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Satellite Multiple Access Techniques

A satellite is a communications node through which all types of user in the network must be interconnected as flexibly as possible. For some applications, it may be necessary that a satellite be simultaneously accessed by hundreds of users, making accessing problems more complex. The aim of Multiple access is to efficiently allocate portions of the satellite’s fixed Communication Resource to a large number of users who seek to communicate digital information to each other at a variety of bit and message rates, and with various traffic requirements.

 

The satellite repeater consists of several adjacent channels (called transponders), whose bandwidth is a fraction of the total repeater bandwidth. In terms of multiple access, there are two aspects to be considered:
— multiple access to a particular repeater channel (i.e. a transponder).
— multiple access to a satellite repeater.

Multiple access to a particular repeater channel (transponder) implies prior multiple access to the satellite repeater.

 

Each satellite repeater channel (transponder) amplifies every carrier whose spectrum falls within its passband at a time when the channel is in an operational state. The resource offered by each channel can thus be represented in the form of a rectangle in the time–frequency plane. In the absence of special precautions, carriers would occupy this rectangle simultaneously and mutually interfere. To avoid this interference, it is necessary for receivers (an earth station receiver for a transparent satellite and an on-board satellite receiver for a regenerative satellite) to be able to discriminate between the received carriers.

 

When this  discrimination is achieved in frequency domain its called FDMA, in the temporal domain called TDMA and code domain it’s called CDMA.

 

The development of packet switching techniques represents an important breakthrough in communications resource sharing. In circuit-switched networks such as the telephone network, calls and message routing are set up prior to the commencement of message transmission. Once the route has been established, the message is transmitted on the dedicated circuit; after completion of the call, the circuit is disconnected.

 

In packet communications, messages are packetized (partitioned into modular groups, each containing an address header). Each packet may be regarded moving autonomously through the network, queueing at specific nodal points together with packets from other traffic. The key feature of packet switching systems is the potential for very efficient utilization of a  communications or computer network, especially in the presence of bursty (high peak-to-average) traffic.

 

The efficiency of a multiple access scheme is conveniently evaluated by the ratio of the capacity available from the transponder in the considered multiple access mode to the capacity that would be available if the transponder were accessed by a single carrier occupying the full bandwidth of the transponder operated at saturation power. The capacity of a carrier is equal to the information bit rate Rb conveyed by the carrier. This is sometimes called the carrier throughput. The efficiency of a multiple access scheme then is the ratio of the sum of the throughputs of all accessing carriers to the maximum throughput of a single carrier in the transponder. Efficiency then appears as a normalized throughput.

 

Frequency Division Multiplex Access (FDMA)

The bandwidth of a repeater channel is divided into sub-bands; each sub-band is assigned to one of the carriers transmitted by the earth stations in the network according to their traffic requirement. . If the spectra of the carriers each occupy a different sub-band, the receiver can discriminate between carriers by filtering. This is the principle of frequency division multiple access (FDMA)

 

With this type of access, the earth stations transmit continuously and the channel conveys several carriers simultaneously at different frequencies. It is necessary to provide guard intervals between each band occupied by a carrier to avoid interference as a result of imperfections of oscillators and filters. The receiver selects the required carrier in accordance with the appropriate frequency.

 

The channel transmits these to all the earth stations situated in the coverage area of the satellite antenna. The carriers must be filtered by the receiver at each earth station and this filtering is easier to realise when the carrier spectra are separated from each other by a wide frequency guard band. However, the use of wide guard bands leads to inefficient use of the channel bandwidth and a higher operating cost, per carrier, of the space segment. There is, therefore, a technical and economic compromise to be made. Whatever the compromise chosen, part of the power of a carrier adjacent to a given carrier will be captured by the receiver tuned to the frequency of the carrier considered. This causes noise due to interference, called adjacent channel interference (ACI).

 

Satellite repeater channel has a non-linear transfer characteristic. In general, when multiple signals at different frequencies pass through a non-linear amplifier, the output contains not only the N signals at the original frequencies but also undesirable signals called intermodulation products. When the center frequency of the passband amplifier is large compared with its bandwidth, which is the case for a satellite repeater channel (compare the center frequency of several GHz to the bandwidth of a few tens of MHz), only the odd order intermodulation products, fall within the amplifier bandwidth. Moreover, the amplitude of the intermodulation products decreases with the order of the product. Hence, in practice, only products of order 3, and to a lesser extent 5, are significant.

 

Frequency division multiple access (FDMA) is characterised by continuous access to the satellite in a given frequency band. This technique has the advantage of simplicity. However, it has some disadvantages:
—Lack of flexibility in case of reconfiguration: to accommodate capacity variations it is necessary to change the frequency plan and this implies modification of transmitting frequencies, receiving frequencies and filter bandwidths of the earth stations.
—Loss of capacity when the number of accesses increases due to the generation of intermodulation products and the need to operate at a reduced satellite transmitting power (back-off). As the number of carriers increases, the power available to each carrier reduces, and this implies use of forward error correction (FEC) schemes to maintain the target bit error rate (BER) at the demodulator output of each carrier. The throughput of each carrier decreases, and so does the total throughput which is the sum of the throughputs of the individual carriers.
—The need to control the transmitting power of earth stations in such a way that the carrier powers at the satellite input are the same in order to avoid the capture effect. This control must be performed in real time and must adapt to attenuation caused by rain on the uplinks.

 

TDMA (Time Division Multiple Access)

According to this multiple earth stations transmits at the same frequency but in different time slots, that is entire frequency band is divided on the basis of time that is, one user will use the complete frequency band for a given time slot and another user will use the same frequency band for some other time slot. The earth stations transmit one after another bursts of carrier with duration TB. All bursts of carrier have the same frequency and occupy the full repeater channel bandwidth.

 

Hence the satellite repeater channel carries one carrier at a time. Bursts are inserted within a periodic time structure of duration TF, called a frame. The earth station receives traffic in the form of a continuous binary stream of rate Rb from the network or user interface. This information must be stored in a buffer memory while waiting for the burst transmission time. The burst  consists of a header, or preamble, and a traffic field.

 

The reference station is the station which defines the frame clock by transmitting its reference burst; all the network traffic stations must synchronise themselves to the reference station by locating their burst with a constant delay with respect to the reference station burst, called the reference burst. The receiving station identifies the start of each burst of the frame by detection of the unique word; it then extracts the traffic which is intended for it and is contained in a sub-burst of the traffic field of each burst.

 

Time division multiple access (TDMA) has certain advantages:
—At each instant, the satellite repeater channel amplifies only a single carrier which occupies all of the repeater channel bandwidth; there are no intermodulation products and the carrier benefits from the saturation power of the channel.

—TDMA efficiency remains high for a large number of accesses.
—There is no need to control the transmitting power of the stations.

—All stations transmit and receive on the same frequency whatever the origin or destination of the burst; this simplifies tuning.

TDMA, however, has certain disadvantages:
—The need for synchronization implies complex procedures and the provision of two reference stations. Fortunately, these procedures can be automated and computer-driven.
—The need to increase power and bandwidth as a result of high burst bit rate, compared to continuous access, as with FDMA, for instance.

Overall, TDMA implies more costly equipment at the earth stations. The cost of this equipment is, however, compensated by better utilisation of the space segment due to the higher efficiency in the case of a large number of accesses.

 

CDMA (Code Division Multiple Access)

With code division multiple access (CDMA), network stations transmit continuously and together on the same frequency band of the satellite repeater channel. There is, therefore, interference between the transmissions of different stations and this interference is resolved by the receiver which identifies the ‘signature’ of each transmitter; the signature consists of a binary sequence, called a code, which is combined with the useful information at each transmitter. Transmission of the code combined with the useful information requires the availability of a greater radio-frequency bandwidth than that required to transmit the information alone hence also called spread spectrum transmission.

Two techniques are used in CDMA: —direct sequence (DS); and —frequency hopping (FH).

Code division multiple access has the following advantages:
—It is simple to operate since it does not require any transmission synchronisation between stations. The only synchronisation is that of the receiver to the sequence of the received carrier.
—It offers useful protection properties against interference from other systems and interference due to multiple paths; this makes it attractive for networks of small stations with large antenna beamwidth and for satellite communication with mobiles.

—With multibeam satellites, it offers the potential of 100% frequency re-use between beams

he main disadvantage is the poor efficiency, of the order of 10%, as a large bandwidth of the space segment is used for a low total network capacity with respect to the throughput of a single unspread carrier. This comment applies only in a single beam network. The possibility of reusing frequency between adjacent beams improves greatly the overall efficiency. Another limitation consists in the limited number of codes (and therefore the number of simultaneous users) offering the required performance in term of inter-correlation properties.

 

SDMA and PDMA

Two additional access schemes useful for satellite communications are space division multiple access (SDMA) and polarization division multiple access (PDMA). To produce SDMA, the signals in different channels (allowed to OCCUPY the same frequency band) are transmitted by using spot beam antennas. The spot beams produce orthogonality by physically separating the signals so they can be collected with physically separated receivers. To produce PDMA, the antennas are orthogonally polarized to separate the electromagnetic fields.

 

A flexible implementation of SDMA, called satellite-switched TDMA (SS/TDMA), uses a microwave switch matrix in the satellite. The switching sequence of the matrix is controlled according to a programmable memory; the TDMA signals are cyclically interconnected among different antenna spot beams in rapid sequence. An earth station in the network communicates with those in other beams by transmitting TDMA bursts in proper timing to the sequence.

 

Fixed and On Demand Multiple Access

Traffic routing implies access by each carrier transmitted by the earth stations to a radio-frequency channel. For each of the three fundamental modes (FDMA, TDMA and CDMA), each carrier is assigned a portion of the resource offered by the satellite, i.e. a satellite channel (a frequency band, a time slot or a fraction of the total power keyed to a code) or a part of it. This assignment can be defined once and for all (a fixed assignment) or in accordance with requirements (on-demand assignment).

 

With fixed assignment, the capacity allocated each earth station is fixed independently of the traffic demand from the terrestrial network to which it is connected. An earth station can receive a traffic request from the network to which it is connected greater than the capacity which is allocated to it. It must then refuse some calls; this is a blocking situation, in spite of the fact that other stations may have excess capacity available. Because of this, the resource constituted by the satellite network is poorly exploited.

 

With on-demand assignment, the satellite network resource can be assigned in a variable manner to the various stations in accordance with demand. There will, therefore, be the possibility of transferring capacity from stations with low demand to stations with excess demand. With on-demand assignment CDMA and FDMA, a given capacity is allocated on request to a given transmitting station by assigning to that station for the duration of the connection a given code within a set of orthogonal codes or a given frequency band.

 

On-demand assignment TDMA offers the greatest flexibility; on-demand assignment is achieved by adjusting the length and position of bursts, requiring a coordinated burst time plan change. This only slightly increases the earth station hardware complexity as the earth stations already have synchronisation equipment. Capacity increments can be as small as one communication channel and the assignment can be performed on a call-by-call basis.

 

Fixed assignment is recommended for networks involved in routing large volumes of traffic between a small number of stations of high capacity. On-demand assignment provides better utilisation of the satellite network in the case of a large number of stations of low capacity per access with large variations in demand. Each station can thus benefit occasionally from a greater capacity than that which it would have in the case of a fixed assignment. Management of the assignment implies a connection set-up time of the order of a second.

 

TDMA, FDMA and CDMA provide dedicated circuits for communications and are therefore suited for continuous traffic, such as voice. However, some types of data traffic, such as those originating in a computer network or a query/response system in a bank, are characterized by periods of inactivity followed by a burst of activity. Dedicated circuits for such ‘bursty’ traffic are inefficient in terms of channel utilization because the circuit remains idle for a significant proportion of a message session. A more efficient channel utilization could be envisaged in which a channel is shared among several users, following a certain set of rules or ‘protocols’ which are ‘matched’ to traffic characteristics.

 

Random Access

This type of access is well suited to networks containing a large number of earth stations where each earth station is required to transmit short, randomly generated messages with long dead times between messages. The principle of random access is to permit transmission of messages almost without restriction in the form of limited duration packets, to which correspond bursts of modulated carriers, which occupy all or part of the bandwidth of the repeater channel. It is, therefore, multiple access with time division and random transmission. The possibility of collisions between carrier bursts at the satellite is accepted. In the case of collision, the earth station receiver is confronted with interference noise which can compromise demodulation with target bit error rate and correct message identification. Retransmission of all or part of the burst is necessary.

 

ALOHA

The main idea is for a population of nodes to transmit a packet to the single receiver whenever it is generated at the local source, regardless of the medium activity. In particular, each node, upon generation of the packet, transmits it immediately. If a collision occurs, the receiver detects the collision via checking the CRC field of the decoded packets and all collided users involved are considered lost.

 

At this point in time, depending whether retransmissions are enabled or not, two different behaviors are followed. In the latter case (no retransmissions), the packets are declared lost and no further action is taken by the transmitters. In the former case, instead (with retransmissions), the receiver feeds back a notification of the occurred collision to the users involved. The collided nodes, after a random interval of time, retransmit the packets.

 

Slotted ALOHA

The main impairment to successful transmission in ALOHA is coming from interference. Whenever two packets collide, even partially, they are lost at the receiver. In ALOHA, this is particularly detrimental because every transmission starting one packet duration before, till one after, the start of a reference packet can cause a destructive collision.

 

In SA this effect is mitigated introducing time slots. A common clock dictates the start of a time slot. Upon local generation of a packet, a node waits until the start of the upcoming slot before transmission. The time slot has a duration equal to the packet length. Although requiring additional delay for a packet transmission w.r.t. ALOHA, SA reduces the vulnerable period from two to one packet duration. In fact, only packets starting in the same time slot cause a destructive collision.

 

Considerations on ALOHA and Slotted ALOHA

RA protocols are particularly attractive for all scenarios where the traffic is unpredictable and random, such as satellite return links and ad-hoc networks, just to mention a few. Unfortunately, the throughput performance of both ALOHA and SA are quite limited but may allow transmission with lower delay compared to demand assigned multiple access (DAMA) schemes, if no collisions happened. This is particularly relevant for satellite applications, in which the request for resource allocation that precedes the transmission is subject to 1 round trip time (RTT) of delay. In geostationary orbit (GEO) satellite systems, this accounts for a delay of at least 500 ms. Instead, when using RA the delay can be drastically reduced.

 

Applications requiring full reliability (all transmitted packets are successfully received) of the packet delivery will operate ALOHA or SA with retransmissions. In these scenarios, the analysis of ALOHA and SA has to take into account the dynamism of the channel load due to the variation of backlogged users over time. In the recent past, thanks to the emerging applications related to machine-to-machine (M2M) type of communications of the Internet of things (IoT) ecosystem the full reliability is not required anymore. In applications like sensor networks, metering applications, etc. in fact, the transmitted data is repetitive so if one transmission is lost, is not particularly dangerous as long as a minimum successful probability can be ensured.

 

Recent RA protocols are able to drastically improve the throughput performance and to guarantee high successful reception probability for a vast range of channel loads. Furthermore, considering satellite communication systems, retransmissions will suffer of at least 1 RTT delay.

 

Optimizing Satellite Network

There is a large variety of solutions to the problem of multiple access to a satellite by a group of network stations. The choice of access type depends above all on economic considerations; these are the global cost in terms of investment and operating costs and the benefits in terms of revenues.

 

Ideally a multiple access scheme must be able to optimize the following parameters: satellite radiated power,  RF spectrum; connectivity; adaptability to traffic and network growth; handling of different types of traffic; economics;  ground station complexity; and secrecy (for some applications).

 

General indications can be given according to the type of traffic. For traffic characterised by long messages implying continuous or quasi-continuous transmission of a carrier (for example, telephone traffic, television transmission and videoconferencing), FDMA, TDMA and CDMA access techniques are the most appropriate. If the volume of traffic per carrier is large and the number of accesses is small (trunking), FDMA has the advantage of operational simplicity.

 

When the traffic per carrier is small and the number of accesses is large, FDMA loses much in efficiency of usage of the space segment and TDMA and CDMA are the best candidates. However, TDMA requires relatively costly earth station equipment. For small stations exposed to inter-system interference, CDMA may be preferred despite its low efficiency.
Selection of FDMA or TDMA multiple access also implies a choice between fixed and on-demand assignment. Economic considerations will prevail; the increase in revenue resulting from higher traffic is compared with the increased expense involved in the installation of equipment to control on-demand assignment.

 

For traffic characterised by short messages and random generation with long dead times between messages, random access is the most appropriate. The choice between a short transmission delay with low efficiency (pure ALOHA) or a higher efficiency with a longer transmission delay (S-ALOHA or DAMA).

 

A single technique cannot optimize all these parameters and therefore a trade-off analysis using the applicable conditions is necessary, For example, if the application at hand is provision of communication to a large number of low-cost mobile terminals, the accessing scheme should be simple but robust so as to permit the use of low-cost mobile receivers. At the same time, a certain degree of flexibility is necessary to enable sharing of the spectrum between a large number of mobiles and to accommodate addition of mobiles to the network.

 

Compare this with an application where a relatively few large earth stations, each carrying heavy traffic, need to be interconnected. In this case the accessing scheme can be complex and the main optimization criterion would be optimal use of the available bandwidth and satellite power rather than the need for simple earth stations.

 

Demand assignment  protocols are effective when the amount of data to be transmitted largely exceeds the overhead required to assign the resources, being the overhead typically some form handshake procedure. In all the cases where the packets to be transmitted are small compared to the handshake messages, DAMA becomes inefficient. Several schemes, often referred to as packet access schemes, have been developed to maximize the use of a channel for bursty data traffic.

 

The increasing demand of efficient solutions for addressing the concurrent access to the medium of heterogeneous terminals in wireless communications calls for the development of advanced MAC solutions. Two main research fields are emerging: on the one hand very large or continuous data transmissions serving streaming services, and on the other hand, small data transmission supporting recent paradigms like Internet of things (IoT) and machine-to-machine (M2M) communications. In the latter scenarios, RA is an effective solution, but old paradigms like ALOHA or SA are not able to meet the requirements in terms of throughput and packet loss rate (PLR).

 

Each type of network has its own idiosyncrasies and set of variables, and regardless of network type, satellite engineers strive to create optimal designs which effectively compete with wireless and terrestrial alternatives and provide reliability, affordability and provide an excellent user experience. As improvements in technology come along, engineers seek to optimize new and existing network designs.

 

Optimization involves weighing a number of variables and making careful choices in order to optimize the overall function to be improved. Engineers tasked with optimizing a satellite network must juggle multiple variables to get the best overall result. Many of the basic design considerations involve the RF link, antenna size, satellite frequencies and satellite modems, but as satellite networks increasingly are interconnected with IP-based networks, network optimization includes both wide area network concerns as well as RF considerations.

 

MF-TDMA

MF-TDMA (Multi-Frequency, Time Division Multiple Access) is the leading technology for dynamically sharing bandwidth resources in an over-the-air, two-way communications network. The access method is a combination of FDMA and TDMA, that is, the frequency band of a transponder contains several different carriers, and each carrier works in the way of narrow-band TDMA. Clock synchronization is the key technology of the system satellite communication system which based on MF-TDMA.

 

For satellite networks MF-TDMA is the dominant technology because it provides the most bandwidth and the greatest overall efficiency and service quality, while also allowing the dynamic sharing of that bandwidth among many (tens of thousands) of transmitters in a two-way communication mode. MF-TDMA networks can have either a star-topology, a fully meshed or partially meshed topologies.

 

ST Engineering iDirect Achieves World’s First Live MF-TDMA Demo on Telesat LEO Satellite in Oct 2020

ST Engineering iDirect, a company of ST Engineering North America, announced the successful completion of the first Over-the-Air (OTA) testing of iDirect’s Multi-Frequency Time Division Multiple Access (MF-TDMA) return link on the Telesat Phase-1 Low Earth Orbit (LEO) satellite. The milestone achievement demonstrated dynamic sharing of bandwidth among multiple terminals within a LEO constellation, a capability that extends the capacity and flexibility of Telesat’s multi-beam beam hopping architecture, and opens up a wide range of use cases for Telesat’s LEO customers in the commercial, government, and defense markets for land, land-mobile, aeronautical, maritime, and other applications.

 

The testing was conducted at Telesat’s Allan Park facility and featured ST Engineering iDirect’s VSAT platform networked across multiple satellite modems. The iDirect platform was able to compensate fully for the LEO satellite link dynamics, including time, frequency, signal variation and Doppler effects. Short guard times (the time intervals required between radio bursts to prevent self-interference) were achieved, comparable in length to guard times used on GEO satellite links, without compromising capacity or spectral efficiency.

 

The ability to leverage MF-TDMA to efficiently share bandwidth on satellite ground-to-space links improves the capacity, performance and affordability of broadband services delivered over LEO satellite constellations.

To put the link to the test, the team conducted a video conference with engineers at Allan Park and achieved seamless connectivity, low jitter and low packet loss, resulting in a high Quality of Experience (QoE) that exceeded the level typically achieved over GEO satellite networks.

 

“This is a significant success for the ST Engineering iDirect and Telesat teams,” said Bart Van Poucke, Vice President of Product Management at ST Engineering iDirect. “We have achieved the benefits of MF-TDMA efficiency whilst unlocking the low latency offered by LEO satellites. This demonstration confirms the wide addressable market for LEO and particularly for applications that require mission-critical communications. We are proud to have been part of these tests and thank Telesat for the opportunity.”

 

“Satellite service providers are eager to take advantage of Telesat LEO’s affordable, low latency, high-speed connectivity to deliver secure Internet, VPN, video conferencing and cloud applications to their customers,” stated Erwin Hudson, Telesat’s Vice President of LEO. “I congratulate the ST Engineering iDirect engineering team on their successful testing campaign. They demonstrated the powerful advantages that MF-TDMA brings to LEO networks, a capability that can provide increased flexibility and higher capacity for our customers while allowing us to support a greater number of end users on each LEO satellite.”

 

MRC Mx-DMA Multi-Resolution coding (MRC) and Mx-DMA MRC (Multi-Resolution Coding)

In a Satellite Return Link (RTN), a single up to thousands of terminals (e.g. cruise ships, fishing boats, broadband users, towers or airplanes) access a single gateway through a single satellite transponder, thereby sharing a common bandwidth. The specifications per terminal may vary greatly, from low (fishing boat) to high throughput (cruise ship), from low (IoT or downloading) to high (audio call) jitter sensitivity, from low-cost (broadband users) to high-end (cruise ships) terminals.

 

Thousands of terminals should potentially be able to log on in a few seconds, e.g. due to mobility or when the network recovers from an outage. For a profitable business, the required number of Multi-Carrier Demodulators (MCDs) needed at the gateway to demodulate up to thousands of terminals should be limited and as low as possible, without compromising the efficiency of transmission (number of bits per Hz that can be transmitted). In order to address this, we have designed and productized a single return technology that captures all the above requirements and which represents a significant improvement on our previous 3 return (RTN) link technologies SCPC, Mx-DMA and CPM.

 

This new RTN link technology is referred to as MRC Mx-DMA. Multi-Resolution coding (MRC) can demodulate, on a single MCD, any combination of terminal transmissions (from high demanding (high throughput, no jitter) to low cost
(low throughput, no jitter sensitive transmissions) terminals). Keep-alive traffic does not cost any noticeable bandwidth. Guard bands are minimized. Jitter is as low as a single FEC word duration, even though a burst from a terminal spans up to 100 FEC words. Automatic in-band regrowth detection without any calibration prevents terminals from saturating BUCs while maximizing power transmission. This results in a single RTN link transmission that is as efficient as SCPC for high throughput terminals while achieving CPM like scalabilities, overbooking ratios and efficiencies for services with high overbooking. There is no need for mode switching between CPM and SCPC, as it is all done within a single time-frequency frame using a single technology on a single MCD.

 

Mx-DMA MRC adjusts the frequency plan, symbol rate modulation, transmission length, code block size and power in
real-time for every terminal in the network, based on return traffic demand, QoS settings and link conditions. But,
designing an Mx- DMA MRC link does not require precise knowledge of the traffic and terminal mix, as the link self optimizes in real-time, providing a far simpler way to manage complex traffic demands. This also eliminates the need for the cumbersome trade-offs needed when predefining return carrier plans for a mix of terminal and service types as required.

 

All terminals share a single bandwidth pool and can log on in an unsolicited way (thousands at the same time in a few seconds). In this paper, we will present the waveform and compare it with our previous award winning, patented and marketleading RTN link technologies, Mx-DMA and CPM. We are confident that this significant performance improvement will enable us to maintain our dominant position in terms of efficiency. We also believe that this very cost-effective and highly scalable solution will open up a lot of new opportunities, especially in vertical markets.

 

The proposed multi-resolution coding (MRC) satellite return channel waveform solves the problem of finding a balance between TDMA flexibility and SCPC efficiency in a unified waveform. The waveform is highly parametrizable allowing to cope with very different user scenarios. The MRC waveform optimizes spectral efficiency in all traffic conditions and minimizes system jitter. The waveform needs to allow nearly continuous carriers minimizing time guards, frequency guard bands and synchronisation overheads. Next, the waveform keeps the possibility to allocate very small time/frequency chunks to serve terminals with low traffic demand.

The efficiency of the proposed waveform varies a lot with the terminal traffic demand. For low bit rates, efficiency is lower because of the smaller FEC codewords, but also, and mainly because the proportionally higher guard times, frequency guard bands and synchronization overheads.

 

The presented MRC waveform supports transmit modes from 100kBaud to 100MBaud, allowing terminal bit rate ranges from 1kbps to 100Mbps. The MCD is such that the whole aggregated bandwidth can be allocated at will by the MRC controller in order to optimize the spectral usage. There is no limitation in MRC on the allocation complexity. The MCD design is such that high and low bandwidth carriers can co-exist, and the allocation is bounded only by the aggregated bandwidth and not by the allocation complexity.

 

A new MF-TDMA waveform is proposed. The new MRC waveform complies with HRC and CPM performances and with a large variety of end user needs (high and low traffic demands). A time multiplexed hardware architecture has been presented based on a time multiplexed demodulator, allowing cost effective implementation and low processing jitter.

 

Building on the well-established, award winning Mx-DMA® HRC (High Resolution Coding) technology, Mx-DMA MRC (Multi-Resolution Coding) offers unprecedented service agility, extending the availability of Mx-DMA to very large networks and expanding the applicability and use of the technology to include a full spectrum of use cases.

 

Mx-DMA MRC brings forth the full scalability of TDMA return link technologies to the original Mx-DMA HRC return at the same SCPC-like efficiency levels. Service providers can cover a myriad of use cases in a single return link, from cruise ships and large enterprise customers to SCADA and broadband access, sharing satellite capacity more efficiently over a group of satellite terminals and applications achieving the lowest Total Cost of Ownership (TCO).

 

Mx-DMA MRC is a return link technology that combines the benefits of MF-TDMA (ideal for bursty traffic and higher contention services) and the spectrum efficiency of Mx-DMA HRC into a single return technology suited to a greatly expanded set of applications. Mx-DMA MRC scales in MHz independent of the number of terminals so customers may be served with a single return link for the majority of their use cases, minimizing operational complexity and maximizing statistic multiplexing. Designing an Mx-DMA MRC link does not require precise knowledge of the traffic and terminal mix as the link self-optimizes in real time. Moreover, the high efficiency enables bandwidth savings, higher throughput, better network availability and substantial terminal cost savings.

 

References and Resources also include:

https://www.idirect.net/news/st-engineering-idirect-achieves-worlds-first-live-mf-tdma-demo-on-telesat-leo-satellite/

 

Cite This Article

 
International Defense Security & Technology (October 6, 2022) Satellite Multiple Access Techniques. Retrieved from https://idstch.com/space/satellite-multiple-access-techniques/.
"Satellite Multiple Access Techniques." International Defense Security & Technology - October 6, 2022, https://idstch.com/space/satellite-multiple-access-techniques/
International Defense Security & Technology April 15, 2022 Satellite Multiple Access Techniques., viewed October 6, 2022,<https://idstch.com/space/satellite-multiple-access-techniques/>
International Defense Security & Technology - Satellite Multiple Access Techniques. [Internet]. [Accessed October 6, 2022]. Available from: https://idstch.com/space/satellite-multiple-access-techniques/
"Satellite Multiple Access Techniques." International Defense Security & Technology - Accessed October 6, 2022. https://idstch.com/space/satellite-multiple-access-techniques/
"Satellite Multiple Access Techniques." International Defense Security & Technology [Online]. Available: https://idstch.com/space/satellite-multiple-access-techniques/. [Accessed: October 6, 2022]

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