Copyright © Philip M. Parker, INSEAD. Terms of Use.
| Year | Description |
| 1993 | Invention patented by Ian J. Dedic and Dominic C. Royce on May 26th, 1993. Abstract: In receiving apparatus of a digital communication system, a received signal burst is demodulated to produce inphase (I) and quadrature (Q) baseband signals which are digitized to provide a set of signal-value pairs for the burst. Each pair consists of an I-value and a corresponding Q-value. The modulation is such that the pairs, if plotted on a complex signal space (I-Q) diagram, would lie substantially on a common circle. To cancel DC offsets in the I and Q signal paths, the average I-value and average Q-value over the burst are found and subtracted respectively from the I- and Q-values of each signal-value pair, to shift the circle so the origin of the I-Q diagram lies within the circle. Then, to restore the DC content of the I and Q signals, the distances I.sub.i1, Q.sub.i2, I.sub.i3 and Q.sub.i4 of signal-value pairs from the I- or Q-axis are averaged in four regions of the I-Q diagram. The difference between the respective average distances for mutually-opposed regions is used to derive I- and Q-direction shift values which, if subtracted respectively from the I- and Q-values of each signal-value pair, would bring the centre of the circle closer to the origin. This can remove DC offsets accurately, whilst preserving the variable DC content of the received signal, in time periods consistent with the burst repetition rate in communication systems such as Global System for Mobile Communications (GSM), thereby permitting correct operation of an equalizer used to extract data from the I- and Q-values. |
| Source: selected by the editor from original sources. | |
Copyright © Philip M. Parker, INSEAD. Terms of Use.
