Wireless Communications and Mobile Computing

Transcription

1 WCMC-MPR-A 1 Wireless Communications and Mobile Computing MAP-I Manuel P. Ricardo Faculdade de Engenharia da Universidade do Porto

2 WCMC-MPR-A 2 Professors Adriano Moreira» Universidade do Minho Manuel P. Ricardo (mricardo@fe.up.pt)» Faculdade de Engenharia, Universidade do Porto» mricardo@fe.up.pt» Tel Rui L. Aguiar» Universidade de Aveiro

3 3 WCMC-MPR-A 3 Topics Scheduled for Today New generation networks overview Mobile Devices platforms Communications networks technologies» Fundamentals of communications» Wireless technologies (WLAN, WMAN)» Wireless technologies (GPRS, UMTS)» Broadcast and satellite technologies (DVB, DMB) Services and applications in novel generation networks...

4 WCMC-MPR-A 4 Mobile vs Fixed networks Mobile communications systems characterised by» wireless links» mobility of terminals Computer Wired link Switch T 1 AP 1 Terminal Mobility switch Computer Wireless link AP T 2 AP 2

5 WCMC-MPR-A 5 To Think About How to obtain a low Bit Error Ratio (BER) in a wireless link?

6 Mobility Security Quality of Service WCMC-MPR-A 6 Reference Model Application Transport Network Data link Physical

7 Wireless Transmission WCMC-MPR-A 7

8 WCMC-MPR-A 8 Electromagnetic Waves Generation and Propagation

9 WCMC-MPR-A 9 Frequencies for Radio Transmission Frequency bands as defined by the ITU-R Radio Regulations wavelength f c = 3 GHz 10 cm

10 WCMC-MPR-A 10 To Think About How does the power of a received signal depend on the» distance?» wavelength ( )?

11 WCMC-MPR-A 11 Signal Propagation and Wireless channels Power of the signal received depends on 3 factors Path loss Dissipation of radiated power; depends on the distance Shadowing caused by the obstacles between the transmitter and the receiver attenuates the signal absorption, reflection, scattering, diffraction Multipath constructive and destructive addition of multiple signal components

12 WCMC-MPR-A 12 Path Loss Free Space Model Gl PGdB 20.log 20.log( d ) b 20x 4

13 WCMC-MPR-A 13 Signal Propagation and Wireless Channels PGdB Path loss Shadowing + Path loss Multipath + Shadowing + Path loss log(d)

14 WCMC-MPR-A 14 Carrier, Bandwidth B 2B f c f What is the difference betweeen B and f c?

15 WCMC-MPR-A 15 Capacity of an Wireless Channel Assuming Additive White Gaussion Noise (AWGN)» Given by Shannon s law (bit/s) N 0 power spectral density of the Noise Capacity in a fading channel (shadowing + multipath) usually smaller than the capacity of an AWGN channel

16 Capacity of an Wireless Channel WCMC-MPR-A 16

17 WCMC-MPR-A 17 To Think About How can we transmit bits using a continuous carrier?

18 WCMC-MPR-A 18 Digital Modulation Digital modulation» maps information bits into an analogue signal (carrier) Receiver» determines the original bit sequence based on the signal received Two categories of digital modulation» amplitude/phase modulation» frequency modulation

19 WCMC-MPR-A 19 Amplitude and Phase modulation sent over a time symbol interval Amplitude/phase modulation can be:» Pulse Amplitude Modulation (MPAM) information coded in amplitude» Phase Shift Keying (MPSK), information coded in phase» Quadrature Amplitude Modulation (MQAM) information coded both in amplitude and phase

20 WCMC-MPR-A 20 Differential Modulation Bits associated to a symbol depend on the bits transmitted over prior symbol times Differential BPSK (DPSK)» 0 no change phase» 1 change phase by Diferential 4PSK (DQPSK) the bit» 00 change phase by 0» 01 change phase by» 10 change phase by -» 11 change phase by

21 WCMC-MPR-A 21 Coding for Wireless Channels Coding enables bit errors to be either detected or corrected by receiver Codes designed for AWGN channels» do not work well on fading channels» cannot correct the long error bursts that occur in fading Codes for fading channels are usually» based on an AWGN channel code» combined with interleaving» objective spread error bursts over multiple codewords

22 WCMC-MPR-A 22 Convolutional Code; Interleaving Example: convolutional code Interleaving

23 WCMC-MPR-A 23 Adaptive Modulation/Coding Adaptive transmission techniques» aim at maintaining the quality low/stable BER» works by varying: data rate, power transmitted, codes Adapting the data rate» symbol rate is kept constant» modulation schemes / constellation sizes depend on multiple data rates Adapting the transmit power» compensate P r /N 0 B variation due to fading» maintain a constant received Adapting the codes» large weaker or no codes» small stronger code may be used

24 WCMC-MPR-A 24 Multicarrier Modulation Multicarrier modulation (e.g. OFDM) consists» dividing a bitstream into multiple low rate sub-streams» sending sub-streams simultaneously over sub-channels Subchannel» has bandwidth B N = B/N» provides a data rate R N R/N» For N large, B N = B/N << 1/T m flat fading (narrowband like effects) on each sub-channel, no ISI Orthogonal sub-carriers» space between carriers minimised» system capacity maximised

25 WCMC-MPR-A 25 Wireless Data Link and Medium Access Control

26 WCMC-MPR-A 26 How to transmit signals in both directions simultaneously? How to enable multiple users to communicate simultaneously?

27 WCMC-MPR-A 27 Duplex Transmission Duplex transference of data in both directions Uplink and Downlink channels required Two methods for implementing duplexing» Frequency-Division Duplexing (FDD) wireless link split into frequency bands bands assigned to uplink or downlink directions peers communicate in both directions using different bands» Time-Division Duplexing (TDD) timeslots assigned to the transmitter of each direction peers use the same frequency band but at different times

28 WCMC-MPR-A 28 To Think About How to place several sender-receiver pairs communicating in the same physical space?

29 WCMC-MPR-A 29 Multi-Access Schemes Multi-access schemes» Identify radio resources» Assign resources to multiple users/terminals Multi-access schemes» Frequency-Division Multiple Access (FDMA) resources divided in portions of spectrum (channels)» Time-Division Multiple Access (TDMA) resources divided in time slots» Code-Division Multiple Access (CDMA) resources divided in codes

30 code WCMC-MPR-A 30 FDMA» Signal space divided along the frequency axis into non-overlapping channels» Each user assigned a different frequency channel» The channels often have guard bands» Transmission is continuous over time channel 2 channel 1 channel k time

31 code WCMC-MPR-A 31 TDMA» Signal space divided along the time axis into non-overlapping channels» Each user assigned a different cyclically-repeating timeslot» Transmission not continuous for any user» Major problem synchronization among the users in the uplink channels users transmit over channels having different delays uplink transmitters must synchronize time

32 code WCMC-MPR-A 32 CDMA Each user assigned a code to spread his information signal» Multi-user spread spectrum (Direct Sequence, Frequency Hopping)» The resulting spread signal occupy the same bandwidth transmitted at the same time Different bitrates to users control length of codes channel k Power control required in uplink» to compensate near-far effect channel 2 channel 1» If not, interference from close user swamps signal from far user time

33 WCMC-MPR-A 33 Combined Multi-access Techniques Cellular planning Current technologies combinations of multi-access techniques» GSM: FDMA and then TDMA to assign slots to users f 3 f 3 f 3 f 2 f 3 f 7 f 1 f 2 f 2 f 3 f 1 f 2 f 1 f 2 f 3 f 1 f 2 f 1 f 4 f 3 f 5 f 1 f 6 f 7 f 2 f 2 f 4 f 5 f 1 f 3 f 2 f f 2 f 1 f 2 1 f 3 f 8 f 5 f 6 f 3 f 4 f 4 f 5 f 6 f 1 f 3 f f 8 f 7 f 8 7 f 9 f 9 f 7 f 9 f 3 f 3 f 3 f 6 f 5 f 2 a) Group of 3 cells b) Group of 7 cells c) Group of 3 cells, each having 3 sectors

34 WCMC-MPR-A 34 Wireless Medium Access Control Issues Medium Access Control (MAC)» Assign radio resources to terminals along the time 3 type of resource allocation methods» dedicated assignment resources assigned in a predetermined, fixed, mode» random access terminals contend for the channel» demand-based terminals ask for reservations using dedicated/random access channels

35 WCMC-MPR-A 35 Alhoa, S-Alhoa, CSMA Alhoa Efficiency of 18 % if station has a packet to transmit transmits the packet waits confirmation from receiver (ACK) if confirmation does not arrive in round trip time, the station computes random backofftime retransmits packet Slotted Alhoa Efficiency of 37 % stations transmit just at the beginning of each time slot Carrier Sense Multiple Access (CSMA) Efficiency of 54 % station listens the carrier before it sends the packet If medium busy station defers its transmission ACK required for Alhoa, S-Alhoa and CSMA

36 WCMC-MPR-A 36 CSMA/CD Not Used in Wireless CDMA/Collision Detection Efficiency < 80% station monitors de medium (carrier sense) medium free transmits the packet medium busy waits until medium is free transmits packet if, during a round trip time, detects a collision station aborts transmission and stresses collision (no ACK packet) Problems of CDMA/CD in wireless networks Carrier sensing carrier sensing difficult for hidden terminal Collision detection near-end interference makes simultaneous transmission and reception difficult

37 WCMC-MPR-A 37 To think about? How to minimize collision in a wireless medium?

38 WCMC-MPR-A 38 CSMA with Collision Avoidance (CSMA/CA) DIFS S1 DATA DIFS S2-bo S2 DATA S3 DIFS S3-bo-e S3-bo S3-bo-r DIFS S3-bo-r DATA - Packet arrival DATA - Transmission of DATA DIFS - Time interval DIFS S2-bo - Backoff time, station 2 S3-bo-e - Elapsed backoff time, station 3 S3-bo-r - Remaining backoff time, station 3

39 WCMC-MPR-A 39 CSMA with Collision Avoidance (CSMA/CA) Station with a packet to transmit monitors the channel activity until an idle period equal to a Distributed Inter-Frame Space (DIFS) has been observed If the medium is sensed busy a random backoff interval is selected. The backoff time counter is decremented as long as the channel is sensed idle, stopped when a transmission is detected on the channel, and reactivated when the channel is sensed idle again for more than a DIFS. The station transmits when the backoff time reaches 0 To avoid channel capture, a station must wait a random backoff time between two consecutive packet transmissions, even if the medium is sensed idle in the DIFS time

40 WCMC-MPR-A 40 CSMA/CA ACK Required DIFS S1 DATA SIFS SIFS AP ACK ACK DIFS S2-Backoff S2 DATA - Packet arrival DATA - Transmission of DATA DIFS - Time interval DIFS

41 WCMC-MPR-A 41 CSMA/CA ACK Required CSMA/CA does not rely on the capability of the stations to detect a collision by hearing their own transmission A positive acknowledgement is transmitted by the destination station to signal the successful packet transmission In order to allow an immediate response, the acknowledgement is transmitted following the received packet, after a Short Inter-Frame Space (SIFS) If the transmitting station does not receive the acknowledge within a specified ACK timeout, or it detects the transmission of a different packet on the channel, it reschedules the packet transmission according to the previous backoff rules. Efficiency of CSMA/CA depends strongly of the number of competing stations. An efficiency of 60% is commonly found

42 WCMC-MPR-A 42 To Think About How to enable hidden terminals to sense the carrier? D A B C Hidden node C is hidden to A

43 WCMC-MPR-A 43 RTS-CTS Mechanism DIFS SIFS S1 RTS DATA SIFS SIFS AP CTS ACK DIFS S2-bo S2 DATA - Packet arrival DATA - Transmission of DATA DIFS - Time interval DIFS

44 WCMC-MPR-A 44 RTS-CTS Mechanism For some scenarios where long packets are used or the probability of hidden terminals is not irrelevant, the efficiency of CSMA/CA can be further improved with a Request To Send (RTS) - Clear to Send (CTS) mechanism The basic concept is that a sender station sends a short RTS message to the receiver station. When the receiver gets a RTS from the sender, it polls the sender by sending a short CTS message. The sender then sends its packet to the receiver. After correctly receiving the packet, the receiver sends a positive acknowledgement (ACK) to the sender This mechanism is particularly useful to transmit large packets. The listening of the RTS or the CTS messages enable the stations in range respectively of the sender or receiver that a big packet is about to be transmitted. Usually both the RTS and the CTS contain information about the number of slots required to transmit the 4 packets. Using this information the other stations refrain themselves to transmit packets, thus avoiding collisions and increasing the system efficiency. SIFS are used before the transmission of CTS, Data, and ACK In optimum conditions the RTS-CTS mechanism may add an efficiency gain of about 15%

45 WCMC-MPR-A 45 Guaranteed Access Control Polling» AP manages stations access to the medium» Channel tested first using a control handshake

46 Fundamental Networking WCMC-MPR-A 46

47 WCMC-MPR-A 47 Packet Switching Technologies: Ethernet, IP Path defined by packet destination address

48 WCMC-MPR-A 48 To Think About Suppose terminal a moves from port 2 to port 1» What needs to be done so that terminal a can continue receiving packets?

49 WCMC-MPR-A 49 L2 Networking Ethernet Format 7x Protocolo=IP Ethernet

50 WCMC-MPR-A 50 L2 Networking - Bridges Bridge builds forwarding tables automatically Address learning» Source Address of received frame is associated to a bridge input port station reachable through that port Frame forwarding» When a frame is received, its Destination Address is analysed If address is associated to a port frame forwarded to that port If not frame transmitted through all the ports but the input port

51 WCMC-MPR-A 51 L2 Networking - Single Tree Required Ethernet frame No hop-count Could loop forever Same for broadcast packet Layer 2 network Required to have tree topology Single path between every pair of stations Spanning Tree Protocol (STP) Running in bridges Helps building the spanning tree Blocks ports L2 Networking - Single Tree Required

52 WCMC-MPR-A 52 L3 Networking Packet Formats Version HLen TOS Length Version Traffic Class Flow Label Ident Flags Offset Payload Lengtht Next Header Hop Limit TTL Protocol Checksum SourceAddr SourceAddr (4 words) DestinationAddr Options (variable) Data Pad (variable) DestinationAddr (4 words) Options (variable number) Data IPv4 IPv6

53 WCMC-MPR-A 53 L3 Networking Multiple Trees Every router» finds the shortest path to the other routers and their attached networks» Calculates its Shortest Path Tree (SPT) Routing protocol» Run in routers» Helps routers build their SPT» RIP, OSPF, BGP A F B E C G D B s routing view Destination Cost NextHop A 1 A C 1 C D 2 C E 2 A F 2 A G 3 A

54 WCMC-MPR-A 54 Traditional TCP/IP Communications Stack IETF IP address based switching APP TCP IP T1 T1 T2 IP T2 T3 IP T3 T4 T4 T5 APP TCP IP T5 host bridge router router bridge host IEEE MAC address based switching

55 WCMC-MPR-A 55 Tunnel IP-in-IP APP TCP IP IP T1 T1 T2 IP T2 T3 IP IP T3 T4 T4 T5 APP TCP IP T5 H1 bridge R1 R2 bridge Server outer IP header inner IP header data ver. IHL TOS length IP identification flags fragment offset TTL IP-in-IP IP checksum SA= red IP address of H1 DA= red IP address of R2 ver. IHL TOS length IP identification flags fragment offset TTL lay. 4 prot. IP checksum SA=H1 DA= Server TCP/UDP/... payload

56 WCMC-MPR-A 56 Tunnel PPP over IP (E.g PPTP) APP TCP IP PPP GRE IP T1 T1 T2 IP T2 T3 IP PPP GRE IP T3 T4 T4 T5 APP TCP IP T5 H1 bridge R1 R2 bridge Server» GRE virtual point-to-point link routers at remote points over an IP network» PPP adequate for Authentication Transporting IP packets

57 IEEE WCMC-MPR-A 57

58 WCMC-MPR-A 58 Infrastructure Networks vs Ad-Hoc Networks Infrastructure AP AP wired network AP: Access Point AP Ad-hoc

59 WCMC-MPR-A 59 IEEE Infrastructure Network STA 1 ESS LAN BSS 1 Access Point BSS 2 Distribution System Access Point 802.x LAN Portal STA LAN STA 3 Station» Terminal with radio access Basic Service Set (BSS)» Set of stations in the same band Access Point (AP)» Interconnects LAN to wired network» Provides access to stations Stations communicate with AP Portal bridge to other networks Distribution System» Interconnection network» Logical network EES, Extended Service Set Based on BSSs

60 WCMC-MPR-A 60 IEEE Ad-Hoc Network LAN Direct communication between stations STA 1 IBSS 1 STA 3 Independent Basic Service Set, IBSS» Set of stations working the the same carrier (radio channel) STA 2 IBSS 2 STA 5 STA LAN

61 WCMC-MPR-A 61 IEEE Protocol Stack mobile terminal fixed terminal application TCP IP access point infrastructure network application TCP IP LLC LLC LLC MAC MAC MAC MAC PHY PHY PHY PHY

62 Protocol Stack WCMC-MPR-A 62

63 PHY DLC Station Management WCMC-MPR-A Layers and Functionalities Data plane» MAC medium access, fragmentation, encryption» PLCP - Physical Layer Convergence Protocol carrier detection» PMD - Physical Medium Dependent modulation, codification Management plane» PHY Management channel selection, MIB» MAC Management synchronisation, mobility, power, MIB» Station Management coordenation management functions LLC MAC PLCP PMD MAC Management PHY Management

64 WCMC-MPR-A 64 MAC Layer Access Methods DCF Distributed Coordination Function PCF - Point Coordination Function MAC-DCF CSMA/CA Carrier sense, collision avoidance using back-off mechanism ACK packet required for confirmations (except for broadcast packets) mandadory MAC-DCF with RTS+CTS Used to avoid hidden terminal problem Optional MAC- PCF Access Point asks stations to transmit Optional

65 WCMC-MPR-A 65 MAC Layer Guard Time Intervals DIFS DIFS medium busy PIFS SIFS contention next frame direct access if medium is free DIFS t» DIFS (DCF IFS) Lowest priority, used for asynchronous data» PIFS (PCF IFS) Medium priority, used for real time traffic /QoS» SIFS (Short Inter Frame Spacing) Maximum priority used for signalling: ACK, CTS, answers to polling

66 WCMC-MPR-A 66 MAC-DCF CSMA/CA Sending a frame in unicast» Station waits DIFS before sending the packet» If packet is correctly received (no errors in CRC) Receiver confirms reception immediatly, using ACK, after waiting SIFS» In case of errors, frame is re-transmitted» In case of retransmission Maximum value for the contention window duplicates Contetion window has minimum and maximum values (eg.: 7 and 255) sender DIFS data receiver SIFS ACK other stations waiting time DIFS contention data t

67 WCMC-MPR-A 67 MAC- PCF t 0 t 1 SuperFrame medium busy point coordinator PIFS D 1 SIFS SIFS D2 SIFS SIFS wireless stations U 1 U 2 stations NAV NAV

68 WCMC-MPR-A 68 MAC-PCF II t 2 t 3 t 4 point coordinator D 3 PIFS D4 SIFS SIFS CFend wireless stations U 4 stations NAV NAV contention free period contention period t

69 WCMC-MPR-A 69 MAC Frame Format bytes Frame types» Data, control, management Sequence number Addresses» destination, source, BSS identifier,... Others» Error control, frame control, data Duration/ Address Address Address Sequence ID Control Frame Control Protocol version Type Subtype To DS More Frag Retry Power Mgmt Address Data 4 bits From DS More Data WEP Order CRC

70 WCMC-MPR-A 70 To Think About STA 1 needs to send a frame to STA 2. In the Infrastructure mode, the frame is sent via the AP. What MAC addresses are required in the frame sent by STA 1 to the AP? Access Point BSS 2 STA LAN STA 2

71 WCMC-MPR-A 71 Addresses in MAC scenario to DS from address 1 address 2 address 3 address 4 DS ad-hoc network 0 0 DA SA BSSID - infrastructure 0 1 DA BSSID SA - network, from AP infrastructure 1 0 BSSID SA DA - network, to AP infrastructure network, within DS 1 1 RA TA DA SA DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address

72 WCMC-MPR-A 72 Special Frames- ACK, RTS, CTS Acknowledgement ACK bytes Frame Duration Receiver Control Address CRC Request To Send RTS bytes Frame Duration Receiver Transmitter CRC Control Address Address Clear To Send CTS bytes Frame Duration Receiver Control Address CRC (Fig do livro está errada)

73 PHY DLC Station Management WCMC-MPR-A 73 MAC Management Synchronization Station discovers a LAN; station associates to an AP stations synchronize clocks; Beacon is generated by AP Power management Roaming Save terminal s power terminal enters sleep mode Periodically No frame loss; frames are stored Station looks for new access points Station decides about best access point Station (re-)associates to new AP LLC MAC PLCP PMD MIB - Management Information Base MAC Management PHY Management

74 Synchronization by Beacon Infrastructure Network WCMC-MPR-A 74 Stations must be synchronised. E.g. To preview PCF cycles To change state: sleep wake Infrastructure networks Access Point sends (almost) periodically a Beacon with timestamp e BSSid sometimes medium is busy Timestamp sent is the correct Other stations adjust their clocks beacon interval access point medium B B B B busy busy busy busy value of the timestamp B beacon frame t

75 WCMC-MPR-A 75 Power Management Objective» If transceiver not in use sleep mode Station in 2 states: sleep, wake Infrastructure network» Stations wake periodically and simultaneously» They listen beacon to know if there are packets to receive» If a station has packets to receive remains awake until it receives them If not, go sleep; after sending its packets!

76 WCMC-MPR-A 76 Power Management Infrastructure Network Infrastructure network traffic information sent in the beacon» Traffic Indication Map TIM: list of unicast receivers» Delivery Traffic Indication Map - DTIM: list broadcast/multicast receivers TIM interval DTIM interval access point medium D B busy T T D D busy busy busy B station P D t T TIM D DTIM awake B broadcast/multicast P PS poll D data transmission to/from the station

77 WCMC-MPR-A Physical Layer 3 versões: 2 rádio, 1 IR Bitrates: 1, 2 Mbit/s FHSS (Frequency Hopping Spread Spectrum) Spreading, despreading 79 sequências de salto pseudo aleatórias. Para 1 Mbit/s, modulação de 2 níveis GFSK DSSS (Direct Sequence Spread Spectrum) 1 Mbit/s Modulation DBPSK (Differential Binary Phase Shift Keying) 2 Mbit/s Modulation DQPSK (Differential Quadrature PSK) Preamble and header of frame transmitted at 1 Mbit/s (DBPSK) Remainning transmitted at 1 (DBPSK) ou 2 Mbit/s (DQPSK) Maximum radiated power 1 W (EUA), 100 mw (UE), min. 1mW Infravermelho nm, distância de 10 m Detecção de portadora, detecção de energia, sincronização All versions provide Clear Channel Assessment (CCA) Used by MAC to detect if medium is free

78 WCMC-MPR-A 78 Frame FHSS PHY» Sincronization » SFD (Start Frame Delimiter » PLW (PLCP_PDU Length Word) Payload length in bytes, including 2 CRC bytes. PLW < 4096» PSF (PLCP Signaling Field) Transmission bitrate of payload (1, 2 Mbit/s) PLCP (preâmbulo and header) sent at 1 Mbit/s Payload sent at 1 ou 2 Mbit/s» HEC (Header Error Check) CRC with x 16 +x 12 +x 5 +1» Data MAC scrambled with z 7 +z variable bits synchronization SFD PLW PSF HEC payload PLCP preamble PLCP header

79 WCMC-MPR-A 79 Frame DSSS PHY Barker sequence of 11 chips +1,-1,+1,+1,-1,+1,+1,+1,-1,-1,-1 Sincronization Sincronization Gain control, Clear Channel Assessement, compensate frequency deviation SFD (Start Frame Delimiter Signal Payload bitrate (0A: 1 Mbit/s DBPSK; 14: 2 Mbit/s DQPSK) Service utilização futura, 00 = conforme Length Payload length in us HEC (Header Error Check) Protection of sinal, service and length, using x 16 +x 12 +x 5 +1 Data (payload) MAC scrambled with z 7 +z variable bits synchronization SFD signal service length HEC payload PLCP preamble PLCP header

80 WCMC-MPR-A 80 IEEE b Bitrate (Mbit/s) 1, 2, 5.5, 11 (depends on SNR) Useful bitrate 6 Transmission range 300m outdoor, 30m indoor Frequencies open, ISM 2.4 GHz band Only physical layer is redefined» MAC and MAC management are the same

81 WCMC-MPR-A 81 IEEE b Trama PHY Long PLCP PPDU format Payload bitrate variable bits synchronization SFD signal service length HEC payload PLCP preamble PLCP header 192 µs at 1 Mbit/s DBPSK 1, 2, 5.5 or11 Mbit/s Short PLCP PPDU format (optional) variable bits short synch. SFD signal service length HEC payload PLCP preamble (1 Mbit/s, DBPSK) PLCP header (2 Mbit/s, DQPSK) 96 µs 2, 5.5 or 11 Mbit/s

82 WCMC-MPR-A 82 Channel Selection Europe (ETSI) channel i = 2412MHz + (i-1)*5mhz There are 14 channels of 5MHz In b only 3 non-overlap channels can be used channel 1 channel 7 channel US (FCC)/Canada (IC) 22 MHz [MHz] channel 1 channel 6 channel MHz [MHz]

83 WCMC-MPR-A 83 IEEE a Bitrate (Mbit/s)» 6, 9, 12, 18, 24, 36, 48, 54 (depends on SNR)» Mandatory 6, 12, 24 Useful bit rate (frames 1500 bytes, Mbit/s)» 5.3 (6), 18 (24), 24 (36), 32 (54) Transmission range» 100m outdoor, 10 m indoor 54 Mbit/s até 5 m, 48 até 12 m, 36 até 25 m, 24 até 30m, 18 até 40 m, 12 até 60 m Frequencies» Free, band ISM» , GHz (Europa) Only the physical layer changes

84 WCMC-MPR-A 84 Operating channels for a / US U-NII channel [MHz] 16.6 MHz channel center frequency = *channel number [MHz] [MHz] 16.6 MHz

85 WCMC-MPR-A 85 OFDM in IEEE a OFDM with 52 used subcarriers (64 in total) 48 data + 4 pilot (plus 12 virtual subcarriers) khz spacing pilot khz channel center frequency subcarrier number

86 WCMC-MPR-A a Rate Dependent Parameters % of useful information 250 ksymbol/s

87 IEEE WCMC-MPR-A 87

88 WCMC-MPR-A 88 IEEE Commonly used terms BS Base Station SS Subscriber Station, (i.e., CPE) DL Downlink, i.e. from BS to SS UL Uplink, i.e. from SS to BS FDD Frequency Division Duplex TDD Time Division Duplex TDMA Time Division Multiple Access TDM Time Division Multiplexing OFDM Orthogonal Frequency Division Multiplexing OFDMA - Orthogonal Frequency Division Multiple Access QoS Quality of Service

89 WCMC-MPR-A 89 IEEE Introduction Source: WiMAX, making ubiquitous high-speed data services a reality, White Paper, Alcatel.

90 Reference Model WCMC-MPR-A 90

91 WCMC-MPR-A 91 Adaptive PHY Source: Understanding WiMAX and 3G for Portable/Mobile Broadband Wireless, Technical White Paper, Intel.

92 WCMC-MPR-A 92 Adaptive Burst Profiles Burst profile - Modulation and FEC On DL» multiple SSs can associate the same DL burst On UL» SS transmits in an given time slot with a specific burst Dynamically assigned according to link conditions» Burst by burst» Trade-off capacity vs. robustness in real time

93 WCMC-MPR-A 93 OFDM PHY TDD Frame Structure Time Frame n-1 Frame n Frame n+1 Adaptive DL Subframe UL subframe pre. FCH DL burst 1 DL TDM DL burst 2 UL TDMA DL... burst n... pre. UL burst 1 pre. UL burst m DL MAP UL MAP DCD opt. UCD opt. Broadcast Conrol msgs

94 WCMC-MPR-A 94 OFDM PHY FDD Frame Structure Time Frame n-1 Frame n Frame n+1 DL Subframe DL TDM DL TDMA pre. FCH DL burst 1 DL burst 2... DL burst k pre. DL burst k+1... pre. DL burst n Broadcast Control Msgs DL MAP UL MAP DCD opt. UCD opt. UL subframe UL MAP for next MAC frame UL bursts pre. UL burst 1 UL TDMA... pre. UL burst m

95 WCMC-MPR-A 95 FDD MAPs Time Relevance DL UL MAP MAP DL UL MAP MAP DOWNLINK UPLINK frame Broadcast Half Duplex Terminal #1 Full Duplex Capable User Half Duplex Terminal #2

96 OFDMA WCMC-MPR-A 96

97 OFDMA WCMC-MPR-A 97

98 OFDMA, TDD WCMC-MPR-A 98

99 WCMC-MPR-A 99 IEEE MAC Addressing and Identifiers SS has 48-bit IEEE MAC address BS has 48-bit base station ID» Not a MAC address; 24-bit operator indicator 16-bit connection ID (CID) 32-bit service flow ID (SFID) 16-bit security association ID (SAID)

100 WCMC-MPR-A 100 Convergence Sub-Layer (CS) ATM Convergence Sub- Layer» Support for VP/VC connections» Support for end-to-end signaling of dynamically created connections» ATM header suppression» Full QoS support Packet Convergence Sub- Layer» Initial support for Ethernet, VLAN, IPv4, and IPv6» Payload header suppression» Full QoS support

101 WCMC-MPR-A 101 MAC CPS Data Packet Encapsulations Packet PDU (e.g., Ethernet) Ethernet Packet CS PDU (i.e., MAC SDU) P H SI Ethernet Packet MAC PDU HT MAC PDU Payload CRC FEC FEC block 1 FEC Block 2 FEC Block 3... FEC block m PHY Burst (e.g., TDMA burst) Preamble OFDM symbol 1 OFDM symbol 2... OFDM symbol n

102 WCMC-MPR-A 102 MAC CPS MAC PDU Transmission MAC PDUs are transmitted in PHY Bursts The PHY burst can contain multiple FEC blocks MAC PDUs may span FEC block boundaries Concatenation Packing Segmentation Sub-headers

103 WCMC-MPR-A 103 MAC CPS MAC PDU Concatenation Multiple MAC PDUs are concatenated into the same PHY burst MAC PDU 1 MAC PDU 2 MAC PDU k HT MAC PDU Payload CRC HT MAC PDU Payload CRC... HT MAC PDU Payload CRC FEC FEC block 1 FEC Block 2 FEC Block 3... FEC block m PHY Burst (e.g., TDMA burst) Preamble OFDM symbol 1 OFDM symbol 2... OFDM symbol n

104 WCMC-MPR-A 104 MAC CPS MAC PDU Fragmentation A MAC SDU can be fragmented into multiple segments, each segment is encapsulated into one MAC PDU Fragmentation Sub-Header (8 bits) HT F S H MAC SDU seg-1 MAC PDU Payload CRC HT MAC SDU F S H MAC SDU seg-2 MAC PDU Payload CRC MAC SDU seg-3 HT F S H MAC PDU Payload CRC FEC FEC block 1... FEC Block m1 FEC block 1... FEC Block m2 Pre. OFDM symbol 1... OFDM symbol n1 Pre. OFDM symbol 1... OFDM symbol n2 PHY Burst PHY Burst

105 WCMC-MPR-A 105 MAC CPS QoS Three components of QoS» Service flow QoS scheduling» Dynamic service establishment» Two-phase activation model (admit first, then activate) Service Flow» A unidirectional MAC-layer transport service characterized by a set of QoS parameters (latency, jitter, throughput)» Identified by a 32-bit SFID (Service Flow ID) Three types of service flows» Provisioned: controlled by network management system» Admitted: the required resources reserved by BS, but not active» Active: the required resources committed by the BS

106 WCMC-MPR-A 106 MAC CPS Uplink Service Classes UGS: Unsolicited Grant Services rtps: Real-time Polling Services nrtps: Non-real-time Polling Services BE: Best Effort

107 WCMC-MPR-A 107 MAC CPS Automatic Repeat request (ARQ) A Layer-2 sliding-window based flow control mechanism Per connection basis Only effective to non-real-time applications Uses a 11-bit sequence number field Uses CRC-32 checksum of MAC PDU to check data errors Maintain the same fragmentation structure for Retransmission Optional