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Review on Multiple Access Techniques Used in Mobile Telecommunication Generations International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 05 Issue: 10 | Oct 2018 www.irjet.net p-ISSN: 2395-0072 REVIEW ON MULTIPLE ACCESS TECHNIQUES USED IN MOBILE TELECOMMUNICATION GENERATIONS Anugrah Nair1, Gaurav Gupta2, Kartik Srinivas3 1,2,3DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION, SVKM’s NMIMS MPSTME ---------------------------------------------------------------------***--------------------------------------------------------------------- ABSTRACT - This review paper presents the analysis of technique which defines which signals are to be used mobile telecommunication generations and the different while the bandwidth or the channel is shared. In other multiple access techniques used in them. The multiple words, multiplexing notifies how the channel is to be access is a technique used by telecommunication networks split while multiple access is the technique which depicts to accommodate more users over the single channel. And which signal needs to be used while the channel or in these channels, the data is in packet form. As the bandwidth is shared. A channel or bandwidth here is telecommunication systems evolved i.e. 1G, 2G, 3G, 4G, so defined as the physical or wireless medium through did the access techniques used in them. The multiple access which multiple users are connected to each other. This techniques (circuit-switching) are mainly of 4 types i.e. channel is used for transfer of data between different FDMA (Frequency Division Multiple Access), TDMA (Time users and is used to establish a connection between Division Multiple Access), CDMA (Code Division Multiple different users. It can also be defined as the system Access), SDMA (Space Division Multiple Access). And the resource allocated for the transfer of data or to establish packet switching used in these circuits are collision- a connection between the users and the network. Each recovery (ALOHA, Slotted ALOHA, etc.), collision-avoidance channel can only support the transfer of data from a (CSMA/CD, CSMA/CA, etc.), collision-free (token bus, token single user to the network or vice versa one at a time. ring). Thus, for different users to send or transfer data to the network on a limited bandwidth or in a channel with a INTRODUCTION limited amount of space simultaneously, multiple access technique is used. In computer networks and in telecommunication technique, the concept of multiple access is commonly Mobile telecommunication generation specifies the encountered. Basically, multiple access is the technique generation of wireless-communication between two where a single channel is accessed by multiple users. users. This communication can be analog or digital, voice This is an important technique in telecommunication or data, audio or video, etc. In wireless communication methodology for effective use of bandwidth between systems, many users are made to transfer different several users. The basic question encountered in the data/signal to the base station. Each base station covers concept of multiple access is the factual difference an area where multiple users which are connected to the between multiplexing and multiple access. Multiplexing network are made to exchange or transfer data to the is the technique which differentiates between how the allocated base station. The base stations are installed to signals are going to be shared in the common channel or increase the capacity of the channel width and to bandwidth but on the other hand, multiple access is the accommodate an increasing number of users. BACKGROUND CONCEPTS 1. Multiple Access Techniques © 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 350 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 05 Issue: 10 | Oct 2018 www.irjet.net p-ISSN: 2395-0072 A) Frequency Division Multiple Access(FDMA): This Statistical Time Division Multiplexing is also another Channel access scheme is based on Frequency Division form of Time Division Multiplexing. In this technique Multiplexing where different frequency bands are dynamic bandwidth allocation takes place. The Media allocated different bandwidths on the same channel. In Access Control (MAC) is required. Common examples of Frequency division multiple access (FDMA), these this technique are CSMA/CD & CSMA/CA. the former is bandwidths are allocated to different users or nodes or used in Ethernet bus and hub networks, while the later is devices connected to the network on the common used in wireless networks. channel. C) Code Division Multiple Access: This technique is In this technique, for every phone call, each and every based on spread spectrum, which means that a wider phone call was assigned a specific uplink frequency and a radio spectrum compared to a data rate of each different downlink frequency. The message signal was transferred bit streams is used. Several message signals modulated on a specific carrier frequency. A similar are transferred over the same channel utilizing different technique used in fiber optic communication was the spreading codes are used. The wide band is used to send WDMA (Wavelength Division Multiple Access). In this the data on a carrier signal with a poor signal to noise technique, wavelength division multiplexing was ratio of much less than 1 dB. In other words, the incorporated, where data streams were represented transmission power can be reduced to a level below the with different colors. level of noise and co-channel interference from message signals sharing the same frequency. An advanced version of FDMA used in the implementation of 4G is OFDMA. Orthogonal Frequency Their different methods which implement CDMA Division Multiple Access encodes digital data on multiple technique: carrier frequencies. It has been developed for wideband digital communication. The basic principle underlying in In MC-CDMA, each user symbol is spread in the this technique is the division of high rate data stream frequency domain.in other words, each symbol is into parallel low rate data streams using FFT (Fast transferred over multiple parallel subcarriers but is Fourier Transformation). The limitations of this phase shifter depending on the code value. These code technique are that all subcarrier signals are needed to be values differ depending on the subcarrier and user. In orthogonal to each other and accurate synchronization the receiver section, by weighing these to compensate of frequency between the transmitter and the receiver is varying signals strength and undo the code shift. The required. receiver can also separate signals from different code values present in different signals sent by different users. One more technique that is used in the implementation In Direct Sequence Spread Spectrum (DS-CDMA), each of Single-Carrier FDMA (SC-FDMA). Basically, in this information symbol is represented by a long sequence of method, single carrier modulation is implemented and codes of several pulses called chips. The spreading code the overall structure used in this method is same as that is the sequence and the information symbol uses a used in OFDMA. Like every method in multiple access different spreading code. technique, this method also segregates the bandwidth/channel among different users. The only Another form of CDMA is the frequency hopping CDMA difference and an advantage of this technique over (FH-CDMA), where the transmitting radio signals are OFDMA is that it has a lower Peak to Average Power done by rapidly switching carriers among many ratio. frequency channels. This is done by using Pseudorandom sequence known to both transmitter and receiver. It is a B) Time Division Multiple Access: In this technique, a wireless technology and "hop" is referred to the carrier channel of limited space is divided into different time switching. slots. These time slots are allocated to different users connected to the network. This technique is based on the D)Space Division Multiple Access (SDMA): time division multiplexing scheme. For example, if node1 is allotted slot1, node 2 would be allotted time slot 2, the same continues with successive nodes until the last transmitter. Then the allotment starts all over again, in a repetitive manner, until the connection has ended and that slot becomes vacant or is allocated to different device or node. Another form of TDMA known as Dynamic TDMA (DTDMA) is the advanced version of this technique, where different slots may be given to different slots in the network depending on the vacancy of time slots. © 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 351 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 05 Issue: 10 | Oct 2018 www.irjet.net p-ISSN: 2395-0072 In this technique smart antenna technology and B) Carrier Sense Multiple Access / Collision difference in spatial location of mobile units within the Avoidance (CSMA/CA): In Carrier sense multiple access cell are used. In traditional mobile cellular network collision avoidance, the station nodes, continuously systems, the base station does not have information on sense the channel to avoid collisions between different the location of the mobile units within the cell and hence frames. Like CSMA CD, the transmission of data frames it radiates the signal in all directions within the cell so as only takes place only when the channel used or shared is to give radio coverage as a result of which there is idle. The stations follow a procedure during wastage of power on transmissions when there are no transmission. First, the station checks whether its frame mobile units to reach and also causing interference to is ready for transmission. Second, the station senses the adjacent cells (co-channel cells) using the same channel whether its idle or not. If not, the station frequency. calculates a random back-off time. After waiting for a random back-off time, the station again senses whether In SDMA the base station is aware of the distance (but the channel is idle or not. If not, again it waits for a not direction) of a mobile phone by use of a technique random back-off time and this process continues until called "timing advance" (TA).
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