Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
1999-04-20
2003-09-02
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S562100, C455S069000
Reexamination Certificate
active
06615024
ABSTRACT:
FIELD OF INVENTION
This invention relates to the field of wireless communication systems, and more specifically, to a method and apparatus for calibrating a communication station that includes an array of antenna elements.
BACKGROUND
Smart Antenna Systems
Antenna arrays may be used in any wireless communication receiver or transmitter or transceiver (herein under “communication station”) that transmits or receives radio frequency signals using an antenna or antennas. The use of antenna arrays in such a communication station provides for antenna performance improvements over the use of a single element antenna. These antenna performance improvements include improved directionality, signal to noise ratio, and interference rejection for received signals, and improved directionality, security, and reduced transmit power requirements for transmitted signals. Antenna arrays may be used for signal reception only, for signal transmission only, or for both signal reception and transmission.
A typical application of antenna array communication stations is in a wireless communication system. Examples include a cellular communication system consisting of one or more communication stations, generally called base stations, each communicating with its subscriber units, also called remote terminals and handsets. In cellular systems, the remote terminal may be mobile or in a fixed location, and when fixed, such a system often is called a wireless local loop system. The antenna array typically is at the base station. Terminology for the direction of communication comes from conventional satellite communication, with the satellite replaced by the base station. Thus, communication from the remote terminal to the base station is called the uplink, and communication from the base station to the remote terminal is called the downlink. Thus, the base station antenna array transmits on the downlink direction and receives on the uplink direction. Antenna arrays also may be used in wireless communication systems to add spatial division multiple access (SDMA) capability, which is the ability to communicate with several users at a time over the same “conventional” (FDMA, TDMA or CDMA) channel. We have previously disclosed adaptive smart antenna processing (including spatial processing) with antenna arrays to increase the spectrum efficiency of SDMA and non-SDMA systems. See Co-owned U.S. Pat. No. 5,515,378 for SPATIAL DIVISION MULTIPLE ACCESS WIRELESS COMMUNICATION SYSTEM, U.S. Pat. No. 5,592,490 for SPECTRALLY EFFICIENT HIGH CAPACITY WIRELESS COMMUNICATION SYSTEMS, U.S. Pat. No. 5,828,658 for SPECTRALLY EFFICIENT HIGH CAPACITY WIRELESS COMMUNICATION SYSTEMS WITH SPATIO-TEMPORAL PROCESSING, and U.S. patent application Ser. No. 08/729,390 for METHOD AND APPARATUS FOR DECISION DIRECTED DEMODULATION USING ANTENNA ARRAYS AND SPATIAL PROCESSING. Systems that use antenna arrays to improve the efficiency of communications and/or to provide SDMA sometimes are called smart antenna systems.
With smart antenna communication systems that use linear spatial processing for the adaptive smart antenna processing, during uplink communications, one applies amplitude and phase adjustments in baseband to each of the signals received at the antenna array elements to select (i.e., preferentially receive) the signals of interest while minimizing any signals or noise not of interest—that is, the interference. Such baseband amplitude and phase adjustment can be described by a complex valued weight, the receive weight, and the receive weights for all elements of the array can be described by a complex valued vector, the receive weight vector. Similarly, the downlink signal is processed by adjusting the amplitude and phase of the baseband signals that are transmitted by each of the antennas of the antenna array. Such amplitude and phase control can be described by a complex valued weight, the transmit weight, and the weights for all elements of the array by a complex valued vector, the transmit weight vector. In some systems, the receive (and/or transmit) weights include temporal processing, and then are called spatio-temporal parameters for spatio-temporal processing. In such cases, the receive (and/or transmit) weights may be functions of frequency and applied in the frequency domain or, equivalently, functions of time applied as convolution kernels. Alternatively, each convolution kernel, if for sampled signals, may itself be described by a set of complex numbers, so that the vector of convolution kernels may be re-written as a complex values weight vector, which, for the case of there being M antennas and each kernel having K entries, would be a vector of KM entries.
The receive spatial signature characterizes how the base station array receives signals from a particular subscriber unit in the absence of any interference or other subscriber units. A receive weight vector for a particular user may be determined using different techniques. For example, it may be determined from spatial signatures. It also may be determined from the uplink signals received at the antennas of the array from that remote user using some knowledge about these uplink signals, for example, the type of modulation used. The transmit spatial signature of a particular user characterizes how the remote user receives signals from the base station in the absence of any interference. The transmit weight vector used to communicate on the downlink with a particular user is determined either from the receive weight vector (see below under “The Need for Calibration”) or from the transmit spatial signature of the particular user and the transmit spatial signatures of the other users in such a way as to maximize the energy to the particular user and minimize the energy to the other users.
U.S. Pat. No. 5,592,490 for SPECTRALLY EFFICIENT HIGH CAPACITY WIRELESS COMMUNICATION SYSTEMS describes spatial signatures and their uses, and U.S. Pat. No. 5,828,658 for SPECTRALLY EFFICIENT HIGH CAPACITY WIRELESS COMMUNICATION SYSTEMS WITH SPATIO-TEMPORAL PROCESSING, incorporated herein by reference, describes how to extend this to spatio-temporal processing using spatio-temporal signatures.
Thus, while the description herein is provided in terms of spatial signatures, adding time equalization to provide spatio-temporal processing is easily accommodated, for example by adding the concepts of spatio-temporal signatures, which may be described by MK vectors (both uplink and downlink) when the temporal processing is using equalizers with K taps (i.e., convolution kernels of length K in the weight convolving functions). Thus, how to modify the invention to accommodate spatio-temporal processing and spatio-temporal signatures would be clear to those of ordinary skill in the art, for example in view of above-referenced and incorporated herein by reference U.S. Pat. No. 5,828,658. Therefore, those in the art would understand that any time the term spatial signature is used, this might indeed be referring to a spatio-temporal signature in the context that the invention is being applied to a communication station equipped with means for spatio-temporal processing.
The Need for Calibration
It is desirable to determine the transmit weight vector from the receive weight vector for a particular user. More generally, it is desirable to determine the appropriate transmit signals to use for transmitting to a particular user from signals received from that user. Practical problems may make difficult determining the transmit weight vector from the receive weight vector for a particular user. Frequency division duplex (FDD) systems are those in which uplink and downlink communications with a particular remote user occur at the different frequencies. Time division duplex (TDD) systems are those in which uplink and downlink communications with a particular remote user occur at the same frequency but in different time slots. In a TDD system, because of the well known principle of reciprocity, it might be expected that determining the transmit weight vector from the receive weight vector is straightfor
Barratt Craig H.
Boros Tibor
Trott Mitchell D.
Uhlik Christopher R.
ArrayComm, Inc.
Chin Vivian
Inventek
Moore James K
Rosenfeld Dov
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