7/30/2019 Introduction to RF Basics
1/22
Introduction to RF Basics
7/30/2019 Introduction to RF Basics
2/22
7/30/2019 Introduction to RF Basics
3/22
7/30/2019 Introduction to RF Basics
4/22
Characteristics of a Radio Signal
These are three characteristics ofan RF signal which are commonlyvaried to carry information:
Amplitude
Magnitude of the signal
Frequency
Number of cycles per unit of time
Phase
The offset of the Signal
7/30/2019 Introduction to RF Basics
5/22
7/30/2019 Introduction to RF Basics
6/22
7/30/2019 Introduction to RF Basics
7/22
7/30/2019 Introduction to RF Basics
8/22
Dominant Mechanisms of Mobile Propagation
Most propagation in the mobile
environment is dominated bythese mechanisms:
Free Space (Line-of-sight) No reflections, no obstructions
Attenuation caused only by air
Obstruction When a signal propagates through anobstruction it is attenuated
Knife-Edge diffraction Direct path is blocked by obstruction,
however some signal can go around
Additional Loss is introduced
Reflection Signal can be reflected off certain
surfaces (i.e. Glass, Water)
This could degrade or improve the signal
7/30/2019 Introduction to RF Basics
9/22
7/30/2019 Introduction to RF Basics
10/22
7/30/2019 Introduction to RF Basics
11/22
Cellular Systems
Single Cell Advantages:
Simple System
Disadvantages: Coverage constraints
Limited number of conversations
Multi-cell Advantages:
More cells allow the samechannels to be reused inmultiple areas, allowing moreconversations and morecapacity
Mobiles can be made smallerwith lower transmit power
Disadvantages: More complicated system:
handoffs required
7/30/2019 Introduction to RF Basics
12/22
Whats a Sector? Why Sectorize
A base station may be set up in variousconfigurations:
Omni for simplicity and low cost
2-sector to cover just a highway or transportationcorridor, with little coverage off to the sides:
Two sectors give more traffic-handling capabilityand more antenna gain than an omni station
3 sector to cover an area with population in alldirections:
Three sectors give almost three times the traffic-handling capability of an omni base station
Sector antennas also give better coverage since
they have more gain than omni antennas The sectors do not have equal widths and can be
grown , shrunk, and aimed to balance the amountsof traffic they get
7/30/2019 Introduction to RF Basics
13/22
Frequency Reuse
7/30/2019 Introduction to RF Basics
14/22
7/30/2019 Introduction to RF Basics
15/22
7/30/2019 Introduction to RF Basics
16/22
7/30/2019 Introduction to RF Basics
17/22
7/30/2019 Introduction to RF Basics
18/22
7/30/2019 Introduction to RF Basics
19/22
7/30/2019 Introduction to RF Basics
20/22
Structure of CDMA Signal
CDMA Carries are spaced 1.25MHz
apart
In the BTS downlink signal, different
codes belong to different users a
mobile only listens to its particular
code The mobile on its uplink uses the
same code to communicate with the
BTS
This allows many simultaneous calls
to be processed during the same
time
7/30/2019 Introduction to RF Basics
21/22
References
Baxter, Scott. Physical Principals of Propagation, 2004
Baxter, Scott. Introduction to Wireless Technologies for Telematics
Applications, 2004
Baxter, Scott. How Wireless Developed, 2005
Baxter, Scott. CDMA Core Principals, 2007
Baxter, Scott. Introduction to Fixed Broadband Wireless Access, 2005 http://www.cellular-expert.com/_Rainbow/images/default/imgl4.jpg
http://static.commentcamarche.net/en.kioskea.net/pictures/telephonie-mobile-images-reseau-
cellulaire.png
7/30/2019 Introduction to RF Basics
22/22
Any Questions?
Top Related