Abstract:
A mechanism for retrieval of carrier frequency and carrier phase in a received modulated carrier waveform. Retrieval of carrier frequency and carrier phase can be implemented in an analog electrical circuit, using a field programmable gate array (FPGA), or in computer code. Independent of the implementation, the mechanism performs frequency and primary phase recovery by forcing transforms of a pilot tone in the upper and lower sidebands to the same frequency using a feedback loop. The difference-in-magnitudes of the channelized pilot are used by a phase lock loop to perform secondary phase recovery in a manner that also resolves phase sign ambiguity. Benefits of this mechanism include improved phase lock loop tracking performance and a reduction of noise in the data demodulated from the received carrier waveform.
Abstract:
A least squares estimator of carrier phase and amplitude in a receiver in a communication system using a phase shift keying modulation scheme that uses both known pilot symbols and unknown data symbols is described. That is, the method exploits knowledge of pilot symbols in addition to the unknown data symbols to estimate carrier phase and amplitude. Further, an efficient recursion based estimation method is described that only requires O(L . log L ) arithmetic operations where L is the number of received signals. This method uses the M -Ary rounded phase offsets to sort the data symbols and this sorted order is used to recursively calculate candidate values in an optimisation process. Simulation results show that the- estimation methods Using data and pilot symbols outperform estimation methods using only data symbols (ie non-coherent detection methods). Further, the system can be used for systems using multiple M -ary phase shift keying digital modulation schemes.
Abstract:
A delay buffer includes a first shift register (50) receiving input data and having a shift signal input port. The first shift register right shifts the input data responsive to a shift signal on the shift signal input port. The shift signal is determined based on an effective bit width of the input data. A first delay line (56) receives the shifted data from the first shift register while a second delay line (58) of equal length to the first delay line receives the shift signal. A second shift register (60) receives the output from the first delay line and receives the output of the second delay line on a shift signal input port (62). The second shift register then left shifts the data contained therein according to the shift signal.
Abstract:
Circuit for the suppression of the carrier for the transmission of digital signals in a communication connection with a coherent demodulation and suppressed wave carriers. The circuit comprises one or a plurality of spectral indicators detecting the shifting of the spectrum of the modulated signal and regulating the variable electronic element appropriately comprised of an adjustable oscillator. The circuit is arranged in the receiver portion of the connection, the output being connected to the reference input. In order to provide for the random process of the modulating digital signal, the circuit comprises, on the transmitter side of the connection, a bit mixer, whereas on the receiver side there is provided a bit separator. In connections with suppressed carrier, the circuit comprises a locked phase loop and/or stages carrying out non-linear operations.
Abstract:
Novel receiver systems and methods are disclosed to facilitate coarse frequency and frame recovery in an adaptive or otherwise variable coding system. Information contained in a header may be used to estimate and minimize phase and frequency errors The header information may also be used to adjust phase estimates. Phase and frequency information may thereafter be corrected using adaptive phase and frequency synchronization techniques on frame-by-frame basis.
Abstract:
A phase detection circuit comprises a quadrant identifying unit (101) for identifying the quadrant of a received signal on the basis of a received base band signal, a rotational projection unit (102) for projecting the received signal, after rotating the received signal according to a predetermined rule, onto the line perpendicular at the origin to the line bisecting the identified quadrant, an integrator (103) for integrating the projected signal, a 1-bit quantitizer (104) for judging whether the sign of the integration result is plus or minus and quantizing the result, a delay circuit (105) for delaying the quantized signal by a predetermined time, an adder (1) for adding the judgment result and the quantized signal by using the phase of pi as a modulo, and a low-pass filter (2) for latching the added phase values sequentially by means of a shift register in the low-pass filter, converting the phase value, if there is data across pi in all the data in the shift register, into a predetermined specific value, and averaging the phase values.
Abstract:
An excitation reference source (Fc) is split through a 90 degree splitter. One output from the splitter is fed to the LO port of a mixer. Data is fed to the mixer's IF port and causes PRK modulation of the LO port's signal. The output of the mixer at the RF port is a PRK modulated quadrature signal. This is attenuated and added back onto the reference by a zero degree combiner ready for transmission to the transponder.
Abstract:
A digital communications DQPSK passband detector having a matched filter, a differential decoder, and a slicer that use elementary circuit components. In the matched filter, recovered carrier references signals are fed along with the received signal to a pair of XNOR gates. This arrangement effectively results in a multiplication operation without any complex circuit elements. The outputs of the XNOR gates control the direction of counting of a pair of binary counters that generate correlated values of the I and Q components in the received signal. Thus, the integrate/dump circuits of a conventional matched filter are replaced with simpler digital counters. A digital differential decoder to extract the phase difference information between two consecutive received symbols is built from a network of delay elements, multipliers, and adders to recover the phase data. The digital differential decoder produces a digital complex-signal output that can be quantized in a digital slicer to decode the plurality of binary bits transmitted through the data symbols. All these operations are performed on digital signals with basic digital circuit elements, thus resulting in a repeatable robust receiver design without complex hardware components.