Code Division Multiple Access Technology Research Articles

Software Design of CDMA based MAC Scheme for Microsatellite

CDMA (Code Division Multiple Access) technology allows many users to access the medium concurrently. The store and forward (S&F) payload is to provide message relay service for terrestrial users with simple ground terminals. The widespread method of MAC (Medium Access Control) in S&F payload is ALOHA and it has poor channel throughput efficiency. This can be improved using CDMA based MAC. In this paper, two methods of code assignment namely, static & dynamic are considered. Their design methodologies and corresponding performance measures are discussed. The performance of the proposed CDMA MAC is compared with the existing ALOHA MAC and the results are presented.

A class of call-fail-safe and distribution-effective multi-band multi-carrier traffic allocation methods for 3GB wireless systems

For better capacity and higher availability, present day third generation (3G) wireless systems based on the code division multiple access(CDMA) technology are evolving to operate on multiple carriers (frequencies) spread over multiple bands. In order to provide better quality of service, the 3GB (3rd generation and beyond) systems need to distribute calls equitably to different carriers on different base-stations accessible to the mobiles irrespective of the bands or carriers on which those mobiles initiated their calls. However, there is a risk of call failure when a call originated on a carrier in a band is migrated to another carrier in a different band, particularly because of the differences in the radio coverage of the base-stations operating in different bands. This paper presents a class of methods that offer equal robustness against call failures and varying degrees of call distribution effectiveness. For call distribution, these methods employ an enhanced carrier capacity measure (ECM) proposed in this paper. ECM augments the gross capacities of the carriers (to house calls) with pre-configured biases specific to the mobile users. We develop here an intuitively appealing distribution-effectiveness measure based on the ECM for comparing the methods. Relative performances of the proposed methods with respect to call failure rate and distribution effectiveness are established by means of simulation results for calls originating anywhere in the cell coverage area as well as calls originating exclusively near the cell boundaries. The latter results help to study the effect of mobility on the performances of the algorithms.

Modern Wireless Telecommunication Technologies and Their Electromagnetic Compatibility with Life-Supporting Equipment

Hospitals rely on pagers and ordinary telephones to reach staff members in emergency situations. New telecommunication technologies such as General Packet Radio Service (GPRS), the third generation mobile phone system Universal Mobile Telecommunications System (UMTS), and Wireless Local Area Network (WLAN) might be able to replace hospital pagers if they are electromagnetically compatible with medical devices. In this study, we sought to determine if GPRS, UMTS (Wideband Code Division Multiple Access-Frequency Division Duplex [WCDMA FDD]), and WLAN (IEEE 802.11b) transmitted signals interfere with life-supporting equipment in the intensive care and operating room environment. According to United States standard, ANSI C63.18-1997, laboratory tests were performed on 76 medical devices. In addition, clinical tests during 11 operations and 100 h of intensive care were performed. UMTS and WLAN signals caused little interference. Devices using these technologies can be used safely in critical care areas and during operations, but direct contact between medical devices and wireless communication devices ought to be avoided. In the case of GPRS, at a distance of 50 cm, it caused an older infusion pump to alarm and stop infusing; the pump had to be reset. Also, 10 cases of interference with device displays occurred. GPRS can be used safely at a distance of 1 m. Terminals/cellular phones using these technologies should be allowed without restriction in public areas because the risk of interference is minimal.

Simple robust receiver structure for gigabit ethernet O-CDMA using matrix codes

We have developed an optical code division multiple access (O-CDMA) technology demonstrator (TD) based on two-dimensional (2-D) codes. The 2-D codes are derived from folded optimum Golomb rulers, implemented as wavelength/time /spl lambda//T codes. The objective of the research is to develop the science and technology for high-performance, low-cost, and robust O-CDMA applications. A key ingredient of the TD is a simple receiver structure that is based on hard-limiting after optical-to-electrical (O/E) conversion and time windowing with a conventional electronic D flip-flop. With the TD, we demonstrate six asynchronous users at less than 10/sup -11/ bit error rate (BER) and up to eight users at 10/sup -8/ BER, limited by saturation in the optical preamplifier.

On Blocking Probability of Multi-Beam CDMA Systems Using SBF Array Antennas

In wireless cellular systems, a code division multiple access (CDMA) technology with array antennas can significantly reduce interferences by taking advantage of the combination of spreading spectrum and spatial filtering. We investigate blocking probabilities of multi-beam CDMA systems using switched beamforming (SBF) array antennas considering non-homogeneous traffic loading over a cell which may cause traffic congestion and introduce large blocking probability in a hot-spot area. We also propose a feasible main beamwidth deployment and a beam reassignment (BR) method to mitigate the hot-spot beam, named the hot-beam. The feasible main beamwidth deployment suggests that we can relieve the hot-beam situation by deploying the feasible main beamwidth which can guarantee below 1% blocking probability. Using the BR method, the blocking probability of hot-beam and total blocking probability over a cell are significantly reduced. Further, it is shown that the feasible traffic load ratio of the hot-beam to the lightly loaded beam is significantly enhanced when the total blocking probability of the cell is maintained below 1%.

Use of CDMA Acoustic Telemetry to Document 3-D Positions of Fish: Relevance to the Design and Monitoring of Aquatic Protected Areas

Knowledge of animal spatial ecology is essential for the design and siting of proposed aquatic protected areas (APAs), as well as the assessment and monitoring of existing ones. Acoustic telemetry is one of the primary tools for the assessment of animal movements in aquatic systems through either manual tracking or the establishment of fixed receiving stations. Recent technological developments in code division multiple access (CDMA) acoustic telemetry now enable the simultaneous real-time monitoring of numerous individual fish at fine time scales providing APA researchers with a robust new tool. Fish can be positioned in three-dimensions with sub-meter accuracy in both deep and shallow waters. Here, we describe a whole-lake environmental observatory that includes a 13-hydrophone acoustic telemetry array that has been used to monitor the position of 22 tagged fish at 15 sec intervals. Although we use a freshwater fish and environment as a case study, this telemetry system is equally useful for marine environments including under-ice. We evaluate the applicability of CDMA MAP technology to address pressing questions in applied APA research. The CDMA MAP system provides the flexibility to collect information at multiple spatial-temporal scales, responding to the varied levels of detail and precision required for different applications in APA research. When combined with the suite of other telemetry and monitoring approaches available, CDMA MAP technology will enable researchers to document the spatial ecology essential for improving APA science. Furthermore, because numerous animals from different trophic levels can be tracked in real time, CDMA MAP technology will also aid in our understanding of complex community-level dynamics consistent with the shift towards ecosystem-based APA management.

Performance of CDMA/PRMA as an Access Technique for Integrated Services in a UMTS High Altitude Platform System

High Altitude Platforms (HAPs) have gained a great interest in recent years. HAP systems will be global in nature but national in service provision. They will deliver IMT-2000 mobile and fixed wireless access using the proposed IMT-2000 terrestrial component radio transmission technologies and protocols. Under the above consideration, in this paper the performance of a MAC protocol based on the combination of the well-known Packet Reservation Multiple Access (PRMA) scheme with Code Division Multiple Access (CDMA) technologies in a Frequency Division Duplex (FDD) mode is studied, for a HAP operating at the 2 GHz frequency band at an altitude of 22 km. The impact of acknowledgement delay has been examined through computer simulations, along with the selection of suitable channel access functions (CAFs) to control the access of mobile users. Moreover the protocol performance is investigated in a cellular HAP environment and compared to that of a ground-based system. Finally, different traffic scenarios have been considered in order to investigate the access delay for non-real time traffic and the packet dropping performance for real time traffic.

Multiple antenna options for high data rate CDMA systems

1xEV-DO (1xEVolution-Data Only) is a method for transmission of wireless packet data at high rates which is based on code division multiple access (CDMA) technology. Adaptive modulation and coding is used together with proportional fairness scheduling to take full advantage of the channels between the base stations and mobile stations when they are at their best. Methods such as receive antenna diversity and multiple input multiple output (MIMO) have the potential to improve the performance of such a system. A model which simulates an 1xEV-DO network with multiple transmit and receive antennas has been developed to investigate this. Results are given showing how the throughput varies with the number of users per cell for different numbers of transmit and receive antennas. The performance of MMSE (minimum mean square error) and MRC (maximal ratio combining) algorithms are also investigated. The effects of introducing multiple paths and Rayleigh and Rician fading are compared. Simulation results for multiple transmit and receive antennas are compared with the channel capacity predicted by the Shannon capacity equation.

Detection and evaluation of I/Q impairments in RF digital transmitters

Troubleshooting of radio-frequency (RF) digital transmitters is considered. A new digital signal-processing method is developed, which is capable of both detecting and evaluating the most recurrent impairments in the I and Q paths of the transmitter. Only the acquisition of either or intermediate-frequency (IF) or RF output signal is needed, thus avoiding any difficulty connected with the inaccessibility of baseband and/or IF section in a fully assembled transmitter. Moreover, the method has the required features of automation and effectiveness, granted by the use of RLS-based algorithms and proved by the results obtained in many experiments on actual IF and RF output signals. Even though the experiments presented in the paper refer to wideband code-division multiple-access technology, the method shows itself suitable for troubleshooting any digital transmitter implementing quadrature-amplitude modulation.

Analysis and Simulation of a Plastic Optical Fiber Access Network Based on OCDMA Technology

In this paper a plastic optical fiber (POF) access network based on optical code-division multiple access (OCDMA) technology is proposed. Recently, optical transmission using POF has received much attention due to its low weight, large core diameter, flexibility, and easy installation. Specially, its high bandwidth makes POF a very attractive candidate for a transmission media in an access network based on OCDMA technology. A conventional OCDMA system only allows a finite number of units to transmit and access simultaneously according to the number of channels which is restricted by BER. To resolve this problem a novel protocol is also proposed in this paper. The protocol can efficiently support variable-sized messages, and any new unit can join the network at any time without requiring network initialization. To implement the demonstration, each optical network unit is equipped with a fixed and a tunable optical encoder/decoder. The optical encoder/decoder employing planar holographic optical processors (HOPs) in this system may be of low fabrication cost. The network throughput and average delay using various system parameters has been investigated by numerical analysis and simulation experiments. It is shown that the dynamic control protocol in this POF access network based on OCDMA technology is valid and efficient.

SMART-a solution for managing the capacity, growth, and performance of wireless networks

The wireless communications industry has shown explosive growth in the recent past. At the same time, new information access technologies for the Internet have gained universal acceptance. In the wireless market, single mobile switching center analog systems have rapidly evolved into hybrid networks with time division multiple access and code division multiple access technologies. These developments have created a need for a comprehensive network performance management tool to measure and analyze capacity, growth, and performance of wireless networks. This need is being addressed by the state-of-the-art Systems Measurement Analysis and Reporting Tool (SMART), which is based on Internet access technology. SMART is being developed as one of the first Web-based tools on the Autoplex® 1000 product line and is designed to run on the operations and maintenance platform (OMP) in a client-server architecture, with the OMP acting as a network management server. SMART has extensive applications in making performance, capacity, and engineering-related decisions that are relevant during wireless systems planning, design, and operation. This paper describes the SMART architecture, its implementation on the Autoplex system, and applications in managing the capacity, growth, and performance of a wireless network. Though some features of SMART discussed here have been developed, SMART must not be construed as an openly available and fully supported product.

Integrated Optimal Cell Site Selection and Frequency Allocation for Cellular Radio Networks

Two major planning problems are encountered when designing a cellular radio network. The initial question is where to locate the base transmitter stations such that full coverage is achieved at low interference. This is relevant for frequency division (FDMA) as well as code division multiple access (CDMA) technology. If the locations of base stations are given, then for an FDMA-system frequencies have to be assigned such that there is a sufficient number of channels per cell available at a low total interference level. Since cell site selection and frequency allocation have mutual influences on each other, the ultimate goal is to deal with both problems in a single design step. The main intention of this paper is to model the above planning issues as linear integer programs, and to discuss solution methods for the corresponding NP-hard problems. According to their increasing complexity we proceed from channel allocation via cell site selection to an integrated single setup.

Optimal admission control algorithms for scheduling burst data in CDMA multimedia systems

The third generation mobile communication systems are widely envisioned to be based on wideband code division multiple access (CDMA) technologies to support high data rate (HDR) packet data services. To effectively harness the precious bandwidth while satisfying the HDR requests from users, it is crucial to use a judicious burst admission control algorithm. In this paper, we propose and evaluate the performance of a novel jointly adaptive burst admission algorithm, called the synergistic burst admission control algorithm to allocate valuable resources (i.e., channels) in wideband CDMA systems to burst HDR requests. We consider the spatial dimension only, and by that we mean the algorithm performs scheduling and admission control, for the current frame only, based solely on the selection diversity in the geographical and mobility aspects. The scheduler does not exploit the temporal dimension in that it does not make allocation decisions about future frames (i.e., requests that do not get allocation are simply ignored and such requests will be treated as new request in future frames). In the physical layer, we use a variable rate channel-adaptive modulation and coding system which offers variable throughput depending on the instantaneous channel condition. In the MAC layer, we use the proposed optimal multiple-burst admission algorithm, induced by our novel integer programming formulation of the admission control and scheduling problem. We demonstrate that synergy could be attained by interactions between the adaptive physical layer and the burst admission layer. Both the forward link and the reverse link burst requests are considered and the system is evaluated by dynamic simulations which takes into account of the user mobility, power control and soft handoff. We found that significant performance improvement, in terms of average packet delay, data user capacity and coverage, could be achieved by our scheme compared to the existing burst assignment algorithms.

Chromosome damage and micronucleus formation in human blood lymphocytes exposed in vitro to radiofrequency radiation at a cellular telephone frequency (847.74 MHz, CDMA).

Peripheral blood samples collected from four healthy nonsmoking human volunteers were diluted with tissue culture medium and exposed in vitro for 24 h to 847.74 MHz radiofrequency (RF) radiation (continuous wave), a frequency employed for cellular telephone communications. A code division multiple access (CDMA) technology was used with a nominal net forward power of 75 W and a nominal power density of 950 W/m(2) (95 mW/cm(2)). The mean specific absorption rate (SAR) was 4.9 or 5.5 W/kg. Blood aliquots that were sham-exposed or exposed in vitro to an acute dose of 1.5 Gy of gamma radiation were included in the study as controls. The temperatures of the medium during RF-radiation and sham exposures in the Radial Transmission Line facility were controlled at 37 +/- 0.3 degrees C. Immediately after the exposures, lymphocytes were cultured at 37 +/- 1 degrees C for 48 or 72 h. The extent of genetic damage was assessed from the incidence of chromosome aberrations and micronuclei. The kinetics of cell proliferation was determined from the mitotic indices in 48-h cultures and from the incidence of binucleate cells in 72-h cultures. The data indicated no significant differences between RF-radiation-exposed and sham-exposed lymphocytes with respect to mitotic indices, frequencies of exchange aberrations, excess fragments, binucleate cells, and micronuclei. The response of gamma-irradiated lymphocytes was significantly different from that of both RF-radiation-exposed and sham-exposed cells for all of these indices. Thus there was no evidence for induction of chromosome aberrations and micronuclei in human blood lymphocytes exposed in vitro for 24 h to 847.74 MHz RF radiation (CDMA) at SARs of 4.9 or 5.5 W/kg.

Benchmarking government’s roles to assure the cooperation in collaborative technology innovation, The case of CDMA technology development

This paper focuses on searching for the conditions of cooperation in collaborative technology innovation including the Government and private enterprises. After assuming the collaborative project of code division multiple access (CDMA) as one of the collective actions, attempts to analyze the case of CDMA technology development process by applying the theoretical propositions derived from two approaches, collective action andprisoner dilemma. Identifies government’s roles and strategies as a third party who guarantees the realistic conditions for cooperation to induce the success of joint ventures which inherently have the potential risk of cooperation collapse caused by the opportunistic or free‐riding behaviors of private collaborators as self‐interest seekers. Finally, suggests therealistic conditions for cooperation, government’s roles, and policy tools for the future collaborative R&D.

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.

Optimizing the Design of a CDMA Cellular System Configuration with Multiple Criteria

This paper deals with the mathematical modeling and optimization of a code division multiple access (CDMA) cellular system configuration that seeks the optimal location, power, and antenna height of each base station in a service area, in order to optimize call quality, service coverage and total cost of system configuration. The factors affecting optimum selection are the non-uniform spatial demand in the service area, the propagation environment, the interference among users and among base stations, and other factors intrinsic to CDMA technology. The simulated annealing method supplemented by a demand allocation algorithm is implemented in a software package to solve this complex multiobjective nonlinear optimization problem. This research shows that simulated annealing is a viable method for obtaining “good quality” solutions to the wireless system configuration problem. A realistic case study dealing with the design of a cellular system configuration for the city of Cambridge, MA, and its surroundings, is developed to illustrate the modeling concept and the steps of the algorithm. Sensitivity analysis is performed to further analyze the configuration decision.

Data detection techniques for DS/CDMA mobile systems: a review

As system requirements in terms of the BER performance and capacity increase, so will the need for more advanced detection techniques. The application of advanced receiver structures is optional for phase 2 of the UMTS FDD mode, while it is mandatory for the time-division duplex mode. Layer 1 of both modes is based on wideband direct sequence code-division multiple access technology, where a physical channel is characterized by the code, frequency, and, in the uplink, the relative phase (I/Q). Furthermore, in the TDD mode the physical channel is also characterized by the time slot (TDMA component).

An adaptive approach to manage traffic in CDMA ATM networks

Wireless Asynchronous Transfer Mode ( WATM) systems are becoming an important field in recent days due to their increasing use and applications. A WATM system is the result of synergy between wireless networks and asynchronous transfer mode ( ATM) technologies. Designing an efficient mobile communication system is considered as a challenging task, given its complexity and operation environments. A major task activity related to these systems addresses the call admission control and resource management. In this paper, we consider these issues in wireless ATM networks integrating the Code Division Multiple Access ( CDMA) technology. An approach for a dynamic resource management is proposed using heterogeneous traffic descriptors as well as the concept of signal-to-interference rate, computed at the base station receivers. An adaptive monitoring scheme that is based on an estimation algorithm and driven by a measurement of the signal-to-interference and predicted traffic parameters of the admitted connections is established. The Dynamic control that we propose at the user network interface, UNI, provides information about the instantaneous bit rate of a source allowing more effective flow control and achieves a good match in terms of predicting the congestion of any switch. It is able to police implicit resource management, which is used for both Constant Bit Rate ( CBR) and Variable Bit Rate ( VBR) traffics as well as explicit resource management that is used for Available Bit Rate ( ABR) traffic.

Optimal scheduling in cdma packet radio networks

Scope and Purpose—A packet radio network provides flexible data communication services among a large number of geographically distributed and mobile users (nodes). Organizing the multiple channel access in packet radio networks is a well known and widely discussed area. The time division multiple access (TDMA) technology has been popularly used and has been studied extensively. On the other hand, the development of the code division multiple access (CDMA) technology raises a new question in this field. In CDMA packet radio networks the channels can be realized by different orthogonal codes and the simultaneous reception of several packets is possible through the use of orthogonal codes. The multiple reception capacity provides an opportunity for significantly increasing system throughput. In this paper, we suggest an efficient heuristic algorithm for scheduling in CDMA packet radio networks. We consider the time slot assignment problem in a CDMA packet radio network. Unlike the classical TDMA packet radio networks, a CDMA packet radio network can provide each node with a multiple reception capacity using orthogonal codes. This multiple reception capacity of each node presents a new challenge for channel access protocols. Also we consider non-uniform traffic demand over nodes which has become important due to the increase of subscribers and the introduction of personal communication system (PCS). We present an algorithm for a general system where the number of nodes and the reception capacity can be any positive integers and the traffic demand can be non-uniform. Computational tests show that our algorithm generates excellent solutions in most cases.