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US 4,908,836 AGranted
Method and apparatus for decoding multiple bit sequences that are transmitted simultaneously in a single channel
AssigneeUnisys Corporation
InventorsCraig K. Rushforth, Zhenhua Xie, Robert T. Short
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Abstract
Data bits are decoded from a composite signal that is formed by coding multiple bit sequences with respective spreading codes, and transmitting the coded bit sequences simultaneously and asynchronously over a single channel in which the bit sequences are added. This decoding involves a metric in combination with a repetitive decision process which is only linearly dependent on the number of bit sequences in the composite signal.
Claims10
A method of decoding superimposed data bits including the steps of:
- receiving a composite signal that is formed by coding multiple bit sequences with respective spreading codes and transmitting the coded bit sequences simultaneously and asynchronously over a single channel;
- comparing the content of several registers, each of which contains an estimate of a particular bit sequence in said composite signal and a metric for that sequence, to determine the largest metric M.sub.max and the corresponding bit sequence b.sub.s ;
- evaluating a new pair of metrics for the very next bit b(x) in said composite signal which follows said bit sequence b.sub.s by using estimated "0" and "1" values for bit b(x), bits from said sequence b.sub.s which immediately precede bit b(x), and matched filter outputs for bits in said composite signal which immediately follow bit b(x);
- replacing the register which contains said bit sequence b.sub.s with two registers, one of which contains the bit sequence b.sub.s b(x)=0 and the metric M.sub.max plus the above evaluated metric for b(x)=0, and the other of which contains the bit sequence b.sub.s b(x)=1 and the metric M.sub.max plus the above evaluated metric for b(x)=1;
- repeating said comparing, evaluating, and replacing steps multiple times;
- and thereafter,
- decoding said composite signal as the bit sequence in the register which contains the largest metric.
4 more elements
A decoder for decoding superimposed data bits comprising:
- a plurality of filters, which are coupled to receive and filter a composite signal that is formed by coding multiple bit sequences with respective spreading codes and transmitting the coded bit sequences simultaneously and asynchronously over a single channel, with each filter being matched to a respective one of said spreading codes;
- a computing means for evaluating a metric for any bit b(x) in said composite signal which includes an estimated value for bit b(x), an estimate of a sequence of bits b.sub.s which immediately precede bit b(x), and matched filter outputs for several bits in said composite signal which immediately follow bit b(x);
- a plurality of register means, each of which is for holding a respective metric and a corresponding bit sequence;
- and
- a control means for repeatedly (a) examining said registers to determine its largest metric M.sub.max and corresponding bit sequence b.sub.s, (b) directing said computing means to compute a new pair of metrics for the bit sequences b.sub.s b(x)=0 and b.sub.s b(x)=1, and (c) replacing the register which contains said bit sequence b.sub.s with two registers, one of which contains the bit sequence b.sub.s b(x)=0 and the metric M.sub.max plus the above evaluated metric for b(x)=0, and the other of which contains the bit sequence b.sub.s b(x)=1 and the metric M.sub.max plus the above evaluated metric for b(x)=1.
2 more elements
Dependencies are inferred from the claim text.