Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].

/pdf/scaling-up-mimo-opportunities-and-challenges-with-very-large-puqp9v7gzk.pdf

Scaling Up MIMO: Opportunities and Challenges with Very Large Arrays

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Table Of Integrals Series And Products

Information Theory and Reliable Communication

The objective of this paper is to give a comprehensive introduction to applied cryptography with an engineer or computer scientist in mind. The emphasis is on the knowledge needed to create practical systems which supports integrity, confidentiality, or authenticity. Topics covered includes an introduction to the concepts in cryptography, attacks against cryptographic systems, key use and handling, random bit generation, encryption modes, and message authentication codes. Recommendations on algorithms and further reading is given in the end of the paper. This paper should make the reader able to build, understand and evaluate system descriptions and designs based on the cryptographic components described in the paper.

[서평]「Applied Cryptography」

The presence of both multiple-access interference (MAI) and intersymbol interference (ISI) constitutes a major impediment to reliable communications in multipath code-division multiple-access (CDMA) channels. In this paper, an iterative receiver structure is proposed for decoding multiuser information data in a convolutionally coded asynchronous multipath DS-CDMA system. The receiver performs two successive soft-output decisions, achieved by a soft-input soft-output (SISO) multiuser detector and a bank of single-user SISO channel decoders, through an iterative process. At each iteration, extrinsic information is extracted from detection and decoding stages and is then used as a priori information in the next iteration, just as in turbo decoding. Given the multipath CDMA channel model, a direct implementation of a sliding-window SISO multiuser detector has a prohibitive computational complexity. A low-complexity SISO multiuser detector is developed based on a novel nonlinear interference suppression technique, which makes use of both soft interference cancellation and instantaneous linear minimum mean-square error filtering. The properties of such a nonlinear interference suppressor are examined, and an efficient recursive implementation is derived. Simulation results demonstrate that the proposed low complexity iterative receiver structure for interference suppression and decoding offers significant performance gain over the traditional noniterative receiver structure. Moreover, at high signal-to-noise ratio, the detrimental effects of MAI and ISI in the channel can almost be completely overcome by iterative processing, and single-user performance can be approached.

/pdf/iterative-turbo-soft-interference-cancellation-and-decoding-4ha12irymu.pdf

Iterative (turbo) soft interference cancellation and decoding for coded CDMA

One of the most important practical problems of blind Digital Watermarking is the resistance against desynchronization attacks, one of which is the Stirmark random bending attack in the case of image watermarking. Recently, new blind digital watermarking schemes have been proposed which do not suffer from host-signal interference. One of these quantization based watermarking scheme is the Scalar Costa Scheme (SCS). We present an attack channel for SCS which tries to model typical artefacts of local desynchronization. Within the given channel model, the maximum achievable watermark rate for imperfectly synchronized watermark detection is computed. We show that imperfect synchronization leads to inter-sample-interference by other signal samples, independent from the considered watermark technology. We observe that the characteristics of the host signal play a major role in the performance of imperfectly synchronized watermark detection. Applying these results, we propose a resynchronization method based on a securely embedded pilot signal. The watermark receiver exploits the embedded pilot watermark signal to estimate the transformation of the sampling grid. This estimate is used to invert the desynchronization attack before applying standard SCS watermark detection. Experimental results for the achieved bit error rate of SCS watermark detection confirm the usefulness of the proposed resynchronization algorithm.

Channel model for watermarks subject to desynchronization attacks

Recently we presented a novel OFDM (orthogonal frequency division multiplexing) signaling concept, where the cyclic prefixes (CPs) are replaced by deterministic sequences which we call unique words (UWs). The UWs are generated by appropriately loading so-called redundant subcarriers. By that a complex number Reed Solomon (RS) code construction is introduced which can advantageously be exploited in an LMMSE (linear minimum mean square error) receiver. The overall concept clearly outperforms CP-OFDM in frequency selective channels. In this paper we introduce a method that significantly reduces the energy of the redundant subcarrier symbols by allowing some systematic noise in the UWs. The concept features a notable performance and bandwidth efficiency gain compared to our original UW-OFDM approach.

Complex number RS coded OFDM with systematic noise in the guard interval

The Gaussian multiple-access channel with weighted energy constraint E~/sub sum/=/spl Sigma//sub k/E/sub k//|d/sub k/|/sup 2/ models the situation in cellular multiuser communication more accurately than the standard approach with d/sub k/=1,/spl forall/k. The minimum weighted sum energy E~/sub sum/ is shown to be only achievable at a unique energy tupel (E/sub 1/, ..., E/sub K/), if all weights differ in amplitude. Moreover, the theory is generalized to a multiple receiver system describing cellular communication systems with optimum multiple cell-site processing. While for single-receiver systems the optimum energy tupel is a vertex of the allowed energy region, i.e. successive cancellation is possible, for a multi-receiver system this does not hold in general.

Gaussian multiple-access channels with weighted energy constraint

The combination of continuous phase modulation (CPM) with direct-sequence code-division multiple access (DS-CDMA) for multiuser transmission over the additive white Gaussian noise channel is discussed. Concentrating on the important special case of generalized minimum-shift keying, particularly simple receiver structures are obtained. To emphasize on low complexity, noncoherent reception is proposed and appropriate transmitter and receiver designs are provided. The application of reduced-state noncoherent sequence detection and noncoherent filter adaptation ensures high power efficiency and robustness against channel phase variations. Simulation results confirm that the chosen approach of CPM for DS-CDMA achieves high performance with very moderate complexity.

Noncoherent continuous-phase modulation for DS-CDMA

The error-floor performance of low-density parity-check (LDPC) codes under iterative decoding is governed by combinatorial configurations in the Tanner graph of the code termed trapping sets. Finding the smallest trapping set in a Tanner graph is an NP-hard problem. However, for codes constructed from designs one can partially characterize trapping sets and enumerate them efficiently. We focus on LDPC codes based on Steiner triple systems (STS), and quantify small trapping sets for bit-flipping decoding over the BSC and small trapping sets for the AWGN channel. Furthermore, we provide simulation results that show that the enumeration scheme at hand provides good estimates for the error-floor behavior of STS LDPC codes.

Johannes B. Huber

Papers

Channel model for watermarks subject to desynchronization attacks

Complex number RS coded OFDM with systematic noise in the guard interval

Gaussian multiple-access channels with weighted energy constraint

Noncoherent continuous-phase modulation for DS-CDMA

Characterization of small trapping sets in LDPC codes from Steiner triple systems