EE5576: Wireless Communication Systems:
Homework Assignment 5
Given: March 18, 2021
Due: March 25, 2021 (11:59)
Submission Instructions:
Submit your assignment in electronic format (.pdf) directly on Canvas
Dr. Elena Bernal Mor
Assistant Teaching Professor
Department of Electrical and Computer Engineering
Northeastern University
e-mail : [email protected]
Problem 1 (100 points)
Consider a wireless communication system that uses CDMA. The codes used are Walsh codes with 4 chips.
At a given moment there are three users, Elena, Laura and Nick, transmitting at the same time with the
same carrier frequency. Consider there is perfect synchronization among the transmitters and the receiver.
Different codes are assigned to each one of the users. The codes assigned to each one of the users are as
follows:
Elena → 0110
Laura → 0101
Nick → 0011
Each user sends 8 bits that encode a letter following the ASCII coding. You will find in the Appendix a
table for the ASCII conversion letter/bits.
Consider that a binary encoding is used by the three users where:
Bit 0 is represented with a −1 pulse
Bit 1 is represented with a 1 pulse
The chips are represented also with pulses using the same conversion.
The signal received is the sum of the signals transmitted by the three users through the channel. The
values of the pulses that are obtained in the receiver after the bandpass demodulation are given by:
[3 − 1 − 1 − 1 − 3 1 1 1 − 3 1 1 1 3 − 1 − 1 − 1
−1 − 1 − 1 3 − 3 1 1 1 1 − 3 1 1 1 1 1 − 3]
a) (25 points) Show that the codes used by Elena and Nick are orthogonal.
b) (75 points) Which is the letter sent by Elena? show all the derivation steps. You can solve it analytically,
but if you prefer to use Matlab to obtain the solution, explain step by step what you are doing in your
code and include the .m file in the submission.
Appendix
ASCII table:
2

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