摘要:
A method is disclosed for PN correlation and symbol synchronization of a spread spectrum signal at a receiver when a symbol boundary of the spread spectrum signal is not on a PN epoch or is otherwise unknown. The method includes the operation of modulating the spread spectrum signal with a PN code to form a potentially despread signal. The potentially despread signal can be integrated for a plurality of symbol times at a rate of N integrations per symbol time to form N symbol energies per symbol for a plurality of symbols. Each of the N symbol energies can correspond to a different symbol time hypothesis. The N symbol energies from the plurality of symbols can be added respectively to form N summed symbol time hypotheses. The Nth summed symbol time hypothesis having maximum power can be found. The Nth summed symbol time hypothesis can relate to a location of the symbol boundary.
摘要:
A first node initiating communications with a second node already in a secure network sends a discovery burst having a preamble portion and a payload portion. The preamble portion is sent at a varying frequency between high and low thresholds that are reflective of Doppler uncertainty between the nodes. The second node continuously listens at a frequency, termed an acquisition frequency. A data sequence in the preamble portion, known to the second node, is received and used to determine the receive instant in the preamble portion, and thereby compare against the known frequency ramp to determine the frequency at which the payload portion will be received. Preferably, the first node varies the preamble portion between thresholds more than once within the time span of a single preamble portion, and the preamble and payload portions are spread with different spreading codes. The preamble portion may also be disguised with noise generated by the first node.
摘要:
A composite code is made for example by exclusive-OR'ing each real element of a first constituent code A with each element of a second constituent code B to obtain a basic composite code. To suppress autocorrelation, differing numbers of doping code elements are inserted between code segments made from combining each element of code A with an element of code B. A matched filter first stage removes from its input the A code and any doping code added to it, summing the elements of code A. A matched filter second stage removes from its input the B code and any doping code added at the second level. The summed elements of code B are the input to the first stage. Optionally, the summed elements of the doping code at any level may be delayed and summed with the elements of the A code in the first stage.
摘要:
A first node seeking entry into a secure spread spectrum communications network sends a discovery burst at a low rate, and sends traffic bursts at a higher rate to exchange data rate for range. A receiving node receives discovery bursts via an omni-directional link and transmits and receives traffic bursts via directional links. As a node within the network detects a fading signal, it transmits a discovery burst at low rate on both its uplink and downlink channels. Other nodes may reply via the original uplink channel, and the fading node updates a list of candidate nodes through which it can relay through the network to its intended recipient by reversing the link direction of its original uplink and original downlink channels.
摘要:
A parallel correlator and method includes temporarily storing in a series of P sequence registers, each of length R1, serial bit-sequences of a code of length N=P*R1. In a first-level of processing, certain unique bit sequences are inverted to reduce the number of unique bit sequences by half. Identical bit-sequences are then combined and temporarily stored in a first-level sub-accumulation register. Alternatively, bit sequences differing by only one bit may be combined in a common first-level sub-accumulation register. Further levels of similar processing may be imposed, where each subsequent level taps and inverts only a portion of the bits in the above level of processing, thereby reducing the number of unique bit sequences. Finally, all negative energy is combined in one register position, inverted, and added to all positive energy in the other register positions. When the spreading code was aligned among the series of sequence registers, the energy is added coherently and an energy peak is output, indicating alignment of the spreading code in the sequence registers.
摘要:
A method is presented for estimating a phase error for first (rI) and second (rQ) orthogonal signal components spread respectively by different first cI and second cQ spreading codes. A cross-despread value IdQ and/or QdI is determined by despreading one signal component with the spreading codes associated with the other signal component (rI with cQ or rQ with cI). In parallel, the same signal component is also despread with its associated spreading code to determine an estimated data symbol for that component. An interference of Q into I or I into Q is calculated and multiplied by the estimated data symbol, and subtracted from the cross-despread value to achieve an estimate of phase error. Preferably, both cross-despread values are obtained, normalized to a common data rate, scaled to maximize signal to noise ratio, and combined into one phase error estimate. A phase error detector includes despreaders, multipliers, and adders to determine the cross-despread value and subtract the interference from it.
摘要:
A system for baseband amplitude limiting is provided. The system includes a CORDIC vector mode rotator device having an angle accumulator in addition to a gain device and limiter. The system also includes a second CORDIC rotator operating in rotation mode, and is coupled to the limiter.
摘要:
A method is disclosed for operating a wireless communications system, such as a DS-CDMA communications system, by transmitting a waveform that includes a plurality of repeating frames each having x header training base symbols in a header training symbol field (TH) and y tail training base symbols in a tail training symbol field (TT). The frame is received and functions as one of a plurality of different types of frames depending on the content of at least TT. In the preferred embodiment the frame functions as one of a normal traffic frame, a termination frame, or a legacy frame providing backwards compatibility with another waveform. A given one of the frames includes four equal-size data fields separated by three equal-sized control fields, the header training symbol field (TH) and the tail training symbol field (TT).
摘要:
A system for the efficient use of CORDIC rotators is provided. The system includes at least one first rotator operating in vector mode and includes a sign storage buffer. The system also includes at least one bit inverter coupled between the first rotator and a second rotator, the second rotator operating in rotation mode.
摘要:
A communications system employs the use of both synchronous CDMA and FDMA to provide a variable bandwidth waveform with multiple bonded transmitters and receivers that are agile in both frequency and PN code to permit a variable bandwidth and variable rate multiple access system. In a first aspect the teachings provide the use of both CDMA and FDMA together to enable an improved concentration efficiency by making a larger pool of bandwidth available to each user. In a second aspect these teachings enable channel bonding across both code space and frequency space, thus making the system capable of operating within a variable (not necessarily contiguous) bandwidth and at a finely variable rate.