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Transmission method and apparatus employing trellis-augmented precoding
| Details |
Inventors: Cherubini, Giovanni; Oelcer, Sedat; Ungerboeck, Gottfried;
Assignee: International Business Machines Corp. (Armonk, NY)
Primary Examiner: Vo; Don
Assistant Examiner: Phu; Phuong
Attorney, Agent or Firm: Cameron; Douglas W., Dougherty; Anne Vachon
Trellis-enhanced precoding for trellis-coded transmission over channels with intersymbol interference allows coding and shaping gains to be achieved with minimal transmit power penalty for arbitrary signal constellations, provided the intersymbol interference channels are linearly invertible. This technique can be employed for trellis-coded transmission over a variety of communication channels. However, if the channel response exhibits spectral nulls, trellis-enhanced precoding cannot be applied because the corresponding inverse precoding operation at the receiver requires inverse channel filtering. For channels with a spectral null, this inverse operation can result in unlimited error propagation. The present invention allows trellis-coded transmission over channels exhibiting spectral nulls without incurring unlimited error propagation in the receiver. Coding gains are achieved with minimal transmit power penalty, like in the case of trellis-enhanced preceding. The invention is applicable for most signal sets used in practice. |
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DETAILED DESCRIPTION The principles of the invention, which can be designated as "trellis-augmented preceding", will be described with reference to FIG.
1.
A specific embodiment is illustrated in FIG.
2.
A system for trellis-coded transmission over channels with intersymbol interference that employs the invention is depicted in FIG.
1.
It includes on the transmitter side encoding means 1 and on the receiver side decoding means 2.
Transmission takes place over a discrete-time channel with transfer characteristic h(D)1+Dh.
sub.
1 (D) and additive noise represented by w(D).
Encoding means 1 comprises a signal mapper 3 which converts an input vector sequence of information bits i(D) provided on line 4 into an output symbol sequence a(D) on line 5, under control of a binary state-bit sequence y.
sup.
0 (D).
It includes furthermore a precoder 6, which generates from the symbol sequence a(D) a sequence of channel input signals x(D) on line 7, and which also provides a trellis-coded sequence u(D) on line 8.
A next-state computation unit 9 is provided to generate, in response to the trellis-coded sequence u(D), the binary state-bit sequence y.
sup.
0 (D) on line 10.
The next-state computation unit comprises storage means to store the trellis code state.
The symbol sequence a(D) has elements a.
sub.
n .
epsilon.
, where .
OR right.
.
LAMBDA.
.
sub.
0 +.
lambda.
is a set of M.
times.
M modulation symbols, M being even, which admits a power-efficient modulo extension, .
LAMBDA.
.
sub.
0 denotes the lattice underlying , and .
lambda.
is a given, possibly non-zero, offset value.
The element a.
sub.
n at time n is taken from .
sub.
y.
sbsb.
n.
spsb.
0, i.
e.
, one of the two first-level subsets .
sub.
0 or .
sub.
1 of , as specified by the value y.
sub.
n.
sup.
0 =0 or 1 of the element of the binary state-bit sequence y.
sup.
0 (D) at time n.
Precoding means 6 determines the sequence of channel input signals x(D) according to x(D)=a(D)-p(D)+c(D), (1) where the sequence p(D)=[h(D)-1]x(D)=Dh.
sub.
1 (D)x(D) (2) on line 12 represents the intersymbol interference at the channel output, which needs to be compensated at the transmitter
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Multiplexer-related 
