Wireless Communications

1. Wireless Communications • Objectives • Understand 802.11 • Bluetooth

2. Wireless (802.11) Hedy Lamarr, seen in 1946, had a string of hit films in the 1930s and 1940s.

3. Hedy Lamarr • Deseret News Jan 30 2000 page E10 • Hedy Lamarr, the Austrian movie siren whose assets included buckets of beauty and a thimble of acting talent, was found dead at her home in Orlando, Fla., last week. She was 86 and only recently had begun to enjoy recognition for her real-life role as the godmother of cell phone technology.

4. On the acting side • She was celebrated more for quotability than ability. Her declamation that "any girl can be glamorous — all you have to do is stand still and be stupid," remains the most accurate description of her presence in movies such as "Algiers" (1938), "Ziegfeld Girl" (1941) and "Tortilla Flat" (1942).

5. Just a pretty face? • While her colleagues in Hollywood plotted their next radio appearance, she immersed herself in the intricacies of spread spectrum radio transmission, the forerunner of cellular technology. It is possible that without Lamarr, modern military communications and cordless phones would not exist. About no other screen legend can it be said that her invention has provided more pleasure than did contemplation of her gorgeous face.

6. Background • Hedwig Eva Maria Kiesler was born in Vienna on Nov. 9, 1913, to Jewish parents, a banker father and a pianist mother. • One of the leading arms manufacturers in Europe, Mandl operated a factory that helped prepare Mussolini for Abyssinia and would later supply Hitler in his European campaigns. • In the luscious Hedwig Kiesler, Mandl found the ideal trophy wife. He forbade her to act and encouraged her to direct her talents to entertaining his "business associates." • Sensing that Jews had no future in Austria, she left homeland and her husband in 1937.

7. Torpedo Communications • The woman who had learned about the latest in German and Austrian technology at her husband's plants met composer George Antheil at a dinner party in 1940 and shared what she knew about the design of remote-controlled torpedoes. Mandl had never gone into production with these torpedoes because their radio signals were vulnerable to detection and jamming. • Lamarr believed the solution was to broadcast the weapons' signals on rapidly shifting frequencies. She and Antheil developed a frequency-hopping system by which both the transmitting and receiving stations of a remote-control torpedo changed at intervals. They received U.S. Patent 2,292,387 in August, 1942, and their research was put to limited use by the U.S. Navy during World War II.

8. What else? • While she raised her children, the military and private sector took a growing interest in spread spectrum technology. However Miss Lamarr didn't receive a nickel for her work until 1997, when a Canadian wireless data communications company acquired the original patent rights from the actress in exchange for an undisclosed number of shares in the firm. • "Films have a certain place in a certain time period," said Miss Lamarr last year in what could be her epitaph. "Technology is forever."

9. Frequency Hopping (Bluetooth, some 802.11) • To avoid Jamming, transmit over a random sequence of frequencies with both ends knowing the random sequence. • The FCC requires a channel to use 75 or more frequencies with a maximum dwell time of 400ms. • If an error occurs on one frequency, retransmit on the next one. • If two stations are transmitting, they wont interfere if they have different hop sequences • Limited to 2Mbps

10. Direct Sequence (Most others including 802.11 ethernet) • Direct Sequence exor the signal with a random sequence and transmits over a wider frequency band • Transmitters are higher cost and can achieve higher bandwidth, however each transmitter must have its own frequency. • They also draw a lot more power

11. Chipping sequence 1 0 Data stream: 1010 1 0 Random sequence: 0100101101011001 1 0 XOR of the two: 1011101110101001

12. Original signal Spread signal Decoded signal Recovering the Signal Direct Sequence :

13. Collisions (hidden node) (C and A want to send to B) A B C D

14. Collisions (Exposed node) (B->A and C->D) A B C D

15. MACA • Multiple Access with Collision Avoidance (MACA) • RTS and CTS signals before transmission starts. This allows all other nodes to know of where the transmission is occurring • Any node who sees the CTS knows that it cant transmit or it will interfere • Any node who sees the RTS, but not the CTS is not close to the receiver, so it can transmit without interfering. • An ACK is sent when the frame is received

16. CTS(A) MACA (hidden node) (C and A want to send to B) RTS RTS A B C D

17. CTS CTS MACA (Exposed Node) RTS RTS A B C D

18. Distribution System • Access Points (AP) are connected by a distribution system and are not mobile. • Roaming Nodes can communicate directly, or through Access Points. • Scanning: • Node sends a Probe frame • All APs within range respond • Node selects AP and sends it a Association Request frame • AP responds with an Association Response frame

19. Access Points

20. Changing APs APs periodically send a beacon frame (passive scanning, or nodes recognize reduced signal strength (active scanning)

21. Frame Format • Up to 2312 bytes of data • 48 bit source, dest addresses • 4 addresses can identify two endpoints and two intermediate Access Points

22. Bluetooth • Spread spectrum frequency hopping radio • 79/23 one MHz channels • Hops every packet • Packets are 1, 3 or 5 slots long • Frame consists of two packets • Transmit followed by receive • Nominally hops at 1600 times a second (1 slot packets)

23. Bluetooth • Radio Designation • Connected radios can be master or slave • Radios are symmetric (same radio can be master or slave) • Piconet • Master can connect to 7 simultaneous or 200+ active slaves per piconet • Each piconet has maximum capacity (1 MSPS) • Unique hopping pattern/ID

24. Piconet • All devices in a piconet hop together • In forming a piconet, master gives slaves its clock and device ID • Hopping pattern determined by device ID (48-bit) • Phase in hopping pattern determined by Clock • Non-piconet devices are in standby • Piconet Addressing • Active Member Address (AMA, 3-bits) • Parked Member Address (PMA, 8-bits)

25. Which Technology • Why Bluetooth? • Why 802.11? • What about IRDA?

26. Network Adaptors

27. Overview Typically where data link functionality is implemented • Framing • Error Detection • Media Access Control (MAC) Network link Bus Link Host I/O bus interface interface Adaptor

28. Host Perspective Control Status Register (CSR) • Available at some memory address • CPU can read and write • CPU instructs Adaptor (e.g., transmit) • Adaptor informs CPU (e.g., receive error) Example LE_RINT 0x0400 Received packet Interrupt (RC) LE_TINT 0x0200 Transmitted packet Interrupt (RC) LE_IDON 0x0100 Initialization Done (RC) LE_IENA 0x0040 Interrupt Enable (RW) LE_INIT 0x0001 Initialize (RW1)

29. Memory buffers 100 1400 1500 1500 … 1500 Buffer descriptor list Moving Frames Between Host and Adaptor Direct Memory Access (DMA) Programmed I/O (PIO)

30. Device Driver Interrupt Handler interrupt_handler() { disable_interrupts(); /* some error occurred */ if (csr & LE_ERR) { print_and_clear_error(); } /* transmit interrupt */ if (csr & LE_TINT) { csr = LE_TINT | LE_INEA; semSignal(xmit_queue); } /* receive interrupt */ if (csr & LE_RINT) { receive_interrupt(); } enable_interrupts(); return(0); }

31. Transmit Routine: transmit(Msg *msg) { char *src, *dst; Context c; int len; semWait(xmit_queue); semWait(mutex); disable_interrupts(); dst = next_xmit_buf(); msgWalkInit(&c, msg); while ((src = msgWalk(&c, &len)) != 0) copy_data_to_lance(src, dst, len); msgWalkDone(&c); enable_interrupts(); semSignal(mutex); return; }

32. Receive Interrupt Routine receive_interrupt() { Msg *msg, *new_msg; char *buf; while (rdl = next_rcv_desc()) { /* create process to handle this message */ msg = rdl->msg; process_create(ethDemux, msg); /* msg eventually freed in ethDemux */ /* now allocate a replacement */ buf = msgConstructAllocate(new_msg, MTU); rdl->msg = new_msg; rdl->buf = buf; install_rcv_desc(rdl); } return; }

33. I/O bus 114 MBps Main memory 560 MBps 100 MBps CPU 2000 MBps L2 cache L1 Crossbar cache Memory Bottleneck With 114MBps max, if there are 5 data copies, the best throughput will be 22MBps (114/5)

34. Divergence Underwater acoustical modems

35. What is a acoustical modem? External modems connect directly to the serial port, internal modems are devices on the I/O bus. Acoustical modems provide a cradle for the telephone and must produce sound for the telephone handset

36. How do you do this underwater • Submarines would like to send email • Connect to an underwater hydrophone transmitter • Frequency modulation • Communicate between a submersible and aircraft or ships • From http://guinness.cs.stevens-tech.edu/~mtalreja/seniord/

37. Architecture

38. FM for alternating 0s and 1s

39. Details • Bandwidth 100bps • Speed of sound 1400-1500m/s (varies with salinity) • Mark=1600Hz, Space=1000 Hz • RS232 framing

40. Considerations • High frequencies are absorbed more quickly than low frequencies in water

41. Name (V24) 25 pin 9 pin Direction Full name TxD 2 3 Output Transmit Data RxD 3 2 Input Receive Data RTS 4 7 Output Request To Send CTS 5 8 Input Clear To Send DTR 20 4 Output Data Terminal Ready DSR 6 6 Input Data Set Ready RI 22 9 Input Ring Indicator DCD 8 1 Input Data Carrier Detect GND 7 5 - Signal ground - 1 - - Protective ground RS232

42. RS232 Details • 1 (MARK, LOW) means -3 V to -15 V; • 0 (SPACE, HIGH) means +3 V to +15 V • Start bit=High, Stop bits=Low • Data is transmitted LSB to MSB, (LSB, Bit 0) first, 0 = HIGH,1=LOW.