Chapter 4 Mobile-Assisted and Channel-Fading-Prediction-Based Power
4.2 Mobile-Assisted and Channel-Fading-Prediction-Based PC schemes
4.2.2 Mobile-Assisted and Channel-Fading-Prediction-Based PC scheme 2
cmdC
cmdF
Note: the P(t), F(t), I(t), SIR , and D are in dB unit
Figure 4.2: The MA CFP PC scheme 2
Figure 4.2 shows the MA CFP PC scheme 2. At the mobile station, the MA PC method 2 is used. Comparing with the MA CFP PC scheme 1, the difference is only the transfer function from slope of channel fading to cmdF at the mobile station. Although we do not change the value of α , the weighting of cmdF can be different when the slope of channel fading is at different value in this scheme. It also can be seen that when the slope of channel fading is large, we are able to adjust the transmission power by larger step size when cmdC and cmdF are consistent.
Noticeably, because the PC command is no longer the only one information for adjusting the transmission power, the MA CFP PC schemes can eliminate effects of PC command error and prediction error, no matter scheme 1 or scheme 2 is. Also, the MA PC methods used at mobile station can cooperate with any kind of PC scheme adopted at base station.
4.3 Simulation Results and Discussions
In this section, the simulations of MA CFP PC schemes CDMA cellular mobile system of 19 cells are shown. The fading model, which includes long-term fading and short-term fading, is defined by (3.1), and is produced by Jakes model (3.5). The SIR model is also shown in section 3.2 and the outage probability is defined in (3.8). The burst error channel model for PC command is shown in Fig. 3.2 and the error probability is kPe. In addition, the problems of sectorization handoff, branch diversity, voice activity are not considered.
Noticeably, in the MA CFP PC scheme 1, the MA PC method 1 is used at the mobile station, and this scheme is denoted by MA1-CFP. Moreover, the MA PC method 1 can also be used by the SIRP PC and LGP PC scheme, and they are denoted by MA1-SIRP and MA1-LGP.
Similarly, the MA CFP PC scheme 2 is denoted as MA2-CFP; when the MA PC method 2 is
schemes 1 versus the weighting α when fmTP equal to 0.01, 0.05, and 0.1 individually. It can
α
Figure 4.3: The outage probability of the MA PC schemes 1 when fmTP is 0.01 (k=0, Pe=0.00)
be seen that, when α equals to 0, it is the performance of original PC scheme. The information of channel fading is not used, so the performance is not very good. When α approaches to 1, the performances become bad. This is because that the mobile station almost adjusts its power only according to the information of channel fading and ignores the effect of interference. When fmTP is 0.01, if α is increased, the outage probability increases rapidly faster. This is because when fmTP is small, the variation of channel fading is small, so there are some drawbacks to decide the transmission power by large weighting of channel fading. In Fig.4.4 and Fig.4.5, it shows that when α is increased, the difference of the three schemes decrease. This is because that the weighting of PC command decrease, so the effects of prediction error decrease.
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0
0.05 0.1 0.15 0.2 0.25
α 1 MA1-SIRP MA1-LGP MA1-CFP
Figure 4.4: The outage probability of the MA PC schemes 1 when fmTP is 0.05 (k=0, Pe=0.00)
α
Figure 4.5: The outage probability of the MA PC schemes 1 when fmTP is 0.1 (k=0, Pe=0.00) Here, we only observe the effects of α on the outage probabilities, and the topic of deciding the value of α is not concerned here. α is set to be 0.5 at later simulations for the
Figure 4.6: The outage probabilities of the prediction-based PC schemes without and with the
MA PC method 1 in error-free channel (Pe=0.00, k=0)
Figure 4.6 shows the outage probabilities of the prediction-based PC schemes without and with the MA PC method 1 versus fmTP; there are eight users in each cell and the PC command is in error-free channel. It can be seen that when the fmTP is increased, the outage probability will increase, too. This is because that the larger fmTP is, the smaller the correlation of the transmission signal is; it is more difficult to predict that signal, and therefore, the outage probability increases. No matter the MA PC method 1 is applied or not, the CFP PC method always holds the superiority. This is because that, as shown in Fig.3.3, the prediction error is the smallest in the CFP PC method. When the MA PC method is used in the mobile station, it can be seen that the outage probabilities is decreased as shown in MA1-SIRP, MA1-LGP, and MA1-CFP. This is because that the MA PC method 1 can mitigate the effect of prediction error.
Therefore, the improvement between SIRP and MA1-SIRP is the most, owing to the largest prediction error in the SIRP PC scheme, and the improvement between CFP and MA1-CFP is
the least also because of the least prediction error in the CFP PC method. Furthermore, the difference between MA2-CFP, MA2-LGP, and MA2-SIRP are much smaller than that between CFP, LGP and SIRP.
Figure 4.7: The outage probabilities of the prediction-based PC schemes with MA PC method 1 and with the MA PC method 2 in error-free channel (Pe=0.00, k=0)
Figure 4.7 shows the outage probabilities of the prediction-based PC schemes with the MA PC method 1 and the MA PC method 2 versus fmTP; there are eight users in each cell and the PC command is in error-free channel. It can be seen that the PC schemes with the MA PC method 2 can result in lower outage probabilities than that with the MA PC method 1. This is because that when the slope of channel fading is larger, the weighting of cmdF can be increased by using the MA PC method 2, however, the weighing of cmdF is always fixed in the MA PC method 1. Also, the adjustment of transmission power can be larger when the channel fading varies violently. Therefore, the PC schemes with the MA PC method 2 not only can mitigate the effect of prediction error, but also has the better ability to compensate the channel fading.
outage probability
Figure 4.8: The outage probabilities of the prediction-based PC schemes without and with the MA PC method 1 in error-prone channel (Pe=0.05, k=1)
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.005
0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
fmTP MA1-SIRP
MA1-LGP MA1-CFP MA2-SIRP MA2-LGP MA2-CFP
Figure 4.9: The outage probabilities of the prediction-based PC schemes with the MA PC method 1 and with the MA PC method 2 in error-prone channel (Pe=0.05, k=1)
Figure 4.8 and 4.9 show the outage probabilities of the prediction-based PC schemes without MA PC method, with the MA PC method 1, and with the MA PC method 2 versus fmTP; there are eight users in each cell and the PC command is in error-prone channel. Even it is in error-prone channel, the PC schemes with the MA PC method 2 still performs the best, that with the MA PC method 1 performs the second, and that without MA PC method performs the worst. It also can be seen that, when the PC command is in error-prone channel, the improvement of the MA PC methods are larger than that when the PC command is in error-free channel. This is because that the MA PC methods can further reduce the effect of PC command error. Therefore, the MA PC methods are robust in error-prone channel. No matter the PC command is in error-prone channel or not, the MA CFP PC scheme always performs the best.
Figure 4.10: The outage probabilities of the PC schemes with the MA PC method 1
outage probability
Figure 4.11: The outage probabilities of the PC schemes with the MA PC method 2
Figure 4.10 and Fig. 4.11 show the outage probability of the PC schemes with the two MA PC methods in error-free and error-prone channels versus fmTP. It can be seen that, when the Pe is increased from 0 to 0.01 and k are increased from 0 to 5, the outage probabilities are approximately increased by the amount of 0.0025. However, the increases of outage probabilities in Fig.3.9- 3.11 are about 0.01; therefore, the MA PC methods indeed have better ability to overcome the PC command error. This is because that the PC command is no longer the only one information for adjusting the transmission power when the MA PC methods are used, so it can decrease the effect of PC command error greatly.
In Figure 4.12, it shows the outage probability of the prediction-based PC schemes without and with the MA PC method 1 versus the number of user. It is also assumed that fmTP is 0.05 and the PC command is in error-free channel. If the outage probability requirement for voice traffic is set to be 5%, in order to maximize the system capacity, the desired level D has to be chosen appropriately for different PC schemes. Therefore, similar with what we
outage probability
Figure 4.12: The outage probabilities of the PC schemes without MA PC method and with the MA PC method 1 in error-free channel (Pe=0.00, k=0)
have done in Fig. 3.8 and Fig. 3.12, the desired levels of the PC schemes are listed in Table 4.1.
It can be found that MA1-CFP improves the system capacity by an amount of 31.8% and 70.5% than LGP and SIRP, respectively.
PC scheme SIRP LGP CFP
Desired level D −12.5dB −13.5dB −14.5dB
PC scheme MA1-SIRP MA1-LGP MA1-CFP
Desired level D −14.2dB −14.7dB −15.2dB
PC scheme MA2-SIRP MA2-LGP MA2-CFP
Desired level D −14.8dB −15.3dB −15.7dB Table 4.1: The desired levels of the PC schemes in error-free channel
outage probability
Figure 4.13: The outage probabilities of the PC schemes without MA PC method and with the MA PC method 1 in error-free channel (Pe=0.05, k=1)
PC scheme SIRP LGP CFP
Desired level D −11.5dB −12.5dB −13.5dB
PC scheme MA1-SIRP MA1-LGP MA1-CFP
Desired level D −14.0dB −14.4dB −14.8dB
PC scheme MA2-SIRP MA2-LGP MA2-CFP
Desired level D −14.4dB −14.9dB −15.3dB Table 4.2: The desired levels of the PC schemes in error-prone channel
In Figure 4.13, it shows the outage probability of the prediction-based PC schemes without and with the MA PC method 1 versus the number of user. It is also assumed that fmTP
is 0.05 and the PC command is in error-prone channel. In order to maximize the system capacity, the desired level D has to be chosen appropriately for different PC schemes to
guarantee the outage probability requirement of 5%. The desired levels of the PC schemes are listed in Table 4.2. It can be found that MA1-CFP improves the system capacity by an amount of 52.9% and 116.6% than LGP and SIRP, respectively. Comparing the result with that in Fig.
4.12, the improvement of the system capacity is larger in error-prone channel, so the MA1-CFP is more robust in error-prone channels.
outage probability
Figure 4.14: The outage probabilities of the prediction-based PC schemes with the MA PC method 1 and method 2 in error-free channel (Pe=0.00, k=0)
In Fig. 4.14, it shows the outage probability of the prediction-based PC schemes with the MA PC method 1, and the MA PC method 2 versus the number of user. It is also assumed that fmTP
is 0.05 and the PC command is in error-free channel. The appropriate desired levels of the PC schemes are listed in Table 4.1 to satisfy the outage probability requirement of 5%. It can be found that MA2-CFP improves the system capacity by an amount of 23.1% (45.5%) than MA1-LGP (MA1-SIRP), respectively. Moreover, MA2-CFP improves the system capacity by an amount of 45.5% and 88.2% than LGP and SIRP, respectively. However, the improvement
of MA1-CFP to MA1-LGP (MA1-SIRP) is smaller than that of CFP to LGP (SIRP) and the improvement between MA2-CFP to MA2-LGP (MA2-SIRP) is the least. This is because that the all the performances in MA1-LGP (MA1-SIRP) and MA2-LGP (MA2-SIRP) are improved.
Figure 4.15: The outage probabilities of the prediction-based PC schemes with the MA PC method 1 and method 2 in error-free channel (Pe=0.05, k=1)
In Fig. 4.15, it shows the outage probability of the prediction-based PC schemes with the MA PC method 1, and the MA PC method 2 versus the number of user. It is also assumed that fmTP is 0.05 and the PC command is in error-prone channel. Similarly, table 4.2 lists the appropriate desired levels of each PC scheme which can guarantee the outage probability requirement and maximize the system capacity. It also can be seen that MA2-CFP improves the system capacity by an amount of 26% and 45% than MA1-LGP and MA1-SIRP, respectively.
Moreover, MA2-CFP improves the system capacity by an amount of 70.5% (141.6%) than the LGP (SIRP) PC scheme, respectively. The improvement is also larger than that in error-free channel; therefore, the MA CFP PC schemes are indeed more powerful in error-prone channels.
4.4 Conclusions
When the PC command is in error-prone channels, not only the transmission power is incorrect but also the prediction will be influenced. Therefore, in this chapter, mobile assisted (MA) channel-fading prediction-based (CFP) PC methods are proposed to overcome this problem. In the MA CFP PC schemes, the mobile station adjusts its transmission power by not only the received PC command but also the slope of channel fading. Therefore, not only effect of PC command error, which is resulted from the error-prone channel, but also that of prediction error of the SIR at the next power control cycle can be mitigated. In addition, the larger the prediction error or the PC command error probability is, the larger improvement can be achieved when the MA PC methods are adopted.
In order to modify some disadvantages in the MA CFP PC scheme 1, the MA CFP PC scheme 2 is proposed, which can increase the weighting of the slope of channel fading when the slope is large. The MA PC method 2 in the MA CFP PC scheme 2 also can adjust the transmission power with larger step size when channel fading vary violently, so it has better ability to deal with the short-term fading. Actually, this method is also one kind of variable-step PC method. It can be expected that this method can outperform other variable-step PC methods.
This is because that the MA CFP PC scheme 2 can eliminate the prediction error. Moreover, when the PC command is in error-prone channel, performance of conventional variable-step PC method would degrade seriously as the significant bit of the PC command errs. However, this will not happen in the MA CFP PC scheme 2.
Chapter 5 Conclusion
n the wireless environment, the third generation (3G) communication system is becoming the leading role and widely used in the world. Differing from the second generation system, which adopts the time-division multiple access (TDMA) technology, the code-division multiple access (CDMA) is the most popular method in the 3G communication system. The CDMA can improve the capacity greatly than the TDMA or the frequency-division multiple access (FDMA) systems; however, the improvement is greatly influenced by the power control method, especially the uplink power control. The CDMA system is interference limited system, that is, the system capacity is determined by the total interference in the system.
Therefore, under the situation that the quality of service (QoS) is satisfied, the mobile station should transmit signals by using less signal power.
There are many factors in the wireless environment increase the difficulty of power control, such as propagation loss, multi-path, shadowing, and near/far. Owing to the propagation loss, the farther the distance between the mobile station and the base station, the larger the degradation of the transmission signal is. The shadowing, which is mainly resulted from the obstruction, also influences the gain of the transmission. The multi-path results the received signal composed of many reflect components, which make the channel gain being Rayleigh or Rican distributed. It is so-called the short-term fading, and the fading frequency is proportional to the velocity of the mobile station. To make sure the QoS is satisfied almost all the time, it is necessary for the power control method to be able to catch both the long-term and short-term fading.
In order to eliminate the above influences to support the appropriate QoS, the power
I
control is needed. In chapter 2, many power control methods are introduced; and the SIR prediction-based (SIRP) and link-gain prediction-based (LGP) power control (PC) scheme are further shown in detail. The SIRP PC scheme is the most common prediction-based PC scheme;
however, there exists some prediction problems in this scheme. Therefore the LGP PC scheme is proposed to remove the disturbance of the transmission power on the prediction error.
However, the disturbance is not removed completely, so the channel fading prediction-based (CFP) PC method is proposed in chapter 3.
In chapter 3, the CFP PC method is shown. In this scheme, not only the transmission power but also the interference is excluded from the input of the predictor. Therefore, the prediction error will not come from the adjustment of transmission power. Although the interference is not predicted, the effect is very small. This is because the interference is composed of the transmission powers of many mobile stations after controlled; therefore, the correlation of the interference is quite small and it is difficult to well predict the interference.
Simulation shows that the prediction error in the CFP PC method is indeed smaller than that in the LGP and SIRP PC scheme, and therefore, it can result in lowest outage probability. It can be seen that the CFP PC method can improve the system capacity by the amount of 22.7%
(58.8%) than the LGP (SIRP) PC scheme, respectively, when the PC command is in error-free channel. When the PC command is in error-prone channel, the CFP PC method still improves the system capacity by an amount of 29% (83.3%) than the LGP (SIRP) PC scheme, respectively. Therefore, the CFP PC method has more resilience from the PC command error.
However, it also can be seen that when the PC command is in error-prone channel, the performance degrades no matter which PC scheme is. Therefore, a mobile-assisted (MA) and channel-fading prediction-based (CFP) PC scheme is proposed in chapter 4.
In chapter 4, the MA CFP PC schemes are proposed. In the MA CFP PC scheme 1, the mobile station adjusts its transmission power only by the received PC command but also the slope of channel fading. Although the MA CFP PC scheme 1 is proposed originally to overcome the effect of PC command error, it also can eliminate the influence of the prediction
error at the base station. To further reform the MA CFP PC scheme 1, in which the maximum adjustment of transmission power is always unchanged and the weighing of the slope of channel fading is fixed, the MA CFP PC scheme 2 is proposed. Simulation shows that the PC schemes with MA PC method indeed outperforms the PC scheme without MA PC method, and
error at the base station. To further reform the MA CFP PC scheme 1, in which the maximum adjustment of transmission power is always unchanged and the weighing of the slope of channel fading is fixed, the MA CFP PC scheme 2 is proposed. Simulation shows that the PC schemes with MA PC method indeed outperforms the PC scheme without MA PC method, and