Satellite Capacity Allocation types
There are various schemes by which resource pool is utilized by satellite users. These schemes are called access schemes. TDMA, FDMA, PAMA and DAMA are main types of satellite capacity allocations. This allocation refers to how available bandwidth or frequency resources are distributed among users or communication channels. The goal is to maximize satellite resource utilization while minimizing interference and maintaining the desired quality of service. There are several capacity allocation types used in satellite communication, including Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Pre-Assigned Multiple Access (PAMA), and Demand Assigned Multiple Access (DAMA). Each of these allocation methods has its own characteristics, advantages, and specific use cases.
FDMA : Frequency Division Multiple Access
In this scheme entire frequency band of satellite is divided into frequency bands with proper guard band in between to avoid interference. Here entire frequency band is used by allocated user on earth all the time. Hence earth user on earth is using dedicated frequencies all the time.
• FDMA divides the available satellite frequency bandwidth into smaller,
separate frequency channels, with each user being assigned a unique frequency band.
• Working Principle:
-Each communication channel is assigned a dedicated frequency band within the satellite transponder bandwidth.
-Users transmit simultaneously at different frequencies, preventing interference with each other.
• Characteristics:
-Continuous and simultaneous data transmission.
-Bandwidth allocation is fixed and remains constant throughout communication.
• Use Cases: Used in analog satellite communication systems and point-to-point communication links.
➨FDMA advantages:
• Suitable for continuous and high-quality transmissions like voice and video.
• Simple and straightforward to implement.
➨FDMA disadvantages:
• Not flexible in allocating bandwidth based on dynamic demand.
• Inefficient use of bandwidth if not all channels are fully utilized.
TDMA : Time division multiple access
In this type, frequency spectrum is available to earth station user based on
the time allocations. Hence frequency resources are not available all the time but are available at regular predetermined intervals.
• TDMA allocates satellite bandwidth by dividing it into time slots. Each user is assigned specific time slots to transmit data, allowing multiple users to share the same frequency band at different times.
• Working Principle:
-The total time is divided into multiple time slots, with each user transmitting during their designated slot.
-The time slots are repeated in a cyclic manner, allowing each user to transmit periodically.
• Characteristics:
-Suitable for digital data transmission.
-Each user’s transmission is interleaved in time, providing flexibility in bandwidth usage.
• Use Cases: Often used in digital satellite communication systems, including satellite TV and internet services.
➨TDMA advantages:
• Efficient utilization of bandwidth with minimal interference.
• Easier to accommodate new users or reassign bandwidth compared to FDMA.
➨TDMA disadvantages:
• Requires precise time synchronization between transmitters and the satellite.
• May not be ideal for real-time applications with strict latency requirements.
PAMA : Pre-Assigned Multiple Access
Pre-assigned types of allocations is referred as PAMA i.e. Pre-assigned Multiple Access. Dynamic on demand type of allocation is referred as DAMA i.e. Demand Assigned Multiple Access. In PAMA, assignment of resource is taken care at the start of the network deployment.
• PAMA is a static capacity allocation method where satellite resources, such as frequencies or time slots,
are permanently allocated to specific users or stations.
• Working Principle:
Each user is assigned a fixed amount of satellite bandwidth or time slots, regardless of whether they are actively using it.
• Characteristics:
-No need for dynamic allocation; each user has a predefined amount of resources.
-Suited for applications where consistent communication is required.
• Use Cases:
Common in military and emergency communication systems where guaranteed availability is critical.
➨PAMA advantages:
• Simple to implement and manage.
• Ensures dedicated bandwidth for critical communication links.
➨PAMA disadvantages:
• Inflexible and inefficient if the allocated capacity is underutilized.
• Limited scalability for additional users or varying bandwidth requirements.
DAMA : Demand Assigned Multiple Access
In DAMA, assignment of resource is taken up at the time of initiation of the call. Now-a-days CDMA type is also explored in satellite network.
• DAMA dynamically allocates satellite bandwidth based on real-time demand,
providing a flexible and efficient way to use satellite resources.
• Working Principle:
-Bandwidth or time slots are assigned to users as needed and are released once the communication session ends.
-The allocation is managed by a central network controller that monitors user demand and satellite capacity.
• Characteristics:
-Dynamic allocation of resources based on user demand and system capacity.
-Efficient use of bandwidth, as resources are only allocated when needed.
• Use Cases: Used in mobile satellite communication systems, VSAT networks, and applications with varying traffic patterns.
➨DAMA advantages:
• Maximizes resource utilization by adapting to varying traffic conditions.
• Ideal for bursty or intermittent traffic patterns.
➨DAMA disadvantages:
• Requires complex algorithms and real-time monitoring.
• May introduce delay or latency during the allocation process, affecting real-time applications.
Summary
FDMA, TDMA, PAMA, and DAMA offer distinct methods of allocating satellite capacity based on specific communication needs. FDMA provides fixed frequency allocations for continuous data transmission, while TDMA offers time-based slots, making it more flexible for dynamic data. PAMA ensures dedicated resources for critical communication but lacks flexibility, whereas DAMA optimizes resource use by dynamically assigning capacity based on real-time demand. Choosing the right method depends on factors like bandwidth efficiency, traffic patterns, scalability, and the nature of the application.