Abstract: A sliding correlator for timing synchronization in HIPERLAN/2 and IEEE 802.11a wireless local area networks by correlating the received signal with a known waveform is disclosed. The disclosed sliding correlator avoids the large number of complex multiplications per second, about 320 million by one estimate, by employing an implementation that avoids multiplication operations while also avoiding complexity. This invention discloses methods and apparatus to implement this correlator, using alternative correlator coefficients well suited for digital implementations, whereby the need to perform multiplication is eliminated.

Abstract: A sliding correlator for timing synchronization in HIPERLAN/2 and IEEE 802.11a wireless local area networks by correlating the received signal with a known waveform is disclosed. The disclosed sliding correlator avoids the large number of complex multiplications per second, about 320 million by one estimate, by employing an implementation that avoids multiplication operations while also avoiding complexity. This invention discloses methods and apparatus to implement this correlator, using alternative correlator coefficients well suited for digital implementations, whereby the need to perform multiplication is eliminated.

Abstract: An all-lag correlator is provided that correlates a received spread-spectrum signal with a reference code and produces at each sampling instance N correlation lags corresponding to the correlation of the received signal with 0, 1, . . . , N?1 lags (or delays) of the reference code, wherein N is the length of the reference code. The correlator includes a spread spectrum signal storage means, subtraction means, multiplication means, correlation lag storage means and addition means configured such that a correlation lag for a present sampling instance is based on a correlation lag of a previous sampling instance.

Abstract: An all-lag rotating-reference correlator correlates a received spread-spectrum signal with a rotating reference code, and produces in each sampling instance N correlation lags corresponding to the correlation of the received signal with 0, 1, . . . , N?1 lags (or delays) of the rotating reference code, wherein N is the length of the rotating reference code. The rotating reference code is time-variant and is generated by a rotation of a basic reference code. The received signal, possibly embedded in noise and interference, consists of periodic replicas of the basic reference code with or without data modulation. The first embodiment of the present invention describes a method and apparatus of an all-lag rotating-reference correlator which is applicable to situations where data modulation is not present in the received signal.

Abstract: A multiple phase shift keying (MPSK) spread spectrum communications receiver uses weighted correlation techniques for carrier recovery and tracking. The receiver includes three subsystems: a synchronization system, a carrier tracking system, and a data demodulation system. To demodulate the received signal, the receiver requires a carrier frequency that matches the frequency of an associated transmitter as well as the sampling (or chip) and symbol clocks that are synchronized with those of the transmitter. In the disclosed receiver, the carrier tracking subsystem continually tracks the carrier frequency of the received signal using a tracking scheme that uses weighted correlation techniques. The weighted correlation technique combines signals from two correlator modules, an R-correlator module and a W-correlator module, to generate the correlation output. The R-correlator is similar to conventional correlators. The W-correlator, however, is unlike conventional correlators.

Abstract: This invention discloses a code division multiple access communications system based on spread sequences designed by using complete factorization of polyphase matrix of a perfect reconstruction (PR) filter bank. The key characteristic is that the length of the spread sequence is longer than the period of the data symbol i.e., the data symbols are spreaded by the spread sequence and overlapped with neighboring data symbols. The design method includes an orthogonal code generator, a number of cascading stages and random permutation matrices. The number of cascading stages and random permutation matrices are selected according to the length of the spread sequence required. The length of the spread sequence could be selected according to the system performance requirement, hence the overlapping factor of spreaded data symbols. Furthermore, this spread sequence assumes integer values instead of binary when the orthogonal code generator generates a Walsh-Hadamard code.

Abstract: This invention relates to a broad band spread spectrum communications receiver with carrier recovery and tracking based on multiple phase shift keying (MPSK) techniques. The receiver comprises three subsystems: the synchronization system, the carrier tracking system and the data demodulation system. To demodulate the received signal, the receiver requires a carrier frequency that matches that of the transmitter as well as the chip and symbol clocks that are synchronized with those of the transmitter. In the disclosed system the carrier tracking subsystem continually tracks the carrier frequency of the received signal using a tracking scheme which is based on correlation techniques. The synchronization subsystem synchronizes the symbol clock and chip clock. These three subsystems interact with each other and result in an improved bit error rate (BER) performance.

Abstract: A multiple phase shift keying (MPSK) spread spectrum communications receiver uses weighted correlation techniques for carrier recovery and tracking. The receiver includes three subsystems: a synchronization system, a carrier tracking system, and a data demodulation system. To demodulate the received signal, the receiver requires a carrier frequency that matches the frequency of an associated transmitter as well as the sampling (or chip) and symbol clocks that are synchronized with those of the transmitter. In the disclosed receiver, the carrier tracking subsystem continually tracks the carrier frequency of the received signal using a tracking scheme that uses weighted correlation techniques. The weighted correlation technique combines signals from two correlator modules, an R-correlator module and a W-correlator module, to generate the correlation output. The R-correlator is similar to conventional correlators. The W-correlator, however, is unlike conventional correlators.

Abstract: A method an apparatus for protecting a configuration data sequence from reverse engineering is provided. The configuration data sequence includes a plurality of configuration bits and is used to configure the operation of a programmable device, such as an FPGA or other reconfigurable logic. According to a method of the present invention, the configuration bits of the configuration data sequence are partially encrypted by altering some, but not all, of the bits, and subsequently storing the partially-encrypted configuration data sequence external to the programmable device. Corresponding decryption information is then stored within the programmable device, which decrypts the partially-encrypted configuration data sequence using the decryption information stored therein to thereby configure internal logic of the programmable device.