Options
K Giridhar
Loading...
Preferred name
K Giridhar
Official Name
K Giridhar
Alternative Name
Giridhar, Krishnamurthy
Krishnamurthy, Giridhar
Giridhar, K.
Main Affiliation
Email
ORCID
Scopus Author ID
4 results
Now showing 1 - 4 of 4
- PublicationIntroducing space sampling for OFDM systems with multipath diversity(01-01-2003)
;Rangaraj, G. V.; Multiple receive antennas are known to provide receiver diversity but typically require considerable separation between them. We introduce the concept of space sampling at the receiver where antennas are placed relatively close to each other. Since the antennas are close, the samples are highly spatially correlated and does not help in performance improvement in a typical wireless system with flat fading. However, this concept is very useful particularly in an OFDM system with frequency selective fading which has an inherent multipath diversity. Under these circumstances, the required space diversity for performance improvement is obtained by the transformation of multipath diversity to useful space diversity in frequency domain inherently by an OFDM system (G. V. Rangaraj et al., June 2003). The minimum separation required between the antennas under such circumstances is derived analytically and we have show that even with a separation of only 0.44λ, the required spatial correlation in the frequency domain becomes sufficiently low. - PublicationPerformance losses in V-BLAST due to fading(01-01-2001)
;Malasani, R.New insights into the information theoretic aspects of multiple antenna systems have led to the development of numerous blind and training-based schemes that exploit the high data rate capacities of diversity systems. One such popular training-based spatial multiplexing technique is the Vertical Bell Labs Layered Space Time Architecture (V-BLAST). The common practice in the literature is to assume that the channel remains constant over some time interval, whose duration is proportional to the coherence time of the channel. This is not often true since the channel is continuously varying, although the variation is slow in some cases. For our analysis, the channel coefficients are modeled as a first-order autoregressive process. We then show that even in slow fading channels, the performance losses are considerable. One surprising and rather non-intuitive result is that the performance losses are higher at higher average signal-to-noise ratios. We have simulated V-BLAST with such a channel model to confirm the validity of our analysis. - PublicationDSP-based noncoherent detectors for multilevel signals in flat fading channels(01-01-1998)
; ; This paper addresses the issue of recovering multilevel signals in the presence of slow, frequency nonselective fading and additive white Gaussian noise (AWGN). First, we present a novel noncoherent detector which performs approximate maximum likelihood detection in unknown amplitude and phase (ML-UAP). This ML-UAP detector is implemented using the Viterbi algorithm (VA), which we call the suboptimal noncoherent VA for multilevel signals (SNVA-M). Next, we propose a forgetting-factor based SNVA-M (FSNVA-M) which is quite insensitive to gain and phase changes of the signal, and thereby, avoids the need for explicit carrier recovery and AGC procedures. For differentially encoded multilevel signals, we propose three other schemes namely: symbol-by-symbol differential detector for multilevel signals (SSDD-M), VA-based multiple symbol differential detection for multilevel signals (MSDDVA-M) and the VA-based quotient space approach (QSVA). Finally, we present-results from computer simulations, which indicate that the FSNVA-M detector is best suited for AWGN and Rician fading channels, whereas the SSDD-M, MSDDVA-M and the and SVA detectors are best suited for Rayleigh fading channels. An important feature of all the proposed detectors is that they do not assume any knowledge of the fade statistics. Moreover, they easily lend themselves to DSP-based implementations. - PublicationPre-processed space-time trellis codes with one-bit feedback(01-08-2005)
;Milleth, J. Klutto; Open-loop (no feedback) pre-processing methods for improving the error-rate performance of space-time trellis codes in additive white Gaussian noise (AWGN) and Ricean channels which nearly preserve the performance in Rayleigh channels are proposed in [1]. The rotation based pre-processing preserves the Rayleigh channel performance, whereas there is a small degradation in performance in the power division based pre-processing. This degradation depends on the trellis complexity, and is more pronounced for the lower state trellis codes. In this letter, we propose a one-bit feedback method, that improves the performance of the power division method in Rayleigh channels. Simulation results for a 2 × 1 system show that this improvement is significant for the higher state trellis codes. The one-bit feedback is used to determine which of the two channels has a higher gain, and the higher power is assigned to the corresponding transmitter. © 2005 IEEE.