Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-02-06
2002-10-08
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S562100
Reexamination Certificate
active
06463295
ABSTRACT:
FIELD OF INVENTION
This invention relates to the field of wireless communication systems and more particularly to controlling radiated RF power level during establishment of a call and on an ongoing basis in a cellular wireless system, such control of power using an estimate of the quality of a received angle-modulated carrier.
BACKGROUND OF THE INVENTION
In a wireless communication system, as a general rule, it is highly desirable that the minimum radiated radio frequency (RF) carrier power necessary to achieve a specified quality level of communications be used in order to conserve energy and, perhaps more importantly, in order to reduce interference with other users of a shared RF spectrum. With the increasing use of cellular wireless communication systems comprising a base station (BS) at each cell, and remote terminals (a remote terminal also is called a subscriber unit (SU) or a subscriber station) communicating with an assigned base station, the problem of interference between stations within a given cellular area, and between neighboring cells, requires intelligent interference management in order to more effectively use the allocated common RF bandwidth. Such interference management is the goal of power control. As a general rule, the minimum radiated RF power required for maintaining an acceptable quality of service should be used.
Two types of power control are necessary: initial power control, and ongoing power control. In initial power control, the goal is to initiate communications with the minimal level of power necessary to achieve an acceptable level of communications. Ongoing power control maintains minimum transmitted power usage on a link as the communication system changes over time by new links being formed while others are being established.
Initial Power Control
Several communications protocols are known for cellular systems, including, for example, the Personal Handiphone System (PHS) and the Global System for Mobile communications (GSM). Both use time division multiple access (TDMA) together with frequency division multiple access (FDMA) techniques. Such communications protocols all include protocols for call establishment, for example for a subscriber unit initiating communications to a BS, or a BS initiating communications with a SU. Some of these protocols may not include initial power control. There thus is a need in the art for an initial power control method that may be applied to an existing communication system without adversely impacting communication system protocols that are in existence.
Ongoing Power Control
Ongoing power control is the control of radiated power as the communication environment changes after initial communications is achieved. For example, when the radiated power is increased in a particular link between a SU and a BS in order to achieve an acceptable quality for the received signal, or for some other reason, such a change may cause unacceptable quality changes for other stations using either the same or adjacent channels. In addition, as new connections are established and on-going connections are disconnected, power assignments might change resulting in changes (for better or worse) in the quality of existing connections. For example, “excess quality” may result, implying that excess RF power is being used under the new conditions. Degraded quality also may be experienced, implying that some connections may require greater radiated RF power. Variations in propagation characteristics, atmospherics, and man-made interference can also cause changes that require adjusting RF power levels. This is the goal of ongoing power control.
Spatial division multiple access (SDMA) techniques are known in which the same “conventional channel” (i.e., the same frequency channel in a frequency division multiple access (FDMA) system, timeslot in a time division multiple access (TDMA) system, code in a code division multiple access (CDMA) system, or timeslot and frequency in a TDMA/FDMA system) may be assigned to more than one subscriber station. This is done by using an antenna array of several antenna elements at the base station, and on the uplink (communications from a subscriber unit to a base station), the signal from each antenna element is weighted in amplitude and phase by a receive weight (also called spatial demultiplexing weight), all the receive weights determining a complex valued receive weight vector which is dependent on the receive spatial signature of the remote user. The receive spatial signature (also called the receive manifold vector) characterizes how the base station array receives signals from a particular subscriber unit. On the downlink (communications from the base station unit to a subscriber unit), transmission is achieved by weighting the signal to be transmitted by each array element in amplitude and phase by a set of respective transmit weights (also called spatial multiplexing weights), all the transmit weights for a particular user determining a complex-valued transmit weight vector which also is dependent on the spatial signature of the remote user. When transmitting to several remote users on the same conventional channel, the sum of weighted signals is transmitted at the antenna arrays.
The weighting of the signals either on the uplink from each antenna element in an array of antennas, or on the downlink to each antenna element is called spatial processing herein. Spatial processing is useful even when no more than one subscriber unit is assigned to any conventional channel. Thus, the term SDMA shall be used herein to include both the true spatial multiplexing case of having more than one user per conventional channel, and the use of spatial processing with only one user per conventional channel to mitigate adjacent channel interference and adjacent cell interference, reduce the cellular frequency reuse factor, etc. The term channel shall refer to a communications link between a base station and a single remote user, so that the term SDMA covers both a single channel per conventional channel, and more than one channel per conventional channel.
Methods for determining spatial receive and transmit weight vectors are known in the art. See for example, U.S. Pat. No. 5,515,378 (issued May 7, 1996) and U.S. Pat. No. 5,642,353 (issued Jun. 24, 1997) entitled SPATIAL DIVISION MULTIPLE ACCESS WIRELESS COMMUNICATION SYSTEMS, Roy, III, et al., inventors; U.S. Pat. No. 5,592,490 (issued Jan. 7, 1997) entitled SPECTRALLY EFFICIENT HIGH CAPACITY WIRELESS COMMUNICATION SYSTEMS, Barratt, et al., inventors; U.S. patent application Ser. No. 08/735,520 (filed Oct. 10, 1996), entitled SPECTRALLY EFFICIENT HIGH CAPACITY WIRELESS COMMUNICATION SYSTEMS WITH SPATIO-TEMPORAL PROCESSING, Ottersten, et al., inventors; U.S. patent application Ser. No. 08/729,390 (filed Oct. 11, 1996) entitled METHOD AND APPARATUS FOR DECISION DIRECTED DEMODULATION USING ANTENNA ARRAYS AND SPATIAL PROCESSING, Barratt, et al., inventors (hereinafter “Our Demodulation Patent”); and U.S. patent application Ser. No. 08/948,772 (filed Oct. 10, 1997) entitled METHOD AND APPARATUS FOR CALIBRATING A WIRELESS COMMUNICATION STATION HAVING AN ANTENNA ARRAY, Parish, et al., inventors (hereinafter “Our Calibration Patent”), each of these incorporated herein by reference in their entirety, these patents or applications collectively referred to herein as “Our Spatial Processing Patents”. For example, in systems that use time division duplexing (TDD) so that uplink and downlink communications occurs over the same frequency (in a FDMA or a TDMA/FDMA system), a receive weight vector of receive weights determined on the uplink can be used to determine the required transmit weight vector of transmit weights for communications on the downlink from the base station to the same remote subscriber unit.
No practical methods of ongoing power control are known in the prior art that are applicable to systems using SDMA techniques, in that the power control methods can effectively adjust all of the SDMA system parameters required for minimizing the total radiated RF power wh
ArrayComm, Inc.
Blakely , Sokoloff, Taylor & Zafman LLP
Cong Le Thanh
Le Lana
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