Radio over Fiber for Beyond 3G Kwansoo Lee

Telecommunication R&D Center, Samsung Electronics Co. Suwon-city, Gyeonggi-do, Korea, 442-600

Abstract This paper introduces radio over fiber (RoF)

as one of enabling technologies of the fourth generation (4G) wireless communication. The RoF is a key technology to solve the problem about the high radio-wave propagation attenuation of 4G systems whose frequency band is expected to be higher than 3 GHz. In addition, this technology enables 4G systems based on pico-cells to decrease transmitting power, increase the efficiency of frequency reuse, and provide cost effective deployment.

Index Terms Broadband communication, Wireless communication, Radio over fiber.

I. INTRODUCTION

Since the advent of wireless communication, they have been developed at a tremendous speed, with growth of the related businesses. During the last several years, wireless communications have not only created new businesses, but also made a great change in our life style.

Second generation (2G) mobile communication systems based on digital signal processing techniques has been very successful for decades. It leads to the development of third generation mobile systems. Third generation (3G) mobile communication systems, wideband code-division multiple access (WCDMA), and CDMA2000, were initially proposed and designed to be a high performance and high bandwidth system to carry high data rate services. During the evolution from 2G to 3G, a variety of wireless systems such as GPRS, Bluetooth, UWB, Wireless LAN (WLAN), and HiperLAN, have been developed. These systems were designed independently, with an aim of different service types, data rates, and users. Because these systems all have their own merits and shortcomings, there will be no single system that is good enough to replace all the other technologies.

Nowadays, researchers, system vendors, and service providers are expressing growing interest in future wireless communication systems that can support various service types and various users demand. Some important features of future wireless communication systems are stated as follows:

Ubiquitous: anywhere, anytime, with any device. Broadband: sufficient data rate to deliver various

services. Convergence: support of various service types, data

rates and users.

Seamless: always best connected, global roaming across multiple wireless and mobile networks.

In this paper, an overview of the beyond 3G (B3G)

and 4G systems will be provided. One of enabling technologies of the next generation wireless communication, RoF technology, will be discussed.

II. SAMSUNGS VIEW ON B3G AND 4G

One of B3G systems in Korea is WiBro (wireless broadband). It is slated to hit the market on April, 2006. WiBro, a new emerging wireless broadband technology, will make people use wireless devices such as cellular phones to use the internet and to watch broadcasts, simultaneously. It is based on the IEEE802.16e standard, and offers true mobility, high performance, and standardization for wireless broadband applications. We have a plan to commercially launch WiBro data access systems and handsets in Korea next year with sector data throughput speeds up to 30 Mbps, with the frequency band of 2.3 GHz. It is expected that WiBro is an initial convergence systems realizing the wireless wideband communications between the 3G cellular technology and the WLAN technology, as shown Fig. 1. In addition, it will provide a bridge between existing wireless systems and futuristic 4G systems.

Fig. 1. Samsungs view on Beyond 3G

We are interested in investigating cost-effective practical implementation methods for 4G which will support data transmission at speed up to 1 Gbps at the stationary and 100 Mbps at the moving, as shown in Fig. 2.

2

Fig. 2. ITU-R vision on 4G.

III. RADIO OVER FIBER FOR 4G

There are plenty of related technological problems on the next generation mobile communication.

Due to the demand of high bandwidth of 4G and the lack of available vacant frequency band, the frequency band of 4G systems is expected to be higher than 3.0 GHz. In case of WiBro, its frequency band is 2.3 GHz which is higher than 3G frequency. This increased frequency band leads to the high radio-wave propagation loss for uplink and downlink, as shown in Fig. 3. In particular, the high propagation loss for uplink increases the power consumption of the mobile handsets. Network operators for 4G will be having tremendous difficulties accommodating the increasing traffic, because the system should guarantee the high data rate for each user.

Fig. 3. Propagation loss versus frequency

The peak data rate of the next generation mobile communication systems will be over 100 Mbps. In order to meet this requirement, the management of wireless resources for future mobile communications should be more flexible.

The reduced cell size and the centralization of base stations could relax the problems. A large number of remote access units should be installed within small areas, and the network should be able to ensure the seamless connections among the numerous remote

access units. The centralization of several base stations can share wireless resource and can improve the flexibility of wireless resources.

RoF technology is one of the best solutions for the implementation of the reduced cell size and the centralization of base station [1], [2]. Using optical fiber with ultra-wide bandwidth, it is possible to transfer the complicated RF modem and signal processing functions to a centralized control station, so called base station hotel [3]. It enables us to implement compact and cost-effective remote access units. In addition, RoF links can support a variety of wireless systems, regardless of their frequency bands, because they have ultra-wide bandwidth and protocol transparent characteristics.

At the beginning stage, we consider RoF technology as in-building solution providing various wireless services. Nowadays, customers expect their mobile terminals to work whether inside or outside the building. Particularly, in-building environment has many difficulties in providing various wireless services because it has a large propagation loss due to a myriad of obstacles. RoF technology can transmit a variety of wireless services over a strand of fiber and make small size remote access units. Moreover, it is suitable for present and future wireless services such as 4G. Therefore, we are developing RoF technologies providing multiple wireless systems including 3G, WLAN, Digital multimedia broadcasting (DMB), and B3G at the hot spot or in-building area, as shown in Fig.4.

Service interface unit

Switchingunit

3G3G

DMBDMB

B3GB3G

WLAN

RAURAUOptical

Transceiver

CAP Fig. 4. System block diagram (CAP : Common access platform, RAU : Remote access unit)

REFERENCES [1] Hamed Al-Raweshidy and Shozo Komaki, Radio

over fiber technologies for mobile communications networks, Norwood: Artech house, 2002.

[2] H. Kim and Y. C. Chung, Passive optical network for CDMA-based microcellular communication systems, Journal of Lightwave Technology, vol. 19, no. 3, March, 2001.

[3] P. P. Smyth, Optical radio a review of a radical new technology for wireless access infrastructure, BT Technology Journal, vol. 21, no. 3, pp. 22-31, July, 2003.