CA1202083A - Means providing novel signal structures for qcm modulation - Google Patents
Means providing novel signal structures for qcm modulationInfo
- Publication number
- CA1202083A CA1202083A CA000411231A CA411231A CA1202083A CA 1202083 A CA1202083 A CA 1202083A CA 000411231 A CA000411231 A CA 000411231A CA 411231 A CA411231 A CA 411231A CA 1202083 A CA1202083 A CA 1202083A
- Authority
- CA
- Canada
- Prior art keywords
- message
- points
- message points
- class
- group
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
Abstract
A B S T R A C T
QCM signals are provided to a transmission link by a device which converts groups of n binary signals each having 2n possible group values into signals representing a set of K signal points defined by Cartesian coordinate pairs where K>2n and the signal message points are located substantially at intersections on a rectangular triangular grid, where each message point corresponds to only one group value of the 2n possible values and each of the 2n possible values corresponds to at least one message point. Means are provided, responsive to said message point signals for providing a pair of coordinates of said complex signal message points.
QCM signals are provided to a transmission link by a device which converts groups of n binary signals each having 2n possible group values into signals representing a set of K signal points defined by Cartesian coordinate pairs where K>2n and the signal message points are located substantially at intersections on a rectangular triangular grid, where each message point corresponds to only one group value of the 2n possible values and each of the 2n possible values corresponds to at least one message point. Means are provided, responsive to said message point signals for providing a pair of coordinates of said complex signal message points.
Description
~'~CI 2~83 This invention relates to quadrature carrier modulation communications systems.
Quadrature-carrier modulation (QC~I) communications methods convey information as pairs of coorclinate signals representing digital values, modulated on an "in phase" and on a "quaclrature p}lase" carrier respectively.
At ~he transmitter a series of binary digital signals is transformed in sequential groups into pairs of coordinate signals which spatially represent in Cartesian ]0 coordinates of two dimensions a message point corresponding to the binary number value of such group. Such pairs of coordinate signals appear as modulations on the carriers. At the receiver the received moclulated carrier signals are demodulated and the digital group identified from the demodulated received coorclinate signals. Durin~ transmission over the network or channel, the transmitted modulated carrier is affected by noise and by many other influences well known to those skilled in the art. Correct detection of the received signals therefore involves determining, on a balance of probabilities, whicll of two or more message ~20 points is represented by the coordinate signals received.
The most common ancl best known of the signalling methocls is dollble side band-clundr.ltllre carrier modulation (otten abbreviated DS~-QC~I), DSB-QC~ inclucles moclulntion techniques such as phase - shift keying (PSK), quaclrature amplitude moclul.ltion (Q~l), and combinecl nlnr)litucle and pll.lse moclulation ~hich have long been known in the art.
This invention is pnrticularly suitable for use with DSB-QCM systems ~ith the elernents of thc? pairs of coordinates 61i33 being sent on the quadrature ~nd in phasc carriers respectively.
Prior developments for signalling such pairs of coordinates include Canadian Patent 985,376 which issued ~arch 9, 1976 to Codex Corporation and U.S. Patent 3,955,141 which issued May ~, 1976 to Intertel Inc. Both such patents show signalling systems where the message points spatially representing the coordinate values display a square or rectilinear pattern and have four-fold symmetry.
llowever> it has becn notcd that mcssage points 1() arranged in hexagons show better performance with regard to .aussian noise or phase jitter than the rcctangular or four-fold symmetry of the prior patents referred to herein. A
discussion of hexa~onal systems is contained in an article ; entitled "Hexagonal Multiple Phase-and-Amplitude-Shift-~eyed Signals Sets" by Marvin K. Simon and Jocl (;. Smith, ap~earing in IEEE Transactions on Communications Vol. COM-21, No. 10, October 1973.
It is an object of this invention to provide apparatus and a method of signall;ng using pairs of coordinates
Quadrature-carrier modulation (QC~I) communications methods convey information as pairs of coorclinate signals representing digital values, modulated on an "in phase" and on a "quaclrature p}lase" carrier respectively.
At ~he transmitter a series of binary digital signals is transformed in sequential groups into pairs of coordinate signals which spatially represent in Cartesian ]0 coordinates of two dimensions a message point corresponding to the binary number value of such group. Such pairs of coordinate signals appear as modulations on the carriers. At the receiver the received moclulated carrier signals are demodulated and the digital group identified from the demodulated received coorclinate signals. Durin~ transmission over the network or channel, the transmitted modulated carrier is affected by noise and by many other influences well known to those skilled in the art. Correct detection of the received signals therefore involves determining, on a balance of probabilities, whicll of two or more message ~20 points is represented by the coordinate signals received.
The most common ancl best known of the signalling methocls is dollble side band-clundr.ltllre carrier modulation (otten abbreviated DS~-QC~I), DSB-QC~ inclucles moclulntion techniques such as phase - shift keying (PSK), quaclrature amplitude moclul.ltion (Q~l), and combinecl nlnr)litucle and pll.lse moclulation ~hich have long been known in the art.
This invention is pnrticularly suitable for use with DSB-QCM systems ~ith the elernents of thc? pairs of coordinates 61i33 being sent on the quadrature ~nd in phasc carriers respectively.
Prior developments for signalling such pairs of coordinates include Canadian Patent 985,376 which issued ~arch 9, 1976 to Codex Corporation and U.S. Patent 3,955,141 which issued May ~, 1976 to Intertel Inc. Both such patents show signalling systems where the message points spatially representing the coordinate values display a square or rectilinear pattern and have four-fold symmetry.
llowever> it has becn notcd that mcssage points 1() arranged in hexagons show better performance with regard to .aussian noise or phase jitter than the rcctangular or four-fold symmetry of the prior patents referred to herein. A
discussion of hexa~onal systems is contained in an article ; entitled "Hexagonal Multiple Phase-and-Amplitude-Shift-~eyed Signals Sets" by Marvin K. Simon and Jocl (;. Smith, ap~earing in IEEE Transactions on Communications Vol. COM-21, No. 10, October 1973.
It is an object of this invention to provide apparatus and a method of signall;ng using pairs of coordinates
2() modulated on in phase and quadrature pil.lse carriers, where the message points represented by the coordinate pairs collectively form a hexagonal pattern arrangecl on the intersections of an etluilateral triangular gricl. In tllC invcntivc apparatus ancl method it will be understootl that a series of binary signals, are encoded in groups of n binary signals requiring a minimum of 2n message points clefined by coorclinatc? pairs. In accord with the invention there are made available, in the hexagonal pattern K message points~ where K>2n. It will bc noted ~c~v that of the 2n possible values for the group of n digits, some of such values will be in one-to-one correspondence with a corresponding number of the K message points. The remainder of such 2n values will have 2 or more message points corresponding thereto. For K~2n it is not necessary but it is certainly preferable if the points K are not only arranged in a hexagonal relationship to one another but are arranged with 120 and preferclbly 6() symmetry. Symmetry of any degree ten~s to reduce and preferably substantially eliminate the carrier component of the received signal. ~urther the higher degree of symmetry renders easier the decision ancl decoding process at the receiver, particularly when combined with differential encoding techniques.
Moreover the power requirements of the communications system will be less if the hexagonally arranged signal points are packed as closely as pos.-ible to the origin or point corresponding to ~ero signal amplitude for both coordinates on a Cartesian coordinate system. That is, the hexagonally arranged message points may be considered to be located on concentric rings about the origin and where nli availahle points on il ring (with the possible exception of several outer rings) are occupied. Although the extra K-2n message points provicle advantages inclependent of the symmetry and density of packing o~ the message poin~s, the principal advantages of the invention accrue when the message points are symmetrically arrangecl about the origin and densely packed outward therefrom and the aclvantageous use of the K-2n extra points will be principally discussed where such symmetry ancl dense packing are present.
The encocling ancl transmitting apparatus ia ~ _ 0~3 preferably designed so tha-t the inner message points relative to ~he origin are in one-to-one correspondence with the values of groups of n binary signals where 2 or more of the outer of the K message points correspond to others of th0 group values.
In this way, there are a plurality of outcr message points which are not used each time the corresponding binary value is to be transmitted, points in such plur;llity of outer message points may be usecl cyclically or in accord with anothcr rule. In any event, the outer points are used with less frequency than the inner and power savings are thus achieved; since in a optimally designe~ system the ener~y required to signal when using the outer points in the pattern will be greater than when using the inner points. The alternate message points corresponding to a digital value of a group of bina~y digits may be used cyclically to improve the symmetry of the collective transmission of sequential message points. The fact that alternate points are available corresponding to some of the group values allows transmission of extra lnformation since the method of selection of alternate point.s may he usecl for signalling. rhuS in accord with a prc-20 ferred arrangement of the invention a class of values comprising K-2 (K-2n) of the group values will be in one-to-one relationship with a corresponding number of the K message points but K-2n of the group values will each have two alternate corresponding message points. This allows the transmission of binary information on a channel additional to that represented by the dclta conveyed by the groups of n digits. Thus the additional binary information will not be regularly transmitted but must be queued for transmission whcnever onc o~ thc K-2 vallJcs outslde thc class is v~
to be transmitted. There are no practical 1imits to the type of binary information which may be sent on the additional channel thus provided. Thus the information transmitted on the additional channel may (for example) relate to the operation of the communications system, to the high speed transmission of the 2n groups or it may be indcpendcnt information.
It will be obvious that; while the advantages specified in the previous paragraph are easier to demonstrate where the hexagonally arranged points are densely packed about the origin and arranged in hexagonal or triangular symmetry;
that some of these advantages (namely the provision of an additional channel and low frequency use of some message points) also accrue when the dense packing and symmetry are absent.
Moreover thc prcsent invention allows the provision of novel message point distributions, determined by the coordinates transmitted by QCM modulation which continue to exhibit near optimum margins against both Gaussian noise and phase jitter as additional points are aclded. Further advantages of the invention are that the apparatus and method allows suppression of carrier and provide 60 or 120 symmetry.
In the drawings which illustrate a preferred embodiment of the invention :
~igure 1 is a schematic diagram having blocks referring to the functional requirements of a transmitter and a receiver for employment with the invention, Figures 2a - 2h show prior art message points mapped on a rectangular grid in the two dimensional Cartesian plane, Figures 3a-3f show prior art message points mapped (largely) on a triangular grid in the two dimensional Cartesian plane. (It should be noted that other message point distributions are known such as those described and compared in an article, "Digital Amplitude-Phase Keying with M-ary Alphabets" by Thomas, Weidner and Durrani, IEEE Transactions on Communications, Vol. COM-22, No. 2, February 1974)l Figures 4a-4j show signal structures of the invention mapped on -the Cartesian plane, Figure S is a schematic block diagram of the trarls~
mission end of a communications link including a signal processorl Figure 5 is on the same sheet as Figure 1, Figure 6 is a flow chart showing the opera-tions of the signal processor and microprocessor of Figure 5, Figure 7 is a schematic block diagram of the receiver end of a communications link including a signal processor, and microprocessor, Figure 8 is a flow chart showing -the operations of the signal processor and microprocessor of Figure 7, and Figure 9 shows the decision areas for received signals which were encoded in accord with the distribution of Figure 4c.
Figure 9 is on the same sheet as Figure.7.
Figure 1 schematically illustrates functional operations perLo 171~U 1~ a ~O~ UiliCat ons systems which would utilize the invention. The functional operations are not intended -to imply particular hardware or choices between analog-vs. digital modes, or hardware vs. software modes at any particular stage, ~2~2~
Thus as functionally illustrated in Figure 1 where, functionally, serial binary data is converted, at a serial to parallel converter, into groups of n digits. Such groups of n digits are encoded to provide the message point Cartesian coordinates for QC~1 modulation. A coordinate signal generator and a carrier generator provide the signals to create the modulated carriers which are combined and transmitted over the channel.
At the receiver the received signal is demodulated, conditioned and equalized and sent to the decision region selection device which rnakes the decision as to the message point coordinates.
Such 'Idecision coordinates" are supplied to the decoder which converts these coordinates into parallel data intended to correspond to the parallel data entered at the transmitter. The received parallel data is converted into serial data for trans-mission to the user. Circuitry for performing the above functions is well known to those skilled in the art and examples are disclosed in the Canadian and U.S. patents referred to.
Applicant's circuitry (the preferred form of which is discussed hereafter) provides a novel relationship between the n binary digit groups and the message points, less vulnerable to noise and phase jitter, and error and whicll allows symmetry, suppression of carrier and, in one alternative, the ability to transmit a~xiliary information. Applicant's preferred ernbodiment also reflects the advances in technology since the dates of the Canadian an{l U.S. patents referrecl to.
There is here discussed the relationship of the message ~oint coordin.ltes to the encoded binary information. In contrast with the prior art the total number of message points 2C~2~13 K employed in a si~nal structure th.lt is in accord with the invention will not be an integral power of 2 such as 8, 16, 32, etc., even though the number of bits to be transmitted per Cartesian coordinate pair is an integer n re~uiring at most ~1=2 message points. In fact the value of K will always ; exceed the value of ~. In a simplc cmbodiment of the invention at least one of the required M values will be identified with more than one of the K message points of the signal structure.
The reasons behind thc seleclion of K>M are firstly, that the total number of points lying on concentric rings is not a power of 2 for either of our type A or B structures, secondly, we desire the carrier signal be suppressed which is accomplished when the centre of the concentric rings is the centroid (centre of gravity) of the K signal points, and thirdly, we will desire to have 60 symmetry for type A
structures and 120 symmetry for type B structures when we anticipate the use of c1ifferential encoding in conjunction with these signal structures. By 'A type structures' we refer to an arrangement of message points having 60 symmetry and a point at the origin7 thus in thc optimllm arran~ement K~6I + 1 where I is any integer nnd is excmpliEiecl by l~igllres ~ta) (c~
(e) ~g) ~ It will be notcd that 60 ~hexagonal) symmetry can be achievecl ancl near optimum arrangement, by omitting thc ori~in point so that K=6I. Ilowever, discussions of the preferred embodiment refer to K=6I ~ 1 arrangements.) By 'B type structures' we refer to 120 symmetry with no points at the origin and K=3I as exemplified by Figures ~(b)(cl)(f)~h)~j).
~Q~3 .~ote that differential encocling is very desirable since techniques which derive a carrier from the received data signal, the carrier being fully suppressed, are generally ambiguous in phase and when there is substantial 60 or 120 symmetry of the signal structure there can be 60 or 120 ambiguity in the recovered carrier.
With differential encoding, information is trans-mitted in terms of the possible transitions from past trans-mitted signal points to now transmitted signal points. In our case, with K>M, there are K possible transitions and at least two different transitions can convey the same information.
Leaving aside likely use of differential encoding and decoding, consider the signal structure shown in Figure 4a which has a total of K = 13 signal points and where the locations of the seven innermost points are shown by solicl dots and six outer points are marked with small circles. In this case we presume that M = 8 and that 7 of the M points are to be ; associated with the inner 7 points and the eighth of the M points will be associated with any of the outmost 6 points. Indeed, in successive occurrences of the neecl to transmit the 8th of the ~l points the fi outer points will be use(l in turn so that each will occur with a frecluency th.lt is l/fi of the frequency of each of the 7 inner points. Thus when calclll.lting the signal energy only one outer point neecl be incluclecl in the calculation. (The 6 outer points may l)e usecl in turn in cyclic order but for many applications the 6 outer points will be used in a pseuclo ranclom manner due to the differential encoding).
_ ~ _ ``` ~Z~ 33 Signal sets can be comparecl on the basis of the average required energy, under the assumption that in each set the minimum distance between points in the set is 2 units in each case and further the rectangular system points are assumed to have integral coordinates. A lower average energy for a given minimum separation results in an improved signal -to noise performance.
As a result the average energy E, for the signal structure shown in Figure 4a will have the value 4.5 versus, for example a value of 5.5 for the prior art structure of Figure 2b where each signal point is chosen from a rectangular grid and each signal point is assumed to occur with the same frequency.
In other figures such as Figure 4c the situation is slightly more complicatcd. Ilere there are a total of K = 19 points and we assume M = 16. In this case a chosen 3 of the ~1 values will each be associated with pairs of the six outer points. Each of the paired outer points will be used in turn so that outer points will occur with 1/2 the frequency that inner points occur, (in one ~lternatc of thc preferred cmbodiment ~he selection of alternates will be in accord with auxiliary channel binary signals). Thus only 3 of the six outer points will enter into the energy calculation giving the rcsult E = 9.
In contrast the 16 point signal structure of Figure 2d results in E = 10 and the structure of Figure 2c in E a 13~5~
Although use of the invention provides for a "good"
selection of signal points, differential encoding becomes more complex as does the detection and decoding processes. In the Type A and Type B codes it is advantageous to use the extra message points in a statistically cqu;ll manner tha~ preserves the 120 and 60 symmetries respectively required. In accord with preferred techniqucs using the invcntion, it may be notcd that differential encoding may be uscd to providc the statisti-cally equal usage. In the preferred embodiment~ the extra message points are selected on a basis that provides an extra signrllling channel.
Type A codes present with regard to differential encoding a complication since there is no angle associated with the central point. This case can be treated by "remembering"
in the encoder the last signal poin~ that was not a central point that was transmitted, whenever a central point is transmitted.
There is also an advantage that can be derived when K>~l. It is possible, through varying the pattern of the statistically equal usage of the extra ~oints, to transmit auxiliary information. This ability can be enhanced by delibe-rately increasing K over the minimum value that would be ; necessary to provide symmetry.
It should be noted that the extra points need not be chosen entirely or partly from an outer ring but can be any of the K points. However, to minimize average energy requirements, points which are less frequently used should be outer rather thrln inncr l)oints.
It should be noted that none of the prior a-rt of Figures 2 and Figures 3 employ signal points at the centre of the signal structure and none employ extra signal points.
In summary as greater datrl transmission rates are employed over telephone channels it becomes more and more important to utilize better performing signal structures even although they are more complex to irnplement.
In ~igure 5 it is shown that a scries of binary signals, for transmission along the communications lin~, are sent to the circuitry along line 10 to a serial-to-parallel converter 12 which converts the infor~ation into output bauds of n binary digits. After processing in the microprocessor 14 and high speed processor 16 as discusscd in connection with Figure 6J the rcsultant signals arc convcrtcd at digital-~o-analogue converter 17 for the transmitter channel interface and transmission along the channel.
The apparatus and procedures of Figures 5 and 6 are operable with n bits per baud where n is 2 or greater.
Figures 4a, 4c, 4e, 4g and 4i represent message point dis-tributions which may be achieved with the apparatus and methods of Figures 5 and 6 for n = 3,4,5,6 and 7 respectively.
The processors 14 and 16 and the flow chart of Figure 6 are more easily discussed in detail using a specific value of bits per baud. Before commencing such description it is desired to set out certain constant values Cl, C2, C3, C4, for n bits/baud where n = 4,5~6 or 7. The usage of these '() constant values will be discllsscd herea~ter.
Thus thc table below givcs valucs for use of the preferred processors and the flow chart of Figure 6 for n = 4,5,6 and 7.
n M Cl C2 C3 C4 K (message Shown in (hits/baud) points) Figure ~ 16 12 3 6 15 19 4c 32 26 5 8 31 37 4e 6 64 54 9 10 63 73 4g 7 128 116 11 14 127 139 4i Figures 5 and 6 will now be described where n is selected as 4 bits/baud. The 4 bits in each baud are provided to the register 20 o a microprocessor 14.
It may be here noted that for bauds of four bits, n=16 tl-at is each b.-ud or group represents one of 16 poss;hle values. It should also be noted that the lowest value for K hexagonally arranged message points (K>2n) is 19 where there is a point at the origin and 60 symmetry (See Figure 4c).
With K=l9 and 2n = 16 it will be notecl that 13 of the 2n possible 1() baud or group values may be a class in one-to-one correspondence with message points while the remaining 3 of the baud values outside the class will each correspond to two of the K message points, makin~ up a total of 19. In Figure 4c the 13 solicl ones of the message points are those in one-to-one correspondence with a class of values consisting of a corresponding number of baud or group values while the 6 message points which are outlined only, comprise 3 pairs with each pair corresponding to one of the remaining 3 of the baud or group values.
Figure 6 is a flow chart showing the operations of microprocessor 14 and high speed processor 16.
The four bits in the register 20 of Figure 6 re~resent a number ,`~I, the baud or group value ot which may have 16 values from 0-15. These bits are scramblecl at 22 to produce another 4 bit value rls in accord with well known techniques.
Although such scrambler is commonly a hardware clevice, we prefer to use the availahle capacity of the microprocessor. The output o~ t1le scrambling provi~es at Register 24 Ms, a scramblecl binary number having 2n group values 0-15.
- 1.~ --2~
Cl is 12, and 13 (counting the ~ero position) is the number of the 2 group values in one-to-one correspondence to a message point.
The decision block 26 determines whether Ms is < 12 (i.e. whether it is in one-to-one correspondence with a message point). If this is so tllc numhcr Ms is sul)pliccl dircctly to decision block 36.
At decision block 26 if Ms > 12 then each group value of Ms will correspond to a pair of alternate message points.
~or Ms > 12, Ms is supplied to the "auxiliarY channel enabled"
block 28. When it is clesircd to use the Auxiliary Channel a switch (not shown) will usually enable the channel between blocks 30 and 31 and provide a signal 'Auxiliary Channel enabled' to decision hlock 2~.
Data to be sent to the auxiliary channel is supplied to storage 31 where it is retained in a queue for transmission in single bits when the auxiliary channel becomes ~ available. It is not relevant to the present description ; whether the auxiliary data is related to the main data sent along line lO or completely independent.
I~ no data is to be sent from thc Auxiliary data queue i.e. the Auxiliary Channel is not enabled, then the number Ms is supplied to block 36. If auxiliary data is to be sent the A~lxiliary Channel is enabled and a signal is sent to block 30 causing it to receive and ac]~llowledge the 1 or 0 which is the 'first-in-line' of the queued bits in Auxiliary Data Queue 31. (Auxiliary Data Queue 31 is designcd to receive binary data and to retain it in a queue and to supply it bit by bit to ~v~
operator block 30. The auciliary binary data may represent any binary data whether inclependent, related to the main channel data or to the transmission). The receipt by block 30 of the bit is acknowledged to block 31 to ready the next bit in the queue for subsequent transmission. By arbitrary convention it is decided that a "1" on the auxiliary channel will not change Ms while a 0 on the auxiliary channel will require a change. Accordingly, iE a "1" is present the decision block 32 sends the number Ms unchanged to block 36. If the auxiliary channel digit is a "~"
then the number ~2 (here 3) is added to Ms. The new Ma = Ms + 3 is supplied to decision block 36. Notc that where the auxiliary channel is disabled the transmitted data is equivalent to a constant binary ~. Note also that Ma can exceed the ran~e 0 to 2n-1 and hence requires an additional bit in its representation.
Decision block 36 is inserted since differential encoding is to be used to avoid the effects of phase ambiguities during transmission and because logic is simplified if such differential encoding is not carried out for Ms=0. ~ccordingly, ; decision block .~6~ if Ms=0 sends Ms forward to block 38. If ;20 Ms ~ 0 (and Ma ~ 0) Ms or Ma as the case may be is transmittecl to block 40 for conversion to coordinates defining the hexagonal message points.
Tllus, Eor example in Figure 4c the values of Ms have been assigned to the message points 0-12. While the assign-ment of a value for Ms to a message point could be arbitrary, the assignment is here chosen to agree with the logic used in Figure 5 where the lower Ms values (0-t2) in one-to-one correspondence with message points are assigned to message points on inner rings~
As will be noted, in the outer ring two message points (shown in outline only) corresponcl to each MS Va1UC from 13-15. For Ms>12 a "1" from Auxiliary Data Queue 15 leaves the number Ms unchanged at 13, 14 or 15 while for a "0" from Queue 15 tlle number MS will be augmented by 3 (C2) to be 16, 17 or 18. The message points for 16, 17, 18 are therefore one set of message points 13,14,15. ~igure 4c also shows sector divisions, Section 0, Sector 1 etc. After conversion at block 40 the message points are designated by sector and a number (1, 2 or 3 therein). Thus or the first two sectors in Figure 4c -the conversion will be :
Ms or Ma R(Sector) Q(No. in Sector) and so on, and where R is the sector number and Q is the position in the sector. Differential encoding is used so that a sector error in transmission will have no effect after 2 bauds.
~perations ~lock ~0 ;Ichicvcs:
Q + L(M-1)/6¦ de-termining a~ number corresponding to the l)osition of the signal point in the sector (wllere Q is the integral part of the quotient (M-1)/~)) R + tM-l) mod fi - determining the sector number ~z~
P + (P~R) mod 6 - where P is the sector number from the previous baud and MD ~ QX6tP~ giving a uniclue designation of the message point.
In fact, of the operations designated in box 40 a look up table is used to obtain the values QX6+1 and ~. P (where 0 < P < 6) is the sector number from the previous baud, allowing the calculation P + (P~R) mod 6.
It will be noted that, due to the differential encoding techniques used the sector locations of the message points are signalled as transitions from one sector to the next, for reconversion to locations at the receiver. In general reference in the application and claims herein such ~` signalling of transitions is considered as a signalling of locations since this is the information ultimately conveyed.
Accordingly, the number MD from block 40 (or ; Ms=0 from 36) is applied to look up table 38 to produce the X~M), Y(M) being the coordinates of the differcntially encoded message points for transmission. The X~r~l), Y~M) coordinates define message points which correspond to the intended 60 symmetry and spatial clistribution. Illat is X~M), Y~M) for P=0 will have counterpart points in the same relative position within the sector for P=l, 2J3J4 or 5 and the outer points in a sector will correspond to higher values of M.
The message points X~M), Y~M) may be converted to analogue values and moclulatecl Oll a carrier in thc manner of ; the DSB-QCM systems shown in Canadian Patent 985J376 and U.S.
Patent 3,955,141 here-tofore referrcd to. However, it is 21~3 . ~
preferred, in the signal processor o~ the preferred embodiment to calculate the values for the mocllllatecl 'in phase' and 'quadrature phase' carriers and convert the result in digital-to-analogue converter 17 for transmission on the communications link.
It will be notecl that all operations and decisions depicted in Figure 6 may equally be performed by hardware.
However, cost and space limitations at this time suggest the programming shown as the best mode.
Transmission on the transmission or communications link takes place to the receiver shown in Figure 7.
It is now proposed to discuss the receiver in accord with the invention. Before doing this it is noted that (excluding the reference to the inventive message point distribution), it is well known to provide receivers to convert message point coordinates modulated on a QCM channel to provide the encoded binary information from the transmitted coordinates. This is evidenced by the receiver designs disclosed in U.S. Paten~
Moreover the power requirements of the communications system will be less if the hexagonally arranged signal points are packed as closely as pos.-ible to the origin or point corresponding to ~ero signal amplitude for both coordinates on a Cartesian coordinate system. That is, the hexagonally arranged message points may be considered to be located on concentric rings about the origin and where nli availahle points on il ring (with the possible exception of several outer rings) are occupied. Although the extra K-2n message points provicle advantages inclependent of the symmetry and density of packing o~ the message poin~s, the principal advantages of the invention accrue when the message points are symmetrically arrangecl about the origin and densely packed outward therefrom and the aclvantageous use of the K-2n extra points will be principally discussed where such symmetry ancl dense packing are present.
The encocling ancl transmitting apparatus ia ~ _ 0~3 preferably designed so tha-t the inner message points relative to ~he origin are in one-to-one correspondence with the values of groups of n binary signals where 2 or more of the outer of the K message points correspond to others of th0 group values.
In this way, there are a plurality of outcr message points which are not used each time the corresponding binary value is to be transmitted, points in such plur;llity of outer message points may be usecl cyclically or in accord with anothcr rule. In any event, the outer points are used with less frequency than the inner and power savings are thus achieved; since in a optimally designe~ system the ener~y required to signal when using the outer points in the pattern will be greater than when using the inner points. The alternate message points corresponding to a digital value of a group of bina~y digits may be used cyclically to improve the symmetry of the collective transmission of sequential message points. The fact that alternate points are available corresponding to some of the group values allows transmission of extra lnformation since the method of selection of alternate point.s may he usecl for signalling. rhuS in accord with a prc-20 ferred arrangement of the invention a class of values comprising K-2 (K-2n) of the group values will be in one-to-one relationship with a corresponding number of the K message points but K-2n of the group values will each have two alternate corresponding message points. This allows the transmission of binary information on a channel additional to that represented by the dclta conveyed by the groups of n digits. Thus the additional binary information will not be regularly transmitted but must be queued for transmission whcnever onc o~ thc K-2 vallJcs outslde thc class is v~
to be transmitted. There are no practical 1imits to the type of binary information which may be sent on the additional channel thus provided. Thus the information transmitted on the additional channel may (for example) relate to the operation of the communications system, to the high speed transmission of the 2n groups or it may be indcpendcnt information.
It will be obvious that; while the advantages specified in the previous paragraph are easier to demonstrate where the hexagonally arranged points are densely packed about the origin and arranged in hexagonal or triangular symmetry;
that some of these advantages (namely the provision of an additional channel and low frequency use of some message points) also accrue when the dense packing and symmetry are absent.
Moreover thc prcsent invention allows the provision of novel message point distributions, determined by the coordinates transmitted by QCM modulation which continue to exhibit near optimum margins against both Gaussian noise and phase jitter as additional points are aclded. Further advantages of the invention are that the apparatus and method allows suppression of carrier and provide 60 or 120 symmetry.
In the drawings which illustrate a preferred embodiment of the invention :
~igure 1 is a schematic diagram having blocks referring to the functional requirements of a transmitter and a receiver for employment with the invention, Figures 2a - 2h show prior art message points mapped on a rectangular grid in the two dimensional Cartesian plane, Figures 3a-3f show prior art message points mapped (largely) on a triangular grid in the two dimensional Cartesian plane. (It should be noted that other message point distributions are known such as those described and compared in an article, "Digital Amplitude-Phase Keying with M-ary Alphabets" by Thomas, Weidner and Durrani, IEEE Transactions on Communications, Vol. COM-22, No. 2, February 1974)l Figures 4a-4j show signal structures of the invention mapped on -the Cartesian plane, Figure S is a schematic block diagram of the trarls~
mission end of a communications link including a signal processorl Figure 5 is on the same sheet as Figure 1, Figure 6 is a flow chart showing the opera-tions of the signal processor and microprocessor of Figure 5, Figure 7 is a schematic block diagram of the receiver end of a communications link including a signal processor, and microprocessor, Figure 8 is a flow chart showing -the operations of the signal processor and microprocessor of Figure 7, and Figure 9 shows the decision areas for received signals which were encoded in accord with the distribution of Figure 4c.
Figure 9 is on the same sheet as Figure.7.
Figure 1 schematically illustrates functional operations perLo 171~U 1~ a ~O~ UiliCat ons systems which would utilize the invention. The functional operations are not intended -to imply particular hardware or choices between analog-vs. digital modes, or hardware vs. software modes at any particular stage, ~2~2~
Thus as functionally illustrated in Figure 1 where, functionally, serial binary data is converted, at a serial to parallel converter, into groups of n digits. Such groups of n digits are encoded to provide the message point Cartesian coordinates for QC~1 modulation. A coordinate signal generator and a carrier generator provide the signals to create the modulated carriers which are combined and transmitted over the channel.
At the receiver the received signal is demodulated, conditioned and equalized and sent to the decision region selection device which rnakes the decision as to the message point coordinates.
Such 'Idecision coordinates" are supplied to the decoder which converts these coordinates into parallel data intended to correspond to the parallel data entered at the transmitter. The received parallel data is converted into serial data for trans-mission to the user. Circuitry for performing the above functions is well known to those skilled in the art and examples are disclosed in the Canadian and U.S. patents referred to.
Applicant's circuitry (the preferred form of which is discussed hereafter) provides a novel relationship between the n binary digit groups and the message points, less vulnerable to noise and phase jitter, and error and whicll allows symmetry, suppression of carrier and, in one alternative, the ability to transmit a~xiliary information. Applicant's preferred ernbodiment also reflects the advances in technology since the dates of the Canadian an{l U.S. patents referrecl to.
There is here discussed the relationship of the message ~oint coordin.ltes to the encoded binary information. In contrast with the prior art the total number of message points 2C~2~13 K employed in a si~nal structure th.lt is in accord with the invention will not be an integral power of 2 such as 8, 16, 32, etc., even though the number of bits to be transmitted per Cartesian coordinate pair is an integer n re~uiring at most ~1=2 message points. In fact the value of K will always ; exceed the value of ~. In a simplc cmbodiment of the invention at least one of the required M values will be identified with more than one of the K message points of the signal structure.
The reasons behind thc seleclion of K>M are firstly, that the total number of points lying on concentric rings is not a power of 2 for either of our type A or B structures, secondly, we desire the carrier signal be suppressed which is accomplished when the centre of the concentric rings is the centroid (centre of gravity) of the K signal points, and thirdly, we will desire to have 60 symmetry for type A
structures and 120 symmetry for type B structures when we anticipate the use of c1ifferential encoding in conjunction with these signal structures. By 'A type structures' we refer to an arrangement of message points having 60 symmetry and a point at the origin7 thus in thc optimllm arran~ement K~6I + 1 where I is any integer nnd is excmpliEiecl by l~igllres ~ta) (c~
(e) ~g) ~ It will be notcd that 60 ~hexagonal) symmetry can be achievecl ancl near optimum arrangement, by omitting thc ori~in point so that K=6I. Ilowever, discussions of the preferred embodiment refer to K=6I ~ 1 arrangements.) By 'B type structures' we refer to 120 symmetry with no points at the origin and K=3I as exemplified by Figures ~(b)(cl)(f)~h)~j).
~Q~3 .~ote that differential encocling is very desirable since techniques which derive a carrier from the received data signal, the carrier being fully suppressed, are generally ambiguous in phase and when there is substantial 60 or 120 symmetry of the signal structure there can be 60 or 120 ambiguity in the recovered carrier.
With differential encoding, information is trans-mitted in terms of the possible transitions from past trans-mitted signal points to now transmitted signal points. In our case, with K>M, there are K possible transitions and at least two different transitions can convey the same information.
Leaving aside likely use of differential encoding and decoding, consider the signal structure shown in Figure 4a which has a total of K = 13 signal points and where the locations of the seven innermost points are shown by solicl dots and six outer points are marked with small circles. In this case we presume that M = 8 and that 7 of the M points are to be ; associated with the inner 7 points and the eighth of the M points will be associated with any of the outmost 6 points. Indeed, in successive occurrences of the neecl to transmit the 8th of the ~l points the fi outer points will be use(l in turn so that each will occur with a frecluency th.lt is l/fi of the frequency of each of the 7 inner points. Thus when calclll.lting the signal energy only one outer point neecl be incluclecl in the calculation. (The 6 outer points may l)e usecl in turn in cyclic order but for many applications the 6 outer points will be used in a pseuclo ranclom manner due to the differential encoding).
_ ~ _ ``` ~Z~ 33 Signal sets can be comparecl on the basis of the average required energy, under the assumption that in each set the minimum distance between points in the set is 2 units in each case and further the rectangular system points are assumed to have integral coordinates. A lower average energy for a given minimum separation results in an improved signal -to noise performance.
As a result the average energy E, for the signal structure shown in Figure 4a will have the value 4.5 versus, for example a value of 5.5 for the prior art structure of Figure 2b where each signal point is chosen from a rectangular grid and each signal point is assumed to occur with the same frequency.
In other figures such as Figure 4c the situation is slightly more complicatcd. Ilere there are a total of K = 19 points and we assume M = 16. In this case a chosen 3 of the ~1 values will each be associated with pairs of the six outer points. Each of the paired outer points will be used in turn so that outer points will occur with 1/2 the frequency that inner points occur, (in one ~lternatc of thc preferred cmbodiment ~he selection of alternates will be in accord with auxiliary channel binary signals). Thus only 3 of the six outer points will enter into the energy calculation giving the rcsult E = 9.
In contrast the 16 point signal structure of Figure 2d results in E = 10 and the structure of Figure 2c in E a 13~5~
Although use of the invention provides for a "good"
selection of signal points, differential encoding becomes more complex as does the detection and decoding processes. In the Type A and Type B codes it is advantageous to use the extra message points in a statistically cqu;ll manner tha~ preserves the 120 and 60 symmetries respectively required. In accord with preferred techniqucs using the invcntion, it may be notcd that differential encoding may be uscd to providc the statisti-cally equal usage. In the preferred embodiment~ the extra message points are selected on a basis that provides an extra signrllling channel.
Type A codes present with regard to differential encoding a complication since there is no angle associated with the central point. This case can be treated by "remembering"
in the encoder the last signal poin~ that was not a central point that was transmitted, whenever a central point is transmitted.
There is also an advantage that can be derived when K>~l. It is possible, through varying the pattern of the statistically equal usage of the extra ~oints, to transmit auxiliary information. This ability can be enhanced by delibe-rately increasing K over the minimum value that would be ; necessary to provide symmetry.
It should be noted that the extra points need not be chosen entirely or partly from an outer ring but can be any of the K points. However, to minimize average energy requirements, points which are less frequently used should be outer rather thrln inncr l)oints.
It should be noted that none of the prior a-rt of Figures 2 and Figures 3 employ signal points at the centre of the signal structure and none employ extra signal points.
In summary as greater datrl transmission rates are employed over telephone channels it becomes more and more important to utilize better performing signal structures even although they are more complex to irnplement.
In ~igure 5 it is shown that a scries of binary signals, for transmission along the communications lin~, are sent to the circuitry along line 10 to a serial-to-parallel converter 12 which converts the infor~ation into output bauds of n binary digits. After processing in the microprocessor 14 and high speed processor 16 as discusscd in connection with Figure 6J the rcsultant signals arc convcrtcd at digital-~o-analogue converter 17 for the transmitter channel interface and transmission along the channel.
The apparatus and procedures of Figures 5 and 6 are operable with n bits per baud where n is 2 or greater.
Figures 4a, 4c, 4e, 4g and 4i represent message point dis-tributions which may be achieved with the apparatus and methods of Figures 5 and 6 for n = 3,4,5,6 and 7 respectively.
The processors 14 and 16 and the flow chart of Figure 6 are more easily discussed in detail using a specific value of bits per baud. Before commencing such description it is desired to set out certain constant values Cl, C2, C3, C4, for n bits/baud where n = 4,5~6 or 7. The usage of these '() constant values will be discllsscd herea~ter.
Thus thc table below givcs valucs for use of the preferred processors and the flow chart of Figure 6 for n = 4,5,6 and 7.
n M Cl C2 C3 C4 K (message Shown in (hits/baud) points) Figure ~ 16 12 3 6 15 19 4c 32 26 5 8 31 37 4e 6 64 54 9 10 63 73 4g 7 128 116 11 14 127 139 4i Figures 5 and 6 will now be described where n is selected as 4 bits/baud. The 4 bits in each baud are provided to the register 20 o a microprocessor 14.
It may be here noted that for bauds of four bits, n=16 tl-at is each b.-ud or group represents one of 16 poss;hle values. It should also be noted that the lowest value for K hexagonally arranged message points (K>2n) is 19 where there is a point at the origin and 60 symmetry (See Figure 4c).
With K=l9 and 2n = 16 it will be notecl that 13 of the 2n possible 1() baud or group values may be a class in one-to-one correspondence with message points while the remaining 3 of the baud values outside the class will each correspond to two of the K message points, makin~ up a total of 19. In Figure 4c the 13 solicl ones of the message points are those in one-to-one correspondence with a class of values consisting of a corresponding number of baud or group values while the 6 message points which are outlined only, comprise 3 pairs with each pair corresponding to one of the remaining 3 of the baud or group values.
Figure 6 is a flow chart showing the operations of microprocessor 14 and high speed processor 16.
The four bits in the register 20 of Figure 6 re~resent a number ,`~I, the baud or group value ot which may have 16 values from 0-15. These bits are scramblecl at 22 to produce another 4 bit value rls in accord with well known techniques.
Although such scrambler is commonly a hardware clevice, we prefer to use the availahle capacity of the microprocessor. The output o~ t1le scrambling provi~es at Register 24 Ms, a scramblecl binary number having 2n group values 0-15.
- 1.~ --2~
Cl is 12, and 13 (counting the ~ero position) is the number of the 2 group values in one-to-one correspondence to a message point.
The decision block 26 determines whether Ms is < 12 (i.e. whether it is in one-to-one correspondence with a message point). If this is so tllc numhcr Ms is sul)pliccl dircctly to decision block 36.
At decision block 26 if Ms > 12 then each group value of Ms will correspond to a pair of alternate message points.
~or Ms > 12, Ms is supplied to the "auxiliarY channel enabled"
block 28. When it is clesircd to use the Auxiliary Channel a switch (not shown) will usually enable the channel between blocks 30 and 31 and provide a signal 'Auxiliary Channel enabled' to decision hlock 2~.
Data to be sent to the auxiliary channel is supplied to storage 31 where it is retained in a queue for transmission in single bits when the auxiliary channel becomes ~ available. It is not relevant to the present description ; whether the auxiliary data is related to the main data sent along line lO or completely independent.
I~ no data is to be sent from thc Auxiliary data queue i.e. the Auxiliary Channel is not enabled, then the number Ms is supplied to block 36. If auxiliary data is to be sent the A~lxiliary Channel is enabled and a signal is sent to block 30 causing it to receive and ac]~llowledge the 1 or 0 which is the 'first-in-line' of the queued bits in Auxiliary Data Queue 31. (Auxiliary Data Queue 31 is designcd to receive binary data and to retain it in a queue and to supply it bit by bit to ~v~
operator block 30. The auciliary binary data may represent any binary data whether inclependent, related to the main channel data or to the transmission). The receipt by block 30 of the bit is acknowledged to block 31 to ready the next bit in the queue for subsequent transmission. By arbitrary convention it is decided that a "1" on the auxiliary channel will not change Ms while a 0 on the auxiliary channel will require a change. Accordingly, iE a "1" is present the decision block 32 sends the number Ms unchanged to block 36. If the auxiliary channel digit is a "~"
then the number ~2 (here 3) is added to Ms. The new Ma = Ms + 3 is supplied to decision block 36. Notc that where the auxiliary channel is disabled the transmitted data is equivalent to a constant binary ~. Note also that Ma can exceed the ran~e 0 to 2n-1 and hence requires an additional bit in its representation.
Decision block 36 is inserted since differential encoding is to be used to avoid the effects of phase ambiguities during transmission and because logic is simplified if such differential encoding is not carried out for Ms=0. ~ccordingly, ; decision block .~6~ if Ms=0 sends Ms forward to block 38. If ;20 Ms ~ 0 (and Ma ~ 0) Ms or Ma as the case may be is transmittecl to block 40 for conversion to coordinates defining the hexagonal message points.
Tllus, Eor example in Figure 4c the values of Ms have been assigned to the message points 0-12. While the assign-ment of a value for Ms to a message point could be arbitrary, the assignment is here chosen to agree with the logic used in Figure 5 where the lower Ms values (0-t2) in one-to-one correspondence with message points are assigned to message points on inner rings~
As will be noted, in the outer ring two message points (shown in outline only) corresponcl to each MS Va1UC from 13-15. For Ms>12 a "1" from Auxiliary Data Queue 15 leaves the number Ms unchanged at 13, 14 or 15 while for a "0" from Queue 15 tlle number MS will be augmented by 3 (C2) to be 16, 17 or 18. The message points for 16, 17, 18 are therefore one set of message points 13,14,15. ~igure 4c also shows sector divisions, Section 0, Sector 1 etc. After conversion at block 40 the message points are designated by sector and a number (1, 2 or 3 therein). Thus or the first two sectors in Figure 4c -the conversion will be :
Ms or Ma R(Sector) Q(No. in Sector) and so on, and where R is the sector number and Q is the position in the sector. Differential encoding is used so that a sector error in transmission will have no effect after 2 bauds.
~perations ~lock ~0 ;Ichicvcs:
Q + L(M-1)/6¦ de-termining a~ number corresponding to the l)osition of the signal point in the sector (wllere Q is the integral part of the quotient (M-1)/~)) R + tM-l) mod fi - determining the sector number ~z~
P + (P~R) mod 6 - where P is the sector number from the previous baud and MD ~ QX6tP~ giving a uniclue designation of the message point.
In fact, of the operations designated in box 40 a look up table is used to obtain the values QX6+1 and ~. P (where 0 < P < 6) is the sector number from the previous baud, allowing the calculation P + (P~R) mod 6.
It will be noted that, due to the differential encoding techniques used the sector locations of the message points are signalled as transitions from one sector to the next, for reconversion to locations at the receiver. In general reference in the application and claims herein such ~` signalling of transitions is considered as a signalling of locations since this is the information ultimately conveyed.
Accordingly, the number MD from block 40 (or ; Ms=0 from 36) is applied to look up table 38 to produce the X~M), Y(M) being the coordinates of the differcntially encoded message points for transmission. The X~r~l), Y~M) coordinates define message points which correspond to the intended 60 symmetry and spatial clistribution. Illat is X~M), Y~M) for P=0 will have counterpart points in the same relative position within the sector for P=l, 2J3J4 or 5 and the outer points in a sector will correspond to higher values of M.
The message points X~M), Y~M) may be converted to analogue values and moclulatecl Oll a carrier in thc manner of ; the DSB-QCM systems shown in Canadian Patent 985J376 and U.S.
Patent 3,955,141 here-tofore referrcd to. However, it is 21~3 . ~
preferred, in the signal processor o~ the preferred embodiment to calculate the values for the mocllllatecl 'in phase' and 'quadrature phase' carriers and convert the result in digital-to-analogue converter 17 for transmission on the communications link.
It will be notecl that all operations and decisions depicted in Figure 6 may equally be performed by hardware.
However, cost and space limitations at this time suggest the programming shown as the best mode.
Transmission on the transmission or communications link takes place to the receiver shown in Figure 7.
It is now proposed to discuss the receiver in accord with the invention. Before doing this it is noted that (excluding the reference to the inventive message point distribution), it is well known to provide receivers to convert message point coordinates modulated on a QCM channel to provide the encoded binary information from the transmitted coordinates. This is evidenced by the receiver designs disclosed in U.S. Paten~
3,955,141 and Canadian Patent 985,356.
~20 It is proposed to discuss the receiver o~ this invention operating with the novel message point arrangement here proposed.
rn ~igure 7 signals receivecl along che communications channel at interface 110 are sllppliecl to A/D converter 114 for conversion to dlgital signals. These digital signals are s~pplied to high speed signal processor 116 w}lere the signals are treated to provide demodulation, equalization etc~, in accord with well known techniques. Although it is within the scope of ~ ~ ~t~ ~
the invention for signc~ roce~sor llG to provide signals of the encoded Cartesian coordinates for later conveIsion into binary data, in this invention it is found preferable, because of the triangular grid distril)ution of thc message points, to provide zones (referred to as RGB coordinates in Figure 7) in triangular coordinates to a microproccssor 118 for dctcction as to the value of the n bit bauds or group transmitted. The values of the n bit bauds or groups transmitted are then converted from parallel to serial form in converter 120. The ]0 microprocessor 11~, as hereinafter explained, also extracts the auxiliary channel data as part of its operation.
In thc higi~ speed sign.ll proccssor 116 demodulation, equalization and conditioning are performed in a manner well known to those skilled in the art.
The high speed signal processor 116 might have been designed in accord with conventional techniques, as in the apparatus in the Canadian and U.S. patents referred to, to convert the quadrature code signals into Cartesian values. However the signal processor, in accord with the invention is designed to convert by a si~ple conversion formula Cartesian coordinates into coordinates at 0, 60 and 120 clockwise from the Y axis (called Red, Blue, Green, respectively) with each coordinate reprcsenting a zone bcing the area bctwccn adjaccnt triangular grid lines perpendicular to the respective Red, Blue or Green axes. Figure 9 shows the decision areasl defined by the dccision hound.lry lincs, corrosl~onding to thc mcssagc points oP Figure ~c. A result from the high speed signal processor 116 that the coordinates received defined in the areas corresponding ~21~2~3 to zones Red 0, Green 0 and Blue 1 is indicated on Figure 9 as the shaded triangle of Figure 9 and one which the decision apparatus (in the microprocessor) will decide is message point 1. It will also be noted that since it is zones rather than lines which are defined, only the integral part of the con-verted Red, Green, Blue values need be transmitted to the micro-processor. It will further be noted that once any two of ~he zones are defined - here Red 0 and Green 0 - the only remaining ambiguity is between the two triangles comprising the rhombus defined by the red and green zones so that the Blue information may be confined to whether it is even or odd. This Red -Blue - Green information is provided to the microprocessor.
The information provided to the microprocessor as lndicated in box 122 of Figure 8 is (Red Zone No. + C3) X-;
(C3 = 6 in the version using the message points of Figure 4c) Green Zone No. + C3 and Blue Zone No. mod 2 (i.e. whether blue is even or odd).
The result is comhined in box 124 to provide the numher I which, in the microprocessor may be used in a look up table to get the message point value M. For M=0, tlle number is supplied directly to the unscrambler For M ~ 0 box 128 performs the operations indicated to perform the differential de-encoding. The decodcd MJ correspondin~ to Ms or Ma at the transmitter, is applied to decision box 130. For M < Cl ~here Cl = 12) no auxiliary data is signalled and the Ms ~2~2~
value is supplied to the unscrambler 140. For M > Cl the decision is macle at 132 whether M ~ (4 ~here 15). If M < C4 then a binary 1 is sent to the au~iliary binary data inter-face (or channel) inclicated at 138. If M > C4 then a binary 0 is sent to the auxiliary binary data interface or channel and M is reduced by C2. On either decision at block 132 the value Ms or Ma is supplied to the unscrambler 140 to provide the value M for the parallel to serial converter 120. The unscrambler 140 of course reverses the scrambling performed at the scrambler 22 of the transmitter so that the original information is recovered.
As previously stated the table previously set out For 4-7 bits/baud covers the values of M, K rmessage point~, Cl, C2, C3 and C4.
It will be noted that although the drawings show a single transmitter at one end of a transmission link and a single receiver at the other, that in fact each end of the lin~
will customarily include a transmittcr and receiver in the form of a MO~EM for two way transmission. Thus the high speed ~20 processor at the transmitter will typically be the same one acting, at the same end as the high specd proccssor of the receiver.
It will be noted that the paired message points ~thosc shown in outline only) For thc altcrn;ltivcs in ligures 4e ancl ~i do not themsclves displ.ly 60 symmctry ~although the collection of points as a whole does). Ilowever, this lack of 60 symmetry in the paired points does not affect the 60 symmetry so far as transmission is concerned bcc.luse of the effect of the differential encoding.
~ I _ ~2C~
The specific embodiment deals with the use of the excess K-2 points for signalling or providing an auxiliary channel. As stated earlier the poir.ts may be used for other purposes, for example merely to achieve lower frequency use of outer message points requiring higl-er signalling power. Statisti-cally even distribution is achieved to approximate symmetry and elimination of carrier because of the differential encoding.
The examples in Figures 4a, c, e, g, i, show message point distributions on a regular triangular grid having symmetry.
The examples in ligures 4b, cl, f, h, j, show message point distributions on a regular triangular grid having 120 symmetry. Although such symmetry may not be as advantageous as 60 symmetry it does provicle the advantages of the invention accuring from the superiority of use of points on a triangular grid and the provision of K>2 points.
These message points distributed as illustrated in Pigures 4b, 4d, 4f, 4h, 4j, show clistributions having only 120 symmetry and no point at the origin but having the advantages discussed for signals representing the coordinates on an equilateral triangular grid for K>2 . On the ligures last listed M=2n is set Ollt as well as K.
It will be appreciated that it is wcll within the abilities of those skilled in the art to convert binary signals in groups of n into the coorclinates of the message points illustrated in Figures 4b, 4d, 4f, 4h, 4j; and at the receiver to convert them back to the hinary cligits encoded all in accord with the techniques cliscussecl herein.
These distributions differ in that special consideration of the point of ori~in may be omitted and that there are only three sectors in ~lace of six and therefore ~dulo three calculations should replace the modulo six calculations.
. 23 -
~20 It is proposed to discuss the receiver o~ this invention operating with the novel message point arrangement here proposed.
rn ~igure 7 signals receivecl along che communications channel at interface 110 are sllppliecl to A/D converter 114 for conversion to dlgital signals. These digital signals are s~pplied to high speed signal processor 116 w}lere the signals are treated to provide demodulation, equalization etc~, in accord with well known techniques. Although it is within the scope of ~ ~ ~t~ ~
the invention for signc~ roce~sor llG to provide signals of the encoded Cartesian coordinates for later conveIsion into binary data, in this invention it is found preferable, because of the triangular grid distril)ution of thc message points, to provide zones (referred to as RGB coordinates in Figure 7) in triangular coordinates to a microproccssor 118 for dctcction as to the value of the n bit bauds or group transmitted. The values of the n bit bauds or groups transmitted are then converted from parallel to serial form in converter 120. The ]0 microprocessor 11~, as hereinafter explained, also extracts the auxiliary channel data as part of its operation.
In thc higi~ speed sign.ll proccssor 116 demodulation, equalization and conditioning are performed in a manner well known to those skilled in the art.
The high speed signal processor 116 might have been designed in accord with conventional techniques, as in the apparatus in the Canadian and U.S. patents referred to, to convert the quadrature code signals into Cartesian values. However the signal processor, in accord with the invention is designed to convert by a si~ple conversion formula Cartesian coordinates into coordinates at 0, 60 and 120 clockwise from the Y axis (called Red, Blue, Green, respectively) with each coordinate reprcsenting a zone bcing the area bctwccn adjaccnt triangular grid lines perpendicular to the respective Red, Blue or Green axes. Figure 9 shows the decision areasl defined by the dccision hound.lry lincs, corrosl~onding to thc mcssagc points oP Figure ~c. A result from the high speed signal processor 116 that the coordinates received defined in the areas corresponding ~21~2~3 to zones Red 0, Green 0 and Blue 1 is indicated on Figure 9 as the shaded triangle of Figure 9 and one which the decision apparatus (in the microprocessor) will decide is message point 1. It will also be noted that since it is zones rather than lines which are defined, only the integral part of the con-verted Red, Green, Blue values need be transmitted to the micro-processor. It will further be noted that once any two of ~he zones are defined - here Red 0 and Green 0 - the only remaining ambiguity is between the two triangles comprising the rhombus defined by the red and green zones so that the Blue information may be confined to whether it is even or odd. This Red -Blue - Green information is provided to the microprocessor.
The information provided to the microprocessor as lndicated in box 122 of Figure 8 is (Red Zone No. + C3) X-;
(C3 = 6 in the version using the message points of Figure 4c) Green Zone No. + C3 and Blue Zone No. mod 2 (i.e. whether blue is even or odd).
The result is comhined in box 124 to provide the numher I which, in the microprocessor may be used in a look up table to get the message point value M. For M=0, tlle number is supplied directly to the unscrambler For M ~ 0 box 128 performs the operations indicated to perform the differential de-encoding. The decodcd MJ correspondin~ to Ms or Ma at the transmitter, is applied to decision box 130. For M < Cl ~here Cl = 12) no auxiliary data is signalled and the Ms ~2~2~
value is supplied to the unscrambler 140. For M > Cl the decision is macle at 132 whether M ~ (4 ~here 15). If M < C4 then a binary 1 is sent to the au~iliary binary data inter-face (or channel) inclicated at 138. If M > C4 then a binary 0 is sent to the auxiliary binary data interface or channel and M is reduced by C2. On either decision at block 132 the value Ms or Ma is supplied to the unscrambler 140 to provide the value M for the parallel to serial converter 120. The unscrambler 140 of course reverses the scrambling performed at the scrambler 22 of the transmitter so that the original information is recovered.
As previously stated the table previously set out For 4-7 bits/baud covers the values of M, K rmessage point~, Cl, C2, C3 and C4.
It will be noted that although the drawings show a single transmitter at one end of a transmission link and a single receiver at the other, that in fact each end of the lin~
will customarily include a transmittcr and receiver in the form of a MO~EM for two way transmission. Thus the high speed ~20 processor at the transmitter will typically be the same one acting, at the same end as the high specd proccssor of the receiver.
It will be noted that the paired message points ~thosc shown in outline only) For thc altcrn;ltivcs in ligures 4e ancl ~i do not themsclves displ.ly 60 symmctry ~although the collection of points as a whole does). Ilowever, this lack of 60 symmetry in the paired points does not affect the 60 symmetry so far as transmission is concerned bcc.luse of the effect of the differential encoding.
~ I _ ~2C~
The specific embodiment deals with the use of the excess K-2 points for signalling or providing an auxiliary channel. As stated earlier the poir.ts may be used for other purposes, for example merely to achieve lower frequency use of outer message points requiring higl-er signalling power. Statisti-cally even distribution is achieved to approximate symmetry and elimination of carrier because of the differential encoding.
The examples in Figures 4a, c, e, g, i, show message point distributions on a regular triangular grid having symmetry.
The examples in ligures 4b, cl, f, h, j, show message point distributions on a regular triangular grid having 120 symmetry. Although such symmetry may not be as advantageous as 60 symmetry it does provicle the advantages of the invention accuring from the superiority of use of points on a triangular grid and the provision of K>2 points.
These message points distributed as illustrated in Pigures 4b, 4d, 4f, 4h, 4j, show clistributions having only 120 symmetry and no point at the origin but having the advantages discussed for signals representing the coordinates on an equilateral triangular grid for K>2 . On the ligures last listed M=2n is set Ollt as well as K.
It will be appreciated that it is wcll within the abilities of those skilled in the art to convert binary signals in groups of n into the coorclinates of the message points illustrated in Figures 4b, 4d, 4f, 4h, 4j; and at the receiver to convert them back to the hinary cligits encoded all in accord with the techniques cliscussecl herein.
These distributions differ in that special consideration of the point of ori~in may be omitted and that there are only three sectors in ~lace of six and therefore ~dulo three calculations should replace the modulo six calculations.
. 23 -
Claims (31)
1. Means for providing QCM signals to a transmission link, comprising:
means for receiving binary signals, means for converting groups corresponding to n of such binary signals having 2n possible group value into signals re-presenting a set of K signal message points each defined by Cartesian coordinate pairs where K>2n, the signal message points being substantially located at intersections on a regular equilateral triangular grid, where each message point corresponds to only one group value of the 2n possible values, and at least one of the 2n possible values corresponds to at least two message points, said converting means including means responsive to one of said at least one possible values for selecting at different times different ones of said at least two corresponding message points, said convering means being designed, responsive to a continuing random sequence of said binary signals, to utilize each of said K message points and to select message points corresponding to the at least one of the values, to substantially reduce the carrier component in said QCM signals, means responsive to said message point signals for providing a pair of quadrature carriers respectively modulated in accord with the coordinates of said signal message points.
means for receiving binary signals, means for converting groups corresponding to n of such binary signals having 2n possible group value into signals re-presenting a set of K signal message points each defined by Cartesian coordinate pairs where K>2n, the signal message points being substantially located at intersections on a regular equilateral triangular grid, where each message point corresponds to only one group value of the 2n possible values, and at least one of the 2n possible values corresponds to at least two message points, said converting means including means responsive to one of said at least one possible values for selecting at different times different ones of said at least two corresponding message points, said convering means being designed, responsive to a continuing random sequence of said binary signals, to utilize each of said K message points and to select message points corresponding to the at least one of the values, to substantially reduce the carrier component in said QCM signals, means responsive to said message point signals for providing a pair of quadrature carriers respectively modulated in accord with the coordinates of said signal message points.
2. Means as claimed in claim 1 where said K message points are arranged substantially in 120° symmetry.
3. Means as claimed in claim 1 where said K message points are arranged substantially in 60° symmetry.
4. Means as claimed in claim 1 where K-2(K-2n) of the group values are in one-to-one correspondence with signal message points.
5. Means as claimed in claim 2 where K-2(K-2n) of the group values are in one-to-one correspondence with signal message points.
6. Means as claimed in claim 3 where K-2(K-2n) of the values are in one-to-one correspondence with signal message points.
7. Means as claimed in claim 1 wherein the values in a class of group values selected from such 2n possible group values are each in one-to-one correspondence with a message point and where each of the group values outside said class corresponds to at least two of said message points, means for detecting the occurrence of a group value not included in said class, means responsive to such detection to determine between alternate corresponding message points, which message points coordinates are modulated on the carriers.
8. Means as claimed in claim 2 wherein each group value of a class of such 2n possible group values is in one-to-one corres-pondence with a corresponding message point and where each of the group values outside said class corresponds to at least two message points, means for detecting the occurrence of groups having values outside said class, means responsive to such detection to determine between alternate corresponding message points which message points coordinates are modulated on the carriers.
9. Means as claimed in claim 3 wherein each group value of a class of such 2n group values is in one-to-one correspondence with a corresponding one of said message points and where each of the group values outside said class corresponds to at least two of said message points, means for detecting the occurrence of a group having a value not included in said class, means responsive to such detection to determine between alternate corresponding message points which message points coordinates shall be sent.
10. Means as claimed in claim 7 wherein there are K-2(K-2n) group values in said class and each of the group values outside said class corresponds to two message points, means for detecting the occurrence of a group having a value outside said class, and means responsive to such detection to determine alternate corresponding message points which of the message point's coordinates corresponding to such value shall be modulated on the carriers.
11. Means as claimed in claim 8 wherein said first class consists of K-2(K-2n) group values and each of the group values outside said class corresponds to two message points, means for detecting the occurrence of one of the group values outside said class, and means responsive to such detection to determine which of the two message points corresponding to such group value shall be transmitted.
12. Means as claimed in claim 9 wherein there are K-2(K-2n) group values in said first class and each of the group values outside said class corresponds to two message points, means for detecting the occurrence of one of the group values outside said class, and means responsive to such detection to determine which of the two message points corresponding to such value shall be transmitted.
13. Means as claimed in claim 10 wherein auxiliary binary data is available for transmission, said means responsive to such detection being actuated in accord with the auxiliary binary data to signal a bit of auxiliary binary data by selection of one or the other of the alternate message points.
14. Means as claimed in claim 11 wherein auxiliary binary data is available for transmission, said means responsive to such detection being actuated in accord with the auxiliary binary data to signal a bit of auxiliary binary data by selection of one or the other of the alternate message points.
15. Means as claimed in claim 12 wherein auxiliary binary data is available for transmission, said means responsive to such detection being actuated in accord with the auxiliary binary data to signal a bit of auxiliary binary data by selection of one or the other of the alternate message points.
16. Means as claimed in claim 1 wherein said intersections may be considered as located on concentric rings and wherein said message points occupy substantially all available intersections on such concentric rings inward of the two outward occupied rings.
17. Means as claimed in claim 2 wherein said intersections may be considered as located on concentric rings and wherein said message points occupy substantially all available intersections on such concentric rings inward of the two outward occupied rings.
18. Means as claimed in claim 3 wherein said intersections may be considered as located on concentric rings and wherein said message points occupy substantially all available intersections on such concentric rings inward of the two outward occupied rings.
19. Means as claimed in claim 1 wherein a class of such 2n possible group values is in one-to-one correspondence with a corresponding number of said K message points and where each of the group values outside said class corresponds to at least two of said message points, wherein said K message points comprise substantially all locations on concentric rings on said equilateral triangular grid inward of the two outward occupied rings, and wherein message points corresponding to group values in said class are located on concentric rings which rings are not outward of the rings containing message points corresponding to group values outside said class.
20. Means as claimed in claim 2 wherein a class of such 2n group values is in one-to-one correspondence with a corresponding number of said message points and where each of the group values outside said class corresponds to at least two message points not included in said number, wherein said K message points comprise substantially all locations on said equilateral triangular grid on concentric rings inward of the two outward occupied rings, and wherein the message points corresponding to group values in said class are located on concentric rings inward of or on the same ring as message points corresponding to group values outside said class.
21. Means as claimed in claim 3 wherein a class of such 2n group values is in one-to-one correspondence with a corresponding number of said message points and where each of the group values out-side said class corresponds to at least two message points not included in said number, wherein said K message points comprise substantially all locations on concentric rings on said equilateral triangular grid inward of the two outward occupied rings, and wherein the message points corresponding to group values in said class are located on concentric rings inward of or on the same ring as message points corresponding to group values outside said class.
22. In a receiver for receiving QCM modulated signals wherein such modulated signals were encoded to represent the rectangular coordinates of signal points arranged at the intersection of lines on a regular equilateral triangular grid, means for deriving said rectangular coordinates from the received signal, means for converting said derived rectangular coordinates into sets of three signal values, each signal value being characteristic of a zone parallel to a different one of said triangular grid directions.
23. In a receiver as claimed in claim 22 including means for converting said set of three zone values into a group of binary digits.
24. Means for providing QCM signals to a transmission link, comprising :
means for receiving binary signals, means for converting groups corresponding to n of such binary signals having 2 possible group values into signals chosen from a set of K signal message points defined by Cartesian oordinate pairs where K>2n the signal message points being substantially located at intersections or a regular equilateral triangular grid, where each message point corresponds to only one group value of the 2n possible values, and each of the 2n possible values corresponds to at least one message point, means for differentially encoding each of said signals representing message points other than that at the centre of said grid to produce a signal also representing one of said message points, said converting means and said differential encoding means being collectively designed, responsive to a continuing random sequence of said binary signals to utilize each of said K signal points, and to select said message points to substantially reduce the carrier component in said QCM signals, means responsive to said message point signals for providing a pair of quadrature carriers respectively modulated in accord with the coordinates of said signal message points.
means for receiving binary signals, means for converting groups corresponding to n of such binary signals having 2 possible group values into signals chosen from a set of K signal message points defined by Cartesian oordinate pairs where K>2n the signal message points being substantially located at intersections or a regular equilateral triangular grid, where each message point corresponds to only one group value of the 2n possible values, and each of the 2n possible values corresponds to at least one message point, means for differentially encoding each of said signals representing message points other than that at the centre of said grid to produce a signal also representing one of said message points, said converting means and said differential encoding means being collectively designed, responsive to a continuing random sequence of said binary signals to utilize each of said K signal points, and to select said message points to substantially reduce the carrier component in said QCM signals, means responsive to said message point signals for providing a pair of quadrature carriers respectively modulated in accord with the coordinates of said signal message points.
25. Means as claimed in claim 24 where said K message points are arranged substantially in 120° symmetry.
26. Means as claimed in claim 24 where said K message points are arranged substantially in 60° symmetry.
27. Means as claimed in claim 24 wherein said inter-sections may be considered as located on concentric rings and wherein said message points occupy substantially all available intersections on such concentric rings inward of the two outward occupied rings.
28. Means as claimed in claim 25 wherein said inter-sections may be considered as located on concentric rings and wherein said message points occupy substantially all available intersections on such concentric rings inward of the two outward occupied rings.
29. Means as claimed in claim 26 wherein said inter-sections may be considered as located on concentric rings and wherein said message points occupy substantially all available intersections on such concentric rings inward of the two outward occupied rings.
30. Means as claimed in claim 25 wherein said message points, other than at the centre of said grid, are divided into three similar patterns each contained in a 120° sector, where said means for differential encoding is designed and constructed so that each differentially encoded message point has the same position in a sector as before differential encoding; and the sector number is the sum, modulo 3, of the sector numbers of the message point before differential encoding and of the previous message point after differential encoding.
31. Means as claimed in claim 26 wherein said message points, other than at the centre of said grid, are divided into six similar patterns each contained in a 60° sector, where said means for differential encoding is designed and constructed so that each differentially encoded message point has the same position in a sector as before differential encoding; and the sector number is the sum, modulo 6, of the sector numbers of the message point before differential encoding and of the previous message point after differential encoding.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411231A CA1202083A (en) | 1982-09-10 | 1982-09-10 | Means providing novel signal structures for qcm modulation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411231A CA1202083A (en) | 1982-09-10 | 1982-09-10 | Means providing novel signal structures for qcm modulation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1202083A true CA1202083A (en) | 1986-03-18 |
Family
ID=4123567
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000411231A Expired CA1202083A (en) | 1982-09-10 | 1982-09-10 | Means providing novel signal structures for qcm modulation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1202083A (en) |
-
1982
- 1982-09-10 CA CA000411231A patent/CA1202083A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP3078448B2 (en) | How to select a signal point sequence | |
| US4597090A (en) | Block coded modulation system | |
| US5408499A (en) | Multilevel code for transmission device | |
| JPH0810880B2 (en) | Multi-dimensional convolutional coded communication system | |
| CA1225743A (en) | Soft decision convolutional code transmission system | |
| US5105443A (en) | Inband coding of secondary data | |
| JP3088238B2 (en) | Improved multidimensional trellis coded communication system | |
| EP0540636B1 (en) | Coded qam system | |
| US4562426A (en) | Symbol coding apparatus | |
| EP0367093A3 (en) | Dc-free line code for arbitrary data transmission | |
| EP0154415B1 (en) | Coded modulation system | |
| CA2203899A1 (en) | Cyclic trellis coded modulation | |
| US4538284A (en) | Signal structures with data encoding/decoding for QCM modulations | |
| US5113412A (en) | Method and apparatus for mapping an eight dimensional constellation of a convolutionally coded communication system | |
| US4894844A (en) | Signal constellations | |
| EP0229923B1 (en) | Multilevel qam transmission system introducing supplementary signal points | |
| EP0209902B1 (en) | Multilevel modulator comprising a compact error correcting code producing unit | |
| CA1202083A (en) | Means providing novel signal structures for qcm modulation | |
| US5048056A (en) | Method and apparatus for mapping an eight dimensional constellation of a convolutionally coded communication system | |
| US4733401A (en) | Block coding into 24 coordinates and detection of transmitted signals | |
| EP0062435A1 (en) | Means providing novel signal structures for QCM modulation | |
| US4660213A (en) | Signal structure for data communication | |
| JP2723002B2 (en) | Uncoded level signal judgment circuit | |
| JPH0648830B2 (en) | Modulator | |
| JPH0795762B2 (en) | Multilevel QAM communication system |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |