCP response.
• SS shall download the configuration file using
  TFTP (Trivial File Transfer Protocol).
• SS notify the BS by transmitting a TFTP-CPLT
  message when the file download has completed
  successfully.
• BS responds a TFTP-RSP message.

59
Establish Provisioned Connections

• In the case of a managed SS
• The reception of the TFTP-CPLT message triggers
  the BS to start connection setup.
• In the case of a unmanaged SS
• The successful completion of registration serves
  as the trigger.
• Both are BS-initiated.
• After at least one service flow has been
  activated, the SS is capable of sending and
  receiving user data.

60
Dynamic Service Establishment

• BS-initiated

61
Dynamic Service Establishment

• SS-initialed DSA
• The standard does not go into details on what
  actually triggers the DSA.
• Triggering is just assumed to happen, stimulated
  by the upper layers when needed.

This allows BS to take it time determining
whether to admin the service flow
62
Bandwidth Request/Grand Mechanism

• The BW request/grand mechanism for the IEEE
  802.16 standard was chosen to be efficient,
  low-latency, and flexible.

63
Requests

• The mechanism that SS use to indicate to the BS
  that they need uplink bandwidth allocation.
• Requests are made on a per-connection basis.
• Grants are made to the SS (Basic CID), not to the
  connection.
• No explicit acknowledgments of requests.

64
Requests (1/2)

• Contention-based bandwidth requests.
• Transmit during contention period.
• Broadcast polling.
• Multicast group polling.
• Focused contention transmission. (OFDM PHY)
• CDMA-based bandwidth requests. (OFDMA PHY)
• Contention-free bandwidth requests.
• Unicast polling.
• PM bit.

65
Requests (2/2)

• Bandwidth stealing
• SS uses a portion of allocated BW for a
  connection to send another BW requests rather
  than sending data.
• Piggyback Request
• The bandwidth request is piggybacked onto a MAC
  PDU on an existing connection with allocated BW.

66
Grants

• GPC mode
• Grand Per Connection mode.
• Only optionally allowed in IEEE Std 802.16-2001.
• No longer specified in IEEE Std 802.16-2004.
• GPSS mode
• Grand per Subscriber Station mode.
• Improves efficiency and latency. (smaller MAP)
• An addition scheduler is required to allocate the
  granted bandwidth in each SS.

67
The Problems

• The reality at the SS and the perception at the
  BS can get out of sync.
• BS does not hear a BW request.
• SS does not hear the allocation in the MAP.
• BS scheduler decides it does not have BW right
  now for the particular service.
• SS used BW for a purpose different from that
  originally requested. (e.g., bandwidth stealing)

68
Aggregate Requests

• BW request/grant mechanism is designed to be
  self-correcting.
• After a period, if the SS still needs BW for a
  service, it simply asks again.
• SS issues an aggregate request.
• To avoid BSs perception becoming further askew
  from reality by duplicate requests.
• An aggregate request tells BS that the current
  state of SSs queue for that service, allowing BS
  to reset its perception of that services needs.

69
Incremental Requests

• There is a chance that a repeated aggregate
  request crosses the grant for that same bandwidth
  in the same frame.
• It can cause wasted allocations to the SS.
• It can be easily avoided by adding the concept of
  incremental requests.
• BS just add this BW requests to it current
  perception of the BW needs for that service.

70
Incremental or Aggregate?

• In general, the airlink should be reliable.
• Therefore
• Most BW requests typically would be incremental.
• Only periodic aggregate requests to ensure BS
  does not deviate too far from reality.

71
Other BW Request Options.

• SI (Slip Indicator) bit.
• SS can set this bit, requesting BS to slightly
  increase the rate at which it automatically
  allocates BW to SS. (up to 1 additional BW)
• PM (Poll Me) bit.
• SS can set this bit, indicating it has a BW need
  on another connection.
• When BS sees the PM bit set, it knows the SS
  needs to make a BW request and may poll it
  immediately.

72
Usage Rules
Service Type Polling Contention Requests PiggyBack Requests Bandwidth Stealing
UGS PM bit Not allowed Not allowed Not allowed
rtPS Unicast Not allowed Allowed Allowed
nrtPS All Allowed Allowed Allowed
BE All Allowed Allowed Allowed
73
Summary

• MAC/PHY Basics
• Frame structure
• Connections Types
• Header formats
• Network Entry Procedures
• After completing the procedures, SS can
  communicate with the network.
• Bandwidth Request/Grand Mechanism
• Contention-based bandwidth requests
• Contention-free bandwidth requests

74
Summary

• More about IEEE 802.16
• QoS
• Scheduling
• Mesh mode
• PHY details

75
References

• 1 IEE Std 802.16-2004, IEEE Standard for Local
  and Metropolitan Area NetworksPart 16 Air
  Interface for Fixed Broadband Wireless Access.
• 2 Carl Eklund et al., WirelessMAN Inside the
  IEEE 802.16 Standard for Wireless Metropolitan
  Area Networks, IEEE Press, 2006.
• 3 http//www.ieee802.org/16/.

76
The End
77
Backup Materials
78
Duplexing

• Duplexing defines how bidirectional communication
  is achieved between two devices or between a BS
  and a set of client devices in a PMP system.
• Frequency Division Duplexing (FDD)
• Time Division Duplexing (TDD)
• Half-duplex transmit or receive but not both
  simultaneously.
• Full-duplex transmit and receive simultaneously.

79
Multiplexing

• Refers to a mechanism in which a single device
  transmits to multiple devices on a single
  channel.
• Frequency Division Multiplexing (FDM)
• The transmitting device divides the time domain
  into multiple slots to communicate with multiple
  devices.
• Time Division Multiplexing (TDM)
• The transmitting device uses different
  frequencies to communicate with multiple devices.
• Orthogonal FDM (OFDM)?

80
Multiple Access

• Refers to the way that multiple devices access
  the medium, regardless of whether the
  communication is many-to-one or many-to-many.
• Time Division Multiple Access (TDMA)
• Frequency Division Multiple Access (FDMA)
• Orthogonal FDMA (OFDMA)
• Code Division Multiple Access (CDMA)

81
Message Formats

• ???????

82
Downlink Channel Descriptor Message

• Define the characteristics of a DL physical
  channel.

83
DCD Channel Encoding (partial)
84
SC Downlink_Burst_Profile
85
DCD Burst Profile Encodings SC (partial)
86
DIUC Allocation SC
87
Uplink Channel Descriptor Message

• Define the characteristics of a UL physical
  channel.

88
UCD Channel Encoding (partial)
89
SC Uplink_Burst_Profile
90
UCD Burst Profile Encodings SC (partial)
91
UIUC Allocation SC
92
DL-MAP Message
93
SC DL-MAP IE
94
UL-MAP Message
95
SC UL-MAP IE
96
RNG-REQ and RNG-RSP
97
SBC/REQ and SBC-RSP
98
REG-REQ and REG-RSP
99
DSA-REQ and DSA-RSP
100
DSA-ACK
101
Service Flow Encodings
102
Grant Management Subheader
103
FDD or TDD?
104
Advantages of FDD Systems

• Continuous UL and DL Transmissions.
• Reduce delay for MAC, ARQ, and channel
  information feedback.
• Higher Immunity to System Interference.
• Due to a large guard band.
• BS-to-BS and SS-to-SS (or MS-to-MS) interference
  are generally negligible.
• Note that there are still interferences between
  BS and MS.

105
Issues and Challenges of FDD Systems

• Feedback Required for CSIT Acquisition.
• CSIT Channel State Information at the
  Transmitter.
• UL and DL channels are generally uncorrelated, so
  the quality of CSIT will degrade.
• Inflexible Traffic Allocation.
• Data traffic and Internet service have more
  variation in traffic symmetry.
• It would be desirable if the system could
  allocate bandwidth dynamically with regard to
  traffic demand.

106
Issues and Challenges of FDD Systems

• Restrictive Band Allocation.
• FDD systems require a pair of frequency channels,
  it makes the FDD systems harder to fit into the
  scarce resource of spectrum.
• Guard Band.
• It represents a waste of resource.
• Higher Hardware Cost.
• Requires a separate oscillator of different
  frequency, an expensive duplexer, and a sharp RF
  filter.

107
Advantages of TDD Systems

• Channel Reciprocity.
• Channel state information at the receiver
  provides CSIT.
• Better CSIT quality.
• Dynamic Traffic Allocation/Traffic Asymmetry.
• Can distribute the bandwidth between UL and DL
  easily by altering their subframe durations.

108
Advantages of TDD Systems

• Higher Frequency Diversity.
• Diversity is a well-known technique to enhance
  the system reliability in fading channels.
• DL and UL signals have wider bandwidth, which
  corresponds to an increase in frequency
  diversity.
• Unpaired Band Allocation.
• Only one single contiguous channel is needed.
• Lower Hardware Cost.
• The sharing of a single oscillator and the
  absence of a duplexer.

109
Issues and Challenges of TDD Systems

• Guard Time between DL/UL Transitions.
• Reduces the efficiency of the system.
• Duplexing Delay in MAC and ARQ.
• The traffic in both directions is discontinuous,
  and there is a delay between consecutive UL/DL
  subframes, called the duplexing delay.
• Outdated CSIT.
• The estimated CSIT may be outdated due to
  duplexing delay.

110
Issues and Challenges of TDD Systems

• Cross-Slot Interference.
• This interference arises when neighboring TDD BSs
  either have different traffic symmetries or do
  not synchronize their frames.
• A major challenge in TDD systems.
• Interoperator Interference.
• Different operators neither coordinate in network
  planning nor synchronize their frames and traffic
  asymmetry.
• Would cause strong adjacent channel interference.

111
FDD or TDD?

• TDD has received significant attention because
• Traffic asymmetry of high-bit-rate multimedia
  application.
• The flexibility of unpaired spectrum.
• To alleviate cross-slot interference, the
  employment of sectored antennas and time slot
  grouping are very effective.

112
FDD or TDD

• More detailed discussion can be found in
• Petwer W. C. Chan et al., The Evolution Path of
  4G Networks FDD or TDD, IEEE Communications
  Magazine, vol. 44, issue 12, Dec. 2006, pp. 42-50.

113
Review of the OFDM System

• OFDM stands for Orthogonal Frequency Division
  Multiplexing.
• It was proposed in mid-1960s and used in several
  high-frequency military system.
• It is a multicarrier transmission technique.
• Divides the available spectrum into many
  subcarriers, each one being modulated by a low
  data rate stream.

114
Single carrier and Multicarrier Transmission

• Single carrier transmission
• Each user transmits and receives data stream with
  only one carrier at any time.
• Multicarrier transmission
• A user can employ a number of carriers to
  transmit data simultaneously.

115
Single carrier and Multicarrier Transmission
Single carrier transmission
Multicarrier transmission
N oscillators are required
116
(No Transcript)
117
Service Classes

• UGS (Unsolicited Grant Service)
• rtPS (Real-Time Polling Service)
• nrtPS (Non-Real-Time Polling Service)
• BE (Best Effort)