Omnipoint Corporation

Xircom, Inc.

Mark T Burbach

Randolph L Durrant

Eugene P Hoyt

Logan Scott

Ryan N Jensen

Claude M Williams

Randy Durrant

A wireless spread spectrum communication system comprises a spread spectrum transmitter and spread spectrum receiver which communicate according to an over-the-air protocol. The spread spectrum transmitter transmits a burst comprising a preamble followed by a short gap, followed by a data message. The spread spectrum receiver receives and demodulates the transmitted burst. The receiver detects the preamble using a non-coherent parallel correlator, and from the preamble correlation peak generates a series of integration periods for serial non-coherent correlation. The short gap between the preamble and the data message allows the receiver time to process the preamble and set the timing of the electronics for receiving the data message. The receiver has a plurality of non-coherent correlators operating in parallel to recover the spread spectrum encoded information. For each of M spread spectrum codes, the receiver simultaneously attempts to correlate the non-preamble portion of the received spread spectrum signal by separating the received signal into real and imaginary parts, correlating both real and imaginary parts for I and Q sequences, and combining the real I, real Q, imaginary I, and imaginary Q correlation signals into a unified correlation signal.

Method and apparatus for wireless spread spectrum communication with preamble sounding gap

A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals. A transmitter divides a signal data stream into a plurality of data streams (such as I and Q data streams), independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and simultaneously attempts to correlate for a plurality of chip sequences (such as I and Q chip sequences), and interleaves the correlated I and Q data streams into a unified signal data stream. In one embodiment, the receiver separates the received spread spectrum signal into real and imaginary parts, attempts to correlate both real and imaginary parts for a plurality of chip sequences, and combines the real I, real Q, imaginary I, and imaginary Q signals into a unified signal data stream. The demodulating reference signal in the receiver may or may not be frequency or phase matched with the transmitter. In other embodiments, single bit or multi-bit digitization of the received spread spectrum signal for both I and Q signals (or real I, real Q, imaginary I, and imaginary Q signals) is carried out prior to correlation. In another embodiment, the transmitter differentially phase encodes the information to be transmitted, and the receiver decodes the phase encoded information by determining a quantized phase angle of the received signal.

Method and apparatus for parallel noncoherent correlation of a spread

A spread spectrum receiver for demodulating a CPM spread spectrum signal receives burst comprising a preamble and a data message that have been transmitted by M-ary encoding of a data signal into a single chip stream, dividing the chip stream into I and Q signal streams, independently modulating the I and Q signal streams, and superposing the resultants for transmission. The receiver detects the preamble using a non-coherent parallel correlator, and from the preamble correlation peak generates a series of integration periods for serial non-coherent correlation. A bank of non-coherent, serial correlators operate in parallel to recover the spread spectrum encoded information. For each of M spread spectrum codes, the receiver simultaneously attempts to correlate the non-preamble portion of the received spread spectrum signal by separating, the received signal into real and imaginary parts, correlating both real and imaginary parts for I and Q sequences, and combining the real I, real Q, imaginary I, and imaginary Q correlation signals into a unified correlation signal. The maximum of the unified correlation signals from the non-coherent, serial correlators dictates the content of the data stream for each integration period. The local clock reference signal in the receiver need not be frequency or phase matched with the clock of the transmitter in order to carry out the integration and recovery of the data stream.

Apparatus for receiving and correlating a spread spectrum signal

Method and apparatus for coherent correlation of a spread spectrum signal

A technique for modulating and demodulating continuous phase modulation (CPM) spread spectrum signals and variations thereof. A transmitter encodes M data bits using a selected spread spectrum code, divides the spread spectrum code into a plurality of chip codes (such as even chips and odd chips), independently modulates the even and odd chips with orthogonal carrier signals using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal, divides the spread spectrum signal into duplicate signals, separately demodulates the duplicate signals into an odd chip signal and an even chip signal, simultaneously attempts to correlate the odd chip signal with a locally generated odd chip sequence and the even chip signal with a locally generated even chip sequence, and interleaves the correlation signals into a unified correlation signal. The unified correlation signal may be compared against other correlation signals to determine the content of the transmitted data.

Method and apparatus for correlating a continuous phase modulated spread

Method and apparatus for coherent serial correlation of a spread

An apparatus and method for receiving spread spectrum signals, and, further, for decoding phase encoded information from such signals, requires correlation of input signals into real and imaginary components and determination of the phase angles of the received signal. A transmitter can divide an input signal into a plurality of data streams, independently modulate these streams, and then superpose the plurality of resultants for transmission. A receiver can receive the superposed signal and separate it into real and imaginary parts. In one embodiment, the receiver uses a plurality of spread spectrum codes to generate a plurality of real correlation signals and a plurality of imaginary correlation signals. A transmitter may also generate a differentially phase encoded signal. Phase encoding of a signal generally involves the imposition of known phase changes in the transmitted signal at selected intervals. Decoding of the phase changes at the receiver allows recognition of the phase encoded information. Differential phase encoding, specifically, involves the imposition of a selected phase upon the signal to be transmitted, giving consideration to a prior phase of the signal. In other embodiments, a receiver uses the generated real and imaginary correlation signals to determine a sector of a phase angle of a received signal. This sector can be compared with a previously generated sector, the resultant being an indication of the differential phase encoding performed at the transmitter.

Method and apparatus for decoding a phase encoded signal

Method and apparatus for serial noncoherent correlation of a spread

A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals. A spread spectrum transmitter includes a chip sequence generator for generating a chip sequence from a data stream, a switch for dividing said chip sequence into an odd chip sequence and an even chip sequence, and a modulator for generating and transmitting a continuous phase modulated signal from said odd chip sequence and said even chip sequence. A spread spectrum receiver comprises a plurality of non-coherent serial CPM correlators, each generating a correlation signal. In a preferred embodiment, the chip sequence generator of the transmitter comprises a table of symbol codes, each symbol code comprising a series of chips corresponding to a unique series of bits in said data stream, and each non-coherent serial CPM correlator is configured to detect one of the symbol codes. The spread spectrum receiver selects a data symbol based on said correlation signals output from the non-coherent serial CPM correlators. A spread spectrum preamble may be used to set initial timing for the non-coherent serial CPM correlators.

Non-coherent spread-spectrum continuous-phase modulation communication

A method and apparatus for phase encoding and decoding a CPM spread spectrum signal. A transmitter divides a data stream into a data symbol portion and an associated phase information portion. The data symbol portion is used to select one of a plurality of spread spectrum codes for transmission from a symbol table. The phase information portion is used to differentially phase encode the data symbol prior to transmission. The transmitter divides the phase encoded spread spectrum codes into a plurality of data streams (such as I and Q data streams), independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and simultaneously attempts to correlate for a plurality of chip sequences (such as I and Q chip sequences), and derives a real correlation signal and an imaginary correlation signal. For each received symbol, the receiver determines which of a plurality of phase sectors the phase angle lies in, and compares the difference between the present phase sector and the immediately preceding phase sector. For biphase encoding, if the difference in closer to 0.degree., then the receiver outputs a first bit, and if the difference is closer to 180.degree., the receiver outputs a second bit. In a particular embodiment, a plurality of correlators operate in parallel to carry out phase decoding of the received signal.

Method and apparatus for differential phase encoding and decoding in

An apparatus and method for synchronizing a spread spectrum receiver comprises a preamble matched filter and a plurality of symbol code correlators for receiving and correlating to a received spread spectrum signal. The preamble matched filter is preferably non-coherent in nature and outputs a correlation signal including a correlation pulse of variable width. The pulse is converted to a square wave having a duration of a discrete number of chip periods. The correlation pulse is used as a timing reference for the symbol code correlators, which are also non-coherent in nature. A center seeking circuit provides an offset to the timing reference according to the width of the correlation pulse. In a preferred TDMA system, a timing window is used for a subsequent time frame for defining a period of time in which the correlation signal output from the preamble matched filter can yield a valid correlation pulse. In addition to synchronizing the symbol code correlators, the receiver clocks for synchronizing to the TDMA time frame may also be adjusted in response to the correlation pulse.

Synchronization apparatus and method for spread spectrum receiver

A technique for demodulating CPM spread spectrum signals and variations thereof. A receiver receives a CPM spread spectrum signal, splits it into two signals, demodulates the signals (either coherently or non-coherently) and simultaneously attempts to correlate for a plurality of chip sequences (e.g., I and Q or even and odd), ultimately combining the results into a unified correlation signal. A plurality of A/D converters quantize the demodulated signals into multi-bit digital signals prior to correlation, and multi-bit correlators operate on the multi-bit digital signals to produce correlation signals that are combined to form a unified correlation signal for detection.

Multi-bit correlation of continuous phase modulated signals

A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals. A transmitter divides a signal data stream into a plurality of data streams (such as I and Q data streams), independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and simultaneously attempts to correlate for a plurality of chip sequences (such as I and Q chip sequences), and interleaves the correlated I and Q data streams into a unified signal data stream. In one embodiment, a spread spectrum transmitter comprises a plurality of lookup tables for storing spread spectrum code chip sequences, at least one preamble code chip sequence, and at least one fill code chip sequence. An output from each of the tables is provided to a selection circuit (e.g., a multiplexer) that selects, under control of a controller, chips from each of the tables to construct a unified chip sequence. The unified chip sequence is divided into a stream of odd chips and a stream of even chips, which are provided to separate waveform generators. An output from each waveform generator is combined and modulated as a continuous phase modulation signal.

Spread spectrum transmitter

A technique for modulating and demodulating continuous phase modulation (CPM) spread spectrum signals and variations thereof. A transmitter encodes M data bits using a selected spread spectrum code, divides the spread spectrum code into a plurality of chip codes (such as even chips and odd chips), independently modulates the even and odd chips with orthogonal carrier signals using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and divides it into a real signal and an imaginary signal. The real signal is connected to a first correlator which divides its input into a real I signal and a real Q signal, serially correlates the real I signal with the odd chips of a chip code and the real Q signal with the even chips of the chip code, and combines the correlation signals into a real correlation signal. The imaginary signal is connected to a second correlator which divides its input into an imaginary I signal and an imaginary Q signal, serially correlates the imaginary I signal with the odd chips of the chip code and the imaginary Q signal with the inverse of the even chips of the chip code, and combines the correlation signals into an imaginary correlation signal. The real and imaginary correlation signals are combined into a unified correlation signal.

Method and apparatus for reception and noncoherent serial correlation of

Apparatus and method for despreading a received continuous phase modulated spread spectrum signal includes a power divider for dividing a received spread spectrum signal into a real signal and an imaginary signal. A real CPM correlator demodulates the real signal into I and Q components and separately correlates the real I component and the real Q component without generating a correlation sequence, thereby performing self-synchronizing correlation. Likewise, an imaginary CPM correlator demodulates the imaginary signal into I and Q components and separately correlates the imaginary I component and the imaginary Q component without generating a correlation sequence, thereby performing self-synchronizing correlation. The real I and imaginary I correlation signals are combined into a final I correlation signal, and the real Q and imaginary Q correlation signals are combined into a final Q correlation signal.

Growing community of inventors

Peyton, CO, United States of America

Mark T Burbach