GB2369942A

GB2369942A - Phase modulation

Info

Publication number: GB2369942A
Application number: GB0029615A
Authority: GB
Inventors: Mel Long
Original assignee: Ubinetics Ltd
Current assignee: Aeroflex Cambridge Ltd
Priority date: 2000-12-05
Filing date: 2000-12-05
Publication date: 2002-06-12
Also published as: WO2002047250A2; GB0029615D0; AU2002223880A1; WO2002047250A3

Abstract

A transmitted signal comprises two components which define a vector. Modulation of the signal entails rotating the vector. The new values of the components needed to represent a change in the rotation of the vector are calculated from the old component values and the desired rotation angle.

Description

SIGNAL PROCESSING The invention relates to signal processing and, in particular, to the modulation of information onto a signal destined for transmission.

A known type of transmitter transmits a signal having two components which together define a vector. The information conveyed by the transmitted signal is represented by a change in the angle of the vector about a notional origin. For example, a clockwise rotation of the vector can indicate the transmission of a bit having value logical one and an anti-clockwise rotation of the vector indicates the transmission of a bit having value logical zero (if the angle of the vector does not change from one instant to the next, then no information has been transmitted during that time). Thus, the data to be transmitted dictates the rotation of the vector.

Ordinarily, in a transmitter of the kind described above, the data to be transmitted is used to index a lookup table which outputs the corresponding values for the components forming the vector so as to impart the necessary rotation to the vector in accordance with the data encoding scheme.

One object of the invention is to provide improved signal modulation.

According to one aspect, the invention provides a method of modulating a signal representing a rotating vector comprising changing the signal by rotating the vector from its present position to a new position by calculating the new position from the old position and the rotation of the vector.

According to another aspect, the invention provides apparatus for modulating a signal representing a rotating vector comprising means for changing the signal by rotating the vector from its present position to a new position by calculating the new position from the old position and the rotation of the vector.

Thus, the invention provides for the calculation of changes in the vector without recourse to, and hence avoiding the disadvantages of, a lookup table (e. g. the consumption of relatively large amounts of memory).

The vector of the signal can be represented by two components, and a change in the vector can be calculated by using the present component values together with the desired angular rotation, 0, of the vector to calculate the new component values for the new vector position.

The new value of the first component can be calculated as the sum of the product of its

present value and sine 8 and the product of the present value of the second component and cosine 8. The new value of the second component can be calculated as the product of its present value and sine 0 subtracted from the product of the present value of the first component and cosine 6.

In a preferred embodiment, the invention is used to modulate information onto a signal destined for transmission.

The invention also extends to a program for causing data processing apparatus to modulate a signal in accordance with the methods described above.

By way of example only, an embodiment of the invention will now be described with reference to the accompanying figures, in which: Figure 1 is a signal space diagram illustrating the modulation scheme of a transmitted signal; and Figure 2 is a block diagram of a transmitter.

Referring now to Figure 1, the signal space diagram shows a transmitted signal represented by a vector 10. The vector 10 is shown relative to an in-phase (I) axis and quadrature (Q) axis. The vector 10 can be represented by a component 12 parallel to the I axis and a component 14 parallel to the Q axis. The transmitted signal comprises these I and Q components, and their magnitudes determine the location of the tip of vector 10 in the signal space diagram.

Data is modulated onto the transmitted signal by rotating the vector 10 about the I, Q origin. This means that the tip of vector 10 traces out a circular path 16 centred on the origin. If no data is to be transmitted, then the vector 10 does not rotate. If a bit of value logical 0 is to be transmitted, then the vector rotates anti-clockwise by a fixed increment 0 from its current position and the tip of vector 10 moves from point 18 to point 20. If a logical one is to be transmitted, then the tip of vector 10 rotates clockwise by the same amount, 0, to point 22.

The transmitter of Figure 2 uses the data encoding scheme described with reference to Figure 1. Processor 24 produces the data for transmission and supplies it to modulator 24 which modulates the data onto a signal comprised of I and Q components which is then transmitted from antenna 26. The modulator 24 adjusts the magnitudes of the I and Q components of the transmitted signal in accordance with the data to be transmitted. The I and Q components of the transmitted signal represent a vector, V=I+Q. Where the present state of the vector is V1+I1+Q1 the vector is rotated during data modulation to V2=l2+Q2.

The modulator 24 calculates the values I2 and Q2 from I, and Q, using the following equations: l2=I, sinO+Qjcos9 Q2=I]cos8-Qlsin8 0 is the rotation of the vector (a positive value indicating clockwise rotation and a negative value indicating anti-clockwise rotation).

Since the system calculates new values for the I and Q components from the current values of the I and Q components the system does not need to rely on a lookup table and avoids the associated memory consumption.

Claims

Claims 1. A method of modulating a signal representing a rotating vector comprising changing the signal by rotating the vector from its present position to a new position by calculating the new position from the old position and the rotation of the vector.
2. A method according to claim 1, wherein the signal comprises two components together representing the vector and the component values of the new position are calculated from the present component values using the angular rotation, 6, of the vector.
3. A method according to claim 2, wherein the new value of the first component is calculated as the sum of the product of its present value and sine 9 and the product of the present value of the second component and cosine 0.
4. A method according to claim 2 or claim 3, wherein the new value of the second component is calculated as the product of its present value and sine 0 subtracted from the product of the present value of the first component and cosine 0.
5. A method according to any preceding claim, wherein the rotation of the vector is determined by data which is to be conveyed by the signal.
6. A method of transmitting information by modulating the information onto a signal using the method of any preceding claim.
7. Apparatus for modulating a signal representing a rotating vector comprising means for changing the signal by rotating the vector from its present position to a new position by calculating the new position from the old position and the rotation of the vector.
8. Apparatus according to claim 7, wherein the signal comprises two components together representing the vector, and the means for changing the signal calculates the component values of the new position from the present component values using the angular rotation, 0, of the vector.
9. Apparatus according to claim 8, wherein the means for changing the signal calculates the new value of the first component as the sum of the product of its present value and sine 6 and the product of the present value of the second component and cosine 0.
10. Apparatus according to claim 8, wherein the means for changing the signal calculates the new value of the second component as the product of its present value and sine 0 subtracted from the product of the present value of the first component and cosine 0.
11. Apparatus according to any one of claims 7 to 10, wherein the rotation of the vector is determined by data which is to be conveyed by the signal.
12. Apparatus for transmitting information by modulating the information onto a signal using the modulating apparatus of any one of claims 7 to 11.
13. A program for causing data processing apparatus to perform the method of any one of claims 1 to 6.
14. A method of modulating a signal, substantially as hereinbefore described with reference to the accompanying figures.
15. A method of transmitting a signal, substantially as hereinbefore described with reference to the accompanying figures.
16. Apparatus for modulating a signal, substantially as hereinbefore described with reference to the accompanying figures.
17. Apparatus for transmitting a signal, substantially as hereinbefore described with reference to the accompanying figures.