ELEC 464/4 WINTER 2007
COMMUNICATIONS SYSTEMS ENGINEERING
LAB REPORT 4
EXPERIMENT 3
CDMA and RAKE Receiver
Rosalynn Nguyen ID: 4711165
Section WM
Lab instructor: Haysam Dahman
Date performed: Wednesday, March14th 2007
Date submitted: Wednesday, March 28th 2007
EXPERIMENT 4
PRELIMINARY REPORT
ROSALYNN NGUYEN 4711165
1) Generate two 31-bit Gold codes by using the circuit in Fig.2,with initial state of:
a. Upper m-sequence:10000 Lower m-sequence 10000
b. Upper m-sequence 10000 Lower m-sequence:10100
2) What is the main difference between a Gold code and an M-sequence?
Gold codes have three-valued autocorrelation and cross-correlation function with
values , where
The generation of Gold codes is very simple. Using two preferred m-sequence
generators of degree r, with a fixed non-zero seed in the first generator, 2 r Gold
codes are obtained by changing the seed of the second generator from 0 to 2 r -
1. Another Gold sequence can obtained by setting all zero to the first generator,
which is the second m-sequence itself. In total, 2r + 1 Gold codes are available.
Shift-register sequences having the maximum possible period for an r-stage shift
register are called maximal length sequences or m-sequences. A primitive
generator polynomial always yield an m-sequence. The maximum period of an r-
stage shift register can be proven to be 2r - 1. The m-sequences has three
important properties, i.e., balance property, run-length property and shift-and-add
property. The periodic autocorrelation function Ra(k) is two-valued and is given by
where l is an integer and N is the period of the m-sequence. The excellent auto-
correlation property comes from the first and the third properties. Refer to [2] for
details. m-sequences have good auto correlation property and are being used in
many applications including IS-95. As the cross-correlation property of these
sequences is relatively poor compared to Gold codes, the same sequence with
different offset are usually used for different users or for different base stations.
With this method, the discrimination property between different spreading codes
only depends on partial autocorrelation property.
3) Is the RAKE receiver capable of tracking a path with a delay more than one data bit? If
not, what device can do this?
A rake receiver is a radio receiver which has a functionality to counter the effects of
multipath fading. By using sub-receivers each delayed slightly in order to tune in to the
individual multipath components. Each component is decoded independently, but in a
future stage, will be comined in order to make the most use of the different transmission
characteristics of each transmission path. Hence, It cannot track a path with a delay of
more than one data bit, due to the analogous function to a garden rake, each finger
collecting bit energy, the same way a rake collect leaves. A few technologies can solve
this problem, as frequency offsets between transmitter and receiver clocks, as well as
relative velocity between the mobile station and the base station. Sometimes, we cansee
a high resolution delay tracking device that can improve an initial timing estimate and
track any changes which occurr, with conjunction of a channel estimator who generates
an initial timing estimate for each multipath component.
I. OBJECTIVES
To get acquainted with CDMA communication systems and RAKE system.
II. PROCEDURES
Section 3.1. Principle Spreading Techniques. After using the DSP/BIOS configuration
Tool, in order to pre-configure our executable program, we have set the files linked to our
code for future building of our application program. The following steps 1 to 12 are as
follows:
Open a project called audio.pjt.
Rebuild this project, after verifying that the output filename field is audio.out.
Open the built program, audio.out.
Add the following parameters in the Watch Window: output_control, data1, data2,
solft_decision1, soft_decision2, fading_co, n_variance.
Connect output of DSP board to Oscilloscope.
Following step 13, we apply the following changes, expressed in Table 1;
Table 1. First, Second, and Third time Fading_co[n] Parameter Changes.
Fading_co[0] Fading_co[1] Fading_co[2] Fading_co[3] Fading_co[4] Fading_co[5]
First
1 0.5 0.0 0.0 0.3 0.0
time
Second
1 0.0 0.0 0.7 0.0 0.2
Time
Third
1 0.5 0.2 0.9 0.3 0.1
Time
After completing these parameter changes, we obtain the following outputs, recording the
signal on the oscilloscope, soft_decision1, and soft_decision2, for n_variances values of 0.0
and 0.5, and with data1 is +1, and data2 is -1.
Table 2. Record of the Measurements when Data1 = +1, and Data2 = -1.
First Time Second Time Third Time
n_variance 0 0.5 0 0.5 0 0.5
Soft
1.1 0.7557564 1.25 1.07011 0.5500004 0.6444615
Decision 1
Soft
-1.600001 -1.386429 -1.75 -1.41587 -2.1500001 -1.970774
Decision 2
A second run of the same testing, with data1 is +1 and data2 is +1, outputs the following
values(step 15):
Table 3. Record of the Measurements when Data1 = +1, and Data2 = +1.
First Time Second Time Third Time
n_variance 0 0.5 0 0.5 0 0.5
Soft
0.6 0.7321475 0.7500001 0.7573649 1.15 1.706296
Decision 1
Soft
1 -0.0554275 0.25 0.4434126 -0.1200001 0.01277415
Decision 2
Section 4.1. A Simple CDMA System.
After loading up the code provided in the laboratory, we follow the same steps as in section 3.1.
We add these parameters: BER, Zm[0…2], data2 and H_decision1, and H_decision2, fading,
n_variance, Zm and co. Here we will use the “ Random Sequence” as spreading codes. Once
the DSP board is running, we apply these parameter changes for three consecutive tries.
Table 4. Random Sequence Parameter Changes.
First Time Second Time Third Time
Fading_co[0] 1 1 1
Fading_co[6] 0 0 0.5
Fading_co[7] 0 0.4 0.4
Fading_co[10] 0 0.45 0.45
After applying Step 13, we record the following parameters applying the “Random Sequence
Code”, applied to n_variances 0.1 and 1.0.
Table 5. Output Records Using Random Sequence Technique.
First Time Second Time Third Time
n_variance 0.1 1.0 0.1 1.0 0.1 1.0
BER 0.0 0 0.64733333 0.02 0.1356 0.1380667
Zm[0] -0.863548 -0.863548 0.8445435 0.6761596 -0.5346441 -0.705702
Zm[1] -0.3732521 -0.3732521 0.3022777 0.5105005 0.301321 -0.4148511
Zm[2] 0.4318694 0.4318694 -0.9500863 -0.4902981 -0.3335121 -0.3838485
data2 -1 -1 -1 +1 +1 -1
H_decision2 -1 -1 -1 +1 -1 -1
We then pass on the second type of spreading code, the “M-Sequence”. In the Watch window it
is imperative to follow these parameter changes:
Table 6. Parameter changes for First, Second and Third Time with M-Sequence
First Time Second Time Third Time
Fading_co[0] 1 0.7 0.7
Fading_co[2] 0 0.6 0.6
Fading_co[5] 0 0 0.9
Fading_co[6] 0.5 0.5 0.5
Fading_co[7] 0.4 0.4 0.4
Fading_co[10] 0.45 0 0
Fading_co[11] 0 0.8 0.8
From Step 14, we record the following output parameters reading from the Watch Window, for
n_variance 0.1 and 0.2.
Table 7. Output Records Using M-Sequence Technique.
First Time Second Time Third Time
n_variance 0.1 1.0 0.1 1.0 0.1 1.0
BER 0 0.006866667 0.024 0.0898 0.04206667 0.0464
Zm[0] 0.8806114 1.063226 -1.047485 0.4027992 0.614334 -0.5614694
Zm[1] 0.4810818 0.2251134 -0.6614413 0.1977741 0.9373034 -0.8199123
Zm[2] 0.6553757 -0.2512069 -0.7212436 0.9175164 0.6836691 0.8737174
data2 +1 +1 -1 -1 +1 -1
H_decision2 +1 +1 +1 +1 -1 -1
We now need to observe the characteristics of the Orthogonal Gold spreading technique.
We activate the code line defining the Orthogonal Gold specifications. Using these tabulated
values from the laboratory manual p.55 we apply these parameters changes:
Table 8. Parameter changes for First, Second and Third Time with Orthogonal Gold Spreading
Technique.
First Time Second Time Third Time
Fading_co[0] 1 0.7 0.7
Fading_co[1] 0 0 0.5
Fading_co[2] 0 0.6 0.3
Fading_co[3] 0 0 0.4
Fading_co[4] 0 0 0
Fading_co[5] 0 0.9 0.2
Fading_co[6] 0 0.5 0.4
Fading_co[7] 0 0.4 0.5
Fading_co[8] 0 0 0
Fading_co[9] 0 0 0.4
Fading_co[10] 0 0 0.3
Fading_co[11] 0 0.8 0.2
Fading_co[12] 0 0 0
Fading_co[13] 0 0 0.5
Fading_co[14] 0 0 0
Table 7. Output Records Using Orthnogonal Gold Technique.
First Time Second Time Third Time
n_variance 0.1 1.0 0.1 1.0 0.1 1.0
BER 0 0.001466667 0.0000667 0.0014 0.0002 0.001733333
Zm[0] 1.009178 -1.213229 1.03852 0.5373583 -0.5400721 -0.8992758
Zm[1] -0.2437126 -0.0040102 0.9452513 -1.2719317 0.6350455 -0.9261029
Zm[2] 0.3650685 -0.3671863 0.4954629 -1.274387 0.6485406 -0.7494239
data2 +1 -1 -1 +1 +1 -1
H_decision2 +1 -1 +1 -1 +1 -1
Step 16. Based on the observations in step 13, 14 and 15 compare the performance of
using these 3 codes in CDMA.
We observe that the Bit Error Rate improves from Random sequence to M-Sequence and
Orthogonal Gold Sequence. Hence the best performance is the Orthogonal Gold
Sequence.
CONCLUSION
After the completion of this fourth experiment which introduces us to CDMA and RAKE
receiver, we can conclude that our objective has been met. We have been acquainted with
CDMA communication systems and RAKE receiver. The results were within the expected
range of values, and as we can see, it has been very instructive and educational..
