25-04-2012, 02:59 PM
OVERSAMPLING TO REDUCE THE EFFECT OF TIMING JITTER ON
HIGH SPEED OFDM SYSTEMS
68 Oversampling to Reduce the Effect of Timing Jitter on.docx (Size: 40.9 KB / Downloads: 52)
Introduction
ORTHOGONAL frequency division multiplexing (OFDM) is used in many wireless broadband communication systems because it is a simple and scalable solution to intersymbol interference caused by a multipath channel. Very recently the use of OFDM in optical systems has attracted increasing interest. Data rates in optical fiber systems are typically much higher than in RF wireless systems. At these very high data rates, timing jitter is emerging as an important limitation to the performance of OFDM systems. A major source of jitter is the sampling clock in the very high speed analog-to-digital converters (ADCs) which are required in these systems. Timing jitter is also emerging as a problem in high frequency band pass sampling OFDM radios. The effect of timing jitter has been analyzed in.
Background
OFDM is becoming widely applied in wireless communications systems due to its high rate transmission capability with high bandwidth efficiency and its robustness with regard to multi-path fading and delay. It has been used in digital audio broadcasting (DAB) systems, digital video broadcasting (DVB) systems, digital subscriber line (DSL) standards, and wireless LAN. The use of differential phase-shift keying (DPSK) in OFDM systems avoids need to track a time varying channel; however, it limits the number of bits per symbol and results in a 3 dB loss in signal-to-noise ratio (SNR). Coherent modulation allows arbitrary signal constellations, but efficient channel estimation strategies are required for coherent detection and decoding.
Proposed methodology
In OFDM, fractional oversampling can be achieved by leaving some band- edge subcarriers unused. These project focuses on the colored low pass timing jitter which is typical of systems using phase lock loops (PLL). They consider only integral oversampling , we investigate both fractional and integral oversampling. We extend the timing jitter matrix proposed in to analyze the detail of the intercarrier interference (ICI) in an oversampled system. Very high speed ADCs typically uses parallel pipeline architecture not a PLL and for these the white jitter which is the focus of this paper is a more appropriate model.
Applications:
1. Timing jitter is the unwelcome companion of all electrical systems that use voltage transitions to represent timing information.
2. Especially for telecom it is crucial that the pulses are synchronous to a clock signal, which is supplied by the system
3. It Characteristics of RZ Pulse Nonlinear Transmission on Dispersion Managed Fiber Link.