A canonical space-time characterization of mobile wireless channels (original) (raw)
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Canonical space-time processing for wireless communications
IEEE Transactions on Communications, 2000
A canonical space-time characterization of mobile wireless channels is introduced in terms of a fixed basis that is independent of the true channel parameters. The basis captures the essential degrees of freedom in the received signal using discrete multipath delays, Doppler shifts, and directions of arrival (DOA). The canonical representation provides a robust representation of the propagation dynamics and eliminates the need for estimating delay, Doppler and DOA parameters of different multipaths. Furthermore, it furnishes a natural framework for designing low-complexity space-time receivers. Single-user receivers based on the canonical channel representation are developed and analyzed. It is demonstrated that the resulting canonical space-time receivers deliver near-optimal performance at substantially reduced complexity compared to existing designs.
Space-Time Receivers for CDMA Multipath Signals
IEEE International Conference on Communications, 1997
We consider the problem of receiving CDMA multipath signals at a receiver with an antenna array. We derive the space-time matched filter for the multipath signals arriving at the array and show that this space-time matched filter consists of a front-end spatial matched filter or a bank of beamformers (one for each multipath component), followed by a temporal matched filter, or a bank of correlators (one for each multipath component). Then we derive the optimum (maximum likelihood) sequence detector that can be implemented via a Viterbi algorithm. We also present a sub-optimal space-time decorrelating receiver structure and discuss its limitations. Based on this space-time matched filter framework, we briefly discuss conventional space-time receiver structures for CDMA multipath signals. Analysis results for a space-time receiver with DPSK signaling show improved bit error rate performance due to the exploitation of the spatial dimension in the received signal
Space-Time Processing Applications for Wireless Communications
2008
Wireless mobile communication networks are rapidly growing at an incredible rate around the world and a number of improved and emerging technologies are seen to be critical to the improved economics and performance of these networks. The technical revolution and continuing growth of mobile radio communication systems has been made possible by extraordinary advances in the related fields of digital computing, high-speed circuit technology, the Internet and, of course, digital signal processing. Improved third generation (3G) and future generation wireless communication systems must support a substantially wider and enhanced range of services with respect to those supported by second generation and basic 3G systems. The never-ending quest for such personal and multimedia services, however, demands technologies operating at higher data rates and broader bandwidths. This combined with the unpredictability and randomness of the mobile propagation channel has created many new technically challenging problems for which innovative, adaptive and advanced signal processing techniques may offer new and better solutions. Space-time processing techniques have emerged as one of the most promising areas of research and development in wireless communications for the efficient utilization of the physical mobile radio propagation channel. Space-time processing signifies the signal processing performed on a system consisting of several antenna elements, whose signals are processed adaptively in order to exploit both the spatial (space) and temporal (time) dimensions of the radio channel. This can significantly improve the capacity, coverage, quality and energy efficiency of wireless systems. This thesis expands the scope of space-time processing by proposing novel applications in wireless communication systems. These include the reduction of possibly harmful electromagnetic radiation from mobile phones, enhancing the quality of
Frequency Domain Realization of Space-Time Receivers in Dispersive Wireless Channels
IEEE Transactions on Signal Processing, 2000
In this paper, we present a class of low complexity space-time receivers for frequency-selective channels in multiple input and multiple output (MIMO) systems. The main idea is that under certain conditions the matrices involved in the implementation of linear and nonlinear equalizers for MIMO systems can be approximated with block circulant matrices which can be inverted via block DFT operations. As result, the computational complexity of the receiver implementation is drastically reduced. First, we extend to MIMO systems two linear approaches originally derived in the framework of joint detection techniques for code division multiple access. Next, we develop a hybrid zero-forcing block decision feedback equalizer (DFE) and a minimum mean square error block DFE for MIMO systems, by performing in the frequency domain the feedback processing as in Benvenuto and Sostrato and the block linear equalizer as in Vollmer et al., while interference cancellation is performed in the time domain. Last, we extend to the frequency domain the fully connected ordered successive interference cancellation DFE. We show that these receivers yield almost the same performance as the original space-time receivers implemented in the time domain, and their computational complexity is lower, even against state of the art fast "time-domain" realizations.
A low complexity receiver for space-time coded CDMA systems
IEEE International Conference on Acoustics Speech and Signal Processing, 2002
A novel receiver for space-time coded systems based on the reduced rank multistage Wiener filter (MWF) is presented. It is shown that this receiver has a complexity that is only a linear function of the processing gain (N ), the number of transmit antennas (L t ), and the rank (D) of the MWF. The complexity of the equivalent MMSE solution is a function of (NL t ) 3 . It is also demonstrated by numerical simulation that this receiver meets MMSE performance at a significantly lower rank. The MMSE implementation is derived and performance is evaluated for highly loaded synchronous CDMA systems in flat fading.
Complex Orthogonal Space-Time Processing in Wireless Communications
2006
Multiple-Input Multiple-Output (MIMO) transmission has recently emerged as one of the most significant technical breakthroughs in modern communication with a chance to resolve the bottleneck of traffic capacity in the future wireless networks. Communication theories show that MIMO systems can provide potentially a very high capacity that, in many cases, grows approximately linearly with the number of antennas. Space-time processing is the main feature of MIMO systems. Space-Time Codes (STCs) are the codes designed for the use in MIMO systems. Among a variety of STCs, orthogonal Space-Time Block Codes (STBCs) possess a much simpler decoding method over other STCs. Because of that, this thesis examines orthogonal STBCs in MIMO systems. Furthermore, Complex Orthogonal STBCs (CO STBCs)
IEEE Transactions on Vehicular Technology, 2003
An orthogonal decomposition of a general wideband space-time frequency selective channel is derived assuming antenna arrays at both the transmitter and receiver. Knowledge of channel state information is assumed at both the transmitter and receiver. The decomposition provides a framework for efficiently managing the degrees of freedom in the space-time channel to optimize any combination of bit-error rate and throughput in single-user or multiuser applications. The decomposition is used to derive efficient signaling schemes and receiver structures for a variety of scenarios. For a fixed throughput system, we investigate a power allocation scheme that minimizes the effective bit-error rate. In addition, a strategy to maximize the throughput under a worst-case bit-error rate constraint is proposed. For multiuser applications, we propose a signaling scheme that achieves orthogonality among users by exploiting the temporal channel modes which are common to all users. The effect of imperfect channel state information at the transmitter is also investigated.
IEEE Transactions on Wireless Communications, 2004
Selective broadcast schemes for point-to-multiple point transmission of identical information to several selected users are studied for a code-division multiple-access wireless system. The channel states for all selected users are assumed known at both the transmitter and the receivers. The goal is to minimize total transmit power while satisfying minimum received signal-to-noise ratio (SNR) requirements. Three designs, namely, time-only, space-time and space-only, are investigated. In the time-only design no spatial diversity is available, and we solve the optimal transmit signature code by developing iterative least distance programming (ILDP) and linear programming (LP) algorithms. In the space-time design, transmit antennas are exploited in addition to the temporal dimension, and we show the ILDP algorithm is still applicable. The LP algorithm can also be adapted with the integration of space-time block codes, which we term the space-time block coding LP (STC-LP) algorithm. In the space-only design, only the spatial dimension is available and we study the optimization of the transmit antenna weights to satisfy the users' SNR requirements. We show that the STC-LP algorithm applies in this case. We also propose an iterative spatial diagonalization algorithm to explore the unique structure of the space-only problem. Index Terms-Broadcast, code-division multiple access (CDMA), multicast, space-time block codes, space-time processing, transmit-receive joint optimization. NOMENCLATURE Transmit signature code. Receive filter for th user. Required signal-to-noise ratio at th user. Hermitian transpose operator for vectors and matrices. Complex conjugate operator. Number of mobile stations in the cell. Length of the maximum multipath delay in chips. Number of antennas at the transmitter. Signature code length, or spreading gain. I. INTRODUCTION T HE field of wireless communication has been dominated by study of transmission of unicast information. The term unicast means that information is intended for only one receiver. Most voice and data traffic in cellular systems falls into this Manuscript
Layered Space–Time Receivers for Frequency-Selective Wireless Channels
Recent results in information theory have demonstrated the enormous potential of wireless communication systems with antenna arrays at both the transmitter and receiver. To exploit this potential, a number of layered space-time architectures have been proposed. These layered space-time systems transmit parallel data streams, simultaneously and on the same frequency, in a multiple-input multiple-output fashion. With rich multipath propagation, these different streams can be separated at the receiver because of their distinct spatial signatures. However, the analysis of these techniques presented thus far had mostly been strictly narrowband. In order to enable high-data-rate applications, it might be necessary to utilize signals whose bandwidth exceeds the coherence bandwidth of the channel, which brings in the issue of frequency selectivity. In this paper, we present a class of layered space-time receivers devised for frequency-selective channels. These new receivers, which offer various performance and complexity tradeoffs, are compared and evaluated in the context of a typical urban channel with excellent results.
Detectors and Asymptotic Analysis for Bandwidth-Efficient Space–Time Multiple-Access Systems
IEEE Transactions on Communications, 2000
In this paper, a narrowband multiple-channel transmission scheme with multiple transmit antennas is proposed and analyzed. The channelization is based on space-time signature matrices, which do not expand bandwidth, unlike conventional schemes such as code division or time division multiplexing (CDM or TDM). The channels can be used by multiple independent users in an uplink or downlink scenario (multiple access or broadcast channels respectively), or by one user in a multiplexing scenario. The data transmitted on each channel is convolutionally encoded, interleaved and then space-time block encoded before space-time channelization. Each channel has a unique interleaver and space-time signature, but the convolutional encoder and space-time block code (STBC) encoder can be identical across channels. It is shown that asymptotic single-user like performance can be achieved with optimal detection and decoding, in a Rayleigh fading channel. Practical receiver algorithms are developed based on the iterative (turbo) detection technique. The simulation results demonstrate that these suboptimal receivers achieve single-user performance at moderate signal-to-noise ratios, and moderate user loads. In It is assumed that each data channel applies convolutional coding followed by space-time block coding, and has a distinct interleaver. It is shown that in the limit of high signal-to-noise ratio (SNR), single-user like performance 1 can be achieved with maximum-likelihood detection and decoding. Furthermore, due to the use of channel encoding and interleaving, designing space-time signature matrices for single-user like performance here is easier than in [9], [10].