AN EFFICIENT TIME-DOMAIN FREQUENCY SHIFTER HARDWARE ARCHITECTURE FOR 4G SYSTEMS
Keywords:LTE, PRACH, NCO, time-domain frequency shift, FPGA
One of the very first operations carried out by the Physical Random Access Channel (PRACH) receiver at base station side in LTE and LTE-A systems is the extraction of relevant preamble signal through a time-domain frequency shift operation. This operation translates the PRACH signal back to base band which is necessary for preamble detection. This paper presents the hardware architecture and implementation details on Field Programable Gate Array (FPGA) devices of a configurable and optimized time-domain frequency shifter. It is a hardware-efficient and accurate architecture for converting the relevant received PRACH signal into base band before further processing. The architecture is manly based on a customized Numerically Controlled Oscillator (NCO) for generating complex exponentials using only adders, a Look-Up Table (LUT) and plain logic resources. The main advantage of the proposed arctecture is that it eliminates the need for storing a large number of long complex exponential sequences by employing a single LUT and exploiting quarter wave symmetry of the basis waveform. Simulation results show that the proposed customized NCO architecture provides high Spurious Free Dynamic Range (SFDR) signals using minimal amount of FPGA resources. The resulting of spur suppression ranges from approximately 62 to 153 dB without using Taylor Series correction.
2] Stefania Sesia, Issam Toufik and Matthew Baker, “LTE - The UMTS Long Term Evolution: From Theory to Practice”, John Wiley & Sons, 2011.
 3GPP TS 36.211, “Physical Channels and Modulation (Release 10)”, September 2009.
 R.L. Frank, S. A. Zadoff and R. Heimiller, “Phase shift pulse codes with good periodic correlation properties”, IRE Transactions on Information Theory, Vol 7, pp.254-257, October 1961.
 David C. Chu, “Polyphase codes with good periodic correlation properties”, IEEE Transactions on Information Theory, pp. 531-532, July 1972.
 Felipe A. P. de Figueiredo et al., “Multi-stage Based Cross-Correlation Peak Detection for LTE Random Access Preambles”, Revista Telecomunicações, 15:17, 2013.
 Xilinx, “DS246 - DDS Logic Core Product Specification - v5”, April 28, 2005.
 Felipe A. P. de Figueiredo, Fabbryccio A. C. M. Cardoso, Karlo G. Lenzi, Jose A. Bianco Filho, and Fabricio L. Figueiredo., “A modified ca-cfar method for lte random access detection, 7th International Conference on Signal Processing and Communication Systems (ICSPCS), 2013, pages 1-6, Dec. 2013.
 3GPP TS 36.104, “Base Station (BS) radio transmission and reception (Release 10), December 2007.