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OFDM increases based on pilot channel estimation window of FFT

In Electronic Infomation Category: O | on April 13,2011

OFDM is the future of 4G wireless broadband access and LA7786 datasheet and the key technology of communication, because of its high spectrum efficiency and LA7786 price and combat multipath interference, etc., is becoming a hot research field of communications. In OFDM system, due to wireless channel in time domain and LA7786 suppliers and frequency domain selective fading characteristics, the need for channel estimation to obtain channel information.

Channel estimation can be divided into non-blind estimation, blind estimation, where the focus on the non-blind pilot-based estimates. Based on pilot OFDM channel estimation of the basic process is: first, in sending the appropriate insert pilot symbols; Then, in the receiver by using the pilot symbols to recover the pilot position of the channel information; Finally, the interpolation algorithm, access to all the time channel information.

Order to reduce the complexity of the interpolation algorithm, using the Van De Beek et al FFT based on pilot interpolation method for channel estimation. However, the FFT algorithm based on requirements of the multipath channel delay spread is an integer multiple of the sampling period, while the actual system, the channel does not meet the conditions, this will result in the energy spectrum of leakage, leading to aliasing errors. This paper presents a window function based on Hamming windowed FFT optimized channel estimation algorithm.

1 OFDM system baseband model

OFDM baseband system model shown in Figure 1, where the channel model is multipath fading channel model. First, the input binary sequence modulated pilot symbols inserted after mapping, denoted by X (k), then the inverse Fourier transform (IDFT), by the time domain signal x (n). In the subsequent discussion, n and k, respectively, the signal in time domain and frequency domain signal subscript.

At the receiving end, channel output response y (n) can be expressed as x (n) and impulse response h (n) of the circular convolution, such as type (1) below:


Where v (n) represents the system noise.

Then Fourier transform (DFT), by frequency response Y (k) is:



Figure 1 OFDM baseband model 2 based on pilot channel estimation

2.1 Pilot Selection and insertion

Using comb pilot pattern shown in Figure 2, D f = N / M is the frequency domain pilot spacing. The pilot structure of the channel frequency selectivity sensitive to channel help to overcome the adverse effects of fast fading. Carrier for each OFDM symbol is the pilot number of N integer multiple of the number of M, and each symbol is the pilot of the first point of the carrier.

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