Cambridge Silicon Radio Limited

Samsung Electronics Co., Ltd.

Chunyang Yu

Andrei Popescu

Fei Tong

Paul C McFarthing

Methods and apparatus are provided for receiving packets on a channel of an Orthogonal Frequency Division Multiplexing (OFDM) system. A time shift value for a packet is estimated using a channel estimation and an FFT size. A synchronization position of the packet on a channel is adjusted using the estimated time shift value, and a filter is applied to the adjusted channel to generate a smoothed channel estimate. Alternatively, a channel with a corrected packet synchronization position is estimated, and a smoothed channel is estimated by applying a filter to the estimated channel. Packets are received on the channel, at a receiver of the OFDM receiving apparatus, in accordance with the estimated smoothed channel.

Method and apparatus for channel smoothing and estimation in OFDM system

The present application relates to a method for reducing the peak-to-mean amplitude ratio of a transmission signal comprising a plurality of coherent replicated signals, and to a transmitted for transmitting such a signal. The transmission signal is separated into the plurality of coherent replicated signals and one of the plurality of replicated signals is delayed with respect to another of the plurality of replicated signals, either in the time domain by introducing a time delay or in the frequency domain by introducing a phase shift. This has the effect of reducing the coherence of the delayed replicated signal with respect to the other replicated signal, reducing the peak power of the signal and therefore reducing the peak-to-mean amplitude ratio of the transmission signal.

Transmitter with reduced peak-to-mean amplitude ratio

An efficient method of OFDM peak reduction is described. In an embodiment, a set of the most significant peaks in a symbol of an OFDM signal are identified and then, for each identified peak, a shifted and scaled version of a template cancellation signal is subtracted from the OFDM signal. The template cancellation signal is shifted such that its peak aligns with the identified peak and it is scaled such that it has the opposite phase to the identified peak. No iterative peak search and cancellation is involved in peak reduction, i.e. a cancellation step is not followed by another peak search for the same OFDM symbol. The process is repeated for each symbol in turn and in some embodiments the OFDM signal is up-sampled before it is analyzed to identify the most significant peaks.

Efficient OFDM peak reduction algorithm

A method of WLAN frame detection in a received signal, wherein the frame comprises first and second training sequences and the method comprises auto-correlating the signal with a delayed version of itself to establish a first frame boundary estimate based on behavior of the autocorrelation result due to the inclusion of the first training sequence in the frame, cross-correlating the signal with a copy of the second training sequence at a range of time offsets in order to generate a first cross-correlation profile, classifying the first cross-correlation profile into one of a number of categories, establishing a second frame boundary estimate from the first cross-correlation profile in a manner dependent upon the category assigned to the first cross-correlation profile and determining a refined frame boundary estimate on the basis of a consideration of the first and second frame boundary estimates. Apparatus for performing the method is also described.

Frame boundary detection

A method of receiving a demodulated waveform according to a protocol in which the waveform represents a block of transmitted bits comprising a first group of bits and a second group of bits, the second group of bits being a function of the first group of bits, the method comprising: sampling the demodulated waveform to recover a first group of sample values corresponding to the first group of transmitted bits and a second group of sample values corresponding to the second group of transmitted bits; assigning bit values to reliable sample values of the first group of sample values; generating a set of candidates for a block of bits corresponding to the demodulated waveform, each candidate comprising a first group of candidate bits and a second group of candidate bits, the first group of candidate bits being generated using the assigned bit values and a combination of bit values unique to that candidate in the set of candidates, and the second group of candidate bits being generated by applying the said function to the first group of candidate bits; performing a correlation operation by determining a correlation between each candidate and the recovered first and second groups of sample values to form a correlation value associated with each candidate; and selecting the candidate associated with the correlation value that is indicative of the strongest degree of correlation between a candidate and the first and second groups of sample values to be the block of bits corresponding to the demodulated waveform.

Growing community of inventors

Cambridge, United Kingdom

Chunyang Yu