Covert acoustic communications (CAC) through solid propagation channels that connect node pairs is achieved by encoding signals using spread spectrum coding techniques that position the encoded signal at a center frequency f.sub.c within a narrow frequency bandwidth BW.sub.NB in which the amplitude of the channel response H(f) between each node pair is relatively high. The channel response H(f), bandwidth BW.sub.NB and center frequency f.sub.c, and accordingly the signal data rate will adapt for each node pair and possibly each side of the node pair. A pre-distortion filter 1/H(f) pre-distorts the encoded signal over bandwidth BW.sub.NB to compensate for material and modal dispersion and multipath between the node pair. This technique avoids the problems associated with frequency dependent attenuation of the continuous solid path and allows for simultaneous transmission and reception of signals among the multiple node pairs.

A code acquisition module for a direct sequence spread spectrum (DSSS) receiver includes: a Sparse Discrete Fourier transform (SDFT) module configured to perform an SDFT on a finite number of non-uniformly distributed frequencies comprising a preamble of a received DSSS frame to calculate Fourier coefficients for the finite number of non-uniformly distributed frequencies; a multiplier configured to multiply the Fourier coefficients for the finite number of non-uniformly distributed frequencies of the received DSSS frame by complex conjugate Fourier coefficients for the finite number of non-uniformly distributed frequencies to generate a cross-correlation of the received DSSS frame and the complex conjugate Fourier coefficients; and a filter module configured to input the cross-correlation and output a delay estimation for the received DSSS frame.

A system and method of DFT-S-OFDM modulation is provided that uses a set of frequency domain patterns. For a given transmitter, for a set of DFT-S-OFDM symbols, the frequency domain pattern changes according to a time domain hopping pattern. Advantageously, the time domain hopping patterns are defined to allow only a certain amount of overlap, for example for only one DFT-S-OFDM symbol, between any two time domain hopping patterns. This functions to reduce the effect of a collision, when two transmitters use the same frequency pattern, they will do so only for part of the overall transmission. Optionally, frequency domain spectral spreading is used in the transmitter. This can further reduce the PAPR. In the receiver, successive interference cancellation may be employed to reduce the effect of colliding transmissions.

A secure training sequence (STS) is included in wireless packets communicated between electronic devices to assist with channel estimation and wireless ranging. The STS includes multiple STS segments generated based on outputs from a cryptographically secure pseudo-random number generator (CSPRNG), the STS segments being separated by guard intervals and formatted in accordance with an 802.15.4 data symbol format that uses burst position modulation (BPM) and binary phase shift keying (BPSK) to map bits from the CSPRNG to burst positions and pulse polarities for the STS symbols. Both a first electronic device, which generates the STS, and a second electronic device, which estimates a communication channel using the STS, have prior private knowledge of cryptographic keys required to generate a non-repetitive single-use pseudo-random (PR) sequence by the CSPRNG. The STS includes two burst position intervals per STS symbol and two possible burst positions within each burst position interval.

Methods and devices for transmitting and receiving data through biological tissue using ultrasonic pulses are described. Methods of the present invention may set an initial time-hopping frame length and an initial spreading code length for data transmission. A request-to-transmit may be sent from a transmitter over a control channel at the initial frame and code length. The receiver may respond to the transmitter with a clear-to-transmit packet having feedback information. The feedback information can be used to improve a forward time-hopping frame length and a forward spreading code length. Embodiments of the invention may involve a body area network or body surface network comprising a plurality of implanted sensor nodes operating according to the disclosed invention.

A code acquisition module for a direct sequence spread spectrum (DSSS) receiver includes: a Sparse Discrete Fourier transform (SDFT) module configured to perform an SDFT on a finite number of non-uniformly distributed frequencies comprising a preamble of a received DSSS frame to calculate Fourier coefficients for the finite number of non-uniformly distributed frequencies; a multiplier configured to multiply the Fourier coefficients for the finite number of non-uniformly distributed frequencies of the received DSSS frame by complex conjugate Fourier coefficients for the finite number of non-uniformly distributed frequencies to generate a cross-correlation of the received DSSS frame and the complex conjugate Fourier coefficients; and a filter module configured to input the cross-correlation and output a delay estimation for the received DSSS frame.

Systems and methods are disclosed for detecting and reporting node power outages in a connected network. A node in the network detects that a power outage has occurred at the node and the node generates a last gasp packet using a packet format containing fewer data units than a regular packet format used by the network for communication. The node broadcasts the last gasp packet to its neighboring nodes. After receiving the last gasp packet, a neighboring node estimates the time of the power outage and converts the last gasp packet into an outage alarm message using the regular packet format. The neighboring node transmits the outage alarm message to a headend system to report the power outage at the node.

Systems and methods are disclosed for detecting node outages in a mesh network. A tracking node in the mesh network detects a set of signals originating from a tracked node in the mesh network. The set of signals includes beacons and communication messages transmitted by the tracked node. The tracking node determines that a threshold number of the alive beacon intervals have passed since receiving a most recent signal from the tracked node. The tracking node then outputs a ping to the tracked node requesting a response to the ping. When the response to the ping is not received from the tracked node, the tracking node transmits an outage alarm message to a next topologically higher layer of the mesh network, the outage alarm message comprising an identification of the tracked node.

Systems and methods are disclosed for detecting node outages in a mesh network. A tracking node in the mesh network detects a set of signals originating from a tracked node in the mesh network. The set of signals includes beacons or communication messages transmitted by the tracked node. The tracking node determines that a threshold number of the beacon intervals have passed since receiving the most recent signal from the tracked node. The tracking node performs outage validation based on data received from another node in the mesh network and updates the status of the tracked node. Based on the updated status, the tracking node outputs a ping to the tracked node requesting a response to the ping. When the response to the ping is not received from the tracked node, the tracking node transmits an outage alarm message to a next topologically higher layer of the mesh network.

A code acquisition module for a direct sequence spread spectrum (DSSS) receiver includes: a Sparse Discrete Fourier transform (SDFT) module configured to perform an SDFT on a finite number of non-uniformly distributed frequencies comprising a preamble of a received DSSS frame to calculate Fourier coefficients for the finite number of non-uniformly distributed frequencies; a multiplier configured to multiply the Fourier coefficients for the finite number of non-uniformly distributed frequencies of the received DSSS frame by complex conjugate Fourier coefficients for the finite number of non-uniformly distributed frequencies to generate a cross-correlation of the received DSSS frame and the complex conjugate Fourier coefficients; and a filter module configured to input the cross-correlation and output a delay estimation for the received DSSS frame.