Abstract: A technique for reducing memory usage during signal processing includes storing least significant portions of a plurality of intermediate results in a first memory. Most significant portions of a subset the plurality of intermediate results are stored in a second memory having a smaller length than the first memory. A data linkage is maintained between the most significant portions and corresponding least significant portions.

Abstract: A method of transmitting a spread spectrum signal in a single communication session between a transmitter and a receiver, stores a series of N unique waveform designs and a hopping sequence in a transmitter memory. A signal is transmitted to a receiver according to the hopping sequence using the plurality of N unique waveform designs. Preferably, each waveform design is characterized by a unique composite spreading code that is formed by at least some of a plurality of constituent code segments. Alternatively or additionally, the waveform designs may differ by any one or more of code length, symbol or chip timing or phase, frame or burst structure, chip offset, modulation, error control coding, encryption scheme, or scrambling code. A transmitter and receiver are also disclosed, as is the concept of appending chips between symbols to expand the universe of unique spreading codes without incurring an increase in processing gain.

Abstract: The exemplary embodiments of the invention provide methods, computer program products and apparatus for determining cross-correlations between the received signals in a set of users. An exemplary method includes: receiving an input signal comprising a plurality of user signals, selecting a first received signal and a second received signal from the plurality of user signals, determining a timing offset between the first signal and the second signal, and using the determined timing offset, a first identification of the first signal, and a second identification of the second signal as indices to retrieve at least one cross-correlation coefficient from a memory.

Abstract: A method of transmitting a spread spectrum signal in a single communication session between a transmitter and a receiver, stores a series of N unique waveform designs and a hopping sequence in a transmitter memory. A signal is transmitted to a receiver according to the hopping sequence using the plurality of N unique waveform designs. Preferably, each waveform design is characterized by a unique composite spreading code that is formed by at least some of a plurality of constituent code segments. Alternatively or additionally, the waveform designs may differ by any one or more of code length, symbol or chip timing or phase, frame or burst structure, chip offset, modulation, error control coding, encryption scheme, or scrambling code. A transmitter and receiver are also disclosed, as is the concept of appending chips between symbols to expand the universe of unique spreading codes without incurring an increase in processing gain.

Abstract: An apparatus and method of determining a signal code. The method comprising steps of acquiring and correlating a signal with a first code sequence. In response to the timing lock is achieved. Also in response to the signal correlation, an acknowledge from a receiver of the signal to a transmitter change to a second code sequence.

Abstract: A system for verifying composite pseudo-noise (PN) encoded signals. The system provides at least three PN component codes, wherein the at least three PN component codes are relatively prime. The system partially correlates a received PN composite encoded signal with a first minor epoch derived from the at least three PN component codes. The system searches for phase alignment of the received PN composite encoded signal with a second minor epoch derived from the at least three PN component codes. The system correlates the received PN composite encoded signal with a receiver PN composite code phase when the first minor epoch and the searched second minor epoch are separated by a predetermined phase.

Abstract: A method and system is disclosed for generating and detecting variable sequence PN codes. PN-Code sequence changes based on varying interceptor threat levels are generated at a rate fast enough to avoid exploitation while maintaining a reasonable correlation search window. The PN code sequence is phase shifted by N-chips based on the severity of the threat environment. A synchronized receiver demodulates the PN encoded signal by correlating over every possible phase of the PN code sequence. The receiver includes first and second correlators and threshold detectors adapted to detect PN signals with varying PN code sequence changes.

Abstract: A Time Division Duplex (TDD), Code Division Multiple Access (CDMA) communication system includes a plurality of Customer Premises Equipment (CPE) and an Access Point (AP) that communicate through RF links. A CPE contains a receiver baseband subsystem and a transmitter baseband subsystem, and further contains receiver circuitry operable during a receive period for receiving an RF carrier from the AP and for deriving a receiver tracking signal that is indicative of a frequency and phase shift between the received RF carrier and a reference signal. The receiver circuitry further includes a frequency to phase accumulator (FPA) and a digital phase shifter (DPS) for correcting the frequency and phase of a receiver baseband signal by an amount and in a direction indicated by the receiver tracking signal.

Abstract: A method and system for compensating digital data demodulation phase uncertainty is provided. The method includes the steps of identifying a phase reference quadrant, the phase reference quadrant having a phase reference axis and four quadrants, I, II, III, and IV; receiving known digital data; and forming a phase vector from the known digital data, determining which quadrant the phase vector is located in and rotating the phase vector to the phase reference quadrant if it is determined that the phase vector is not located in the phase reference quadrant. The last step generates a phase error signal proportional to the resulting angle by rotating the phase vector ?45° and measuring the resulting angle between the phase vector and the phase reference axis.

Abstract: A novel MODEM and method of operating a MODEM usable in spread spectrum communication utilizing multiple waveforms in orthogonal spread signals imbeds a tracking signal in one of the spread signals for efficient tracking by a receiver so that both spread signals can have wideband characteristics. Therefore, one spread signal contains a tracking channel and a wideband channel, allowing for higher order modulation in the wideband channel for transmitting information, while still providing good tracking features. The second spread signal is an orthogonal wideband channel serving as the main high data rate conduit. In the preferred embodiment, the first portion of the waveform (in the first spread signal) is modulated using Bi-Bi-Phase Shift Keying (Bi-BPSK), while the second portion of the waveform (in the second spread signal) is modulated using Multiple Phase Shift Keying (MPSK). The two waveform portions are Time Division Multiplexed (TDM) at the chipping rate.

Abstract: A method and device for frame sync detection using signal combining and correlation. The method comprises the steps of despreading PN coded signals to provide in-phase I1–In, and quadrature phase Q1–Qn signals, wherein each I1–In and each Q1–Qn signal contains at least one sync bit and n?2. The at least one sync bit from each I1–In, and quadrature phase Q1–Qn signals are summed to form sums Is1 and Qs1, respectively. The next step provides a reference sync having at least one bit and compares each sum Is1 and Qs1 with the at least one reference bit. The results of each Is1 and Qs1 comparison are accumulated so as to form two accumulates, IA and QA, respectively. Each accumulate IA and QA, is squared to form IA2 and QA2 from which the sum IA2 and QA2 is formed. The sum IA2+QA2 is compared with a predetermined threshold and as a result of the comparison a determination of whether frame sync has been achieved is made.

Abstract: An apparatus and method of determining a signal code. The method comprising steps of acquiring and correlating a signal with a first code sequence. In response to the correlation of the signal with a first code sequence a timing lock is achieved. Also in response to the signal correlation, an acknowledgement from a receiver of the signal to a transmitter of the signal is sent where upon the receiver and transmitter change to a second code sequence.

Abstract: A novel MODEM and method of operating a MODEM usable in spread spectrum communication utilizing multiple waveforms in orthogonal spread signals imbeds a tracking signal in one of the spread signals for efficient tracking by a receiver so that both spread signals can have wideband characteristics. Therefore, one spread signal contains a tracking channel and a wideband channel, allowing for higher order modulation in the wideband channel for transmitting information, while still providing good tracking features. The second spread signal is an orthogonal wideband channel serving as the main high data rate conduit. In the preferred embodiment, the first portion of the waveform (in the first spread signal) is modulated using Bi-Bi-Phase Shift Keying (Bi-BPSK), while the second portion of the waveform (in the second spread signal) is modulated using Multiple Phase Shift Keying (MPSK). The two waveform portions are Time Division Multiplexed (TDM) at the chipping rate.

Abstract: A maximum likelihood (ML) detector provides improved performance in the presence of multiple user interference (MUI), particularly performance of a multiuser receiver for asynchronous CDMA. The detector can be implemented using a Viterbi algorithm, this greatly reducing system sensitivity to MUI. An approximation to the ML detector provides a sparse trellis search based on the structure of the ML detector. The resulting detector, which may be referred to as a reduced-complexity recursive detector (RCRD), has a dynamic structure that allows a trade-off between complexity and performance. Use is made of a unique metric to define the trellis-structure and the M-algorithm to reduce the number of surviving paths. The metric calculation is then repeated at decision points to provide soft-decision information for further signal processing, soft-decision decoding of an error-correction code, or iterative reception of the multiuser signal.

Abstract: A demodulator for demodulating clear mode waveforms such as Phase Shift Keyed and Quadrature Amplitude Modulated waveforms, is capable of demodulating signals with much greater data rates than the clock rate of the device in which the demodulator resides by converting serial input samples into vectors. The input vectors are converted to “soft-decision” (data estimate) vectors which are input to a parallel-to-serial multiplexer, and the vector elements are output serially at the symbol clock rate to represent demodulated data. In the preferred embodiment, the vector demodulator at least includes a preprocessor, a digital phase shifter, and a symbol demodulator which, inter alia, outputs a phase rotator command signal to control the carrier recover phase rotation process in the digital phase shifter.

Abstract: A method and device for frame sync detection using signal combining and correlation. The method comprises the steps of despreading PN coded signals to provide in-phase I1-In, and quadrature phase Q1-Qn signals, wherein each I1-In and each Q1-Qn signal contains at least one sync bit and n≧2. The at least one sync bit from each I1-In, and quadrature phase Q1-Qn signals are summed to form sums Is1 and Qs1, respectively. The next step provides a reference sync having at least one bit and compares each sum Is1 and Qs1 with the at least one reference bit. The results of each Is1 and Qs1 comparison are accumulated so as to form two accumulates, IA and QA, respectively. Each accumulate IA and QA, is squared to form IA2 and QA2 from which the sum IA2 and QA2 is formed. The sum IA2+QA2 is compared with a predetermined threshold and as a result of the comparison a determination of whether frame sync has been achieved is made.

Abstract: A method is disclosed for operating a fixed wireless system having a radio base unit (RBU) that uses a code division multiple access (CDMA) airlink for communicating with a plurality of subscriber units (SUs). The method includes steps of (a) estimating a signal to noise ratio (SNR) of the FWS; (b) comparing the estimated SNR to a threshold SNR value; and (c) one of allowing service to another SU or not allowing service to another SU based on the result of the step of comparing. The step of estimating preferably uses a normalized SNR, and further employs the use of a null PN code detection technique. More particularly, the step of estimating determines a normalized signal to noise ratio given by Eb/No=20 log (SUT/MUT)-xdB, wherein SUT represents a single user test measurement, wherein MUT represents a multiple user test measurement, and wherein xdB is an adjustment factor. Other types of CDMA systems may also use this technique.

Abstract: Disclosed are methods for acquiring a forward channel in a point-to-multipoint CDMA system. One method includes the steps of (a) despreading a received CDMA signal with a first pn code that is known to be present in the received CDMA signal and obtaining a first measure of received signal level; (b) despreading the received CDMA signal with a second pn code that is known not to be present in the received CDMA signal and obtaining a second measure of received signal level; and (c) synchronizing to a desired channel using a difference between the first and second signal levels. In this method the first step of despreading despreads a continuously transmitted side-channel, and the step of synchronizing synchronizes to the side-channel. Also, the step of obtaining a first measure of received signal level obtains a correlation peak, and the step of obtaining a second measure of received signal level obtains a correlation null.

Abstract: Disclosed are methods for acquiring a forward channel in a point-to-multipoint CDMA system. One method includes the steps of (a) despreading a received CDMA signal with a first pn code that is known to be present in the received CDMA signal and obtaining a first measure of received signal level; (b) despreading the received CDMA signal with a second pn code that is known not to be present in the received CDMA signal and obtaining a second measure of received signal level; and (c) synchronizing to a desired channel using a difference between the first and second signal levels. In this method the first step of despreading despreads a continuously transmitted side-channel, and the step of synchronizing synchronizes to the side-channel. Also, the step of obtaining a first measure of received signal level obtains a correlation peak, and the step of obtaining a second measure of received signal level obtains a correlation null.