Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
2000-02-25
2004-08-10
Pham, Chi (Department: 2663)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S280000, C375S143000, C375S152000
Reexamination Certificate
active
06775260
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to wideband code division multiple access (WCDMA) for a communication system and more particularly to space time block coded transmit antenna diversity for WCDMA.
BACKGROUND OF THE INVENTION
Present code division multiple access (CDMA) systems are characterized by simultaneous transmission of different data signals over a common channel by assigning each signal a unique code. This unique code is matched with a code of a selected receiver to determine the proper recipient of a data signal. These different data signals arrive at the receiver via multiple paths due to ground clutter and unpredictable signal reflection. Additive effects, of these multiple data signals at the receiver may result in significant fading or variation in received signal strength. In general, this fading due to multiple data paths may be diminished by spreading the transmitted energy over a wide bandwidth. This wide bandwidth results in greatly reduced fading compared to narrow band transmission modes such as frequency division multiple access (FDMA) or time division multiple access (TDMA).
New standards are continually emerging for next generation wideband code division multiple access (WCDMA) communication systems as described in U.S. patent application Ser. No. 90/205,029, filed Dec. 3, 1998, and incorporated herein by reference. Therein, Dabak et al. describe a method of space-time transmit diversity (STTD) for frequency division duplex (FDD) WCDMA systems. These FDD systems are coherent communications systems with pilot symbol assisted channel estimation schemes. These pilot symbols are transmitted as quadrature phase shift keyed (QPSK) known data in predetermined time frames to any receivers within range. The frames may propagate in a discontinuous transmission (DTX) mode. For voice traffic, transmission of user data occurs when the user speaks, but no data symbol transmission occurs when the user is silent. Similarly for packet data, the user data may be transmitted only when packets are ready to be sent. The frames include pilot symbols as well as other control symbols such as transmit power control (TPC) symbols and rate information (RI) symbols. These control symbols include multiple bits otherwise known as chips to distinguish them from data bits. The chip transmission time (T
C
), therefore, is equal to the symbol time rate (T) divided by the number of chips in the symbol (G).
Time division duplex (TDD) provides an alternative communication standard for WCDMA, FDD systems. TDD data are transmitted as QPSK symbols in data packets of a predetermined duration or time slot. Each data packet includes a predetermined training sequence or midamble within the time slot. Data packets are exchanged within a cell formed by a base station in communication with nearby mobile units. Data in adjacent cells are modulated by different periodic codes. The midamble is formed by adding time shifted versions of the same basic sequence, wherein each time shift corresponds to a mobile unit within the cell. The spreading factor (SF) or chips per symbol of the modulation is preferably sixteen or less. The basic periodic code that modulates midamble symbols within the cell is shifted to uniquely identify each mobile unit within the cell. Since the periodic code within the cell is the same and the spreading factor is small, however, interference from the base station and other mobile units within the cell is not received as Gaussian noise. Typical matched filter circuits used in FDD systems, therefore, are unsuitable for eliminating this intra cell interference. A solution to this problem was presented by Anja Klein et al.,
Zero Forcing and Minimum Mean
-
Square
-
Error Equalization for Multiuser Detection in Code
-
Division Multiple
-
Access Channels,
IEEE Trans. on Vehicular Technology, 276-287 (1996), and incorporated by reference herein. Therein, Klein et al. teach zero forcing (ZF) and minimum mean-square-error (MMSE) equalization with and without decision feedback (DF) to reduce both inter-symbol interference (ISI) and multiple-access interference (MAI). Klein et al. further cites P. Jung, J. Blanz, and P. W. Baier,
Coherent Receiver Antenna Diversity for CDMA Mobile Radio Systems Using Joint Detection,
Proc. IEEE Int. Symp. Pers. Indoor and Mobile Radio Communications, 488-492 (1993), for the proposition that these techniques may be used in combination with antenna diversity. A. Naguib, N. Seshadri and A. R. Calderbank,
Applications of Space
-
Time Block Codes and Interference Suppression for High Capacity and High Data Rate Wireless Systems,
Proc. of the Asilomar Conference, 1803-1810 (1998) further expand the work of Klein et al. Space time transmit diversity, however, was unknown at the time of either work. Thus, neither Klein et al. nor Jung et al. teach or suggest a method to combine STTD with joint detection of TDD systems. Moreover, neither Klein et al. nor Jung et al. teach a communication system having the advantages of STTD and joint detection of TDD systems.
SUMMARY OF THE INVENTION
These problems are resolved by a circuit designed with a matched filter circuit including a plurality of fingers coupled to receive a data symbol. Each finger corresponds to a respective path of the data symbol. Each finger produces a respective output signal. A plurality of decoder circuits receives the respective output signal from a respective finger of the plurality of fingers. Each decoder circuit produces a respective output signal. A joint detector circuit is coupled to receive each respective output signal from the plurality of decoder circuits. The joint detector circuit produces an output signal corresponding to a predetermined code.
The present invention improves reception by providing at least 2L diversity over time and space for TDD systems. No additional transmit power or bandwidth is required. Power is balanced across multiple antennas.
REFERENCES:
patent: 5737327 (1998-04-01), Ling et al.
patent: 6178196 (2001-01-01), Naguib et al.
patent: 6317411 (2001-11-01), Whinnett et al.
patent: 6449314 (2002-09-01), Dabak et al.
patent: 2001/0024426 (2001-01-01), Zeira et al.
patent: 2002/0027948 (2002-03-01), Schilling
patent: 2003/0058929 (2003-03-01), Cox et al.
patent: 1 006 676 (2000-07-01), None
patent: 1 056 237 (2000-11-01), None
Mohr, W. “UTRA FDD and TDD, a harmonized proposal for IMT-2000”. IEEE Communication Tecnology Proceedings. Oct. 22, 1998-Oct. 24, 1998. pp. 495-499.*
Jeong et al. “A Novel Diversity System in TDD-CDMA”. IEEE. Sep. 2, 1998-Sep. 4, 1998. pp. 771-775.*
Dabak et al. “Equalization and multi-user detection for space time block coding based transmit diversity (STDD) in freqeuncy selective channels”. IEEE. 2000 pp. 506-513.*
Dabak et al. “Space Time Block Coded Transmit Antenna Diversity Scheme for WCDMA”. IEEE. Sep. 21, 1999-Sep. 24, 1999.*
“Zero Forcing and Minimum Mean-square-Error Equalization for Multiuser Dtection in Code Division Multiple-Access Channels”, Anja Klein, et al., IEEE Transactions on Vehicular Technology, vol. 45, No. 2, 05/96, pp. 276-287.
“3G TS 25.221, V3.1.0 (Dec. 1999) Technical Specification”, Version 3.1.0., pp. 1-47.
“A Simple Transmit Diversity Technique for Wireless Communications”, Siavash M. Alamouti, IEEE Journal on Selected Areas In Communications, IEEE Inc., New York, US, vol. 16, No. 8, Oct. 1998, pp. 1451-1458, XP002100058, ISSN: 0733-8716.
“Space Time Block Coded Transmit Antenna Diversity Scheme for WCDMA”, Anand G. Dabak, et al., Wireless Communications and Networking Conference, 1999, IEEE New Orleans, LA, USA Sep. 21-24, 1999, Piscataway, NJ, Sep. 21, 1999, pp. 1466-1469, XP01035636, ISBN: 0-7803-5668-3.
Dabak Anand G.
Schmidl Timothy M.
Sengupta Chaitali
Brady III Wade James
Ferris Derrick W.
Neerings Ronald O.
Pham Chi
Telecky , Jr. Frederick J.
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