The Digital Tracking Loop Enhancements for Mitigating Signal Interference in DVB-H and DVB-T Salauddin Mohammad, Piyush Kuchhal, and Rajeev Kumar Gupta Abstract---In a Wireless Communication System, a Signal (Signal includes series of symbols) can travel from the transmitter to receiver over multiple paths. This phenomenon is referred to as Multipath Propagation, where signal attenuation varies on different paths. The propagation over different paths is caused by scattering, reflection, diffraction and refraction of the radio waves by stationary and moving objects, as well as the medium. The Delay spread can cause Inter Symbol Interference (ISI) when adjacent data symbols overlap and interfere with each other due to different delays on different propagation paths. For high data rate applications (especially in 4G & 5G Technologies) with very short symbol duration, the effect of ISI and the receiver complexity can increase significantly. When attempting to decode the signal, only part of a symbol for a signal path may be captured in a Fast Fourier Transform (FFT) window due to multiple path delays. In this paper, a Time Tracking Loop is proposed for OFDM based broadcast systems. The proposed time tracking topology is a fast digital feed- back loop which corrects the timing errors for OFDM based broadcast based systems, such as DVB-H and DVB-T, efficiently. The loop is implemented with VHDL code targeting the Xilinx EP3C25Q240C8N FPGA Chip and it gives effective signal to error ratio 35dB. Keywords---Inter Symbol Interference (ISI), Fast Fourier Transform (FFT), OFDM. I. INTRODUCTION The receiver oscillator frequency will never be perfectly aligned with the transmitter frequency; this in turn will produce phase errors. Both sample period and phase errors degrade the performance of the OFDM receivers. Sample period errors lead to drifting the OFDM symbol start with time, for example assume 1 ppm (part per million) sampling clock offset while receiving 2048 samples per OFDM symbol, the symbol window will move one sample every ~488 symbols. The higher the sampling clock offset, the more the influence on the symbol time synchronization. This problem becomes more pressing in broad cast based systems, such as Md.Salauddin, University of Petroleum and Energy Studies, Dehradun- India. Email ID -msalauddin@ddn.upes.ac.in) Piyush Kuchhal, University of Petroleum and Energy Studies, Dehradun- India. Email ID -pkuchhal@ddn.upes.ac.in) Rajeev Gupta, University of Petroleum and Energy Studies, Dehradun- India. Email ID -rajeev@ddn.upes.ac.in) DVB-T and DVB-H. There are two main different methods for timing errors correction, namely, the synchronous sampling and the asynchronous sampling. Fig. 1 The OFDM Transmitter Block Fig. 2 The OFDM Receiver Block The Synchronous samp 1 ling systems depend on the system to Control the Crystal Oscillator (VCXO). Compared to the asynchronous digital sampling systems, they have significant timing fluctuations due to high-level phase noises. Also needed analog circuits are complex and make the system integration more difficult. For asynchronous systems, a free running oscillator is used for sampling and OFDM frame reconstruction is achieved by means of interpolation or decimation filters. In this paper, an asynchronous fast tracking and efficient implementation of the timing errors correction are introduced for OFDM based broadcast DVB-H, DVB-T and other similar standards which have a periodic repetition of pre-known scattered pilots each given number of OFDM symbols [1-3]. The system uses the time domain correlation of the sampled signal and a locally generated group of the scattered pilots to calculate the timing errors. Hence the system does interpolation and decimation of the sampled signal by introducing (P+1) or (P-1) samples for each P samples digitized by the system ADC depending on the detected error. The System can correct sample period errors up to 200 ppm. The loop response time to lock on the correct sampling frequency is a major issue, and as described in [3], the current systems used for synchronization of the DVB-H take around 75 OFDM symbols, and vary from 17 to 68 symbols in case of DVB-t before the estimation start. The proposed system can find the symbol start after maximum time of 4 OFDM International Conference on Intelligent Systems, Control & Manufacturing Technology (ICICMT’2015) March 16-17, 2015 Abu Dhabi (UAE) http://dx.doi.org/10.15242/IIE.E0315513 27