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Fft spreading among selected OFDM sub-carriers

A sub-carrier and carrier technology, applied in the field of orthogonal frequency division multiplexing equipment, can solve problems such as limiting frequency diversity

Inactive Publication Date: 2010-03-17
NXP BV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The difficulty is that the Walsh-Hadamard transform is only defined for blocks with lengths given by powers of 2
Therefore, only very small Walsh-Hadamard spreading block lengths can be used when pilot symbols are to be kept in place, and this limits the frequency diversity that can be obtained

Method used

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  • Fft spreading among selected OFDM sub-carriers
  • Fft spreading among selected OFDM sub-carriers
  • Fft spreading among selected OFDM sub-carriers

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Embodiment Construction

[0015] While the invention should be subject to various modifications and alternative forms, the specification of the invention has been shown as examples in the accompanying drawings and the details will be described in detail. It should be understood, however, that the invention is not limited to the particular embodiments described. On the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0016] OFDM is a multicarrier modulation technique that effectively divides the total system bandwidth into multiple (N) orthogonal subbands, tones, subcarriers, bins, frequency channels, and the like. Traditionally, each subband is associated with a corresponding subcarrier that can be modulated with data.

[0017] A radio frequency (RF) modulated signal can travel from a transmitter to a receiver through multiple signal paths, often with different delays. The rece...

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Abstract

An improved communications system for frequency-selective fading channels spreads the data-bearing modulation symbols across many OFDM sub-carriers using a discrete Fourier transform (FFT) at the transmitter, and despreads them using an inverse discrete Fourier transform (IFFT) at the receiver. An IFFT is included at the transmitter to form the OFDM symbols in the usual way, and a corresponding FFT is used at the receiver for the frequency-domain processing of the received signal. The difference is, the size of the FFT used for spreading at the transmitter is smaller than that of an IFFT usedjust after the FFT to create the OFDM symbols for transmission. This results in improved bit-error-rate, similar to single carrier block transmission (SCBT), while retaining the frequency domain benefits of conventional OFDM, e.g., low out of band emissions and the ability to control the power spectral density using active interference cancellation and other frequency-domain techniques. The improved frequency diversity is especially useful in the higher data rate modes of WLAN or WiMedia Physical Layer Standards, and in other cases where low redundancy forward error correction is employed.

Description

technical field [0001] The present invention relates to a communication system, and more particularly, to an OFDM device and method. Background technique [0002] There are three different variants of wireless local area networks (WLANs) defined by IEEE standards: eg (1) 802.11a, (2) 802.11b, and 802.11g. IEEE-802.11a operates in the 5GHz frequency band, while 802.11b and 802.11g operate in the 2.4GHz ISM frequency band. Data rates varying from 1 Mb / s to 54 Mb / s are encoded using multiple data rates and modulation techniques. All of these systems use time division multiple access and transmit data in frames of variable length. Each IEEE standard also specifies several test patterns with fixed times and duty cycles. [0003] 802.11b WLAN transmitters can use binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK). Modulation in the power envelope has an effect on the peak-to-average power ratio. 802.11a and 802.11g WLAN transmitters can use Orthogonal Fr...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H04L27/26
CPCH04L5/0007H04L5/0048H04L27/2602
Inventor 查尔斯·拉泽
Owner NXP BV
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