The Repeater for WCDMA Cellular Mobile

Telecommunication Systems

He Songbai, Wang Bin, You Fei, Yan Xiaohuan, Bao JingfuSchool of Electronic Engineering,

University of Electronic Science and Technology,Chengdu 610054, China

E-mail: sbhe@uestc.edu.cn

Abstract-This paper presents the principles and constitutions ofRF and fiber optic repeaters to provide wideband code divisionmultiple access(WCDMA) mobile communication services toprevious blind areas such as places far away from the city, vastand sparsely populated, inside the buildings or in theunderground mall. The thermal noise generated by the repeaterincreases the uplink noise level and degrades the uplink capacityof a BS(Base Station). In this paper, we analyze the noise floorincrease and capacity degradation, as well as propose to selectthe operation carrier frequency and fix the channel bandwidth to5MHz by using a surface acoustic wave(SAW) filter to degradethe noise floor in the WCDMA repeater. Finally, it gives someexperiment results, and the developed repeater has been used forthe WCDMA mobile communication networks in the Hangzhouand Suzhou telecom. of China telecom..

I. INTRODUCTION

As an engineering technology to solve the problem of blindareas and enhance the network coverage, repeater plays animportant part in present GSM and CDMA mobilecommunication business network0l]. With granting of theWCDMA license in China and large-scale construction ofWCDMA mobile communication network, the repeater(especially RF repeater), by right of its convenient installationand low cost(which is only about 20% cost of that of the basestation), will inevitably be widely used in the WCDMAmobile communication systems. It is applicable not only in theinitial network construction stage, but also in network quicklydeveloping and optimizing stagel1 4]1 The repeater in networkapplication is shown in Fig. 1.

1SLk seieantenna antenna

BS Repeater MS

Fig. 1 The scheme of RF intelligent repeater in network optimization

This system is applicable for areas and zones as follows:areas far away from the city, vast and sparsely populated areas,wide plain zones, areas where repeaters fail to solve mattersconcerning antenna isolation, directional coverage to zonalareas such as expressways and railways, weak zones or deadzones caused by complex landforms, land features, high

mountains or lofty buildings, areas with no significantincrease of speech volume, but increase of activity radius ofusers and areas with high call drop rate, low handover successrate, poor coverage effect, low connection rate, or poor calleffect.

The main components of a repeater are uplink and downlinktransceivers, management module and power supply module.For different ways of application, there are different kinds ofrepeaters such as RF wideband repeater, fiber optic repeaterand band selective repeater, et.. The main specifications ofevaluating a repeater are its intelligence (i.e. local and remotemonitor), Adjacent Channel Power Ratio(ACPR), noise figureand reliability.

However, when used in network optimization, a problemoccurs in current repeaters[5]. The limit of output noise floor ofthe uplink leads to closure of the base station, which makes itimpossible to accomplish the communication.

In this paper, design of RF intelligent repeater and fiberoptic repeater is proposed, as well as the solution to closure ofthe base station resulting from noise level of the repeateruplink. The test result of repeater for WCDMA cellular mobiletelecommunication systems, which is researched by theauthors' group, is also included.

II. THE PERFORMANCE OF WCDMA COVERAGE SYSTEMWhen a repeater is located in a cell, the model ofWCDMA

coverage system is shown in Fig.2, the BS equipment in thesystem receives output noise from the repeater. It can be seenthat because the gain of repeater is usually big, uplink noisefloor of the repeater will possibly exceed reception sensitivityof the base station and thus results in closure of the base

hikantenia

ternneanLtena

LS1

r

LS2

Fig.2 The model ofWCDMA coverage system

station, so communication is not able to be carried through.Furthermore, as the repeater brings noise, system capacity willbe reduced.

0-7803-9584-0/06/$20.00O2006 IEEE. 2511

A. Relationship between noise level of BS from repeatersand the gain and bandwidth of repeater uplink

The generated noise power inside the repeater uplink can bewritten as:

PNR = KTBFG (1)

Where K is Boltzmann constant= 1.38 x 10 23J / K, T isabsolute temperature in kelvins(K), B is bandwidth, F is thenoise figure of repeater uplink, and G is the gain of repeateruplink.

Take the design of fiber optic repeater as an example. Letthe downlink power of the fiber optic repeater PO= 43dBm andsomeone makes a call by a mobile phone in a place which has-9OdBm reception power level. Assume sending power ofthemobile phone is 2W. Now let us analyze noise level ofBSfrom the repeater.

Solution:

a. Space loss between the repeater and the mobile phoneL,2 is

LS2 = PO - Pi = 43dB -(-9OdB) = 133dB. (2)

b. Uplink reception power ofthe repeater is

PiR= 33dB 133dB =-1OOdB. (3)

c. Total gain of the uplink is

G+LS = PlB- PiR (4)

Let input power level ofBS P1B = -lOOdBm, thenG+LSl = -lOOdB -(-0OOdB) =OdB.

d. If LS=O, thus, G = 0, the base station receives noisepower level PNR from the repeater.

Let the uplink noise figure of the repeater F = 3dB.When the repeater does not use the band selective filter,B = 60MHz, and under the room temperature, PNR = -

93.3dBm. If using the band selective filter, B = 5MHz,PNR= -103.3dBm.

Generally, the reception sensitivity of the base station is-11 8dBm[l], so when uplink gain of the repeater G+LS,= OdB, for broadband amplification, the noise levelof the base station is required to be more than 24.7dB,and for band selective repeater, the noise power level ofthe base station is required to be more than 14.7dB. Inorder to satisfy such requirements, the total uplink gainof coverage system is -24.7dB and -14.7dB,respectively. In order to satisfy the received sensitivityof the repeater downlink, we prefer to choose the totalgain of uplink -14.7dB.

B. Analysis of coverage system capacity

The uplink capacity of a BS is described by

C = B log2 (1 + ) (5)

Where B is signal bandwidth, and B=3.84MHz in WCDMAcommunication system for IMT-2000[3]. SIN is the available

Fig.3 The block diagram of RF band selective repeater

signal-to-noise at the input port of BS. When a repeater is usedto extend cellular service, the BS in the coverage systemreceives output noise from the repeater. The signal-to-noiseS'IN' at the input port ofBS becomes worse. In this case, thecapacity ofthe BS is given by

C =Blog2(1+ S /,)N

Thus

C -<C

(6)

(7)

III. RF INTELLIGENT BAND SELECTIVE REPEATER

A block diagram of the developed repeater employing RFband selective is shown in Fig.3. The repeater comprisesduplexers, mixers, SAW filters, LNA, IHPA, managementmodule, power supply module, link antenna, and serviceantenna.

Link antenna receives signal from BS, and the frequency is2110 to 2170 MHz. The signal is amplified through downlinkof the repeater, and then outputted to service antenna. Thegain of downlink is usually 80 to 90 dB, and the output powerhas 5 different scales, 500mW, 1W, 2W, 5W and lOW.Require Adjacent Channel Power Ratio < -45dBC. Serviceantenna receives signal from Mobile Station(MS), the signalfrequency is 1920 to 1980MHz. The signal is amplifiedthrough uplink of the repeater, and sent to BS through linkantenna. The gain of uplink is about 80dB.

In Fig.3, we can use the mixer to convert RF signal to IF.The signal is filtered by 5MHz-bandwidth SAW filter, andthen up converts the radio frequency. In that case, the noisepower level of uplink and downlink[6] can be reduced.

Management module uses ARM embedded system torealize local and remote monitor functions, including LCDdisplaying.

IV. FIBEROPTIC REPEATER

Fiber optic repeater in network optimization is shown inFig.4. The fiber optic repeater consists of two parts: one localunit(Master) and multiple remote units(Slave), which both canbe custom configured due to the modular design. The localunit can receive the BS signal via a directional coupler orwireless donor antenna. In the local unit, the link frequency isamplified and transmitted on a electronic optic(E/0) module.

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At the remote site, another E/O module is mounted, whichpicks up the link signal into the remote unit. The signal is

ter SleseiceaxLtenL

f3ber:

MwEater SSlaLve

Fig.4 The block diagram of fiber optic repeater

shifted back to the original frequency and retransmitted on theservice antenna. Using the fiber optic repeater, the antennaisolation at the remote site has to be 75 dB, regardless of thegain set in the repeater..

Signal from MS received by remote unit is coupled fromlocal unit to BS through contrary process.

V. EXPERIMENT RESULTS

Fig. 5 Exterior of developed repeater

Fig.5 shows the exterior of the developed repeater. Theequipment is supplied by 220V AC and includes the RFconnector, remote control interface.

Fig.6 shows the downlink adjacent channel power ratio(ACPR). The ACPR satisfied at less -45dBc, which is therequired specification described in the 3GPP TS25.104. Themeasured noise figure of the uplink is listed in Table.1.Simultaneously, Table.1 gives the required RF specificationsfor the proposed repeaters.

Table.1 The main technical specification of developedrepeaters

Frequency bands 1920MHz - 1980MHz Up-link211OMHz - 2170MHz Down-link

Duplex spacing 190MHz

Channel bandwidth 5MHz

Maximum average 3OdBm,33dBm,4OdBm ,Down-linkoutput power (one 30dBm , Up-link, WCDMA testchannel) mode 1.

Noise figure at < 3.5dB Up-linkmaximum gain < 3.5dB Down-link

ACPR -47dBc (±5MHz

-55dBc @±IOMHz

Frequency error 20Hz

Gain control 30dB/ldBrange/step

ALC When it is in Max output power,output power will keep within 2dBfluctuate or turn off if input powerincrease lOdB

Local management USB or RJ45interface

Remote management GSM/GPRSinterface

RF connectors BNC

Operating temperature -30 up to 50°C

Power supply 90-23OVac

Fig.6 Characteristics of downlink ACPR

VI. CONCLUSION

The novel RF and fiber optic repeaters with choosingoperation carrier frequency and using SAW filter to reduce theuplink noise level of the BS are developed for WCDMAmobile communication systems. The paper presents theWCDMA mobile communication systems coverage solutionsand coverage systems model. It analyzes the uplink of therepeater noise floor, and then proposes a scheme to reduce thesystems noise level. The radio characteristics of the developed

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repeaters satisfy the required specifications in the 3GPPTS25. 101, TS25.106 and TS25.104 specifications.

ACKNOWLEDGMENT

This project is supported by UESTC-VARA laboratory.

REFERENCES[1] Zu Huahong, et.al, RF Engineering of Cellular mobile

communication, Pos and telecom press, 2005.[2] Ramjee Parsad Werner Mohr Walter Konhauser, Third

Generation Mobile Communication Systems, ArtechHouse.

[3] 3GPP TS25.106 UTRA repeater radio transimission andreception.

r41 www.tekotelecom.itr5i Yasushi ITO, et al., "Novel Repeater with Automatic Gain

Control for Indoor Area", 20 5 Asia-Pacific MicrowaveConference Proceedings, p'2963-2965, Dec.2005.

[6] Cotter W.Sayre, Complete Wireless Design, The McGraw-Hill Companies, Inc.

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