142,368 research outputs found
Families of sequences with good family complexity and cross-correlation measure
In this paper we study pseudorandomness of a family of sequences in terms of
two measures, the family complexity (-complexity) and the cross-correlation
measure of order . We consider sequences not only on binary alphabet but
also on -symbols (-ary) alphabet. We first generalize some known methods
on construction of the family of binary pseudorandom sequences. We prove a
bound on the -complexity of a large family of binary sequences of
Legendre-symbols of certain irreducible polynomials. We show that this family
as well as its dual family have both a large family complexity and a small
cross-correlation measure up to a rather large order. Next, we present another
family of binary sequences having high -complexity and low cross-correlation
measure. Then we extend the results to the family of sequences on -symbols
alphabet.Comment: 13 pages. Comments are welcome
A Family of Binary Sequences with Optimal Correlation Property and Large Linear Span
A family of binary sequences is presented and proved to have optimal
correlation property and large linear span. It includes the small set of Kasami
sequences, No sequence set and TN sequence set as special cases. An explicit
lower bound expression on the linear span of sequences in the family is given.
With suitable choices of parameters, it is proved that the family has
exponentially larger linear spans than both No sequences and TN sequences. A
class of ideal autocorrelation sequences is also constructed and proved to have
large linear span.Comment: 21 page
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Large Families of Ternary Sequences with Aperiodic Zero Correlation Zone Sequences for a Multi-Carrier DS-CDMA System
A new method for generating families of ternary spreading sequences is presented. The sequences have aperiodic zero correlation zones and large families are created for a specific sequence length. The sequences are proposed as spreading sequences to provide high capacity and cancel multipath and multiple access interference (MAI) in a single carrier (SC) or multi-carrier (MC) direct-spread code division multiple access (DS-CDMA) system. A Multi-carrier DS-CDMA system is simulated that employs the new sequences as spreading sequences in a multipath channel. Bit error rates (BER) and frame error rates (FER) for a range of Eb/No values are presented and it is demonstrated that the proposed sequences improve the BER and FER performance when used in place of masked Walsh Codes for the frequency selective fading channel evaluated, when a single correlator receiver is used on each sub-carrier
New Constructions of Zero-Correlation Zone Sequences
In this paper, we propose three classes of systematic approaches for
constructing zero correlation zone (ZCZ) sequence families. In most cases,
these approaches are capable of generating sequence families that achieve the
upper bounds on the family size () and the ZCZ width () for a given
sequence period ().
Our approaches can produce various binary and polyphase ZCZ families with
desired parameters and alphabet size. They also provide additional
tradeoffs amongst the above four system parameters and are less constrained by
the alphabet size. Furthermore, the constructed families have nested-like
property that can be either decomposed or combined to constitute smaller or
larger ZCZ sequence sets. We make detailed comparisons with related works and
present some extended properties. For each approach, we provide examples to
numerically illustrate the proposed construction procedure.Comment: 37 pages, submitted to IEEE Transactions on Information Theor
Null Models of Economic Networks: The Case of the World Trade Web
In all empirical-network studies, the observed properties of economic
networks are informative only if compared with a well-defined null model that
can quantitatively predict the behavior of such properties in constrained
graphs. However, predictions of the available null-model methods can be derived
analytically only under assumptions (e.g., sparseness of the network) that are
unrealistic for most economic networks like the World Trade Web (WTW). In this
paper we study the evolution of the WTW using a recently-proposed family of
null network models. The method allows to analytically obtain the expected
value of any network statistic across the ensemble of networks that preserve on
average some local properties, and are otherwise fully random. We compare
expected and observed properties of the WTW in the period 1950-2000, when
either the expected number of trade partners or total country trade is kept
fixed and equal to observed quantities. We show that, in the binary WTW,
node-degree sequences are sufficient to explain higher-order network properties
such as disassortativity and clustering-degree correlation, especially in the
last part of the sample. Conversely, in the weighted WTW, the observed sequence
of total country imports and exports are not sufficient to predict higher-order
patterns of the WTW. We discuss some important implications of these findings
for international-trade models.Comment: 39 pages, 46 figures, 2 table
Comparative Analysis of Peak Correlation Characteristics of Non-Orthogonal Spreading Codes for Wireless Systems
The performance of a CDMA based wireless system is largely dependent on the
characteristics of pseudo-random spreading codes. The spreading codes should be
carefully chosen to ensure highest possible peak value of auto-correlation
function and lower correlation peaks (side-lobes) at non-zero time-shifts.
Simultaneously, zero cross-correlation value at all time shifts is required in
order to eliminate the effect of multiple access interference at the receiver.
But no such code family exists which possess both characteristics
simultaneously. That's why an exhaustive effort has been made in this paper to
evaluate the peak correlation characteristics of various non-orthogonal
spreading codes and suggest a suitable solution.Comment: 12 Pages, 8 Figures, 3 Table
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