Abstract:
Space time coding (STC) may be applied at the transmitter adding redundant information in both space and time dimensions. At the receiver, the received STC signal may be decoded using a spatial multiplexing MIMO decoding, for example, based on either Minimum Mean Square Error (MMSE) or maximum-likelihood (ML) algorithms. A selective STC decoder may incorporate both the conventional maximum ratio combining (MRC) decoding scheme and a MIMO decoding scheme. One of the STC decoding schemes may be selected, for example, based on estimated channel conditions in order to achieve a trade-off between error rate performance and computational complexity. Components used for a non-selected scheme may be powered down.
Abstract:
Apparatus and methods are provided for accounting for the effects of automatic gain control (AGC) in a multi carrier communications system when combining pilot tone interlaces by essentially reversing the effects of the AGC. In an aspect, a method for adjusting for the effects of automatic gain control when combining pilot interlaces in an interlace filter of a communication system is disclosed. The method includes determining a normalization gain of an applied automatic gain control normalized to a predefined time. Additionally, two or more combining coefficients for an interlace filter are determined based on a selected criterion. Each of the two or more combining coefficients is then modified based on the determined normalization gain to yield adjusted combining coefficients. Corresponding apparatus are also disclosed.
Abstract:
Apparatus and methods are provided for making timing adjustments in a multi carrier communications system. In an aspect, a timing correction method is provided for a multi-carrier system. This includes adjusting the time basis of two or more pilot interlaces with respect to each other in order to account for timing differences between the interlaces when combining the interlaces, and then adjusting or matching the time bases of the combined interlaces with a symbol to be demodulated. The alignment and matching is performed in order to generate channel estimates for data demodulation. The channel estimates, thus generated, along with the timing alignment information are in turn used for determining timing corrections to be applied to demodulation of a particular symbol. Corresponding apparatus are also disclosed that implement the methodology.
Abstract:
Techniques for deriving a channel estimate using a scattered pilot and a continual pilot are described. The scattered pilot is sent on different sets of carriers in different symbol periods. The continual pilot is sent in each symbol period on irregularly spaced carriers. The scattered pilot is used to identify the indices of channel taps of interest, e.g., L strongest channel taps. The continual pilot is used to determine the complex gains of these L channel taps. A receiver derives a channel impulse response estimate based on received pilot symbols for the scattered pilot, identifies the L strongest channel taps, and determines the indices of these L strongest channel taps. The receiver forms a Fourier sub-matrix based on the L tap indices and determines the gains of the L channel taps based on received pilot symbols for the continual pilot and the Fourier sub-matrix.
Abstract:
A method for correcting operation of the sleep oscillator (116) of a wireless communications device (100). Sleep oscillator frequency is estimated (412) so as to compensate for estimated temperature induced errors. In estimating temperature induced errors, errors (504) in sleep oscillator frequency are treated as being temperature induced errors (522), but probable multipath errors are bounded (410, 520) to predetermined sleep clock error maxima (602) corresponding to sleep duration over which the error occurred.
Abstract:
Certain aspects of the present disclosure provide techniques for wireless communications, wherein first number of transit antennas is advertised, but a different number of transmit antennas are actually used for transmission.
Abstract:
Techniques proposed in the present disclosure may used to update an FFT window position and perform linear phase compensation for OFDM wireless systems with up to two antennas at the receiver. Techniques presented herein may help resolve a problem of determining an optimum FFT window position under the condition that the length of channel impulse response is larger than the length of cyclic prefix.
Abstract:
Techniques for initial wireless network synchronization by a mobile station are provided. For certain embodiments, the techniques may involve a joint search for the cell identification (ID-cell index) and the coarse carrier frequency offset (CFO) estimation. For certain embodiments, the techniques may be based on hard correlation and binary differential despreading that substantially simplifies computational complexity compare to known techniques that independently search for the ID-cell index and perform CFO estimation.
Abstract:
Disclosed are methods and apparatus for initial acquisition in a communication system, and in particular Time Division Duplex (TDD) systems such as those found in LTE. A disclosed method, for example, includes running a plurality of predetermined amplifier gain states for a low noise amplifier (LNA) during initial acquisition in a time division duplex (TDD) system, and determining acquisition of a received signal based on searching across the plurality of predetermined amplifier gain states. Forcing the amplifier gain into a set of predetermined gain states affords quicker resolution of initial acquisition for setting the gain of the LNA, which in TDD systems is complicated due to an uncertain uplink/downlink timeline that precludes continuous operation of a gain setting algorithm run in the LNA.
Abstract:
In OFDM communication, a pre-FFT cyclic shift is used to achieve time basis matching among symbols, and/or between symbols and their corresponding channel estimates.