3. Conventional DF Relay System under κ−µ and η−µ Fading
0 10 20 30
10−6 10−5 10−4 10−3 10−2 10−1 100
SNR, P/N
0 (dB)
Average SER
κ−µ fading
analytical simulation asymptotic
0 10 20 30
10−6 10−5 10−4 10−3 10−2 10−1 100
SNR, P/N
0 (dB)
Average SER
η−µ fading
analytical simulation asymptotic
(a) (b)
M = 16
M = 8
M = 4 M = 2
M = 16
M = 8 M = 4 M = 2
κij=1, µij=1.5 ηij=0.5, µij=0.5
Figure 3.1: Average SER performance of the relay system underκ−µandη−µfading for different modulation orders.
respectively. We observe that asymptotic results provide good approximation at high SNRs.
Figure 3.2 presents performance comparison based on channel quality under κ−µ fading. Data is considered to be 8-PSK modulated. In Figure 3.2 (a), the average SER is plotted for fixed µSD and κij, and varyingµSR and µRD. In Figure 3.2 (a), we observe that the increment in performance is more for increase in µRD as compared to increase in µSR. In Figure 3.2 (b), µij and κij are kept constant for SR and SD links, and varied for RD link. We observe that increase in µRD has better impact on performance than increase in κRD. The SR and RD links with greater values of fading parameters κ and µshow better performance and among them the parameters of RD link dominate.
Moreover, increase in µRD has better impact compared to increase in κRD.
In Figure 3.3, average SER is plotted for different channel conditions under η−µ fading. 4-PSK modulation is considered. In Figure 3.3 (a), the average SER is plotted for fixed µij and ηSD, and varyingηSRandηRD. We find from the plots that the performance improvement is higher with increase in ηRD as compared to increase in ηSR. In Figure 3.3 (b), parameters of SR and SD links are kept constant and the effect of change in parameters of RD link is observed. As seen from plots, increase
3.6 Numerical Results
15 20 25 30
10−6 10−5 10−4 10−3 10−2
SNR, P/N
0 (dB)
Average SER
8−PSK
µSR = 1, µRD = 1 µSR = 2, µRD = 1 µSR = 1, µRD = 2 µSR = 2, µRD = 2 µSR = 3, µRD = 2 µSR = 2, µRD = 3
15 20 25 30
10−6 10−5 10−4 10−3 10−2
Average SER
8−PSK
SNR, P/N
0 (dB)
µRD = 1, κRD = 1 µRD = 1, κRD = 2 µRD = 1, κRD = 5 µRD = 2, κRD = 1 µRD = 2 κRD = 2 µRD = 2, κRD = 5
(a) (b)
µSD=1 κij=1 µ
SD=1, κ
SD→0 µSR=2, κSR→0
Figure 3.2: Average SER performance of 8-PSK underκ−µfading channels with different values ofκij and µij.
15 20 25 30
10−6 10−5 10−4 10−3 10−2 10−1
SNR, P/N
0 (dB)
Average SER
4−PSK
ηSR = 0.02, ηRD = 0.02 ηSR = 0.2, ηRD = 0.02 ηSR = 0.02, ηRD = 0.2 ηSR = 0.2, ηRD = 0.02
15 20 25 30
10−6 10−5 10−4 10−3 10−2
10−1 4−PSK
Average SER
SNR, P/N
0 (dB)
µRD = 0.5, ηRD = 0.001 µRD = 0.5, ηRD = 0.02 µRD = 0.5, ηRD = 0.2 µRD = 2.0, ηRD = 0.001 µRD = 2.0, ηRD = 0.02 µRD = 2.0, ηRD = 0.2
(a) (b)
µSD=1.0,ηSD=0.2 µSR=2.0,ηSR=0.2
µij=0.5, ηSD=0.2
Figure 3.3: Average SER performance of 4-PSK underη−µfading channels with different values of ηij and µij.
3. Conventional DF Relay System under κ−µ and η−µ Fading
in µRD gives better performance as compared to increase in ηRD. The performance improvement is more for increase in parameters of the RD link compared to increase in parameters of SR link, and increase inµRD has better impact compared to increase in ηRD.
In Figure 3.4, the average SER results for the relay system with equal and optimal power allocation are presented. Mixed fading environment is considered, whereSDlink isη−µfaded andSR andRD links are κ−µ faded. 4-PSK and 8-PSK modulated data is considered in Figure 3.4 (a) and (b), respectively. Optimal power allocated to nodes S and R are evaluated by implementing and solving (3.61) in MATLAB. The results are also compared with that of direct transmission. Total transmission power in relay system and direct transmission is considered same, that is, P. In both system, each transmission requires equal duration, that implies relay system requires twice the time required in the direct transmission. We observe in Figure 3.4 that for better SDlink quality, direct transmission can outperform the relay system with equal power allocation scheme. Although, optimal power allocation in the relay system performs better than direct transmission under all channel conditions. It also outperforms the equal power allocation in the relay system.
Assume N0 = 1, the variation in average SER in Figure 3.4 is with total transmission power P. Furthermore, in (3.62), we can see that the optimal power allocated to nodeS,PS depends on power P and the channel conditions. Although, through numerical computation we observed that there is not much variation in the optimal power-ratioPS/P obtained for different values ofP. Moreover, for a wide range of channel conditions, the corresponding average SER is close to the average SER obtained for P = 24 dB. In Figure 3.4, the curves with circle marker correspond to the average SER with optimal power allocation that depends onP. The average SERs obtained forP = 24 dB are found to overlap with the optimal curves, but not shown in the figure for the sake of clarity. In Figure 3.4, the value x∗ =PS/P corresponds to the optimal power allocated to node S for P = 24 dB. We observe that for higher modulation order, the optimal power allotted to the source node increases (and hence the optimal power allotted to the relay node decreases).
In order to compare the derived analytical results with those presented in [72] and [73], the average SER of system with Nakagami-m faded channel and 4-PSK modulated data is shown in Figure 3.5.
η−µ fading and κ−µ fading reduce to Nakagami-m fading for ηij = 1 (Format-1) and κij → 0, respectively. The results are shown for the mixed fading scenario1 whenµSD={0.25,0.5,0.75,1} and
1 SDlink is underη−µfading andSRandRDlinks are underκ−µfading. SDlink reduces to Nakagami-mfading forηSD= 1 andSRandRDlinks correspond to Nakagami-mfading forκSR, κRD →0.
3.6 Numerical Results
6 12 18 24 30
10−6 10−5 10−4 10−3 10−2 10−1
100 8−PSK
Average SER
SNR, P/N
0 (dB)
6 12 18 24 30
10−6 10−5 10−4 10−3 10−2 10−1
100 4−PSK
SNR, P/N
0 (dB)
Average SER
relaying (optimal PA) relaying (equal PA) direct transmission
µSD = 0.5 (x* = 0.6270)
µSD = 2.5 (x* = 0.8470)
µSD = 0.5 (x* = 0.6358)
µSD = 2.5 (x* = 0.8480)
(a) (b)
µSR = 1, κSR = 1 µRD = 1, κRD = 1 ηSD = 1
Figure 3.4: Average SER versus average SNR plots showing comparison of the relay system with optimal and equal power allocation (PA) and direct transmission under mixed κ−µ andη−µ faded (SD link asη−µ,SR andRD links asκ−µfaded).
0 5 10 15 20 25 30
10−5 10−4 10−3 10−2 10−1
100 4−PSK
SNR, P/N
0 (dB)
Average SER
mij = 0.5 (x* = 0.6592) mij = 1.0 (x* = 0.6270) mij = 1.5 (x* = 0.6067) mij = 2.0 (x* = 0.5925)
ηSD = 1, κSR → 0, κRD → 0
mSD = 2µSD, mSR = µSR, mRD = µRD
Figure 3.5: Average SER versus SNR plot for 4-PSK under Nakagami-mfading as a special case of the fixed fading scenario.
3. Conventional DF Relay System under κ−µ and η−µ Fading
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
10−6 10−5 10−4 10−3 10−2 10−1 100
M = 2, P/N
0 = 20 dB
Source−to−relay distance (d
SR)
Average SER
equal PA (analytical) equal PA (simulation) optimal PA (analytical) optimal PA (simulation)
µSD = 0.5, ηSD = 1 µSR = 2, κSR = 2 µRD = 2, κRD = 2
µSD = 1, ηSD = 1 µSR = 2, κSR = 2 µRD = 2, κRD = 2
µSD = 0.5, ηSD = 1 µSR = 1, κSR → 0 µRD = 1, κRD → 0
µSD = 0.5, ηSD = 1 µSR = 2, κSR → 0 µRD = 2, κRD → 0
Figure 3.6: Average SER versus source-to-relay distance for the relay system with equal and optimal PA under mixed fading for different fading parameters,dSR+dRD=dSD, dSD= 2 unit,αij= 3,λij = 1.
µSR, µRD ∈ {0.5,1.0,1.5,2}. Let the Nakagami-m fading parameters of the links be mSD = 2µSD, mSR=µSR, andmRD =µRD. Thus we havemij ∈ {0.5,1,1.5,2}. It can be noted that the plot for different values of mij resembles that for the corresponding value of the fading parameter m in [73, Figure 3] for Nakagami-m fading. Furthermore, for mij = 1 the plot resembles that in [72, Figure 4]
for Rayleigh fading environment. Moreover, the optimal fractions of total power allotted to the source node is obtained as x∗ =PS/P = 0.6270, which is identical to that obtained in [72, Figure 4]. This suggests that the average SER expressions for Rayleigh fading and Nakagami-m fading can be traced using expressions for the generalized fading models.
In Figure 3.6, the average SER is plotted with variation in source-to-relay distance for the relay system with equal and optimal power allocation under different channel conditions. The nodes are considered to be collinear and follow the relationdSR+dRD =dSD. The results are shown fordSD = 2 unit,αij = 3, andλij = 1. We observe that when power at nodesS andR are equally allocated then the optimal relay location lies near midway with approximate distance ratio dSR/dSD ≈0.6. This is in accordance with the result in [160]. Furthermore, when power is optimally allocated and channel