Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2001-02-06
2004-02-24
Nguyen, Lee (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S067110, C455S446000
Reexamination Certificate
active
06697644
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to wireless communications and, more particularly, to wireless communication system communication link optimization.
BACKGROUND
In communication systems it is typically desired to provide at least a threshold level of service quality while maximizing system capacity. For example, in point to multipoint wireless communication systems, such as those commonly used in providing cellular telephone and personal communication services (PCS), subscribers generally require that a service provider provide communications having at least a minimum level signal quality, such as link quality equivalent to plain old telephone service (POTS), that service be available substantially all the time, e.g., limited number of blocked calls, and that communications be successfully completed, e.g., no dropped calls.
In wireless communication systems in particular communication quality and communication capacity often have an inverse relationship. For example, as communication capacity is increased, such as through more dense reuse of traffic channels, signal quality may be decreased, such as through each such traffic channel experiencing higher levels of interference energy. Accordingly, service providers must often balance providing desired levels of communication capacity with service quality issues.
In code division multiple access (CDMA) networks, for example, a number of communication signals are allowed to operate over the same frequency band simultaneously. Each communication unit is assigned a distinct, pseudo-random, chip code which identifies signals associated with the communication unit. The communication units use this chip code to pseudo-randomly spread their transmitted signal over the allotted frequency band. Accordingly, signals may be communicated from each such unit over the same frequency band and a receiver may despread a desired signal associated with a particular communication unit. However, despreading of the desired communication unites signal results in the receiver not only receiving the energy of this desired signal, but also a portion of the energies of other communication units operating over the same frequency band. Accordingly, CDMA networks are interference limited, i.e., the number of communication units using the same frequency band, while maintaining an acceptable signal quality, is determined by the total energy level within the frequency band at the receiver.
In order to provide reasonable capacity in the CDMA network, transmitted signals are often power controlled to reduce energy transmitted within the CDMA frequency band while maintaining sufficient power to provide an acceptable signal at a receiving unit. Through intelligent power control, excess energy within the service area may be limited and, therefore, signal quality improved and/or capacity increased.
Accordingly, in a cellular communication network, a base transceiver station (BTS) or the like, may operate to receive information from mobile units with respect to a received signal as experienced by the mobile unit in order to make determinations as to the transmit power level to be utilized in communications with this particular mobile unit. This is an example of closed control loop operation.
However, a problem that has been experienced in implementing such a closed loop system is that, in order for the control loop to perform correctly, typically a relatively large amount of information must be communicated in the reverse link, e.g., a mobile unit provides substantial data in the reverse link in order for the BTS to adequately and accurately control transmit power levels. Moreover, generally speaking, the better the desired performance, e.g., more the transmit power is optimized for experienced conditions, the more information which is required to be fed back. It should be appreciated that, when providing feedback information for the closed control loop operation, the control system is occupying resources of the reverse link. In a system in which communications are substantially symmetric, such as is typical in two way voice communication, utilization of reverse link capacity for transmission of information not directly associated with subscriber payload is often a critical concern. Accordingly, it is often desirable to minimize the use of reverse link capacity for such control loop operation.
Further capacity and/or signal quality improvement may be provided in communication systems, such as the aforementioned point to multipoint wireless communication systems, through the use of directional antenna beams in the communication links. For example, adaptive array antennas may be utilized to provide enhanced signal quality through advanced “beam forming” techniques as shown and described in the above referenced patent application entitled “Practical Space-Time Radio Method for CDMA Communication Capacity Enhancement.” For example, angle of arrival (AOA) information determined from a received signal at an adaptive array antenna may be utilized in accurately determining beam forming coefficients for use in the reverse link in order to provide improved capacity.
Although it is possible to estimate suitable forward link beam forming coefficients from corresponding reverse link beam forming coefficients, this solution does not always provide desired results. Specifically, this method relies upon a sufficiently high correlation between reverse link and forward link spatial structure. However, this is not always the case. For example, a difference in forward link and reverse link frequencies may result in there being insufficient correlation between the links. Additionally, the various multi-paths experienced in the two links may be significantly different.
A mobile unit might be adapted to accurately evaluate the forward link channel (spatial and temporal) in order to provide forward link channel information to a BTS for use in beam forming. However, there is a challenge in relaying this channel information to the serving BTS. Initially, it should be appreciated that current BTS infrastructure does not provide reverse link signaling adapted to communicate such information and, therefore, would require adaptation of the BTS systems as well as the mobile units. For example, the IS-95, GSM, and G3 interface standards provide very little reverse link capacity for such control signals. Moreover, as discussed above, it is desirable to minimize the use of reverse link capacity for control loop operation in order to provide desired subscriber payload capacity. Accordingly, the addition of forward link channel information to the aforementioned power control information, which itself is already consuming valuable reverse link capacity, is typically undesirable.
A need therefore exists in the art for systems and methods which allow for optimization of communication system capacity and signal quality without requiring an unacceptable amount of feedback information. A further need exists in the art for such systems and methods to provide forward link beam forming for optimized operation utilizing information with respect to evaluation of the forward link spatial channel by a receiving unit.
SUMMARY OF THE INVENTION
The present invention is directed to systems and methods which provide optimized communication links for communication conditions experienced by a plurality of subscriber units. For example, preferred embodiments of the present invention utilized in optimizing communication links in a cellular wireless communication system operate to control antenna beam width (e.g., antenna beam main lobe contour), length (e.g., antenna beam signal transmission power level), and/or direction (e.g., bore sight azimuthal and/or elevation orientation) selected and/or refined to thereby provide effective communications.
Although forward link characteristics may be optimized given enough feedback from mobile units, the amount of information required for accurate and adequate forward link channel optimization typically exceeds the reverse link capacity available for such uses. For exam
Scherzer Shimon B.
Tesler Alexander V.
Wong Piu Bill
Wu Jiangfeng
Fulbright & Jaworski L.L.P.
Kathrein-Werke KG
Nguyen Lee
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