A spread-spectrum transmitter is disclosed. The transmitter includes a modulator configured to produce an intermediate frequency signal, a frequency shifter configured to shift the intermediate frequency factor by a first factor, and a local oscillator (LO) configured to generate a LO signal. The transmitter further includes a ramp signal generator configured to determine the value of the first factor and a second factor, is configured to transmit the value of the factor to the frequency shifter, is configured to transmit the value of the second factor to the LO, where the frequency of the intermediate frequency signal shifted by the first factor is shifted synchronously with the frequency of the LO signal shifted by the second factor. The transmitter includes a mixer configured to mix the shifted intermediate frequency with the shifted LO signal that has been shifted by the second factor, producing a spread leaked LO signal.

A system and method for generating communications waveforms that can operate in congested frequency spaces and in applications in which the receiver is moving with respect to the transmitter is provided. In one or more examples, each symbol to be encoded and transmitted is converted into a sequence of frequency chirps. The sequence of frequencies used by the sequence of chirps is based on the symbol that is to be encoded. Each chirp can have a center frequency, and the frequency can be swept over the duration of the chirp. In this way each chirp can have a varying frequency over the duration of the chirp, but the phase of the chirp can be continuous throughout the duration of the chirp. The bandwidth and sweep rate of the chirp can be based on the expected maximum velocity of the receiver and the transmitter relative to one another.

A node is provided that is configured to communicate in a cooperative broadcast multi-hop network that employs broadcast flood routing and multi-hop transmission using a direct-sequence spread-spectrum (DSSS) waveform. The node includes an antenna and a waveform module having a receiver processing chain. The antenna can receive a plurality of DSSS signals from other nodes on a particular channel, and output a channel that includes the plurality of DSSS signals. The plurality of DSSS signals include transmissions that are directly received from other nodes and multi-path components of those transmissions. The receiver processing chain can include a multi-user RAKE receiver that can combine, when performing demodulation processing, a plurality of transmissions directly received from the other nodes and multipath components of transmissions received from the other nodes. In some implementations, the node can perform cooperative beamforming and adaptive space-spectrum whitening.

A receiver is provided that includes a multi-user RAKE receiver that can receive a plurality of transmissions directly received from a plurality of nodes of a cooperative broadcast multi-hop network and multipath components of those transmissions, a combiner module and a data despreader module. The multi-user RAKE receiver includes correlator blocks for each node and a finger selection module. Each correlator block generates one or more candidate fingers for that particular node. The finger selection module can select a subset of the candidate fingers having sufficient correlation for further processing. The combiner module can combine aligned symbols for the subset of candidate fingers to generate and combine soft decisions across each of a plurality of channels into a joint soft decision. The data despreader module can despread chips of information from each of the plurality of channels to generate demodulated data symbols that are converted into data soft-decision bits.

A system may include a first radio comprising a first radio processor, a first radio modem, and a first radio transmitter configured to transmit non-hopping transmissions and hopping transmissions. The system may further include a second radio comprising a second radio processor, a second radio modem, and a second radio hopping receiver, wherein the second radio hopping receiver is a non-staring second radio receiver. The first radio may be configured to: receive a message and a destination for the message, the destination being the second radio; upon a determination that the destination has a non-staring receiver, store the message; determine a time interval start time for a cyclical hop pattern associated with the second radio; output the message from the memory to the first radio modem; output the message from the first radio modem to the first radio transmitter; and/or transmit the message to the second radio.

Disclosed is a channel-dependent multi-carrier code division multiple access (MC-CDMA) technique with adaptive spreading codes. Adaptive spreading codes are used for each subcarrier per user which increase the security level of conventional MC-CDMA. Two different map designs are proposed: fixed and adaptive interval maps. These maps are shared among all nodes and gives information about the spreading code sequences for corresponding channel gains.

Disclosed is a channel-dependent multi-carrier code division multiple access (MC-CDMA) technique with adaptive spreading codes. Adaptive spreading codes are used for each subcarrier per user which increase the security level of conventional MC-CDMA. Two different map designs are proposed: fixed and adaptive interval maps. These maps are shared among all nodes and gives information about the spreading code sequences for corresponding channel gains.

A frequency hopping Global Positioning System (GPS) system comprises an on-orbit reprogrammable digital waveform generator configured to generate a GPS signal comprising a resilient frequency-hopping spread spectrum GPS signal that hops at a hop rate between two or more GPS channels. The GPS signal further comprises a legacy direct-sequence spread spectrum signal for at least two of the two or more GPS channels. Further, a receiver is configured to receive the GPS signal, wherein the receiver is further configured to decode the GPS signal.

A node is provided for a cooperative broadcast multi-hop network that employs broadcast flood routing and multi-hop transmission. The node includes antennas and a waveform module having a receiver processing chain that can include an adaptive space-spectrum whitener (ASSW) module and a multi-user RAKE (mRAKE) receiver. Each antenna can receive output a channel that includes direct-sequence spread-spectrum signals received from other nodes and multi-path components of those transmissions. The ASSW module can perform adaptive space-spectrum whitening to detect and remove interference signals received from each of the channels by performing a covariance analysis to generate channelized signals. The ASSW module can include modified Discrete Fourier Transform (MDFT) analysis and synthesis modules that generate an interference mitigated time-domain channelized signals. The mRAKE receiver, when performing demodulation processing, can combine the interference mitigated time-domain channelized signals to generate fingers that combine components of transmissions received from the other nodes.

A method and apparatus for reception of signals with unpredictable transmission properties enabling physically secure, unscheduled and interference-resistant communication over machine-to-machine (M2M) networks is claimed. A physical structure comprising combinations of unpredictable physical dwells, spreading vectors, and selection of intended receivers is described. Reception methods employing blind detection and signal separation techniques are then described, which can detect and extract transmissions intended for a receiver, and excise transmissions not intended for that receiver, as part of the despreading procedure, even if received at much higher power levels than the intended transmissions. The resultant receiver eliminates the ability for an adversary to predict and override M2M transmissions; allows reception of ad-hoc transmissions in dense environments without scheduling, CSMA/CA protocols, or feedback paths enabling scheduling, and allows macrodiverse reception of transmissions at networks of connected receivers, thereby providing additional efficiency and security improvements by exploiting the route diversity of the network.