Motorola Corporation

Digi International Inc.

Terry Michael Schaffner

Brian Keith Classon

Fuyun Ling

Michael D Kotzin

Anthony P Van Den Heuvel

Robert Mark Harrison

Michael Mao Wang

Vipul Anil Desai

Donald P Cordell

John Robert Schwartz

Kevin P Koehler

Theodore A Trost

Jeffrey H Moy

A radio frequency locator system and method. First, second and third reference devices are operable to transmit a plurality of spread spectrum chirp signals frequency offset from one another. An object device is operable to receive the plurality of spread spectrum chirp signals, the object device is further operable to evaluate the received plurality of spread spectrum chirp signals for relative phase shifts between the plurality of spread spectrum chirp signals and derive a fine propagation time between the reference devices and the object device using the phase shifts between the spread spectrum chirp signals. The reference devices determine their location independent of the object device and determine the location of the object device as a function of each of their locations and of their range to the object device.

Indoor positioning with radio frequency chirp signal propagation delay measurement

A radio frequency receiver for receiving an interleaved single carrier chirp spread spectrum signal based on a chirp sequence includes: a demodulator configured to receive, demodulate, and digitize a modulated radio frequency (RF) signal to form a digital baseband signal; and a signal decoder configured to: despread the digital baseband signal by at least: buffering signal data into blocks of L samples; multiplying the blocks of data with a conjugate of the chirp sequence to form a result; and performing a Fast Fourier Transform (FFT) on the result; equalize data from the FFT to form N data values, where N is the number of subchannels; transform the N data values into N demodulation symbols via an N-point inverse Fourier transform; and decode the demodulation symbols to form codec symbols.

Chirp spread spectrum system and method

A radio frequency communication system includes a radio frequency transmitter having a chirp generator operable to transmit a first chirp signal, and transmit a second chirp signal that is circular shifted relative to the first chirp signal. A receiver receives the first chirp signal and the second chirp signal, such that the proportion of phase offset between the first and second chirp signals is proportional to the frequency offset of the received signals. The first and second chirp signals are despread, and the phase difference between the first and second chirp signals is used to determine a frequency offset of the received first and second chirp signals that is proportional to the phase difference between the first and second chirp signals.

RF chirp receiver synchronization

A method and apparatus for acquiring time and frequency synchronization in a DSSS receiver are disclosed. An iterative approach is used in acquiring a DSSS signal when the phase coherency of the signal is less than the symbol length.

Iterative method, and apparatus for acquiring time and frequency synchronization in a DSSS receiver

In one embodiment a method for suppressing narrowband interference in an RF signal is provided. The method includes providing a block of baseband digital samples of the RF signal and computing n-1 stages of an n stage fast Fourier transform (FFT) on the block of the baseband digital samples to produce a first block of intermediate data points. A final threshold is computed based on values of the intermediate data points. A final stage of the n stage FFT is computed from the first block of intermediate data points to produce a block of output data points, and the output data points that have an energy above the final threshold are attenuated.

Low complexity narrowband interference suppression

This document discusses, among other things, a system and method of measuring and correcting for frequency offset in wideband signals of bandwidth X within a communications system. A synchronization signal is generated and transmitted, wherein generating a synchronization signal includes generating a first chirp signal that sweeps a portion of bandwidth X and generating a second chirp signal to sweep approximately the same portion of bandwidth X but in the opposite direction. The synchronization signal is received at a receiver. The receiver then detects a first offset as a function of the first chirp signal and a second offset as a function of the second chirp signal and calculates the frequency offset as a function of the first and second offsets.

System and method for obtaining frequency and time synchronization in a wideband communication system

This document discusses, among other things, a system and method of detecting wideband signals of bandwidth X within a communications system having a coherency time constant of T. A synchronization signal is generated as a function of a chirp signal that sweeps a portion of bandwidth X. The synchronization signal is transmitted and received as a wideband signal at a receiver. The receiver detects the synchronization signal within the wideband signal received at the receiver by generating a detection signal, correlating the received wideband signal with the detection signal and indicating when the synchronization signal is detected within the wideband signal. The detection signal is a complex conjugate of the synchronization signal.

System and method for transmitting and detecting spread spectrum signals

A radio frequency communication system. The system includes a radio frequency transmitter and a radio frequency receiver, wherein the radio frequency transmitter includes a modulation circuit and an RF modulator, wherein the radio frequency transmitter maps each block of K information bits into a block of N transmit symbols, transforms the block of N transmit symbols by using symbol block repetition and spreads the symbol blocks by multiplying the symbol blocks by a predefined chirp signal, and wherein the radio frequency receiver includes a chirp receiver operable to receive, demodulate and digitize a modulated radio frequency (RF) signal to form a digital baseband signal, and to recover a signal modulated using interleaved single carrier chirp spread spectrum modulation.

Distance between two radio frequency devices is estimated by receiving a plurality of spread spectrum chirp signals frequency offset from one another, and evaluating the received plurality of spread spectrum chirp signals for relative phase shifts between the plurality of spread spectrum chirp signals. A fine propagation time is derived using the phase shifts between the spread spectrum chirp signals. A frequency domain despreading window is shifted to reduce the influence of time-delayed near multipath signals in receiving the plurality of spread spectrum chirp signals.

RF chirp signal propagation delay measurement

Decoding signals represented by a trellis of block length N divided into windows of length L includes a step of decoding a forward recursion from a point P that is before the beginning of a window up to the beginning of the window. P is chosen at a sufficient distance from the beginning of the window such that forward recursion determines a known state metric at the beginning of the window. A next step includes decoding the window using forward recursion from the known state at the beginning of the window up to the end of the window to define a set of known forward recursion state metrics which are stored. A next step includes decoding using backward recursion starting from a known state at the end of the window and moving backward. A next step includes calculating a soft output at each stage of the backward recursion using the stored forward recursion state metrics, and branch metrics at each stage, and outputting the soft output for that stage in a LIFO format.

Soft output decoder for convolutional codes

Decoding signals represented by a trellis of block length N divided into windows of length L includes a step of decoding a forward recursion from a point Pthat is before the beginning of a window up to the beginning of the window and decoding a backward recursion from a point Pthat is after the end of a window back to the end of the window to define known states at the beginning and end of the window. A next step includes decoding the window using backward recursion from the known state at the end of the window back to the beginning of the window to define a set of backward recursion state metrics. A next step includes decoding using forward recursion starting from a known state at the beginning of the window and moving forward to the end of the window to define a set of forward recursion state metrics. A next step includes calculating a soft output at each stage of the window using the forward and backward recursion state metrics, and branch metrics at each stage, and outputting the soft output for that stage.

A method and cache for caching encoded symbols for a convolutional decoder with forward and backward recursion includes storing different encoded symbols of an encoded frame in each of a plurality of symbol memory elements ( ) and routing the same encoded symbols from one of the plurality of symbol memory elements ( ) to at least both a forward recursion decoder ( ) and a backward recursion decoder ( ). The plurality of symbol memory elements may be, for example, single port RAM cells, each operatively controlled to receive different encoded symbols of an encoded frame as input. Control logic ( ) routes the same encoded symbols from one of the plurality of symbol memory elements ( ) to all of the recursion decoders ( ).

Cache and caching method for conventional decoders

A method and apparatus is provided for creating a composite waveform. This composite waveform is created by coding a plurality of input digital information signals. Subsequently, the plurality of coded input digital information signals are communicated over a communication medium to a digital combiner. The digital combiner combines the plurality of coded input digital information signals. Finally, the digitally combined information signal is spectrally shaped to form a composite waveform. These composite waveform creation principals may be applied to digitally encoded voice subbands in a subband coding system as well as channel information in a direct sequence code division multiple access (DS-CDMA) communication system transmitter.

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Warrenville, IL, United States of America

Terry Michael Schaffner