712 research outputs found
Cross Z-Complementary Pairs for Optimal Training in Spatial Modulation Over Frequency Selective Channels
The contributions of this article are twofold: Firstly, we introduce a novel class of sequence pairs, called “cross Z-complementary pairs (CZCPs),” each displaying zero-correlation zone (ZCZ) properties for both their aperiodic autocorrelation sums and crosscorrelation sums. Systematic constructions of perfect CZCPs based on selected Golay complementary pairs (GCPs) are presented. Secondly, we point out that CZCPs can be utilized as a key component in designing training sequences for broadband spatial modulation (SM) systems. We show that our proposed SM training sequences derived from CZCPs lead to optimal channel estimation performance over frequency-selective channels
Enhanced Cross Z-Complementary Set and Its Application in Generalized Spatial Modulation
Generalized spatial modulation (GSM) is a novel multiple-antenna technique
offering flexibility among spectral efficiency, energy efficiency, and the cost
of RF chains. In this paper, a novel class of sequence sets, called enhanced
cross Zcomplementary set (E-CZCS), is proposed for efficient training sequence
design in broadband GSM systems. Specifically, an E-CZCS consists of multiple
CZCSs possessing front-end and tail-end zero-correlation zones (ZCZs), whereby
any two distinct CZCSs have a tail-end ZCZ when a novel type of cross-channel
aperiodic correlation sums is considered. The theoretical upper bound on the
ZCZ width is first derived, upon which optimal E-CZCSs with flexible parameters
are constructed. For optimal channel estimation over frequency-selective
channels, we introduce and evaluate a novel GSM training framework employing
the proposed E-CZCSs
Asymptotically Locally Optimal Weight Vector Design for a Tighter Correlation Lower Bound of Quasi-Complementary Sequence Sets
A quasi-complementary sequence set (QCSS) refers to a set of two-dimensional matrices with low nontrivial aperiodic auto- and cross-correlation sums. For multicarrier code-division multiple-access applications, the availability of large QCSSs with low correlation sums is desirable. The generalized Levenshtein bound (GLB) is a lower bound on the maximum aperiodic correlation sum of QCSSs. The bounding expression of GLB is a fractional quadratic function of a weight vector w and is expressed in terms of three additional parameters associated with QCSS: the set size K, the number of channels M, and the sequence length N. It is known that a tighter GLB (compared to the Welch bound) is possible only if the condition M ≥ 2 and K ≥ K̅ + 1, where K̅ is a certain function of M and N, is satisfied. A challenging research problem is to determine if there exists a weight vector that gives rise to a tighter GLB for all (not just some) K ≥ K̅ + 1 and M ≥ 2, especially for large N, i.e., the condition is asymptotically both necessary and sufficient. To achieve this, we analytically optimize the GLB which is (in general) nonconvex as the numerator term is an indefinite quadratic function of the weight vector. Our key idea is to apply the frequency domain decomposition of the circulant matrix (in the numerator term) to convert the nonconvex problem into a convex one. Following this optimization approach, we derive a new weight vector meeting the aforementioned objective and prove that it is a local minimizer of the GLB under certain conditions
New Correlation Bound and Construction of Quasi-Complementary Code Sets
Quasi-complementary sequence sets (QCSSs) have attracted sustained research
interests for simultaneously supporting more active users in multi-carrier
code-division multiple-access (MC-CDMA) systems compared to complete
complementary codes (CCCs). In this paper, we investigate a novel class of
QCSSs composed of multiple CCCs. We derive a new aperiodic correlation lower
bound for this type of QCSSs, which is tighter than the existing bounds for
QCSSs. We then present a systematic construction of such QCSSs with a small
alphabet size and low maximum correlation magnitude, and also show that the
constructed aperiodic QCSSs can meet the newly derived bound asymptotically
Direct Construction of Optimal Z-Complementary Code Sets for all Possible Even Length by Using Pseudo-Boolean Functions
Z-complementary code set (ZCCS) are well known to be used in multicarrier
code-division multiple access (MCCDMA) system to provide a interference free
environment. Based on the existing literature, the direct construction of
optimal ZCCSs are limited to its length. In this paper, we are interested in
constructing optimal ZCCSs of all possible even lengths using Pseudo-Boolean
functions. The maximum column sequence peakto-man envelop power ratio (PMEPR)
of the proposed ZCCSs is upper-bounded by two, which may give an extra benefit
in managing PMEPR in an ZCCS based MC-CDMA system, as well as the ability to
handle a large number of users
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