evaluation of inter-freq quality handover criteria in E-UTRAN

Evaluation of Inter-Frequency Quality Handover

Criteria in E-UTRAN

Muhammad Kazmi1, Olof Sjöbergh2, Walter Müller2

Wireless Access Networks, Ericsson Research1

Research and Development2

SE-164 80 Stockholm, Sweden

{Muhammad.Kazmi, Olof.Sjobergh,

Walter.Muller}.ericsson.com Jonas Wiorek2 and Bengt Lindoff3

Ericsson Mobile Platforms, Ericsson Research3

SE-223 70 Lund, Sweden

{Jonas.Wiorek, Bengt.Lindoff}.ericsson.com

Abstract— In E-UTRAN multiple co-located carriers will typically be deployed requiring efficient inter-frequency (IF)

handover procedures and algorithms for retaining service quality, better coverage and load balancing between the carriers. Five IF handover criteria using RSRP, RSRQ or combination thereof are investigated in synchronous and asynchronous E-

UTRAN deployment scenarios. The results depict that an IF handover solely based on RSRP significantly increases number of handovers. Conversely the handover criterion based only on RSRQ reduces handovers but it slightly increases the packet loss

rate. The overall best performance is achieved with the combined handover criterion, which uses both RSRP and RSRQ and thus guarantees that the received pilot strength as well as the signal quality stays within the desired limit after the handover.

Keywords; OFDMA, LTE, Radio Resource Management, Co-located carriers, RSRP, RSRQ, Inter-frequency HO.

I. INTRODUCTION

Handover is one of the most fundamental radio resource

management features in a mobile network. The E-UTRAN or

the so-called 3GPP long term evolution (LTE) [1] supports

mobility in several deployment scenarios: E-UTRA intra-

frequency, E-UTRA inter-frequency and inter radio access

technology (inter-RAT). The inter-RAT handover enables the

mobility between E-UTRAN and other access technologies,

which may comprise of WCDMA, GSM, High Rate Packet

Data (HRPD) or cdma2000 1xRTT.

In E-UTRAN the handover decision, which is taken by the

serving cell, relies on the downlink measurements and/or the

network configured events reported by the user equipment

(UE). The evaluation of the handover related events specified

in [2] are in turn based on one or more downlink measurements

performed by the UE. To support inter-frequency and inter-

RAT mobility scenarios the corresponding measurements and

event evaluation are carried out by the UE during the network

configured measurement gaps.

Our goal is to devise and analyze suitable criteria for

performing E-UTRA inter-frequency handover in E-UTRAN

system. The E-UTRAN supports both time division duplex

(TDD) and frequency division duplex (FDD) modes. Our

analysis is though based on the E-UTRAN FDD but the

conclusions related to the synchronous FDD scenario are also

applicable to the E-UTRAN TDD mode. II. E-UTRA INTER-FREQUENCY HANDOVER SCENARIOS

To support various mobility scenarios in E-UTRAN two E-

UTRAN specific UE downlink measurement quantities are

specified [3]: reference symbol received power (RSRP) and

reference symbol received quality (RSRQ).

The RSRP and RSRQ measurements are indeed analogous

to WCDMA CPICH Ec/No and CPICH RSCP measurements

respectively [4]. Thus RSRP is equivalent to the signal strength

measurement and is defined as the linear average of the

received power of the resource elements carrying cell-specific

reference signals within the considered measurement frequency

bandwidth. RSRQ is used to depict the cell quality and is

defined as the ratio of RSRP to E-UTRA carrier received signal

strength indicator (RSSI). The E-UTRA carrier RSSI is the

linear average of the total received power in OFDM symbols

containing the reference symbols. It should be noted that

except the first OFDM symbol in a sub-frame, the remaining

ones can also contain data resource elements [1] [5]. This

means the E-UTRA carrier RSSI also incorporates the

contributions from resource elements carrying the user data.

This property of the E-UTRA carrier RSSI component in the

denominator of RSRQ enables the depiction of the cell quality.

An operator would typically deploy more than one E-

UTRA carrier frequency in the same coverage area. In order to

ensure efficient use of multiple carrier frequencies deployed in

the same coverage area, the 3GPP E-UTRAN standard

provides necessary procedures, mechanisms and radio resource

management requirements pertaining to the E-UTRA inter-

frequency handovers (IF) [2] [6]. In both E-UTRAN FDD and

TDD the UE is required to perform RSRP and RSRQ

measurements of at least 4 inter-frequency identified cells per

E-UTRA carrier [6]. There is also a requirement on the UE to

monitor up to at least 3 E-UTRA carriers [6]. This means in