Abstract: Methods and apparatus for frequency tracking of a received signal. In an aspect, a method is provided wherein the received signal comprises one or more symbols having a periodic structure. The method comprises receiving a plurality of samples of a selected symbol that comprises pilot signals scrambled with data and determining a window size and a periodicity factor. The method also comprises accumulating a correlation between samples in a first window and samples in a second window to produce an accumulated correlation value, wherein the first and second windows have a size and a separation based on the window size and the periodicity factor, respectively, and deriving a frequency error estimate based on the accumulated correlation value.

Abstract: Channel estimation in a spectrally shaped wireless communication system in which an initial frequency response estimate is obtained for a first set of P uniformly spaced subbands (1) based on pilot symbols received on a second set of subbands used for pilot transmission and (2) using extrapolation and/or interpolation. A channel impulse response estimate is obtained by performing an IFFT on a frequency response estimate. The number of taps in the channel impulse response can be truncated to a predetermined number of taps determined based on an operating mode of the second set of P uniformly spaced subbands. The energy of each tap value remaining after truncation can be compared to a predetermined threshold and modified based on the results of the comparison. The predetermined threshold can be determined based on an operating mode. A final frequency response estimate for each mode within each OFDM symbol is derived.

Abstract: Techniques for performing frequency control using dual-loop automatic frequency control (AFC) are described. The dual-loop AFC includes an inner loop that corrects short-term frequency variations (e.g., due to Doppler effect) and an outer loop that corrects long-term frequency variations (e.g., due to component tolerances and temperature variations). In one design, a first inner loop is implemented for frequency control of a first system (e.g., a broadcast system), a second inner loop is implemented for frequency control of a second system (e.g., a cellular system), and at least one outer loop is implemented for adjusting a reference frequency used to receive signals from the first and second systems. Each inner loop estimates and corrects the frequency error in an input signal for the associated system and may be enabled when receiving the input signal from the system. The reference frequency may be used for frequency downconversion, sampling and/or other purposes.

Abstract: Dynamic channel estimation thresholds allow for determining optimal threshold values for channel estimation in a layered-modulation wireless communication system. A channel estimation threshold can be used to remove or otherwise filter out channel estimate components that may be significantly influenced by noise. The channel estimation threshold value can be used to generate a refined channel estimate that is used in decoding multiple layers of a layered modulation signal. The channel estimation threshold value can be varied based on the performance of the various signal layer decoders. The adaptive channel estimation threshold provides for decoding a base layer based on an optimal threshold value for the base layer; determining an error rate associated with decoding the base layer; and using an optimal threshold value for an enhancement layer in a channel estimation algorithm if the error rate is lower than a predetermined level.

Abstract: A media access control (MAC) layer controller can manage base layer data and enhancement layer data in a layered modulation system. The MAC layer controller can process both base layer data and enhancement layer data and map the encoded symbols to a layered modulation constellation when both are present. If data for one of the layers terminates, then the MAC layer controller can generate and supply predetermined stuffing data to the layer lacking additional data. The MAC layer controller can send a control signal to the physical layer hardware to cause the hardware to map the layered signals having the stuffing data to a modified signal constellation. The MAC controller can also generate an overhead message that indicates the occurrence of the stuffing data. The receiver can receive the overhead message and can use the information to configure the receiver for the layered modulation constellation or the modified signal constellation.

Abstract: A system and method are provided for generating bit log likelihood ratio (LLR) values for two-layered Quadrature Phase-Shift Keying (QPSK) turbo decoding in a wireless communications user terminal (UT). The method includes receiving a two-layered QPSK signal with an energy ratio that is unknown, but typically defined as either k12 or k22. The method selects a mismatched energy ratio (k2) between k12 and k22, and generating bit LLR values for two-layered QPSK turbo decoding, using the mismatched k2 energy ratio. For example, if the received two-layered QPSK signal is known to have an energy ratio of about 4 or about 6.25. Then, k2 is selected to be about 5.0625. Alternately stated, the mismatched k2 energy ratio in selected by determining the approximate midpoint between k12 and k22.

Abstract: A decoder for a layered modulation system can be configured to independently and concurrently decode each of a base and enhancement layer. The base layer decoder and enhancement layer decoder can be configured substantially in parallel and can each operate concurrently on the same received layered modulation symbol. Each of the base and enhancement layer decoders can be configured with a bit metric module that is configured to determine a signal quality metric based on the received symbol. In systems having turbo encoded data, the bit metric module can be configured to determine a log likelihood ratio. The ratio is based in part on a channel estimate and an energy ratio used in the layered modulation constellation.