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VSATs: Novel Technologies?

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VoicenData Bureau
New Update

If one looks at the past, there is a clear trend of satellites being

developed with increasingly higher transponder power and RF signals using higher

frequencies that enable the use of this higher power. The balance is slowly

tilting from bandwidth-intensive satellites to the power-intensive ones. The

bandwidth crunch is hitting the satellite industry too, with more and more

bandwidth-hungry applications like broadband services, being operated on

satellites.

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Paired Carrier Multiple Access (PCMA)

PCMA is a novel method for frequency re-use that allows two

different earth stations to use the same frequency, time slots, and/or Code

Division Multiple Access (CDMA) code at the same time. The benefit of PCMA is

that it may effectively double the throughput of satellite systems in terms of

bits/sec/Hz, in simple words ‘Bandwidth’.

CRMA Brings the Benefits of Spread Spectrum to Satellite

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A combination of CRMA and Asymmetric Paired Carrier Multiple

Access (A-PCMA) brings the benefits of spread-spectrum technology to satellite

networking, for the first time. CRMA is a direct sequence spread-spectrum

technique, similar to conventional CDMA used in cellular telephony.

How CRMA Changes the Economics of Satellite Communications

CRMA technology offers several benefits that will enable

users and service providers the opportunity to keep in pace with the

communications trends, and take advantage of the declining costs for service and

terminals:

  • CRMA is an enhanced CDMA: CRMA uses a single spreading

    code for all subscriber terminals, allowing a single corelator to feed

    multiple demodulators in the hub. This enhancement over the normal CDMA,

    makes it highly economical as well as less complex–features that the

    traditional CDMA lacked.

  • Much more efficient use of bandwidth: CRMA provides much

    more efficient use of the channel capacity than contention or reservation

    schemes needed for multi-frequency TDMA-based systems, because it takes up

    very little bandwidth for frequency overhead. Users gain access to the full

    system burst rate.

  • Next generation CRMA terminals cost less: The CRMA return

    channel does not require the expensive, fast frequency-hopping synthesizers

    needed for multi-frequency TDMA return-channel architectures.

  • CRMA subscriber terminals reduce RF costs: The TDMA-based

    systems achieve an actual throughput equal only to a fraction of their burst

    rate, yet TDMA terminals must be sized to achieve the maximum burst rate.

    With CRMA, terminal throughput equals burst rate for the duration of any

    transmission. The CRMA terminal can therefore, achieve the same rate as the

    TDMA terminal using the less powerful (and as a result, less costly) RF

    equipment. Even with its advanced design, the CRMA modulator includes a

    standard L-band interface that makes it compatible with commodity VSAT

    Transmit Blocks.

  • When CRMA is combined with PCMA, data transmissions

    coming back to the hub from remote sites can be combined within the same

    bandwidth as an outbound channel. Rather than requiring additional bandwidth

    as current systems do, such advanced technology-based networks would need

    only the space segment required by the outbound channel, to support two-way

    satellite services.

  • An expandable data pipe to reach customers who need a

    higher value of broadband services.

  • Less power required by spread-spectrum transmissions.

  • Combined with PCMA, CRMA gives you forward and return

    channels in the same satellite transponder bandwidth that used to provide

    traffic only in one direction. In addition, the RF power efficiency and

    reduction in hardware components provide a path to more savings, and future

    price points that other technologies cannot achieve. CRMA and PCMA would be

    the enablers to reach more markets through a combination of bandwidth

    efficiency and hardware cost savings that change the economics of satellite

    communications.

Feroz Khan, country manager, and Gaurav R Kharod, marketing

manager, India and South-East Asia, Viasat Satellite Networks.

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