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Wireless communication system having linear encoderRelated Patent Categories: Pulse Or Digital Communications, Systems Using Alternating Or Pulsating Current, Plural Channels For Transmission Of A Single Pulse TrainWireless communication system having linear encoder description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070253496, Wireless communication system having linear encoder. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application claims priority from U.S. Provisional Application Ser. No. 60/374,886, filed Apr. 22, 2002, U.S. Provisional Application Ser. No. 60/374,935, filed Apr. 22, 2002, U.S. Provisional Application Ser. No. 60/374,934, filed Apr. 22, 2002, U.S. Provisional Application Ser. No. 60/374,981, filed Apr. 22, 2002, U.S. Provisional Application Ser. No. 60/374,933, filed Apr. 22, 2002, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD [0003] The invention relates to communication systems and, more particularly, transmitters and receivers for use in wireless communication systems. BACKGROUND [0004] In wireless mobile communications, a channel that couples a transmitter to a receiver is often time-varying due to relative transmitter-receiver motion and multipath propagation. Such a time-variation is commonly referred to as fading, and may severely impair system performance. When a data rate for the system is high in relation to channel bandwidth, multipath propagation may become frequency-selective and cause intersymbol interference (ISI). By implementing Inverse Fast Fourier Transform (IFFT) at the transmitter and FFT at the receiver, Orthogonal Frequency Division Multiplexing (OFDM) converts an ISI channel into a set of parallel ISI-free subchannels with gains equal to the channel's frequency response values on the FFT grid. Each subchannel can be easily equalized by a single-tap equalizer using scalar division. [0005] To avoid inter-block interference (IBI) between successive IFFT processed blocks, a cyclic prefix (CP) of length greater than or equal to the channel order is inserted per block at the transmitter and discarded at the receiver. In addition to suppressing IBI, the CP also converts linear convolution into cyclic convolution and thus facilitates diagonalization of an associated channel matrix. [0006] Instead of having multipath diversity in the form of (superimposed) delayed and scaled replicas of the transmitted symbols as in the case of serial transmission, OFDM transfers the multipath diversity to the frequency domain in the form of (usually correlated) fading frequency response. Each OFDM subchannel has its gain being expressed as a linear combination of the dispersive channel taps. When the channel has nulls (deep fades) close to or on the FFT grid, reliable detection of the symbols carried by these faded subcarriers becomes difficult if not impossible. [0007] Error-control codes are usually invoked before the IFFT processing to deal with the frequency-selective fading. These include convolutional codes, Trellis Coded Modulation (TCM) or coset codes, Turbo-codes, and block codes (e.g., Reed-Solomon or BCH). Such coded OFDM schemes often incur high complexity and/or large decoding delay. Some of these schemes also require Channel State Information (CSI) at the transmitter, which may be unrealistic or too costly to acquire in wireless applications where the channel is rapidly changing. Another approach to guaranteeing symbol detectability over ISI channels is to modify the OFDM setup: instead of introducing the CP, each IFFT-processed block can be zero padded (ZP) by at least as many zeros as the channel order. SUMMARY [0008] In general, techniques are described for robustifying multi-carrier wireless transmissions, e.g., OFDM, against random frequency-selective fading by introducing memory into the transmission with complex field (CF) encoding across the subcarriers. Specifically, instead of sending a different uncoded symbol per subcarrier, the techniques utilize different linear combinations of the information symbols on the subcarriers. These techniques generalize signal space diversity concepts to allow for redundant encoding. The CF block code described herein can also be viewed as a form of real-number or analog codes. [0009] The encoder described herein is referred to as a "Linear Encoder (LE)," and the corresponding encoding process is called "linear encoding," also abbreviated as LE when no confusions arise. The resulting CF coded OFDM will be called LE-OFDM. In one embodiment, the linear encoder is designed so that maximum diversity order can be guaranteed without an essential decrease in transmission rate. [0010] By performing pairwise error probability analysis, we upper bound the diversity order of OFDM transmissions over random frequency-selective fading channels. The diversity order is directly related to a Hamming distance between the coded symbols. Moreover, the described LE can be designed to guarantee maximum diversity order irrespective of the information symbol constellation with minimum redundancy. In addition, the described LE codes are maximum distance separable (MDS) in the real or complex field, which generalizes the well-known MDS concept for Galois field (GF) codes. Two classes of LE codes are described that can achieve MDS and guarantee maximum diversity order: the Vandermonde class, which generalizes the Reed-Solomon codes to the real/complex field, and the Cosine class, which does not have a GF counterpart. [0011] Several possible decoding options have been described, including ML, ZF, MMSE, DFE, and iterative detectors. Decision directed detectors may be used to strike a trade-off between complexity and performance. [0012] In one embodiment, a wireless communication device comprises an encoder that linearly encodes a data stream to produce an encoded data stream, and a modulator to produce an output waveform in accordance with the encoded data stream for transmission through a wireless channel. [0013] In another embodiment, a wireless communication device comprises a demodulator that receives a waveform carrying a linearly encoded transmission and produces a demodulated data stream, and a decoder that applies decodes the demodulated data and produce estimated data. [0014] In another embodiment, a method comprises linearly encoding a data stream with to produce an encoded data stream, and outputting a waveform in accordance with the data stream for transmission through a wireless channel. [0015] In another embodiment, a computer-readable medium comprises instructions to cause a programmable processor to linearly encode a data stream with to produce an encoded data stream, and output a waveform in accordance with the data stream for transmission through a wireless channel. [0016] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS [0017] FIG. 1 is a block diagram illustrating an exemplary wireless communication system in which a transmitter and receiver implement linear preceding techniques. [0018] FIGS. 2A, 2B illustrate uncoded and GF-coded BPSK signals. [0019] FIG. 3 illustrates an example format of a transmission block for CP-only transmissions by the transmitter of FIG. 1. [0020] FIG. 4 illustrates an example format of a transmission block for ZP-only transmissions by the transmitter of FIG. 1. [0021] FIG. 5 illustrates sphere decoding applied in one embodiment of the receiver of FIG. 1. Continue reading about Wireless communication system having linear encoder... 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