Các mạng UTMS và công nghệ truy cập vô tuyến P8

RESOURCE AND NETWORK MANAGEMENTINTRODUCTIONOperating a 3G network involves managing resources and Network Elements (NE). This chapter covers these two aspects to complete the deployment issues started in Chapter 7. Resources here refer primarily to the radio resources and NE refers to the 3G building blocks, i.e. elements in the CS, PS and radio access networks.
Nội dung trích xuất từ tài liệu:
Các mạng UTMS và công nghệ truy cập vô tuyến P8 The UMTS Network and Radio Access Technology: Air Interface Techniques for Future Mobile Systems Jonathan P. Castro Copyright © 2001 John Wiley & Sons Ltd Print ISBN 0-471-81375-3 Online ISBN 0-470-84172-9 RESOURCE AND NETWORK MANAGEMENT8.1 INTRODUCTIONOperating a 3G network involves managing resources and Network Elements (NE).This chapter covers these two aspects to complete the deployment issues started inChapter 7. Resources here refer primarily to the radio resources and NE refers to the 3Gbuilding blocks, i.e. elements in the CS, PS and radio access networks.8.2 RADIO RESOURCE MANAGEMENT AND SIGNALLINGPower control constitutes one of the major tasks of Radio Resource Management(RRM). Other tasks such as admission control, load control and packet scheduling alsocorrespond to RRM; however, we will not emphasize them in this section. Power con-trol aims to minimize interference levels in order to maintain an expected transmissionquality in the air-interface. The UTRA FDD mode depends on soft blocking to effi-ciently manage multi-rate services. This takes place according to appropriate RRM al-gorithms covered in Chapter 4.8.2.1 Managing PowerPower control becomes more critical in the FDD than in the TDD mode. Thus, this sec-tion concentrates primarily on managing power in WCDMA. The impacts on handoverare also presented.In WCDMA all users share the same RF band separated by spreading codes. As a result,each user appears as a random noise to other users. Non-controlled individual powercan therefore interfere unnecessarily with those sharing the same frequency band. Toillustrate the need for power control Figure 8.1 shows two MSs in the UL. MS1 getscloser to the BS than MS1, now if there was no power control both MSs would transmitat their fixed power PT. But since MS1 is closer, it would have higher power than that ofMS2 if we assume that the distance of the latter is three times greater than that of MS1.Thus, if the required SNR (S/Nrequired) is (1/3), then S/N1 = 3 and S/N2 = 1. Thus, MS2will suffer the classical near-far effect and may not satisfy the quality of service re-quired in the link. Furthermore, any 3rd MS coming into the cell will not get the its re-quired S/N either, and may even cause MS2 to drop its S/N even lower. Power controlwill thus aim to overcome near-far effects and thereby increase capacity with acceptablelink quality.302 The UMTS Network and Radio Access Technology 3G 3G 37 37 06 %6 06 Figure 8.1 Power control to prevent near-far effect.8.2.1.1 Fast Power Control (FPC)The FDD mode uses fast power control with 1.5 kHz frequency (i.e. 1500 times/s) inboth UL and DL. It operates at a faster rate than any path loss change. The FPC uses theclosed-loop option as noted in Chapter 4. We see higher gains of FPC in low mobilespeeds than for high mobile speeds, and in received powers than in transmitted powers.At speeds above 50 km/h, e.g. FPC does not contribute much due to the higher multi-path gains. We can find more information about fast power control in [1].Other gains of FPC depend on diversity, e.g. multi-path diversity, receive, transmit antennadiversity, and macro-diversity. Less diversity implies more variations in the transmittedpower. Thus, we get smaller power rise1 in the presence of more multi-path diversity.In DL macrocell coverage with WCDMA, power rise gets critical because it directlyintervenes in the required transmission power, which determines the transmitted inter-ference. Hence, to maximize the DL capacity, we should select the quantity of diversity,such that it minimizes the transmission power required by a link, since the receivedpower level does not affect the capacity in the DL.In the UL, the level of transmission power from the different MSs does have direct impacton the interference to the adjacent cells, and the received power determines the level ofinterference to other users in the same cell. Diversity in this case does not have much im-pact, which means that UL capacity of a cell would be maximized by minimizing the re-quired received powers, and the amount of diversity would not affect the UL capacity.When MSs move at high velocities, the FPC does not follow fast fading; we would re-quire higher received power level to obtain the expected quality. Thus, in this scenariodiversity does help to maintain the received power level constant, thereby allowing alower average received power level to provide the required quality of service.8.2.1.2 Power Control in Handover (HO)Before we discuss power control in HO, we briefly review the HO types. The two typesof HO in our FDD mode include Softer and Soft HO._______1 If we define power rise as the relative average transmission power in a fading channel compared to the non- fading, while the received power level is the same both in fading and in non-fading channels with ideal power control.Resource and Network Management 3038.2.1.2.1 Softer HandoverAs illustrated in Figure 8.2 softer HO occurs when a MS passes through the overlappingcoverage of two adjacent sectors of a BS. Communications between the BS and MStake place concurrently through two channels (i.e. one to each sector or cell). The con-current links use 2 separate DL codes so the signals are perceived by ...