Abstract—During the evolution of mobile networks, reusability of network components has been always a main concern. At the same time, keeping operational and maintenance cost at reasonable levels is a major task. This paper presents and quantifies the advantages of using multimode remote radios capable of operating according to various standards (WCDMA, WiMAX and LTE) for resolving these challenges. Keywords—multimode radio, optical fiber, WiMAX, LTE I. INTRODUCTION T is rather an objective comment to characterize this decade as the decade of mobile communication. It has also become obvious that end-users will continue demanding higher speeds for data services and lower prices. Their requirements are concentrated on the variety and quality of services, as well as the cost of accessing them. The objective is to be able to enjoy the same services that nowadays all fixed-line operators provide and being charged on a similar low flat rate basis. This paper provides an overall description of distributed base station architectures concentrating on the remote radio module. The benefits and limitations of the remote radio module are highlighted, as well as the system requirements. Finally, several features providing software defined radio capabilities are analyzed. II. PLANNING THE RADIO ACCESS NETWORK Planning the radio access network is strictly associated with the radio coverage provided by the wireless standard used. Among other reasons, the GSM standard was extremely successful because it was able to offer large cell coverage. The main reason for this was the fact that GSM operates in low frequency bands, 900-1100MHz, where signal attenuation is low. This enables operators to use fewer base stations, deploying robust wireless systems. However, the limited bandwidth provided by GSM systems was a major restriction. Due to spectrum regulations, 3G and upcoming 4G standards operate mainly in higher frequency bands, 1.8GHz – 3.6GHz. Using sophisticated modulation schemes and digital signal processing techniques, spectrum is managed efficiently offering wider channel bandwidth and overall throughput [4]. WiMAX standard specifies 70Mbps in the downlink direction and LTE 100Mbps. However, the trade-off of operating in the range of 2-3GHz frequency band is the reduced coverage because of high signal attenuation. Therefore, the number of necessary cells and antennas increases. The fact that the number of subscribers and traffic volume are constantly augmenting will inevitably force operators to design very dense networks. For this reason, the concept of micro and pico cells is introduced with a cell radius from 100m to 1km. These are intended to provide wireless connectivity to limited in size areas both indoor and outdoor. Designing and planning this type of wireless networks is a challenging and costly task. The increased number of radio elements raises complicated issues regarding: installation and integration, infrastructure upgrades, rental spaces etc. Decreasing the cost of network deployment and maintenance is a prerequisite for operators. The necessary initial investment for upgrading the radio access components of a mobile network is extremely high. Additionally, the cost of operating these networks has to be kept within a reasonable range. Therefore, operators are oriented towards a universal solution supporting multiple wireless standards, easily integrated with current infrastructure. Fiber To The Antenna (FTTA) is a technological approach offering a number of the already enlisted advantages. III. FIBER TO THE ANTENNA (FTTA) A. Delivering Wireless through Fiber Modern broadband network architectures have been using optical fiber for the “last mile” communication replacing the traditional copper access network. The advantages of this approach can be summarized as: high speed, low cable losses and easy upgrades. Communication over fiber is capable of delivering services to multiple end-users directly in the building. The range of available speed depends on the equipment used and the communication standard applied. Therefore, network upgrades require only modifying the end equipment without changing the fiber cable network. The latter can save time and money for operators who eventually would like to integrate new technologies in their current infrastructure. The generic term used, Fiber to the x (FTTx), defines the end destination of the fiber cable. Fiber to the Fiber to the Antenna: A Step towards Multimode Radio Architectures for 4G Mobile Broadband Communications Georgios Kardaras # , Jose Soler * , Lukasz Brewka * , and Lars Dittmann * , Members, IEEE # Radiocomp ApS, Krakasvej 17, 3400 Hillerød ,Denmark * Networks Technology & Service Platforms group, Department of Photonics Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark I 2010 IEEE 4th International Symposium on Advanced Networks and Telecommunication Systems 978-1-4244-9854-3/10/$26.00 ©2010 IEEE 85