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Browse Prior Art Database

Fourier Transform Division Multiplexing for Fading Channels

IP.com Disclosure Number: IPCOM000108364D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Feig, E: AUTHOR

Abstract

Disclosed is a communications channel which tolerates fades over some regions in the frequency domain. The channel, in the frequency domain, is broken up to several independent subunits Mj, each of which is composed of smaller subchannels transmitting identical amounts of information, as described in the FTDM scheme [1]. Consider here one such subunit, e.g., M1, composed of, e.g., N subchannels each transmitting one word (k bits) of data per block-time. The scheme will accommodate K erasures due to fades.

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Fourier Transform Division Multiplexing for Fading Channels

       Disclosed is a communications channel which tolerates
fades over some regions in the frequency domain.  The channel, in the
frequency domain, is broken up to several independent subunits Mj,
each of which is composed of smaller subchannels transmitting
identical amounts of information, as described in the FTDM scheme
[1].  Consider here one such subunit, e.g., M1, composed of, e.g., N
subchannels each transmitting one word (k bits) of data per
block-time.  The scheme will accommodate K erasures due to fades.

      There are various erasure channel schemes one can utilize.  One
standard method utilizes BCH coding.  Suppose the message is {cO, c1
N-K-1}, and each cj is mapped onto a subchannel as some member of an
appropriately sized constellation (QAM, PSK, CROSS, etc.).  The
entries cj are viewed as elements in some finite field, whose nonzero
elements form a multiplicative cyclic group with generator g.

      A particular implementation is as follows.  The encoder assigns
the remaining subchannels the values {cN-K  ... cN-1}, where

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The encoder computes first

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and then determines the redundancies {cN-K  ... cN-1} by solving the
linear equations

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      At regular intervals, the transmitter sends a predetermined
message which maps onto the largest possible magnitude elements of
the constellation.  This will be used by the receiver to...