Pulse or digital communications – Apparatus convertible to analog
Reexamination Certificate
1999-03-16
2002-05-07
Chin, Stephen (Department: 2734)
Pulse or digital communications
Apparatus convertible to analog
C375S269000, C375S273000, C375S298000, C375S308000, C332S103000, C332S144000, C455S069000, C455S108000, C455S110000
Reexamination Certificate
active
06385233
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to signal modulation strategies. More specifically, the present invention relates to utilizing unbalanced modulation to provide signals with different modulation energies to different users of a communication system.
Phase modulation (“PM”) is widely used in communication systems. In phase modulation schemes, data is encoded in either the absolute phase of the waveform or by changes in the phase of the waveform. One reason for the popularity of PM is the robustness of PM with respect to additive white Gaussian noise. Common examples of PM include Binary Phase Shift Keying (“BPSK”), Quadrature Phase Shift Keying (“QPSK”), and Gaussian Minimum Shift Keying (“GMSK”).
QPSK, for example, represents two bits of information (which may assume a total of four different values) in every symbol. A symbol consists of a phase shift by one of four possible phase shift values. The phase shift values are typically chosen to be plus/minus 45 degrees and plus/minus 135 degrees. QPSK systems in which the phase shift values are such that there are 90 degrees between each resultant phase are referred to as balanced QPSK systems. A balanced QPSK approach is usually chosen because it minimizes the likelihood of confusion between any two of the four possible symbols.
As the demand for communication bandwidth rises, the concern over efficient use of available bandwidth similarly rises. Bandwidth efficiency concerns are sometimes addressed through relatively efficient modulation techniques, such as GMSK. Another technique for increasing the efficiency of bandwidth usage is cellular communication. In cellular communication, the physical area in which communication is to occur is divided up into many physical regions referred to as cells. A sub-band of the total system frequency bandwidth is allocated to each cell. In order to reduce cross-cell interference, sub-bands are generally allocated to the cells such that no adjacent cells utilize the same sub-band. However, the same sub-band may be allocated to many non-adjacent cells. Because the cells that share the same sub-band are not adjacent to each other, cross-cell interference is reduced.
One problem with past cellular systems, both satellite-based and terrestrial, results from the non-uniformity of antenna gain patterns. Signals destined for users located within a cell are generally modulated consistently from user to user. In addition, users located within a cell are generally serviced by the same downlink transmitter, which generates a set amount of signal power for all users in the cell. The signal generated by the transmitter is then sent through an antenna, which distributes the signal energy throughout the cell according to the antenna gain pattern. The highest antenna gain is typically at the cell center, and the lowest antenna gain is typically at the cell boundary. Thus, users near the cell center receive much stronger signals than users near the cell boundary. However, since users near the cell boundary are relatively close to neighboring cells, cross-cell interference is stronger near the cell boundary than near the cell center. Therefore, a stronger signal is actually desired near the cell boundary than near the cell center. However, past systems provide just the opposite.
Since the majority of cross-cell interference problems in a cell occur near the cell boundary, the cell boundary is where the poorest quality communication occurs. In order to compensate, the downlink transmission power level for an entire cell is typically set so that some minimum communication quality level is obtained near the cell boundary. This results in a large disparity in communication quality between the cell boundary and the cell center. While communication quality at the cell boundary meets some minimum requirement, the communication quality at the cell center greatly exceeds the minimum requirement. Thus, there is often a significant amount of energy wasted in communication with users near the cell center. In communication systems with limited power resources, particularly satellite communication systems, the resultant wasted energy is extremely detrimental.
A need exists for a method and apparatus to provide different effective signal energy levels to users within a cell or other area of coverage, depending on their respective needs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide different users of a communication system with different amounts of effective communication energy.
It is another object of the present invention to provide different users of a communication system with different amounts of effective communication energy using unbalanced modulation.
It is another object of the present invention to provide different users of a communication system with different amounts of effective communication energy using unbalanced quadrature phase shift keyed modulation.
It is yet another object of the present invention to provide users near the boundary of a cell in a cellular communication system with a different amount of communication energy than users near the center of the cell.
One or more of the foregoing objects is met in whole or in part by a preferred embodiment of the present invention, which provides a method and apparatus for providing users in a cell of a cellular communication system with different amounts of effective communication energy depending on their respective communication requirements. The method of the preferred embodiment determines the signal energy requirements for a particular user. A modulation strategy is then chosen which comprises high energy modulation components and/or low energy modulation components depending on the requirements of the user. The present invention provides an unbalanced quadrature phase shift keyed modulation strategy, in which the in-phase and quadrature components have unbalanced amplitudes. Once a particular modulation strategy is chosen for a communication, the transmitting entity and receiving entity are synchronized so that each knows which modulation strategy was chosen. The data to be communicated is then modulated and transmitted from the source to the destination, at which point the signal is demodulated and data decisions are made.
The apparatus of the preferred embodiment provides a data source, which supplies information to be sent from a source to a destination. A modulation controller is provided to determine the amount of effective communication energy required by the communicating entities and to decide upon the appropriate modulation strategy to supply that energy. An unbalanced modulator is provided which modulates the information according to the modulation strategy chosen by the modulation controller. The preferred unbalanced modulator is an unbalanced quadrature phase shift keying modulator. In one embodiment of the present invention, a timeslot controller is provided to balance TDMA timeslots and effective bit rate thereby ensuring that communication takes place in a timely manner.
REFERENCES:
patent: 4736170 (1988-04-01), Wu et al.
patent: 5093840 (1992-03-01), Schilling
patent: 5241565 (1993-08-01), Kloc et al.
patent: 5594454 (1997-01-01), Devereux et al.
patent: 5675611 (1997-10-01), Lehtinen et al.
patent: 5963870 (1999-10-01), Chheda et al.
patent: 6035209 (2000-03-01), Tiedemann, Jr. et al.
Ha Dac V.
McAndrews Held & Malloy Ltd.
TRW Inc.
LandOfFree
Unbalanced quadrature waveform does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Unbalanced quadrature waveform, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Unbalanced quadrature waveform will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2860020