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 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 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 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:
This invention provides a highly flexible multiplexing scheme for Direct Sequence CDMA systems enabling the CDMA system to flexibly allocate CDMA channel resources between packet-switched broadcast channels and fast-circuit-switched dedicated channels in order to optimize system throughput. A method and system are provided for operating a communication system. The method has steps of: flexibly allocating CDMA channel resources between packet-switched broadcast channels and fast-circuit-switched dedicated channels in order to optimize system throughput, and employing a side channel as required to send all or a part of a total amount of data, depending on the total amount of the data. A bandwidth allocation scheme allocates a set of CDMA channels for burst packet-switched channels, and data is time division multiplexed over the set of burst CDMA channels providing a wide bandwidth data pipe for packet-switched data. Subscriber stations are equipped with multiple CDMA channel receivers tuned to the burst CDMA channels.
摘要:
The present invention concerns methods and apparatus for use in a spread spectrum communications system. In particular, in a method of the present invention information useful for acquiring a target signal is selected; the information is incorporated in an acquisition signal; the acquisition signal is transmitted; the target signal is spread with a spreading code; and the target signal is transmitted. At a receiving node, the acquisition information useful for acquiring the target signal is recovered from the acquisition signal and used to acquire the target signal. Apparatus in accordance with the present invention implement methods of the present invention. The methods and apparatus of the present invention can be used in node- and network-discovery situations.
摘要:
A matched filter decorrelator is described for efficiently performing a carrier frequency search while despreading a P/N long code constructed from two or more constituent codes such as codes A, B, C. The received signal is phase rotated into a frequency bin and partially despread, preferably over all but one of the constituent codes. To despread the final constituent code, the partially despread signal is input in parallel into frequency bins, where a phase rotator sets each input to a different bin. The frequency bins are then despread in parallel over the final constituent code, and an energy peak in one accumulator indicates which bin is the carrier frequency. Alternatively, a Fourier transform could be used over each of the frequency bins. By partially despreading prior to division into carrier frequency bins, hardware and computational burden are reduced as compared to prior art decorrelators. The present invention is particularly apt for use with an acquisition burst in a secure network.
摘要:
A system and method for detecting a spread spectrum encoded message within a received signal is described. The spread spectrum encoded message has an unknown code phase, unknown code frequency offset, and unknown carrier frequency offset. A plurality of code phase hypotheses, code frequency offset hypotheses, and carrier frequency offset hypotheses are searched in parallel. The unknown code phase, unknown code frequency offset, and unknown carrier frequency offset may also be estimated.
摘要:
An apparatus and method for correlating a signal over a correlation interval while accommodating spreading code frequency offset is described. In one embodiment, the apparatus includes a plurality of correlators, where each correlator forms a correlation result corresponding to a unique code frequency offset hypothesis. Each correlator selects samples from a tapped delay line at a tap position moved along the delay line at a rate corresponding to the correlator unique code frequency offset hypothesis.