MS&E 237
Summer 2002
Ivanek, Chiu
Handout #5
August 1, 2002
Page 1 of 3
COURSE INFORMATION
PROGRESS IN WORLDWIDE TELECOMMUNICATIONS
Program of August 1 session
6:30 - 7:00
Follow-up discussion of July 25 session
Introduction to August 1 session
7:00 - 8:30
Guest spealers:
Donald C. Cox
Harald Trap Friis Professor of Engineering
and Professor of Electrical Engineering, Stanford University
Subject: Wireless Data Evolution
Stanley Chia
Director, Strategic Technologies
Vodafone Group R&D-US
Subject: 3G Network Convergence
8:30 - 8:45
Break
8:45 - 9:30
Questions, answers and general class discussion
The guest speakers’ biographies are posted on the MS&E 237 web site:
http://www.stanford.edu/class/msande237
Recommended reading
For an introduction to wireless communications and wireless data evolution Professor
Cox recommends chapters 1 and 2 of T. S. Rappaport, Wireless Communications,
Principles and Practice, Prentice Hall, Upper Saddle River, NJ, 2nd edition, 2002.
Articles in 2002 issues of the IEEE Communications Magazine:
Global Roaming in Next-Generation Networks,
February, pages 145 - 151
Next-Generation Wireless Communications concepts and Technologies,
March, pages 108 - 116
Wireless Internet Access for Mobile Subscribers Based on the GPRS/UMTS Network,
2
April, pages 38 - 49
Wireless Communications: Past Events and a Future Perspective,
May, pages 148 – 161
Articles in 2002 issues of IEEE Wireless Communications:
WCDMA abd WLAN for 3G and Beyond,
April, pages 14 - 18
A Framework for the Dimensioning of Broadband Mobile Networks Supporting Wireless
Internet Services
June, pages 6 - 13
The Economist, June 22, Watch this airspace - Wireless telecoms: Four disruptive
technologies are emerging that promise to render not only the next wave of so-called 3G
wireless networks irrelevant, but possibly even their 4G successors
http://www.economist.com/displayStory.cfm?Story_ID=1176136&CFID=6559983&CFTO
KEN=5d38fbc-026620e3-e6b9-422c-955e-737e6df29f9d
InfoWorld, July 24, MIT scholars predict shift in telecom model
http://www.infoworld.com/articles/hn/xml/02/07/24/020724hntelecommit.xml
NYT, July 26, Telecom Giants Are Retrenching in Europe as Finances Wither
http://www.nytimes.com/2002/07/26/business/worldbusiness/26EURO.html?todaysheadl
ines=&pagewanted=print&position=top
Attachment to Handout #5
Some Homework #3 comments indicate that the July 18 presentation, SELECTING
FREQUENCY BANDS FOR FIXED WIRELESS ACCESS (BWA), requires additional
information regarding the impact of electromagnetic wave propagation conditions
(viewgraph 5). The issue is that the limitations on usable link length in the BWA
frequency bands above 20 GHz are imposed by rain attenuation and frequency reuse
requirements which we have not covered in class, whereas the increase of the isotropic
free-space attenuation, proportional to the square of frequency, is of secondary
importance. Only the net free-space attenuation which takes into account the gains of
commonly used directive antennas is of practical importance. In the following illustrative
example, based on a representative link length of 5 km, and a conventional 60 cm dia
antenna with 65% efficiency, the net free-space attenuation actually decreases with
increasing frequency.
Frequency
Isotropic free-space
Antenna gains
Net free-space
(GHz)
attenuation (dB)
(dB)
attenuation (dB)
-------------------------------------------------------------------------------------------------20
132.5
39.2 + 39.2
54.1
40
138.5
45.2 + 45.2
48.1
The exemplified frequencies are chosen to show that the isotropic free-space attenuation
3
and antenna gain both increase by 6 dB when the frequency doubles. The following well
known formulas have been used.
Isotropic free-space attenuation = 32.5 + 20 log d + 20 log f
where distance d is in km, frequency f in MHz, and free-space attenuation in dB
Antenna gain = 10 log 4  A / 2
where the effective antenna area A is 65% of the geometrical area,  is the operating
wavelength, A and  are expressed in the same unit, and the antenna gain is in dB
Rain attenuation
Graphs and tables of rain attenuation as a function of rainfall rate and frequency can be
found in the literature. The following data is sufficient for our illustrative purpose.
Rain rate
Attenuation at 20 GHz
Attenuation at 40 GHz
--------------------------------------------------------------------------------------------------------5 mm/h (moderate)
~ 0.5 dB/km
~ 1.5 dB/km
100 mm/h (cloud burst)
~ 10 dB/km
~ 20 dB/km
This data shows that heavy rain has a moderate impact at 20 GHz, whereas it can
seriously impair a 40 GHz link. The actual impact depends on the local rain statistics, on
the performance and availability objectives, and on the link design fade margin.
Frequency reuse
High-density BWA deployment requires frequency reuse optimization. Subscriber
densities in a 39 GHz network in New York, for example, range up to above 100 stations
per square kilometer. To serve such a number of subscribers with the comparatively
small number of available radio-frequency channels requires frequency reuse within the
same cell and among adjacent cells. This can be achieved by using the lowest
transmitter powers that can assure the performance and availability objectives. Small
cells with short links are the straightforward solution which is consistent with high
deployment densities in urban centers. The great majority of the existing several
thousand 39 GHz BWA links in the U.S. are shorter than 1 km. This is a type of
deployment in which, as a rule, link lengths are not limited by propagation impairments
but by frequency reuse requirements.