It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

This document provides updates to IEEE Std 802.16's MIB for the MAC, PHY and asso- ciated management procedures in order to accommodate recent extensions to the standard.

IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems Draft Amendment: Management Information Base Extensions

Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.

OFDM and Its Wireless Applications: A Survey

This paper presents a genetic algorithmic approach to the shortest path (SP) routing problem. Variable-length chromosomes (strings) and their genes (parameters) have been used for encoding the problem. The crossover operation exchanges partial chromosomes (partial routes) at positionally independent crossing sites and the mutation operation maintains the genetic diversity of the population. The proposed algorithm can cure all the infeasible chromosomes with a simple repair function. Crossover and mutation together provide a search capability that results in improved quality of solution and enhanced rate of convergence. This paper also develops a population-sizing equation that facilitates a solution with desired quality. It is based on the gambler ruin model; the equation has been further enhanced and generalized. The equation relates the size of the population, quality of solution, cardinality of the alphabet, and other parameters of the proposed algorithm. Computer simulations show that the proposed algorithm exhibits a much better quality of solution (route optimality) and a much higher rate of convergence than other algorithms. The results are relatively independent of problem types for almost all source-destination pairs. Furthermore, simulation studies emphasize the usefulness of the population-sizing equation. The equation scales to larger networks. It is felt that it can be used for determining an adequate population size in the SP routing problem.

A genetic algorithm for shortest path routing problem and the sizing of populations

Techniques are described for efficiently estimating and compensating for the effects of a communication channel in a multi-carrier wireless communication system. The techniques exploit the fact that the transmitted symbols are drawn from a finite-alphabet to efficiently estimate the propagation channel for multi-carrier communication systems, such systems using OFDM modulation. A transmitter transmits data through a communication channel according to the modulation format. A receiver includes a demodulator to demodulate the data and an estimator to estimate the channel based on the demodulated data. The channel estimator applies a power-law operation to the demodulated data to identify the channel. The techniques can be used in both blind and semi-blind modes of channel estimation.

Channel estimation for wireless ofdm systems

A method for controlling errors in a wireless link layer using a simultaneous multiple copy scheme and an adaptive forward error correction (FEC) scheme in a wideband wireless communication is provided. The method for controlling errors in a link layer in wideband wireless communication using an automatic repeat request (ARQ) scheme, in which a wideband wireless channel is used for communication between a first node and a second node, includes the steps of (a) estimating the error ratio of a forward (a direction in which a cell is transmitted from the first node to the second node) channel using the state of a backward (a direction in which a cell is transmitted from the second node to the first node) channel, and transmitting a cell, in which a forward error correction (FEC) code having an encoding ratio that varies depending on the estimated error ratio is included in a protocol data unit (PDU) of a wireless link layer, through the forward channel and (b) re-transmitting the copy of a cell transmitted in the step (a), when feedback information that indicates that an error exists in the cell transmitted in the step (a) is received through the backward channel. It is possible to reduce the number of times of re-transmission by improving the probability of correcting forward errors using more error controlling bits as the state of the channel is worse and to minimize the waste of resources using less error controlling bits as the state of the channel is better, to thus obtain the optimal performance and guarantee the minimum delay time.

Method for controlling errors in link layer in wideband wireless communication and computer readable media therefor

We consider a mobile content delivery network (mCDN) in which a special form of mobile devices designated as caching servers (caching-server device: CSD) can provide the near-by devices with some popular contents on demand via device-to-device (D2D) communication links. On the assumption that mobile CSDs are randomly distributed by a Poisson point process (PPP), an optimization problem is formulated to determine the probability of storing the individual content in each server in a manner that minimizes the average caching failure rate. Further, we present a low-complexity search algorithm, optimum dual-solution searching algorithm (ODSA), for solving this optimization problem. We identify the important characteristics of the optimal caching policies in the mobile environment that would serve as a useful aid in designing an mCDN.

Mobile caching policies for device-to-device (D2D) content delivery networking

In this paper, an iterative receiver for a joint data-detection and channel-estimation scheme is presented for orthogonal frequency-division multiplexing systems, which incorporates iterative decoding in the receiver. In the proposed scheme, a maximum a posteriori-based decoder and a channel estimator provide more reliable information on the coded bits for each other in an iterative manner. We first consider a practical implementation issue for the optimal minimum mean squared error two-dimensional (2-D) channel estimator as an essential element in the iterative receiver. To reduce the complexity of the 2-D estimator as suited to the iterative receiver, we focus on rigorously investigating how a separable estimator must be designed so that its structure may become asymptotically equivalent to that of the optimal 2-D estimator. Furthermore, we derive an analytical expression of the iterative process to evaluate a convergence performance as a function of the number of iterations and discuss its convergence property. Our simulation results demonstrate that the proposed iterative receiver achieves a near-ideal performance with only a few iterations under time-variant multipath fading channels.

Iterative receiver for joint detection and channel estimation in OFDM systems under mobile radio channels

A near-optimal routing algorithm employing a modified Hopfield neural network (HNN) is presented. Since it uses every piece of information that is available at the peripheral neurons, in addition to the highly correlated information that is available at the local neuron, faster convergence and better route optimality is achieved than with existing algorithms that employ the HNN. Furthermore, all the results are relatively independent of network topology for almost all source-destination pairs.

Shortest path routing algorithm using Hopfield neural network

In multiple measurement vectors (MMV) problems, the sparsity structure, i.e., the support of the measurement vectors, remains constant for multiple instants. For machine type communication (MTC) context, this sparsity structure may remain constant over all symbols in a frame, which can be termed as frame-wise sparsity. Instead of employing symbol-by-symbol detection based on algorithms such as orthogonal matching pursuit (OMP), group orthogonal matching pursuit (GOMP) can take advantage of this constant sparsity structure and decodes group of symbols together in order to improve the accuracy. Unfortunately, the exponential growth in computational complexity of the GOMP algorithm with the group size prohibits it from increasing the group size and fully exploiting the frame-wise sparsity. This letter presents an iterative order recursive least square (IORLS) algorithm, which can exploit the frame-wise sparsity and increase accuracy. IORLS iteratively employs a modified OMP operations over a frame to gather the sparsity support information with manageable complexity. IORLS substantially reduces complexity by avoiding the matrix inversions in OMP and GOMP algorithms. Furthermore, it has been shown that the proposed algorithm is robust against noise, achieving near-oracle estimation performance.

Chung G. Kang

Papers

Method for controlling errors in link layer in wideband wireless communication and computer readable media therefor

Mobile caching policies for device-to-device (D2D) content delivery networking

Iterative receiver for joint detection and channel estimation in OFDM systems under mobile radio channels

Shortest path routing algorithm using Hopfield neural network

Iterative Order Recursive Least Square Estimation for Exploiting Frame-Wise Sparsity in Compressive Sensing-Based MTC