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   Channel Estimation (WMSA)       

Channel Estimation (WMSA)

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Notes

1. The weighted multi-slot averaging (WMSA) channel estimation model can be used to estimate channel characteristics for all paths using pilot symbols. The WMSA channel estimation is shown in Fig.1.

2. Algorithm description: Let r_l(n,k) be the nth received symbol at the output of the matched filter in the kth slot for the lth resolved path, and p(n,k) is the nth local standard pilot symbol in the kth slot. The instantaneous channel estimation of the lth resolved path is performed using the pilot symbols belonging to the kth slot as follows


(1)
where N_f is the number of pilot symbols per slot, N₀ is the number of the first pilot symbol. In the case of slow fading, since the channel gain remains almost the same over a period of sev­eral slots, we can extend the observation interval to more than one slot to add coherently sev­eral consecutive channel estimates. We apply a linear filter with 2K taps. The filter output is expressed as


(2)
where a_i is the real-valued weighting factor (or tap coefficient). Since the magnitude of the autocorrelation function of the time-varying complex-valued channel gain is an even function with respect to the time difference, the contribution from the past and future channel gains to the channel estimate should be the same. Therefore, we set the filter coefficients, a_i and a_-i, equal to each other. Term n_l(k) is used as the channel estimate at all symbol positions in thee kth slot, so the channel estimate is represented as


for (3)

Fig. 1 Block diagram of WMSA channel estimation

3. In order to understand this model better, a block diagram of Rake receiver used in time-multi­plexed pilot channel is given, as shown in Fig.2.

Fig. 2 Block diagram of Rake receiver

References

1. [1]K. Higuchi, H. Andoh, et al, “Experimental evaluation of combined effect of coherent RAKE combining and SIR-based fast transmit power control for reverse link of DS-CDMA mobile radio,” IEEE Journal on Selected Areas in Communications, vol. 18, No.8, pp.1526-1535, Aug. 2000.

2. [2]H. Andoh, M. Sawahashi, and F. Adachi, “Channel estimation filter using time-multiplexed pilot channel for coherent Rake combining in DS-CDMA mobile radio,” IEICE Trans. Com­mun., vol. E81-B, no. 7, pp. 1517–1526, July 1998.

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