Abstract: This paper compares two different handover criteria in WCDMA through simulations. The simulations are carried out in a WCDMA HCS system where ...
Performance of RSCP-Triggered and Ed"-Triggered Inter-Frequency Handover Criteria for UTRA Wang Yingl, Gong Fei', B a n g Ping', Wang Hai2 'Wireless Technologies Innovation Laboratory, Beijing University of Posts and Telecommunications, P.O.Box 92, BUPT, Beijing 100876, China, 2 . Encsson (China) Company Ltd., 9A, Hanwei Plaza, N0.7 Guanghua Lu, Cbaoyang District, Beijing 100004, China, Fax:++86-10-62283627 Tel: ++86-10-62283622-211 E-mail: wanm+M2ilbuDt.edu.cn Abstract: This paper compares two different handover criteria in WCDMA through simulations. The simulations are carried out in a WCDMA HCS system where the hexagonal macro and the Manhattan-like micro layer use different frequencies. Two possible handover triggering schemes Le. CPICH RSCP and CPICH EcINo, are compared under the same simulation environments and various cell loads. The handover performance are observed in terms of system efficiency including signalling and QoS such as call dropping probability and call blocking probability.
I INTRODUCTION Hierarchically layered cell structures based on pico, micro, and macro cells, partly or in some cases even fully overlapping, will be vital for third-generation mobile systems. Since the same frequency allocated to the different layers in the HCS could result in severe self-interference and make the WCDMA unstable, different frequencies have to be assigned to different layers in order to avoid power control problems and excessive interference[l]. So in thirdgeneration mobile systems, one of possible types of Handover is FDD inter-frequency hard handover[2]. Inter-frequency handover presupposes that a mobile station is able to monitor pilot channels and to transmit and receive signaIs quasi-simultaneously on two different frequencies. This can be accomplished by using a costly second radio transceiver in a CDMA mobile station or using compressed mode technique. In order to limit the complexity of a UE and reduce the cost, compressed mode is used to perform inter-frequency measurement. However, this will introduce new problems. The disadvantage of using compressed mode is the performance degradation of the network because of the power rising[31[4][51. What we focus in this report is the criteria to trigger an inter-frequency handover. Currently, some parameters used to trigger handover are as follows[6]: 1 CPICH RSCP: Received Signal Code Power, the received power on one code measured on the Primary CPICH.
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CPICH EcINo: The received energy per chip divided by the power density in the band. Measurement shall be performed on the Primary CPICH. SIR: Signal to Interference Ratio. The SIR shall be measured on DPCCH after RL combination. There have been some research results about handover criteria[7][8][9][10]. According to [8], the SIR measurement needs significantly longer averaging than the EdNo measurement. This ~ h l r a l l ycauses significant delay to the bandover preparation process meaning that in case SIR on CPICH is used for the handover evaluation, the actual bandover is delayed. On the other hand if the averaging period is not lengthened for the SIR measurement, the probability of the correct evaluation of neighbor cell strengths becomes poorer and thereby undesirable. Since we do not see any practical reason why the SIR should he added as a measurement quantity for the handover evaluation, after long time discussions within the 3GPP TSG-RAN WG4[9], the SIR is not listed as a handover criterion in the 3GPP technical specifications. So in this report the focus is laid on the comparison between RSCP and E m o . The structure of the report is described as follows. Section U analyzes two different handover criteria theoretically. Section III describes Inter-frequency handover model which involves models for compressed mode operation, inter-frequency bandover execution and handover delay. Simulation results are presented in section lV followed by the conclusions in sectionv .
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II EcMo VS. RSCP [lo] shows that in case of inter-frequency handover the EcINo provides load sharing between different carrier frequencies, while the RSCP does not take the load situation. RSCP and EcINo are defined as follows:
RSCP =
VTC 2002
where
is the effectively received total wide-band power after receiver filtering, and P,cp,,, is the received CPICH power, and
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and P
'fi
is the total wide-band received power
fi
from frequency f, and respectively, and ACIRi is adjacent channel interference power ratio between frequency f,and ,and P' is the power of thermal noise.
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(RSCP)
Assuming that the traffic load on frequency 1 is larger than the traffic load on frequency 2, consequently the received power from frequency 1 is larger than the received power from frequency 2 P,/, > P,rl, and moreover
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