Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Patent
1996-04-08
2000-01-11
Cumming, William
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
H04Q 700
Patent
active
060145706
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention pertains to the field of combining electromagnetic signals from separated antennas, in order to cancel co-channel interference and to mitigate frequency selective fading.
BACKGROUND ART
The following references are cited in this specification, using the following reference numbers: Proceedings, Vol. 75, No. 4, pp. 436-477, April 1987. Interference Environment", IEEE Journal on Selected Areas in Communications, vol. 7, no. 1, pp. 49-58, January 1989. Cancellation and Macroscopic Diversity for High Capacity PCS", Conf. Record IEEE ICC '95, Seattle, Wash., pp. 852-857, Jun. 18-22, 1995. Communications Systems (WACS)", Bellcore, Issue 1, October 1993; Revision 1, June 1994. Personal Communications, pp. 20-35, April 1995. language, 2nd ed. Boston: Kluwer Academic Pub., 1995. Jose, Calif.: Automata Pub. Co., 1993. With Combined Symbol Timing, Frequency Offset Estimation, and Diversity Selection", IEEE Transactions on Communications, vol. 39, no. 7, pp. 1157-64, July 1991. Robust Frequency and Timing Estimation for Portable Radio Communications", Conf. Record IEEE GLOBECOM '88, Hollywood, Fla., pp. 804-9, Nov. 28-Dec. 1, 1988. Communications Channels with Digital Modulation", IEEE Journal on Selected Areas in Communications, vol. sac-5, no. 5, pp. 879-889, June 1987.
DISCLOSURE OF INVENTION
The present invention is a method and apparatus for diversity-combining two electromagnetic signals (11,21) within a receiver (25). Coupled to the receiver (25) are two antennas, a first antenna (10) for receiving said first signal (11) and a second antenna (20) for receiving said second signal (21). Coupled to at least one of the antennas (10,20) is a circuit (12) for varying the gain and the phase of the signal (11 or 21) received at said antenna (10 or 20). The gain and the phase are constrained to be selected from within a finite set of preselected discrete gains and a finite set of preselected discrete phases.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other more detailed and specific objects and features of the present invention are more fully disclosed in the following specification, reference being had to the accompanying drawings, in which:
FIG. 1 is a block diagram illustrating the microscopic diversity combining of the present invention using two receiving antennas 10, 20.
FIG. 2 illustrates an example of a set of complex weights A used for diversity combining. Complex weights A used for the coarse step search are represented by the hexagonal markers and those used for a particular example of a fine step search are represented by the shaded rectangular markers.
FIG. 3 is a set of three time-related graphs showing signals s, S, and S'. Signal S is delayed by 1 sample period to change its phase by -45.degree. to S'. s and S' are then in phase and can be added constructively.
FIG. 4 is a process flow diagram illustrating the diversity combining of the present invention in a receiver 25. Functional units enclosed in the solid boxes are unique to the present invention.
FIG. 5 is a functional block diagram showing data-path circuitry for primary, secondary, and back-up (relatively low speed) phase recovery states of the present invention (those components enclosed in dashed rectangular box 29).
FIG. 6 is a functional block diagram showing parallel (relatively high speed) data-path circuitry for searching for the optimum complex weights A for signal combining and for the corresponding optimum symbol timing.
FIG. 7 is a timing schedule for phase recovery 29 and searching states 6, and their corresponding clock frequencies in one PACS TDMA frame period. Data are assumed to be received in the first time slot, T1 (the shaded area).
FIG. 8 is a set of two graphs showing simulated average normalized signal quality (y) versus SIR in an interference limited environment.
FIG. 9 is a set of three graphs showing hardware computer simulation results for two receiving antennas 10, 20 located at the statistically worst area. Macroscopic diversity based on channel power measurement is incorporate
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P.B. Wong and D.C. Cox, "A Low-Complexity Wireless Receiver for Co-channel Interference Cancellation and Frequency Selective Fading Mitigation", hard copy of viewgraphs shown at meeting of Bay Area Wireless Communications Alliance, Hewlett-Packard, Santa Clara, CA, Oct. 17, 1995.
Cox Donald Clyde
Wong Piu Bill
Cumming William
The Board of Trustees of the Leland Stanford Junior University
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