ECEN 5032 Data Networks Wireless Networks Peter Mathys - - PowerPoint PPT Presentation

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ECEN 5032 Data Networks Wireless Networks Peter Mathys - - PowerPoint PPT Presentation

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ECEN 5032 Data Networks Wireless Networks Peter Mathys mathys@colorado.edu University of Colorado, Boulder Data Networks, Wireless LANs, c 19962005, P . Mathys p.1/39 Wireless Networks Data Networks, Wireless LANs, c

slide-1
SLIDE 1

ECEN 5032 Data Networks

Wireless Networks

Peter Mathys

mathys@colorado.edu

University of Colorado, Boulder

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.1/39

slide-2
SLIDE 2

Wireless Networks

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.2/39

slide-3
SLIDE 3

1G Wireless Standards

Forward Reverse Channel Band Band Spacing Standard (MHz) (MHz) (kHz) Region AMPS 824-849 869-894 30 US NMT 450 453-457.5 463-467.5 25 EU NMT 900 890-915 935-960 12.5 EU NTT 925-940 870-885 25/6.25 Japan

All use analog frequency modulation (FM). AMPS: Advanced Mobile Phone System (1983). NMT: Nordic Mobile Telephony (1982). Analog FM voice, 1200/4800 bps data. NTT: Nippon Telephone and Telegraph.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.3/39

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SLIDE 4

2G Wireless Standards

Freq Channel Band Modulation Access Bitrate Standard (MHz) Method Method kb/s Region GSM 935-960 GMSK TDMA/FDD 270.8 Europe/Asia 890-915 IS-54 869-894

  • ✁
  • DQPSK

TDMA/FDD 48.6 US 824-849 JDC 810-826

  • ✁
  • DQPSK

TDMA/FDD 42 Japan 940-956 IS-95 869-894 SQPSK/QPSK CDMA/FDD 1228.8 US/Asia 824-849

2G standards are all digital, speech coding

✂ ✄☎

kb/s. FDD: Frequency division duplex, TDMA: Time-division multiple access, CDMA: Code-division multiple access, DQPSK: Differential 4-PSK, SQPSK: Staggered 4-PSK. GSM: Global system of mobile communications. IS: North American Interim Standard.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.4/39

slide-5
SLIDE 5

3G Wireless Standards

The purpose of migration to 3G networks is to develop an international standard that combines and gradually replaces 2G cellular, PCS (personal communication services) and mobile data services. Two main proposals: W-CDMA (wideband CDMA, proposed by Ericsson), also called UMTS (universal mobile telecommunications system) in EU, and CDMA2000 (extension of IS-95, proposed by Qualcomm). W-CDMA: Direct-sequence spread spectrum (DSSS) with chip rate 3.84 Mc/s (using about 5 MHz bandwidth). Modulation and spreading modulation is QPSK for uplink and downlink. Data rates from 384 kb/s (mobile users) to 2 Mb/s (fixed indoor users). Must have QoS support and operate from megacells to picocells.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.5/39

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SLIDE 6

802.11 Overview

Standard Modulation Method Frequencies Data Rates (Mb/s) 802.11 legacy FHSS, DSSS, infrared 2.4 GHz, IR 1,2 802.11b DSSS, HR-DSSS 2.4 GHz 1,2,5.5,11 “802.11b+” DSSS, HR-DSSS (PBCC) 2.4 GHz 1,2,5.5,11,22,33,44 802.11a OFDM 5.2,5.8 GHz 6,9,12,18,24,36,48,54 802.11g FHSS, HR-DSSS 2.4 GHz 1,2,5.5,11 OFDM 2.4 GHz 6,9,12,18,24,36,48,54

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.6/39

slide-7
SLIDE 7

Spread Spectrum Signals

The term spread spectrum is used to describe any technique in which the bandwidth of the transmitted signal is much wider than the bandwidth of the information signal. Pure spread spectrum includes only those techniques that perform the spreading function by a signal that is independent of the information signal.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.7/39

slide-8
SLIDE 8

Spread Spectrum

The characteristics of spread spectrum signals are:

Low power spectral density

  • Low probability of

intercept. High immunity to jamming and interference. High resolution ranging. Possibility for code division multiple access.

FCC in 1985 made decision to allow the use of spread spectrum signals in the ISM bands. Three types of signals were allowed intially: Frequency hop (FH), direct sequence (DS), and hybrid FH/DS.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.8/39

slide-9
SLIDE 9

FH Spread Spectrum

FHSS was invented by Austrian-born movie star Hedy Lamarr to protect guided torpedos from jamming. In order to avoid a jammer, the transmitter shifts the center frequency of the transmitted signal in a random pattern only known to the receiver. If 100 different frequencies are used, then the signal spectrum is spread over a band that is 100 times larger than the original spectrum. The hopping of the carrier frequency does not affect the performance in additive noise. Thus, in a noninterfering environment the performance of a FHSS system is exactly the same as the performance of a traditional system.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.9/39

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SLIDE 10

FH Spread Spectrum

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.10/39

slide-11
SLIDE 11

FH Spread Spectrum

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.11/39

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SLIDE 12

FH Spread Spectrum

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.12/39

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SLIDE 13

802.11 Legacy FHSS

Two data rates, 1 Mb/s and 2 Mb/s (using 2/4 GFSK, respectively). Headers and synchronization always transmitted at 1 Mb/s. In the US there are 79 hop channels with center frequencies in 1 MHz steps from 2.402 to 2.480 GHz. In the US there are three sets of pseudo-random hopping patterns of 26 hops each to choose from. The minimum hop rate is 2.5 hops/sec (400 ms dwell time corresponding to 400 kb of data or

  • ✁✂
✄

data packets).

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.13/39

slide-14
SLIDE 14

2GFSK/4GFSK Modulation

Modulation index

  • ✂
✁ ✂☎✄ ✆ ✂

(

✝ ✁✞ ✂

kHz at 1 Mbaud). Modulation index

  • ✟
✁ ✂☎✄ ✁ ✟ ✟

(

✝ ✠ ✂

kHz and

✝ ✂ ✁✞

kHz at 1 Mbaud).

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.14/39

slide-15
SLIDE 15

2GFSK/4GFSK Prob. Error

Compare: Coherent orthogonal 2-FSK needs

  • ✁
✄

dB SNR for

✂✁ ✄ ☎ ✆ ✁ ✁ ✂ ✝ ✞

(4-FSK:

  • ✁✂

dB for same

  • ✁
✄ ☎

)).

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.15/39

slide-16
SLIDE 16

DS Spread Spectrum

Like FHSS, direct-sequence spread spectrum (DSSS) also uses a PN sequence to spread the signal, but in this case the PN sequence directly modulates the data signal. The 802.11 (legacy) standard specifies the use of Barker codes for the PN sequence. Barker codes have good aperiodic correlation properties, but there are

  • nly 8 known codes.

802.11a,b,g also allow the use of complementary code keying (CCK) to transmit 4 or 8 bit symbols at 11/8=1.375 Mbaud, resulting 5.5 Mb/s and 11 Mb/s data rates.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.16/39

slide-17
SLIDE 17

Barker Codes

Length

  • Barker Code

1

✁

2

✁ ✁
  • r
✁ ✝

3

✁ ✁ ✝

4

✁ ✁ ✁ ✝

++-+ 5

✁ ✁ ✁ ✝ ✁

7

✁ ✁ ✁ ✝ ✝ ✁ ✝

11

✁ ✁ ✁ ✝ ✝ ✝ ✁ ✝ ✝ ✁ ✝

13

✁ ✁ ✁ ✁ ✁ ✝ ✝ ✁ ✁ ✝ ✁ ✝ ✁

The length

✂ ✁ ✁ ✁

Barker code is used for 802.11.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.17/39

slide-18
SLIDE 18

DS Spread Spectrum

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.18/39

slide-19
SLIDE 19

DS Spread Spectrum

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.19/39

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SLIDE 20

DS Spread Spectrum

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.20/39

slide-21
SLIDE 21

DS Spread Spectrum

0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 −2 −1 1 2 s(t) 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 −2 −1 1 2 t c(t)

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.21/39

slide-22
SLIDE 22

DS Spread Spectrum

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 x 10

4

−40 −30 −20 −10 f [Hz] 10log10(Sx(f)) [dB] PSD, Px=0.5, Px(f1,f2) = 49.9457%, Fs=200000 Hz, N=200000, NN=2, ∆f=1 Hz 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 x 10

4

−40 −30 −20 −10 f [Hz] 10log10(Sx(f)) [dB] PSD, Px=0.5, Px(f1,f2) = 49.3946%, Fs=200000 Hz, N=200000, NN=2, ∆f=1 Hz

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.22/39

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SLIDE 23

Processing Gain

Processing Gain:

✂✁ ✁ ✄☎ ✆ ✆ ✝✟✞✡✠ ☛✌☞

. At 1 Mb/s,

  • ✁
✁ ✁ ✂ ✍✏✎ ✑✓✒✔ ✕ ✕

MHz

✒

Mb/s

✁ ✁ ✆ ✄ ✟

dB At 2 Mb/s,

  • ✁
✁ ✁ ✂ ✍✏✎ ✑✓✒✔ ✕ ✕

MHz

✕

Mb/s

✁ ✁ ✂☎✄ ✟

dB

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.23/39

slide-24
SLIDE 24

DSSS with Jammer

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 x 10

4

−60 −50 −40 −30 −20 −10 f [Hz] 10log10(Sx(f)) [dB] PSD, Px=0.62508, Px(f1,f2) = 49.5233%, Fs=200000 Hz, N=200000, NN=2, ∆f=1 Hz 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 x 10

4

−60 −50 −40 −30 −20 −10 f [Hz] 10log10(Sx(f)) [dB] PSD, Px=0.62508, Px(f1,f2) = 49.8259%, Fs=200000 Hz, N=200000, NN=2, ∆f=1 Hz

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.24/39

slide-25
SLIDE 25

802.11 DSSS Parameters

Chip rate of 11 Mc/s. Thus DSSS occupies about 22 MHz channel bandwidth. There are 11 overlapping 22 MHz channels, spaced 5 MHz apart from 2.412 GHz to 2.462 GHz. Choosing

✂✁ ✒ ✁ ✂ ✄ ✟ ✁✂

GHz

✄ ✂✁ ✒ ✁ ✂ ✄ ✟ ✆ ✠

GHz

✄ ✂✁ ✒ ✁ ✂ ✄ ✟ ✞ ✂

GHz

✄

yields 3 non-overlapping bands for cell planning with frequency reuse. Using DBPSK and the Barker code of length 11 gives a data rate of 1 Mb/s. Using DQPSK and the Barker code of length 11 gives a data rate of 2 Mb/s (and about 3 dB less coding gain).

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.25/39

slide-26
SLIDE 26

802.11 1/2 Mb/s DSSS

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.26/39

slide-27
SLIDE 27

Frequency Reuse

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.27/39

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SLIDE 28

Increasing Data Rate

Use complementary code keying (CCK) instead of Barker code. HR-DSSS uses spreading codes of length 8 (

  • ✁
✁ ✁ ✂ ✁ ✁ ✄ ✆ ✠ ✄

Mbaud symbol rate at 11 Mc/s). Either 4 or 8 bits are transmitted per spreading code (or symbol), yielding data rates of

✟ ✄ ✁ ✄ ✆ ✠ ✄ ✁ ✄ ✄ ✄

Mb/s or

✂ ✄ ✁ ✄ ✆ ✠ ✄ ✁ ✁ ✁

Mb/s. Use orthogonal frequency division multiplexing (OFDM) with BPSK, QPSK, 16-QAM, and 64-QAM and error control coding to achieve rates of 6, 9, 12, 18, 24, 36, 48, 54 Mb/s in bands of width 20 MHz.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.28/39

slide-29
SLIDE 29

Complementary Code Keying

8-bit CCK codewords (

  • ✁
✁
  • ✔
✄
  • ✒
✄ ✄ ✄ ✄
  • ✂
✄

): This is a generalized form of Hadamard transform encoding. Cover code: 4-th and 7-th chip are rotated

✁ ✂ ✂ ☎

by a cover sequence to optimize the sequence correlation properties and minimize dc offsets in the codes. At 5.5 Mbit/s 4 bits (d0 to d3; d0 first in time) are transmitted per symbol. At 11 Mbit/s, 8 bits (d0 to d7; d0 first in time) are transmitted per symbol.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.29/39

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SLIDE 30

Complementary Code Keying

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.30/39

slide-31
SLIDE 31

Orthogonal FDM

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.31/39

slide-32
SLIDE 32

OFDM

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.32/39

slide-33
SLIDE 33

OFDM

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.33/39

slide-34
SLIDE 34

OFDM

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.34/39

slide-35
SLIDE 35

OFDM

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.35/39

slide-36
SLIDE 36

OFDM

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.36/39

slide-37
SLIDE 37

802.11a OFDM

Nominal signal bandwidth is 20 MHz, symbol time + guard time (0.8

  • s) is 4
  • s, subdivided into 64 samples.

Uses 52 subcarriers (48 for data + 4 for pilots) spaced

✂ ✂

MHz

✁ ✞ ✟ ✁ ✂☎✄ ✆ ✁✂ ✄

MHz apart. 4

  • s symbol time
✁ ✂ ✄ ✂

kbaud per carrier. 48 carriers used for data

✁ ✟ ✂ ✄ ✂☎✄ ✂ ✄ ✁ ✁✂

Mbaud. Using BPSK and rate 1/2 or rate 3/4 encoder yields 6

  • r 9 Mb/s. Using QPSK and rate 1/2 or rate 3/4

encoder yields 12 or 18 Mb/s. Using 16-QAM and rate 1/2 or rate 3/4 encoder yields 24 or 36 Mb/s. Using 64-QAM and rate 2/3 or rate 3/4 encoder yields 48 or 54 Mb/s.

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.37/39

slide-38
SLIDE 38

802.15 WPAN Overview

Standard Modulation Method Frequencies Data Rates (Mb/s) 802.15.1 GFSK+FHSS 2.4 GHz 1 802.15.3 QPSK,8-state TCM 2.4 GHz 11 DQPSK 2.4 GHz 22 16-QAM,8-state TCM 2.4 GHz 33 32-QAM,8-state TCM 2.4 GHz 44 64-QAM,8-state TCM 2.4 GHz 55 802.15.4 BPSK 0.9 GHz 0.02 BPSK 0.9 GHz 0.04 OQPSK 2.4 GHz 0.25

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.38/39

slide-39
SLIDE 39

802.16 WiMAX Overview

Standard Modulation Method Frequencies Data Rates BW 802.16 QPSK, 16/64QAM 10-66 GHz 32-134 Mb/s 20-28 MHz 802.16a QPSK, 16/64QAM <11 GHz 75 Mb/s 20 MHz OFDM 256 subcarr 802.16e QPSK, 16/64QAM < 6 GHz 15 Mb/s 5 MHz OFDM 256 subcarr

Data Networks, Wireless LANs, c

  • 1996–2005, P

. Mathys – p.39/39