Amol Rajkotia

Characterization of UWB transmit-receive antenna system

An ultra-wideband (UWB), stripline-fed Vivaldi antenna is characterized both numerically and experimentally. Three-dimensional far-field measurements are conducted and accurate antenna gain and efficiency as well as gain variation versus frequency in the boresight direction are measured. Using two Vivaldi antennas, a free-space communication link is set up. The impulse response of the cascaded antenna system is obtained using full-wave numerical electromagnetic time-domain simulations. These results are compared with frequency-domain measurements using a network analyzer. Full-wave numerical simulation of the free-space channel is performed using a two step process to circumvent the computationally intense simulation problem. Vector transfer function concept is used to obtain the overall system transfer function and the impulse response.

UWB Channel Estimation: Design and Performance Evaluation

In this paper, we investigate channel estimation for a single-carrier direct-sequence ultra-wideband (DS-UWB) system based on the realistic IEEE P802.15.3a UWB channel model. In the preamble of each packet, pilot symbols are spread by the pseudorandom acquisition code and sent through the channel. At the receiver, the well known sliding window algorithm is applied to estimate the multipath channel coefficients. For channel models CM1 through CM4, we determine the length of the acquisition code to mitigate the impact of intersymbol interference on channel estimation with negligible redundant search space. We also develop a generic approach to design the pilot sequence length based on the UWB channel statistics. Furthermore, a general analytical framework is developed to accurately evaluate the symbol error rate performance with imperfect Rake tap coefficients. Simulation results are shown to verify the theoretical evaluation

MAC performance for second generation UWB

Next generation UWB design needs higher data rates than those proposed by ECMA-368 in order to be competitive. This paper investigates ECMA-368 MAC performance for extended data rates. It is shown that throughput improves at these extended PHY rates, when PHY frame size (L) is increased to 8190 octets under reasonable BER values. This improvement is a function of the transfer size. L=8190 octets exhibits >16% (>100 Mbps) improvement over L=4095 octets, for large transfers (>65 K octets). This is a worthwhile change since doubling PHY frame size imposes minor incremental complexity relative to the overall effort to support the extended PHY rates. It is shown also that scaling L does not improve throughput for bad channels (PER>12% normalized to 4095 octet payload). To maintain higher throughput under bad channel conditions, we need the ability to increase L without increasing PER. This can be achieved by packing multiple MPDUs into a single PSDU, each with its own frame check sum. This reduces PER by making it a function of the MPDU size and not PHY frame size. Complex MAC changes are needed for such a scheme. Fortunately, this scheme is only needed under bad channel conditions which are not suitable for extended data rates to start with.

Extended data rates for next generation UWB

For UWB to be a competitive solution, its next generation design must support higher data rates than those proposed by ECMA 368. The purpose of this paper is to investigate methods to double the UWB current maximum data rate. The options considered are 16-QAM and bandwidth expansion. The potential solutions to double the data rates are compared in terms of system performance. Three metrics are used as figure of merit for such comparison.