Source codec parameters determined by modern source encoders are usually very sensitive to noise on the transmission link. Natural residual redundancy of these parameters can be utilized by Soft Decision Source Decoding (SDSD)to increase the error resistance. Serially concatenating Forward Error Correction (FEC) and SDSD leads to a Iterative Source-Channel Decoding (ISCD) scheme which offers further improvements in robustness. ISCD exploits natural residual source redundancy by SDSD and artificial channel coding redundancy due to FEC in an iterative Turbo-like process. The convergence behavior of ISCD schemes can be analyzed by EXtrinsic Information Transfer (EXIT) charts. However, if an advanced ISCD system design is applied, offering incremental quality improvements for many iterations, the EXIT curves for SDSD do not specify a tight bound for the decoding trajectory anymore. In the initial iterations, the decoding trajectory "overshoots" the EXIT curves of SDSD, e.g.. In this paper, we give reasons for this overshooting effect. In addition, we propose a novel solution for determining the EXIT curve of SDSD which allows a more precise convergence analysis.

This paper deals with 2ndorder cyclostationarity of orthogonal frequency division multiplex (OFDM) signals. A new generalized formula for the spectral correlation density (SCD) function is derived. Compared to related work in the literature, our derivation is not restricted to the case that all sub-carriers of an OFDM signal carry statistically independent data. The reason for that is that correlated data in terms of pilot tones are typically introduced on different carriers for channel estimation and synchronization purposes. The new formula allows us to analyze the impact of such pilot tones on the SCD. In addition, it gives extra information about the impact of the cyclic prefix.

Library based waveform (WF) development approaches have the potential to address one of the key challenges in software defined radio technology, developing portable and at the same time implementation-efficient WFs. The term WF, in this paper, represents a complete wireless standard with several modes. Upon standardizing the library and the interfaces of its components, different vendors can provide Flavors, which are efficient implementations, for some/all components of a WF as a board-support-package. Flavors might provide different trade-offs with respect to key performance related properties like bit error rate, throughput, latency, area, etc. This paper analyzes such a scenario by using FFT as an example. We use 10 Flavors of FFT from 2 vendors for 3 processing elements to analyze the influence of configuration parameters like input data-width, scaling, etc. on the performance properties. Analysis has been performed by doing two tests: using a simple OFDM transceiver system, calculating root mean square error. Based on our analysis, we have identified the main parameters that influence the properties. Our investigations stress the need for modeling the differences in performance on key properties in terms of the influencing parameters. Such a model can assist in selecting a set of appropriate Flavors for implementing a WF and enable tool assisted WF-development. Furthermore, it is evident from our investigations that Flavors exhibit trade-offs in properties and pose tough constraints in several aspects.

In mountainous propagation scenarios for digital mobile radio communications with moderate fading and with rapidly changing channel characteristics adaptive equalization concepts must be applied to achieve a sufficient low bit error rate in the demodulator. It is shown that the decision feedback equalizer (DFE) with its coefficients derived from the estimation of the channel impulse response yields a better performance with less implementation complexity than the recursive least squares (RLS) lattice equalizer which directly adapts its coefficients.>

Introduces construction methods for synthesizing new classes of perfect sequences and arrays. Time discrete sequences and arrays are perfect, if their periodic autocorrelation function sidelobes are zero. The construction of perfect three-level and three-phase sequences is performed in two steps. In the first step, a maximal length shift-register sequence with elements in GF(q) is built for a length of g/sup m//spl minus/1, where q is a prime power and m is a positive integer. In the second step, a sequence is constructed by mapping the elements of the shift-register sequence to 1, b/sub 1/ or b/sub 2/. Two real numbers b/sub 1/ and b/sub 2/ are determined such that the sequence becomes perfect and has high energy efficiency. The phase values for complex numbers b/sub 1/ and b/sub 2/ with magnitude 1 are given for perfect three-phase sequences. It is shown that the phase values of b/sub 1/ and b/sub 2/ tend for growing lengths to 2/spl pi//3 and 4/spl pi//3. A different similar synthesizing method starts with Legendre sequences. The construction of perfect three-level and three-phase arrays is performed by several methods, which make use of the new respective sequences.>

The cross-correlation function of p-ary (p prime) GMW sequences is investigated. The well-known m-sequences are incorporated in these sequences. GMW sequences also have the two-level autocorrelation function, but their linear span may be much larger than those of m sequences. The calculation of the cross-correlation function of GMW sequences is reduced to the cross-correlation of the m-sequences because many results on this kind of sequence are known. In the literature, only the cross-correlation function of an m sequence with a GMW sequence has been known up to now.>

Perfect arrays are defined by having zero out-of-phase autocorrelation sidelobes. Such arrays find many applications, e.g. in two-dimensional synchronization techniques. With a known construction method, it is shown that perfect phase arrays can be obtained for every size. However, the phase alphabets of these constructed phase arrays increase by the size of the arrays. With further construction schemes the phase alphabet of perfect phase arrays can be reduced for particular sizes. Classes of perfect phase arrays are obtained whose phase alphabet does not increase with the size of the arrays.>

Perfect sequences and arrays have periodic autocorrelation functions whose out-of-phase values are zero. Time-discrete N-phase sequences and arrays have complex elements of magnitude one, and one of (2 pi /N)n, 0>

New complex sequences with elements are proposed that have constant absolute values of 1. The periodic autocorrelation functions of these sequences are shown to be two-level. The sequences are generated by three consecutive mapping processes. The number of sequences of fixed length is determined, which is larger than the number of binary sequences. For cryptographical reasons, the large linear span of the sequences is of great interest. The linear span of the new sequences is examined and is proven to be larger than the linear span of complex m-sequences, if the parameters of the mapping processes are appropriately chosen. The formula for generating the sequences is generalized to enlarge the linear span of sequences.>

An iterative method for increasing the energy efficiencies of given Huffman sequences is introduced. The iteration scheme works by varying the roots and the radius of the Z-transformation of Huffman sequences. The algorithm allows the intensity of the variations of the possible root positions to be changed. In this way the energy efficiencies of long real and complex valued Huffman sequences can be optimized. The algorithm has been applied to known Huffman sequences. The resulting efficiencies of real and complex valued Huffman sequences are given up to 100 elements.>

Binary sequences and arrays with the highest possible PACF merit factor, which is a measure for a low PACF (periodic autocorrelation function) sidelobe energy, are investigated. It is shown that some of these sequences and arrays can be obtained with known construction schemes; others are found by methods of complete computer search. The resulting PACF merit factors are given in a table up to 39 elements. A transformation from pseudonoise sequences into biphase sequences is introduced for the construction of a new class of biphase sequences and arrays with zero autocorrelation sidelobes.>

Signals of two or more dimensions with ideal impulse-like periodic autocorrelation functions are used in higher-dimensional signal processing or in radar systems. Four synthesizing methods for perfect ternary arrays are presented. Based on known perfect binary and ternary sequences and arrays, many new perfect ternary arrays with increasing number of elements are constructed. New strong conditions for the existence of perfect arrays are developed. By combining these conditions with an advanced computer search, new ternary arrays are found. These new ternary arrays can be used as starting arrays to construct additional perfect ternary sequences and arrays.>

Perfect binary arrays can exist for numbers of elements that are even square numbers. Two-dimensional (2-D) perfect binary arrays are 4, 16, 36, and 144 elements are known. Perfect binary arrays with 64 elements can be constructed for three or more dimensions. Here, two-dimensional binary arrays with 64 elements are examined. The results of computer search for symmetric binary arrays with 64 elements are presented in the form of two 2-D perfect binary arrays with sizes 8*8 and 4*16. Applications of these perfect binary arrays are in 2-D synchronization, time-frequency coding, and coding loudspeaker fields.>

Existence conditions and recursive construction procedures for sets of periodic complementary binary sequences are given. Relationships to sets of aperiodic complementary binary sequences and to perfect binary arrays, whose two-dimensional periodic autocorrelation function is a delta function, are noted. The connections of periodic complementary binary sequences and difference families are given. Sets of periodic complementary binary sequences, which result from computer search, are presented. A diagram showing what is currently known about the existence of periodic complementary binary sequences with P>

A survey is presented of different methods for constructing binary arrays with constant PACF sidelobes. For each method the sizes, numbers of elements, and PACF sidelobe level of the resulting binary arrays are specified. Binary arrays with vanishing sidelobes are considered in detail. Properties of the discrete Fourier transform of arrays with constant PACF sidelobes are examined. These properties are shown to be of great importance in acoustics.>