In the last decades, the increasing demands on communication systems have required more development and improvement on the communicating technologies. While many scientists agree that the classical frequency division multiple access technique for communicating is a de-facto standard, new generations of communications devices require more efficient techniques such as the time division multiple access technology. This paper identifies the methods of using time division multiple access as an alternative to the original frequency division transmission technique. The paper clarifies the principle of multiple access technologies, and compares the old method with the newest one. This study points out the ways of replacing the frequency division with the time division multiple access, and identifies the main obstacles that might be faced.
Using Time Division Multiple Access as an Alternative to Frequency Division Multiple Access in the New Telecommunication Technologies During the past 30 years, the world has witnessed on the rapidly growth of telecommunication technologies. These technologies have been made to make the communication process among humans easier than ever before. The increasing demands on communications leads to the technological development.
Most of our communication systems serve many users using a multiple access transmission technique. Bott and Lescuyer (2004) indicated that many systems depend on the oldest transmission technology for communicating, which is the Frequency Division Multiple Access (FDMA) technique. Wang (2005) identified three main reasons of using FDMA such as the implementation simplicity, high capacity, and low overhead.
The contradicting studies of developing the communication systems suggest either keeping FDMA or replacing it with the Time Division Multiple Access (TDMA) technique. A research by Sheikh (2004) indicated that despite its advantages, FDMA suffers from essential drawbacks while a study by Harle and Irvine (2002) indicated that using TDMA alone will create several problems. Although many studies have been made, more studies are required to assure that TDMA technology is better.
The purpose of this research was to clarify that the Time Division Multiple Access technique could replace the Frequency Division Multiple Access technique in the new telecommunication technologies. This topic is beneficial to communication engineers in terms of supporting them with the sufficient ideas of improving and developing the telecommunication systems.
Main Principle of Multiple Access
Multiple access is technique used in the field of telecommunication technologies. It has many forms, and it is done with respect to many references. According to Goldsmith (2005), multiple access can be defined as separating the information signals into frequency channels, then allocating them to different users at different locations. The most common methods of dividing signal space are along the time and frequency axes (p. 11). As shown in Figure 1, the difference between each technique is the reference used for modulating data signals.
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Figure 1, Adapted from "Multiple Access Technologies", by Dr. Eric Haas, Communication Systems, n.d
Definition of FDMA
It is known that the FDMA technology is built on the frequency division multiplexing FDM method. This technique is the oldest and the simplest form of multiplexing, which is commonly used in the telephone, and commercial radio and television broadcasting industries. The FDMA technique can be applied for both digital and analog systems. Since FDMA is an old technology, it is widely used in analog communications. The FDMA technique is based on dividing the signaling dimensions along the frequency axes to create separate channels. These channels will be allocated to users with a bandwidth of 30 kHz (Hill Association, 2002, p. 285).
TDMA is an advanced multiple access technology that allows more than one user to access radio frequency (RF) channels without interference. According to Garg (2007), in a TDMA system, there are Guard Times which have an important role in decreasing the effects of the transmission impairments and "used between each user's transmissions to minimize cross talk between channels" (p. 154). TDMA system can use the available bandwidth depending on the data rate and the amount of time slots dedicated for each frame.
In the last 10 years, many communication systems and devices have started using the time division multiple access technique in their equipments, because TDMA provide many advantages compared with the older FDMA technique. TDMA is an excellent choice for its transmission efficiency and less impairments.
Power saving: Transmitted and received. TDMA system makes a good usage of the transmitting and receiving power of the signal, because it has less inter-modulation noise (Bagad, 2009).
Digital utilization. TDMA utilize the advantages of digital communication in applications such as speech interpolation, and data encryption (Bagad, 2009).
Less Transmission Impairments
The design of TDMA technology is immunity to transmission impairments such as the delay distortion and noise. Also, it is not affected by interference.
Talking about communication technologies means we have to keep working on finding the optimum technology for best tradeoff between the cost and efficiency. In the last two decades, people have witnessed on the transformation process from analog to digital communications. Now, we are witnessing the usage of TDMA for many FDMA-based applications. The main question is: why FDMA is not effective anymore?
In 2005, a research by Wang concluded that FDMA suffers from serious problems such as wasting bandwidth. This problem is very costly to all communication companies in terms of needing for extra equipments and devices for providing more bandwidth. Also, he noted that any connection using FDMA will suffer from interference (p. 1005). Ryan and Frater (2002) realized that it is difficult for an FDMA station to serve many users at the same time (p. 46). As a result, new technologies, such as TDMA, are needed to solve these problems.
Moving Toward TDMA
Nowadays, there are many communication applications that use TDMA for its transmission operations. In addition, communication companies produce products based on TDMA. According to Bott and Lescuyer (2002), TDMA can be used with FDMA or as "an alternative to FDMA. The users of a TDMA system all use the same frequency band… "(p. 99). In a smoothly move, we are taking further steps from using FDMA. However, we cannot get rid of FDMA technologies or use only TDMA. There are many obstacles that might face us during upgrading.
The main obstacle of TDMA/FDMA transformation is the old used infrastructure. It is very costly to change the whole FDMA-based stations into TDMA ones. Also, the construction of FDMA devices is inexpensive and simple. On the other hand, TDMA circuits take more work, time, cost, and complexity. According to Harle and Irvine (2002), using TDMA alone is quite difficult, because all users will use the same frequency when they communicate. As a result, a combination of TDMA and FDMA systems should be used (p. 224).
The new generations of telecommunication devices depends mainly on TDMA technology. For example, TDMA is used in personal digital cellular and Europe's GSM (Ipatov, 2005, p.11). In addition, computer local area networks (LAN) use TDMA in order to serve multiple devices communicating on the same channel. The following table (Table 1) shows the usage of FDMA and TDMA among wireless systems with related technical information.
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Table1. The usage of TDMA and FDMA in different systems
The increasing demands on communication technologies lead to the usage of TDMA. This technology has many advantages over FDMA, and it is used in many applications. Although TDMA is the best choice, future technologies, such as Code Division Multiple Access (CDMA), are required to fulfill other purposes of communications. These new technologies will protect the transmitted data, and make an efficient usage of multiple algorithms (Ipatov, 2005, p. 121). As the applications of communications increase, the development and improvement on communicating technologies also increase in order to satisfies the users of communications services.
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