Chapter 3 Performance Analysis
3.4 Power Saving for One-Bit System
In the previous section, transmitted power decreases while lowering the threshold.
However, BER would be much worse. If we do not adjust the threshold while ISI and the current data have different polarity, the transmitter should spend more power to let the received amplitude equal to the threshold. Therefore, if ISI is destructive to the current data, we could lower the threshold to save power. That is, we would allow the received amplitude under the threshold. In this simulation, we let ξ =1 and adjust 'ξ in Table 2.2 to see the change of BER and the average transmitted power. Fig 3.12 represents the BER according to different thresholds. Table 3.5 records the related average transmitted power.
Fig. 3.12BER vs. received SNR for modified threshold smaller than 1
threshold
average transmitted power 1 1.9679 0.9 1.6422 0.8 1.3571 0.7 1.1102 0.6 0.9029 0.5 0.7326
Table 3.5 The simulated average transmitted power of modified threshold smaller than 1
In Fig. 3.12 and Table 3.5, it can be shown that BER would be worse as the threshold getting smaller, and the related average transmitted power would decrease. If the threshold decreases, from Table 2.2, the amplitude of received data rk =ξ' will be reduced. Therefore, the received data would be more sensitive to noise. Hence, BER
would get worse as the threshold decreases. On the other hand, the average transmitted power decreases obviously as the threshold decreases. That is because we only lower the transmitted power while ISI is destructive to the upcoming data, the average transmitted power would decrease while the threshold decreases.
3.5 Analysis of Power Saving for Two-Bit System
After clarifying the case of modifying the threshold in one-bit system, we now consider two-bit system. In Chapter 2.3.2.3, we explained that there was another information we can obtain at transmitter, which is the content of upcoming data.
Therefore, as channel coefficients are accurately measured in advance, we could find out which subsequent data would be affected mostly by the current data. And then, ISI induced by the current data would be checked if it is helpful to this mostly-affected data.
If it is not, we will reduce the threshold as the same setup of one-bit system to save power.
Fig 3.13 depicts the BER performance of different threshold and the comparison of one-bit and two-bit systems. Table 3.6 records the simulated average transmitted power and compare with one-bit system.
Fig 3.13 Comparison of one bit and two bits BER vs. received SNR
threshold
average transmitted power (one bit)
average transmitted power (two bit)
1 1.968 1.968
0.9 1.642 1.615 0.8 1.357 1.306
0.7 1.11 1.039
0.6 0.903 0.82
0.5 0.733 0.645
Table 3.6 The simulated average transmitted power under one-bit and two-bit systems
In Fig. 3.13, BER performance for two-bit system is close to that of one-bit system.
However, the BER of two-bit system is a little better than one-bit system. It is because the ISI effect of the proceeding data is reduced in advance. Also, besides modifying threshold while ISI effect is destructive to the current data, the threshold is also modified.
Therefore, average transmitted power is saved as comparing with one-bit system.
Chapter 4 Conclusions
This thesis presents a transmission scheme to solve the ISI problem while transmit speed raises to Gbps. This method utilizes measured channel coefficients to manage multipath-induced ISI and set the amplitude of noiseless received signal. The proposed system structure moves the equalization functionality to the transmitting end. The developed MP circuit at TX can first measure the channel response coefficients. Next, the modified MP can estimate the related ISI effect. According to the estimated ISI, the threshold mechanism is excuted to determine the amplitude of transmitted signal. After transmitting these signals through the multipath channel, the related output signal will be defined by a threshold. While the threshold equals to the data magnitude, the BER performance can approach the ideal multipath-free transmission. The BER could be improved by transmitting more power. The transmitted power could be reduced by lowering the threshold while ISI and the current data have different polarity. While the channel SNR is high, we can choose small threshold so as to save power but still maintain acceptable BER. At last, a two-bit system is proposed to improve BER performance and save transmitted power. Although its improvement is not obvious, it could be a useful system for future study.
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