Communications Presentation 13a

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Communications Presentation 13a

• Answers to Midterm Examination
• Homework 4 due Monday, March 3
• Digital Modulation, BBSK, QPSK, etc
• Error detection and correction coding
• TDMA and packet switching networks
• Television standards
• Microwave Relay Performance Fading and Rain Loss
• WiFi and WiMax links

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I. An astronaut is stuck in space with only a 0.1
watt 2.5 GHz ipod. He makes an antenna out of a
hubcap that is 0.5 Meters in diameter (assume 55
efficiency) and transmits his distress call with
a signal using 2 kHz bandwidth and requiring a 10
dB C/N ratio.(a)                How far can he
be from a space station with an omni-directional
antenna (0dB gain) and a noise temperature of 100
deg K?(b)               The ground station on
earth is 1000 Km away. It has a receiver with 150
deg K temperature. How big an antenna (55
efficiency) does it need to receive the
astronauts distress signal?(c)               
What is the 3-dB beam-width of the ground station
antenna?

• (a) In dB link equations
• l C/f 3x10 8/2.5x10 9 0.12 M
• Gt 0.55(pD/l)2 0.55(p0.5/.12)2 94gt19.7dB
• Gr0dB Tr100 deggt20 dBdegK
  B2,000gt33dBHz C/N 10 dB k-228.6
• W 0.1gt -10dBW EIRP -1019.79.7 dBW
• EIRPGr/TrLfs BC/Nk LfsBC/Nk-EIRP-Gr/Tr
  3310-228.6-9.7- 020
• Lfs-175.3gt2.9x10-18 (l/ 4 p R )2 R0.12
  /Sqrt(2.9x10-18 )4p 5,600 km

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• In linear link equations
• (a) Aeff l2 Gr/4p 0.12x0.12x1.0/4p0.0011 M2
  k1.38x10-23
• C/N P/N 10 WxGtxAeff/4p R2 x k x T x B
• RSqrtWx Gt xAeff/4p x kxTxBx10
• RSqrt0.1x 94 x 0.0011 /4p x 1.38x10-23 x 100 x
  2,000 x 10
• R 5,460,102 M 5,460 km
• (b) 10 WxGtxAeff/4p R2 x k x T x B Aeff
  10x 4p R2 x k x T x B/WxGt
• 10x 4p1,000,0002 x 1.38x10-23 x 150 x
  2,000/ 1.0 x 94.00000176 M2
• A Aeff/0.55.000032 M2 D 2 sqrtA/p
  .0063 M 0.63 cm
• Check (a) and (b) 5.4x5.4/1.0x1.0 29.2
  29.2x.000032 .00093 ltgt .0011 close
• Sorry I should have transmitted a MHz. You could
  receive the astronaut with your cell phone in
  your pocket.
• (c) The beam width is obviously omni directional.

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II. Were relaying a TV signal (5 MHz and 7 dB
C/N) from one mountain top to another at 12 GHz
radio frequency. Transmit and receive antennas
are 1 Meter in diameter, 55 efficiency. The
distance is 50 Km. Receiver temperature is 100
deg K. (a)                How much transmitter
power is needed in clear skies?(b)              
How much power is needed if there is 8 dB of rain
absorption on the path?(c)                How
much power if we need to work with the 8 dB rain
absorption and an extra fade margin of 15 dB?

• (a) l C/f 3x10 8/12x10 9 0.025 M
• Gt Gr 0.55(pD/l)2 0.55(p x 1.0/0.025)2
  8685gt39.4dB
• Tr100 deggt20 dB deg B5 Mhzgt67dBHz C/N
  7 dB k-228.6
• Lfs 20 log(l/ 4 p R) 20 log(.025/ 4 p 50.000)
  -148 dB
• EIRPGr/TrLfs BC/Nk EIRP -Gr/Tr-Lfs
  BC/Nk
• EIRP -39.420148 67 7-228.6 -26 dB
• PtEIRP-Gt -26-39.4 -65.4 dBW
• (b) 8 dBgt6.3 Tr 100290(6.3-1)/6.3343 deg
  Kgt25.3 dB deg K
• EIRP-39.425.3148677-228.68
  -12.7Pt-12.7-39.4-52.1dBW
• (c) 15 dB more -52.115 -37 dBW (For 12 GHz
  we could use 1 ft diameter antennas and get by
  with 20 dB more power 17 dBW 20mW)

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III. The THAICOM-4 synchronous satellite is at
120 deg East longitude. (a)    What is the
elevation and azimuth to the satellite from
Tokyo, 35.7 deg North, 139.75 deg East?(b)   How
many Km is it from Tokyo to Sydney, Australia, at
34 deg South, 151 deg East?(c)    How far is
Sydney from the North Pole?

• (a) c 139.75-12019.75 deg b 35.7 deg A90
  deg
• a ArccosCos35.7xCos19.75 40.15 deg r
• Elevation ArccosSin 40.15/sqrt(1.0227-0.302
  Cos 40.15) 43.56 deg
• Sinc/SinCSina/Sin A
• CArcsinSin 19.75Sin 90/Sin 40.15 31.6 deg
  Azimuth 18031.6211.6 deg

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(b)   How many Km is it from Tokyo, 35.7 deg
North, 139.75 deg East, to Sydney, Australia, at
34 deg South, 151 deg East?(c)    How far is
Sydney from the North Pole?

• (b) A151-139.7511.25 deg b 9034124 deg c
  90-35.754.3 deg
• A ArccosCos124 Cos 54 Sin 124 Sin 54 Cos
  11.25
• A Arccos-0.328 0.6578Arccos0.3298 70 deg
• Distance Tokyo to Sydney 2px 6,370x(70/360)
  7,782 km
• (c) b124 Distance Sydney to N pole 2px
  6,370x(124/360) 13,787 km

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IV. The Latin American C-Band Satellite (6 GHz
up, 4 GHz down) has a saturation flux density of
-93 dBW/M2, a maximum EIRP of 39 dBW, and a G/T
of 2 dB/deg K.(a)    What is the C/N on a 30
MHz bandwidth uplink signal that saturates the
satellite transponder?(b)   What G/T does the
receiving station on the downlink need to achieve
a 10 dB C/N on the 30 MHz bandwidth signal?

• (a) EIRP up 10log( 4pR2) -93dBW/M2
  R40,000,000M
• EIRP up 163-93 70 dBW G/T-2
  Lfs6-200 B30 MHzgt74.8
• EIRPGr/TrLfs BC/Nk k-228.6
• C/N EIRPGr/TrLfs- B - k 70-2-200-74.8228.
  6 21.8 dB
• (b) B 74.8 Lfs -196.5 C/N10
• EIRPGr/TrLfs BC/Nk G/T -EIRP-Lfs
  BC/Nk
• G/T -39195.674.810 228.6 12.8 dB
• note if T 150 deggt21.7dB Gr
  12.821.734.5 dB
• This is about a 5 foot diameter antenna

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Homework 4Due Mar 3, 2008

• I. WiMax Rural Service Provider
• A cooperative buys a WiMax Base station and
  network link for 3,670 and installs it on the
  mountain side for another 500. They install 18
  customer premise units for 250 each. Their
  expected rate of return is 12. What is the
  monthly charge to each user site to recover the
  investment in 10 years?
• The coop adds a WiMax nerd to manage the system
  for 14,000/ year. Now what is the monthly charge
  to each user site?
• The 500 gentry in the area with WiMax phones can
  use the WiMax network for X/min. Assuming each
  one on the average uses 20 minutes/day, What
  should X be to fully support the service for the
  other 18 coop member sites?

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II. Rural Phone Service

• A loan at 10 rate/year is given to a rural phone
  operator to provide service in the community. The
  phone costs 200 and has a call cost of
  0.02/minute. In addition there is a 10/year
  maintenance cost on the phone. On the average
  she processes 10 three-minute calls a day,
  collecting money for each call.
• How much does she have to charge per call to earn
  8,000/yr for her work and fully pay off the loan
  in 10 years.
• What does she charge per call to earn
  10,000/year and pay off the loan in 5 years?

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Rural Development needs phones

• Though the urban-rural divide continues to widen,
  Gallup's 2006 survey results point to a
  significant rise in the average income among
  rural Chinese. As consumerism in rural areas
  begins to grow, the huge gaps between those
  living in urban and rural areas in terms of
  consumer product ownership will present lucrative
  business opportunities for those savvy enough to
  market to the hinterlands. Currently, about half
  of rural Chinese (49) say they own a mobile
  phone, compared with 82 of urban Chinese. Just
  4 of rural residents own a computer, versus
  about one-third (33) of urban dwellers.

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III. Mobile Phone Services

• Mobile service needs to provide good quality
  service with 40 dB S/N over a distance including
  terrain blockage.
• For years the standard was a 25 kHz bandwidth
  with a 12 dB C/N threshold, requiring 20 watts of
  power. For the same range (assuming the receiving
  and transmitting antennas and temperature are the
  same) what would be the power requirement for
• Sideband with 3.3 kHz bandwidth and 35 dB C/N?
• Companded Sideband with 3.3 kHz bandwidth and 7
  dB C/N?
• Digital voice with 4 kHz (8kb/s) and 6 dB C/N?

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IV. WiMax Relay Performance

• Were going to relay 50 Mb/sec from our community
  to a mountain top repeater 50 km away,we will use
  QPSK modulation with a BER 10-4, and Eb/No9.9
  dB. Our antennas are 1 M diameter with 65
  efficiency. We need a fade margin of 25 dB. The
  receivers have temperatures of 200 deg K.
• What power is required at a radio frequency of
  2.5 GHz?
• Whats needed at 5.0 GHz with 2 dB added rain
  loss?

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Systems with 1 kB/sec at 10 -4 BER
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Modulation Noise Sensitivity
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Parity Bit for simple error detection bit set so
that even number of 1s occur in word
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Use of Receive Confirmationto Retransmit Data
Block
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Optimum size of Packet vs BER
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Parity Bits for Forward Error Correction
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Simple FEC Code reduces 10-4 to 1.5 x 10-6
BER
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With three parity Check bits we can correct many
errors by using the most likely valid word, 16
out of 128 possible 7-bit words
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Summary of Coding Performance

• PE (121xp) 2 /100 146 p2
•  where p raw bit error rate
• The code is rate (121/100) meaning for every 121
  bits, 100 data bits are sent.
• This is obviously a simple approximation.
  Particular combinations of errors can fake out
  this simple code. The conditional probability of
  all combinations must be included in an exact
  analysis. This is done in Appendix A in the
  notes.

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Appendix A For a raw error rate,p 10-4, the
results are

• The undetected error rate for the simple parity
  is 5.5 x 10-7 (instead of 10-6 for the simple
  assumption.)
• The detected but uncorrected error rate for the
  simple FEC code is 7.2 x 10-5 (instead of 15 x
  10-5 for the simple assumption).
• In addition there is an undetected error rate of
  about 10-7 to 10-8 depending on some assumptions.

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Each code can be represented by a probability
error function and a code rate

• Probability error function PE F(p)
• Code rate (R,D)
• where R bit rate on the channel
• where D data bit rate on the channel
• where p raw error rate on the channel

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A hamming code (7,4) meaning 4 bits of data for 7
bits transmitted, has an error rate given by PE
9 p 2 26 p3
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Creating a Convolutional Code
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Trellis decoder for Convolutional Code
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Comparing Block Code (127, 60) BCHwith Conv.
Code(2, 1) Shift RegisterM4
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Performance vs Block Size and Channel error rate
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Time Division Multiplex (TDM)
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Variations on TDMA
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Packet Switched Networks
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TDMA in Satellite Linksmust allow gap to avoid
overlap and correct for range
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On Demand Systems
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On Demand Systems
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Performance of Aloha Systems
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TV Scan, Sync Black-White Range
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Details of Horizontal Synch Pulse
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Analog TV Vestigial Sideband
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Color information is encoded on a phase modulated
carrier in the brightness (black and white)
spectrum

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International TV Standards
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In FM TV Relay Pre-emphasis gives 2.8 dB S/N
improvement
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Quality Factors in 4 MHz TV Signal
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FM Improvement for TV
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What do we need for good quality TV (40 dB S/N)
and threshold extension receiver C/N 8.5 dB ?
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What quality do we get with basic Satellite
Relay. C/N12 dBBandwidth 36 MHz ?
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What is the power difference or antenna diameter
difference between Relay and Direct Broadcast
TVRO?
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Microwave Frequency Assignments
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Atmospheric absorption
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With Microwave Relay we must add a fading margin
to account for multi-path fading caused by
bending of rays by the atmosphere.
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Microwave Line-of-Sight
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Use of diversity to avoid multi-path
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Rayleigh Multi-path Fading
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Approximate interference fading distribution for
a non-diversity system with Rayleigh fading
versus frequency diversity systems for various
percentages of frequency separation (F.S.).
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ExampleSend an FM television signalthrough a
microwave relay

• 25 miles separation
• 4m antenna transmit and receive.
• 11 GHz frequency
• rain margin for 0.4 (inch/hr) rain fall .
• Fading margin for 99.9 percent reliability
• TR 5000 oK gt 27 dB .

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. rain margin for 0.4 (inch/hr) rain fall0.3
dB/Mi
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From earlier examples on television for relay

• FM carrier with C/N of 12 dB, B of 36 MHz gives
  52 dB S/N
• "'C/kT" 12 75.5 87.6 (dB . dBHz)
• For 99.9 percent reliability fading margin (F.M.)
  28 dB
• in 25 Mi the attenuation is 7.5 dB Att.
• ERP -(GR - TR) - Lf.s Att FM "C/kT" k
• ERP -(40.4 - 27) 145 7.5 28 87.6
  228.6 26.1 dBW
• RP ERP - GT 26.1 - 40.4 -14.3 dBW gt 37
  mi1liwatts

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How much power is needed at 6 GHz?Increased gain
overcomes increased attenuation in ground
microwave

• l. O.O5M
• GT GR 35 dB. (40.4 _at_ 11 GHz)
• Lfs -140 dB. (-145_at_ 11 GHz)
• .Attenuation is .09 dB/Mi Att ' 2.25 dB. (75 _at_
  11 GHz)
• ERP -(35 - 27) 140 2.25 28 87.6 - 228.6
  21.25 dBW
• RP 21.25 - 35 -13.75 dBW gt 42/milliwatts.
• (37 millliwatts _at_ 11 GHz)

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II. WiFi and WiMAX
Antenna Factory 2.4 GHz Grid
Antenna 13.5 dBi, SMA female connector 65.00
Each

• WiFi is a band at 2.4 GHz, limited to 40
  milliwatts transmitter power and 6 dB antenna
  gain. The bandwidth is 20 MHz and the C/N is 10
  dB.
• (a) Assuming the transmitter has 40 milliwatts
  and 6dB gain, what is the range for a receiver
  with 0 dB gain and 300 deg K receiver Temp.?
• (b) Where allowed, WiFi can be connected to
  high-gain antennas costing only 65 and having a
  gain of 13.5 dB. What is the range if the
  antennas are used at both transmit and receive
  with the 40 milliwatt transmitter?
• (c) What is the range for part (b) if in addition
  we cut the bandwidth to 2 MHz?

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• (a)            EIRP 6 10 log .040 -8 dB B
  206gt 73 dBHz C/N 10
• G/T 0 - 10 log 300 -24 dB.
• EIRP G/T Lfs B C/N k
• Lfs B C/N k EIRP G/T
• Lfs 73 10 - 228.6 8 24 -113.6gt 4.36 x
  10-12 Lfs (l/4pR)2
• l 3x108/2.4x109 .125 M
• R (l/(4p sqrt 4.36 x10-12) 4.76 Km
• (b) Total improvement 13.5 13.5 6 21 dB
  gt 125
• Range goes as sqrt( gain )
• Rb 4.76 x sqrt(125) 53 Km
• (c) Reducing B by 10/2 5 increases range by
  sqrt(5) Rc 119 Km

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WiFi and WiMAX with 18dB fading

• (c) Reducing B by 10/2 5 increases range by
  sqrt(5) Rc 119 Km from before.
• Same link equations but with 18 dB for 99
  reliability. 18 dB gt 63 sqrt63 7.9
• Reliable range of WiFi with two 13.5 dBi antennas
  119/7.9 15 Km

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Longley-Rice Propagation Models
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Issues for Country Reports

• How does the target rural population do as far as
  education, health and income?
• During the Colonial Era What were the crops or
  minerals of interest to the world traders?
• What constraints are there on them owning and
  operating the farms or mines for export income?
• What value added work could they create with
  their resource advantage?
• What local jurisdiction (national, state, or
  city is most responsive to their interests.)
• Is there an International Peace-keeping Force
  present?

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Cultural Issues

• Give a general description of the culture with
  history and pictures
• What are the local, national and international
  (trade) languages?
• What are the sites and monuments of their
  culture? Does this and/or scenic sites offer
  tourist income opportunities?
• What is the traditional governing structure of
  the society?
• How widespread is the language/culture in the
  nation?
• Are there family links to cities and other
  nations?

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Items for Development Plan

• A network plan to connect the rural region with
  low-cost WIMAX and cell phone links. VSAT where
  needed.Use local labor where possible.
• Public access through roving cell phones and
  internet cafes or kiosks.
• Local Banking (micro) to keep capital in the
  community and bring in remissions and development
  loans
• Commerce based on internet trade with WTO
• Local ownership or regulation with cooperative
  marketing.
• Local radio broadcasting.

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Education and Health Care

• Educational computer supplement to Classrooms.
• Adult education in literacy and local economic
  issues.
• Local Teacher Education
• Online textbook distribution and local printing.
• Local addition of culture to courses with
  enrichment of cultural values.
• Distribution of local supplements Wikipedia
• Training health workers and linking with field
  hospitals