Due to orthogonality each carrier will have a number

Info icon This preview shows pages 5–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Due to orthogonality, each carrier will have a number of cycles of a symbol period, which will in turn cause each carrier to have a null value midway through the frequency of each of the other carriers. By doing this, interference between the carriers is prevented. The carrier for an OFDM signal will have a very narrow bandwidth, typically about 1 kHz, causing the symbol rate to be low. By having a low symbol rate, inter-symbol interference (ISI) is avoided, since low symbol rate gives the signal high tolerance to multipath spread. [2]
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Comparison in Terms of Performance In order to compare between the performance of CDMA and OFDM, we need to define the systems in use and the environment in which the performance analysis will be made in. We need to make sure that we build these two systems at the same bandwidth, and compare their performance in multipath fading and Additive White Gaussian Noise (AWGN) channels. After that, a binary modulating signal with the same bit rate is transmitted using both systems and the BER is analyzed. The use of a RAKE receiver for the CDMA system and a coherent OFDM detector in the OFDM system are to be used. Following are figures displaying both the CDMA and OFDM systems in use. The figures include both the transmitter and receiver of each system: Figure 2: CDMA Transmitter/Receiver Figure 3: OFDM Transmitter/Receiver
Image of page 6
The performance analysis is done with the use of a simulation tool called Simulink. For the CDMA system, the performance is analyzed as the system performs through multipath fading and AWGN. Walsh codes with period of 64 chips are use as spreading sequences and the simulation is run. The following two figures show both the transmitted signal and the received signal in the CDMA system: Figure 4: CDMA Transmitted/Received Signal As we can see, the received signal through the CDMA receiver is full of distortions, which increases the BER. For the OFDM system, we run the simulation through multipath fading and AWGN as well, but the encoder uses Binary-Input Reed Solomon (RS) Encoder block. The RS code generated has message length of 11 and a codeword length of 15.
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
The following two figures show both the transmitted and received signal of the OFDM system: Figure 5: OFDM Transmitted/Received Signal From these graphs, we notice that the received signal by the OFDM receiver also suffers from some distortions, but comparatively less than the amount of distortions suffered by the CDMA receiver. If we compare the transmitted signal by the CDMA transmitter and the OFDM transmitter, we can notice that both the systems have almost the same transmission bandwidth. However, in terms of BER, the performance of the OFDM system exceeds that of the CDMA system, as the BER in the CDMA is very high compared to that of the OFDM system.
Image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern