Tokunbo Ogunfunmi

Wireless LAN Comes of Age: Understanding the IEEE 802.11n Amendment

During the initial development of the IEEE 802.11n (11n) amendment for improving the throughput of wireless LANs, a lot of excitement existed surrounding the potential higher throughput (i.e., faster downloads), and increased range (distance) achievable. However, delays in the development of this standard (which began in 2003, and is still in the final draft stages) as well as vendor, customer reluctance to adopt the pre-11n offerings in the marketplace, have generally slowed interest in this next-generation technology. However, there is still much to be excited about. The latest draft of IEEE 802.11n (Draft 3.0) offers the potential of throughputs beyond 200 Mbps, based on physical layer (PHY) data rates up to 600 Mbps. This is achieved through the use of multiple transmit and receive antennas, referred to as MIMO (multiple input, multiple output). Using techniques such as spatial division multiplexing (SDM), transmitter beamforming, and space-time block coding (STBC), MIMO is used to increase dramatically throughput over single antenna systems (by two to four times) or to improve range of reception, depending on the environment. This article offers an exposition on the techniques used in IEEE 802.11n to achieve the above improvements to throughput and range. First, the current generation WLAN devices (11a/b/g) are described in terms of the benefits offered to end users. Next, the evolution of the Tin amendment is discussed, describing the main proposals given, and illustrating reasons for the delay in standardization. Then, the changes to the PHY for 11n are presented. A description of channel modeling with MIMO is shown, followed by the signal processing techniques employed, including MIMO channel estimation and detection, space-time block coding (STBC), and transmitter beamforming. Simulation results are presented which illustrate the benefits of these techniques, versus the existing a/g structures, for both throughput and range. Finally, a brief section outlining considerations for the rapid prototyping of a baseband design based on the 802.11n PHY is presented. We conclude with a discussion of the future for 11n, describing the issues addressed with Drafts 2.0 and 3.0, as well as its place in a wireless market with WiMAX and Bluetooth.

Adaptive Nonlinear System Identification

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Algorithm and Architecture Co-Design of Hardware-Oriented, Modified Diamond Search for Fast Motion Estimation in H.264/AVC

In this paper, we present a new hardware-oriented, modified diamond search (HMDS) algorithm, for fast integer pel, motion estimation in H.264/AVC. We also present our co-designed, low power very large scale integration (VLSI) architecture for HMDS. The goal of HMDS is to enable the support of high quality video on low power mobile devices and low bit rate applications which typically use H.264/AVC baseline profile at levels 1-2. Our experiments use standard test sequences ranging from QCIF to high-definition 1280 × 720p video. The proposed VLSI architecture is prototyped as an field-programable gate array (FPGA)-based field programable system-on-chip. Our results show that HMDS on average has better rate-distortion performance and speedup, compared to previous state-of-the-art fast motion estimation algorithms, while its losses compared to full search motion estimation, are insignificant. Our prototyped architecture is more hardware-efficient than previous FPGA-based architectures in terms of power consumption, area, throughput, and memory utilization. We also show that its performance in terms of maximum frequency, minimum frequency, transistor count, and power consumption are comparable to that of state-of-the-art architectures implemented on application-specific integrated circuits.

On the Convergence Behavior of the Affine Projection Algorithm for Adaptive Filters

The affine projection class of algorithms (APA) provides faster convergence than LMS-based adaptive filters. Its convergence analysis is not as extensively studied as Normalized LMS (NLMS), and remains an active area of research. For tractability, most works on APA make many assumptions on the statistics of the input, as well as correlation between signals. Here we consider the effect of the correlation between filter coefficients and past measurement noise on MSE error. The effect of this correlation was found to be dependent on step-size mu, increasing or decreasing the predicted MSE depending on whether mu is less than or greater than 1, irrespective of the input statistics. Simulations are used to verify the analysis results presented.

An affine projection-based algorithm for identification of nonlinear Hammerstein systems

There are parametric and non-parametric methods for adaptive Hammerstein system identification. The most commonly used method is the non-parametric. In reality, the linear subsystem of a Hammerstein system is not of finite impulse response and non-parametric adaptive algorithms require large matrices and therefore increase computational complexity. The objectives of this paper are to identify the Hammerstein system adaptively based on the affine projection criterion using a parametric algorithm. We also develop a bound for control of step size of the proposed algorithm and derive an expression for its mean square error performance. The error surface of the nonlinear Hammerstein filter was determined by examining the non-quadratic nature and the global and local minima of the mean square error cost function. A bound was determined for the adaptive step size and an expression was derived for the mean square error convergence based on energy conservation theory. Simulations of system identification applications showed that convergence speed of the proposed algorithm was faster and the convergence was superior to previously existing Hammerstein algorithms. Applying the new algorithm to the identification of the human muscles stretch reflex dynamics showed good convergence results. The proposed algorithm is of practical value in real life situations.

Evolution, insights and challenges of the PHY layer for the emerging ieee 802.11n amendment

IEEE 802.11n is a newly emerged WLAN standard capable of providing dramatically increased throughput, as well as improved range, reduced signal fading, over the existing IEEE 802.11a/g WLAN standards. These benefits are achieved through use of MIMO (multiple-input,multiple-output). The latest draft for IEEE 802.11n describes rates up to 600 Mbps, exceeding the maximum rate with the 11a/g standards by more than ten times. In addition, techniques such as space-time block coding and beamforming provide the potential of increasing signal strength at the receiver with optimal efficiency, based on the diversity order used. In this paper, a comparative analysis of the physical (PHY) layers in the original main proposals for the 11n amendment (the TGn Sync, WWiSE and TGn Joint proposals) is presented. The key architectural differences governing the performance of these proposals are outlined. In addition, insights are provided into the choices leading to the TGn Joint proposal, which reflects the PHY architecture described in the 11n standard. The insights and challenges described relate to the choices made in the TGn Joint proposal regarding the areas of channel estimation (considering the use of beamforming, channel smoothing), bit interleaving techniques (for maximizing coding gain under channels with high frequency diversity), space-time block coding (STBC) options (designed in an effort to achieve a good balance between achieving high diversity gain and low receiver design complexity), and pilot tone selection (for a reasonable tradeoff of robustness and link-level performance). Performance curves (based on simulation models developed in MATLAB/SIMULINK) are used to verify the analysis presented. This paper also includes a discussion of some of the future challenges for the 11n amendment.

A Kernel Adaptive Algorithm for Quaternion-Valued Inputs

The use of quaternion data can provide benefit in applications like robotics and image recognition, and particularly for performing transforms in 3-D space. Here, we describe a kernel adaptive algorithm for quaternions. A least mean square (LMS)-based method was used, resulting in the derivation of the quaternion kernel LMS (Quat-KLMS) algorithm. Deriving this algorithm required describing the idea of a quaternion reproducing kernel Hilbert space (RKHS), as well as kernel functions suitable with quaternions. A modified HR calculus for Hilbert spaces was used to find the gradient of cost functions defined on a quaternion RKHS. In addition, the use of widely linear (or augmented) filtering is proposed to improve performance. The benefit of the Quat-KLMS and widely linear forms in learning nonlinear transformations of quaternion data are illustrated with simulations.

Hardware-oriented Modified Diamond Search for motion estimation in H.246/AVC

We present a new Hardware-oriented, Modified Diamond Search (HMDS) algorithm, for fast integer pel, motion estimation in H.264/AVC. This algorithm is particularly suitable for low bit rate applications and low power mobile devices. Our results show that our algorithm on average outperforms previous state-of-the-art fast motion estimation algorithms, while its losses in rate-distortion performance, when compared with Full Search Motion Estimation, are insignificant.

Speech over VoIP Networks: Advanced Signal Processing and System Implementation

Speech communication using the Voice over Internet Protocol (VoIP) is very common today. The underlying network channel may be the public switched telephone network (PSTN channel), satellite channels or cellular wireless channels to name a few. The packetization of speech and its transmission through packet switched networks, however, introduce numerous impairments such as delay, jitter, packet loss and decoder clock offset, which degrade the quality of the speech. We present an overview of the challenges and a description of the advanced signal processing algorithms used to combat these impairments and render the perceived quality of a VoIP conversation to be as good as that of the existing telephone system. We also present an example of a speech coder designed for packet-switched networks and discuss the possibilities for hardware implementations.

A new hardware implementation of the H.264 8×8 transform and quantization

H.264/AVC is the most powerful technology in video compression/transmission area because of its high coding efficiency and robustness. In this paper, we propose a new hardware architecture of 8×8 integer transform and quantization for H.264 which promises very low resource utilization. In the architecture, each pixel is processed one by one on a simplified pipeline without multiplication. Thus, redundant modules, which are used for block-based or row-based parallel processing, can be reduced. Experimental results show that it can reduce resource usage 30% compared to previously proposed models. It can be used for mobile applications. It covers a wide range of parameters as well.