Attachments: ECET 380 NA Week 5 iLab CD Multiple A 3G Cellular MA Scheme.docx [ Preview Here ]
Code Division Multiple Access A 3G Cellular Multiple Access Scheme
TutorTIMS – Version 2.0 Advanced
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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:
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: