Communication systems

Claim 2

Communication apparatus characterised in that it comprises: a transmitter adapted to send a sequence of signal points in successive time intervals, said signal points being drawn from a constellation of available signal points such that said sequence is one of a set of permissible sequences that-is smaller than the set of all possible sequences of said signal points, ' said sequence of signal points being organized as a series of frames, each frame beginning at a predetermined time; and a receiver adapted to determine said predetermined time when each said frame begins in order to maintain frame synchronization with said transmitter; said receiver including a decision device adapted for determining said sequence of signal points which were sent by determining the minimum next path metric based on current path metrics and current branch metrics, and monitoring means adapted for monitoring the rate of occurrence of non-zero difference between said minimum next path metric and the minimum of said current branch metrics as an indication of loss of frame synchronization.

Claim 3

Communication apparatus according to Claim 1, further characterised in that said apparatus further comprises an interleaver adapted to change the original said sequence of signal points to a revised sequence for transmission, and a deinterleaver adapted to change the received sequence of signal points in a manner that will restore said original sequence when said receiver is in frame synchronization with said transmitter, and will restore a sequence not within said set of permissible sequences when frame synchronization has been lost.

Claim 4

Communication apparatus characterised in that it comprises: a transmitter adapted to send a sequence of signal points in successive time intervals, said signal points being drawn from a constellation of available signal points such that said sequence is one of a set of permissible sequences that is smaller than the set of all possible sequences of said signal points, said sequence of signal points being organized as a series of frames, each frame beginning at a predetermined time, said transmitter having associated therewith an interleaver adapted to change the original said sequence of signal points to a revised- sequence for transmission; and a receiver adapted to determine said predetermined time when each said frame begins in order to maintain frame synchronization with said transmitter, and having associated therewith a deinterleaver adapted to change the received sequence of signal points in a manner that will restore said original sequence when said receiver is in frame synchronization with said transmitter, and will restore a sequence not within said set of permissible sequences when frame synchronization has been lost, and detection means adapted for detecting that said sequence of signal points is not within said set of permissible sequences as an indication that synchronization has been lost.

Claim 5

Communication apparatus characterised in that it comprises: a transmitter adapted to send a sequence of signal points in successive time intervals, said signal points being drawn from a constellation of available signal points such that said sequence is one of a set of permissible sequences that is smaller than the set of all possible sequences of said signal points, said sequence of signal points being organized as a series of frames, each frame beginning at a predetermined time, said transmitter having associated therewith an interleaver adapted to change the original said sequence of signal points to a revised- sequence for transmission; and a receiver adapted to determine said predetermined time when each said frame begins in order to maintain frame synchronization with said transmitter, and having associated therewith a deinterleaver adapted to change the received sequence of signal points in a manner that will restore said original sequence when said receiver is in frame synchronization with said transmitter, and will restore a sequence not within said set of permissible sequences when frame synchronization has been lost, and detection means adapted for detecting that said sequence of signal points is not within said set of permissible sequences as an indication that synchronization has been lost.

Claim 6

Communication apparatus according to Claim 3, further characterised in that said detection means comprises: a decision device adapted for determining said sequence of signal points which were sent, by determining the minimum next path metric based on current path metrics and current branch metrics, and monitoring means adapted for monitoring the rate of occurrence of non-zero difference between said minimum next path metric and the minimum of said current branch metrics as an indication of loss of frame synchronization.

Claim 7

Communication apparatus according to any preceding claim, further characterised in that it comprises a trellis-coded modulation system.

Claim 8

Communication apparatus according to Claim 5, further characterised in that said communication system is a multi-dimensional, trellis-coded modulation system, in thit each said two-dimensional signal points are grouped into multi-dimensional signal points, and in that each said frame comprises at least one said multi-dimensional signal point.

Claim 9

Communication apparatus according to Claim 6, further characterised in that each said multi-dimensional signal point is 8 dimensional.

Claim 10

Communication apparatus according to Claim 7, further characterised in that each said frame comprises two 8-dimensional points.

Claim 11

Communication apparatus according to any preceding claim, further characterised in that said sequence of signal points corresponds to a stream of information bits to be transmitted, in that said transmitter includes multiplexer means arranged to receive said information bits from a plurality of ports, and in that said information bits are organized into groups corresponding to said frames of signal points such that the bits from each given said port always appear in the same particular positions in each said group.

Claim 12

Communication apparatus according to Claim 9, further characterised in that said information bits are transmitted at a rate of Q bits per signalling interval, the bits from a given said port not occupying the same particular positions in groups of Q bits transmitted in said signalling intervals.

Claim 13

Communication apparatus according to Claim 10, further characterised in that there are eight said ports, Q is 7, and each said frame comprises 56 said bits.

Claim 14

Communication apparatus according to Claim 1 or to Claim 4, or any other claim as appendant to either Claim 1 or Claim 4, further characterised in that said monitoring means is adapted to deliver a synchronization loss signal when said rate of occurrence of non-zero difference with respect to a plurality of said time intervals is greater than a predetermined threshold, preferably 0.4.