Multiplex communications – Generalized orthogonal or special mathematical techniques – Particular set of orthogonal functions
Reexamination Certificate
2000-09-08
2003-01-28
Chin, Wellington (Department: 2664)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Particular set of orthogonal functions
C370S335000, C370S347000
Reexamination Certificate
active
06512737
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to radio communications and more specifically to communication technologies for multiple access in difficult and hostile environments combined with dynamic environment changes.
2. Description of the Prior Art
The communication technology developed in the 1940's during World War II included “frequency diversity communication” or “stacked carrier communications” to aid high frequency (HF) band traffic. J. Proakis refers to frequency diversity communication technology in,
Digital Communications,
McGraw-Hill, 1989, see, sections 7.4 to 7.7. Diversity techniques are said by Proakis to be based on the notion that errors occur in the reception of largely attenuated channels, e.g., channels in deep fade. Supplying the receiver with several duplicates of the original signal, but over channels that fade independent from one another, has the potential of securing continuous communication except during the unlikely event that all the duplicate channels fade out together. Such probability can be estimated.
Frequency diversity is one of many diversity methods. The same modulation is carried by several carrier channels separated by nominally the coherence bandwidth of each respective channel. In time diversity, the same information is transmitted over different time slots.
Multiple antennas can be used in a diversity scheme. Several receiving antennas can be used to receive the signals sent from a single transmitting antenna. For best effect, the receiving antennas are spaced enough apart to vary different multipath interference amongst the group. A separation of nominally ten wavelengths is generally needed to observe independent signal fading.
A signal having a bandwidth much greater than the coherence bandwidth of the channel can be used in a more sophisticated diversity scheme. Such a signal with a bandwidth W will resolve the multipath components and provide the receiver with several independently fading signal paths.
Other prior art diversity schemes have included angle-of-arrival or spatial diversity and polarization diversity.
When a bandwidth W much greater than the coherence bandwidth of each respective channel is available to a user, the channel can be subdivided into a number of frequency division multiplexed sub-channels having a mutual separation in center frequencies of at least the coherence bandwidth of each respective channel. The same signal can then be transmitted over the frequency-division multiplex sub-channels to establish frequency diversity operation. The same result can be achieved by using a wideband binary signal that covers the bandwidth W.
G. K. Kaleh describes such in an article, “Frequency-Diversity Spread-Spectrum Communication System to Counter Band-limited Gaussian Interference”, IEEE Transactions on Communications, September 1994. Here a secure setup is outlined that can operate in deliberately hostile signal environments.
J. Proakis describes frequency diversity spread spectrum and multiple access concepts in chapter eight, “Spread Spectrum Signals for Digital Communication”, supra. Diversity transmission combined with frequency-hopping spread spectrum is detailed for protection against multipath fading and partial-band jamming.
Retro-directivity was proposed and used as early as 1959 to adapt a multi-element antenna array to provide identical spatial gain patterns during transmission and reception operations. See, R. Monzingo, T. Miller, Introduction to Adaptive Arrays, Wiley Interscience Publications, 1980; L. Van Atta, “Electromagnetic Reflection,” U.S. Pat. No. 2,908,002, 1959; and B. Glance, P. Henry, “High Capacity Mobile Radio System,” U.S. Pat. No. 4,383,332, May 10, 1983, for a discussion of such techniques. TDD systems provide an effective means for implementing retrodirective antenna arrays, e.g., by minimizing the channel variation between the reception and transmission paths.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a radio communication system for spreading data over widely separated frequency bands manifesting differences in channel distortion without physically spreading signals between intervening frequencies, as is required with direct-sequence spread spectrum.
It is another object of the present invention to provide a radio communication system for communication under strong narrow-band interference, e.g., conventional cellular signal waveforms, by turning off affected frequency channels at a receiver's despreader.
It is an object of the present invention to provide a radio communication system with simple equalization of linear channel multipath distortion.
It is an object of the present invention to provide a radio communication system that is compatible with discrete multitone and orthogonal frequency-division multiplex-like channelization techniques. And that is compatible with time-packetized discrete multitone and orthogonal frequency-division multiplex-like modulation/demodulation techniques for frequency channelization and inverse channelization.
It is another object of the present invention to provide a radio communication system that is compatible with time-division duplex systems where the stacked-carrier spread spectrum modulation format is packetized, e.g., if the stacked-carrier spread spectrum signal is generated using discrete multiple tone and/or orthogonal frequency-division multiplex-like based frequency channelizers and inverse channelizers.
It is an object of the present invention to provide a radio communication system for frequency-division multiple-access like multiple access capability.
It is an object of the present invention to provide a radio communication system for code-division multiple-access like capability in a stacked carrier multiple access arrangement.
It is an object of the present invention to provide a radio communication system compatible with high-order digital modulations.
It is an object of the present invention to provide a radio communication system for bandwidth-on-demand flexible data rate connections.
It is an object of the present invention to provide a radio communication system for space-division multiple-access like multiple access, interference excision, and channel equalization capability in a code nulling application.
It is an object of the present invention to provide a radio communication system for use with adaptive antenna arrays by spatially extending a spreading code to spread data using independent complex gains on each spatial channel, or antenna beam, to control the channel-bandwidth array dispersion.
It is an object of the present invention to provide a radio communication system compatible with advanced array adaptation techniques, e.g., non-blind pilot-directed, blind data-directed, and other techniques that take advantage of underlying properties of the baseband data, channel structure, or stacked carrier spreading format.
It is an object of the present invention to provide a radio communication system compatible with retrodirective communication techniques.
It is an object of the present invention to provide a radio communication system for back-compatibility with conventional code-division multiple access, data activation systems.
Briefly, an embodiment of the present invention comprises a “stacked-carrier” spread spectrum communication system wherein the spreading is done in the frequency domain by multiplying a time-domain representation of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In practice, the spreading is done by simply energizing the bins of a large fast Fourier transform (FFT). This provides a considerable savings. in computational complexity for moderate output FFT sizes. A Kaiser-Bessel window, e.g., with &bgr;=9, can be used to “fill out” the space between the tones without subjecting those tones to unacceptable interference from adjacent tones, e.g., inter-tone interference. In particular, a high value of &bgr; provides acceptable interference betwee
Beamreach Networks, Inc.
Chin Wellington
Duong Frank
Pillsbury & Winthrop LLP
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