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Example Wireless Networks: WaveLAN, Bluetooth

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Example Wireless Networks: WaveLAN, Bluetooth Y. Richard Yang 01/26/2004 – PowerPoint PPT presentation

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Title: Example Wireless Networks: WaveLAN, Bluetooth


1
Example Wireless NetworksWaveLAN, Bluetooth
  • Y. Richard Yang
  • 01/26/2004

2
Outline
  • Admin. and recap
  • Bluetooth networks

3
Admin Homework 1
  • A mini-paper on MAC protocols for directional
    antennas
  • due 1159pm on Friday the 30th
  • send result to yry_at_cs.yale.edu
  • pdf, ps, or word should be fine
  • no longer than 6 pages (double/single space, or
    single/double column, your decision)

4
Recap Cellular Networks
  • GSM and GPRS
  • GSM
  • GSM combines TDMA and FDMA
  • GSM data rate is low, e.g., 9.6kbps
  • GPRS higher data rates
  • discussion a comparison of GSM and GPRS
  • which one is better
  • Eight servers each can process X packets per
    second
  • One server which can process 8 X packets per
    second
  • IMT-2000
  • UMTS uses W-CDMA as radio interface

5
GPRS User Data Rates in kbps
Coding scheme 1 slot 2 slots 3 slots 4 slots 5 slots 6 slots 7 slots 8 slots
CS-1 9.05 18.2 27.15 36.2 45.25 54.3 63.35 72.4
CS-2 13.4 26.8 40.2 53.6 67 80.4 93.8 107.2
CS-3 15.6 31.2 46.8 62.4 78 93.6 109.2 124.8
CS-4 21.4 42.8 64.2 85.6 107 128.4 149.8 171.2
GPRS channel structure - time is divided into
multiframe (240ms) - each multiframe contains
48 data frames - 4 slots form a block
6
GPRS Coding
convolution code
g(1)(D) 1 D3 D4 g(2)(D) 1 D D3 D4
,
Coding scheme Pre-cod. USF Infobits without USF Parity bits BC Tail bits Output conv encoder Punctured bits Code rate Data rate kbit/s
CS-1 3 181 40 4 456 0 1/2 9.05
CS-2 6 268 16 4 588 132 2/3 13.4
CS-3 6 312 16 4 676 220 3/4 15.6
CS-4 12 428 16 456 1 21.4
7
Computation Examples
  • CS-1 and 1 slot

8
Recap 802.11 Architecture
Ad hoc mode
Infrastructure mode
9
Recap Wireless LAN (802.11) PHY
10
DSSS PHY
3 non-overlapping channels
11
Recap 802.11 MAC Layer
  • Traffic services
  • Asynchronous Data Service (mandatory)
  • exchange of data packets based on best-effort
  • support of broadcast and multicast
  • Time-Bounded Service (optional)
  • exchange of bounded delay service
  • Use Inter framing spacing (IFS) to combine the
    two modes
  • Use RTS/CTS/DATA/ACK
  • Power saving mode
  • Use beacon interval to allow sleep

12
802.11 - Frame Format
  • 802.11 frame has more fields than other media
    type frames
  • 30 bytes frame header appears too long!
  • Duration ID NAV
  • CRC check sum

13
802.11 Frame Control Field
14
Background Cyclic Redundancy Check
  • For a given data D, consider it as a polynomial
    D(x)
  • consider the string of 0 and 1 as the
    coefficients of a polynomial
  • e.g. consider string 10011 as x4x1
  • addition and subtraction are modular 2, thus the
    same as xor
  • Choose generator polynomial G(x) with r1 bits,
    where r is called the degree of G(x)
  • For example the degree of the G(x) for 802.11 is
    32

15
Cyclic Redundancy Check Objective
  • Given data G(x) and D(x), choose R(x) with r
    bits, such that
  • D(x)xrR(x) is exactly divisible by G(x)
  • The bits correspond to T(x)D(x)xrR(x) are sent
    to the receiver
  • Since G(x) is global, when the receiver receives
    the transmission T(x), it divides T(x) by G(x)
  • If non-zero remainder error detected!
  • If zero remainder, assumes no error


x
16
CRC Steps and an Example
  • Suppose the degree of G(x) is r
  • Append r zero to D(x), i.e. consider D(x)xr
  • Divide D(x)xr by G(x). Let R(x) denote the
    reminder
  • Send ltD, Rgt to the receiver

17
The Power of CRC
  • Let T(x) denote D(x)xrR(x), and E(x) the
    polynomial of the error bits, i.e
  • the received signal T(x) T(x)E(x)
  • Since T(x) is divisible by G(x), we only need to
    consider E(x) divided by G(x)
  • A single bit of error E(x) xi
  • If G(x) contains two or more terms, E(x) is not
    divisible by G(x)
  • An odd number of errors E(x) has an odd number
    of terms
  • Lemma if E(x) has an odd number of terms, E(x)
    cannot be divisible by (x1)
  • suppose E(x) (x1)F(x), let x1, the left hand
    will be 1, while the right hand will be 0
  • If G(x) contains x1 as a factor, E(x) will not
    be divided by G(x)
  • Many more errors can be detected by designing the
    right G(x)

18
Outline
  • Admin. and recap
  • Bluetooth networks

19
Bluetooth Design Objective
  • Design objective a cable replacement technology
  • 1 Mb/s
  • range 10 meters
  • single chip radio baseband (means digital part)
  • low power
  • low price point (target price 5)

20
Bluetooth Use Scenarios
  • Synchronization
  • Data access points
  • Headset
  • Conference table
  • Business card exchange
  • Instant postcard

Cordless headset
21
Bluetooth Architecture
22
Bluetooth Radio Link
  • Bluetooth shares the same freq. range as 802.11
  • Radio link is the most expensive part of a
    communication chip (discussion compare with
    802.11)
  • Bluetooth uses frequency hopping spread spectrum
  • 2.402 GHz k MHz, k0, , 78
  • 1,600 hops per second
  • GFSK (Gaussian FSK) modulation
  • 1 Mb/s symbol rate
  • transmit power 1mW

23
Bluetooth Physical Layer
  • Nodes form piconet one master and upto 7 slaves
  • Each radio can function as a master or a slave
  • The slaves follow the pseudorandom jumping
    sequence of the master

A piconet
24
Physical Channel Setup (Piconet formation)
  • An inquiry/scan/page protocol
  • Master sends Inquiry messages, with Inquiry
    Access Code (IAC), hoping at a universal
    frequency hopping sequence (32 frequencies)
  • announce the master
  • Joining slave
  • jump at a much lower speed
  • after receiving an Inquiry message, wait for a
    random time, then send a request to the master
  • The master sends a paging message to the slave to
    join it

25
Inquiry Hopping
26
The Bluetooth Link Establishment Protocol
FS Frequency Synchronization
DAC Device Access Code
IAC Inquiry Access Code
27
Bluetooth Links
28
Bluetooth Packet Format
29
Multiple-Slot Packet
30
Background Forward Error Correction
Code/Erasure Code
  • Widely used in wireless communications

y
x
31
FEC Example
  • Suppose data signal is x, and the encoded signal
    y Gx, where G is the generator matrix
  • Example Vandermonde Matrix gij aij-1, where ai
    are different numbers

32
FEC An Example
  • Suppose k3, and n5
  • Suppose y2 and y3 are dropped, then we have y1,
    y4, and y5. Given the relationship (we know they
    are y1, y4, y5)
  • Since the matrix is not singular, we can recover
    x1, x2, and x3

33
Further Enhancements of Bluetooth
  • Power management modes
  • e.g., PARK
  • Scatternets multiple piconets
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