Showing papers on "Codebook published in 2007"

On the performance of random vector quantization limited feedback beamforming in a MISO system

Abstract: In multiple antenna wireless systems, beamforming is a simple technique for guarding against the negative effects of fading. Unfortunately, beamforming requires the transmitter to have knowledge of the forward-link channel which is often not available a priori. One way of overcoming this problem is to design the beamforming vector using a limited number of feedback bits sent from the receiver to the transmitter. In limited feedback beamforming, the beamforming vector is restricted to lie in a codebook that is known to both the transmitter and receiver. Random vector quantization (RVQ) is a simple approach to codebook design that generates the vectors independently from a uniform distribution on the complex unit sphere. This correspondence presents performance analysis results for RVQ limited feedback beamforming

Systematic Codebook Designs for Quantized Beamforming in Correlated MIMO Channels

Abstract: The full diversity gain provided by a multi-antenna channel can be achieved by transmit beamforming and receive combining. This requires the knowledge of channel state information (CSI) at the transmitter which is difficult to obtain in practice. Quantized beamforming where fixed codebooks known at both the transmitter and the receiver are used to quantize the CSI has been proposed to solve this problem. Most recent works focus attention on limited feedback codebook design for the uncorrelated Rayleigh fading channel. Such designs are sub-optimal when used in correlated channels. In this paper, we propose systematic codebook design for correlated channels when channel statistical information is known at the transmitter. This design is motivated by studying the performance of pure statistical beamforming in correlated channels and is implemented by maps that can rotate and scale spherical caps on the Grassmannian manifold. Based on this study, we show that even statistical beamforming is near-optimal if the transmitter covariance matrix is ill-conditioned and receiver covariance matrix is well-conditioned. This leads to a partitioning of the transmit and receive covariance spaces based on their conditioning with variable feedback requirements to achieve an operational performance level in the different partitions. When channel statistics are difficult to obtain at the transmitter, we propose a universal codebook design (also implemented by the rotation-scaling maps) that is robust to channel statistics. Numerical studies show that even few bits of feedback, when applied with our designs, lead to near perfect CSI performance in a variety of correlated channel conditions.

Multiple Antenna Broadcast Channels With Shape Feedback and Limited Feedback

Abstract: In this paper, we consider two different models of partial channel state information at the base station transmitter (CSIT) for multiple antenna broadcast channels: 1) the shape feedback model where the normalized channel vector of each user is available at the base station and 2) the limited feedback model where each user quantizes its channel vector according to a rotated codebook that is optimal in the sense of mean squared error and feeds back the codeword index. This paper is focused on characterizing the sum rate performance of both zero-forcing dirty paper coding (ZFDPC) systems and channel inversion (CI) systems under the given two partial CSIT models. Intuitively speaking, a system with shape feedback loses the sum rate gain of adaptive power allocation. However, shape feedback still provides enough channel knowledge for ZFDPC and CI to approach their own optimal throughput in the high signal-to-noise ratio (SNR) regime. As for limited feedback, we derive sum rate bounds for both signaling schemes and link their throughput performance to some basic properties of the quantization codebook. Interestingly, we find that limited feedback employing a fixed codebook leads to a sum rate ceiling for both schemes for asymptotically high SNR.

A Generic Construction of Complex Codebooks Meeting the Welch Bound

Abstract: Codebooks (also called signal sets) meeting the Welch bound on the maximum correlation amplitude are called MWBE codebooks and are desirable in code-division multiple-access systems. Two different but related constructions of MWBE codebooks from difference sets were developed by Xia and Ding recently. The objectives of this correspondence are to present a generic construction of MWBE codebooks that contains the previous two constructions as special cases and describe new MWBE codebooks that cannot be produced by the earlier two constructions.

Diversity–Multiplexing Tradeoff in MIMO Channels With Partial CSIT

Abstract: The diversity-multiplexing (D-M) tradeoff in a multi antenna channel with optimized resolution-constrained channel state feedback is characterized. The concept of minimum guaranteed multiplexing gain in the forward link is introduced and shown to significantly influence the optimal D-M tradeoff. It is demonstrated that power control based on the feedback is instrumental in achieving the D-M tradeoff, and that rate adaptation is important in obtaining a high diversity gain even at high rates. A criterion to determine finite-length codes to be tradeoff optimal is presented, leading to a useful geometric characterization of the class of extended approximately universal codes. With codes from this class, the optimal D-M tradeoff is achievable by the combination of a feedback-dependent power controller and a single code-book for single-rate or two codebooks for adaptive-rate transmission. Finally, lower bounds to the optimal D-M tradeoffs based on Gaussian coding arguments are also studied. In contrast to the no-feedback case, these random coding bounds are only asymptotically tight, but can quickly approach the optimal tradeoff even with moderate codeword lengths.

Signal generation using phase-shift based pre-coding

Abstract: A phase-shift based pre-coding scheme used in a transmitting side and a receiving side that has less complexity than those of a space-time coding scheme, that can support various spatial multiplexing rates while maintaining the advantages of the phase-shift diversity scheme, that has less channel sensitivity than that of the pre-coding scheme, and that only requires a low capacity codebook is provided.

MIMO Transmit Beamforming Under Uniform Elemental Power Constraint

Abstract: We consider multi-input multi-output (MIMO) transmit beamforming under the uniform elemental power constraint. This is a nonconvex optimization problem, and it is usually difficult to find the optimal transmit beamformer. First, we show that for the multi-input single-output (MISO) case, the optimal solution has a closed-form expression. Then we propose a cyclic algorithm for the MIMO case which uses the closed-form MISO optimal solution iteratively. The cyclic algorithm has a low computational complexity and is locally convergent under mild conditions. Moreover, we consider finite-rate feedback methods needed for transmit beamforming. We propose a simple scalar quantization method, as well as a novel vector quantization method. For the latter method, the codebook is constructed under the uniform elemental power constraint and the method is referred as VQ-UEP. We analyze VQ-UEP performance for the MISO case. Specifically, we obtain an approximate expression for the average degradation of the receive signal-to-noise ratio (SNR) caused by VQ-UEP. Numerical examples are provided to demonstrate the effectiveness of our proposed transmit beamformer designs and the finite-rate feedback techniques.

Filter Lookup Table Method for Power Amplifier Linearization

Abstract: This paper presents a new method of digital adaptive predistortion for linearization of power amplifiers (PAs) exhibiting memory effects. The predistorter (PD) device consists of a lookup table (LUT) gain followed by a codebook of filters addressed by the index of the LUT. The adaptation is derived from direct learning for the LUT gains and indirect learning for the filter coefficients. We compared our results with those of two reference methods: a simple LUT system (with direct learning) and a memory polynomial system (with indirect learning). The performances of the new approach lie between those of the two reference methods in terms of adjacent channel power regrowth and error vector magnitude. The LUT is the less complex of the three methods, but it is a memoryless system, and it cannot correct the memory effects in the PA. The memory polynomial PD is more powerful, but its complexity is very high. The new technique, due to the addition of filters to the LUT, has possibilities to compensate not only for the nonlinearity but also for the memory effects in the PA, and it is one order of magnitude less complex than the memory polynomial system

Reference signaling scheme using compressed feedforward codebooks for MU-MIMO systems

Abstract: A multi-user MIMO downlink beamforming system with limited feed forward ( 200 ) is provided to enable preceding matrix information to be efficiently provided to a subset of user equipment devices ( 201. i ), where zero-forcing transmit beamformers (w i ) are computed at the base station ( 210 ) and assembled into a precoding matrix (W). The precoding matrix is encoded using a compact reference signal codebook ( 225, 207. i ) for forward link signaling, either by sending bits indicating the index of the transmission matrix used, or by transmitting one or more precoded pilots or reference signals wherein the pilot signals are precoded using vectors uniquely representative of the transmission matrix used which includes candidate reference signal matrices which meet a predetermined condition number requirement, such as a condition number threshold. The preceding matrix information ( 227 ) is extracted at the user equipment devices ( 201. i ) using the compact reference signal codebook ( 207. i ) and used by the MMSE receiver ( 209. i ) to generate receive beamformers (v i ).

Method and device for coding audio data based on vector quantisation

Abstract: A wideband audio coding concept is presented that provides good audio quality at bit rates below 3 bits per sample with an algorithmic delay of less than 10 ms. The concept is based on the principle of Linear Predictive Coding (LPC) in an analysis-by-synthesis framework. A spherical codebook is used for quantisation at bit rates which are higher in comparison to low bit rate speech coding for improved performance for audio signals. For superior audio quality, noise shaping is employed to mask the coding noise. In order to reduce the computational complexity of the encoder, the analysis-by synthesis framework has been adapted for the spherical codebook to enable a very efficient excitation vector search procedure. Furthermore, auxiliary information gathered in advance is employed to reduce a computational encoding and decoding complexity at run time significantly. This auxiliary information can be considered as the SCELP codebook. Due to the consideration of the characteristics of the apple-peeling-code construction principle, this codebook can be stored very efficiently in a read-only-memory.

Evolutionary fuzzy particle swarm optimization vector quantization learning scheme in image compression

Abstract: This article develops an evolutional fuzzy particle swarm optimization (FPSO) learning algorithm to self extract the near optimum codebook of vector quantization (VQ) for carrying on image compression. The fuzzy particle swarm optimization vector quantization (FPSOVQ) learning schemes, combined advantages of the adaptive fuzzy inference method (FIM), the simple VQ concept and the efficient particle swarm optimization (PSO), are considered at the same time to automatically create near optimum codebook to achieve the application of image compression. The FIM is known as a soft decision to measure the relational grade for a given sequence. In our research, the FIM is applied to determine the similar grade between the codebook and the original image patterns. In spite of popular usage of Linde–Buzo–Grey (LBG) algorithm, the powerful evolutional PSO learning algorithm is taken to optimize the fuzzy inference system, which is used to extract appropriate codebooks for compressing several input testing grey-level images. The proposed FPSOVQ learning scheme compared with LBG based VQ learning method is presented to demonstrate its great result in several real image compression examples.

Fast Planar-Oriented Ripple Search Algorithm for Hyperspace VQ Codebook

Abstract: This paper presents a fast codebook search method for improving the quantization complexity of full-search vector quantization (VQ). The proposed method is built on the planar Voronoi diagram to label a ripple search domain. Then, the appropriate codeword can easily be found just by searching the local region instead of global exploration. In order to take a step further and obtain the close result full-search VQ would, we equip the proposed method with a duplication mechanism that helps to bring down the possible quantizing distortion to its lowest level. According to the experimental results, the proposed method is indeed capable of providing better outcome at a faster quantization speed than the existing partial-search methods. Moreover, the proposed method only requires a little extra storage for duplication

Beamforming with Limited Feedback in Amplify-and-Forward Cooperative Networks

Abstract: A relay selection approach has previously been shown to outperform repetition-based scheduling for both amplify-and-forward (AF) and decode-and-forward (DF) cooperative networks. The selection method generally requires some feedback from the destination to the relays and the source, raising the issue of the interplay between performance and feedback rate. In this paper, we treat selection as an instance of limited- feedback distributed beamforming in cooperative AF networks, and highlight the differences between transmit beamforming in a traditional multi-input single-output (MISO) system and the distributed case. Specifically, Grassmanian line packing (GLP) is no longer the optimal codebook design, and orthogonal codebooks are no longer equivalent to each other. We derive the high signal-to-noise ratio expressions for outage probability and probability of symbol error for unlimited-feedback and selection schemes. The gap in performance between unlimited-feedback and selection beamforming is found analytically to grow rapidly with the number of relays. We compare the selection protocol to a limited-feedback distributed beamformer that assigns codebooks based on the generalized lloyd algorithm (GLA), and one that uses random beam-vectors. The main conclusion is that the performance improvement to be seen using the very complex GLA is small, and that many more feedback bits are required with random beamforming than selection for the same performance. These results indicate that the selection protocol is a very attractive protocol with low-complexity that provides excellent performance relative to other known methods.

Wireless communication method and system for indexing codebook and codeword feedback

Abstract: The present invention is related to indexing channel information feedback in a multiple-input multiple-output (MIMO)-based wireless communication system. In one embodiment, at least one measurement of a channel metric is performed. The measured channel metric is quantized and a codeword is selected that represents the measured channel metric. Feedback is generated based on the channel metric measurement. The feedback includes an index to the selected codeword. A codebook is generated by partitioning a plurality of codewords into two or more tiers, assigning indices to the codewords and correlating the codewords in complex vector space and Hamming distance in binary indices. For any given codeword, a first subset of the codewords may have a higher correlation with respect to the given codeword. In another embodiment, the number of bits used to report codebook indexing is determined based on the frequency of the generation of the feedback.

Video compression using adaptive variable length codes

Abstract: Adaptive variable length coding techniques may be used for entropy coding of residual block coefficients produced by predictive video coding. The techniques may be applied to schemes that code positions of nonzero transform coefficients using zero runs. Coding parameters such as end of block (EOB) shift and VLC codebook selection tables may be maintained as internal states, instead of sending them with coded video slice data. Table entries may be periodically updated based on statistics collected during a coding pass. A special EOB shift table may adapt the position of a special EOB symbol in a symbol set to probability of significant coefficients with magnitude greater than one for a coding condition, such as a coding cycle. Chroma blocks may be coded independently of luma blocks using separate EOB shift, special EOB shift, and VLC codebook selection tables.

System and method for performing precoding in a wireless communication system

Abstract: A base station capable of performing precoding in a wireless communication system is provided. The base station includes a plurality of codebooks and a codebook selector. Each codebook comprises a plurality of composite precoding matrices that are generated based on a corresponding diversity precoding matrix. The codebook selector is operable to select one of the codebooks for use in a communication session with a subscriber station.

Design of Spherical Lattice Codes for Lattice and Lattice-Reduction-Aided Decoders

Abstract: Methods and apparatus for designing spherical lattice codebooks for use in data transmission systems are provided. A spherical lattice codebook is constructed by determining the channel statistics of one or more channels, which can be accomplished by observing a sufficiently large set of channel realizations. After determining the channel statistics, an expression for the error probability of the decoder or expressions for bounds on the error probability and expressions for the corresponding gradients are determined. The gradient is then used in an optimization technique to produce a spherical lattice codebook which is subsequently used for transmission.

Interpolation-Based Multi-Mode Precoding for MIMO-OFDM Systems with Limited Feedback

Abstract: Spatial multiplexing with multi-mode precoding provides a means to achieve both high capacity and high reliability in multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. Multi-mode precoding uses linear transmit precoding that adapts the number of spatial multiplexing data streams or modes, according to the transmit channel state information (CSI). As such, it typically requires complete knowledge of the multi-mode precoding matrices for each subcarrier at the transmitter. In practical scenarios where the CSI is acquired at the receiver and fed back to the transmitter through a low-rate feedback link, this requirement may entail a prohibitive feedback overhead. In this paper, we propose to reduce the feedback requirement by combining codebook-based precoder quantization, to efficiently quantize and represent the optimal precoder on each subcarrier, and multi-mode precoder frequency down-sampling and interpolation, to efficiently reconstruct the precoding matrices on all subcarriers based on the feedback of the indexes of the quantized precoders only on a fraction of the subcarriers. To enable this efficient interpolation-based quantized multimode precoding solution, we introduce (1) a novel precoder codebook design that lends itself to precoder interpolation, across subcarriers, followed by mode selection, (2) a new precoder interpolator and, finally, (3) a clustered mode selection approach that significantly reduces the feedback overhead related to the mode information on each subcarrier. Monte-Carlo bit-error rate (BER) performance simulations demonstrate the effectiveness of the proposed quantized multi-mode precoding solution, at reasonable feedback overhead

Quantization Methods for Equal Gain Transmission With Finite Rate Feedback

Abstract: We consider the design and analysis of quantizers for equal gain transmission (EGT) systems with finite rate feedback-based communication in flat-fading multiple input single output (MISO) systems. EGT is a beamforming technique that maximizes the MISO channel capacity when there is an equal power-per-antenna constraint at the transmitter, and requires the feedback of t-1 phase angles, when there are t antennas at the transmitter. In this paper, we contrast two popular approaches for quantizing the phase angles: vector quantization (VQ) and scalar quantization (SQ). On the VQ side, using the capacity loss with respect to EGT with perfect channel information at transmitter as performance metric, we develop a criterion for designing the beamforming codebook for quantized EGT (Q-EGT). We also propose an iterative algorithm based on the well-known generalized Lloyd algorithm, for computing the beamforming vector codebook. On the analytical side, we study the performance of Q-EGT and derive closed-form expressions for the performance in terms of capacity loss and outage probability in the case of i.i.d. Rayleigh flat-fading channels. On the SQ side, assuming uniform scalar quantization and i.i.d. Rayleigh flat-fading channels, we derive the high-resolution performance of quantized EGT and contrast the performance with that of VQ. We find that although both VQ and SQ achieve the same rate of convergence (to the capacity with perfect feedback) as the number of feedback bits B increases, there exists a fixed gap between the two

Compressed random-access trees for spatially coherent data

Abstract: Adaptive multiresolution hierarchies are highly efficient at representing spatially coherent graphics data. We introduce a framework for compressing such adaptive hierarchies using a compact randomly-accessible tree structure. Prior schemes have explored compressed trees, but nearly all involve entropy coding of a sequential traversal, thus preventing fine-grain random queries required by rendering algorithms. Instead, we use fixed-rate encoding for both the tree topology and its data. Key elements include the replacement of pointers by local offsets, a forested mipmap structure, vector quantization of inter-level residuals, and efficient coding of partially defined data. Both the offsets and codebook indices are stored as byte records for easy parsing by either CPU or GPU shaders. We show that continuous mipmapping over an adaptive tree is more efficient using primal subdivision than traditional dual subdivision. Finally, we demonstrate efficient compression of many data types including light maps, alpha mattes, distance fields, and HDR images.

Noisy Speech Enhancement Using Harmonic-Noise Model and Codebook-Based Post-Processing

Abstract: This paper presents a post-processing speech restoration module for enhancing the performance of conventional speech enhancement methods. The restoration module aims to retrieve parts of speech spectrum that may be lost to noise or suppressed when using conventional speech enhancement methods. The proposed restoration method utilizes a harmonic plus noise model (HNM) of speech to retrieve damaged speech structure. A modified HNM of speech is proposed where, instead of the conventional binary labeling of the signal in each subband as voiced or unvoiced, the concept of harmonicity is introduced which is more adaptable to the codebook mapping method used in the later stage of enhancement. To restore the lost or suppressed information, an HNM codebook mapping technique is proposed. The HNM codebook is trained on speaker-independent speech data. To reduce the sensitivity of the HNM codebook to speaker variability, a spectral energy normalization process is introduced. The proposed post-processing method is tested as an add-on module with several popular noise reduction methods. Evaluations of the performance gain obtained from the proposed post-processing are presented and compared to standard speech enhancement systems which show substantial improvement gains in perceptual quality

Codebook and pre-coder selection for closed-loop mimo

Abstract: A method of transmitting a communication signal is disclosed. The method includes receiving a data signal (102). The method further includes receiving a codeword index (pre-coder selection) from a remote transceiver. A codeword is selected from a Householder matrix based codebook in response to the index. The data signal is precoded (104) in response to the selected codeword. The precoded data signal is transmitted (100) to the remote transceiver.

Method and system for an alternating channel delta quantizer for mimo pre-coders with finite rate channel state information feedback

Abstract: Aspects of a method and system for an alternating channel delta quantizer for MIMO pre-coders with finite rate channel state information feedback may include quantizing a change in channel state information in a MIMO pre-coding system onto a codebook using a cost function and selecting the codebook from a set of codebooks; and generating the set of codebooks from a plurality of codebooks, where each may comprise one or more unitary matrices. The channel state information may be a matrix V that may be generated using Singular Value Decomposition (SVD) and/or Geometric Mean Decomposition (GMD). The selecting of the codebooks may be enabled by alternating between the elements of the set of codebooks. The cost function f(A) may be defined by the following relationship: f  ( A ) = ( 1 N  ∑ j = 1 N   a jj  2 ) where A is a matrix of size N by N and a ij is element (i,j) of matrix A.

MIMO transmit beamforming under uniform elemental power constraint

Abstract: We consider multi-input multi-output (MIMO) transmit beamforming under the uniform elemental power constraint. This is a non-convex optimization problem, and it is usually difficult to find the optimal transmit beamformer. First, we show that for the multi-input single-output (MISO) case, the optimal solution has a closed-form expression. Then we propose a cyclic algorithm for the MIMO case which uses the closed- form MISO optimal solution iteratively. The cyclic algorithm has a low computational complexity and is locally convergent under mild conditions. Moreover, we consider finite-rate feedback methods needed for transmit beamforming. We propose a novel vector quantization method, where the codebook is constructed under the uniform elemental power constraint and the method is referred as VQ-UEP. Numerical examples are provided to demonstrate the effectiveness of our proposed transmit beamformer designs and the finite-rate feedback technique.

Mimo communication system and method for beamforming using polar-cap codebooks

Abstract: Embodiments of a multiple-input multiple-output (MIMO) communication system and methods for beamforming using polar-cap codebooks are generally described herein. Other embodiments may be described and claimed. In some embodiments, beamforming is based on codewords of a polar-cap codebook which represents deviations in the channel with respect to codewords of a full-manifold codebook.

Rank-Independent Codebook Design from a Quaternary Alphabet

Abstract: Single-user as well as multi-user MIMO systems employ codebook-based feedback to customize the signal transmission to the current channel conditions The two competing metrics for evaluating a codebook are packet-error-rate/throughput performance and codebook search complexity at the mobile To address this issue structured unitary codebooks are proposed where each codebook entry is restricted to a power of i and a single codebook is optimized for all ranks Such codebooks are shown to perform favorably with the best known (unconstrained) codebooks in terms of distance measures and are also shown to perform well in multi-user MIMO link-level simulations

Finite Rate Feedback for Spatially and Temporally Correlated MISO Channels in the Presence of Estimation Errors and Feedback Delay

Abstract: In this paper, the problem of finite-rate feedback for spatially and temporally correlated Rayleigh fading multiple input single output (MISO) channels with estimation errors at the receiver and feedback delay is addressed. A model that captures estimation errors, feedback delay, and finite-rate quantization of the channel is developed. A novel codebook design algorithm that minimizes the loss in ergodic capacity is proposed. Simulation results show that the new codebook designed under the consideration of estimation errors and feedback delay outperforms the codebook designed assuming ideal conditions. Analysis for the loss in ergodic capacity for spatially i.i.d channels with channel estimation errors and delay (EED) is presented and validated through simulations.

Variable feedback for universal terrestrial radio access

Abstract: A wireless communication system includes a wireless transmit/receive unit (WTRU). The WTRU is configured to generate at least one local codebook based on a baseline codebook, and select a codeword from the local codebook that is associated with feedback.

Combination of colour and thermal sensors for enhanced object detection

Abstract: In uncontrolled environments, with dynamic background and lighting changes, performing efficient and real-time foreground - background segmentation is very challenging. This work is based on the hypothesis that the combination of long wave infrared (LWIR) (8-12 mum) and colour cameras can significantly improve the robustness of moving objects extraction. Pros and cons of colour and thermal imagers in outdoor video monitoring applications are discussed. In order to fuse information from both sensors, we favoured an approach based on "analytical fusion" rather than "representative fusion". Starting from a state-of-the-art algorithm for moving objects extraction in colour video (non-parametric codebook model), we first adapted the method for processing of "red-green-blue-thermal" video format. A preliminary objective performance evaluation of detection accuracy is presented. Original image sequences grabbed with co-aligned thermal and visible fields of view was used. Finally, some improvements to the original codebook model are proposed.