Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-05-12
2002-12-31
Chin, Vivian (Department: 2682)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S442000, C375S148000, C375S150000
Reexamination Certificate
active
06501747
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to wireless communication systems, and in particular, to using adaptive antenna arrays in PCS and cellular CDMA networks for capacity enhancement.
2. Description of Related Art
A standard technique used by commercial wireless phone systems for increasing capacity is to divide the service region into spatial cells. Instead of using just one base station to serve all users in the region, a collection of base stations is used to independently service separate spatial cells. In such a cellular system, multiple users can reuse the same frequency channel without interfering with each other, provided the users access the system from different spatial cells. The cellular concept, therefore, is a simple type of spatial division multiple access (SDMA). Note that throughout this description, various acronyms will be used, which are listed and defined in the Table below.
Acronym
Definition
AOA
Angle of arrival
ARIB
Association of Radio Industries
BS
Base station
CDMA
Code division multiple access
CM
Constant modulus
DSP
Digital signal processing
EMP
Extended manifold processor
FDD
Frequency division duplexing
FHT
Fast Hadamard transformers
FL
Forward link
MAC
Multiply-and-accumulate
MAD
Manifold assisted demodulator
MMSE
Minimum mean-squared error
MS
Mobile station
OTD
Orthogonal transmit diversity
PN
Pseudo-noise
PSC
Primary spatial correlator
RL
Reverse link
SDMA
Spatial division multiple access
SIR
Signal-to-interference ratio
SNR
Signal-to-noise ratio
SVD
Singular value decomposition
TOA
Time of arrival
In the case of digital communication, additional techniques can be used to increase capacity. One well-known method is to use spatial signal processing in code division multiple access (CDMA) systems. CDMA is normally a spread-spectrum technique that does not limit individual signals to narrow frequency channels but spreads the signals throughout the frequency spectrum of the entire band. Signals sharing the band are distinguished by assigning different orthogonal digital code sequences or spreading signals to each signal. Practical techniques for capacity enhancement in CDMA systems using an antenna array are described in commonly-owned U.S. patent application Ser.No. 08/929,638 entitled “PRACTICAL SPACE-TIME RADIO METHOD FOR CDMA COMMUNICATION CAPACITY ENHANCEMENT” and U.S. Prov. patent application Ser. No. 60/071,473, entitled “FADING MITIGATION USING WIDE APERTURE ANTENNA ARRAY IN SPREAD SPECTRUM COMMUNICATION SYSTEMS” and 60/077,979, entitled “CAPACITY ENHANCEMENT FOR W-CDMA SYSTEMS”, all of which are incorporated by reference in their entirety.
Spatial signal processing can be used in both the forward link (base station to mobile station) and reverse link (mobile station to base station) of a CDMA communication system to provide significant signal-to-noise ratio and capacity improvements. In the reverse link, spatial signal processing includes estimating a spatial signature (defined herein as the vector of antenna output signals, including multipath components, at a given time due to a transmitted signal at a certain location, such as described in “Experimental Studies of Spatial Signature Variation at 900 MHz for Smart Antenna Systems” by S. S. Jeng, G. Xu, H. P. Lin, and W. J. Vogel, IEEE Trans. on Antennas and Propagation, vol. 46, no. 7, July 1998, pp. 953-962, which is incorporated by reference in its entirety) of an IS-95 based CDMA signal to determine multipath angle of arrival (AOA) values and coefficients. An IS-95 system is described in TIA/EIA/IS-95-A, “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular Systems”, May 1995, which is incorporated by reference in its entirety. The reverse link coefficients are then used to combine a plurality of antenna output signals (after down-conversion to base band), i.e. beamforming. Thus, the ability to accurately estimate the spatial signature is an important objective in CDMA systems. However, with a frequency division duplexing (FDD) system, the forward link and the reverse link occupy different carrier frequencies or bands, but overlap in time. This difference between the forward and reverse link frequencies reduces the correlation between fading of the two links so that the two links have significantly different spatial signatures. Therefore, forward link beamforming using the reverse link spatial signature estimate is not possible. However, average AOA is generally preserved in FDD systems between the forward and reverse links for mobile stations far away from the base station.
Factors which limit the ability to provide for accurate spatial signature estimation include the fading rate (Doppler spread), angle spread, and delay spread profiles of the incoming signals. In particular, fast fading, which is created by the combination of multipath components of a signal being reflected from various elements (“scatterers”) in the neighborhood (“scattering zone”) of a moving transmitter with random phases, is a major concern in accurate spatial signature estimation. The wireless communication channel is assumed to have multiple scattering zones characterizing the signal propagation between the base station (BS) and the mobile station (MS). “Mobile Cellular Telecommunications” by W. C. Lee, McGraw-Hill, New York, 1995, which is incorporated by reference in its entirety, describes scattering zones around the mobile station. The main scattering zone is in the neighborhood of the MS. Large objects, such as buildings and waterways, create other scattering zones. Metal objects in the vicinity of the BS can cause the signal to be reflected and can influence the transmission path. However, in most cases, the BS antenna array is located above the nearby scatterers, which are assumed to be less significant. As the fading rate or Doppler spread increases, the time available to collect coherent data (integration time) decreases. This problem becomes more severe as cellular systems move from the 800 MHz range to the 1900 MHz range or higher, which can increase the fading or Doppler spread by a factor of two or more. For example, a vehicle moving at 60 mph can induce a Doppler spread in excess of 180 Hz in a 1900 MHz system. In general, spatial signature estimation must take place in a duration that is an order of magnitude shorter than the period of the fading rate. For example, if the fading rate is 100 Hz, then spatial signature estimation must take place within 1 msec.
Various methods for spatial signature estimation or beamformer generation have been proposed. These methods can be characterized by the level of knowledge of the structure of the signal impinging on the antenna array and whether or not a training sequence is present. Characteristics of the temporal, spatial, spectral, or modulation structure of the impinging signal may be known and can be exploited in the spatial signature estimation, such as described in “Algebraic Methods for Deterministic Blind Beamforming” by A. J. Van der Veen, Proceedings of IEEE, vol. 86, no. 10, October, 1998, pp. 1987-2008, which is incorporated by reference in its entirety. Many adaptive algorithms based on minimum mean-squared error (MMSE) or constant modulus (CM) and exploiting temporal or modulation signal structure to perform estimation of the spatial signature are well known, such as described in “Algebraic Methods for Deterministic Blind Beamforming” by A. J. Van der Veen, referenced above, and in “Space-Time Processing for Wireless Communications” by A. J. Paulraj and C. B. Papadias, IEEE Signal Processing Magazine, vol. 14, no. 6, November 1997, pp. 49-83 and “Adaptive Filter Theory” by S. Haykin, Prentice-Hall, Englewood Cliffs, N.J., 1986, both of which are incorporated by reference in their entirety.
A disadvantage of these adaptive algorithms is that they generally do not exploit knowledge of the array spatial information or array manifold and generally require substantial time to converge.
The array manifold is a collection of array response vectors (where each array response
Abbott William L.
Friedlander Benjamin
Scherzer Shimon B.
Chin Vivian
Fulbright & Jaworski L.L.P.
Lee John J
Metawave Communications Corporation
LandOfFree
Manifold assisted channel estimation and demodulation for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Manifold assisted channel estimation and demodulation for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Manifold assisted channel estimation and demodulation for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2985610