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## Blind Adaptive MIMO Receivers for Space-Time Block-Coded DS-CDMA Systems in Multipath Channels Using the Constant Modulus Criterion

de Lamare, Rodrigo C.; Sampaio-Neto, Raimundo
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We propose blind adaptive multi-input multi-output (MIMO) linear receivers for DS-CDMA systems using multiple transmit antennas and space-time block codes (STBC) in multipath channels. A space-time code-constrained constant modulus (CCM) design criterion based on constrained optimization techniques is considered and recursive least squares (RLS) adaptive algorithms are developed for estimating the parameters of the linear receivers. A blind space-time channel estimation method for MIMO DS-CDMA systems with STBC based on a subspace approach is also proposed along with an efficient RLS algorithm. Simulations for a downlink scenario assess the proposed algorithms in several situations against existing methods.; Comment: 4 figures, IEEE Transactions on Communications, 2010

## Performance Analysis of Wavelet Based MC-CDMA System with Implementation of Various Antenna Diversity Schemes

Islam, Md. Matiqul; Kabir, M. Hasnat; Ullah, Sk. Enayet
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The impact of using wavelet based technique on the performance of a MC-CDMA wireless communication system has been investigated. The system under proposed study incorporates Walsh Hadamard codes to discriminate the message signal for individual user. A computer program written in Mathlab source code is developed and this simulation study is made with implementation of various antenna diversity schemes and fading (Rayleigh and Rician) channel. Computer simulation results demonstrate that the proposed wavelet based MC-CDMA system outperforms in Alamouti (two transmit antenna and one receive antenna) under AWGN and Rician channel.

## Channel Estimation for MIMO MC-CDMA Systems

Sureshkumar, K.; Rajalakshmi, R.; Vetrikanimozhi, A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The concepts of MIMO MC-CDMA are not new but the new technologies to improve their functioning are an emerging area of research. In general, most mobile communication systems transmit bits of information in the radio space to the receiver. The radio channels in mobile radio systems are usually multipath fading channels, which cause inter-symbol interference (ISI) in the received signal. To remove ISI from the signal, there is a need of strong equalizer. In this thesis we have focused on simulating the MIMO MC-CDMA systems in MATLAB and designed the channel estimation for them.

## The Size of Optimal Sequence Sets for Synchronous CDMA Systems

Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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The sum capacity on a symbol-synchronous CDMA system having processing gain $N$ and supporting $K$ power constrained users is achieved by employing at most $2N-1$ sequences. Analogously, the minimum received power (energy-per-chip) on the symbol-synchronous CDMA system supporting $K$ users that demand specified data rates is attained by employing at most $2N-1$ sequences. If there are $L$ oversized users in the system, at most $2N-L-1$ sequences are needed. $2N-1$ is the minimum number of sequences needed to guarantee optimal allocation for single dimensional signaling. $N$ orthogonal sequences are sufficient if a few users (at most $N-1$) are allowed to signal in multiple dimensions. If there are no oversized users, these split users need to signal only in two dimensions each. The above results are shown by proving a converse to a well-known result of Weyl on the interlacing eigenvalues of the sum of two Hermitian matrices, one of which is of rank 1. The converse is analogous to Mirsky's converse to the interlacing eigenvalues theorem for bordering matrices.; Comment: 18 pages, 2 figures, technical report

## Bounds for the Sum Capacity of Binary CDMA Systems in Presence of Near-Far Effect

Pad, P.; Shafinia, M. H.; Mansouri, S. M.; Kabir, P.; Marvasti, F.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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In this paper we are going to estimate the sum capacity of a binary CDMA system in presence of the near-far effect. We model the near-far effect as a random variable that is multiplied by the users binary data before entering the noisy channel. We will find a lower bound and a conjectured upper bound for the sum capacity in this situation. All the derivations are in the asymptotic case. Simulations show that especially the lower bound is very tight for typical values Eb/N0 and near-far effect. Also, we exploit our idea in conjunction with the Tanaka's formula [6] which also estimates the sum capacity of binary CDMA systems with perfect power control.

## Randomness and metastability in CDMA paradigms

Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.090366%
Code Division Multiple Access (CDMA) in which the signature code assignment to users contains a random element has recently become a cornerstone of CDMA research. The random element in the construction is particularly attractive in that it provides robustness and flexibility in application, whilst not making significant sacrifices in terms of multiuser efficiency. We present results for sparse random codes of two types, with and without modulation. Simple microscopic consideration on system samples would suggest differences in the phase space of the two models, but we demonstrate that the thermodynamic results and metastable states are equivalent in the minimum bit error rate detector. We analyse marginal properties of interactions and also make analogies to constraint satisfiability problems in order to understand qualitative features of detection and metastable states. This may have consequences for developing algorithmic methods to escape metastable states, thus improving decoding performance.; Comment: 5 pages, 3 figures, prepared IEEE.cls, accepted physcomnet-08

## On Optimum Asymptotic Multiuser Efficiency of Randomly Spread CDMA

Sedaghat, Mohammad Ali; Müller, Ralf; Marvasti, Farokh
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.090366%
We extend the result by Tse and Verd\'{u} on the optimum asymptotic multiuser efficiency of randomly spread CDMA with Binary Phase Shift Keying (BPSK) input. Random Gaussian and random binary antipodal spreading are considered. We obtain the optimum asymptotic multiuser efficiency of a $K$-user system with spreading gain $N$ when $K$ and $N\rightarrow\infty$ and the loading factor, $\frac{K}{N}$, grows logarithmically with $K$ under some conditions. It is shown that the optimum detector in a Gaussian randomly spread CDMA system has a performance close to the single user system at high Signal to Noise Ratio (SNR) when $K$ and $N\rightarrow\infty$ and the loading factor, $\frac{K}{N}$, is kept less than $\frac{\log_3K}{2}$. Random binary antipodal matrices are also studied and a lower bound for the optimum asymptotic multiuser efficiency is obtained. Furthermore, we investigate the connection between detecting matrices in the coin weighing problem and optimum asymptotic multiuser efficiency. We obtain a condition such that for any binary input, an $N\times K$ random matrix whose entries are chosen randomly from a finite set, is a detecting matrix as $K$ and $N\rightarrow \infty$.; Comment: 19 pages, 1 figure, submitted to Transaction on Information Theory

## Improved Algorithm for Throughput Maximization in MC-CDMA

Kale, Hema; Dethe, C. G.; Mushrif, M. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The Multi-Carrier Code Division Multiple Access (MC-CDMA) is becoming a very significant downlink multiple access technique for high-rate data transmission in the fourth generation wireless communication systems. By means of efficient resource allocation higher data rate i.e. throughput can be achieved. This paper evaluates the performance of criteria used for group (subchannel) allocation employed in downlink transmission, which results in throughput maximization. Proposed algorithm gives the modified technique of sub channel allocation in the downlink transmission of MC-CDMA systems. Simulation are carried out for all the three combining schemes, results shows that for the given power and BER proposed algorithm comparatively gives far better results; Comment: 12 pages

## Secure CDMA Sequences

Leukhin, Anatolii; Moreno, Oscar; Tirkel, Andrew
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.090366%
Single sequences like Legendre have high linear complexity. Known CDMA families of sequences all have low complexities. We present a new method of constructing CDMA sequence sets with the complexity of the Legendre from new frequency hop patterns, and compare them with known sequences. These are the first families whose normalized linear complexities do not asymptote to 0, verified for lengths up to 6x108. The new constructions in array format are also useful in watermarking images. We present a conjecture regarding the recursion polynomials. We also have a method to reverse the process, and from small Kasami/No-Kumar sequences we obtain a new family of 2n doubly periodic (2n+1)x(2n-1) frequency hop patterns with correlation 2.; Comment: 10 pages, 8 figures

## Relay-Assisted Partial Packet Recovery with IDMA Method in CDMA Wireless Network

Luo, Zhifeng; Han, Zhu; Wong, Albert Kai-sun; Qiu, Shuisheng
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.090366%
Automatic Repeat Request (ARQ) is an effective technique for reliable transmission of packets in wireless networks. In ARQ, however, only a few erroneous bits in a packet will cause the entire packet to be discarded at the receiver. In this case, it's wasteful to retransmit the correct bit in the received packet. The partial packet recovery only retransmits the unreliable decoded bits in order to increase the throughput of network. In addition, the cooperative transmission based on Interleave-division multiple-access (IDMA) can obtain diversity gains with multiple relays with different locations for multiple sources simultaneously. By exploring the diversity from the channel between relay and destination, we propose a relay-assisted partial packet recovery in CDMA wireless network to improve the performance of throughput. In the proposed scheme, asynchronous IDMA iterative chip-by-chip multiuser detection is utilized as a method of multiple partial recovery, which can be a complementarity in a current CDMA network. The confidence values' concept is applied to detect unreliable decoded bits. According to the result of unreliable decoded bits' position, we use a recursive algorithm based on cost evaluation to decide a feedback strategy. Then the feedback request with minimum cost can be obtained. The simulation results show that the performance of throughput can be significantly improved with our scheme...

## Bounds on the Sum Capacity of Synchronous Binary CDMA Channels

Alishahi, K.; Marvasti, F.; Aref, V.; Pad, P.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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In this paper, we obtain a family of lower bounds for the sum capacity of Code Division Multiple Access (CDMA) channels assuming binary inputs and binary signature codes in the presence of additive noise with an arbitrary distribution. The envelope of this family gives a relatively tight lower bound in terms of the number of users, spreading gain and the noise distribution. The derivation methods for the noiseless and the noisy channels are different but when the noise variance goes to zero, the noisy channel bound approaches the noiseless case. The behavior of the lower bound shows that for small noise power, the number of users can be much more than the spreading gain without any significant loss of information (overloaded CDMA). A conjectured upper bound is also derived under the usual assumption that the users send out equally likely binary bits in the presence of additive noise with an arbitrary distribution. As the noise level increases, and/or, the ratio of the number of users and the spreading gain increases, the conjectured upper bound approaches the lower bound. We have also derived asymptotic limits of our bounds that can be compared to a formula that Tanaka obtained using techniques from statistical physics; his bound is close to that of our conjectured upper bound for large scale systems.; Comment: to be published in IEEE Transactions on Information Theory

## Partial Cross-Correlation of D-Sequences based CDMA System

Chalasani, Sandeep
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.090366%
Like other pseudorandom sequences, decimal sequences may be used in designing a Code Division Multiple Access (CDMA) system. They appear to be ideally suited for this since the cross-correlation of d-sequences taken over the LCM of their periods is zero. But a practical system will not, in most likelihood, satisfy the condition that the number of chips per bit is equal to the LCM for all sequences that are assigned to different users. It is essential, therefore, to determine the partial cross-correlation properties of d-sequences. This paper has performed experiments on d-sequences and found that the partial cross-correlation is less than for PN sequences, indicating that d-sequences can be effective for use in CDMA.; Comment: 6 pages

## Joint Receiver and Transmitter Optimization for Energy-Efficient CDMA Communications

Buzzi, Stefano; Poor, H. Vincent
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.090366%
This paper focuses on the cross-layer issue of joint multiuser detection and resource allocation for energy efficiency in wireless CDMA networks. In particular, assuming that a linear multiuser detector is adopted in the uplink receiver, the case considered is that in which each terminal is allowed to vary its transmit power, spreading code, and uplink receiver in order to maximize its own utility, which is defined as the ratio of data throughput to transmit power. Resorting to a game-theoretic formulation, a non-cooperative game for utility maximization is formulated, and it is proved that a unique Nash equilibrium exists, which, under certain conditions, is also Pareto-optimal. Theoretical results concerning the relationship between the problems of SINR maximization and MSE minimization are given, and, resorting to the tools of large system analysis, a new distributed power control algorithm is implemented, based on very little prior information about the user of interest. The utility profile achieved by the active users in a large CDMA system is also computed, and, moreover, the centralized socially optimum solution is analyzed. Considerations on the extension of the proposed framework to a multi-cell scenario are also briefly detailed. Simulation results confirm that the proposed non-cooperative game largely outperforms competing alternatives...

## Optimization of sequences in CDMA systems: a statistical-mechanics approach

Kitagawa, Koichiro; Tanaka, Toshiyuki
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Statistical mechanics approach is useful not only in analyzing macroscopic system performance of wireless communication systems, but also in discussing design problems of wireless communication systems. In this paper, we discuss a design problem of spreading sequences in code-division multiple-access (CDMA) systems, as an example demonstrating the usefulness of statistical mechanics approach. We analyze, via replica method, the average mutual information between inputs and outputs of a randomly-spread CDMA channel, and discuss the optimization problem with the average mutual information as a measure of optimization. It has been shown that the average mutual information is maximized by orthogonally-invariant random Welch bound equality (WBE) spreading sequences.; Comment: 17pages, submitted to Special Issue on Interdisciplinary Paradigms for Networking in International Journal of Computer and Telecommunications Networking

## Counting solutions for the CDMA multiuser MAP demodulator

Hatchett, J. P. L.; Inoue, Jun-ichi
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.090366%
We evaluate the average number of locally minimal solutions for maximum-{\it a-posteriori} (MAP) demodulation in code-division multiple-access (CDMA) systems. For this purpose, we use a sophisticated method to investigate the ground state properties for the Sherrington-Kirkpatrick-type (i.e. fully connected) spin glasses established by Tanaka and Edwards in 1980. We derive the number of locally minimal solutions as a function of several parameters which specify the CDMA multiuser MAP demodulator. We also calculate the distribution function of the normalized-energies for the locally minimum states. We find that for a small number of chip intervals (or equivalently a large number of users) and large noise level at the base station, the number of local minimum solutions becomes larger than that of the SK model. This provides us with useful information about the computational complexity of the MAP demodulator.; Comment: 23pages, 4figures, using jpsj2.cls, 2 figures were replaced

## Guard Zones and the Near-Far Problem in DS-CDMA Ad Hoc Networks

Torrieri, Don; Valenti, Matthew C.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.090366%
The central issue in direct-sequence code-division multiple-access (DS-CDMA) ad hoc networks is the prevention of a near-far problem. This paper considers two types of guard zones that may be used to control the near-far problem: a fundamental exclusion zone and an additional CSMA guard zone that may be established by the carrier-sense multiple-access (CSMA) protocol. In the exclusion zone, no mobiles are physically present, modeling the minimum physical separation among mobiles that is always present in actual networks. Potentially interfering mobiles beyond a transmitting mobile's exclusion zone, but within its CSMA guard zone, are deactivated by the protocol. This paper provides an analysis of DS-CSMA networks with either or both types of guard zones. A network of finite extent with a finite number of mobiles is modeled as a uniform clustering process. The analysis uses a closed-form expression for the outage probability in the presence of Nakagami fading, conditioned on the network geometry. By using the analysis developed in this paper, the tradeoffs between exclusion zones and CSMA guard zones are explored for DS-CDMA and unspread networks.; Comment: to appear at Milcom-2012

## Equalization with oversampling in multiuser CDMA systems

Vrcelj, Bojan; Vaidyanathan, P. P.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Relevância na Pesquisa
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Some of the major challenges in the design of new-generation wireless mobile systems are the suppression of multiuser interference (MUI) and inter-symbol interference (ISI) within a single user created by the multipath propagation. Both of these problems were addressed successfully in a recent design of A Mutually Orthogonal Usercode-Receiver (AMOUR) for asynchronous or quasisynchronous code division multiple access (CDMA) systems. AMOUR converts a multiuser CDMA system into parallel single-user systems regardless of the multipath and guarantees ISI mitigation, irrespective of the channel locations. However, the noise amplification at the receiver can be significant in some multipath channels. In this paper, we propose to oversample the received signal as a way of improving the performance of AMOUR systems. We design Fractionally Spaced AMOUR (FSAMOUR) receivers with integral and rational amounts of oversampling and compare their performance with the conventional method. An important point that is often overlooked in the design of zero-forcing channel equalizers is that sometimes, they are not unique. This becomes especially significant in multiuser applications where, as we will show, the nonuniqueness is practically guaranteed. We exploit this flexibility in the design of AMOUR and FSAMOUR receivers and achieve noticeable improvements in performance.

## Optical-CDMA in InP

Broeke, Ronald G.; Cao, Jin; Ji, Chen; Seo, Sang-Woo; Du, Yixue; Fontaine, Nick K.; Baek, Jong-Hwa; Yan, John; Soares, Francisco M.; Olsson, Frederik; Lourdudoss, S.; Pham, Anh-Vu; Shearn, Michael; Scherer, Axel; Yoo, S. J. Ben
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Relevância na Pesquisa
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This paper describes the InP platforms for photonic integration and the development on these platforms of an optical code division multiple access (O-CDMA) system for local area networks. We demonstrate three building blocks of this system: an optical pulse source, an encoder/decoder pair, and a threshold detector. The optical pulse source consists of an integrated colliding pulse-mode laser with nearly transform-limited 10 Gb/s pulses and optical injection locking to an external clock for synchronization. The encoder/decoder pair is based on arrayed waveguide gratings. Bit-error-rate measurements involving six users at 10 Gb/s showed error-free transmission, while O-CDMA codes were calibrated using frequency resolved optical gating. For threshold detection after the decoder, we compared two Mach--Zehnder interferometer (MZI)-based optical thresholding schemes and present results on a new type of electroabsorber-based MZI.

## Optimal CDMA signature sequences, inverse eigenvalue problems and alternating minimization

Tropp, Joel A.; Heath, Robert W., Jr.; Strohmer, Thomas
Tipo: Book Section; PeerReviewed Formato: application/pdf