Multi-Tier Wireless Data Access

1. Multi-Tier Wireless Data Access • Macro Cellular Network • Ardis, RAM Mobitex • CDPD • ASM/CSD/SMS/GPRS/EDGE: 9.6~384Kbps; circuit or packet data. • CDMA (IS-95): 9.6 and 14.4 Kbps circuit data. • WCDMA/CDMA 2000: up to 2 Mbps~10Mbps for wireless multimedia services.

2. Micro Cellular Network • Metricom: packet forwarding; ISM band at 902-928MHz; up to 128Kbps. • PHS: circuit operation; 64/128Kbps. • DECT • PACS

3. Wireless LAN • Wave LAN: by NCR for banking services; 2Mbps at 900MHz ISM band. • IEEE 802.11 • HIPERLAN: high-performance wireless LAN • Wireless ATM • Bluetooth: sub-wireless LAN. • Home RF: relax PHY specs from 802.11

4. CMU Project Andrew has demonstrated multi-tier wireless packet data access using WaveLAN and CDPD equipment providing 2 Mbps within a campus and about 10 Kbps over wide areas. • Dual-mode PHS-PDC • Dual-mode GPRS-HiperLAN

5. ISM (Industrial, Scientific, and Medical) band • 902-928MHz, 2400-2483.5 MHz, and 5725-5850 MHz • Must be shared with other users (neighboring wireless LAN) and devices (microwave ovens) • Required to use spread spectrum transmission techniques.

6. Two Classes of Wireless LANs • Infrastructure Wireless LAN: an infrastructure of wireless access points that the portable devices can communicate with to access a backbone network. • Ad hoc wireless LAN: a set of portable devices communicate one with another to form, on demand, a self-contained LAN.

7. IEEE 802.11 • 2 Mbps DS and FH modes at 900 MHz and 2.4 GHz • 11 Mbps DS mode at 2.4 GHz (802.11b) • 20 Mbps HIPERLAN at 5 GHz. • 30 Mbps OFDM mode at 5.7 GHz • IrDA for high speed infrared system.

9. 802.11 Wireless Local Area Network

10. Extended Service Set server Distribution System Access Point Access Point station station station station station Architecture Basic Service Set

11. IEEE 802.11 Architecture • BSS consists of some number of stations executing the same MAC protocol and competing for access to the same shared medium. • The smallest building block • Can be isolated or connected by a distribution system. • ESS consists of two or more BSS’s interconnected by a distribution system. • Appeared as a single logical LAN to LLC level

12. Three Types of Stations ( based on mobility ) • No-transition • Stationary station or stations that move within a BSS. • BSS-transition • stations that move between BSS in the same ESS • ESS-transition • Stations that move across ESS boundary.

14. Physical Medium • Infrared at 1 Mbps and 2 Mbps at a wavelength between 850 and 950 nm. • Direct-sequence spread spectrum in the 2.4 GHz ISM band. • Frequency-hopping spread spectrum in the 2.4 GHz ISM band.

15. Medium Access Control • DFWMAC (distributed foundation wireless MAC): • provides a distributed access-control mechanism with an optional centralized control built on top of that. • DCF (distributed coordination function) uses a contention algorithm to provide access to all traffic. • PCF (point coordination function) uses a centralized algorithm over DCF to provide contention-free service.

17. Distributed Coordination Function (DCF) • Use CSMA with prioritized fair control. • A set of delays called interframe space (IFS) is used for priority control. • A station transmits data if the medium is sensed idle for IFS. • If the medium is busy, defer transmission and continue to monitor the medium until the current transmission is over. • Once the transmission is over, the station delay another IFS. If the medium remains idle for this period, then the station backs off using a binary exponential backoff scheme and again sense the medium. If the medium is still idle, the station may transmit.

18. Prioritized Access Control • SIFS (short IFS). • The shortest IFS, used for all immediate response actions. • PIFS (point coordination function IFS). • A mid-length IFS, used by the centralized controller in the PCF scheme when issuing polls to take precedence over normal-contention traffic. • DIFS (distributed coordination function IFS). • The longest IFS, used as a minimum delay for asynchronous frames contending for access.

20. Prioritized Access Control (cont’) • Any station using SIFS to determine transmission priority has the highest priority.The SIFS is used when • Acknowledgment (ACK): to speed up multi-frame LLC PDU transmission. • Clear to Send (CTS): A station can ensure that its data frame will get through by first issuing a small Request to Send (RTS) frame. All other stations defer using the medium until they see a corresponding CTS, or until a timeout occurs. • Poll response.

21. Point Coordination Function (PCF) • A centralized polling master ( Point Coordinator ( PC ) ) polls in a round-robin fashion to all stations configured for polling. • Once a polling cycle is started, the medium is seized by the PC and asynchronous traffic is locked out. • A superframe is defined in which the PC may optionally seize control and issue polls for a given period of time. The interval is varied. The remainder of the superframe is available for contention-based access.

22. Future Wideband OFDM for WLAN • Multicarrier modulation techniques • Multigate the effect of frequency selective fading • Peak power reduction techniques • Dynamic packet assignment techniques can provide very high spectral efficiency. • Asymmetrical access • The use of diversity/interference suppression/smart antenna with OFDM

24. Wireless Networking for the Connected Home • PC/Internet lacks mobility and convenience of location ( last 150 feet ). • Major opportunity in home networking is to extend PC/Internet throughout yard and home. • Resource sharing in multi-PC home. • Home RF working group in 1997 • Enable interoperable wireless voice and data networking within the home.

26. Home RFTechnical Summary • Hybrid TDMA/CSMA frame • Beacon from Connection Point (CP) sets frame structure • Frequency hopping, 50 hops/sec • 2 or 4 FSK yields 1 or 2 Mb/s • Also supports TCP/IP voice • Range up to 50 meters

27. Home RF Technical Summary--Data • Relaxed PHY specs from 802.11 • Lowers radio cost significantly • Same hop sequences • Localized for France, Spain, Japan, US, EC • Different BW for Japan, France, Spain • Comparable backoff, packet structure, ad-hoc capabilities

28. Home RF Technical Summary--Voice • DECT with retransmission • Uses DECT calling stack • Uses DECT A/B fields • 32kb/s ADPCM • 20ms frames—retransmit in beginning, outbound at end • Up and down link packets interleaved

29. Home RFNetwork Architecture • Isochronous • Used for cordless tele/videophones • Can make calls with no PC • PC connected gives enhanced services • Asynchronous • Peer-peer • For resource sharing (file, modem, printer) • Mixed I and A • Power Management

30. SWAP • Shared Wireless Access Protocol (SWAP) • TCP/IP networking • Internet access • Voice telephony via PSTN (VoIP) • Revision 1.2 specification is available. • Support both isochronous clients and an asynchronous network of peer devices.

31. Applications • PC-enhanced cordless telephone. • Mobile viewer appliance. • Resource sharing among multiple PCs in the same home.

32. SWAP Architecture • Support isochronous services and ad hoc peer-to-peer network that provides traditional data networking. • Three kinds of devices: • A connection point (CP): a gateway between PC, PSTN, and SWAP-compatiable devices. • Voice devices ( I node ) • Asynchronous data devices ( A-nodes ) • TDMA for client/server interactive voice and CSMA for data services.

34. MAC Overview • Interoperate with PSTN using a subset of Digital Enhanced Cordless Telecom (DECT) standard. • Use frequency-hoping radio and TDMA for isochronous data • Use CSMA/CA to support delivery of asynchronous data.

35. Feature of SWAP MAC • Good support for voice and data by using both TDMA and CSMA/CA access mechanisms. • Support four high-quality voice connection with 32 kb/s ADPCM • High data throughput of 1.6 Mb/s • Data security • Power management for both I and A nodes • 24-bit network ID

36. Frequency Hopping Frame Structure Connection requect Synchronization & Retransmission signal 20 msec TDM

37. Superframe Structure • Two Contention-Free Periods ( CFPs) and a contention period. • A frame is 20 msec long. • A beacon is transmitted immediately after the hop for • maintain network synchronization • control the format of the superframe • manage when each node should transmit and receive data

38. Superframe Structure (cont.) • CFP2 is used for the initial transmission of the voice data. • CFP1 is used for optional up to four retransmission of any data which was not received or incorrectly received in the previous dwell. • Each voice channel contain 640 bit ADPCM data and 56 bits of control data.

39. Superframe Structure (cont.) • CFP2 and CFP1 are separated by frequency hop, giving freq. And time diversity. • Piggy back ack in each uplink packet for acknowledgement. • A service slot after CFP1 for connection request by voice devices.

40. CSMA/CA • Use a contention window and backoff counter. • Algorithm: Select a backoff counter and start listen while backoff counter \=0 { if medium is free up to DIFS while the medium is free and backoff counter \= 0 decrease backoff counter by one for each free contention slot; if backoff counter = 0 and the medium is free { transmit data immediately; if success, break; else { enlarge collision window from 8 exponentially to 64 select a new backoff counter } }

41. Countdown

42. Power Management • I-node with an Active connection, • wake CPB ( CP Beacon ) & receive assignment • wake when assigned slots are due • I-node without active connection • wake every N dwell times • N is system configuration

43. Power-Saving Asynchronous nodes ( PS-nodes ) • CP maintains a countdown to the next dwell when PS-nodes should wake up, which is broadcast in CPB • PS-nodes receives the countdown from CPB and goes back to sleep. • Countdown is a system parameter depending on the buffer size and latency.

44. Broadcast for PS-nodes 1 4 2 3 5

45. Unicast for PS-nodes Wake up flag

46. Bluetooth Radio System • Piconet based networking with dynamically formed master and slave nodes. • At most 8 nodes in a pico net. • Master node ID is used to identify each pico net. • (FH)-CDMA is used for bandwidth sharing. • Frequency 2.45 MHz in ISM band.

47. FH/TDD Channel Frequency Hoping TDD Dwell time

48. FH-CDMA • 79 hop carriers are defined at 1 MHz spacing • minimum well time is 625 micro sec. • A large number of pseudo-random hopping sequence are defined • master determines the hop sequence used. • The native clock of master also defines the phase in the hopping sequence. • Slave selects sequence and tune clock to master

49. MAC Protocol • A pico net is dynamically generated and identified by master’s identity and clock. • Peer communication. Master/slave is applied only when pico net is formed. • Master controls the traffic and access control of the pico net. • Master implements centralized control in alternately manner ( M ==> S & S ==>M)

50. MAC ( cont. ) • Master uses a polling technique: • for each slave-to-master slot, the master decides which slave is allowed to transmit. • Per-slot basis • Master-to-slave data transmission is implicitly polling • No data, master must explicitly polls slaves.