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In radio systems, TDMA is usually used alongside [[frequency-division multiple access]] (FDMA) and frequency-division duplex (FDD); the combination is referred to as FDMA/TDMA/FDD. This is the case in both GSM and IS-136 for example. Exceptions to this include the [[DECT]] and [[Personal Handy-phone System]] (PHS) micro-cellular systems, [[UMTS-TDD]] UMTS variant, and China's [[TD-SCDMA]], which use time-division duplexing, where different time slots are allocated for the base station and handsets on the same frequency.
A major advantage of TDMA is that the radio part of the mobile -only needs to listen and broadcast for its own time slot. For the rest of the time, the mobile can carry out measurements on the network, detecting surrounding transmitters on different frequencies. This allows safe inter -frequency [[handover]]s, something which is difficult in CDMA systems, not supported at all in [[IS-95]] and supported through complex system additions in [[Universal Mobile Telecommunications System]] (UMTS). This in turn allows for co-existence of [[microcell]] layers with [[macrocell]] layers.
CDMA, by comparison, supports "soft hand-off" which allows a mobile phone to be in communication with up to 6 base stations simultaneously, a type of "same-frequency handover". The incoming packets are compared for quality, and the best one is selected. CDMA's "cell breathing" characteristic, where a terminal on the boundary of two congested cells will be unable to receive a clear signal, can often negate this advantage during peak periods.
A disadvantage of TDMA systems is that they create [[electromagnetic interference|interference]] at a frequency whichthat is directly connected to the time slot length. This is the buzz whichthat can sometimes be heard if a TDMA phone is left next to a radio or speakers.<ref>{{cite web | url=http://www.eetimes.com/design/microwave-rf-design/4019057/Minimize-GSM-buzz-noise-in-mobile-phones | title=Minimize GSM buzz noise in mobile phones | publisher = EETimes | date=July 20, 2009 | access-date=November 22, 2010}}</ref> Another disadvantage is that the "dead time" between time slots limits the potential bandwidth of a TDMA channel. These are implemented in part because of the difficulty in ensuring that different terminals transmit at exactly the times required. Handsets that are moving will need to constantly adjust their timings to ensure their transmission is received at precisely the right time, because as they move further from the base station, their signal will take longer to arrive. This also means that the major TDMA systems have hard limits on cell sizes in terms of range, though in practice the power levels required to receive and transmit over distances greater than the supported range would be mostly impractical anyway.
== Advantages of TDMA ==
=== Advantages of TDMA ===
# '''Enhanced Spectrumspectrum Efficiencyefficiency''': TDMA maximizes the use of available bandwidth by allowing multiple users to share the same channel without overlapping. Each user is assigned a specific time slot, ensuring that the channel's capacity is fully utilized, thereby increasing overall system efficiency.
# '''Reduction of Intersymbolintersymbol Interferenceinterference''': By assigning nonoverlappingnon-overlapping time slots to users, TDMA significantly reduces the risk of intersymbol interference. This interference occurs when signals from adjacent symbols overlap, leading to distortion and communication errors. The clear separation of time slots ensures that each symbol is transmitted distinctly, enhancing the reliability and clarity of the signal.
# '''Elimination of Guardguard Bandsbands''': Since adjacent channels in TDMA do not interfere with one another, there is no need for guard bands—unused frequency ranges that typically separate channels to prevent interference in other systems. This absence of guard bands allows for more efficient use of the available spectrum, providing additional capacity for more users.<ref>{{Cite journal |last1=Kaur |first1=Amritpreet |last2=Kaur |first2=Guneet |date=2017-03-15 |title=The Enhanced ECC Approach to Secure Code Dissemination in Wireless Sensor Network |url=http://dx.doi.org/10.5120/ijca2017913237 |journal=International Journal of Computer Applications |volume=161 |issue=7 |pages=30–33 |doi=10.5120/ijca2017913237 |issn=0975-8887}}</ref>
# '''Flexible Raterate Allocationallocation''': TDMA supports dynamic allocation of time slots, allowing the system to adapt to varying user demands. Users can be assigned multiple time slots based on their data transmission needs, which can vary due to factors such as call duration or data requirements. This flexibility optimizes resource usage and can improve overall user experience.
# '''Low Batterybattery Consumptionconsumption''': Unlike FDMA (Frequency Division Multiple Access), which requires continuous transmission, TDMA operates in a noncontinuous manner. Each transmitter can be turned off when not in use, leading to significant power savings. This is particularly advantageous for mobile devices, as it prolongs battery life and reduces the need for frequent recharging.
# '''Simplified Implementationimplementation''': The time-based nature of TDMA simplifies the implementation of synchronization mechanisms between users. As users take turns using the channel, the system can more easily manage timing and coordination compared to more complex methods like CDMA (Code Division Multiple Access), where signals overlap.<ref>{{Citation |title=Multiple access techniques: FDMA, TDMA, CDMA; system capacity comparisons |date=2004-12-16 |work=Mobile Wireless Communications |pages=137–160 |url=http://dx.doi.org/10.1017/cbo9780511811333.007 |access-date=2024-10-28 |publisher=Cambridge University Press|doi=10.1017/cbo9780511811333.007 |isbn=978-0-521-84347-8 }}</ref>
# '''Scalability''': TDMA systems can be scaled effectively to accommodate a growing number of users. As demand increases, additional time slots can be introduced without the need for significant changes to the existing infrastructure, making it easier to expand the network capacity.
# '''Improved Qualityquality of Serviceservice (QoS)''': With the ability to assign specific time slots and manage user access dynamically, TDMA can enhance the overall quality of service. This can lead to reduced latency and increased throughput, ensuring that users experience reliable and efficient communication.
=== Disadvantages of TDMA ===
# '''Guard Intervalsintervals''': To prevent interference between adjacent TDMA slots, guard intervals must be added. These intervals, typically ranging from 30 to 50 microseconds, serve as buffers to ensure that transmissions do not overlap. However, this requirement for extra time means that the overall throughput of the system can be reduced, as valuable time is spent in guard intervals rather than transmitting data. This is particularly problematic in cellular networks where time and energy efficiency are paramount.<ref>{{Cite journal |last1=Nguyen |first1=Kien |last2=Golam Kibria |first2=Mirza |last3=Ishizu |first3=Kentaro |last4=Kojima |first4=Fumihide |date=2019-02-14 |title=Performance Evaluation of IEEE 802.11ad in Evolving Wi-Fi Networks |journal=Wireless Communications and Mobile Computing |volume=2019 |pages=1–11 |doi=10.1155/2019/4089365 |doi-access=free |issn=1530-8669}}</ref>
# '''Energy Consumptionconsumption''': While TDMA allows for some energy savings by turning off transmitters during idle periods, the inclusion of guard intervals can offset these benefits. The need for synchronization and the overhead associated with managing time slots can lead to increased energy consumption, particularly in scenarios where numerous users are competing for access to the channel. This can be a critical issue for mobile devices that rely on battery power.
# '''Synchronization Challengeschallenges''': TDMA requires precise synchronization between all users to ensure that each user transmits within their designated time slot. This can complicate system design and implementation, especially in dynamic environments where users may frequently join or leave the network. Maintaining synchronization becomes increasingly difficult as the number of users grows, leading to potential disruptions and communication errors if not managed effectively.
# '''Limited Datadata Ratesrates''': TDMA generally provides medium data rates compared to other multiple access techniques like CDMA (Code Division Multiple Access). This limitation arises from the fixed time slot allocation, which can restrict the amount of data that can be transmitted in a given timeframe. As a result, users with higher data requirements may experience slower transmission speeds, leading to potential dissatisfaction and reduced performance for data-intensive applications.
# '''Moderate Systemsystem Flexibilityflexibility''': TDMA offers moderate flexibility in terms of user allocation and data transmission rates. Unlike CDMA, which allows for a more dynamic and adaptive use of bandwidth, TDMA's fixed time slot assignment can lead to inefficiencies. In scenarios where user demand fluctuates significantly, the rigid structure of TDMA may result in underutilization of resources, as not all time slots may be filled during periods of low demand.<ref>{{Citation |title=Multiple access techniques: FDMA, TDMA, CDMA; system capacity comparisons |date=2004-12-16 |work=Mobile Wireless Communications |pages=137–160 |url=http://dx.doi.org/10.1017/cbo9780511811333.007 |access-date=2024-10-28 |publisher=Cambridge University Press|doi=10.1017/cbo9780511811333.007 |isbn=978-0-521-84347-8 }}</ref>
# '''Latency Issuesissues''': Due to the time-sharing nature of TDMA, users may experience increased latency. When multiple users are connected, each must wait for their designated time slot to transmit data. In applications that require real-time communication, such as voice calls or video conferencing, this added delay can affect the quality of service, leading to lag and reduced responsiveness.
# '''Scalability Constraintsconstraints''': While TDMA can accommodate a growing number of users by adding more time slots, this scalability is limited by the need for synchronization and the fixed nature of time slot assignments. As user demand increases, the system may face challenges in maintaining performance levels without significant investment in infrastructure upgrades or more complex management systems.<ref>{{Cite book |last=Le Gouable |first=R. |chapter=Performance of MC-CDMA systems in multipath indoor environments. Comparison with COFDM-TDMA system |date=2000 |title=First International Conference on 3G Mobile Communication Technologies |chapter-url=http://dx.doi.org/10.1049/cp:20000018 |publisher=IEE |volume=2000 |pages=81–85 |doi=10.1049/cp:20000018|isbn=0-85296-726-8 }}</ref>
== Dynamic TDMA ==
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