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Closed loop Power Control in CDMA Systems Based on New SIR estimation

Pengarang: Adit Kurniawan

Oleh : Adit Kurniawan, University of South Australia (adit@spri.levels.unisa.edu.au)

Dibuat : 2000-00-00, dengan file

**Keyword :**Closed Loop Power Control, DS-CDMA, SIR estimation

In this paper, the problem of closed loop power contraol based on Signal-to-Interference Ratio (SIR) is investigated for the reverse link of a Direct Sequence Code Division Multiple access (DS-CDMA) system in slow multipath fading environments. The investigation is focused on the issue of SIR estimation methods, which is crucial for a good power control performance. A novel and simple method foe SIR estimation using an auxiliary spreding sequence is proposed and simulated in this work. The performance of closed loop power control (CLPC) using tne new SIR estimator is evaluated in terms of bit error rates (BER) versus Eb /Io (ratio of bit energy-to-interference power spectral density). The result is compared with the BER performance using another standard SIR estimator, which is based on the estimation of the average power and variance of the received signal. Simulation results show that for low SIRs, the mean value of the estimated SIR based on the proposed method is better than that obtained by the standard estimator. Furthermore, the proposede SIR estimator can be preferred for practical reason because the estimation process is performed at the symbol level (after dispreading) . While in the standard method, processing partly takes place at the chip level, which requires more complex operation. The SIR estimation using the auxiliary spreading sequence, however, yields a higher variance on the estimated SIR compared to that when standard technuique is used. This is due to the fact that the new technique operates at the symbol level to perform the averaging process, while the standard technique utilizes the chip sequence, which is N times higher in the number of samples to be averaged, where N is the processing gain. However, the complexity of the new technique is N times lower compqred to the standard method, which makes the proposed method more attractive from the implementation point of view. The BER performance of CLPC is better when power control updating rates are much higher than the fading rates. This indicates that higher rates of power control can track the fading more accurately. The BER performance is also affected by the accuracy of the SIR estimate (mean and variance). Despite the higher variance, the new SIR estimator results in better estimates of the mean values for low SIRs, and therefore has better performance. For higher SIRs, the performance of the standard technique is slightly better due to the lower variance of the SIR estimates. This issue is identified, and a possible pollution using a prediction filter algorithm to reduce the variance has been suggested for further research.

**Deskripsi Alternatif :**

*In this paper, the problem of closed loop power contraol based on Signal-to-Interference Ratio (SIR) is investigated for the reverse link of a Direct Sequence Code Division Multiple access (DS-CDMA) system in slow multipath fading environments. The investigation is focused on the issue of SIR estimation methods, which is crucial for a good power control performance. A novel and simple method foe SIR estimation using an auxiliary spreding sequence is proposed and simulated in this work. The performance of closed loop power control (CLPC) using tne new SIR estimator is evaluated in terms of bit error rates (BER) versus Eb /Io (ratio of bit energy-to-interference power spectral density). The result is compared with the BER performance using another standard SIR estimator, which is based on the estimation of the average power and variance of the received signal. Simulation results show that for low SIRs, the mean value of the estimated SIR based on the proposed method is better than that obtained by the standard estimator. Furthermore, the proposede SIR estimator can be preferred for practical reason because the estimation process is performed at the symbol level (after dispreading) . While in the standard method, processing partly takes place at the chip level, which requires more complex operation. The SIR estimation using the auxiliary spreading sequence, however, yields a higher variance on the estimated SIR compared to that when standard technuique is used. This is due to the fact that the new technique operates at the symbol level to perform the averaging process, while the standard technique utilizes the chip sequence, which is N times higher in the number of samples to be averaged, where N is the processing gain. However, the complexity of the new technique is N times lower compqred to the standard method, which makes the proposed method more attractive from the implementation point of view. The BER performance of CLPC is better when power control updating rates are much higher than the fading rates. This indicates that higher rates of power control can track the fading more accurately. The BER performance is also affected by the accuracy of the SIR estimate (mean and variance). Despite the higher variance, the new SIR estimator results in better estimates of the mean values for low SIRs, and therefore has better performance. For higher SIRs, the performance of the standard technique is slightly better due to the lower variance of the SIR estimates. This issue is identified, and a possible pollution using a prediction filter algorithm to reduce the variance has been suggested for further research.*

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