ECET 380 Week 5 iLab Code Division Multiple Access A 3G Cellular Multiple Access Scheme

ECET 380 Week 5 iLab Code Division Multiple Access A 3G Cellular Multiple Access Scheme

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Code Division Multiple Access A 3G Cellular Multiple Access Scheme



  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.




            IBM PC or Compatible with Windows 2000 or Higher


            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



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  • FDMA - Frequency Division Multiple Access: Deployed in the now mostly outdated 1G standards, this scheme was highly bandwidth inefficient.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.





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 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:

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