Wireless Code Division Multiple Access Research Articles

A Framework for Code Division Multiple Access Wireless Power Transfer

The availability of energy is one of the major hindrances to unlocking the massive potential of electronic devices. Powering a highly connected network of devices requires multiple access and a wireless power transfer (WPT) solution that is scalable and capable of maintaining a constant power flow regardless of reconfiguration (mutability) and electromagnetic environment (power flow selectivity). In this paper, we present a framework for the implementation of code division multiple access wireless power transfer (CDMA-WPT) for enabling WPT among multiple transmitters and multiple receivers simultaneously. CDMA-WPT maintains power flow selectivity and is easily scalable. An inverter/rectifier topology is presented for the hardware implementation of CDMA-WPT. A design process for practical co-design of high-performance hardware and obtaining a code set is also presented. We demonstrate the hardware implementation of CDMA-WPT using two transmitters and two receivers maintaining a nearly constant 5W operation with nearly 75% dc-dc efficiency, and four transmitters and four receivers maintaining a constant 4W operating with greater than 70% dc-dc efficiency. . This paper is accompanied by a video hardware demonstration in real-time the difference between using orthogonal codes in CDMA versus conventional single-frequency WPT using 4 transmitter-receiver pairs; conventional single-frequency WPT shows up to a 100% deviation from the intended transfer power as opposed to 8.1% for orthogonal codes in CDMA.

Code Division Multiple Access Wireless Power Transfer for Energy Sharing in Heterogenous Robot Swarms

Energy is one of the key enablers for robotic swarms. The feasibility of heterogeneous swarms to perform complex missions depends upon the energy stored in the robot batteries. Allowing multiple access energy transfer (MAET) in robot swarms provides more flexibility to accomodate uncertain missions. In this paper, we present a MAET solution for heterogeneous swarms using code division multiple access wireless power transfer (CDMA-WPT). CDMA-WPT allows robots in heterogeneous swarms to exchange energy while in motion, allows faster charging rates by enabling multiple robots to exchange energy, is easily scalable, offers power flow selectivity to enable energy encryption, and does not require a centralized controller. The encoding scheme, power flow model, and code construction algorithm for a particular implementation of CDMA-WPT is presented. The proof of concept is verified using a hardware implementation for a heterogeneous swarm of four robots. Finally, the application of CDMA-WPT to a heterogeneous swarm with 30 robots is presented.

An Integrated Linearization Technique for GaAs Bipolar WCDMA Power Amplifier

Here we report a novel linearization and efficiency improvement technique for heterojunction bipolar transistor (HBT)-based Wireless Code Division Multiple Access (WCDMA) power amplifier. A process solution is proposed where a tantalum nitride (TaN) layer is strapped to the HBT base metal layer that resolves the current hogging issue. This is known as the strap ballasting technique. The resistance introduced by TaN improves the linear output power without trading-off its power added efficiency. At supply voltage of 4 V, the strap ballasting methodology improves the adjacent channel leakage ratio by 4.5 dB compared to the conventional base ballasting technique at output power of 28 dBm. The corresponding improvement in power added efficiency is 4%. The maximum output power delivered by power amplifier is 36 dBm. The proposed technique can be employed in the WCDMA power amplifier to minimize the fundamental trade-off issue between linear output power and efficiency.

Performance of multihop CDMA ad hoc networks with diversity combining techniques over fading environments

This study investigates the impact of the diversity combining techniques on the performance of wireless code division multiple access (CDMA) ad hoc networks operating over κ-μ fading channels, where the performance criterion in this study is in terms of the expected progress per hop. The probability density function (PDF) and the cumulative density function (CDF) of the interference power are obtained in κ-μ fading conditions. Furthermore, expression for the unconditional CDF of the signal-to-noise-and-interference ratio (SNIR) is derived, which is utilized to derive expressions for the expected progress per hop with selecting combining (SC) and maximal ratio combining (MRC) diversity. Corresponding expressions for Nakagami-m and Rician fading are presented in this paper as special cases of κ-μ fading. Numerical results are presented for illustration purposes.

Joint Quality Enhancement and Power Control for Wireless Visual Sensor Networks based on the Nash Bargaining Solution

We propose a cooperative method for resource allocation with power control in a multihop Direct Sequence Code Division Multiple Access Wireless Visual Sensor Network (WVSN). Typical multihop WVSNs consist of visual sensors that record different scenes and relay nodes that retransmit video data until the base station is reached. The error prone wireless environment contributes to the end-to-end video quality degradation. Moreover, the limited battery life span of the network nodes poses challenges on the management of power consumption. The different resource requirements of the WVSN nodes necessitate a quality-driven and power-aware resource allocation mechanism. We formulate the joint Quality Enhancement and Power Control problem based on a utility function that reflects both the benefit in terms of video quality and the cost in terms of transmission power. This function is employed by the Nash Bargaining Solution, which achieves higher fairness in terms of end-to-end video quality among all nodes. For the fairness assessment, a new metric is introduced. The experiments demonstrate the effectiveness of the proposed approach and explain the video quality-power consumption tradeoff as well as the resulting fairness-power consumption tradeoff.

Impact of Dirty Devices on CDMA Network Coverage and Capacity

The introduction of cellphones with poor receiver sensitivity, known as dirty devices, to the Code Division Multiple Access (CDMA) cellular network results in a reduction in cell edge coverage, degraded capacity, and higher drop-call rates. This poor network performance has a negative impact on customer experience and satisfaction, which may result in increased churn for CDMA wireless carriers. Previous research on the impact of dirty devices has used computer-based simulations. This paper demonstrates the influence of dirty devices on a live commercial CDMA network using two distinct approaches. The first approach deploys dirty and non-dirty devices in a live commercial cell, and measures the impact on forward base transceiver station (BTS) power and forward link Ec/Io (Ec is the received pilot chip energy and Io is the spectral density of the total power seen by the device). A series of tests on a live CDMA network with known dirty devices shows an increase in BTS transmit power resources compared with non-dirty devices, leading to the degradation of forward link Ec/Io. The second approach uses a statistical study of the aggregated pilot strength measurement messages reported by the mobile to ascertain the impact of known dirty devices on the overall network Ec/Io of non-dirty devices.

A Survey on Complementary-Coded MIMO CDMA Wireless Communications

In this paper, we present a comprehensive survey on complementary code (CC)-based multiple-input multiple-output (MIMO) code-division multiple access (CDMA) for futuristic wireless communications. This paper starts with the construction of CCs and then proceeds to describe the design of CC-based CDMA and MIMO wireless communication systems. Complementary-coded chip-level space–time coding offers a unique paradigm to implement multiuser MIMO systems, opening up a new dimension to combine multiple-access and multiple-antenna techniques in a unified platform for a possible system design optimization of a wireless communication system in the future. In this paper, we will also discuss various potential research topics and technical challenges that need to be tackled before a complementary-coded MIMO CDMA system can be implemented in practical wireless applications.

Power-Controlled Multicarrier and Multiuser Detection Techniques in Wireless CDMA Systems

This paper describes power-controlled multi carrier and multiuser detection techniques for Code Division Multiple Access (CDMA) systems. In conventional CDMA systems, a RAKE receiver is employed to overcome wireless channel effect due to frequency selective characteristics of wireless CDMA systems. Alternatively, multi carrier technique can also be used to overcome the effect of frequency selective channel. Conventional CDMA systems also employ single-user detection scheemes, in that interference between users, called the multiple access interference (MAI), is considered as interference which contributes to the statistics of detection variables affecting the quality of detection. Now, multiuser detection method is proposed to mitigate the inter user interference in CDMA systems. In multiuser detections, the MAI component can be eliminated or cancelled by the use of all user’s spreading code in the system to be available to each user. Another technique that is commonly employed in CDMA system is power control, to mitigate the effects of near-far and fading channel fluctuations. In this study, the basic concept of multi carrier and multiuser detection technique is described in a simple model and the performance for various number of users is simulated and evaluated. The performance of power-controlled multi-carrier and multiuser detection technique is then evaluated and compared with that of the singleuser detection to show a significant improvement.

Efficient pre‐equalisation strategies for the downlink of a multi‐carrier code division multiple‐access wireless network

In this study, the problem of optimal synthesis of pre-equalisation factors for a multi-carrier code division multiple-access wireless network is studied under different quality of service (QoS) restrictions and performance objectives. The downlink is particularly addressed, where the QoS is evaluated by the signal-to-interference-noise ratio (SINR) after signal detection by matched filtering. First, the minimum energy formulation under inequality QoS constraints is analysed, and it was concluded that the optimal performance is always achieved at the lower bounds. Next, the minimisation of the peak magnitude of the pre-equalisation factors was addressed by an optimal synthesis scheme through the infinity norm, where a linear programming strategy is proposed by using an upper bound. Finally, by combining the minimum energy and minimum peak strategies, the minimisation of an upper bound on the peak-to-average-power ratio (PAPR) is suggested, which can be solved through quadratic programming by incorporating the QoS constraints. The new synthesis schemes take into account two important transmitter-based properties: peak magnitude and PAPR. These ideas were extensively validated in simulation, where the synthesis schemes were compared by Monte Carlo tests at different load and noise levels, and objective SINRs.

Motion–Related Resource Allocation in Dynamic Wireless Visual Sensor Network Environments

This paper investigates quality-driven cross-layer optimization for resource allocation in direct sequence code division multiple access wireless visual sensor networks. We consider a single-hop network topology, where each sensor transmits directly to a centralized control unit (CCU) that manages the available network resources. Our aim is to enable the CCU to jointly allocate the transmission power and source-channel coding rates for each node, under four different quality-driven criteria that take into consideration the varying motion characteristics of each recorded video. For this purpose, we studied two approaches with a different tradeoff of quality and complexity. The first one allocates the resources individually for each sensor, whereas the second clusters them according to the recorded level of motion. In order to address the dynamic nature of the recorded scenery and re-allocate the resources whenever it is dictated by the changes in the amount of motion in the scenery, we propose a mechanism based on the particle swarm optimization algorithm, combined with two restarting schemes that either exploit the previously determined resource allocation or conduct a rough estimation of it. Experimental simulations demonstrate the efficiency of the proposed approaches.

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.

On spectrum sensing in cognitive radio CDMA networks with beamforming

In this paper, the performance of cognitive radio (CR) code division multiple access (CDMA) networks is analyzed in the presence of receive beamforming at the base stations (BSs). More precisely, we analyze, through simulations, the performance achievable by a CR user, with and without spectrum sensing, in a three-cell scenario. Uplink communications are considered. Three different schemes for spectrum sensing with beamforming are presented, together with a scheme without spectrum sensing. CR users belong to a cognitive radio network (CRN) which is coexisting with a primary radio network (PRN). Both the CRN and the PRN are CDMA based. The CRN is assumed to utilize beamforming for its CR users. Soft hand-off (HO) and power control are considered in both the CRN and the PRN. The impact of beamforming on the system performance is analyzed, considering various metrics. In particular, we evaluate the performance of the proposed systems in terms of outage probability, blocking probability, and average data rate of CR users. The results obtained clearly indicate that significant performance improvements can be obtained by CR users with the help of beamforming. The impact of several system parameters on the performance of the three considered spectrum sensing schemes with beamforming is analyzed. Our results, in terms of probability of outage, show that the relative improvement brought by the use of beamforming is higher in the absence of spectrum sensing (reduction of 80%) than in the presence of spectrum sensing (reduction of 42%).

Optimal pre‐equalisation for wireless multi‐carrier code division multiple access systems under quality of service requirements

This work addresses an optimal pre-equalisation scheme to provide power and phase compensation in multi-carrier code division multiple access wireless systems under quality of service (QoS) restrictions. Two assignation schemes are studied: independent and uniform pre-equalised transmission (IPT and UPT) per subcarrier. First, the QoS was quantified in terms of the signal-to-interference noise ratio (SINR) after using a linear detector in the receiver. The SINR expressions for IPT and UPT were explicitly derived, to highlight their dependence on the pre-equalisation factors. These relations are exploited to derive analytical procedures to obtain the required pre-equalisation factors that satisfy an objective SINR per active user. The author's proposal for IPT achieves the lowest power while requiring a simple detector independent of the channel state information (CSI). For IPT, two minimum norm solutions are derived by translating the SINR restrictions into linear equations: one based on spectral factorisation, and a second one based on a simultaneous zero-forcing effect plus an energy scaling. On the other hand, for UPT, multi-user detectors like zero-forcing (ZF) and minimum-mean-square error (MMSE) have to be employed at the receiver to achieve a solution to the QoS requirements. In the numerical evaluations, IPT attained roughly a 2.5–3% reduction in the overall transmission power compared to UPT with ZF and MMSE by varying the objective SINR and noise variance. Although this reduction is further expanded as the number of active users increases, achieving a reduction in transmission power larger than 50% for a fully-loaded system.

Cognitive radio CDMA networking with spectrum sensing

SUMMARYIn this paper, the performance of cognitive radio (CR) code division multiple access (CDMA) systems is analyzed. More precisely, CR users belong to a cognitive radio network (CRN), which coexists with a primary radio network (PRN). Both CRN and PRN are CDMA‐based, with colocated base stations. Soft hand off and power control are considered in both the CRN and the PRN. Upon the development of an accurate simulator for a representative three‐cell cellular scenario, we evaluate the performance of the proposed CR system in terms of outage probability, blocking probability and average data rate of secondary users. Three different spectrum sensing techniques are. Two new schemes, based on interference limit, are proposed and compared with an existing adaptive spectrum sensing scheme. Spectrum activity measurements and spectrum sharing decisions have been considered for evaluating the performance of the three schemes. The paper proposes a new CR‐CDMA networking model and a simulation testbed for evaluating performances of secondary users and primary users in terms of outage, blocking, BER and average data rate in the presence of soft hand‐off and power control. For comparison purposes, the analysis in the absence of spectrum sensing is also investigated.Copyright © 2012 John Wiley & Sons, Ltd.

A Fuzzy Logic Based Power Control for Wideband Code Division Multiple Access Wireless Networks

Problem statement: Resource management is one of the most important engineering issues in 3G systems where multiple traffic classes are supported each being characterized by its required Quality of Service (QoS) parameters. Call Admission Control (CAC) is one of the resource management functions, which regulates network access to ensure QoS provisioning. Efficient CAC is necessary for the QoS provisioning in WCDMA environment. The effective functioning of WCDMA systems is influenced by the power control utility. Approach: In this study, we propose to design a fuzzy logic based power control for Wideband Code Division Multiple Access Wireless Networks. This proposed technique is aimed at multiple services like voice, video and data for multiclass users. The fuzzy logic technique is used to estimate the optimal admissible users group inclusive of optimum transmitting power level. This technique reduces the interference level and call rejection rate. Results: By simulation results, we demonstrate that the proposed technique achieve reduced energy consumption for a cell with increased throughput. Conclusion: The proposed technique minimizes the power consumption and call rejection rate.

Efficient and Distributed SINR-Based Joint Resource Allocation and Base Station Assignment in Wireless CDMA Networks

We formulate the resource allocation problem for the uplink in code division multiple access (CDMA) networks using a game theoretic framework, propose an efficient and distributed algorithm for a joint rate and power allocation, and show that the proposed algorithm converges to the unique Nash equilibrium (NE) of the game. Our choice for the utility function enables each user to adapt its transmit power and throughput to its channel. Due to users' selfish behavior, the output of the game (its NE) may not be a desirable one. To avoid such cases, we use pricing to control each user's behavior, and analytically show that similar to the no-pricing case, our pricing-based algorithm converges to the unique NE of the game, at which, each user achieves its target signal-to-interference-plus-noise ratio (SINR). We also extend our distributed resource allocation scheme to multi-cell environments for base station assignment. Simulation results confirm that our algorithm is computationally efficient and its signalling overhead is low. In particular, we will show that in addition to its ability to attain the required QoS of users, our scheme achieves better fairness in allocating resources and can significantly reduce transmit power as compared to existing schemes.

Link layer solutions for supporting real‐time traffic over CDMA wireless mesh networks

AbstractWith recent advances in the development of wireless communication networks, wireless mesh networks (WMNs) have been receiving considerable research interests in recent years. The need to support integrated services and ensure quality of service (QoS) satisfaction for various applications is one of the fundamental challenges for successful WMN deployment. In order to provide differentiated services, medium access control (MAC) should have priority management at the link layer. In code division multiple access (CDMA)‐based WMNs, the interference phenomenon and simultaneous transmissions must be considered. We propose two priority schemes for MAC in a distributed CDMA‐based WMN, taking into account interference, multimedia services, QoS requirements, and simultaneous transmissions. The first priority scheme is within a node. Each node has an independent queue for each traffic class. According to QoS requirements, the queue that should be served first is determined. The second priority scheme is among neighbor nodes. It is proposed for multiple simultaneous transmissions in the CDMA network. This scheme gives a larger chance of correct transmission to high priority traffic than low priority traffic. In addition, we propose to use adaptive spreading gain and a frame structure to achieve high resource utilization. Simulation results demonstrate that the proposed schemes can achieve effective QoS guarantee. Copyright © 2009 John Wiley & Sons, Ltd.

Emergency Handling Guides in a Wireless Sensor Network and Code Division Multiple Access Technology Based Mobile Healthcare System

Emergency Handling Guides in a Wireless Sensor Network and Code Division Multiple Access Technology Based Mobile Healthcare System

Compact integrated monopole antenna with CPW-fed meander resonators

A monopole antenna integrated with various coplanar waveguide (CPW)-fed meander resonators is presented. A CPW-fed meander resonator combined with a folded one is integrated into a single monopole to produce a multiband antenna in the applications of global system for mobile communication (GSM), global positioning system, personal communication systems and wireless code division multiple access (WCDMA) services. The antenna has exhibited impedance bandwidths from 50 MHz at GSM to 370 MHz at WCDMA less than −10 dB of S11. The antenna gains are −5.8, −3.8, +0.6 dBi at 880, 1570, 2100 MHz, respectively.

Transmitter Waveform and Widely Linear Receiver Design: Noncooperative Games for Wireless Multiple-Access Networks

The issue of noncooperative transceiver optimization in the uplink of a multiuser wireless code division multiple access data network with widely linear detection at the receiver is considered. While previous work in this area has focused on a simple real signal model, in this paper, a baseband complex representation of the data is used so as to properly take into account the I and Q components of the received signal. For the case in which the received signal is improper, a widely linear reception structure, processing separately the data and their complex conjugates, is considered. Several noncooperative resource allocation games are considered for this new scenario, and the performance gains granted by the use of widely linear detection are assessed through theoretical analysis. Numerical results confirm the validity of the theoretical findings and show that exploiting the improper nature of the data in noncooperative resource allocation brings remarkable performance improvements in multiuser wireless systems.