UWB Receiver Design Simplification through Channel Shortening

1. UWB Receiver Design Simplification through Channel Shortening Imtiaz Husain Syed and Dr. Jinho Choi School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney-2052, Australia. Background: Ultra Wide Band (UWB) systems are baseband communication systems which use extremely narrow pulses for information transfer and occupy a huge bandwidth with low power spectral density. Due to very large bandwidths, channel impulse responses contain 100 to 300 resolvable multipaths in different propagation scenarios. UWB channel models are standardized and known as CM1, CM2, CM3 and CM4. • Proposed Algorithm and Comparative Analysis: • Most of the recent applications of channel shortening are developed to maximize the bit rate or channel capacity in Multi Carrier Modulation (MCM) or Discrete Multi Tone (DMT) systems. These are designed for wired line static channels with less number of multipaths. • Some Existing Algorithms: • Maximum Shortening Signal to Noise Ratio (MSSNR) Algorithm: Maximizes the energy inside desired time window with constrained out side energy or vice versa. 2. Target Impulse Response (TIR) Based Minimum Mean Squared Error (MMSE) Algorithm: Minimizes the MMSE between actual channel impulse response and desired TIR with constrained input-output cross correlation. • Proposed Algorithm: It is based on unconstrained optimization and shortens the channel by maximizing the single tap energy in the effective channel. Hence, it shortens the dense multipath channel to just one significant tap and enables single fingered RAKE design. • Comparison Parameters: Performance of each of the above algorithms is evaluated in terms of the following parameters: • Captured Energy • Consistency in Shortening the Channel • SINR Improvement • Bit Error Rate Simulation Results: Simulations are performed for all four standard channel models. 1.Energy Capture and Performance Consistency: Proposed algorithm is found more consistent and capturing more energy in almost all scenarios specially in dense multipaths. 2. SINR Improvement: 3. Bit Error Rate Problem Definition: UWB receivers are implemented through RAKE with large number of fingers because of dense multipath channels. This structure is complex from design and analysis point of view and involves high manufacturing costs. Channel Shortening – A Novel Approach: Channel shortening is an equalization technique which forces the channel impulse response to be confined within a desired time window or to a certain number of taps. Thus, channel shortening can help in designing a simplified and cost effective UWB receiver. Conclusion: The proposed algorithm outperforms existing algorithms for channel shortening. It enables a simple, cost effective and single correlator based UWB receiver design. Channel shortening to an extent of single significant tap also eliminates the burden of on-line template waveform evaluation at receiver side. • Future Directions: • Future directions of this research work include: • Testing of the proposed algorithm in further dense multipath environments like indoor industrial or office scenarios. • Modifying the current version to a blind and adaptive design. • Performance analysis of UWB system with channel shortening.