Fundamentals of Wimax


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A presentation by IEEE Wireless MAN and Wimax Forum for understanding the Wimax technology

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Fundamentals of Wimax

  1. 1. IEEE Standard 802.16: A Technical Overview of the Mobile WiMAX Air Interface and BeyondEyal Verbin
  2. 2. Contents 1. Overview of WiMAX • Quality of Service • Background on IEEE 802.16 and WiMAX • Scheduling • Salient Features of WiMAX • Adaptive Modulation and Coding 2. Physical Layer • Security • Network Entry Procedures • The Broadband Wireless Channel • Power saving Modes • OFDM Principles • Mobility Management • Channel Coding • Hybrid-ARQ 4. WiMAX Network Architecture • OFDM Symbol Structure • Network Reference Model • Frame Structure • Protocol Layering • Fractional Frequency Reuse • IP Address Assignment • Transmit Diversity and MIMO • Authentication and Security Architecture • Ranging • Quality of Service Architecture • Power Control • Mobility Management • Channel Quality Measurements • Paging 3. Medium Access Control Layer • Convergence Sublayer • MAC PDU Construction and Transmission • Bandwidth Request and Allocation • ARQ
  3. 3. Background on IEEE 802.16 and WiMAX  Air interface is based on IEEE 802.16-2009  IEEE 802.16 was formed in 1998 to develop LOS point to multipoint for operation in the 10GHz – 66GHz band  The original 802.16 standard was based on single carrier  Many of the MAC concepts were adopted from the cable modem DOCSIS  In December 2005 IEEE 802.16e-2005 was approved as a standard for mobile wireless system, which forms the basis for Mobile WiMAX and adopts multi carrier technology  WiMAX forum used IEEE work to develop interoperable standard  For practical reasons a smaller set of design choices (profiles) were selected  System profile defines the subset of mandatory and optional PHY and MAC features  WiMAX forum also defines higher layers networking specifications
  4. 4. Salient Features of WiMAX (1) OFDM based physical layer  Enables good resistance to multipath and allows operation in NLOS conditions High peak data rates  Typically, using 10MHz spectrum using TDD scheme with 3:1 DL/UL split, the peak PHY data rate is about 25Mbps (DL) and 7Mbps (UL) Scalable bandwidth  FFT size may scale from 128 bit to 1024 bit FFT allowing channel bandwidths of 1.25MHz to 10MHz. Adaptive modulation and coding  WiMAX supports a number of modulation and channel coding schemes and allows the scheme to be changed on a per user and per frame basis Link layer retransmission  Auto retransmission requests (ARQ) are supported on top of physical layer error correction schemes to enable reliable data transmission Orthogonal frequency division multiple access (OFDMA)  Different users can be allocated with different subsets of the OFDM tones
  5. 5. Salient Features of WiMAX (2) Flexible and dynamic per user resource allocation  DL and UL resources and transmission schemes are controlled by the scheduler in the base station. Advance antenna techniques  Beamforming, space time coding and spatial multiplexing may be used to improve system capacity and spectral efficiency Quality of service support  Connection oriented architecture to support variety of applications, each with its own characteristics. Robust security  Strong encryption using Advance Encryption Standard (AES) and flexible authentication architecture based on Extensible Authentication Protocol (EAP) Support for mobility  Secure seamless handover for full mobility applications and various power saving mechanisms IP based architecture  Network architecture is based on an all IP platform. All end to end services are delivered over an IP architecture
  6. 6. Part IWiMAX Physical Layer
  7. 7. The Broadband Wireless Channel (1) The main challenge of broadband wireless system is the multipath propagation  Fast Fading: different reflection arrive at the receiver with different phases. The combined effect can be constructive or destructive, which causes very large observed difference in amplitude of the receive signal  Different symbols arrive at different time to the receiver, resulting in Inter Symbol Interference (ISI) Different approached for mitigation of fading:  Spread spectrum and rake receivers  Equalization  Multicarrier transmission
  8. 8. The Broadband Wireless Channel (2)
  9. 9. Open Loop MIMO in WiMAX (2) Spatial Multiplexing  Used to increase system capacity by exploiting the dispersive nature of the wireless channel  System capacity grows linearly with Min{NTx, NRx}  Spatial Multiplexing (MIMO Matrix B)  Multiple data streams are transmitted at the same time and in the same frequency from different BS antennas  Mandates multiple receive antennas at the MS  Assuming channels are uncorrelated, receiver can retrieve the data using decoding algorithm known as VBLAST  Collaborative Spatial Multiplexing (CSM)  Multiple data streams are transmitted at the same time and in the same frequency from different MS  Assuming channels are uncorrelated, BS can retrieve the data using the same Matrix B technique
  10. 10. OFDM Principles (1) Multicarrier transmission  Dividing high bit rate data stream into several parallel lower bit rate streams (subcarriers)  Minimize intersymbol interference (ISI) by making the symbol time substantial larger than the channel delay spread OFDM is a spectrally efficient version of multicarrier scheme  Subcarriers are orthogonal, so that guard bands between subcarriers is not required  Created using inverse discrete Fourier transform (IDFT) To completely eliminate ISI, guard intervals are inserted between consecutive OFDM symbols  The duration of the guard interval is a tradeoff between the delay spread that can be handled and the power loss associated with it. Size of FFT is chosen as a balance between protection against multipath, Doppler shift and design complexity.
  11. 11. OFDM Principles (2) Advantages  Robustness to channel delay spread  Reduced computational complexity  Exploitation of frequency diversity  Coding and interleaving the information across the subcarriers  Provides a flexible multiple access scheme  Resources are allocated in a frequency-time grid  Robustness against narrowband interference  Suitable for coherent demodulation using pilot based channel estimation Drawbacks  High peak to average ratio that causes non linearities and clipping distortion  Can be mitigated using digital pre-distortion techniques  Sensitivity to phase noise and frequency dispersion  Requires accurate frequency synchronization
  12. 12. Channel Coding Subcarrier Antenna #0 Mapping IFFT D/A and Pilot InsertionFrom MAC Space Channel Symbol Randomizer Interleaver Time Encoder Mapping Encoder Subcarrier Antenna #1 Mapping IFFT D/A and Pilot Insertion
  13. 13. Channel Coding Randomizer  Improves FEC performance and synchronization capabilities Channel Encoder  Convolution Code (CC)  Used for encoding of Frame Control Header (FCH)  Convolution Turbo Code (CTC)  Used for all transport and management connections  Repetition Code  Further increase signal margin over the modulation and FEC mechanisms  Applies only to QPSK modulation Interleaver  Improves FEC performance by ensuring that adjacent coded bits are mapped onto non adjacent subcarriers (frequency diversity) and that adjacent bits are alternately mapped to less and more significant bits of modulation constellation Symbol Mapping  QPSK  16QAM  64QAM (optional for UL)
  14. 14. Hybrid ARQ (1)  HARQ is an optional part of the PHY and can be enabled on a per connection basis.  HARQ renders performance improvements due to SNR gain and time diversity achieved by combining previously erroneously decoded sub packets and retransmitted sub packet.  Based on N ‘Stop and Wait’ mechanism  Transmitter waits for ACK/NACK before transmitting again  Multiple HARQ processes (channels) may be activated per connection to increase the rate  Operates at the FEC block level and combines PHY and MAC (Hybrid)  The FEC encoder is responsible for generating HARQ sub packets.  The sub packets are combined by the receiver FEC decoder as part of the decoding process.  The receiver combines the newly received burst with the formerly received bursts to enhance decoding performance.  Based on 16 bit CRC, the receiver replies with an ACK if the sub packet decoding succeeded and with a NACK if the decoding failed.
  15. 15. Hybrid ARQ (2)  ACK/NACK signaling  DL: Dedicated PHY layer ACK/NACK UL channel  Feedback is synchronized with the transmission, i.e. receiver provides feedback in a fixed delay relative to the transmission (default is one frame)  UL: ARQ ACK message.  Feedback is implicitly indicated through the UL allocation  Feedback is unsynchronized, i.e. receiver may provide feedback any time following the HARQ transmission  In order delivery  Due to the N ‘Stop and Wait’ scheme, out of order delivery of HARQ packets is possible.  Since some applications are sensitive to the delivery order, e.g. TCP, there is an option to guarantee in order delivery by using PDU SN subheaders.
  16. 16. Symbol Structure Frequency Domain Representation  Mobile WiMAX Profile includes support of 512 and 1024 FFT, depending on channel BW  512FFT: 3.5MHz, 5MHz  1024FFT: 7MHz, 8.75MHz, 10MHz  The guard interval used to prevent ISI is a cyclic prefix. This structure is needed to prevent Inter Carrier Interference (ICI) Time Domain Representation
  17. 17. OFDM Symbol Parameters Primitive parameter definitions  BW: Nominal channel bandwidth (e.g. 10MHz)  Nused : Number of used subcarriers (e.g. 840 for 10MHz)  Ndata: Number of data subcarriers (e.g. 720 for 10MHz)  n: Over sampling factor (e.g. 28/25 for 10MHz)  CP: Cyclic prefix, i.e. Tg/Tu (1/8) Derived parameter definitions  NFFT : Smallest power of two greater than Nused (e.g. 1024 for 10MHz)  Sampling Frequency Fs = nBW: (e.g. 11.2 MHz for 10MHz)  Subcarrier spacing ∆f=Fs/NFFT: (e.g. 10.9 KHz for 10MHz)  Useful symbol time Tu = 1/∆f: (e.g. 91.4 Sec 10MHz)  CP time Tg = CP∙Tu: (e.g. 11.4 Sec for 10MHz)  OFDMA symbol time Ts = Tg + Tu: (e.g. 102.9 Sec for 10MHz)
  18. 18. OFDM Spectral Efficiency Data Rate R  N data  bm  cr / Ts R N data bm cr n Spectral Efficiency Efficiency   BW (1  CP ) N FFT 5 DL Example (10 MHz, 64QAM 5/6) 35Mbps  720  6  /102.9 6  Spectral efficiency = 3.5 bit/sec/Hz
  19. 19. OFDM Symbol Structure: Terminology  Slot: Smallest allocation unit in the time-frequency domain. Consists of a single subchannel and of one to three OFDM symbols. Contains 48 data subcarriers  Data Region: A contiguous allocation of slots in the time- frequency domain  Subchannel Group: A single set of contiguous logical subchannels. Each logical subchannel is mapped to a set of physical subcarriers  Segment: One or more subchannel groups that are controlled by a single instance of BS MAC
  20. 20. Symbol Structure & Permutation  Permutation: The mapping of physical subcarriers to logical subchannels  Permutation Zone: A set of OFDM symbols over which the same permutation is used. A frame may contain one or more permutation zones  Two categories of permutations:  Distributed Permutation: Draws subcarriers pseudo randomly to form subchannel. Provides frequency diversity and inter cell interference averaging. Includes two permutations:  Contiguous Permutation: Groups a block of contiguous subcarriers to form a subchannel. Enables multi user diversity by choosing the subchannel with the best frequency response.  In general, distributed permutation perform well in mobile applications, while contiguous permutation are well suited for fixed or low mobility environments.
  21. 21. DL Partial Use of Subcarriers (PUSC) Symbol Structure  Used subcarriers are split into clusters of fourteen contiguous subcarriers.  Clusters are mapped to six major groups as a function of Cell ID and DL Permutation Base parameters  Three segments are created from the groups  Logical subchannels are created from a permutation of cluster pairs such that each group is made up of clusters that are distributed throughout the subcarriers space  Slot is one subchannel by two OFDM symbols. It contains 48 data subcarriers and eight pilot subcarriers
  22. 22. DL PUSC Symbol Structure Parameter 1024 FFT 512 FFT DC subcarriers 1 1 Guard subcarriers 183 91 Data subcarriers 720 360 Pilot subcarriers 120 60 Subcarriers per cluster 14 14 Clusters 60 30 Data subcarriers per slot 48 48 Subchannels 30 15
  23. 23. UL PUSC Symbol Structure  Subcarriers are split into groups of four consecutive physical subcarriers over three OFDM symbols. Each group is termed a tile  Six tiles generate a subchannel. Tiles are mapped to logical subchannels based on UL Permutation Base parameter  Slot is one subchannel by three OFDM symbols. It is comprised of 48 data subcarriers and 24 pilot subcarriers in 3 OFDM symbols  Pilot density is higher than DL since no preamble is available on the UL
  24. 24. OFDMA PHY: UL PUSC Symbol StructureParameter 1024 FFT 512 FFTDC subcarriers 1 1Guard subcarriers 183 103Used subcarriers 840 408Tiles 210 102Subcarriers per tile 4 4Data subcarriers per slot 48 48Subchannels 35 17Tiles per subchannels 6 6
  25. 25. Frame Structure (Time Division Duplex)  IEEE 802.16e PHY supports both FDD and TDD. Mobile WiMAX profiles currently available for TDD only  Each frame is divided into DL and UL sub frames separated by Transmit To receive Gap (TTG) and Receive to Transmit Gap (RTG)  Profiles define a finite set of possible DL/UL splits (UL varies between 25% and 45% of the frame)  Frame duration: 5msec  Subframe may be divided into multiple zones on OFDM symbol boundaries. Each Zone is characterized by a specific permutation mode and multiple antenna scheme
  26. 26. Preambles & Pilots The first symbol in the DL transmission used for synchronization and channel estimation. Preamble subcarriers are boosted BPSK modulated with a specific PN code To generate the preamble the PHY uses a series of 114 binary PN sequences. The sequence to be used is determined by the segment number and the Cell ID. It is mapped to every third subcarrier except the DC carrier. Enables MS to obtain signal measurements and extract Cell ID for multiple co- channel cells with a single reception of preamble No preambles are available on the UL (except for AAS zone). Channel estimation on the UL is derived from the pilots
  27. 27. DL Subframe (1) Multiplexing: OFDMA Preamble Time DL Burst #8 DL Burst #12  First symbol of the DL subframe FCH DL Burst #2 DL Burst #9 Frequency DL MAP DL Burst #1 (Cont’d) (UL MAP)  Used for time and frequency DL MAP DL Burst #3 DL Burst #10 DL Burst #13 DL Burst #11 synchronization, initial channel estimation, noise and interference DL Burst #14 Preamble estimation  Carries BS information (Cell ID and Not Allocated DL Burst #15 segment) Frame Control Header (FCH) DL Burst #16  Transmitted with QPSK ½ and Zone #1: PUSC 1/3 SISO Zone #2: PUSC 1/3 MIMO Zone #3: PUSC All MIMO repetition of four and occupies the first four subchannels of the segment  Indicates used subchannel groups (PUSC zone)  FEC scheme for the MAPS  MAPS are transmitted at QPSK ½ with FEC and repetition as indicated by FCH  Indicates MAP length
  28. 28. DL Subframe (2) DL MAP and UL MAP are broadcast messages carrying information elements (IE) Time DL Burst #8 DL Burst #12  IE defines the DL and UL bursts FCH DL Burst #2 DL Burst #9 Frequency  The scope of the DL MAP is the current frame DL MAP DL Burst #1 (Cont’d) (UL MAP) DL Burst #10 DL MAP DL Burst #13  The scope of the UL MAP is the next frame DL Burst #3 DL Burst #11 Standard DL IE includes:  Connection Identifier (CID) DL Burst #14 Preamble  Downlink Interval Usage Code (DIUC), which defines the MCS and the FEC used for the Not Allocated DL Burst #15 burst  Repetition coding indication DL Burst #16  Burst boundaries  Symbol offset (start of burst in time domain)  Subchannel offset (start of burst in frequency domain) Zone #1: PUSC 1/3 SISO Zone #2: PUSC 1/3 MIMO Zone #3: PUSC All MIMO  Number of symbols (burst duration in time domain)  Number of subchannels (burst duration in frequency domain)  Boosting (power boosting for the burst +6 dB to - 12 dB to provide DL power control)
  29. 29. UL Subframe Multiple Access: OFDMA Time No Preambles 3 Symbols 3 Symbols Perio Standard UL IE includes: Initial dic Frequency UL Burst #1 6 SC Ranging/HO Rang Ranging ing/ BWR CQICH 12 SC  Connection Identifier (CID) 6 SC ACK UL Burst #2  Uplink Interval Usage Code  Duration (in OFDMA slots) UL Burst #3  Repetition coding indication Dedicated Control Zones Not Allocated Not Allocated  UL Ranging Noise Burst 10 SC  Dedicated UL ranging subchannel  Used for BW requests as well Zone #1 Zone #2 Segmented PUSC Un-Segmented PUSC  Quality Information Channel  UL CQICH is allocated for the MS to feedback channel state information  UL ACK Channel  Allocated to feedback DL HARQ acknowledgement
  30. 30. Fractional Frequency Reuse (1) F1 Frequency reuse is defined as (C N S): F3  C - number of BS in the reuse cluster F1 F2  N - number of the channels (or channel group) F3 F2 F1  S - number of the sectors of each BS F3 Examples of classical frequency reuse schemes: (1x3x3) F2  Reuse 3: Marked as (1 3 3) and requires 3 frequency assignment F1  Reuse 1: Marked as (1 1 3) and requires one F1 frequency assignment F1 F1 F1 Segmentation F1 F1  PUSC symbol structure enables division of the F1 subcarriers into three segments and allows a reuse 3 (1x1x3) F1 scheme with a single channel assignment Reuse 1 scheme has higher capacity at the center F1 of the cell but is susceptible to interference at the F1 {Seg. 0} cell edge. F1 {Seg. 2} F1 {Seg. 0} {Seg. 1} F1 Reuse 3 scheme has lower capacity but provides a {Seg. 2} F1 F1 more reliable link at the cell edge {Seg. 1} F1 {Seg. 0} {Seg. 2} F1 (1x3x3) {Seg. 1}
  31. 31. Fractional Frequency Reuse (2)  Fractional Frequency Reuse (FFR): By exploiting the frequency – time grid structure of the OFDM frame it is possible to combine Reuse 1 and Reuse 3  FFR can be implemented in both time and frequency domain  Time domain FFR  Subframe is divided into two zones  R3 zone in which a single segment is allocated and subcarriers are boosted by 5dB  R1 zone in which all subcarriers are allocated  The zones boundary is static across the whole coverage area  Users are allocated dynamically to one of the zones based on their CINR reports
  32. 32. Frequency Reuse Parameters Selection  Cell ID  Each three sector BS is assigned with Cell ID (range: 0..31)  Should be unique among neighbors  Each sector in the BS is assigned with unique segment (range: 0..2)  The preamble index is calculated as 32*Segment + Cell ID  DL Permutation Base  Used to randomize pilot modulation and subcarrier permutation  If R1 is used, DL Permutation Base should be set to a unique value among neighbors (range: 0..31)  UL Permutation Base  Used to randomize pilot modulation and subcarrier permutation  If R1 is used, UL Permutation Base should be set to a unique value among neighbors (range: 0..127)  If R1 is not used  UL Permutation Base for neighbor BS with the same FA should be set with an offset of 35 (e.g. 0, 35, 70, 115)  UL Permutation Base the three sectors in the same BS should be set to the same value (to maintain orthogonality)
  33. 33. Multiple Antenna Techniques Open Loop MIMO (IO-MIMO)  Channel State Information (CSI) is not available at the transmitter  Space Time Block Coding (STBC) – Matrix A  Spatial Multiplexing – Matrix B  Collaborative UL MIMO (CSM) Closed Loop MIMO (IO-BF)  CSI is required at the transmitter, through feedback channels or reciprocity in TDD  Beamforming techniques
  34. 34. Open Loop MIMO (1) Diversity  Improves probability of the receiver to overcome fades.  Diversity order (d) = NTx x NRx  BER is proportional to CINR-d  Maximum Receive Ratio Combining (MRC)  Multiple receive paths are combined coherently  Space Time Block Code (STBC or Matrix A)  A single data stream is replicated and transmitted over two antennas  Redundant data is encoded using a mathematical algorithms known as STBC.  Receiver may combine this with MRC to increase diversity order
  35. 35. Open Loop MIMO (2) Spatial Multiplexing  Used to increase system capacity by exploiting the dispersive nature of the wireless channel  System capacity grows linearly with Min{NTx, NRx}  Spatial Multiplexing (MIMO Matrix B)  Multiple data streams are transmitted at the same time and in the same frequency from different BS antennas  Mandates multiple receive antennas at the MS  Assuming channels are uncorrelated, receiver can retrieve the data using decoding algorithm known as VBLAST  Collaborative Spatial Multiplexing (CSM)  Multiple data streams are transmitted at the same time and in the same frequency from different MS  Assuming channels are uncorrelated, BS can retrieve the data using the same Matrix B technique
  36. 36. Closed Loop MIMO Beamforming  Leverage arrays of transmit and receive antennas to control the directionality and shape of the radiation pattern.  Channel information is communicated from the MS to the BS using Uplink Sounding. Based on CSI, the BS utilizes signal processing techniques to calculate weights to be assigned to each transmitter controlling the phase and relative amplitude of the signal  Can be used for interference cancellation.  Can be used for both coverage and capacity enhancements
  37. 37. Dynamic Selection of MIMO Mode Adaptive Mode Selection  Dynamic adaptation algorithms are required to optimize system performance and select the appropriate mode based on DL SNR and channel conditions
  38. 38. Ranging Ranging is an UL PHY procedure that maintains the quality of the radio link communication between BS and MS. BS estimates CINR, time of arrival and frequency error of MS transmission and provides power, timing and frequency adjustment commands Initial and periodic ranging procedures are defined Both regular transmission and contention transmission can be used Contention transmission is done in special UL regions using ranging (CDMA code) Codes are created using PRBS generator and are BPSK modulated Each MS randomly chooses one ranging code from a bank of specified binary codes.  256 distinct codes are available and are divided by configuration into four groups:  IR codes  PR codes  BR codes  HO codes  Since codes are orthogonal, BS can process multiple codes transmitted simultaneously by different MS
  39. 39. Power Control (1) Power control mechanisms are supported in the UL to maintain the quality of the link. Basic requirements of the power control mechanism are:  Power control is designed to support fluctuations of 30dB/sec  BS accounts for the effect of various bust profiles on amplifier saturation while issuing power control commands  MS reports maximum transmission power for each modulation  MS maintains the same transmitted power spectral density (PSD), regardless of the number of assigned subchannels. Therefore, transmission power level is proportionally decrease or increased with the subchannel assignment without specific power control messages The requirements calls for a complex link adaptation algorithm that makes a joint decision regarding MCS, resource allocation and power adjustment MS reports available power headroom periodically and on a per demand basis
  40. 40. Power Control (2) Closed Loop Power Control  MS adjust its PSD based on BS commands only.  BS command may be explicit or implicit (by modifying the MCS) Open Loop Power Control  MS adjust its PSD independently, based on changes in the DL signal level according the following formula P(dBm)= L+C⁄N+NI – 10log10(R)+Offset_SSperSS+Offset_BSperSS  L: Estimated propagation loss  C/N: Carrier to noise for the burst profile in the current transmission  NI: Estimated average power level of noise an interference  R: repetition rate  Offset SS per SS: Correction factor employed by the SS (set to zero for passive mode)  Offset BS per SS: Correction factor employed by the BS  Closed loop power control may be combined with open loop as an outer mechanism, using the ‘Offset BS per SS’ parameter
  41. 41. Channel Quality Measurements MS provides BS with feedback on the quality of the DL signal. This feedback drives the link adaptation algorithm. Reported metrics include:  Received Signal Level (RSSI)  Carrier to Interference and Noise Ratio (CINR)  Based on preamble for R3 and R1 frequency reuse schemes  Based on pilots in specific zone  Preferred MIMO mode Feedback can be carried over the Channel Quality Indication Channel (CQICH) in a special UL region or over MAC control message
  42. 42. Throughput Calculation Example 1. Calculate number of OFDM symbols in frame  47 symbols for 10MHz channel 2. Determine DL/UL split based on profile  26/21 3. Deduce one symbol from DL subframe for preamble 4. Deduce overhead  DL: 4 symbols for the MAPs  UL 3 symbols for ranging, HARQ feedback and CQICH zones 5. Calculate number of slots available for data  DL: PUSC 30 x (20/2)=300  UL: PUSC 35 x (18/3)=210 6. Determine burst profile and MIMO mode  DL: 64QAM 5/6 Matrix B  UL: 16QAM 1/2 7. Calculate bits per frame  DL: 300 x 48 x 6 x (5/6) x 2=144,000  UL: 210 x 48 x 4 x (1/2)=20,160) 8. Calculate bits per second by dividing by frame duration  DL: 28.8Mbps  UL: 4Mbps
  43. 43. Part IIMedium Access Control Layer
  44. 44. MAC Functions  Segment or concatenate service data units (SDU) received from higher layers into the MAC protocol data unit (PDU)  Select the appropriate burst profile and power level to be used for transmission (link adaptation)  Retransmission of MAC PDU (ARQ)  Provide QoS control and priority handling of MAC PDU associated with different data and signaling bearers (Packet Scheduling)  Schedule MAC PDU over PHY resources (frame building)  Mobility management (handover)  Security and key management  Provide power saving modes (Idle/Sleep)
  45. 45. MAC: Protocol Layers Network Network Interface Received SDU’s MAC-CS Con #1 Con #2 Con #n MAC-CPS Fragmentation Radio Link Resource Maintenance BW Request Control Scheduler ARQ AMC Manager Security Data Encryption PHY and RF Link Quality ACK PHY module Feedback Feedback (e.g. CINR) UL ACK channel DL burst Ranging channel CQICH channel
  46. 46. Convergence Sublayer (CS)  Convergence sublayer is an adaptation layer that masks the higher layer protocol and its requirements from the MAC layer  Several convergence sublayers are supported  IPv4/IPv6 with and without ROHC  802.3 (Ethernet)  802.1/Q VLAN Upper Layer Entity (e.g. bridge, router) Upper Layer Entity (e.g. bridge, router)  IPv4/IPv6 over 802.3 SDU  IPv4/IPv6 over 802.1/Q VLAN SAP SAP CID 1 CID 2 Classification Reconstruction text (e.g. undo PHS) text CID n {SDU, CID,...} {SDU, CID,...} SAP SAP 802.16 MAC CPS 802.16 MAC CPS
  47. 47. Convergence Sublayer Functions  Classification  WiMAX MAC is connection oriented. Each unidirectional logical connection between MS and BS is identified by a Connection Identifier (CID). Connection can carry user plane data and control plane information  CS performs many-to-one mapping between higher layer applications and a specific connection. Applications with different QoS requirements are mapped to different connections.  The mapping is performed on the basis of the header fields of the higher layer protocol, e.g. VLAN, IP source address.  Classification may be performed at the BS or at the ASN-GW  Packet Header Suppression (PHS):  Repetitive portion of the packet header may be suppressed by the transmitter and restored by the receiver  Improves efficiency of the network, especially for applications with small packet size (e.g. VoIP)  PHS rules at the transmitter and the receiver are synchronized during service flow initiation and modification  PHS may be performed at the BS or at the ASN-GW  Robust Header Compression (ROHC) is an alternative to PHS, which is transparent to the MAC operation. Defined by RFC 3095, ROHC compress the IP, UDP, RTP and TCP headers of IP packets (can compress 60 bytes of overhead into 3 bytes)
  48. 48. MAC PDU Construction and Transmission  SDU arriving from higher layer are assembled to create MAC PDU.  Depending on the size of allocation, multiple SDU can be packed on a single PDU, or a single SDU can be fragmented over multiple PDUs.  Multiple MAC PDUs intended for the same receiver can be concatenated onto a single transmission burst SDU 1 ARQ Block SDU 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Fragment 1 Fragment 2 Fragment 1 Fragment 2 Header Fragment 1 Header Fragment 2 Fragment 1 Header Fragment 2 PDU 1 PDU 2 PDU 3 DL/UL Burst
  49. 49. ARQ  For application sensitive to packet error (TCP), ARQ can be used on top of HARQ to eliminate residual error rate.  ARQ can be enabled on a per connection basis.  For ARQ-enabled connection, SDU is first partitioned into fixed length ARQ blocks and a block sequence number (BSN) is assigned to each block.  The length of the ARQ blocks and the ARQ window size (number of blocks managed by the transmitter and receiver at an given time) are set during connection establishment.  Once SDU is partitioned into ARQ blocks, the partition remains in effect until all the blocks have been received and acknowledged by the receiver  ARQ enable connection are limited in throughput by Block Size x Window Size / ACK Latency  For ARQ enabled connection, fragmentation and packing subheader contains the BSN of the first ARQ block following the subheader.  Receiver feedback (ACK) can be sent as a stand alone MAC PDU or piggybacked on the payload of a regular MAC PDU  ARQ feedback can be selective or accumulative
  50. 50. MAC PDU Structure (1)  Each MAC PDU consists of a header which may followed by a payload and a cyclic redundancy check (CRC) MSB LSB Generic MAC Payload: SDU’s & Subheaders CRC Header (Optional) (Optional) 6 bytes 0-2038 bytes 4 bytes  Generic MAC Header (GMH) is used for carrying user plane data and MAC control messages  HT: Header type (HT = 0 for GMH) HT=0 (1) Rsv (1) Rsv (1) EC (1)  EC: Encryption control CI (1) EKS LEN Type (6)  Type: Indicates subheaders included in the payload (2) MSB (3)  CI: CRC indicator  EKS: Encryption key sequence LEN LSB (8) CID MSB (8)  LEN: Length of MAC PDU in bytes  CID: Connection ID associated with the PDU  HCS: Header check sequence CID LSB (8) HCS (8)
  51. 51. MAC PDU Structure (2)  Signaling MAC header is defined used for the UL (this header is not followed by payload)  Signaling header type I  BW request header (aggregate/incremental)  BW request and UL TX power report header  BW request and CINR report header  CQICH allocation request header  PHY channel report header (DIUC, TX power, TX power headroom)  BW request and UL sleep control header  SN report header (ARQ)  Signaling header type II  Used for MS feedback report  14 feedback permutations are defined: CINR, TX power, DIUC, AMC band indication bitmap, MIMO feedback, etc.
  52. 52. Bandwidth Request and Allocation  All decisions related to DL resource allocation to various MS are made by the BS on a per CID basis. BS schedules MAC PDUs based on the connection QoS requirements. The allocation is indicated in the DL MAP.  MS requests UL BW in bytes on a per connection basis by using either stand alone BW requests or piggybacking BW requests on generic MAC PDU.  BW request can be incremental or aggregate  UL grants are done on a per MS basis and indicated in the UL MAP. MS UL scheduler distribute the granted allocation among its various connections.  BS supports BW polling, whereby dedicated (unicast polling) or shared (multicast polling) UL resources are provided to the MS to make BW requests.  Multicast polling is based on contention mechanism, in which MS sends a randomly selected code in a dedicated UL region.  Contention is resolved using an exponential backoff window mechanism
  53. 53. Quality of Service  Each service flow is associated with QoS parameters: maximum traffic rate, guaranteed traffic rate, maximum latency and Priority. MAC layer is responsible to ensure QoS requirements subject to loading conditions.  Each service flow is mapped to a certain transport connection with its own QoS parameters. Transport connections may be Unicast, Multicast or Broadcast  Two Management connections are established for each MS to reflect different levels of QoS requirements  Basic management connection: Used to transfer short, time-critical MAC and radio control messages  Primary management connection: Used to transfer longer, more delay-tolerant messages such as authentication and connection setup
  54. 54. QoS Architecture Data Packet Classification Scheduler (SDU) Classification Service Flow Attributes Scheduler •IP Protocol •Maximum traffic rate •Select PDU based on SF •Source/Dest IP Address •Minimum reserved traffic rate attributes and subject to •ToS •Latency available resources •Source/Dest MAC Address •Priority •VLAN •Grant/polling interval
  55. 55. Service Flows: Three Phase Activation  SF defined in BS/MS  QoS parameters known to BS/MS. Usually defined by Provisioned higher layer entity  SFID assigned  Traffic disabled  Transient stage  QoS parameters are a subset of the provisioned Admitted set, following BS admission control  Resources are allocated  CID assigned  Traffic disabled  Traffic enabled Active
  56. 56. Data Services & Scheduling Types  Five scheduling services used to collect BW requirements from MS’s:  Unsolicited Grant Service (UGS)  Real time applications generating fixed rate data  Provides fixed size grants on periodic basis and does not need the MS to explicitly request BW.  Extended Real Time Polling Service (ertPS)  Real time applications with variable rate, guaranteed rate and latency, e.g. VoIP with silence suppression  Similar to UGS, but allows dynamic adaptation of grant size based on MS feedback  Real Time Polling Service (rtPS)  Real time applications generating variable rate data  BS provides unicast polling opportunities for the MS to request BW  Non Real Time Polling Service (nrtPS)  Delay tolerant applications with guaranteed data rate  Similar to nrtPS, except that MS is allowed to use contention BW requests in addition to the polling  Best Effort (BE)  Applications with no rate or delay requirements  Based on contention based polling opportunities
  57. 57. Scheduling Algorithms  The scheduler prioritizes the backlogged SDUs in the DL and the pending BWR in the UL. Prioritization is done on a per SF basis based on the various attributes associated with the service flow.  Scheduler target: Maximize system capacity subject to service requirements of each flow. Scheduling procedure is outside the scope of the WiMAX standard and has been left to the equipment manufacturers to implement. It has a profound impact on the overall capacity and performance of the system, thus it serves as a key differentiator among vendors.  Classical scheduling algorithm  Strict Priority (SP) SFi = argmax(iPi)  Proportional Fairness (PF) SFi = argmin(iri /Ri)  Adaptive PFS takes into account link condition (spectral efficiency) in order to maximize system capacity  APFS metric SFi = argmin(iwiri /Ri)  Combination of different algorithms is possible, e.g. SP for the guaranteed rate and APFS for the excess bandwidth
  58. 58. Adaptive Modulation and Coding Algorithms (1)  WiMAX supports dynamic adaptation of modulation and coding scheme as well as MIMO mode on a per connection and per frame basis.  Link adaption algorithms aim to maximize spectral efficiency while maintaining link quality metric (typically target packet error rate)  DL adaptation  Input:  DL CINR feedback from the MS based on DL preamble and/or DL pilots  Preferred MIMO mode based on channel conditions as perceived by the MS  HARQ error rate based on MS feedback received on the HARQ ACK UL channel  Output:  MCS  MIMO Mode (Matrix A/Matrix B)  Zone (e.g. R1 zone or R3 zone)
  59. 59. Adaptive Modulation and Coding Algorithms (2)  UL adaptation  Input:  UL CINR as measured by the BS PHY  MS transmission power headroom as reported by the MS  HARQ error rate as indicated by BS PHY  Output:  MCS  Power adjustment  Maximum number of subchannels that may be allocated  MIMO mode  Two modes of operation are supported: The first selects a solution that maximize the spectral efficiency (highest order possible MCS) and the second selects a solution that maximizes the user throughput, i.e. the spectral efficiency multiplied by the maximum number of subchannels
  60. 60. Security  Security architecture of mobile WiMAX support the following requirements:  Privacy: Provide protection from eavesdropping as the user data traverse the network  Data integrity: Ensure the user data and control messages are protected from being modified while in transit  Authentication: A mechanism to ensure that a given user/device is the one it claims to be. Conversely, the user/device should be able to verify the authenticity of the network that it is connecting to (mutual authentication)  Authorization: Mechanism to verify that a given user is authorized to receive a particular service  Access control: Ensure that only authorized users are allowed to get access to the offered services
  61. 61. Public Key Infrastructure (PKI)  On way to enable secure symmetric key encryption is to establish a shared secret between transmitter and receiver.  Asymmetric key encryption is a solution to the key distribution problem.  Based on a public key and a private key that are generated simultaneously using the same algorithm, RSA  Ciphertext that is encrypted with one key can be decrypted by the other key  Public key infrastructure can be used for variety of security applications:  Authentication (see example in next slide)  Shared secret key distribution  Message integrity  Digital certificates
  62. 62. PKI – Mutual Authentication User A User B Send (Random Number A, My Name) encrypted with public key of B Send (Random Number A, Random Number B, Session Key) encrypted with public key of A Send (Random Number B) encrypted with session key Begin transferring data encrypted with session key
  63. 63. Authentication and Access Control  In general, access control system has three elements:  Supplicant: an entity that desired to get access  Authenticator: an entity that controls the access gate  Authentication server: an entity that decides whether the supplicant should be admitted  Extensible Authentication Protocol (EAP)  A simple encapsulation protocol that can run on any L2 protocol  Based on a set of negotiated messages that are exchanged between the supplicant and the authentication server  EAP includes a number of EAP methods, which define the rules for authenticating a user and/or a device and the set of credentials.  EAP Transport Layer Security (TLS) defines a certificate based strong mutual authentication.  In WiMAX, EAP runs from the MS to the BS over PKMv2 (Privacy Key Management) security protocol. The BS relays the authentication protocol to the authenticator in the ASN-GW. From the authenticator to the authentication server, EAP is carried over RADIUS or DIAMETER.
  64. 64. Encryption  Mobile WiMAX encryption is based on Advanced Encryption Standard (AES) which is a symmetric key encryption system.  AES algorithm operates on a 128 bit block size of data. The encryption key size in the case of WiMAX is 128 bits long.  The AES Traffic Encryption Key (TEK) is also AES encrypted using the Key Encryption Key (KEK)  The KEK is a derivative of the Authorization Key (AK) which is a shared secret between the MS and the BS.  Cipher based MAC (CMAC) is used as the mandatory mode for message authentication  AES data encryption provides a built in data authentication capability  AES encryption adds 12 bytes of overhead.
  65. 65. Network Entry Frequency Scanning Authentication DL & UL Synchronization Registration Initial Ranging Service Provisioning Negotiate Basic Capabilities
  66. 66. Network Entry: Frequency Scanning • MS scans frequency bands in search for the DL Frequency Scanning Authentication preamble DL & UL Synchronization Registration • Scanning is performed on a predefined list of frequencies Initial Ranging Service Provisioning • MS selects best carrier frequency base on signal Negotiate Basic Capabilities strength or CINR • MS scans for all preamble indexes in the selected carrier (114 indexes) and selects the best based on RSSI or CINR
  67. 67. Network Entry: Downlink and Uplink Acquisition • BS regularly broadcasts control messages: Frequency Scanning Authentication – Downlink Channel Descriptor (DCD) DL & UL Synchronization Registration – Uplink Channel Descriptor (UCD) – DL-MAP Initial Ranging Service Provisioning – UL MAP Negotiate Basic Capabilities • MS acquires DL once valid DCD and DL-MAP are decoded – To make a valid DCD and DL-MAP BSID and NAI should match MS configuration and DCD and DL MAP should indicate the same DCD change counter – To maintain DL SYNC MS should periodically receive DL-MAP and DCD • MS acquires UL once valid UCD and UL-MAP are decoded – To make a valid UCD and UL-MAP UCD and UL MAP should indicate the same UCD change counter – To maintain UL SYNC MS should periodically receive UL-MAP and UCD
  68. 68. Network Entry: Ranging • Ranging is required to align BS and MS in terms of Frequency Scanning Authentication power, frequency and timing DL & UL Synchronization Registration • BS measure MS offsets from the UL transmission and Initial Ranging Service Provisioning provides appropriate adjustments Negotiate Basic Capabilities MS CDM BS ( IR C A ode) BS measures arrival time and signal power and determines -RSP e) required adjustments RNG Continu t, djus tmen (A MS makes adjustments CDM ( IR C A ode) -RSP RNG ess) (Su cc IE ation A Alloc CDM R (MS NG-REQ MAC A ddr ess) -RSP D) RNG imary CI d Pr ic an (Bas
  69. 69. Network Entry: Negotiation of Basic Capabilities • Basic capabilities include supported modulations, FEC, Frequency Scanning Authentication MIMO modes, HARQ, Privacy, etc. DL & UL Synchronization Registration Initial Ranging Service Provisioning MS BS Negotiate Basic Capabilities SBC-R EQ SP S BC-R
  70. 70. Network Entry: Authentication • Based on PKMv2 which uses EAP as the underlying Frequency Scanning Authentication authentication mechanism Authenticator DL & UL Synchronization Registration MS BS AAA Server (ASN) SBC-REQ MS Status Update SBC-RSP Initial Ranging Service Provisioning EAP Request/Identity Negotiate Basic Capabilities EAP Response/Identity (my ID, e.g. MS MAC address) EAP Request/EAP TLS (TLS Start) EAP Response/EAP TLS (TLS Client Hello) EAP Request/EAP TLS (TLS Server Hello, TLS Certificate) EAP over RADIUS EAP Response/EAP TLS (TLS Certificate) EAP Request/EAP TLS (TLS Finished) EAP Response/EAP TLS EAP Success MSK, PMK, AK MSK Established Established MSK PMK, AK Established AK Transferred to BS SA-TEK Challenge SA-TEK Request SA-TEK Response Key Request Key Reply
  71. 71. Network Entry: Registration • Registration capabilities include management mode, IP Frequency Scanning Authentication version supported, ARQ support, supported CS, etc. DL & UL Synchronization Registration Initial Ranging Service Provisioning Negotiate Basic Capabilities MS BS REG-R EQ -RSP REG
  72. 72. Network Entry: Service Provisioning Frequency Scanning Authentication • Creation of service flows can be initiated by either the MS or the BS DL & UL Synchronization Registration Initial Ranging Service Provisioning MS BS Negotiate Basic Capabilities -REQ DSA DSA-R SP -A CK DSA
  73. 73. Power Saving Modes  Power saving modes enable the MS to conserve its battery resources – a critical feature required for handheld devices.  Two power saving modes are defined:  Sleep Mode  Idle Mode
  74. 74. Sleep Mode  Sleep Mode is a state in which an MS conducts pre-negotiated periods of absence from the Serving BS air interface. These periods are characterized by the unavailability of the MS, as observed from the Serving BS, to DL or UL traffic. Sleep Mode is intended to minimize MS power usage.  Power Saving class may be activated per connection basis. Activation of certain Power Saving Class means starting sleep/listening windows sequence associated with this class. There are three types of Power Saving Classes, which differ by their parameter sets, procedures of activation/deactivation and policies of MS availability for data transmission.
  75. 75. Example: Sleep mode operation
  76. 76. Idle (Paging) Mode  Idle Mode is a mechanism that allows MS to become periodically available for DL broadcast traffic messaging without registration at specific BS.  Idle Mode benefits MS by removing the active requirement for Handovers and all normal operation requirements. By restricting MS activity to scanning at discrete intervals, Idle Mode allows the MS to conserve power and operational resources.  Idle Mode helps the network and BS to conserve resources by eliminating the need to perform any link maintenance activity and handover related procedures for MS in idle mode.
  77. 77. Idle Mode: Theory of Operation (1)  The BS are divided into logical groups called paging groups. A BS may be a member of one or more paging groups.  MS in idle mode periodically monitors DL broadcast to determine the paging group of its current location. When MS detects that it has moved to a new paging group it performs location update, in which it informs the network its new location.  In case of pending DL traffic, the network needs to page the MS only in all BS belonging to the current paging group of the MS
  78. 78. Idle Mode: Theory of Operation (2)  On a periodic basis, the MS shall scan and synchronize on the DL for the preferred BS in order to decode any BS broadcast paging message  A BS Broadcast Paging message is an MS notification message indicating either the presence of DL traffic pending, through the BS or some network entity, for the specified MS or to poll the MS and request a location update without requiring a full network entry.  During idle mode MS can be in one of two states: paging-unavailable or paging-listen interval.  Paging-unavailable: MS is not available for paging and can power down or scan for neighbouring BS.  Paging-listen interval: MS listens to DCD and DL MAP of the serving BS to determine when the broadcast paging message is scheduled  Paging broadcast message can indicate pending DL traffic and instruct the MS to perform network re-entry, request MS to perform location update or indicate to the MS to return to paging unavailable state.
  79. 79. Mobility Management  Handover: The migration of the MS from the air interface of one BS to the air interface of another BS, while maintaining connection  Network topology advertisement: BS broadcasts information about the network topology using the MOB_NBR-ADV message:  The message provides channel information for neighbouring base stations, which is normally provided by each BS own DCD/UCD message. The BS obtains that information over the backbone.  MS scanning of neighbour BS: A BS may allocate time intervals to MS for the purpose of monitoring and measuring the radio conditions of neighbouring BS. The time during which the MS scans for available BS will be referred to as a scanning interval.  Handover may be MS initiated (typically in order to improve link quality) or BS initiated (typically to perform load balancing)
  80. 80. Handover Process  Scanning and target cell selection  Based on certain triggers (e.g. CINR of target BS falls below 20dB, MS scans link quality of neighbouring BS and select a suitable target BS.  Handover Initiation  MS initiated using MOB_MSHO-REQ  BS initiated using MOB_BSHO-REQ  Network re-entry with target BS  Target BS DL SYNC and acquisition of DL/UL channel parameters  Using information from NBR-ADV, this process can be shortened  Initial ranging or Handover ranging  MS RNG-REQ includes serving BS ID and target BS ID  If the Target BS had previously received HO notification from Serving BS over the backbone then Target BS may place a non-contention based Initial Ranging opportunity  Negotiate Basic Capabilities, Authorization, etc.  Handover optimization: target BS may request MS data from backbone to accelerate network entry. This data may be used by the target BS to skip certain NE steps.  Termination of context with previous BS
  81. 81. Handover Messaging - Example MS Serving BS Target BS ASN-GW Operational V BR-AD MOB_N MOB_S CN-REQ CN-RSP MOB_S Scanning & Association Association Coordination RNG-REQ RNG-RSP MOB_M SHO-RE Q P SHO-RS MOB_B MOB_H O-IND Obtain MS operational parameters Network re-entry Operational
  82. 82. Part IVNetwork Architecture
  83. 83. General Design Principles of the Architecture  Functional decomposition: Required features are decomposed into functional entities. The architecture shall specify open and well defined reference points between the functional entities.  Deployment modularity and flexibility: The architecture shall support a broad range of deployment options. It shall scale from the simple case of a single operator with a single base station to a large scale deployment by multiple operators with roaming agreements  Support of variety of usage models: Architecture shall support fixed, nomadic, portable and mobile usage models. Both Ethernet and IP services shall be supported.  Decoupling of access and connectivity services: The architecture shall allow decoupling of the access network from the IP connectivity network and services  Support for a variety of business models: The architecture shall allow for logical separation between the network access provider (NAP), the network service provider (NSP) and the application service provider (ASP)  Extensive use of IETF protocols: Network layer procedures and protocols used across the reference points shall be based on appropriate IETF RFCs.
  84. 84. Network Reference Model
  85. 85. Access Service Network (ASN) Functions  Access Service Network (ASN): Owned by the NAP and includes a complete set of network functions needed to provide radio access to a WiMAX subscriber:  WiMAX L2 connectivity with the MS  Network discovery and selection of the WiMAX subscriber’s preferred NSP  AAA proxy: transfer of device and/or user credentials to selected NSP AAA and temporary storage of user profiles.  Relay functionality for establishing IP connectivity between MS and CSN  Mobility related functions, such as handover, location management and paging within the ASN, including support for mobile IP  ASN comprises network elements such as one or more Base Stations and one or more ASN Gateways.  BS is defined as representing one sector with one frequency assignment implementing the R1 interface. BS functions include scheduling, service flow management, admission control, tunnelling toward the ASN-GW, DHCP proxy, authentication relaying, user plane encryption  ASN-GW functions include ASN location management and paging, temporary caching of subscriber profiles and keying material, authenticator, service flow authorization and user plane routing
  86. 86. Connectivity Service Network (CSN) Functions  Connectivity Service Network (CSN): A set of network functions that provide IP connectivity services to the WiMAX subscribers. CSN provides the following functions:  IP address allocation to the MS for user sessions  AAA proxy or server for user and/or device authentication, authorization and accounting  Policy and access control based on user subscription profiles  Subscriber billing and inter-operator settlement  Inter-CSN tunnelling for roaming  Inter-ASN mobility and mobile IP home agent functionality  Connectivity infrastructure for services such as Internet access, VPN and IP multimedia  CSN comprises network elements such as routers, AAA proxy/servers and subscribers database.
  87. 87. Protocol Layering  Control plane is based on UDP/IP  Data plane is based on GRE tunnelling within the ASN and IP in IP tunnelling between ASN and CSN  WiMAX architecture is designed to support both IP packets and Ethernet packets, using IP-CS and ETH-CS, respectively.  Within the ASN packets can be either routed or bridged
  88. 88. Protocol Layer Architecture: IP-CS  Example presents a routed ASN. For bridged ASN, the shaded layers (GRE, IP) would be replaced by Ethernet layer
  89. 89. Protocol Layer Architecture: Ethernet-CS  Example presents a routed ASN. For bridged ASN, the shaded layers (GRE, IP) would not be needed
  90. 90. GRE Tunneling  Generic Routing Encapsulation (GRE) may be used as tunnelling mechanism across R4 or R6.  Allows for tunnelling of IP packets, Ethernet frames or WiMAX specific payload  DSCP in the Encapsulation IP Header specifies the QoS Class. Note that it MAY differ from the DSCP in the Encapsulated Payload.  Source and Destination IP Addresses specify the tunnel end points.  The meaning of the GRE Key value is defined by the node that allocates the Key value. GRE Key can indicate one of the following: Specific connection, in case classification is done by ASN-GW or Specific MS, in case classification is done by BS  The Sequence Number may be used for synchronization of Data Delivery during HO.
  91. 91. Network Discovery and Selection  In the general case, it is assumed that MS operates in an environment in which multiple access networks are available and multiple service providers are offering services over those networks. Mobile WiMAX specifies a process for network discovery and selection  NAP discovery  MS detects available NAPs in a wireless coverage area based on information broadcasted by BS (Operator ID). Operator ID is assigned by IEEE  NSP discovery  MS discovers available NSPs associated with the discovered NAPs based on information either broadcasted by the BS using System Identity Information message (SII-ADV) or unicasted to the MS (SBC-RSP). NSP ID is assigned by IEEE  NSP enumeration and selection  MS selects preferred NSP based on dynamic information obtain through the air interface and configuration information. Selection may be automatic or manual.  ASN attachment  MS indicates its NSP selection by attaching to an ASN associated with the selected NSP, and by providing its identity and home NSP domain in the form of NAI  The ASN uses the realm portion of the NAI to determine the next AAA hop to where the MS’s AAA packets should be routed.
  92. 92. IP Address Assignment (1)  Network Architecture supports either Mobile IP or Simple IP  Mobile IP requires Home Agent  Simple IP reduces scope of network and does not support mobility  Mobile IP is used to provide CSN Anchored Mobility  CSN Anchored Mobility Management or Macro mobility is when the MS changes to a new anchor Foreign Agent  Mobile IP allows an MS to communicate with other nodes after changing its point of attachment to the network For example, handover between BS on separate ASN-GW, or inter-technology handover  Mobile IP is achieved by allocating an MS both a Home Address (HoA) and a Care-of Address (CoA)  Two forms of Mobile IP are defined; Proxy Mobile IP (PMIP) and Client Mobile IP (CMIP)  CMIP is required to enable Inter-technology handover
  93. 93. IP Address Assignment (2)  Dynamic Host Control Protocol (DHCP) is used as the primary mechanism to allocate IP address to the MS  The network architecture provides flexibility in allocating IP addresses to MS  ASN-GW provides a DHCP Proxy Server  Mobile IP or Simple IP  Home Agent can be configured with local pool of Mobile IP Addresses  Mobile IP only  ASN-GW can be configured with local pool of IP addresses  Simple IP only  AAA Server can allocate IP addresses using IP Address Manager  Mobile IP or Simple IP  Simple IP  IP address is either assigned from local address pool, or retrieved as RADIUS attributes from AAA Server  The ASN-GW DHCP proxy is used to transfer IP address information to MS
  94. 94. Authentication and Security Architecture  Designed to support all IEEE 802.16 security services using EAP based AAA framework.  Supports both user and device authentication  Supported EAP methods: EAP-TLS and EAP-TTLS  In addition, AAA framework is used for service flow authorization, QoS policy control and secure mobility management  AAA framework basic steps:  MS sends a request to the network access server (NAS) function in the ASN  NAS forwards the request to the service provider AAA server (NAS acts as an AAA client on behalf of the user)  AAA server evaluates the request and returns an appropriate response to the NAS  NAS sets up a service and notifies the MS
  95. 95. ASN Security Architecture  Authenticator (ASN-GW or BS)  Communicates with the AAA server using RADIUS/DIAMETER  Authentication Relay (BS)  Functional entity that relays EAP packets to the authenticator via an authentication relay protocol  Key Distributor (ASN-GW or BS)  Functional entity that holds the keys (MSK and PMK) generated during the EAP exchange  The MSK is sent to the Key Distributor from the home AAA server, and the PMK is derived locally from the MSK.  Derives AK and creates AKID for an <MS, BS> pair and distributes the AK and its context to the Key Receiver in a BS via an AK Transfer protocol  Key Receiver (BS)  Holds the AK and responsible for generation of IEEE 802.16e specified keys from AK
  96. 96. Authentication Protocols  PKMv2 is used to perform over-the-air user/device authentication. PKMv2 transfers EAP over the IEEE 802.16 air interface between MS and BS in ASN.  Depending on the Authenticator location in the ASN, a BS may forward EAP messages over authentication relay protocol (e.g. over R6 reference point) to Authenticator.  The AAA client on the Authenticator encapsulates the EAP in AAA protocol packets and forwards them via one or more AAA proxies to the AAA Server in the CSN of the home NSP
  97. 97. Authentication Procedure  Initial network entry and Authenticator MS BS AAA Server negotiation (ASN)  Exchange of EAP messages Network Entry Link Activation  Establishment of the shared entity EAP Request/Id master session key (MSK) EAP Response/ Identity  Generation of authentication EAP over RADIUS key (AK) ement MSK and EMSK Establish MSK  Transfer of authentication key PMK derivation from MSK AK derivation from MSK  Transfer of security AK associations SA-TEK Challenge  Generation and transfer of SA-TEK Request traffic encryption keys SA-TEK Response (TEK) Key Request  Service flow creation Key Reply
  98. 98. Quality of Service Architecture Architecture designed to support static and dynamic service flow provisioning Home Policy Function (PF)  Contains policy database of the home NSP and evaluates service requests against these policies. Requests may come from the SFA or from the AF Application Function (AF)  An entity that can initiate service flow creation on behalf of a user, e.g. SIP proxy client AAA server  Holds users QoS profile and associated policy rules  Option 1: The information is downloaded to the SFA during NE as part of the authentication and authorization procedure  Option 2: AAA server can provision the PF with subscriber related information and the PF shall determine how incoming SF are handled Service Flow Authorization (SFA)  Evaluates SF request against user QoS profile (in case AAA information was downloaded to SFA) Service Flow Management (SFM)  Responsible for creation, admission, activation, modification and deletion of SF
  99. 99. Service Flow Creation (Static)  Example assumes users associated policies were downloaded to the SFA from the AAA  Based on Resource Reservation Request/Response
  100. 100. ASN Gateway: Mobility Function  Handover may be MS initiated (typically for link quality maintenance) or ASN initiated (typically for HA load balancing)  ASN anchored mobility – anchored Foreign Agent R3 (FA) unchanged R3 ASN- ASN-  No impact on IP level GW1 GW2  Data Path function (DPF): responsible for setting up and R4 managing bearer paths needed for data packet transmission.  Handover function (HO): responsible for making HO decisions R6 and performing the signalling procedures related to HO R6 R6  Context function: responsible for exchange of state information among network elements impacted by HO  CSN anchored mobility – anchored FA changed BS1 BS2 BS3 R8  Involves mobility across different IP subnets and therefore requires IP layer mobility management  R1 Two types of Mobile IP implementations are defined R1 R1  Client MIP – based on mobile IP client at the MS  Proxy MIP – ASN-GW implements the mobile IP client on behalf of the MS. PMIP is transparent to the MS.
  101. 101. Handover ProceduresMS Initiated – preparation phase
  102. 102. Handover ProceduresMS Initiated – action phase Serving/ Anchor ASN- MS Serving BS Target Target BS’s Authenticator GW ASN-GW MOB_HO-IND HO_cnf HO_cnf HO_Ack HO_Ack Context_Req Context_Req Context_Rpt Context_Rpt Path_Prereg_Req Path_Prereg_Req Path_Prereg_Rsp Path_Prereg_Rsp Path_Prereg_Ack Path_Prereg_Ack RNG-REQ Path_Reg_Req Path_Reg_Req Path_Reg_Rsp Path_Reg_Rsp RNG-RSP CMAC_Key_Count_Update CMAC_Key_Count_Update CMAC_Key_Count_Update_Ack CMAC_Key_Count_Update_Ack Path_Dereg_Req Path_Dereg_Req Path_Dereg_Rsp Path_Dereg_Rsp Path_Dereg_Ack Path_Dereg_Ack HO_Complete HO_Complete
  103. 103. Paging and Idle Mode Operation  Paging is the method used to alert an idle MS about incoming message.  Paging architecture is based on three functional entities  Paging Controller (PC)  Administrates activities of idle mode MS  Typically located at the ASN-GW  Paging Agent (PA)  BS functional entity that handles interaction between PC and air interface related paging functionalities  One or more PA can form a Paging Group (PG), which is managed by the network operator. PA may belong to more than one PG  Location Register (LR)  A database containing information on idle mode MS (e.g. PGID, paging cycle, paging offset, SF information)