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Wireless Communications. Objectives Understand 802.11 Bluetooth. Wireless (802.11). Hedy Lamarr, seen in 1946, had a string of hit films in the 1930s and 1940s. Hedy Lamarr. Deseret News Jan 30 2000 page E10

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wireless communications
Wireless Communications
  • Objectives
    • Understand 802.11
    • Bluetooth
wireless 802 11
Wireless (802.11)

Hedy Lamarr, seen in 1946, had a string of hit films in the 1930s and 1940s.

hedy lamarr
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.
on the acting side
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).
just a pretty face
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.
background
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.
torpedo communications
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.
what else
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."
frequency hopping bluetooth some 802 11
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
direct sequence most others including 802 11 ethernet
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
chipping sequence
Chipping sequence

1

0

Data stream: 1010

1

0

Random sequence: 0100101101011001

1

0

XOR of the two: 1011101110101001

recovering the signal

Original signal

Spread signal

Decoded signal

Recovering the Signal

Direct Sequence :

slide15
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
slide16

CTS(A)

MACA (hidden node) (C and A want to send to B)

RTS

RTS

A

B

C

D

slide17

CTS

CTS

MACA (Exposed Node)

RTS

RTS

A

B

C

D

distribution system
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
changing aps
Changing APs

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

frame format
Frame Format
  • Up to 2312 bytes of data
  • 48 bit source, dest addresses
  • 4 addresses can identify two endpoints and two intermediate Access Points
bluetooth
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)
bluetooth1
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
piconet
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)
which technology
Which Technology
  • Why Bluetooth?
  • Why 802.11?
  • What about IRDA?
overview
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

host perspective
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)

moving frames between host and adaptor

Memory buffers

100

1400

1500

1500

1500

Buffer

descriptor

list

Moving Frames Between Host and Adaptor

Direct Memory Access (DMA)

Programmed I/O (PIO)

device driver
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);

}

slide31
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;

}

slide32
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;

}

memory bottleneck

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)

divergence

Divergence

Underwater acoustical modems

what is a acoustical modem
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

how do you do this underwater
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/
details
Details
  • Bandwidth 100bps
  • Speed of sound 1400-1500m/s (varies with salinity)
  • Mark=1600Hz, Space=1000 Hz
  • RS232 framing
considerations
Considerations
  • High frequencies are absorbed more quickly than low frequencies in water
rs232

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
rs232 details
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.