Abstract: Apparatus for decoding a stream containing codes of a variable length code (VLC) takes advantage of the fact that a trie representation of the VLC can be pruned to leaves that each represent a complete binary trie. Combinational circuits or ROMs are then employed to decode the pruned trie, thereby substantially reducing the complexity of decoding a VLC. In one embodiment the decoding problem is partitioned into segments by considering a few bits at a time, starting with the most significant bits. Each segment either outputs a valid code or informs the next segment that the decoding process is incomplete and provides information to assist the next segment in its decoding effort. In applications where the VL code can be selected for greater efficiency of the decoder, the offered VL code can be restructured to minimize the number of k-nodes, to thereby minimize the pruned trie, and to concomitantly minimize the sizes of the ROMs in the decoder.

Abstract: A high performance global positioning system receiver including a first circuit section adapted for operative association with an antenna means and including components for receiving, amplifying, and converting transmitted signals from analog-to-digital signals; and a second circuit section including components for correcting Doppler frequency shifts in the transmitted signal, removing any codes from the digitized transmitted signal, and processing and preparing the digitized transmitted signals for operative utilization by a computer processor. A substantial part of the first circuit section is reducible to micronized format, whereas the entire second circuit section is reducible to micronized format.

Abstract: A method of protecting computer software is provided by storing a first key in a plug-in hardware device, storing an algorithm for processing a purality of keys including the first key in software to be protected, loading the software containing the algorithm in the computer and plugging in a hardware device in a communications port of the computer. A second key, external to the software, to be protected which bears a relationship to the first key by the algorithm is loaded into the computer where processing takes place of the first and second keys in the algorithm for deriving a control key, if present, for the continued processing of the software being protected. The step of loading the second key is performed using a computer keyboard, any input/output port, a hard disk file or any other method of entry in the computer. Additional keys external to the software which bear a relationship to the first and second keys configured in the algorithm may be provided.

Abstract: Cryptographic techniques for enciphering computer messages or the like include a unit for generating a cipher program for enciphering message data or plaintext by using a plurality of kinds of basic involution processing programs and desired key data, and a unit for enciphering the message data into ciphertext by executing the generated cipher program for the message data. A part of the involution processing program includes a substitution transformation portion and a permutation transformation portion. In accordance with the bit pattern of the above key data, a sequence for executing each of the involution processing programs and a sequence for executing the substitution transformation portion and the permutation transformation portion are determined. The above plurality of transformation processes include an operation of circular shifting to the right or left by X bits and an operation of circular shifting to the right or left by Y bits, with the X and Y being mutually different numbers.

Abstract: An improved sequence generator. The inventive generator (10) is adapted for use with a source (12) for providing successive bits of random data. The invention (10) includes a shift register (18) with a feedback loop. The shift register (18) stores bits of random data. Input to the shift register (18) is determined by a switch (16) which selects between the random data source (12), in a first mode of operation, and the feedback loop, in a second mode of operation. A control logic circuit (20) triggers the switch from the second mode to the first mode, for one clock cycle, as the random data source (12) provides a each successive bit of random data. Thus, optimum performance is obtained without the need to gate clock signals or to control the operation of the shift register.

Abstract: A novel range based acquisition system includes a receiver for receiving PN encoded signals coupled to a novel range based variable dwell correlator which detects and acquires uniquely timed received transmitter PN encoded signals employing different search dwell times for each of the estimated ranges from which the receiver transmitted PN encoded signals are being propagated so as to enhance the speed of acquisition of said PN encoded signals.

Abstract: Method for controlling the use of a data-processing workstation (1) by password, comprising storage of the password within the workstation and, at each initialization of this latter, acquisition of a password proposition followed by a comparison of this proposition with the stored password. The password is stored in a controlled-erasure permanent memory unit. In order to release the workstation (1) in the event of loss of the password, provision is made for generation (D1) of a set (36) of data associated with the blocked workstation, communication (D2) of part of these data by the user to an authorized service (S), supply (D3) in return by this service of coded release data (43), acquisition (D4) of these latter by the user on the workstation, thereby resulting, in the event of compliance, in erasure of the initial password and in release of the workstation. Application in an industrial environment to control of the use of offline or network workstations.

Abstract: A NICAM compatible baseband television signal converter is provided. A television signal including a NICAM digital audio subcarrier is converted to baseband and the NICAM subcarrier is filtered therefrom. The video and analog audio portions of the baseband television signal are demodulated. The demodulated video is descrambled and the demodulated analog audio is descrambled and/or volume controlled. The demodulated video and analog audio signals are then remodulated onto respective video and analog carriers. The filtered NICAM digital audio subcarrier is mixed with the video carrier to provide a modulated NICAM carrier. The remodulated video and analog audio signals are combined with the modulated NICAM carrier for output to a video appliance such as a television or video recorder.

Abstract: The submersible propulsor unit of the invention comprises a cylindrical shroud having a water inlet and a water outlet, a propeller having a hub rotatably mounted within the shroud on a shaft, and an electric motor for driving the propeller that includes a rotor mounted around the periphery of the propeller, and a stator circumscribing the shroud, and a bearing assembly that includes means for circulating ambient water around the bearing surfaces to both lubricate and cool them. A stationary cover is detachably secured over the bearing assembly on the water inlet end of the shaft to provide easy access to the bearings in the bearing assembly. The vane members that concentrically mount the shaft within the interior of the shroud are all connected on the downstream side of the propeller to reduce the cavitation and resulting noise when the propeller rotates. The magnetization of the rotor is provided by a plurality of permanent magnets for both improved efficiency, and lower noise.

Abstract: A mechanism is described for controlling access to a target application (TA) in a distributed computer system. A user sponsor (US) acting on behalf of an end user is issued with a privilege attribute certificate (PAC) containing initiator qualifier attributes (IQA) identifying permitted users of the PAC. The US obtains a key from a key distribution server (KDS), the key having initiator qualifier attributes of the US cryptographically associated with it.The US uses this key to communicate with the TA, and presents its PAC for verification. If the IQA in the PAC do not match the IQA associated with the key, this indicates that the PAC is being presented by the wrong initiator, and so access is not permitted.If a receiving entity subsequently wishes to act as an initiator and to use the PAC by proxy, it acquires a key from the KDS, the key having the receiving entity's attributes cryptographically associated with it. This provides a way of regulating proxy use of PACs.

Abstract: Subtractive CDMA demodulation optimally decodes a coded information signal embedded in many other overlapping signals making up a received, composite signal. A radio receiver correlates a unique code corresponding to the desired signal to be decoded with the composite signal. Moreover, after each information signal is successfully decoded, it is recoded and removed from the composite signal. Subtractive CDMA demodulation is enhanced by decoding the composite signal in the order of strongest to weakest signal strength. The individual information signals are spread using block error correction codes which are correlated with the composite signal using Fast Walsh transforms. Correlated signals identified as the largest transform component are removed from the composite signal and the remaining composite signal is reformulated using an inverted Fast Walsh transform.

Abstract: A method and apparatus for carrying out limited encipherment broadcast by generating a cipher key obtained from destination information added to service information are provided. An information service station transmits to each receiving station a random number, destination information for designating a destination station, and enciphered data obtained by enciphering service information by a common key generating by using the random number and destination information. An IC card at each receiving station which is provided in advance with a key generating function from the information service station, generates the common key by using the received random number and destination information only when it is confirmed from the destination information that the receiving station has a data reception right, and deciphers the enciphered data by using the common key to obtain the original service information.

Abstract: According to the invention, the chip card issues a first certificate comprising its letter of credentials (Crc), an exponential (X), an optional message (M), these quantities being signed. The security module verifies the signature and in return issues a second certificate containing its letter of credentials (Crm), an exponential (Y), an optional message (M'), a cryptogram (C), these quantities being signed. A common secret key is constituted between the card and the security module by the exponentials and allows the card to interpret the cryptogram addressed to it and to act in accordance therewith.

Abstract: Method and apparatus for changing the bit rate of a digitized analog signal stream from a first bit rate to a second bit rate. A first sequence generator provides a digital predictor sequence clocked at the first bit rate. A combiner has an output providing a combined digital stream at the first bit rate, combining the digital predictor sequence at the first bit rate and the digital analog signal stream at the first bit rate. An adaptive processor has its input coupled to at the output of the signal combiner. The adaptive processor has variable weights which are responsive to an error signal, an output providing a processed combined digital stream having a bit rate responsive to the weights, and an error signal input port. A second sequence generator provides the same digital predictor sequence, but clocked at the second bit rate.

Abstract: A method and apparatus is provided for maintaining received signal power levels at an average level when a signal power estimate is on average similar to the average of actually received signal power levels. The maintaining of the received signal power levels is accomplished by generating an estimate of the power of a received signal. Subsequently, a difference signal is generated by subtracting the estimated received signal power from a predetermined reference signal power. Finally, a signal power control threshold is adjusted as a function of the difference signal.

Abstract: A ferromagnetic material on an optical fiber assures that the fiber is held n a proper position on a spool by a magnetic field. This stabilizes the optical fiber during winding to permit an automation of the spooling process and provides a constant force for holding the spooled optical fiber during storage. The constant and predictable holding force helps assure a constant and predictable peel force during deployment of the optical fiber.

Abstract: A communication system having a site employing a plurality of communication channels. Each channel is assigned a desired received signal strength threshold. A channel is assigned to a subscriber unit based upon the strength of the signal received at the site and the power control range of the subscriber unit. The selection of a channel may be performed either by the site or the subscriber unit. In an FDMA environment, each separate frequency division channel may be assigned different received signal strength thresholds. In a non-overlapping time interval (TDMA) environment, each separate time division channel may be assigned different received signal strength thresholds. In another embodiment, a combination of FDMA and TDMA environments can be used.

Abstract: In a wireless local area network in which data packets are spread spectrum encoded, method and apparatus are provided for determining phase values that synchronize noise codes at network stations with received data packets. A synchronizing packet is first transmitted from a source station to various network stations. Each network station performs a wide-range search for a phase value that synchronizes the noise code of the station with the synchronizing packet. Thereafter, each network station performs narrow-range searches for phase values synchronizing the noise code of the station with subsequently received network packets. The stations switch to the wide-range search mode whenever a synchronizing phase angle has not been detected for predetermined period of time and switch to a narrow-range search mode whenever a synchronizing phase angle is detected.

Abstract: According to the disclosed method, decoys which are the reproduction of the corresponding interpolated sequence are inserted into the scrambled line, at the end of the first section and at the start of the second section.

Abstract: A system for scrambling and descrambling complex signals, such as video signals, employs a system for encoding the decoding information, in the form of two security keys, directly onto the scrambled signal being transmitted, without the need of a second communications link for delivering one of the keys. In a video embodiment, several of the video lines during the vertical scan period are encoded with identification information which identifies a specific one of multiple decoders at the receiving stations, and a scrambled security code. The security code can only be descrambled by the decoder which is specifically identified in the identification code. A security code descrambling algorithm which is specific to the respectively associated decoder is permantently installed in the decoder along with the identification information. The relationship between the security code descrambling algorithm and the identification code for each of the decoders is stored in a memory at the transmitting station.