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

� 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

� Wireless Networks Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.2/39

� 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

✄☎ ✂ ✁ � � ✁ � 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

� 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

� 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

� 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

� � 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

� 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

� FH Spread Spectrum Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.10/39

� FH Spread Spectrum Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.11/39

� FH Spread Spectrum Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.12/39

� � ✁✂ ✄ 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

✟ ✂ ✟ ✁ ✠ ✁ � � ✂ ✝ ✁ ✞ ✝ ✝ ✂ ✂ ✆ ✁ ✞ ✁ ✂ � ✟ 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

✝ ✆ � ✞ ✁ ✂ ✁ ✁ ☎ ✁✂ ✄ ✄ ☎ � ✄ ✁ � � 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

� 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 only 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

✁ ✁ ✝ ✁ ✁ ✁ ✝ ✝ ✝ ✁ ✝ ✝ ✁ ✝ � ✁ ✝ ✁ ✁ ✁ ✝ ✝ ✁ ✁ ✝ ✁ ✝ ✁ ✁ ✂ ✁ ✝ ✁ ✁ � ✁ ✁ ✁ ✁ ✝ ✁ ✁ ✝ ✁ ✁ ✁ ✝ ✁ ✁ ✁ ✝ ✁ ✁ ✁ Barker Codes Length Barker Code 1 2 or 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

� DS Spread Spectrum Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.18/39

� DS Spread Spectrum Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.19/39

� DS Spread Spectrum Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.20/39

� DS Spread Spectrum 2 1 s(t) 0 −1 −2 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 2 1 c(t) 0 −1 −2 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 t Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.21/39

� DS Spread Spectrum PSD, P x =0.5, P x (f 1 ,f 2 ) = 49.9457%, F s =200000 Hz, N=200000, NN=2, ∆ f =1 Hz 0 10log 10 (S x (f)) [dB] −10 −20 −30 −40 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 f [Hz] 4 x 10 PSD, P x =0.5, P x (f 1 ,f 2 ) = 49.3946%, F s =200000 Hz, N=200000, NN=2, ∆ f =1 Hz 0 10log 10 (S x (f)) [dB] −10 −20 −30 −40 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 f [Hz] 4 x 10 Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.22/39

✆ ✂ ✟ ✄ ✁ ✁ ✁ ✁ ✒ ✂ ✕ ✕ ✕ ✕ ✁ � ✁ ✁ � ✕ ✁ ✁ ✟ ✆ ✆ ✄☎ ✁ � ✁ Processing Gain Processing Gain: . �✂✁ ✝✟✞✡✠ ☛✌☞ MHz At 1 Mb/s, dB ✍✏✎ ✑✓✒✔ Mb/s MHz At 2 Mb/s, dB ✍✏✎ ✂☎✄ ✑✓✒✔ Mb/s Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.23/39

� DSSS with Jammer PSD, P x =0.62508, P x (f 1 ,f 2 ) = 49.5233%, F s =200000 Hz, N=200000, NN=2, ∆ f =1 Hz 0 −10 10log 10 (S x (f)) [dB] −20 −30 −40 −50 −60 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 f [Hz] 4 x 10 PSD, P x =0.62508, P x (f 1 ,f 2 ) = 49.8259%, F s =200000 Hz, N=200000, NN=2, ∆ f =1 Hz 0 −10 10log 10 (S x (f)) [dB] −20 −30 −40 −50 −60 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 f [Hz] 4 x 10 Data Networks, Wireless LANs, c 1996–2005, P . Mathys – p.24/39