K Giridhar

In multicarrier systems, cyclic prefix (CP) is introduced between two symbols to mitigate inter block interference (IBI). The CP length should be equal or more than channel impulse response (CIR) to ensure IBI free system. However, in the interest of spectral efficiency, if the CP is chosen to be less than the (worst case) CIR length, then a time domain channel shortening prefilter (CSP) can be used to truncate or shape the CIR. In [1], we proposed a null-space exploiting CSP (NE-CSP) which is has a lower complexity when compared to the linear minimum mean square error (LMMSE) [2]. In this paper, we propose a symbol-by-symbol adaptive null-space exploiting CSP (SANE-CSP) scheme based on the NE-CSP structure, which is computationally inexpensive. The order of complexity of SANE-CSP is O(n c2), whereas the computational complexity order for NE-CSP [1] is O(n c3) and that of the decoding-delay optimised LMMSE [2] is close to for O(n c4). The SANE-CSP for n c = 100, has a block error rate performance 3 dB poorer than the decoding-delay optimised LMMSE, but with only 0.01% computational complexity. © 2011 National Institute of Inform.

Performance of spatial multiplexing multiple-input multiple-output (MIMO) wireless systems can be improved with channel state information (CSI) at both ends of the link. This paper proposes a new linear diagonal MIMO transceiver, referred to as co-ordinate interleaved spatial multiplexing (CISM). With CSI at transmitter and receiver, CISM diagonalizes the MIMO channel and interleaves the co-ordinates of the input symbols (from rotated QAM constellations) transmitted over different eigenmodes. The analytical and simulation results show that with co-ordinate interleaving across two eigenmodes, the diversity gain of the data stream transmitted over the weaker eigenmode becomes equal to that of the data transmitted on the stronger eigenmode, resulting in a significant improvement in the overall diversity. The diversity-multiplexing tradeoff (DMT) is analyzed for CISM and is shown that it achieves higher diversity gain at all positive multiplexing gains compared to existing diagonal transceivers. Over rank n MIMO channels, with input symbols from rotated n-dimensional constellations, the DMT of CISM is a straight line connecting the endpoints (0,NtNr) and (min{Nt,Nr}, 0), where Nt, and Nr} are the number of transmit and receive antennas, respectively. © 2006 IEEE.

Distributed MIMO radar systems offer tremendous advantage in the detection of airborne platforms employing stealth and are resilient to single point failure. However, when multiple targets are present over the surveillance region, the reflected signals at various receivers from these targets cannot be uniquely associated to the targets easily. Incorrect associations of the received data lead to the creation of ghost targets, and hence, de-ghosting is an inherent problem in distributed radar systems. Exploiting the geometry of the measurement model into the association process, we devise algorithms that are practically implementable and computationally feasible. In this work, a novel, efficient and fast data association scheme followed by a localization algorithm is proposed that utilizes Time-of-Arrival and Doppler frequency measurements of the targets with respect to the transmitter-receiver pairs to accurately determine 3D position and velocities of the targets. The proposed approach is non-parametric as it does not need the assumption of initial states, number of targets and their motion models. It simultaneously associates up to four targets present within a minimum horizontal separation of 100m× 100m for signals of bandwidth 20MHz and any number of targets that are flying far away from this minimum separation in the observation region. It can also associate and track up to nine targets that have sequential birth and random death, flying with random realizable velocities.