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Outline

Outline. Wireless introduction Wireless cellular (GSM, CDMA, UMTS, WiMAX) Wireless LANs, MAC layer Wireless Ad hoc networks routing: proactive routing, on-demand routing, scalable routing, geo-routing multicast TCP QoS, adaptive voice/video apps Sensor networks.

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  1. Outline Wireless introduction Wireless cellular (GSM, CDMA, UMTS, WiMAX) Wireless LANs, MAC layer Wireless Ad hoc networks routing: proactive routing, on-demand routing, scalable routing, geo-routing multicast TCP QoS, adaptive voice/video apps Sensor networks

  2. Cellular Wireless Network Evolution • First Generation: Analog voice • AMPS: Advance Mobile Phone Systems • Residential cordless phones • FDMA • Second Generation: Digital voice • GSM: European Digital Cellular - TDMA • IS-54/136: North American - TDMA • IS-95: CDMA (Qualcomm) • DECT: Digital European Cordless Telephone

  3. Cellular Evolution (cont) • Third Generation: Packet data • will combine the functions of: cellular, cordless, wireless LANs, paging etc. • will support multimedia services (data, voice, video, image) • Requirements • 384 Kbps for full area coverage • 2 Mbps for local area coverage • variable bit rate • packet traffic support • flexibility (eg, multiple, multimedia streams on a single connection)

  4. Cellular Evolution (cont) • Third Generation: Packet data • 2.5 G • GPRS (for GSM) (General Packet Radio Service ) • EDGE (for GSM) (Enhanced Data rates for Global Evolution) • 1xRTT (for CDMA) • 3G (W-digital CDMA) • IMT-2000/UMTS (International Mobile Telecommunications) (Universal Mobile Transport Service) • CDMA 2000, WCDMA, TD-CDMA, TD-SCDMA • 3+G, 4G systems • OFDM, Software radio, Array antennas • WiMAX

  5. Architecture • System architecture • networking • addressing • Physical (PHY) layer • radio band • modulation • error control (FEC/interleaving) • frame structure • multiple access (multi-user, up/down) • MAC/DLC layer • channel mapping (control/traffic) • medium access techniques • call setup • standby behavior

  6. BS BS BS Backbone Network BS BS BS Cellular Concept • Geographical separation • Capacity (frequency) reuse • Backbone connectivity

  7. B B B C C C G G G A A A D D D F F F E E E 1G: AMPS (Advanced Mobile Phone System) ---- FDMA • Frequencies are not reused in a group of 7 adjacent cells • To add more users, smaller cells can be used • In each cell, 57 channels each for A-side carrier and B-side carrier respectively Channels are divided into 4 categories: 1. Control (base to mobile) to manage the system 2. Paging (base to mobile) to alert mobile users to incoming calls 3. Access (bidirectional) for call set up and channel assignment 4. Data (bidirectional) for voice, FAX, or data

  8. Handoff • Handoff: Transfer of a mobile from one cell to another • Each base station constantly monitors the received power from each mobile • When power drops below given threshold, base station asks neighbor station (with stronger received power) to pick up the mobile, on a new channel • The handoff process takes about 300 ms

  9. HLR (home location register) – information MSC (mobile switching center) VLR (visitor location register) – information BS (base station) - modulation, antenna Organization of Cellular Networks

  10. To register and make a phone call • When phone is switched on , it scans a preprogrammed list of 21 control channels, to find the most powerful signal • It transmits its ID number on it to the MSC which • informs the local HLR • adds it to VLR and informs the home MSC which informs the HLR • registration is done every 15 min • To make a call, user transmits dest Ph # on random access channel; MSC will assign a data channel • At the same time MSC pages the destination cell for the other party (idle phone listens on all page ch.)

  11. How does a call get to the mobile ? • Suppose (310) 643 - 1111 is roaming in the (408) area code • Cell phone registers with the (408) MSC, which adds it to (408) VLR and informs the (310) HLR of the location of the cell phone • A call comes in for (310) 643 – 1111. Then (310) MSC queries its HLR, and directs the call to the (408) MSC • The (408) MSC forwards the call to the mobile

  12. (Freq Division Duplex)

  13. 2G: Digital Cellular: IS-54 TDMA System • Second generation: digital voice • FDMA / TDMA • Same frequency as AMPS – 416 ch • Each 30 kHz RF channel is used at 48.6 kbps • 6 TDM slots/RF band (2 slots per user) • 8 kbps voice coding • 16.2 kbps TDM digital channel (3 channels fit in 30kHz) • 4 cell frequency reuse (not 7) • Capacity increase per cell per carrier • 3 x 416 / 4 = 312 (instead of 57 in AMPS) • Additional factor of two with speech activity detection.

  14. Frame 1944 bits in 40 ms( 48600 b/s) SLOT 1 SLOT 2 SLOT 3 SLOT 4 SLOT 5 SLOT 6 DATA1122 DATA1122 DVCC 12 SYNC228 SACCH112 R6 G6 DATA116 MOBILE TO BASE G:GUARD TIME R:RAMP TIME DVCC: DIGITAL VERIFFICATION COLOR CODE RSVD: RESERVE FOR FUTURE USE RSVD 12 DATA1130 DATA1130 DVCC 12 SYNC228 SACCH 12 IS-54 slot and frame structure BASE TO MOBILE

  15. 2G: European GSM (Group Special Mobile) • Second Generation: Digital voice • FDMA / TDMA • Frequency Division duplex (890-915 MHz Up; 935-960 MHz Down) • 125 frequency carriers, Carrier spacing: 200 Khz • 8 channels per carrier (Narrowband Time Division) • Physical ch 124x8 = 992, reuse factor N = 3 or 4 • Capacity per cell per carrier: 992/ N = 330 or 248 • Speech coder: linear predictive coding (13 Kbps) • Modulation: Frequency Shift Keying (Gaussian Minimum Shift Keying) • Multilevel, time division frame structure • Slow frequency hoppingto overcome multipath fading

  16. Access techniques for mobile communications FDMA (TACS) P F TDMA (GSM, DECT) ATDMA (UMTS) T P F CDMA (UMTS) T P F P - Power T - Time F - Frequency T

  17. Spread Spectrum

  18. CDMA (Code Division Multiple Access) • unique “code” assigned to each user; i.e., code set partitioning • all users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode data • Note: chipping rate >> data rate (eg, 64 chips per data bit) • encoded signal = (original data bit) X (chipping sequence) • decoding:inner-product of encoded signal and chipping sequence • allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)

  19. CDMA Encode/Decode

  20. CDMA: two-sender interference

  21. . m inner-product S T = = 0 1 SSi.Ti m i=1 . S S = 1 C = (1,1,1,1) 4,1 C = (1,1) 2,1 C = (1,1,-1,-1) 4,2 = (1,-1,1,-1) C 4,3 = (1,-1) C 2,2 C = (1,-1,-1,1) 4,4 Orthogonal Variable Spreading Factor

  22. CDMA (Code Division Multiple Access): IS-95 QUALCOMM, San Diego • Based on DS spread spectrum • Two frequency bands (1.23 Mhz), one for forward channel (cell-site to subscriber) and one for reverse channel (sub to cell-site) • CDMA allows reuse of same spectrum over all cells. Net capacity improvement: • 4 to 6 over digital TDMA (eg. GSM) • 20 over analog FM/FDMA (AMPS)

  23. CDMA (cont’d) • One of 64 PS (Pseudo Random) codes assigned to subscriber at call set up time • RAKE receiver (to overcome multi path-fading) • Pilot tone inserted in forward link for: • power control • coherent reference • Speech activity detection • Voice compression to 8 kbps (16 kbps with FEC) • IS-95: 20 wideband channels, BW=1.25 MHz

  24. Third generation services-- vs 2G 2M 384K 64K 32K 16K 9.6K 2.4K 1.2K video conference remote medical service video on demand video catalogue shopping mobile TV electronic newspaper ISDN internet telephone conference voice mail distribution services (voice) mobile radio pager electronic publishing distribution services (data) telephone FAX bidirectional unidirectional multicast point to point multipoint

  25. Third generation bandwidth assignment -- high frequency 2 GHz, wideband 150 MHz ITU IMT-2000 IMT-2000 MSS MSS 1885 1920 1980 2010 2025 2110 2170 2200 MHz EUROPE IMT-2000 DECT MSS IMT-2000 MSS 1880 1900 1980 2010 2025 2110 2170 2200 MHz JAPAN IMT-2000 PHS MSS IMT-2000 MSS 1885 1895 1918.1 1980 2010 2025 2110 2170 2200 MHz

  26. Site Contr Site Contr Site Contr Site Contr BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS UTRAN Architecture(UMTS Terrestrial Radio Access Net) Core Network Iu Iu UTRAN RNS Iur RNS RNC RNC Iub Iub Iub Iub B-node B-node B-node B-node

  27. W-CDMA (Wide Band CDMA) Key features • Improved capacity and coverage (over second generation); thus, backward compatible • high frequency 2 GHz, wideband 150 MHz • High degree of service flexibility: multiple, parallel services per connection; efficient packet access • Operator flexibility: asynchronous interstation operation; hierarchical cell structures (HCS); adaptive antenna arrays (enabled by uplink pilot symbols); TDD (Time Division Duplex) mode for asymmetric traffic & uncoordinated environments

  28. Radio Interface - protocol architecture C-plane U-plane L3 RRC LAC LAC L2/LAC LAC Logical channels RLC RLC RLC RLC L2/MAC MAC Transport channels Physical Layer L1

  29. Layer 1 - up link physical channels(W-CDMA example) Dedicated Physical Data Channel Data 0.667 ms Dedicated Physical Control Channel Transport format ind. Transmit power control Pilot Feedback indicator Slot#2 Slot#i Slot#15 Slot#1 frame Frame#i superframe Frame#72 Frame#1 Frame#2 10 ms

  30. Layer 1 - down link physical channels(W-CDMA example) DPCCH DPDCH Pilot Data TFI TPC 0.667 ms frame Slot#1 Slot#2 Slot#i Slot#15 superframe Frame#72 Frame#2 Frame#i Frame#1 10 ms

  31. WiMAX - IEEE 802.16a - 3G/4G? • Worldwide Interoperability for Microwave Access (WiMAX) is an industry trade organization to promote and certify compatibility and interoperability of broadband wireless access equipments that conform to the IEEE 802.16a specified wireless metropolitan area networks (WMAN) • IEEE 802.16a - support WMAN operating at 2-11 GHz that will provide broadband wireless connectivity to fixed, portable and nomadic devices • It supports WMAN to connect 802.11 hot spots to the Internet providing a wireless alternative to cable and DSL for last mile broadband access

  32. WAN Configuration The core components of a WAN system are the subscriber station (SS) and the base station (BS) A BS and one or more SSs can form a cell with a point-to-multipoint (P2MP) structure The BS controls activity within the cell including access to the medium by SSs, allocations to achieve QoS and admission to the network Multiple BSs can be configured to form a cellular wireless network. The radius of a cell can be 2-40 km while practical one is around 7-8 km with data rate as 70 Mbps per RF channel at a BS A point-to-point (P2P) or mesh topology also supported by the IEEE 802.16 standard

  33. WMAN (wireless metropolitan area networks)

  34. Protocol Stack

  35. WiMAX: Physical Layer WiMAX can operate in both licensed and unlicensed bands The 2.5 and 3.5 GHz licensed bands will be the most common bands for WiMAX applications On 2.4 GHz and 5 GHz non-licensed bands, their usage could be limited due to interference, which can degrade QoS services The minimum channel bandwidth for WiMAX usage is 1.75MHz per channel, while 10 MHz is considered as an optimum

  36. WiMAX: Physical Layer • IEEE 802.16a standard featured with 256 OFDM physical layer specification conforms the ETSI HiperMAN standards • OFDM (Orthogonal Frequency Division Multiplexing) 正交频分复用技术 • Multi-Carrier Modulation 多载波调制 • 将信道分成若干正交子信道，将高速数据信号转换成并行的低速子数据流，调制到在每个子信道上进行传输 • 正交信号可以通过在接收端采用相关技术来分开，可以减少子信道之间的相互干扰

  37. WiMAX: Physical Layer The transmission time is divided into frames that are divided into slots In an FDD system, uplink (SS to BS) and downlink (BS to SS) subframes are time aligned on separate frequency channels In a TDD system, each frame is divided into a downlink subframe and an uplink subframe In both modes, the length of any frame can vary under the control of the BS scheduler In TDD mode, the length of any uplink and downlink subframe can also vary, allowing asymmetric allocation between uplink and downlink

  38. WiMAX: Physical Layer IEEE 802.16 has specified several physical layers: physical layer for 10-66 GHz physical layer for 2-11 GHz, which can be further divided into subgroups

  39. WiMAX: MAC Layer Features The on-air timing is based on consecutive frames that are divided into slots The size of frames and the size of slots within the frames can be varied under the control in the BS The 802.16 MAC provides a connection-oriented service to upper layers of the protocol stack The QoS parameters for a connection can be varied by the SSs making requests to the BS to change them while a connection is maintained While extensive bandwidth allocation and QoS mechanisms are specified, the details of scheduling and reservation management are left unstandardized

  40. WiMAX: MAC Layer Features MAC protocal data units (MPDUs) are transmitted in time slots. MPDUs are the packets transferred between the MAC and the PHY layer A privacy sublayer performs authentication of network access and connection establishment, key exchange and encryption of MPDUs MAC service data units (MSDUs) are the packets transferred between the top of the MAC and the layer above A convergence sublayer at the top of the MAC enables Ethernet, ATM, TDM voice and IP services to be offered over the MAC layer

  41. WiMAX: MAC Layer Features • The MAC is concerned much with performing the mapping from MSDUs to the MPDUs • Across MPDUs, MSDUs can be fragmented. Within MPDUs, MSDUs can be packed (aggregated). • Automatic retransmission request (ARQ) is used to request the retransmission of unfragmented MSDUs and fragments of MSDUs

  42. WiMAX: MAC Layer Features Each connection in the uplink is mapped to a scheduling service associated with rules for BS to allocate the uplink capacity The specification of the rules and the scheduling service for a particular uplink connection is negotiated at setup 4 scheduling services defined in the standard Unsolicited grant service (UGS) carries traffic of periodical fixed units of data. The BS grants of the size negotiated at setup regularly and preemptively without an SS request.

  43. WiMAX: MAC Layer Features Used with UGS, an SS can report status of its transmission queue and request more by the grant management subheader The BS can allocate some additional capacity to the SS to allow it recover the normal queue state The real-time polling service serves traffic with dynamic nature and offers periodic dedicated request opportunities to meet time requirements An SS issues explicit requests and capacity is granted only as the real need. The overhead and latency is more. It is well suited for connections carrying VoIP, streaming video or audio traffic

  44. WiMAX: MAC Layer Features The non-real-time polling service is similar to the real-time polling service. But connections send bandwidth requests by random access. The served traffic needs to tolerate longer delays and is insensitive to delay jitter suitable for Internet access with a minimum guaranteed rate; A best effort service is defined without throughput and delay guarantees. An SS can send requests for bandwidth by random access or dedicated transmission opportunities if available.

  45. WiMAX: Mesh Networks Three types of important nodes in Mesh systems: The SSs with direct links to a node are the neighbors of the node. A node’s neighbors are one-hop away from the node. Neighbors of an SS form a neighborhood. ` An extended neighborhood contains all the neighbors of the neighborhood.

  46. WiMAX: Mesh Networks

  47. WiMAX: Mesh Networks--centralized scheduling The centralized scheduling is more determined than that in the distributed scheduling mode The network connections and topology are the same as in the distributed scheduling mode The request and grant process uses the Mesh Centralized Scheduling (MSH-CSCH) message The BS determines the flow assignments from the resource requests from the SSs Then, the SSs determine the actual schedule from the flow assignments

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