- I j interference power from an MS in the jth cell at the zeroth BS. - k slot number in the TDMA frame 151. - S 0 received power at the BS in the presence of power control errors. - W width of the streets in street microcells x normalised distance. - χ fraction of channels for signalling δ random variable of the error in S 0 (dB). - δ 0 random variable of the power control error in the received interference power. - ϒ 0 j ϒ j in the presence of power control errors ζ rv ( λ 0 λ ) with standard deviation. - After calculating the SIR the capacity of the microcellular GSM network is computed. - Figure 3.1 shows the pattern of co-channel hexagonal cells in a macrocellular network. - We consider a mobile station (MS) in Figure 3.3 occupying an area da, at a distance r from the jth BS. - The received power at a distance r from the BS will be different at different angles because of the variations in the terrain and the distribution of buildings and streets. - From Equation (3.1) the power transmitted by the MS is. - Figure 3.1: Co-channel cells in a mosaic of tessellated hexagonal cells. - Figure 3.3: Up-link: an MS in the jth cell interfering with the zeroth BS.. - The interference due to the MS in the jth cell at the zeroth cell site is. - The standard deviation σ of the shadow fading is 8 dB, and E [ 10 ζ = 10 ] is calculated using Equation (3.19). - Three values of the VAF, i.e. - Note the low gradient of the curves. - Figure 3.4: Up-link: three cells per cluster, omnidirectional sites. - Figure 3.6: Up-link SIR versus number of cells per cluster.. - Figure 3.7 shows a three-cell cluster with three sectors per cell, while Figure 3.8 displays a four-cell cluster with three sectors per cell. - This equation is the interference-to-signal ratio (ISR) for the total interference in the zeroth sector from the jth sector. - The improvement in SIR due to sectorisation is 9.5 dB as a result of the lower E [ ϒ j. - Figure 3.10 shows the cellular arrangement.. - Figure 3.7: Up-link: three-cell cluster with three sectors per cell. - Figure 3.8: Up-link: four-cell clusters with three sectors per cell. - Figure 3.9: Up-link: two-cell clusters with three sectors per cell.. - Figure 3.10: Up-link: single-cell cluster with three sectors per cell.. - 3.3.2.4Effect of imperfect power control in the SIR. - (3.29) where δ 0 is the random variable of the interference power due to imperfect power control.. - The average of the received power from mobiles located anywhere within the jth cell using the kth timeslot can be found by inserting 10 δ0 10 into Equation (3.10), namely. - in the interference-to-signal ratio due to imper- fect power control. - The corresponding decrease in the SIR is 0.2 dB, 0.9 dB, and 2.1 dB for δ having a standard deviation of 1 dB, 2 dB and 3 dB, respectively, irrespective of the voice activity factor and cluster size.. - Figure 3.11 shows an MS at a distance r from its BS in the zeroth cell. - In Figure 3.11 we display a ring distance r j from the jth cell site. - Figure 3.11: Down-link: two-cell cluster with three sectors per cell.. - This average transmitted power from the jth BS is the source of interference to MSs in the zeroth cell. - The N f carriers in the zeroth cell, associated with N f users assigned to the kth slot, are uniformly distributed over the area of the cell. - We will now consider the average interference experienced by mobiles in the zeroth cell from the jth BS. - Graphs of the SIR as a function of the number of cells per cluster are displayed in Figure 3.13 for three different voice activity factors (VAFs) of 1, 1 = 2, and 3 = 8. - We now examine the SIR of the three-cell cluster arrangement for MSs at different locations within its cell, from the immediate vicinity of the BS ( r = 0 ) to the cell boundary, r = R.. - For three cells per cluster, the graphs of the SIR for MSs along a line from the zeroth BS site to a corner of the zeroth cell, is shown in Figure 3.14. - Figure 3.12: Down-link: three-cell cluster, omnidirectional sites.. - Figure 3.13: Down-link SIR as a function of cluster size for different VAFs. - Figure 3.14: Down-link: the SIR for mobiles at normalised distance r = R from the BS, for different VAFs. - The down-link SIR of the two-cell cluster TDMA system with three sectors per cell is cal- culated for the two different interference situations considered on the up-link. - Figure 3.15: Down-link: three cells per cluster with three sectors per cell. - Figure 3.17: Down-link: two-cell cluster with three sectors per cell.. - The SIRs for MSs located along these bound- aries are shown in Figure 3.18. - From Figure 3.18, the difference between the two extreme values of the SIR due to different mobile locations is about 3 : 5 dB.. - The down-link SIR of the one-cell cluster TDMA system with three sectors per cell is cal- culated using the same assumptions as for the up-link case. - From Figure 3.19, there are seven significant co-channel interfering BSs. - Mobiles located along the sector boundaries extending from the zeroth cell site in Figure 3.19 receive more interference power than MSs elsewhere in the sector. - The SIRs for MSs located along these boundaries are shown in Figure 3.20. - Figure 3.19: Down-link: single-cell cluster with three sectors per cell.. - Figure 3.20: Down-link: the SIR for mobiles as a function of normalised distance r = R along the sector boundaries extending from the zeroth cell site for different VAFs. - Hence, an approximate expression for the SIR in the presence of shadow fading is. - the situation is more complex as shown in Figure 3.21, where there are 10 significant co-channel cells. - Figure 3.21: Down-link: two-cell cluster without sectorisation. - Figure 3.22: SIR versus number of cells per cluster with and without shadow fading. - Although the average SIR of the two-cell cluster with sectorisation is above 9 dB for a VAF of 1 = 2, as shown in Figure 3.18, the worst SIR on the down-link is below 9 dB for mobiles located near the BS ( r <. - Representing this gain as the ratio of the carried traffic in the four- cell cluster with three sectors per cell, i.e. - four-cell/three-sector, to the carried traffic in the seven-omnicell, we obtain the curve shown in Figure 3.24. - Figure 3.23: Offered traffic per cell as a function of the number of carriers per cell site, N f , for systems with and without sectorisation.. - Rectangular-shaped microcells that occupy a side of a city block are shown in Figure 3.26. - During any particular time slot the interference is decreased if some of the co-channel users are not. - Figure 3.25: Cross-shaped city street microcells in a two-cell per cluster arrangement.. - Figure 3.26: Rectangular-shaped city street microcells in a four-cell per cluster arrangement.. - Figure 3.27: The propagation paths in street microcells.. - Consider the zeroth BS receiver experiencing interference from mobiles in the jth co- channel cell. - Even for the normal distribution, this range ( 4 σ to 2 σ ) occurs 98% of the time.. - On the up-link, the significant interference at the zeroth BS does not come from MSs in the B2 areas because of the OOS paths. - The majority of the interference is generated by mobiles located in the B1 areas where the LOS conditions prevail. - Figure 3.28: Up-link interfering microcells, shown shaded, for the centre zeroth cross-shaped mi- crocell. - between the zeroth BS and the interfering MS in the jth microcell. - for W X, where X and W are defined in Figure 3.28. - The average interference power received at the zeroth BS is the average of the powers from mobiles located anywhere within the jth cell using the kth timeslot, namely. - In the first and third sections, r >. - X b , while in the second section r X b . - X, as shown in Figure 3.30, j r j X b , because r is integrated from X to X. - The average interfering power from mobiles in the jth co-channel cell is given by E [ v j ] E [ ϒ j. - For the path loss exponent α given by Equation (3.54), a standard deviation of the shadowing fading of 4 dB, we compute E. - There are six co-channel microcells in Figure 3.32. - Figure 3.29: Path loss exponent for the interfering MSs in co-channel microcells when X b X. - Figure 3.30: Path loss exponent for the interfering MSs in co-channel microcells when X b >. - Figure 3.32: Up-link interfering microcells, shown shaded, for the zeroth rectangular-shaped mi- crocell. - However, because the number of significant co-channel interfering microcells in the rectangular-shaped microcells is half that of the cross-shaped microcells, the average interference-to-signal power ratio is twice that experienced in a cross-shaped microcellular system. - Consequently the SIR of the TDMA system in the rectangular-shaped microcellular network is the same as that of the cross- shaped microcellular network and the curves of Figure 3.31 apply for both microcellular arrangements.. - The system capacity of the GSM in a microcellular environment is defined by Equation (3.50).. - The SIRs versus normalised path loss break-distance, X b = X, are shown in Figure 3.33. - This is because the number of co-channel microcells is only half that of the cross-shaped microcells. - From the graphs, we observe that the optimal size of the microcell is X b 1 : 25X , where the SIRs are 15.1 and 18.1 dB for the cross-shaped and the rectangular-shaped microcells, respectively. - Figure 3.33: SIRs v ersus X b = X for TDMA systems without power control, frequency hopping, and DTX in the cross-shaped and the rectangular-shaped microcellular arrangements.. - The position of the BS antenna is shown as a white arrow. - The dimensions of the plot are 430 m by 420 m.. - The situation is illustrated in Figure 3.36. - large cells with antennas on the roofs of the tallest buildings. - Figure 3.37: A network of tessellated street microcells. - Analysis of the digital SFH900 mobile system, IEEE J. - [17] Steele R., The cellular environment of lightweight handheld portables, IEEE Commun.
Xem thử không khả dụng, vui lòng xem tại trang nguồn hoặc xem
Tóm tắt