QAM encoding for high-definition television system

In a video signal processing system comprising an encoder apparatus;

• wherein said encoder apparatus includes means for providing a bitstream of symbols representing video data, each of said symbols representing plural bits, and modulation means responsive to said symbol bitstream for producing a carrier quadrature amplitude modulated (QAM) with said symbols, said symbols being assigned to responsive points at prescribed locations of a grid-like constellation in a plane defined by orthogonal I,Q axes;
• wherein said constellation is divided into first and second separate partitions arranged so that (a) points that are closest in distance to a point of said first partition belong to said second partition, and (b) points that are closest in distance to a point of said second partition belong to said first partition;
• the improvement wherein
• said first and second partitions are interleaved and exhibit a diagonal-like orientation relative to said axes.

In video signal transmitter apparatus comprising means including a quadrature amplitude modulator (QAM) and an encoder therefor;

• wherein said QAM derives any particular point in a given rotationally-symmetrical constellation of between 2.sup.n-1 +1 and 2.sup.n points in the in-phase (I), quadrature (Q) plane in response to that particular point being selected by said encoder in accordance with an n-segment code, where n is an integer having a value of at least 4;
• wherein said encoder assigns an n-bit segment having a unique binary value to each individual point of said constellation, said n-bit segment comprising (1) two phase bits for distinguishing each of four rotationally-symmetrical sets of between 2.sup.n-3 +1 and 2.sup.n-2 constellation points situated respectively in each of the four quadrants of said I,Q plane in accordance with different ones of the four binary values defined by the two phase bits, and (2) n-2 invariant bits for distinguishing each of the constellation points in a rotationally-symmetrical set in accordance with different ones of the binary values defined by the n- 2 invariant bits, thereby providing insensitivity to rotation of said constellation;
• the improvement wherein:
• the bit assignment by said encoder in such that said constellation points are divided into first and second separate partitions arranged so that constellation points that are closest in distance in said I,Q plane to any constellation point of said first partition belong to said second partition, and constellation points that are closest in distance in said I,Q plane to any constellation point of said second partition belong to said first partition, said first and second partitions being distinguishable from one another by the lowest significant phase bit of all n-bit segments belonging to said first partition having a certain binary value, and all n-bit segments belonging to said second partition having a binary value opposite to said certain binary value.

In video signal receiver apparatus for receiving a transmitted signal that has been encoded by a quadrature-amplitude-modulator (QAM) at the transmitter of said signal in accordance with a given code;

• said receiver comprising digital means for demodulating and decoding said received signal transmitted thereto;
• wherein each of a given pair of first and second particular points in a given rotationally-symmetrical constellation of between 2.sup.n-1 +1 and 2.sup.n points in a plane defined by in-phase (I) and quadrature phase (Q) axes, where n is an integer having a value of at least 4, are respectively selected at the transmitter for consecutive first and second transmissions to said receiver in accordance with said given code;
• wherein said constellation points are divided in accordance with said given code into separate first partition points and second partition points arranged so that constellation points that are closest in distance in said I,Q plane to any constellation point of said first partition belong to said second partition and constellation points that are closest in distance in said I,Q plane to any constellation point of said second partition belong to said first partition;
• and wherein said decoding means includes digital means for deciding, in accordance with the following process, whether a first of a pair of first and second constellation points in the I,Q plane consecutively received by said receiver is a first-partition constellation point or a second-partition constellation point:
• 1. Store the I and Q values of the closest first-partition constellation point to the I and Q values of the received point in the I,Q plane of the first received transmission of the given pair;
• calculate and store the I and Q distance and phase values of the vector interconnecting the received point to the closest first-partition constellation point;
• 2. Store the I and Q values of the closest second-partition constellation point to the I and Q values of the received point in the I,Q plane of the first received transmission of the given pair;
• compute and store the I and Q distance and phase values of the vector interconnecting the received point to the closest second-partition constellation point;
• 3. Store the I and Q values of the closest first-partition constellation point to the I and Q values of the received point in the I,Q plane of the second received transmission of the given pair;
• compute and store the I and Q distance and phase values of the vector interconnecting the received point to the closest partition first-partition constellation point;
• 4. Store the I and Q values of the closest second-partition constellation point to the I and Q values of the received point in the I,Q plane of the second received transmission of the given pair;
• compute and store the I and Q distance and phase values of the vector interconnecting the received point to the closest second-partition constellation point;
• 5. Calculate the vector sum of the first-partition vectors derived in steps 1 and 3;
• 6. Calculate the vector sum of the second-partition vectors derived in steps 2 and 4;
• 7. Compare the first partition vector sum with second partition vector sum to determine (A) if the first partition vector sum is less than the second partition vector sum whereby the partition of the first received transmission of the given pair is the first partition, or (B) if the first partition vector sum is more than the second partition vector sum whereby the partition of the first received transmission of the given pair is in the second partition.