4G mobile communication technologies and the key issues facing

Abstract: This paper focuses on the key technology of 4G mobile communication a brief exposition of the 4G network architecture and key technologies of 4G, in this based on the detailed discussion of the current global and progress of China's 4G technologies and the problems facing the prospect of finally 4G predicted.

Keywords: 4G; 4G key technology; OFDM SAMIMO SDR4G Development Status

1 Introduction

the ITU's work, collected in 2009 will focus on technical standards for 4G, 2010 4G version will be introduced first, and in 2011 by the World Radiocommunication Conference. 4G is expected to commercially around 2015. The rapid Development of 4G technology, so customers enjoy the newer, more efficient, richer communication life possible.


2 4G network in the key technology

4G system for a variety of different services access system, through the media access port to connect to based on the core network. Network architecture based on IP technology allows users to achieve the 3G, 4G, WLAN seamless roaming and fixed interconnection. 4G network structure can be divided into three layers: the physical network layer, middle layer of the environment, the application network layer.

(1) the physical network layer and the road south to provide access to selected functions.

(2) the middle layer function network environment, quality of service mapping, address change and complete management.

(3) the physical network layer and the middle layer and its environment, the interface between the application environment is open, to develop and deliver new services more easily, providing seamless high data rate wireless services. And run on multiple frequency bands, this service can be adaptive to multiple wireless standards and multi-mode terminal, across multiple operators and service providers to provide wider services.

Defined according to the International Telecommunication Union, 4G technology for mobile users in the provision of 100 Mb / S data transfer, for the rest of the users 1Gb / S data transmission of wireless communication technologies, including OFDM, smart antennas (SA ) and many more antennas (MIMO) technology, software radio technology (SDR) of three key technologies.


2.1 OFDM
OFDM or orthogonal frequency division multiplexing, OFDM is the fact MCM Multi-CarrierModulation, a multi-carrier modulation. OFDM technology has many advantages: You can eliminate or reduce the interference between the signal waveform, the multipath fading and Doppler frequency shift is not sensitive to improved spectrum efficiency; suitable for high-speed data transmission; anti-fading capability; anti-ISI (ISI) ability.


2.2 Smart Antenna (SA) and Multiple Input Multiple Output antennas (MIMO) smart antenna technology
inhibit the signal interference, automatic tracking, and intelligent features such as digital beam conditioning is considered the key to future mobile communication technology. Beam-forming smart antenna can suppress crosstalk in the space domain to enhance the desired signal within a particular range, this technique can improve signal quality and can increase the transmission capacity. The basic principle is used in wireless base station antenna array and the coherent realization of the wireless transceiver to receive and transmit radio signals. At the same time by the baseband digital signal processor, for each antenna link signal received by a certain algorithm to merge to achieve uplink beamforming. At present the work of smart antennas, there are two main ways: fully-adaptive multi-beam mode and beam-based pre-switching mode.

Mobile communication environment, multipath propagation in the validity and reliability of communication caused a serious impact. The multiple-input multiple-output (M1MO) are in communication with multiple antennas at both ends of the link, the originator of the serial output of the source code into multiple parallel sub-flow stream, were launched by different antenna elements with frequency, At the same time to send, receive Fangze Li caused by multipath signals on multiple receive antennas are not related to separate from the mixed signal to estimate the original sub-stream, which is equivalent to frequency of recycling, the spectral efficiency and link reliability greatly improved.


2.3 Software Defined Radio (SDR)
Software Defined Radio (SDR) is standardized, modular hardware functional unit by a common hardware platform, software loading method used to implement various types of radio communication system an open architecture technology. The central idea is to make broadband ADC (A / D) and digital to analog converter (D / A) and other advanced modules as close as possible the requirements of the RF antenna. As much as possible in software defined radio functionality. The software system includes all types of wireless signaling rules and processing software, the signal stream transformation software, modem software algorithms, channel error correction coding software, source code software. Software radio technology mainly involves digital signal processing hardware (DSPH), field programmable devices (FPGA), digital signal processing (DSP) and so on.

Links to Research Papers Download http://www.hi138.com