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Method for carrier frequency offset estimation for packet-based wireless communication with multiple antennas

IP.com Disclosure Number: IPCOM000020734D
Publication Date: 2003-Dec-10
Document File: 4 page(s) / 125K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for carrier frequency offset estimation for packet-based wireless communication with multiple antennas. Benefits include improved functionality and improved performance.

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Method for carrier frequency offset estimation for packet-based wireless communication with multiple antennas

Disclosed is a method for carrier frequency offset estimation for packet-based wireless communication with multiple antennas. Benefits include improved functionality and improved performance.

Background

Packet-based wireless communication systems conventionally require estimation of the carrier frequency offset between the transmitter and the receiver to enable coherent demodulation of the received signal. This process must be performed very rapidly due to the short preamble sequence available for training and the requirement to minimize packet overhead. The use of multiple antennas in wireless systems is expected to become more common to provide dramatically better range, rate, and service availability relative to single antenna systems.

Technical standards all facilitate rapid acquisition of required receiver parameters, including carrier frequency offset, through the use of a repetitive preamble sequence (see Figure 1). The advantage of the conventional repetitive preamble sequence for carrier frequency offset estimation is that the frequency offset can be readily estimated through autocorrelation of two adjacent preamble sequences. The frequency estimate is then obtained from the phase of the autocorrelation (see Figure 2). For example, consider the case in which one of the antenna branches has very low SNR (perhaps less than 0 dB) due to a fade. The phase estimate obtained from that branch produces an unreliable estimate. It may not be sufficiently de-weighted in the combining process because very low SNRs are difficult to accurately measure. They can exhibit a minimum value, which results in the phase estimate obtained from that branch being overvalued.

The key feature of this technique is that it is insensitive to intersymbol interference (ISI) due to multiple paths and being insensitive to symbol timing alignment. Carrier frequency offset can be estimated prior to the receiver establishing correct symbol timing or performing channel estimation and equalization. This property is highly successful for the rapid acquisition of the packet by the receiver. It is a key reason why repetitive preamble sequences are typically used in packet based wireless standards.

One way to extend the single antenna technique is to make a carrier frequency measurement separately for each antenna. A weighted average of the individual results is computed using the signal-to-noise ratio (SNR) of the signal in each corresponding branch as its weight. However, this solution is complex and does not provide maximum accuracy.

General description

This disclosed method is carrier frequency offset estimation for packet-based wireless communication with multiple antennas. Data received from more than one antenna can be combined to improve upon the accuracy of the initial carrier frequency estimate, provide robustness to channel fading, and minimize implementati...