Introducing space sampling for OFDM systems with multipath diversity
14 Dec 2003-pp 427-430
TL;DR: The concept of space sampling at the receiver where antennas are placed relatively close to each other is introduced and it is shown that even with a separation of only 0.44/spl lambda/, the required spatial correlation in the frequency domain becomes sufficiently low.
Abstract: 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 0.44/spl lambda/, the required spatial correlation in the frequency domain becomes sufficiently low.
Citations
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TL;DR: The minimum antenna separation required for a target spatial correlation in the frequency domain in situations with low multipath diversity is evaluated and it is found to be within 1 dB (at BER=10/sup -3/) of spatially uncorrelated reception for QPSK modulation.
Abstract: Spatial correlation is introduced when antennas are not well separated, which typically leads to performance degradation in space diversity systems for flat fading wireless channels. However, in a frequency-selective environment with orthogonal frequency division multiplexing (OFDM), multipath diversity can help in overcoming this performance degradation. This is due to transformation of a highly spatially correlated channel impulse response to less spatially correlated channel frequency response inherently by an OFDM system in the presence of multipath diversity . In this letter, we numerically evaluate the minimum antenna separation required for a target spatial correlation in the frequency domain in situations with low multipath diversity. Performance results for two highly spatially correlated receive antennas with such spacing are provided for low multipath diversity channels and it is found to be within 1 dB (at BER=10/sup -3/) of spatially uncorrelated reception for QPSK modulation.
7 citations
Cites methods from "Introducing space sampling for OFDM..."
...Digital Object Identifier 10.1109/LSP.2004.836939...
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...In [6], the technique of exploiting multipath diversity with spatially correlated channels in OFDM systems is discussed....
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TL;DR: This review article focuses on MIMO-OFDM wireless systems, and the usefulness of multipath diversity in such systems are addressed, and space-frequency linear dispersion codes which are particularly useful at low rate and for low complexity systems are reviewed.
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) technology hold much promise in realizing broadband wireless systems which are both power efficient and bandwidth efficient. This review article focuses on MIMO-OFDM wireless systems, and the usefulness of multipath diversity in such systems are addressed. With increasing data rate requirements for wireless access, the technology challenges of the physical layer designers are moving towards wideband wireless communications. One of the key issue to be confronted in such systems is the frequency selective fading of the wireless channel due to multipath propagation. Orthogonal frequency division multiplexing helps in transforming this frequency selective channel into multiple narrowband flat sub-channels which facilitate a computationally efficient equalization. Usually multipath delay spread is considered as an annoyance factor. However, such channels are rich in multipath diversity, which could potentially be exploi...
3 citations
Dissertation•
01 Jan 2008
TL;DR: A low-complexity iterative interference cancellation and detection scheme is designed to provide a good compromise between the exponential computational complexity of the soft interference cancellation linear MMSE algorithm and the near-capacity performance of a scheme which uses iterative turbo processing for soft interference suppression in combination with multiuser detection.
Abstract: The combination of multiple-input multiple-output (MIMO) technology and orthogonal frequency division multiplexing (OFDM) is likely to provide the air-interface solution for future broadband wireless systems. A major challenge for MIMO-OFDM systems is the problem of multi-access interference (MAI) induced by the presence of multiple users transmitting over the same bandwidth. Novel signal processing techniques are therefore required to mitigate MAI and thereby increase link performance. A background review of space-time block codes (STBCs) to lever age diversity gain in MIMO systems is provided together with an introduction to OFDM. The link performance of an OFDM system is also shown to be sensitive to time-variation of the channel. Iterative minimum mean square error (MMSE) receivers are therefore proposed to overcome such time-variation. In the context of synchronous uplink transmission, a new two-step hard-decision interference cancellation receiver for STBC MIMO-OFDM is shown to have robust performance and relatively low complexity. Further improvement is obtained through employing error control coding methods and iterative algorithms. A soft output multiuser detector based on MMSE interference suppression and error correction coding at the first stage is shown by frame error rate simulations to provide significant performance improvement over the classical linear scheme. Finally, building on the "turbo principle", a low-complexity iterative interference cancellation and detection scheme is designed to provide a good compromise between the exponential computational complexity of the soft interference cancellation linear MMSE algorithm and the near-capacity performance of a scheme which uses iterative turbo processing for soft interference suppression in combination with multiuser detection.
References
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Book•
29 May 2003
TL;DR: This book is an accessible introduction to every fundamental aspect of space-time wireless communications and a powerful tool for improving system performance that already features in the UMTS and CDMA2000 mobile standards.
Abstract: Wireless networks are under constant pressure to provide ever-higher data rates to increasing numbers of users with greater reliability. This book is an accessible introduction to every fundamental aspect of space-time wireless communications. Space-time processing technology is a powerful tool for improving system performance that already features in the UMTS and CDMA2000 mobile standards. The ideal volume for graduate students and professionals, it features homework problems and other supporting material on a companion website.
3,798 citations
TL;DR: The analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel using the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel is discussed.
Abstract: This paper discusses the analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel. This system uses the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel. When this technique is used with pilot-based correction, the effects of flat Rayleigh fading can be reduced significantly. An improvement in signal-to-interference ratio of 6 dB can be obtained over the bursty Rayleigh channel. In addition, with each subchannel signaling at a low rate, this technique can provide added protection against delay spread. To enhance the behavior of the technique in a heavily frequency-selective environment, interpolated pilots are used. A frequency offset reference scheme is employed for the pilots to improve protection against cochannel interference.
2,627 citations
Book•
01 Jan 1965
TL;DR: Textbook on communication engineering emphasizing random processes, information and detection theory, statistical communication theory, applications, etc.
Abstract: Textbook on communication engineering emphasizing random processes, information and detection theory, statistical communication theory, applications, etc
1,519 citations
TL;DR: It is found that, in the MIMO case, unlike the single-input single-output (SISO) case, delay spread channels may provide advantages over flat fading channels not only in terms of outage capacity but also in termsof ergodic capacity.
Abstract: This paper deals with the capacity behavior of wireless orthogonal frequency-division multiplexing (OFDM)-based spatial multiplexing systems in broad-band fading environments for the case where the channel is unknown at the transmitter and perfectly known at the receiver Introducing a physically motivated multiple-input multiple-output (MIMO) broad-band fading channel model, we study the influence of physical parameters such as the amount of delay spread, cluster angle spread, and total angle spread, and system parameters such as the number of antennas and antenna spacing on ergodic capacity and outage capacity We find that, in the MIMO case, unlike the single-input single-output (SISO) case, delay spread channels may provide advantages over flat fading channels not only in terms of outage capacity but also in terms of ergodic capacity Therefore, MIMO delay spread channels will in general provide both higher diversity gain and higher multiplexing gain than MIMO flat fading channels
1,004 citations