TDMA stands for Time division multiple entree.
It is chiefly a channel entree method that is used for shared medium webs every bit good as a digital transmittal engineering that allows its users to entree a individual radio-frequency channels without any intervention. and it allocates to its users alone clip slots within each channel.TDMA is the widespread type of service that is used in North America.
Mainly.TDMA is used in 2G cellular system ( GSM, PDC, IDEN, IS-136, DECT ) . In this instance a individual channel is divided into six clip slots and each signal is utilizing two clip slots. To do the transmittal possible each company is assigned a specific clip slot. TDMA offers high public presentation with regard to capacity, bravery and mobility.TDMA chiefly transmit informations in a buffer-and-burst method and the transmittal of any user is non- uninterrupted.TDMA Frame StructureIn TDMA frame construction a information watercourse divided into frames and those frames divided into clip slots.
And we explain the construct of TDMA frame construction with the aid of an illustration:In this instance there is the TDMA frame shown which use seven set of frequences that are sufficient to cover the big country that provides the maximal distance vitamin D that is larger than twice the maximal radius R, the radius that is being covered by each transmitter.and the length of each clip slots that are generated from the frequence channels is 0.577ms and these 8 slots make a TDMA frame of length 4.615ms.There are chief three burst nowadays in the TDMA:
- Normal Burst ( NB )
- Frequency Correction Burst ( FB )
- Synchronization Burst ( SB )
- Access Burst ( AB )
Normal Burst: – The transmittal of the information during the individual clip slot is known as a burst.and the guard clip that is used to forestall the explosion enduring from the imbrication is 8.
25 spots.In the Normal Burst there are four types of spots as given below: –
- Tail Spots: – In the diagram of TDMA there is 3 spots at both of the two terminals, in which there is no transmittal of the data.At the get downing the the spot is used to lift up the power upto its extremum during the transmittal and the terminal it is used to toss off the power used at the terminal of the transmittal.
- Data Bit: – Around the preparation spots there are two informations spots each of 57 spots.
- Stealing Flags: – These are the flags around the preparation spots that are of length 1 spot and it is used to bespeak that whether the explosion is being used for voice or the informations ( set to 0 ) or whenever it is used for signalling ( set to 1 ) .
- Training Sequence: – In the preparation bits a method is being used to get the better of the job of multi-path attenuation and the other extension effects.and in this 26 spots are used.
Frequency Correction Burst: – FCB is chiefly an unmodulated bearer which so after displacement in frequence. The guard clip used in the FCB is same as that of the normal spot.
It is used for frequence synchronism of the nomadic Stationss.Synchronism Burst: – The clip synchronism of the Mobile is possible with the aid of synchronism explosion.The warhead used in this carries the FDMA frame figure ( FN ) and Base Station Identity Code ( BSIC ) . and the broadcast medium in this instance is with the frequence rectification burst.and besides airing occurs on the synchronism channel.Access Burst: – First the guard explosion used in this really longer as compared to the normal explosion, so it is 68.25bits. The nomadic Stationss use this type of the explosion for random entree.
It besides helps to mensurate the unknown distance of any nomadic station from the tower, when the MS wants to entree to the new BTS.Features of TDMA
- In instance of TDMA a individual bearer frequence is shared among several users. and each user use the clip slots. The clip slots used by the users depends on several factors such as transition techniques and the available bandwidth.
- Data Transmission in the instance of the users of TDMA is non uninterrupted but it occurs in explosions which consequences in low usage of the battery ingestion because the endorser is turned off, when it is non in the usage.
- The Handoff procedure is much simpler in the instance of TDMA because of its discontinuity and it is able to listen to the other base Stationss during its idle slot clip.
- The Transmission rates are really high in the instance of TDMA as compared to the FDMA because of the Adaptive Equalization which is necessary in the instance of TDMA.
- The guard clip nowadays in the instance of TDMA should be minimal.
- The chief advantage of TDMA is that it is really cost-efficient engineering which is used for upgrading a current parallel system to digital.
- In this the battery used is of drawn-out life and the talk clip, since the Mobile is merely conveying the part of the clip of the clip during conversations.
- TDMA engineering is used to separate users in clip and guarantee that there will non be any intervention which is presented from any other coincident transmittals.
Disadvantages of TDMAThe chief disadvantages of TDMA are given as below: –
- The chief disadvantage of the TDMA is that each user that is used in the TDMA has a predefined clip slot that is defined by the system and if the users rolling from one cell to another cell or from one topographic point to any other topographic point and are non alloted a clip slot or if all the clip slot available for the user are already occupied, so the user will non have any call.
- The another chief disadvantage of TDMA systems is interference that is created by it at a frequence which is straight connected to the clip slot length.In this instance or job with the TDMA is the multiple deformation, so whenever the signal coming from one topographic point or tower to another tower, so there are many edifices that create job in the signal for geting at the finish because of the intervention.
- Efficient clip agenda that is possible in the instance of TDMA but it is non ever easy to happen it.
- Clock synchronism needed.
- Whenever there is the instance of dynamic position alterations of nodes on the programming is besides handled by it.
- The channel use in the instance of TDMA is really low as compared to CSMA during low contention.
TDMA in Mobile Phone Systems2G Systems: – Many 2G Systems are based on the TDMA.So we can state the TDMA as TDMA cellular systems which include the chief illustrations of the TDMA cellular systems are GSM, IS-95, D-AMPS, PDC, iDEN and PHS. As in the instance of GSM it combines the TDMA with frequence hopping and the wideband transmittal, so as to minimise the intervention.
So in the instance of GSM system, base station direct the timing bids which is so helpful in the synchronism of the nomadic phones which are helpful in easier transmittal and make up one’s mind the clip.There is the guard interval in the instance of GSM.There is the RACH in GSM. Whenever the Mobile is in the following base ststion, so the call arrived sucessfully without any delay.and if the Mobile is located beyond the 35 kilometer scope in GSM, so the RACH used in this will get in the clip slot that is in the neighboring.So there is no particular technique to restrict the scope of the GSM cell to 35 kilometers.
So to get the better of this job, the synchronism is changed between the uplink and downlink in the base station.3G Systems: – 3G system use the combination of both CDMA and TDMA. So it take the advantage of both the techniques.
The most popular 3G systems are UMTS which use CDMA instead so TDMA, and in TD-CDMA and TD-SCDMA, the TDMA is combined with CDMA and TDD.Comparison Between GSM, TDMA and CDMATDMAFirst we all know that the TDMA go a engineering of the past.In the instance of TDMA the information is compressed in to packages within its same bandwidth.Some of import things about the TDMA are given as below: –
- It act as a span between the parallel and the digital engineerings which led to the development of the GSM and iDEN.
iDEN: – It is a Incorporate Digital Enhanced Network and it is similar to as that of the GSM engineering and it is runing at 800 MHz,1900MHz and 1.
5 GHz in the US. It is used to manage the CDMA and GSM technology.It can manage three users per channel and for the intent of more capacity and demand, it is necessitating the usage of more towers which is dearly-won.
- The Data capacity in the instance of TDMA is is around the 56 kbps.
- GSM stands for Global System for Mobile Communication uses a narrow – set alteration of TDMA.
- GSM can manage up to eight users per channel.
- GSM chiefly operates on 1900MHz.
- GSM is incapable of the dependable informations velocities which requires the surrogate engineerings.
- GSM is more widespread around the universe
CDMACDMA stand s for Code Division Multiple Access which is a engineering that sent as a changeless flow across larger bandwidth alternatively of directing a signal into packages and sent on rhythms, CDMA transmittals.
- CDMA can manage 10 users per channel, but it require more frequence to supply service.
- In the US, CDMA uses the standard 800MHz and 1900MHz.
- The information capacity in the CDMA, is fastest, which is equal to the 144 kbps.