574 research outputs found
Single-RF spatial modulation requires single-carrier transmission: frequency-domain turbo equalization for dispersive channels
In this paper, we propose a broadband single-carrier (SC) spatial-modulation (SM) based multiple-input multipleoutput (MIMO) architecture relying on a soft-decision (SoD) frequency-domain equalization (FDE) receiver. We demonstrate that conventional orthogonal frequency-division multiplexing (OFDM)-based broadband transmissions are not readily suitable for the single–radio frequency (RF) assisted SM-MIMO schemes, since this scheme does not exhibit any substantial performance advantage over single-antenna transmissions. To circumvent this limitation, a low-complexity soft-decision (SoD) FDE algorithm based on the minimum mean-square error (MMSE) criterion is invoked for our broadband SC-based SM-MIMO scheme, which is capable of operating in a strongly dispersive channel having a long channel impulse response (CIR) at a moderate decoding complexity. Furthermore, our SoD FDE attains a near-capacity performance with the aid of a three-stage concatenated SC-based SM architecture
Frequency Domain Hybrid-ARQ Chase Combining for Broadband MIMO CDMA Systems
In this paper, we consider high-speed wireless packet access using code
division multiple access (CDMA) and multiple-input multiple-output (MIMO).
Current wireless standards, such as high speed packet access (HSPA), have
adopted multi-code transmission and hybrid-automatic repeat request (ARQ) as
major technologies for delivering high data rates. The key technique in
hybrid-ARQ, is that erroneous data packets are kept in the receiver to
detect/decode retransmitted ones. This strategy is refereed to as packet
combining. In CDMA MIMO-based wireless packet access, multi-code transmission
suffers from severe performance degradation due to the loss of code
orthogonality caused by both interchip interference (ICI) and co-antenna
interference (CAI). This limitation results in large transmission delays when
an ARQ mechanism is used in the link layer. In this paper, we investigate
efficient minimum mean square error (MMSE) frequency domain equalization
(FDE)-based iterative (turbo) packet combining for cyclic prefix (CP)-CDMA MIMO
with Chase-type ARQ. We introduce two turbo packet combining schemes: i) In the
first scheme, namely "chip-level turbo packet combining", MMSE FDE and packet
combining are jointly performed at the chip-level. ii) In the second scheme,
namely "symbol-level turbo packet combining", chip-level MMSE FDE and
despreading are separately carried out for each transmission, then packet
combining is performed at the level of the soft demapper. The computational
complexity and memory requirements of both techniques are quite insensitive to
the ARQ delay, i.e., maximum number of ARQ rounds. The throughput is evaluated
for some representative antenna configurations and load factors to show the
gains offered by the proposed techniques.Comment: Submitted to IEEE Transactions on Vehicular Technology (Apr 2009
Multiuser MIMO-OFDM for Next-Generation Wireless Systems
This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment inmultiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems
Performance comparison of multi-user detectors for the downlink of a broadband MC-CDMA system
In this paper multi-user detection techniques, such as Parallel and Serial Interference Cancellations (PIC & SIC), General Minimum Mean Square Error (GMMSE) and polynomial MMSE, for the downlink of a broadband Multi-Carrier Code Division Multiple Access (MCCDMA) system are investigated. The Bit Error Rate (BER) and Frame Error Rate (FER) results are evaluated, and compared with single-user detection (MMSEC, EGC) approaches, as well. The performance evaluation takes into account the system load, channel coding and modulation schemes
Robust frequency-domain turbo equalization for multiple-input multiple-output (MIMO) wireless communications
This dissertation investigates single carrier frequency-domain equalization (SC-FDE) with multiple-input multiple-output (MIMO) channels for radio frequency (RF) and underwater acoustic (UWA) wireless communications. It consists of five papers, selected from a total of 13 publications. Each paper focuses on a specific technical challenge of the SC-FDE MIMO system. The first paper proposes an improved frequency-domain channel estimation method based on interpolation to track fast time-varying fading channels using a small amount of training symbols in a large data block. The second paper addresses the carrier frequency offset (CFO) problem using a new group-wise phase estimation and compensation algorithm to combat phase distortion caused by CFOs, rather than to explicitly estimate the CFOs. The third paper incorporates layered frequency-domain equalization with the phase correction algorithm to combat the fast phase rotation in coherent communications. In the fourth paper, the frequency-domain equalization combined with the turbo principle and soft successive interference cancelation (SSIC) is proposed to further improve the bit error rate (BER) performance of UWA communications. In the fifth paper, a bandwidth-efficient SC-FDE scheme incorporating decision-directed channel estimation is proposed for UWA MIMO communication systems. The proposed algorithms are tested by extensive computer simulations and real ocean experiment data. The results demonstrate significant performance improvements in four aspects: improved channel tracking, reduced BER, reduced computational complexity, and enhanced data efficiency --Abstract, page iv
Performance evaluation of IB-DFE-based strategies for SC-FDMA systems
The aim of this paper is to propose and evaluate multi-user iterative block decision feedback equalization (IB-DFE)
schemes for the uplink of single-carrier frequency-division multiple access (SC-FDMA)-based systems. It is assumed
that a set of single antenna users share the same physical channel to transmit its own information to the base
station, which is equipped with an antenna array. Two space-frequency multi-user IB-DFE-based processing are
considered: iterative successive interference cancellation and parallel interference cancellation. In the first approach,
the equalizer vectors are computed by minimizing the mean square error (MSE) of each individual user, at each
subcarrier. In the second one, the equalizer matrices are obtained by minimizing the overall MSE of all users at each
subcarrier. For both cases, we propose a simple yet accurate analytical approach for obtaining the performance of
the discussed receivers. The proposed schemes allow an efficient user separation, with a performance close to the
one given by the matched filter bound for severely time-dispersive channels, with only a few iterations
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