Telecommunications – Receiver or analog modulated signal frequency converter – With wave collector
Reexamination Certificate
1998-02-03
2001-05-01
Le, Thanh Cong (Department: 2684)
Telecommunications
Receiver or analog modulated signal frequency converter
With wave collector
C455S277200, C455S278100, C375S347000
Reexamination Certificate
active
06226507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to microcellular communications terminals utilizing at least two antennas for reception of a signal and, more particularly, to an apparatus and method for selecting between a plurality of antennas having unequal gains to receive such signal.
2. Description of Related Art
Antenna diversity is a commonly used technique to overcome the effects of fading, which is typically the dominant impairment in wireless communication. The most common methods of performing diversity combining are maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SC). It has been found, however, that MRC and EGC require the co-phasing of the signals from the antennas before combining, which is difficult in practice.
While diversity combining can be performed either before or after detection of a signal, pre-detection selection combining, or pre-selection diversity, is preferred since it requires a terminal to have only a single receive chain and is therefore less expensive. At the same time, it will be understood that the signal format must allow sampling (or receipt) of the signal on the antennas prior to reception. Thus, pre-selection diversity is more suited to systems with slotted modes of transmission (e.g., TDMA systems). It will also be noted that pre-selection diversity is appropriate only when the fading rates on the signal are low enough to assume that the sample of the channel obtained at the beginning of the slot is valid for the duration of the entire slot. An example of a diversity receiving system is disclosed in U.S. Pat. No. 5,361,404 to Dent, which is also assigned to the owner of the present invention and is hereby incorporated by reference herein.
Pre-selection diversity has been utilized previously, but this process of determining the best performer at a given time has involved antennas with equal gains. One concern with the use of antenna diversity in a microcellular communications terminal is that the second antenna typically has a smaller gain than the main antenna. This oftentimes stems from the second antenna being located internal to the terminal for aesthetic purposes, where a user's hand wrapped around the terminal serves to reduce the gain of such second antenna. Since large gain differentials have been experienced (e.g., up to 4 dB in some cases), they must be taken into account or the receiving system will almost always choose the antenna having the greater gain even if the carrier power/interference ratio from the antenna having the lesser gain would otherwise have been larger.
Accordingly, it is a primary object of the present invention to provide an apparatus and method for selecting between a plurality of antennas utilized by a microcellular communications terminal for reception of a signal when such antennas have unequal gains.
It is another object of the present invention to provide an apparatus and method for selecting between a plurality of antennas utilized by a microcellular communications terminal for reception of a signal using preselection diversity.
It is still another object of the present invention to provide an apparatus and method for selecting between a plurality of antennas utilized by a microcellular communications terminal for reception of a signal in which the gain difference between such antennas is determined and/or continuously updated.
Yet another object of the present invention is to provide an apparatus and method for selecting between a plurality of antennas utilized by a microcellular communications terminal for reception of a signal which takes into account noise and interference encountered by the antennas.
These objects and other features of the present invention will become more readily apparent upon reference to the following description when taken in conjunction with the following drawings.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, a method of selecting between a plurality of antennas utilized by a microcellular communications terminal for reception of a signal is disclosed, where a gain imbalance exists between the antennas. The method includes the steps of measuring the power of the signal received by each antenna and selecting one of the antennas for reception of the signal based on the measured power of the signal received by each antenna and the gain imbalance. This method also may include the steps of compensating for the gain imbalance between the antennas to derive a compensated signal power for each antenna, comparing the compensated signal powers of the antennas, and selecting the antenna having the greatest compensated signal power for reception of the signal. The method may further include determining and/or updating the gain imbalance between the antennas, as well as adjusting a gain imbalance factor applied to the measured signal power for each antenna depending on noise and interference encountered by the antennas.
In accordance with a second aspect of the present invention, an alternative method of selecting between a plurality of antennas utilized by a microcellular communications terminal for reception of a signal is disclosed where a gain imbalance exists between the antennas. This method includes the steps of receiving the signal by all the antennas concurrently, weighting the signals received by each antenna according to certain desired conditions, combining the signals received by each antenna, measuring the power of the combined signal received by the antennas for each weighted condition, and selecting one of the combined signals for reception of the signal based on the measured power of the combined signals received and the gain imbalance between the antennas. This method further includes the steps of compensating for the gain imbalance between the antennas to derive a compensated signal power for each combined signal, storing the compensated signal power for each combined signal, comparing the compensated signal powers for all the combined signals, and selecting the combined signal having the greatest compensated signal power for reception of the signal. The method may also include determining and/or updating the gain imbalance between the antennas, as well as adjusting the compensated signal power for each combined signal depending on noise and interference encountered by the antennas.
In accordance with a third aspect of the present invention, a receiver for a microcellular communications terminal is disclosed, wherein the terminal includes a plurality of antennas having different gains for receiving a signal. The receiver includes a circuit for measuring power of the signal received by each antenna, a control for selecting one of the antennas for reception of the signal after compensating for the gain differential between the antennas, and a switching device activated by the control which permits reception of the signal only from the selected antenna.
In accordance with a fourth aspect of the present invention, a receiver for a microcellular communications terminal is disclosed, wherein the terminal includes a plurality of antennas having different gains for receiving a signal. The receiver includes a circuit for measuring power of the signal received by the antennas and a control for weighting the reception of said signal by said antennas to provide a combined signal for certain desired conditions, said control selecting a combined signal which provides the greatest signal power taking into account the gain differential between said antennas.
In accordance with a fifth aspect of the present invention, a diversity receiving system for a microcellular communications terminal is disclosed as including at least two antennas of unequal gain for receiving a signal. A receiver for demodulating the signal is provided which includes a control for selecting prior to such demodulation which antenna to receive the signal based upon signal power of each antenna measured during receiving of the signal, wherein the measured signal power is modified by a ga
Chennakeshu Sandeep
Ramesh Rajaram
Cong Le Thanh
Davidson & Gribell, LLP
Ericsson Inc.
Nguyen Thuan T.
LandOfFree
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