TDMA, FDMA, and CDMA

What are the differences between FDMA, CDMA and TDMA?
How they work?
Adv and DisAdv of them.
Real life applications etc

1. MULTIPLE ACCESS TECHNIQUES PRESENTED BY: NAJEEBULLAH SHAISTA AMIR MUHAMMAD FAROOQ MOBIN

2. BACKGROUND Multiple Access techniques are used to allow many mobile users to share simultaneously a finite amount of radio spectrum. The sharing of spectrum is required to achieve high capacity by simultaneously allocating the available bandwidth (or the available amount of channels) to multiple users. There are five basic access or multiple access methods: frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), orthogonal frequency division multiple access (OFDMA), and spatial division multiple access (SDMA).

3. DIFFERENCE BETWEEN MULTIPLE ACCESS AND MULTIPLEXING MULTIPLE ACCESS MULTIPLEXING It is a technique that permit many users to simultaneously access a given frequency allocation. It is process to combine multiple signals for transmit it over a single channel or media.

4. FREQUENCY DIVISION MULTIPLE ACCESS (FDMA)

5. INTRODUCTION FDMA is the division of the frequency bands allocated for wireless cellular telephone communication into channels. Each channel can be assigned to only one user at a time All users transmit and receive at different frequencies because every user receives an individual frequency slot.

6. HOW IT WORKS? FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing the bandwidth of the channel into separate non overlapping frequency sub channels. Then allocating each sub channel to a separate user. Users can send data through a sub channel by modulating it on a carrier wave at the sub channel's frequency.

7. HOW IT WORKS FDMA is implemented at the media access control (MAC) layer of the data-link layer in the Open Systems Interconnection (OSI) reference model for networking protocol stacks. In FDMA, the user is assigned a specific frequency band in the electromagnetic spectrum, and during a call that user is the only one who has the right to access the specific band. In the AMPS cellular phone system, these frequency bands are allocated from the electromagnetic spectrum as follows:

8. In FDMA method, guard bands are used between the adjacent frequency slots to minimize crosstalk between the channels. A specific frequency band is given to one person, and it will received by identifying each of the frequency on the receiving end. It is often used in the first generation of analog mobile phone. CONT..

9. DIFFERENCE BETWEEN FDMA AND FDM FDMA is also different from Frequency-division multiplexing (FDM). FDM refers to a physical layer method that blends and transmits low-bandwidth channels via a high-bandwidth channel. FDMA, in contrast, is a channel access technique in the data link layer.

10. USES OF FDMA: FDMA is used in the Total Access Communication System (TACS). It is used in satellite communication systems and telephone lines. The Digital-Advanced Mobile Phone Service (D-AMPS) also uses FDMA but adds time division multiple access(TDMA)

11. ADVANTAGES OF FDMA Due to the frequency filtering, FDMA is not sensitive to near- far problem. Many of the problems experienced in TDMA due to different propagation delays are eliminated in FDMA as there is no need for network timing Fairly efficient when the number of stations is small and the traffic is uniformly constant No restriction regarding the type of baseband or type of modulation

12. DISADVANTAGES OF FDMA One disadvantage of FDMA is crosstalk, which can cause interference between frequencies and interrupt the transmission.  Between the different used frequency channels is a small amount of bandwidth not used. The maximum flow rate per channel is fixed and small. Relatively expensive and complicated band pass filters required

13. EXAMPLES CABLE TELEVISION SYSTEM The best example of this is the cable television system. The medium is a single coax cable that is used to broadcast hundreds of channels of video/audio programming to homes. The coax cable has a useful bandwidth from about 4 MHz to 1 GHz. This bandwidth is divided up into 6-MHz wide channels.

14. EXAMPLES ANALOG TELEPHONE SYSTEM One of the older FDMA systems is the original analog telephone system, which used a hierarchy of frequency multiplex techniques to put multiple telephone calls on single line.

15. TIME DIVISION MULTIPLE ACCESS (TDMA)

16. WHAT IS TDMA TECHNOLOGY? Time Division Multiple Access(TDMA) is a digital cellular telephone communication technology. It facilitates many users to share the same frequency without interference. It’s technology divides a signal into different time slots. Hence increase the data carrying capacity.

17. HOW IT WORKS? TDMA takes a cellular communication channel(frequency band) and slices it in to a series of time segments. Each cellular user is assigned the time slices with a given number. Each user transmit information only for the duration of their time segments using TDMA scheme. By Small time segments and High slicing frequency user Perceives a continuous Communication channel.

18. FEATURES OF FDMA Shares a single channel by several users High synchronization overhead is required Data transmission is not continuous Possible to allocate different number of slots to a user

19. FDMA VS TDMA FDMA TDMA Entire band of frequencies is divided into multiple RF channels/carriers. Each carrier allocated to different users. It’s entire bandwidth is shared among different subscribers at fixed predetermined or dynamically assigned time intervals.

20. CDMA VS TDMA CDMA TDMA Entire bandwidth is being used by users all the time. Each have their unique code to recover data. It’s entire bandwidth is shared among different subscribers at fixed predetermined or dynamically assigned time intervals.

21. ADVANTAGES Carry data rates from 64 kbps to 120 Mbps More number of users can use same spectrum. Operational costs are lower than traditional FDMA. Different types of traffics easily achieved by allocation of different time slots. Resources utilized effectively as per need basis and battery life enhanced.

22. DISADVANTAGES Network and spectrum planning require more efforts. Multipath interference affects call quality. Switching from one base station cell to the other cell results into dropped calls.

23. CODE DIVISION MULTIPLE ACCESS (CDMA)

24. ROAD MAP What is CDMA technology? Advantages and Disadvantages Working of CDMA Steps in CDMA modulation Code-division multiplexing (Asynchronous CDMA) Code-division multiplexing (synchronous CDMA) Applications of CDMA technology

25. WHAT IS CDMA TECHNOLOGY? Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies.

26. CONT…

27. ADVANTAGES Improvement in capacity and security Improvement in hand over/ hand off Use of Wide Bandwidth It has more number of users can share the same bandwidth. It is well-matched with other cellular technologies.

28. DISADVANTAGES The system is more complicated. Guard band and guard time both are required to be provided. As the number of users increases, the overall quality of services decrease

29. WORKING OF CDMA Code Division Multiple Access is entirely a different approach from the Time Division Multiple Access. CDMA, after digitizing the data, spreads out the data over the entire available bandwidth. Multiple calls are overlapped to each other on a channel which is assigned with a unique sequence code. CDMA is a form of Spread-Spectrum technique, which means data can be sent in small pieces over a number of frequencies available to use at any time in the specified range.

30. CONT… Below diagram show that there is only one channel which is accessing by four stations (i.e. mobile) at the same time. Each channel has it’s own Code ( i.e C1) and each channel wants to transmit data (i.e. D1=0=-1). Code will be assigned if it satisfies following to properties. Property 1: Pick any two stations’ code up and multiply them you will get a resultant and sum up the resultant if the it becomes to zero ‘0’, it will satisfy first property. i.e. C1 x C2 = 0, (1111)(1-111-1) = (1-11-1)=0. Property 2: Pick any station’s code up and multiply it with ownself if you get the answer as equal to total number of stations, it will satisfy property two as well. i.e. C1 x C1 = total No. stations. C1xC1 = 1111x1111 = 1111 = 4

31. CONT… The next step is to multiply each Station’s code with it’s own data ( i.e C1xD1) you will get a resultant and sum up the resultants of all stations you will get a Channel code (i.e. 0 -4 0 0)

32. CONT… Once you have done with above steps at the Transmitter side the next step is to decode the data at receiver side. At the reciver side you will have to multiply the channel code with Spreading code you will get a resultant The next step is to sum up the resultant and divide the answer with total no. of stations you will get the actual data as shown in figure.

33. SPREAD SPECTRUM TECHNIQUES Types of Spread Spectrum Communications: There are two types of spread spectrum communications: Frequency Hopping Direct Sequence

34. FREQUENCY HOPPING Frequency hopping is the easiest of all the spread spectrum modulation technique to use. The idea behind frequency hopping is to transmit data across a broad spectrum; the frequency can be rapidly switched from one to another. The transmitter and receiver are synchronized every time, and an accurate clocking system, and pseudo generating system make this frequency hopping very simple.

35. Cont … Following diagram shows that frequency is changing after each interval of time So that, It would be difficult for any third party to know about which frequency is being used

36. CONT.. FHSS can be done by using two techniques Slow-FHSS : Here one frequency hop transmits several number of Symbols (data). Fast-FHSS: Here one frequency hop will transmit only one symbol.

37. DIRECT SEQUENCE Direct sequence is the most famous spread spectrum technique in which the data signal is multiplied by a Pseudo-random noise code. A PN code is a sequence of chips which is given values as -1 and 1 where -1 indicates 0. The data encodes at the transmitter side and decodes at receiver side by using the same Spreading code.

38. HOW DSSS WORKS? In the following diagram we have data (1 -1 1) and Spreading code (100001) and we also know that 0 = -1 so that spreading code becomes (1-1-1-1-11). The next step is to encode the data by multiplying each bit of the data with entire spreading code

39. CONT… At the receiver side to decode the data you will just have to multiply the encoded data (as shown in diagram) with spreading code. After multiplying you will get actual data.

40. APPLICATIONS OF CDMA TECHNOLOGY It is used in military and some commercial application. It is used in mobile communication. It is used in Radar and navigation systems. CDMA is considered as the highest mode of wireless communications and is responsible for fast and safe mode of data exchange such as 3G.

41. REFERENCES https://searchmobilecomputing.techtarget.com/definition/FDMA https://www.tutorialspoint.com/cdma/fdma_technology.htm http://www.thenetworkencyclopedia.com/entry/frequency-division-multiple-access-fdma/ https://en.wikipedia.org/wiki/Frequency-division_multiple_access https://www.electronicdesign.com/communications/fundamentals-communications-access-technologies-fdma-tdma-cdma-ofdma-and-sdma https://www.techopedia.com/definition/5669/frequency-division-multiple-access-fdma https://www.slideshare.net/milesgalario/frequency-division-multiple-access-fdma https://www.slideshare.net/SammarKhan2/fdmatdmacdma

42. Thank You!