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Soft Handoff and Uplink Capacity in a Two-Tier CDMA System

Kishore, Shalinee; Greenstein, Larry J.; Poor, H. Vincent; Schwartz, Stuart C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/03/2005 Português
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This paper examines the effect of soft handoff on the uplink user capacity of a CDMA system consisting of a single macrocell in which a single hotspot microcell is embedded. The users of these two base stations operate over the same frequency band. In the soft handoff scenario studied here, both macrocell and microcell base stations serve each system user and the two received copies of a desired user's signal are summed using maximal ratio combining. Exact and approximate analytical methods are developed to compute uplink user capacity. Simulation results demonstrate a 20% increase in user capacity compared to hard handoff. In addition, simple, approximate methods are presented for estimating soft handoff capacity and are shown to be quite accurate.; Comment: To appear in IEEE Transactions on Wireless Communications

Randomly Spread CDMA: Asymptotics via Statistical Physics

Guo, Dongning; Verdu, Sergio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/03/2005 Português
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This paper studies randomly spread code-division multiple access (CDMA) and multiuser detection in the large-system limit using the replica method developed in statistical physics. Arbitrary input distributions and flat fading are considered. A generic multiuser detector in the form of the posterior mean estimator is applied before single-user decoding. The generic detector can be particularized to the matched filter, decorrelator, linear MMSE detector, the jointly or the individually optimal detector, and others. It is found that the detection output for each user, although in general asymptotically non-Gaussian conditioned on the transmitted symbol, converges as the number of users go to infinity to a deterministic function of a "hidden" Gaussian statistic independent of the interferers. Thus the multiuser channel can be decoupled: Each user experiences an equivalent single-user Gaussian channel, whose signal-to-noise ratio suffers a degradation due to the multiple-access interference. The uncoded error performance (e.g., symbol-error-rate) and the mutual information can then be fully characterized using the degradation factor, also known as the multiuser efficiency, which can be obtained by solving a pair of coupled fixed-point equations identified in this paper. Based on a general linear vector channel model...

A CDMA multiuser detection algorithm based on survey propagation

Kabashima, Yoshiyuki
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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A computationally tractable CDMA multiuser detection algorithm is developed based on survey propagation.; Comment: Abstract for my presentation at Randomness and Computation Joint Workshop ``New Horizons in Computing'' and ``Statistical Mechanical Approach to Probabilistic Information Processing'' (18-21 July, 2005, Sendai, Japan)

Optimal Power Control for Multiuser CDMA Channels

Feiten, Anke; Mathar, Rudolf
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/09/2005 Português
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In this paper, we define the power region as the set of power allocations for K users such that everybody meets a minimum signal-to-interference ratio (SIR). The SIR is modeled in a multiuser CDMA system with fixed linear receiver and signature sequences. We show that the power region is convex in linear and logarithmic scale. It furthermore has a componentwise minimal element. Power constraints are included by the intersection with the set of all viable power adjustments. In this framework, we aim at minimizing the total expended power by minimizing a componentwise monotone functional. If the feasible power region is nonempty, the minimum is attained. Otherwise, as a solution to balance conflicting interests, we suggest the projection of the minimum point in the power region onto the set of viable power settings. Finally, with an appropriate utility function, the problem of minimizing the total expended power can be seen as finding the Nash bargaining solution, which sheds light on power assignment from a game theoretic point of view. Convexity and componentwise monotonicity are essential prerequisites for this result.; Comment: To appear in the proceedings of the 2005 IEEE International Symposium on Information Theory, Adelaide...

Blind Adaptive Subcarrier Combining Technique for MC-CDMA Receiver in Mobile Rayleigh Channel

Shakya, Indu; Ali, Falah H.; Stipidis, Elias
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/02/2011 Português
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A new subcarrier combining technique is proposed for MC -CDMA receiver in mobile Rayleigh fading channel. It exploits the structure formed by repeating spreading sequences of users on different subcarriers to simultaneously suppress multiple access interference (MAI) and provide implicit channel tracking without any knowledge of the channel amplitudes or training sequences. This is achieved by adaptively weighting each subcarrier in each symbol period by employing a simple gradient descent algorithm to meet the constant modulus (CM) criterion with judicious selection of step-size. Improved BER and user capacity performance are shown with similar complexity in order of O(N) compared with conventional maximum ratio combining and equal gain combining techniques even under high channel Doppler rates.

Bidirectional MMSE Algorithms for Interference Mitigation in CDMA Systems over Fast Fading Channels

Clarke, Patrick; de Lamare, Rodrigo C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/06/2013 Português
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This paper presents adaptive bidirectional minimum mean-square error (MMSE) parameter estimation algorithms for fast-fading channels. The time correlation between successive channel gains is exploited to improve the estimation and tracking capabilities of adaptive algorithms and provide robustness against time-varying channels. Bidirectional normalized least mean-square (NLMS) and conjugate gradient (CG) algorithms are devised along with adaptive mixing parameters that adjust to the time-varying channel correlation properties. An analysis of the proposed algorithms is provided along with a discussion of their performance advantages. Simulations for an application to interference suppression in DS-CDMA systems show the advantages of the proposed algorithms.; Comment: 3 figures, ISWCS, 2012

An Analysis of the DS-CDMA Cellular Uplink for Arbitrary and Constrained Topologies

Torrieri, Don; Valenti, Matthew C.; Talarico, Salvatore
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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A new analysis is presented for the direct-sequence code-division multiple access (DS-CDMA) cellular uplink. For a given network topology, closed-form expressions are found for the outage probability and rate of each uplink in the presence of path-dependent Nakagami fading and shadowing. The topology may be arbitrary or modeled by a random spatial distribution with a fixed number of base stations and mobiles placed over a finite area. The analysis is more detailed and accurate than existing ones and facilitates the resolution of network design issues including the influence of the minimum base-station separation, the role of the spreading factor, and the impact of various power-control and rate-control policies. It is shown that once power control is established, the rate can be allocated according to a fixed-rate or variable-rate policy with the objective of either meeting an outage constraint or maximizing throughput. An advantage of variable-rate power control is that it allows an outage constraint to be enforced on every uplink, which is impossible when a fixed rate is used throughout the network.; Comment: IEEE Transactions on Communications, vol. 61, no. 8, pp. 3318 - 3326, August 2013

An Efficient Paging Algorithm for Multi-Carrier CDMA System

Mostafa, Sheikh Shanawaz; Reza, Khondker Jahid; Rashid, Gazi Maniur; Moinuddin, Muhammad; Amin, Md. Ziaul; Nahid, Abdullah Al
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/09/2011 Português
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To cope with the increasing demand of wireless communication services multi-carrier systems are being used. Radio resources are very limited and efficient usages of these resources are inevitable to get optimum performance of the system. Paging channel is a low-bandwidth channel and one of the most important channels on which system performance depends significantly. Therefore it is vulnerable to even moderate overloads. In this paper, an efficient paging algorithm, Concurrent Search, is proposed for efficient use of paging channel in Multi- carrier CDMA system instead of existing sequential searching algorithm. It is shown by the simulation that the paging performance in proposed algorithm is far better than the existing system.

Adaptive Reduced-Rank Processing Using a Projection Operator Based on Joint Iterative Optimization of Adaptive Filters For CDMA Interference Suppression

de Lamare, Rodrigo C.; Sampaio-Neto, Raimundo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/05/2013 Português
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This paper proposes a novel adaptive reduced-rank filtering scheme based on the joint iterative optimization of adaptive filters. The proposed scheme consists of a joint iterative optimization of a bank of full-rank adaptive filters that constitutes the projection matrix and an adaptive reduced-rank filter that operates at the output of the bank of filters. We describe minimum mean-squared error (MMSE) expressions for the design of the projection matrix and the reduced-rank filter and simple least-mean squares (LMS) adaptive algorithms for its computationally efficient implementation. Simulation results for a CDMA interference suppression application reveals that the proposed scheme significantly outperforms the state-of-the-art reduced-rank schemes, while requiring a significantly lower computational complexity.; Comment: 4 figures. Published in SSP 2010. arXiv admin note: substantial text overlap with arXiv:1205.4390, arXiv:1304.7548

Joint SIC and Relay Selection for Cooperative DS-CDMA Systems

Gu, J.; de Lamare, R. C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/10/2014 Português
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In this work, we propose a cross-layer design strategy based on a joint successive interference cancellation (SIC) detection technique and a multi-relay selection algorithm for the uplink of cooperative direct-sequence code-division multiple access (DS-CDMA) systems. We devise a low-cost greedy list-based SIC (GL-SIC) strategy with RAKE receivers as the front-end that can approach the maximum likelihood detector performance. %Unlike prior art, the proposed GL-SIC algorithm %exploits the Euclidean distance between users of interest, multiple %ordering and their constellation points to build an effective list %of detection candidates. We also present a low-complexity multi-relay selection algorithm based on greedy techniques that can approach the performance of an exhaustive search. %A cross-layer %design strategy that brings together the proposed GL-SIC algorithm %and the greedy relay selection is then developed. Simulations show an excellent bit error rate performance of the proposed detection and relay selection algorithms as compared to existing techniques.; Comment: 5 figures, conference

Performance Improvement of Iterative Multiuser Detection for Large Sparsely-Spread CDMA Systems by Spatial Coupling

Takeuchi, Keigo; Tanaka, Toshiyuki; Kawabata, Tsutomu
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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Kudekar et al. proved that the belief-propagation (BP) performance for low-density parity check (LDPC) codes can be boosted up to the maximum-a-posteriori (MAP) performance by spatial coupling. In this paper, spatial coupling is applied to sparsely-spread code-division multiple-access (CDMA) systems to improve the performance of iterative multiuser detection based on BP. Two iterative receivers based on BP are considered: One receiver is based on exact BP and the other on an approximate BP with Gaussian approximation. The performance of the two BP receivers is evaluated via density evolution (DE) in the dense limit after taking the large-system limit, in which the number of users and the spreading factor tend to infinity while their ratio is kept constant. The two BP receivers are shown to achieve the same performance as each other in these limits. Furthermore, taking a continuum limit for the obtained DE equations implies that the performance of the two BP receivers can be improved up to the performance achieved by the symbol-wise MAP detection, called individually-optimal detection, via spatial coupling. Numerical simulations show that spatial coupling can provide a significant improvement in bit error rate for finite-sized systems especially in the region of high system loads.; Comment: submitted to IEEE Trans. Inf. Theory

Energy-Efficient Power Control in Multipath CDMA Channels via Large System Analysis

Buzzi, Stefano; Massaro, Valeria; Poor, H. Vincent
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/07/2008 Português
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This paper is focused on the design and analysis of power control procedures for the uplink of multipath code-division-multiple-access (CDMA) channels based on the large system analysis (LSA). Using the tools of LSA, a new decentralized power control algorithm aimed at energy efficiency maximization and requiring very little prior information on the interference background is proposed; moreover, it is also shown that LSA can be used to predict with good accuracy the performance and operational conditions of a large network operating at the equilibrium over a multipath channel, i.e. the power, signal-to-interference-plus-noise ratio (SINR) and utility profiles across users, wherein the utility is defined as the number of bits reliably delivered to the receiver for each energy-unit used for transmission. Additionally, an LSA-based performance comparison among linear receivers is carried out in terms of achieved energy efficiency at the equilibrium. Finally, the problem of the choice of the utility-maximizing training length is also considered. Numerical results show a very satisfactory agreement of the theoretical analysis with simulation results obtained with reference to systems with finite (and not so large) numbers of users.; Comment: Proceedings of the IEEE International Symposium on Personal...

Blind Adaptive MIMO Receivers for CDMA Systems with Space-Time Block-Codes and Low-Cost Algorithms

de Lamare, R. C.; Sampaio-Neto, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/10/2014 Português
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In this paper we present low-complexity blind multi-input multi-output (MIMO) adaptive linear multiuser receivers for direct sequence code division multiple access (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 and low-complexity stochastic gradient (SG) adaptive algorithms are developed for estimating the parameters of the space-time linear receivers. The receivers are designed by exploiting the unique structure imposed by both spreading codes and STBC. A blind space-time channel estimation scheme for STBC systems based on a subspace approach is also proposed along with an efficient SG algorithm. Simulation results for a downlink scenario assess the receiver structures and algorithms and show that the proposed schemes achieve excellent performance, outperforming existing methods.; Comment: 10 pages, 4 figures, Signal Processing, 2012

Energy Efficiency in Multi-Hop CDMA Networks: a Game Theoretic Analysis Considering Operating Costs

Betz, Sharon; Poor, H. Vincent
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/01/2008 Português
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A game-theoretic analysis is used to study the effects of receiver choice and transmit power on the energy efficiency of multi-hop networks in which the nodes communicate using Direct-Sequence Code Division Multiple Access (DS-CDMA). A Nash equilibrium of the game in which the network nodes can choose their receivers as well as their transmit powers to maximize the total number of bits they transmit per unit of energy spent (including both transmit and operating energy) is derived. The energy efficiencies resulting from the use of different linear multiuser receivers in this context are compared for the non-cooperative game. Significant gains in energy efficiency are observed when multiuser receivers, particularly the linear minimum mean-square error (MMSE) receiver, are used instead of conventional matched filter receivers.; Comment: To appear in the Proceedings of the 2008 IEEE International Conference on Acoustics, Speech and Signal Processing, Las Vegas, NV, March 30 -- April 4, 2008

Large-System Analysis of Joint Channel and Data Estimation for MIMO DS-CDMA Systems

Takeuchi, Keigo; Vehkaperae, Mikko; Tanaka, Toshiyuki; Mueller, Ralf R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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This paper presents a large-system analysis of the performance of joint channel estimation, multiuser detection, and per-user decoding (CE-MUDD) for randomly-spread multiple-input multiple-output (MIMO) direct-sequence code-division multiple-access (DS-CDMA) systems. A suboptimal receiver based on successive decoding in conjunction with linear minimum mean-squared error (LMMSE) channel estimation is investigated. The replica method, developed in statistical mechanics, is used to evaluate the performance in the large-system limit, where the number of users and the spreading factor tend to infinity while their ratio and the number of transmit and receive antennas are kept constant. The performance of the joint CE-MUDD based on LMMSE channel estimation is compared to the spectral efficiencies of several receivers based on one-shot LMMSE channel estimation, in which the decoded data symbols are not utilized to refine the initial channel estimates. The results imply that the use of joint CE-MUDD significantly reduces rate loss due to transmission of pilot signals, especially for multiple-antenna systems. As a result, joint CE-MUDD can provide significant performance gains, compared to the receivers based on one-shot channel estimation.; Comment: The paper was resubmitted to IEEE Trans. Inf. Theory

Performance Analysis of Uplink & Downlink Transmission in CDMA System

Hossain, Md. M.; Rahman, Md. M.; Alim, Md. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/02/2010 Português
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CDMA is a multiple access method in which the user's uses spread spectrum techniques and occupy the entire spectrum whenever they transmit. In wireless communication signal-to-noise ratio (SNR) is the very important parameter that influences the system performance. Any mode of mobile transmission is not free from channel impairment such as noise, interference and fading. This channel impairment caused signal distortion and degradation in SNR.Also there are differences between uplink (forward channel) and downlink (reverse channel).Along with these differences, both the links use different codes for chanellizing the individual users. This paper simulates the expressions for the pdfs of the SNR for both uplink and downlink transmission assuming that the system is operating at an average signal-to-noise ratio is 6dB per information bit.; Comment: Journal of Telecommunications,Volume 1, Issue 1, pp84-86, February 2010

Errorless Codes for Over-loaded CDMA with Active User Detection

Pad, Pedram; Soltanolkotabi, Mahdi; Hadikhanlou, Saeed; Enayati, Arash; Marvasti, Farokh
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/10/2008 Português
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In this paper we introduce a new class of codes for over-loaded synchronous wireless CDMA systems which increases the number of users for a fixed number of chips without introducing any errors. In addition these codes support active user detection. We derive an upper bound on the number of users with a fixed spreading factor. Also we propose an ML decoder for a subclass of these codes that is computationally implementable. Although for our simulations we consider a scenario that is worse than what occurs in practice, simulation results indicate that this coding/decoding scheme is robust against additive noise. As an example, for 64 chips and 88 users we propose a coding/decoding scheme that can obtain an arbitrary small probability of error which is computationally feasible and can detect active users. Furthermore, we prove that for this to be possible the number of users cannot be beyond 230.

Performance Estimation of 2*3 MIMO-MC-CDMA using Convolution Code

Kushwah, Atul Singh; Manglasheril, Sachin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/03/2014 Português
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In this paper we estimate the performance of 2by3 MIMOMCCDMA system using convolution code in MATLAB which highly reduces BER by increasing the efficiency of system. MIMO and MCCDMA system combination is used to reduce bit error rate and also for forming a new system called MCCDMA which is multi user and multiple access schemes used to increase the performance of the system. MCCDMA system is a narrowband flat fading in nature which converts frequency selective to numerous narrowband flat fading multiple parallel sub-carriers to increase the efficiency of the system. Now this MCCDMA system can also be enhanced by grouping with 2by3 MIMO system which utilizes ZF decoder at the receiver to decrease BER in which half rate convolutionally encoded Alamouti STBC block code is used for channel encoding scheme as transmit diversity of MIMO with multiple transmit antenna. And convolution encoder is also used as source encoder or FEC encoder in MIMOMCCDMA. Advantage of using MIMO-MC-CDMA using convolution code is due to reduce complexity of system and also for reducing BER and finally to increase gain of system. Now after this we examine system in various modulation techniques like, 8PSK, 16QAM, QPSK, 32QAM, 8QAM and 64QAM using MATLAB in Rayleigh fading channel.; Comment: 5 pages...

Point-to-point and Point-to-multipoint CDMA Access Network with Enhanced Security

Alfredo, Ortega A.; Bettachini, Victor A.; Alvarez-Hamelin, José Ignacio; Grosz, Diego F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We propose a network implementation with enhanced security at the physical layer by means of time-hopping CDMA, supporting cryptographically secure point-to-point and point-to-multipoint communication. In particular, we analyze an active star topology optical network implementation capable of supporting 128 simultaneous users up to 20 km apart. The feasibility of the proposed scheme is demonstrated through numerical simulation.

A New Analysis of the DS-CDMA Cellular Uplink Under Spatial Constraints

Torrieri, Don; Valenti, Matthew C.; Talarico, Salvatore
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/04/2013 Português
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A new analysis is presented for the direct-sequence code-division multiple access (DS-CDMA) cellular uplink. For a given network topology, closed-form expressions are found for the outage probability and rate of each uplink in the presence of path-dependent Nakagami fading and log-normal shadowing. The topology may be arbitrary or modeled by a random spatial distribution for a fixed number of base stations and mobiles placed over a finite area with the separations among them constrained to exceed a minimum distance. The analysis is more detailed and accurate than existing ones and facilitates the resolution of network design issues, including the influence of the minimum base-station separation, the role of the spreading factor, and the impact of various power-control and rate-control policies. It is shown that once power control is established, the rate can be allocated according to a fixed-rate or variable-rate policy with the objective of either meeting an outage constraint or maximizing throughput. An advantage of the variable-rate policy is that it allows an outage constraint to be enforced on every uplink, whereas the fixed-rate policy can only meet an average outage constraint.; Comment: 6 pages, 6 figures, to appear at International Conference on Communications (ICC) 2013