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NTC362 Time Division Multiple Access, Frequency Division, Multiple Access, and Orthogonal Frequency Division Multiplexing

An assignment explaining TDMA, FDMA, and OFDM in networking.

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    Running head: TIME DIVISION MULTIPLE ACCESS,FREQUENCY 1 Time Division Multiple Access, Frequency Division, Multiple Access, and Orthogonal Frequency Division Multiplexing NTC362 Daniel Aldama Explain the key differences between Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA) in terms of their channel access methods, advantages, and disadvantages. In your response, provide real - world applications of each technology, discussing their impact on network efficiency and user experience. Additionally, consider the advancements in CDMA technology, such as CDMA 2000, and explain how it enhances performance and security. Your response should be 800 - 900 words.

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    T IME DIVISION MULTIPLE ACCESS,FREQUENCY 2 Frequency Division Multiple Access As the name implies, Frequency Division Multiple Access (FDMA), utilizes Frequency Division Modulation (FDM) to separate the given spectrum into individual analog bands or channels. A simplified view of how this is done can be seen in figure 1 below. Each of these channels is then able to facilitate communication for a single user. According to ( Goleniewski, 2007) each FDMA cell is able to facilitate about 60 users, which is very a low number by current standards. Figure 1. Goleniewski, L. (2007). Example of FDMA channel separation. FDMA was short lived as a viable option for commercial use on its own; however, it was an important step in the right direction. I say this because it is now a critical part of multiple other techniques, where it is used to divide spectrum into channels before other modulation techniques are applied. Once such techn ology is the one explained next. Time Division Multiple Access

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    T IME DIVISION MULTIPLE ACCESS,FREQUENCY 3 Time Division Multiple Access or TDMA is a channel access that is shared out and is used on medium networks. This is also known as the 2G network that is slowly being phased out. What TDMA does is it allows multiple users to share the same channel within a network. This is accomplished by splitting a single channeling into two or three different time slots to maximize the data flow. The communication then can take place by allowing the users communication to pass through the channel at different intervals. When the communication is picked up on the other end the intervals are reconstructed as if each user was using a single line by themselves. This communication technology is used in the cell phone industry. “ DMA is used by Digital - American Mobile Phone Service (D - AMPS), Global System for Mobile communications (GSM), and Personal Digital Cellular (PDC)” (Time division multiple) . Since TDMA cannot be used in the exact same way these companies have to implement it in different ways. There are many advantages to using this system and here are a few of them: o TDMA can easily adaptable o TDMA provides users with an extended battery life o TDMA is the most cost effective Since TDMA is use a split channel it can be easily adapted to not only data transmissions, but voice communications as well. This is a great feature because anything that can do two things is going to be an asset. Having that ability to adapt on the fly without flipping a switch can save time and money for a company. Having the

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    T IME DIVISION MULTIPLE ACCESS,FREQUENCY 4 ability to adapt to either communication type is great, but adding that to a channel that can support two or three users id even better. Another advantage that this provides is a longer battery life for user. This might seem a little strange, but since the channel is divided into two or three segments and communication takes place in intervals the devices is not in constant communication. The only time that the devices are used in when data or voice communication is taking place; this is why the battery life is extended. Now how much battery life it does save, is a different question. The last advantage that is listed is the fact that the system is truly cost effective in terms of signal conversions. Having the ability to convert analog signals to digital signals is a plus because the technology already does so much. When taking into account everything that the technology can do you can see why it is truly cost effective. It is like a Swiss army knife by providing multiple functions to a cell phone network while maximizing the signal to its full capacity. There are however disadvantages that this can bring a caller. Since users are not assigned a specific channel then can lose or drop calls. This happens because the slot time is not assigned to the user and when they go to roaming this may or may not allow the user to call out because the particular slot time is being occupied. This can really stink especially if you are trying to make an important call. The bottom line is that with new technology, comes better improvements with existing systems. These systems are not that bad because without them we would have nothing, but as we are always looking for the next best thing.

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    T IME DIVISION MULTIPLE ACCESS,FREQUENCY 5 CDMA Code Division Multiple Access (CDMA), is a technology based on spread spectrum: Direct Sequence Spread Spectrum (DSSS) to be precise. What makes it unique in relation to TDMA or FDMA is that spread spectrum allows users to operate on the same frequency simultaneously. Early CDMA operated at 1.25 MHz, with newer generations, also known as Wideband CDMA, operate at 3 MHz, 10 MHz, or 15 MHz ( Goleniewski, 2007). The larger channels of the latter allow it to carry more calls and implement superior encryption. Compared to the analog technologies discussed in the previous two sections the spectral efficiency of first generation CDMA was 10 to 20 times greater. This translates into being able to squeeze 10 to 20 times the data given the same amount of spectrum. As mentioned above CDMA allows users to share the same frequency. This is accomplished by using code to delineate users instead of frequency, which as the name implies is the heart of CDMA. This provides CDMA networks with a better resistance to interference and better security. This is how. DSSS converts each bit into micro pulses called chips. Chips are very fast pulses used to represent each bit as its own pseudorandom bit pattern (PN code). First generation CDMA utilizes a 64 - bit (read chip) PN code. What this means is that each 1 bit is represented by a 64 chip pattern, and a 0 bit is represented by the exact inverse of the 1 bit. Consequently, even if some 1s and 0s are lost from the pattern, there are usually still enough intact for the receiver to determine the intended bit. The result is much higher quality, less error prone signal.

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