Code Division Multiple Access Mobile Research Articles

Mobile phones for mobility or morbidity: Is there an evidence for morbidity?

Objectives: Potential health risks are posed by long-term electromagnetic exposure due to mobiles. This study was undertaken to assess changes in the hearing at the level of the inner ear and central auditory pathway due to chronic exposure to the electromagnetic waves from mobile phones using both global system for mobile communication (GSM) and code division multiple access (CDMA) types of mobile technology. Study Design: Cross-sectional study. Materials and Methods: A total of 321 individuals who were long-term mobile users (more than 1 year, 238 GSM and 83 CDMA) and 46 individuals who had never used mobile phones underwent investigations including pure tone audiometry (500 Hz to 16 KHz), distortion product otoacoustic emissions (DPOAEs), auditory brain responses, and middle latency responses (MLR). The changes in the parameters were studied in mobile and nonmobile using ears of both GSM and CDMA individuals and corresponding ears of the controls to ascertain the effects of electromagnetic exposure. Results: GSM and CDMA users had a higher risk of having DPOAE absent as compared to controls (P = 0.000) more so if used longer during the day. They were found to have higher speech frequency thresholds and lower MLR wave Na amplitudes. More than 3 years of use emerged as a risk factor (P < 0.05). The damage was bilateral. Individuals using CDMA phones had more high-frequency loss than GSM user. The amplitudes of waves in MLR were lower in mobile phone users than nonusers. Conclusions: Long-term GSM and CDMA mobile phone use is associated with damage to the cochlea and auditory cortex.

Improvement of Memory Effects and ACPR of Power Amplifiers in CDMA Cellular Mobile and OFDM WLAN Transmitters

In this article, improvement of the memory effects and adjacent channel interference introduced by the nonlinearity of the power amplifier in the both Code division multiple access (CDMA) and Orthogonal frequency division multiplexing based (OFDM) transmitters is evaluated through Feedforward linearization method. For CDMA system, more than 17.27 dB increasing in OIP3 is and at least 25 dB improvement in adjacent channel power ratio (ACPR) is obtained. For OFDM system, achieved improvement through Feedforward linearization method is at least 39.03 dB in third output intercept point (OIP3 ), more than 26.6 dB in ACPR and 5.44 dB in peak-to- average ratio. It is observed that the designed Feedforward circuit can efficiently improve the nonlinearity caused by memory effects and saturation of the power amplifiers of CDMA cellular mobile telephony and OFDM wireless local area network (WLAN) transmitters.

Auditory Changes in Mobile Users

Genuine concerns are being raised as to the potential health risks posed by electromagnetic frequency exposure secondary to mobile phone usage. This study was undertaken to assess and compare potential changes in hearing function at the level of the inner ear and central auditory pathway due to chronic exposure to electromagnetic waves from both global system for mobile communications (GSM) and code division multiple access (CDMA) mobile phone usage. Cohort study. Tertiary referral center. One hundred twenty-five subjects who were long-term mobile phone users (more than 1 year; 63 GSM and 62 CDMA) and 58 controls who had never used mobile phones underwent audiological investigations including pure tone audiometry (250-12 kHz), tympanometry, distortion product otoacoustic emissions (DPOAE), auditory brain responses (ABR), and middle latency responses (MLRs). The changes in various parameters were studied in mobile-using and non-mobile-using ears of both GSM and CDMA subjects and corresponding ears of the controls to ascertain the effects of electromagnetic exposure. GSM and CDMA users were found to be at a significantly higher risk of having DPOAE absent as compared with controls (P < .05). They were found to have higher speech frequency thresholds and lower MLR wave and Na and Pa amplitudes. More than 3 years of mobile phone usage emerged as a risk factor (P < .05). The damage done was bilateral, with the quantum of damage being the same for both GSM and CDMA. Long-term and intensive GSM and CDMA mobile phone use may cause damage to cochlea as well as the auditory cortex.

Evaluation of Downlink Performance of a Multiple-Cell, Rake Receiver Assisted CDMA Mobile System

In wireless Code Division Multiple Access (CDMA) system, the use of power control is indispensable to combat near-far and fading problems. Signals transmitted over a multipath propagation channel which exhibits inter-path interference and fading. The receiver has to employ measures to mitigate these effects or it will incur severe performance degradation. A classic approach in CDMA communications is the rake receiver. In this paper, the downlink performance is estimated for a CDMA mobile system at the vertex of multiple adjacent cells. At the base station the received signal is coherently dispread and demodulated using a rake receiver. The effects of power control, error correction and rake receiver were also investigated on the assumption that the received signals undergo Rayleigh fading, lognormal shadowing, and frequency selective fading. The evaluation of performance measures of base to mobile link (downlink) of a multiple-cell CDMA mobile system is presented. This study demonstrates that significant performance improvements are achievable with combined use of power control, rake receiver and error correction scheme.

Topology-Independent Link Activation Scheduling Schemes for Mobile CDMA Ad Hoc Networks

In this paper, we study medium access control (MAC) protocols with quality-of-service (QoS) support, that is, topology-independent link activation transmission scheduling, for mobile code-division multiple-access (CDMA) ad hoc networks. QoS provisioning for each communication link is guaranteed without the need to adopt transmission schedules in mobile environments. An interference model, which captures the difference between transmission and interference ranges, is considered. Under this interference model, an approach to guaranteeing conflict-free transmission slots in each frame (QoS provisioning) for each communication link is proposed. Compared with the previously known method, superior performance is obtained. We then present a topology-independent link activation scheduling framework based on the theory of group-divisible (GD) designs. By the mathematical properties of GD designs, the proposed framework guarantees conflict-free transmission slots in each frame for each communication link, without the overhead due to the recomputation of transmission schedules when the network topology changes. With the proposed framework, we study and evaluate one series of GD design constructions. Based on the results derived, topology-independent link activation scheduling algorithms are then presented. The proposed schemes are designed for different objectives: maximizing the minimum system throughput and/or minimizing the schedule frame length. Numerical results show that the proposed algorithms outperform previously known schemes. The average performance of the proposed schemes is also derived.

Combinative Exposure Effect of Radio Frequency Signals from CDMA Mobile Phones and Aphidicolin on DNA Integrity

The aim of present study is to assess DNA integrity on the effect of exposure to a radio frequency (RF) signal from Code Division Multiple Access (CDMA) mobile phones. Whole blood samples from six healthy male individuals were exposed for RF signals from a CDMA mobile phone for 1 h. Alkaline comet assay was performed to assess the DNA damage. The combinative exposure effect of the RF signals and APC at two concentrations on DNA integrity was studied. DNA repair efficiency of the samples was also studied after 2 h of exposure. The RF signals and APC (0.2 μg/ml) alone or in synergism did not have any significant DNA damage as compared to sham exposed. However, univariate analysis showed that DNA damage was significantly different among combinative exposure of RF signals and APC at 0.2 μg/ml (p < 0.05) and at 2 μg/ml (p < 0.02). APC at 2 μg/ml concentration also showed significant damage levels (p < 0.05) when compared to sham exposed. DNA repair efficiency also varied in a significant way in combinative exposure sets (p < 0.05). From these results, it appears that the repair inhibitor APC enhances DNA breaks at 2 μg/ml concentration and that the damage is possibly repairable. Thus, it can be inferred that the in vitro exposure to RF signals induces reversible DNA damage in synergism with APC.

Deterministic-based performance modeling of a cluster of nodes handling subscriber profile query and update in CDMA mobile switching center

This paper presents performance modeling of processor occupancy in a cluster of nodes handling subscriber profile query and update in a code division multiple access (CDMA) mobile switching center (MSC). It also presents a simplified method to determine the profile update ratio that represents the fraction of autonomous registration (AR) and call events requiring subscriber profile updates. Four models are presented. The performance models developed offer a number of advantages, including enabling prediction of the home visitor location register (HVLR) capacity in a deterministic fashion to facilitate subscriber profile management and planning and to provide a simple method to determine the subscriber profile update ratio. The models are simple to use and provide accurate predictions. The models are platform-independent and can be easily applied to other platforms by substituting a new set of costs per message. Performance improvement by update bundling is also demonstrated, and future work on modeling update bundling is presented. © 2007 Alcatel-Lucent.

Blind adaptive multiuser detector for nonlinearly modulated satellite mobile CDMA systems

This paper presents a novel blind adaptive noncoherent decorrelative multiuser detector for nonlinearly modulated satellite mobile Code Division Multiple Access (CDMA) systems. By using the known signature waveforms of the counterpart earth station in the blind adaptive multiuser detector, the system performance has been improved obviously. The computation results about the convergence properties of the new detector and the previous detectors demonstrate that the proposed multiuser detector has better performance than previous multiuser detectors for nonlinearly modulated CDMA systems.

The cdma2000 system for mobile communications (vanghi, v. et al; 2004) [book review

The authors declare that the aim of their book is to present how the principles of spread spectrum communication in general and code-division multiple access (CDMA) in particular are applied to the cdma2000 standards; to distill the information described in thousands of pages of cdma2000 standards and create a comprehensive description of cdma2000 1X The authors believe that their book can be used by those approaching CDMA systems for the first time, but also by practitioners, system designers, and network operators. The authors foresee their book also being applied as a secondary academic text for courses in mobile communications systems and CDMA.

Achievable-SIR-based predictive closed-loop power control in a CDMA mobile system

A power control algorithm with two prediction models based on an achievable signal-to-interference power ratio (SIR) has been proposed under a multipath Rayleigh fading environment in a code-division multiple-access (CDMA) mobile system. An achievable SIR is defined as the maximum-minimum SIR among all users at a particular time step. The corresponding mobile transmission powers are denoted as the "optimum transmission powers." In the individual power predictor (IPP) model, a linear transversal filter is assigned to each user. The output of the IPP, which is a linear combination of the optimum transmission powers of the mobile during the current and previous power measurement periods, predicts the optimum transmission power of the mobile in the next time step. In the global power predictor (GPP) model, a single predictor, constructed by a linear neural network, is used to predict the optimum transmission powers of all mobiles in the next time step. In both predictor models, the weights of the predictors are updated by using the recursive least squares algorithm. To further improve the performance, a reduced power-measurement period has been studied. Simulation results show that the proposed power control algorithm can achieve a lower outage probability and a smaller dynamic range of transmission power compared with a conventional power control scheme.

Using RF filtering to reduce competitor-induced interference

This paper examines the success of RF filtering on mitigating interference that occurs between two wireless multiple-access systems operating within the same geographic area. Such interference is referred to as "competitor-induced interference" and can significantly degrade system capacity and performance. Three dual-system scenarios are considered: a dual code-division multiple-access (CDMA) (IS-95) system, a CDMA mobile in an FM (AMPS) cell, and an FM mobile in a CDMA cell.

Application of a Recurrent Neural Network to Space Deversity in SDMA and CDMA Mobile Communication Systems

Linear and non-linear adaptive algorithms are investigated for Space Division Multiple Access (SDMA). SDMA is one of the emerging techniques for multiple access of users in mobile radio, which uses spatial distribution of users for their differentiation. The performance of the linear Square Root Kalman (SRK) algorithm for SDMA is compared to that of the non-linear Recurrent Neural Network (RNN) technique. The proposed SDMA-RNN technique is evaluated over Rician fading channels, and it shows improved Bit Error Rate (BER) performance in comparison with the linear SRK-based technique. The performance of SDMA-RNN is also compared with that of Code Division Multiple Access (CDMA) systems, showing that it could be used as a viable alternative scheme for multiple access of users. Finally, a Hybrid CDMA-SDMA system is proposed combining CDMA and SDMA-RNN systems. Hybrid CDMA-SDMA exhibits a very good potential for increase in the capacity and the performance of mobile communications systems.

Integrated call control in a CDMA cellular system

Soft handoff is an essential component of code-division multiple-access (CDMA) digital mobile communication systems. While soft handoff has some advantages of system capacity and communication quality, it also has some disadvantages arising from the excessive use of channel resources. In this study, we propose a new control policy to alleviate effectively this excessive use of channel resources. For CDMA cellular mobile systems consisting of homogeneous cells, a variety of traffic parameters are estimated by the detailed traffic analysis, based on which a Markovian queueing model is developed to analyze the performance of the proposed call control policy. With a well-known performance objective, a mathematical problem of finding optimal call control parameters is proposed, along with its solution method.

Efficient Design of Voice Carrying Fixed-Network Links in CDMA Mobile Communication Systems

Code Division Multiple Access (CDMA) technology is gaining momentum as the preferred wireless system for the next generation Personal Communication Systems (PCS). In CDMA systems, voice is encoded and packaged in variable length packets that are transported between the mobile station and the switching center. Although the packetization provides a great flexibility in resource allocation, it poses a Quality of Service (QoS) problem on voice. In this paper, we discuss link dimensioning for a typical CDMA system. We consider a T1/E1 link between a CDMA Basestation Transceiver System (BTS) and the Base Station Controller (BSC). Traffic from various voice sources is subject to a framing scheme, which presents a semi-periodic batch input at the T1/E1 interface cards. We analyze the resulting queuing system using discrete-time analysis and large deviations theory and verify our results by simulation. We provide results for the minimum link capacity needed to support a given number of CDMA voice sources. Our results show the potential statistical gain that can be achieved by voice packetization for all practical values of link capacities.

Capacity unbalance between uplink and downlink in spectrally overlaid narrow-band and wide-band CDMA mobile systems

In this paper, we discuss unbalance between uplink (mobile-to-base) and downlink (base-to-mobile) in future code division multiple access (CDMA) radio networks where both narrow-band and wide-band CDMA systems are coexisted. Since the two links are not operated in an identical condition, their capacities are unequal and either of the links determines the whole system capacity. The purpose of this paper is to examine which link limits the system and what are the limiting factors. To facilitate the examination, transmission capacity and connection capacity are defined, and simplified formulas are presented to compute those capacities, respectively for uplink and downlink. Signal quality required for each link, effectiveness of power control, spatial distribution of mobile users and other-cell as well as same-cell user interference are usually determining the limiting link. Besides, the traffic unbalance between the links imposed by specific service applications and the network evolution scenarios are also shown to be very influencing factors.

Optimal mode selection and synchronization for robust video communications over error-prone networks

We describe an effective method for increasing error resilience of video transmission over bit error prone networks. Rate-distortion optimized mode selection and synchronization marker insertion algorithms are introduced. The resulting video communication system takes into account the channel condition and the error concealment method used by the decoder, to optimize video coding mode selection and placement of synchronization markers in the compressed bit stream. The effects of mismatch between the parameters used by the encoder and the parameters associated with the actual channel condition and the decoder error concealment method are evaluated. Results for the binary symmetric channel and wideband code division multiple access mobile network models are presented in order to illustrate the advantages of the proposed method.

Smart antennas for combined DOA and joint channel estimation in time-slotted CDMA mobile radio systems with joint detection

In cellular mobile radio systems, the directional inhomogeneity of the mobile radio channel can be exploited by smart antennas to increase the spectral efficiency. In this paper, a novel smart antenna concept applying receiver antenna diversity at the uplink receiver is investigated for a time-slotted code-division multiple-access (CDMA) mobile radio air interface termed time-division CDMA (TD-CDMA), which has been selected by the European Telecommunications Standards Institute (ETSI) in January 1998 to form part of the Universal Mobile Telecommunications System (UMTS) air interface standard. First, a combined direction-of-arrival (DOA) and joint channel estimation scheme is presented, which is based on DOA estimation using the Unitary ESPRIT algorithm and maximum likelihood estimation of the channel impulse responses associated with the estimated DOA's, which can also be used as an input for advanced mobile positioning schemes in UMTS. The performance of the combined DOA and joint channel estimation is compared with the conventional channel estimation through simulations in rural and urban propagation environments. Moreover, a novel joint data detection scheme is considered, which explicitly takes into account the signal DOA's and the associated channel impulse responses. The link level performance of a TD-CDMA mobile radio system using these novel schemes is evaluated by Monte Carlo simulations of data transmission, and average bit error rates (BER's) are determined for rural and urban propagation environments. The simulation results indicate that, depending on the propagation environment, the exploitation of the knowledge of the directional inhomogeneity of the mobile radio channel can lead to considerable system performance enhancements.

Mobile frequency-hopping CDMA systems

Through analysis and simulation, a unified evaluation of the potential performance of both mobile peer-to-peer and sectorized cellular frequency-hopping code-division multiple-access (CDMA) systems is presented. The equivalent number of frequency channels and the minimum area-mean signal-to-noise ratio are defined and shown to be important parameters in understanding and predicting network capacity. The effects of spectral splatter are analyzed. Separated orthogonality is defined and shown to be useful in completely eliminating intracell or intrasector interference. Spatial diversity by postdetection rather than predetection combining is proposed and shown to be invaluable. Noncoherent demodulation by a frequency discriminator rather than parallel matched filters and envelope detectors is proposed and shown to be effective. It is shown that even without exploiting either its natural bandwidth advantage or power control, frequency-hopping CDMA provides a reverse-link capacity nearly the same as direct-sequence CDMA with realistic power-control imperfections.

Rate-regulated power control for supporting flexible transmission in future CDMA mobile networks

In code division multiple access (CDMA) mobile networks, transmitted power is controlled to provide each user an acceptable connection by limiting the interference seen by other users. Previous work has focused on finding a power assignment that maximizes the minimum carrier-to-interference ratio where the transmission rate of each user is known and fixed. In future mobile networks, however, fluctuations in mobiles' transmission rate should be considered in designing power control algorithms. In this work, we present an algorithm for controlling mobiles' transmitter power levels while explicitly handling their time-varying transmission rates. During the whole power control process, the required signal quality is always maintained. The traffic-carrying performance of the algorithm is evaluated by simulation where different types of users are sending burst data.

Performance of optimum transmitter power control in CDMA cellular mobile systems

Efficient power control is of great importance in the design of high-capacity cellular radio systems. Optimum power control scheme (OPCS), in the sense that it minimizes the outage probability, has been fully investigated for frequency-division multiple-access/time-division multiple-access (FDMA/TDMA) cellular systems. In this paper, optimum power control theory is introduced to code-division multiple-access (CDMA) cellular systems to derive upper performance bounds for all types of transmitter power control schemes. Simulation results indicate that the OPCS will increase the CDMA system capacity by more than 1.9 dB over the perfect average power control scheme under IS-95-defined radio condition.