This document describes two lab experiments using the TIMS modeling system: 1) A CDMA lab to generate and detect CDMA signals with and without noise using modules like the sequence generator, multiple sequence source, and CDMA decoder. 2) An OFDM lab to implement an OFDM generator using modules like the sequence generator, multiplier, and adder and generate/analyze OFDM waveforms. The document provides background on CDMA and OFDM multiple access schemes.

1. DEVRY ECET 380 Week 5 Lab Code Division
Multiple Access A 3G Cellular Multiple Access
Scheme NEW
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Code Division Multiple Access A 3G Cellular
Multiple Access Scheme
I. OBJECTIVES
1. Use the TIMS modeling system to generate a
CDMA signal.
2. Detect the messages transmitted in the CDMA
signal in a noiseless channel.
3. Add degradation in the form of noise to a CDMA
signal.
4. Study the effects of noise on a CDMA signal.
II. PARTS LIST
Equipment:
IBM PC or Compatible with Windows 2000 or
Higher

2. Software:
TutorTIMS – Version 2.0 Advanced
The following TIMS modules will be required for
the lab. Read about the modules required for the
particular lab section before proceeding:
1. Sequence Generator
2. Multiple Sequence Source
3. Master Signals
4. Adder
5. Digital Utilities
6. Quadrature Utilities
7. Noise Generator
8. CDMA Decoder
9. Error Counting Utilities (Error Counter)
10. Phase Shifter
III. INTRODUCTION
The scarcity of the available spectrum and the
explosive growth in the popularity of wireless
communications devices absolutely imposes the
need for the sharing of the available bandwidth
among wireless applications subscribers. A
number of multiple access schemes exist to meet
this demand, each with its own merits and
demerits, including:
• FDMA - Frequency Division Multiple Access:

3. Deployed in the now mostly outdated 1G
standards, this scheme was highly bandwidth
inefficient.
• TDMA - Time Division Multiple Access: More
spectrally efficient than FDMA and still in
operation in 2G standards such as GSM, which is
still widely deployed in many countries around the
world. TDMA is also the multiple access scheme of
choice for most of the wireless data-centric
standards.
• CDMA - Code Division Multiple Access: This is the
access scheme of choice for 3G and other evolving
standards such as CDMA 2000 and W-CDMA. This
scheme, when combined with spread spectrum,
imparts certain advantages, as we shall observe in
this lab. It should be noted that the combination of
the multiple access scheme and the duplexing
method (TDD, FDD) used in an application is
known the “air interface” method for that
particular application.
CDMA
In the CDMA scheme, each subscriber is assigned a
unique code which is as different from that
assigned to all other subscribers as possible. This
setup allows the subscribers to use the same

4. allotted spectrum, say in a particular cellular
communications cell, with minimal interference to
one another.
In the CDMA scheme, there is no need to divide the
spectrum into tiny bands, as in FDMA, and
subscribers do not have to take turns occupying a
relatively large available bandwidth, as in TDMA.
This means that in CDMA applications, a relatively
large bandwidth is occupied all of the time when
allotted to a subscriber.
One can thus see why CDMA is the scheme of
choice for the 3G and beyond cellular standards.
Little frequency planning is needed. It also has a
large occupied bandwidth, without the latency
issues that arise from time division sharing. This
all leads to the possibility of supporting very high
data rates, when combined with other PHY layer
schemes such as modulation and compression. In
addition, the technique of spread spectrum, which
is bandwidth driven, can be exploited. This helps
mitigate channel-imposed degradations, such as
multipath fading.
Table 1 shows CDMA deployment in 2G and
beyond cellular standards with 2G GSM shown for
comparison:

5. Introduction to OFDM Generation
IV. OBJECTIVES
1. Introduce the student to the underlying theory
of operation of Orthogonal Frequency Division
Multiplexing (OFDM).
2. Learn to use TIMS modules to implement an
OFDM generator scheme.
3. Generate and analyze OFDM waveforms.
V. PARTS LIST
Equipment:
IBM PC or Compatible with Windows 2000 or
Higher
Software:
TutorTIMS – Version 2.0 Advanced
The following TIMS modules will be required for
the lab. Read about the modules required for the
particular lab section before proceeding:
11. Sequence Generator
12. Multiplier
13. M-Level Encoder
14. Phase Shifter
15. Master Signals
16. Adder
17. Tunable LPF

6. 18. 100 KHz Channel Filters
19. Decision Maker
VI. INTRODUCTION
OFDM (Orthogonal Frequency Division
Multiplexing) is a combination of modulation and
multiplexing, and more specifically, is a special
case of Frequency Division Multiplexing (FDM), as
the name implies.
A single main data stream is split into many lower
rate data streams (multiplexing). Each of these
streams is then individually modulated onto a
separate sub-carrier (modulation) and finally
recombined into a single composite OFDM signal
to be transmitted.
The addition of a cyclic prefix is also an important
part of OFDM, however, this feature will be
discussed but not implemented in this
introductory experiment. The coding blocks will
not be covered in detail within this experiment.

7. 18. 100 KHz Channel Filters
19. Decision Maker
VI. INTRODUCTION
OFDM (Orthogonal Frequency Division
Multiplexing) is a combination of modulation and
multiplexing, and more specifically, is a special
case of Frequency Division Multiplexing (FDM), as
the name implies.
A single main data stream is split into many lower
rate data streams (multiplexing). Each of these
streams is then individually modulated onto a
separate sub-carrier (modulation) and finally
recombined into a single composite OFDM signal
to be transmitted.
The addition of a cyclic prefix is also an important
part of OFDM, however, this feature will be
discussed but not implemented in this
introductory experiment. The coding blocks will
not be covered in detail within this experiment.