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TDMA: Time Department Multiple Access

TDMA stands for Time division multiple access. It is mainly a channel gain access to method that can be used for distributed medium networks as well as a digital transmitting technology that allows its users to gain access to a single radio-frequency channels with no interference. and it allocates to its users unique time slots within each route. TDMA is the common kind of service that is employed in North America. Mainly. TDMA is used in 2G cellular system(GSM, PDC, IDEN, IS-136, DECT). In cases like this a single route is divided into six time slots and each signal is using two time slot machine games. To help make the transmission possible each caller is allocated a particular time slot. TDMA offers high performance regarding capacity, courage and freedom. TDMA mainly transmit data in a buffer-and-burst method and the transmitting of any individual is non- constant.

TDMA Body Structure

In TDMA frame framework a data stream divided into frames and those frames split into time slot machines.

and we clarify the concept of TDMA frame structure by using a good example:-

In this case you have the TDMA structure shown designed to use seven group of frequencies that are sufficient to pay the top area that delivers the maximum distance d that is bigger than twice the utmost radius r, the radius that is being included in each transmitter. and the space of each time slots that are produced from the occurrence channels is 0. 577ms and these 8 slots make a TDMA shape of span 4. 615ms.

There are main three burst present in the TDMA:-

  1. Normal Burst(NB)
  2. Frequency Correction Burst(FB)
  3. Synchronization Burst(SB)
  4. Access Burst(Stomach)

Normal Burst:- The transmitting of the data during the one time slot is known as a burst. and the shield time that is employed to avoid the burst suffering from the overlapping is 8. 25 parts.

In the standard Burst there are four types of bits as given below:-

  1. Tail Pieces :- In the diagram of TDMA there may be 3 bits at both of the two ends, in which there is absolutely no transmission of the data. At the start the the bit is used to go up up the energy upto its optimum during the transmission and the finish it is used to down the power used at the end of the transmitting.
  2. Data Little bit:- Around working out pieces there are two data pieces each of 57 parts.
  3. Stealing Flags :- They are the flags around working out bits that are of period 1 little bit and it can be used to point that whether the burst is being used for tone or the data (place to 0)or whenever it is employed for signalling (established to at least one 1 ).
  4. Training Series :- In working out bits a method has been used to conquer the challenge of multi-path fading and the other propagation results. and in this 26 bits are widely-used.

Frequency Modification Burst:- FCB is mainly an unmodulated carrier which then after shift in regularity. The officer time found in the FCB is identical to that of the standard bit. It is used for regularity synchronization of the mobile channels.

Synchronization Burst:- Enough time synchronization of the mobile can be done by using synchronization burst. The payload used in this holds the FDMA frame amount (FN) and Foundation Station Individuality Code (BSIC). and the broadcasting in cases like this is with the frequency modification burst. and also broadcasting occurs on the synchronization channel.

Access Burst:- Firstly the officer burst used in this very longer as compared to the normal burst, so that it is 68. 25bit is. The mobile stations use this type of the burst for random access. In addition, it helps to gauge the undiscovered distance of any mobile train station from the tower, when the MS wants to gain access to to the new BTS.

Features of TDMA

  1. In case of TDMA an individual carrier regularity is distributed among several users. and each end user use the time slots. Enough time slots utilized by the users depends on several factors such as modulation techniques and the available bandwidth.
  2. Data Transmission regarding the users of TDMA is not constant but it occurs in bursts which results in low use of the battery pack utilization because the subscriber is switched off, when it's not in the use.
  3. The Handoff process is a lot simpler in the case of TDMA because of its discontinuity which is able to listen to the other platform stations during its idle slot machine game time.
  4. The Transmission rates are very high in the situation of TDMA as compared to the FDMA due to Adaptive Equalization which is necessary regarding TDMA.
  5. The guard time within the case of TDMA should be minimal.
  6. The main benefit of TDMA is that it is very cost-effective technology which is employed for upgrading an up-to-date analog system to digital.
  7. In this the battery pack used is of prolonged life and the talk time, because the mobile is merely transmitting the portion of the time of the time during discussions.
  8. TDMA technology is used to separate users with time and ensure that there will not be any disturbance which is provided from some other simultaneous transmissions.

Disadvantages of TDMA

The main drawbacks of TDMA receive as below:-

  1. The main downside of the TDMA is that all user that is used in the TDMA has a predefined time slot that is described by the machine if the users roaming from one cell to another cell or from one place to some other place and are not alloted a period slot or if at all times slot available for the user are already occupied, then your user will not receive any call.
  2. The another main downside of TDMA systems is interference that is established by it at a regularity which is directly connected to the time slot length. In cases like this or problem with the TDMA is the multiple distortion, so whenever the sign via one place or tower to some other tower, then there are many buildings that induce problem in the transmission for arriving at the destination as a result of interference.
  3. Efficient time schedule that is possible regarding TDMA but it isn't always no problem finding it.
  4. Clock synchronization needed.
  5. Whenever you have the case of active status changes of nodes on the arranging is also handled because of it.
  6. The channel utilization regarding TDMA is very low as compared to CSMA during low contention.

TDMA in CELLULAR PHONE Systems

2G Systems:- Many 2G Systems derive from the TDMA. So we can say the TDMA as TDMA cellular systems such as the main examples of the TDMA cellular systems are GSM, IS-95, D-AMPS, PDC, iDEN and PHS. As regarding GSM it combines the TDMA with occurrence hopping and the wideband transmitting, to be able to minimize the interference. So regarding GSM system, base train station send the timing commands which is then helpful in the synchronization of the mobile phones that are helpful in easier transmission and decide the time. You have the guard interval regarding GSM. There is the RACH in GSM. Whenever the mobile is within the next base ststion, then the call arrived sucessfully with no delay. of course, if the mobile is situated beyond the 35 kilometres range in GSM, then the RACH used in this will get to the time slot that is in the neighboring. So there is absolutely no special technique to limit the range of the GSM cell to 35 km. So to get over this problem, the synchronization is evolved between the uplink and downlink in the base station.

3G Systems:- 3G system use the mixture of both CDMA and TDMA. So it take the advantage of both techniques. Typically the most popular 3G systems are UMTS which use CDMA instead of TDMA, and in TD-CDMA and TD-SCDMA, the TDMA is combined with CDMA and TDD.

Comparison Between GSM, TDMA and CDMA

TDMA

Firstly we all know that the TDMA become a technology of the past. Regarding TDMA the info is compressed in to packets within its same bandwidth. Some important things about the TDMA receive as below:-

    1. It act as a bridge between the analog and the digital systems which resulted in the introduction of the GSM and iDEN.

iDEN:- It is a Integrated Digital Enhanced Network and it is comparable to as that of the GSM technology and it is functioning at 800 MHz, 1900MHz and 1. 5 GHz in the US. It can be used to take care of the CDMA and GSM technology. It could take care of three users per channel and for the purpose of more capacity and demand, it is require the utilization of more towers which is costly.

  1. The Data capacity regarding TDMA is is just about the 56 kbps.

GSM

  1. GSM means Global System for Mobile Communication uses a narrow - group changes of TDMA.
  2. GSM are designed for up to eight users per channel.
  3. GSM mainly operates on 1900MHz.
  4. GSM is incapable of the reliable data speeds which requires the alternate technologies.
  5. GSM is more widespread throughout the world

CDMA

CDMA stand s for Code Division Multiple Access which is a technology that delivered as a constant flow across larger bandwidth instead of sending a sign into packets and directed on cycles, CDMA transmissions.

  1. CDMA can handle ten users per route, but it require more occurrence to provide service.
  2. In the united states, CDMA uses the typical 800MHz and 1900MHz.
  3. The data capacity in the CDMA, is fastest, which is add up to the 144 kbps.
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