Telecommunications – Receiver or analog modulated signal frequency converter – With wave collector
Reexamination Certificate
1998-05-29
2001-03-13
Hunter, Daniel S. (Department: 2684)
Telecommunications
Receiver or analog modulated signal frequency converter
With wave collector
C455S276100
Reexamination Certificate
active
06201955
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to communication devices, and in particular to the antenna and receiver portions of a communication device.
BACKGROUND OF THE INVENTION
The evolution of digital wireless communications has resulted in an array of communication devices that can wirelessly communicate both voice and data information. Among such products are handsets that are being marketed as today as personal communication systems. Such digital handsets may be used not merely for traditional telephony or two-way radio voice communications but also as radio frequency (RF) modems to wirelessly transmit or receive data communications.
One RF modem-type application of these handsets, or other digital wireless communication device, is to connect a handset or device to a data port of a personal computer and to use the handset or device to transmit data from the computer or to receive data transmissions that are broadcast to the computer. An example of such a use could be a utility company employee with a laptop computer transmitting information back to a central office from a remote location in the field and in turn receiving data or other communications from that central office. He could also wirelessly correspond with others and obtain whatever informational assistance he might need without ever having to leave the location at which he is working. In such an application, the wireless modem receives data from the personal computer through its interface with the computer. The modem then modulates that data into an RF signal. Once modulated, the data is then wirelessly transmitted by the modem. The wireless modem is also capable of receiving an RF signal that has been broadcast wirelessly from another data source, demodulating that RF signal, recreating the data that had been sent by the originating data source, and then transmitting that data to the personal computer to which that modem is connected.
A problem presented by such an application is wideband near-field electromagnetic interference that is generated by a personal computer. This interference can cause unacceptable degradation of the RF signal quality if a wireless RF modem is being used. One method of combating this problem is to use two-antenna diversity. Two-antenna diversity uses two antennas to receive a signal and then applies an optimization technique to improve the quality of the received signal over the performance that would be afforded by the use of a single antenna.
One of the simplest forms of two-antenna diversity is two-antenna selection diversity. As its name implies, this method involves selecting one of two antennas as the antenna that will be utilized as the receptor for a particular communication. There are several methods of making that selection. One involves choosing the antenna that has the highest received power. A major drawback to such a system is that it fails to discriminate between signal and interference power. To overcome that problem, J. C. Chang and N. R. Sollenberger proposed in “Burst Coherent Demodulation with Combined Symbol Timing, Frequency Offset Estimation, and Diversity Selection,”
IEEE Transactions on Communications,
Vol. 39, No. 7, July 1991, using a system that indirectly analyzes the clarity, or average opening, of the eye pattern in a QPSK (Quadrature Phase Shift Keying) digital modulation scheme. QPSK is one of many modulation schemes by which digital information is impressed upon an RF carrier by modulation of the carrier's amplitude, frequency, and/or phase. One can represent these modulation schemes as combinations of particular individual points, or constellations, in a complex two-dimensional plane, each point, or symbol, representing one or more data bits and each point being defined by its amplitude and phase location in the complex plane. When an RF carrier is demodulated and sampled at its optimum sampling time, each sample should yield an amplitude and phase measurement that maps to one of the points predesignated by that modulation scheme. Interfering signals and noise can introduce variations in these amplitude and phase measurements, moving the sampled point away from the predesignated points and inserting ambiguity into the determination of which symbol was intended. The eye pattern is a complex plane representation of these measured samples, and the clarity of the eye pattern is an indication of the degree of precision by which the sampled points can be mapped to the predesignated symbols.
In general terms, Chang and Sollenberger propose choosing the antenna that produced the clearest eye pattern. However, they had to come up with a system to estimate its clarity since it would be impractical to actually observe the eye pattern. Their system searches for the optimal sampling point of the signal from an antenna by taking K (k=1, . . . , K) samples of each of N (n=1, . . . , N) symbols in a data burst (a string of symbols). These samples are then split into an in-phase component (I(n,k)) and a quadrature component (Q(n,k)) and mapped into vectors in the complex (I,Q) plane. The vectors from the kth sample of each of the N symbols are then added together to create K vector sums (of N vectors each). The ideal sampling point for that signal is then determined to be the sampling point that results in the maximum vector sum magnitude. This sampling point gives, on average, the highest “signal-to-impairment ratio (maximum eye-opening)” and the magnitude of its vector sum is a good measure of the quality of the signal from that antenna, according to Chang and Sollenberger.
Further improvement in the performance of the diversity system can be obtained by combining the signals from the two antennas rather than just selecting one or the other as the receptor. Amplitude and phase adjustments may be made to the signal from each antenna, or element, before the signals are combined. An adaptive antenna array is a diversity system that can make these adjustments and change its pattern in response to changes in the signal environment, seeking to optimize signal quality at the array output through a system of feedback control. Such systems are discussed in
Adaptive Antennas, Concepts and Performance,
by R. T. Compton, Jr., published by Prentice-Hall, Englewood Cliffs, N.J., 1988. A block diagram of a typical adaptive two-antenna array is shown in FIG.
1
. The adaptive antenna array includes two antennas,
102
and
104
, a summer
110
, a signal quality measurement block
112
, a weighter
114
, and mixers
106
and
108
which are located between each of the antennas
102
and
104
and their respective inputs to the summer
110
. In these systems, complex weights (amplitude and phase) set by the weighter
114
are applied in the mixers
106
and
108
to the signals from both antennas
102
and
104
before these signals are combined in the summer
110
. After combining there is some measure of the quality of the received signal, and via a system of feedback control these weights are readjusted until the quality measurements are optimized. One method of weight optimization discussed by Compton is based on a minimum mean square error concept. A block diagram illustration of a quality measurement block
112
utilizing this concept is shown in FIG.
2
. The receiver has a reference signal
204
to which it compares a correlated array output signal
202
. An error signal
208
is generated and the weighter
114
adjusts the weights to minimize this error signal
208
. Compton also discusses adjusting the weights to maximize the ratio of desired signal power to undesired interference plus noise power (SINR) at the output of the array but has no proposal of how to go about measuring this. See also “Signal Acquisition and Tracking with Adaptive Arrays in the Digital Mobile Radio System IS-54 with Flat Fading,” authored by J. H. Winters, in the November 1993 issue of
IEEE Transactions on Vehicular Technology,
Vol. 42, No. 4, pp. 377-384 (Winters proposes using the sequence of symbols in a frame that are sent for synchronization pu
Jasper Steven C.
Makhlouf Isam R.
Hunter Daniel S.
Jacobs Jeffrey K.
May Steven A.
Motorola Inc.
Wyche Myron K.
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