Wideband CDMA Systems Research Articles

Outage Throughput Capacity of Hybrid Wireless Networks Over Fading Channels

How much information can be transported, i.e., the transmission rate, is a subject of great interest in hybrid wireless networks. The main focus of this paper is the effect of channel fading in hybrid wireless network, in which a wired network of base stations is deployed to support long-range communications between wireless nodes. Two types of transmission mode in hybrid wireless network, i.e., intra-cell mode and infrastructure mode, are considered. To effectively overcome fading impairment, optimal multiple access technique is applied, allowing opportunistic sources to transmit concurrently with the scheduled source. Those different sources, much like in wideband CDMA system, share the entire bandwidth. A successive interference cancellation (SIC) strategy is then introduced at receiver side to limit the intra-cell interference and achieve the maximum capacity. Meanwhile, frequency reuse scheme is employed to minimize the inter-cell interference. Since the outage capacity over different fading channels will exhibit different asymptotic behaviors, in this paper we examine the Rayleigh, Rician and Nakagami-m models, which are the most commonly used fading models. Close-form solutions for outage throughput capacity at high signal-to-noise-plus-interference ratio (SNIR) are derived. It is showed that, with opportunistic sources, the intra-cell mode effectively combats fading as wireless nodes increases; however, the infrastructure mode is bottlenecked by the downlink transmission since base station is the only transmitter in the cell during the downlink phase. The theoretical bounds obtained and proofs are instrumental to the future network modeling and design.

Space-time diversity signal processing employed by W-CDMA systems

Transmit diversity under transmission of signals from the base station to mobile station using the code-division multiple-access (CDMA) system allows us obtaining the performance gains close to the mobile station receiver diversity without complexity of the mobile station receiver antenna array. The multipath diversity can be achieved using the pre-RAKE precoding at the transmitter that could be employed and there is no need to install the RAKE receiver at the mobile station. We investigate several transmitter diversity techniques employed by wideband CDMA (W-CDMA) systems. We also study a possibility to combine transmitter diversity and precoding that achieves the gain of maximum ratio combining of all space and frequency diversity branches jointly with long-term prediction algorithm. It was demonstrated that the performance of the space-time pre-RAKE method approaches the performance of the maximum ratio combining for all space and frequency diversity branches. It is shown that all closed loop methods depend on the long range prediction to approximate the ideal performance in the fast fading environment.

Postmatching Doherty Power Amplifier With Extended Back-Off Range Based on Self-Generated Harmonic Injection

In this paper, an asymmetric drain biased postmatching Doherty power amplifier (DPA) using harmonic injection is proposed for further back-off extension. The injected harmonic components are generated by the two active devices. Aided by the proposed harmonic injection network, drain waveform amplitude modulation for both devices can be achieved at saturation, which results in enhanced saturated power for both carrier and peaking devices, while carrier back-off power remains unchanged. As a consequence, the back-off region is extended. Moreover, the power utilization factor of the asymmetric drain biased DPA is also improved. A DPA for wideband code-division multiple access systems was designed and fabricated based on commercially available gallium nitride HEMT (Cree CGH 40010F) devices to validate the proposed technique. Measured results of the proposed DPA demonstrated that operation at 10-dB back off is possible between 1.6 and 1.9 GHz, with efficiency better than 46%.

A Comparative Study of InGaP/GaAs Collector-Up HBTs for High-Reliability Small-Scale PA Applications

In this paper, the characteristics of InGaP/GaAs collector-up (C-up) pnp and npn heterojunction bipolar transistors (HBTs) with the graded InGaAs base and the nonuniform doped collector are demonstrated, and the performances as well as the reliability of the novel HBTs have been compared with the conventional InGaP/GaAs HBTs with various collector structures and thermal schemes. Compared to conventional HBTs, the studied C-up HBTs exhibited better current-driving capability, higher RF efficiency, and improved long-term reliability. Note that the pnp device displayed greater thermal stability enhancements, which are distinct and reproducible, than the npn device. The favorable data of the pnp C-up HBT could be attributed to higher electron mobility, resulting in low base resistance and higher emitter resistance improving the thermal stability. The comparison results, based on pragmatic observations from the C-up HBTs without relatively large heat-dissipation configurations, should be very useful for the reliable and the cost-effective design as small-scale power amplifiers in the wideband CDMA system.

Adaptive Blind CDMA Receivers Based on ICA Filtered Structures

Code division multiple access (CDMA) is a channel access method adopted by various radio technologies worldwide. In particular, CDMA is used as an access method in many mobile standards such as CDMA2000 and WCDMA. We address the problem of blind multiuser equalization in the wideband CDMA systems in the noisy multipath propagation environment. Herein, we propose three new blind receiver schemes based on variations of independent component analysis within several filtering structures. These adaptive blind CDMA receivers do not require knowledge of the propagation parameters or spreading code sequences of the users--they primarily exploit the natural assumption of statistical independence among the symbol signals. We also develop three semi-blind adaptive detectors by incorporating new adaptive methods into the standard Rake receiver structure. Extensive comparative case studies based on bit error rate performance are carried out as a function of (i) the number of users, (ii) the number of symbols per user, and (iii) the signal-to-noise ratio. The conventional detectors include the baseline linear minimum mean squared error detector. The results show that the proposed methods outperform other detectors in estimating the symbol signals from the received mixed CDMA signals. Moreover, the new blind detectors mitigate the multiaccess interference in CDMA.

Design of Effective Receiver in Hospital Wireless Network Using Turbo Code

In this paper, we considered the received signal of the wideband CDMA systems using turbo code in the multipath channel environments, and analyze the performance of the system. This study is to analyze the performance for the variable system bandwidth according to the number of branches of rake receiver by passing the received signal through a rake receiver with a turbo code in Rayleigh fading channel environments. For the design of receiver in wideband CDMA systems, we presented the efficient parameters for the number of iterative decoding and the number of branches of rake receiver.

Comparative Analysis of the BER Performance of WCDMA Using Different Spreading Code Generator

In recent times the Wideband Code Division Multiple Access (WCDMA) is one of the most used. This is because it provides higher data rates in mobile communication and it provides the users with many multimedia applications such as video streams and high resolution pictures. In other to enhance the performance of the technology a suitable modulation technique and error correcting technique is implemented.in this paper I have done performance analysis of different spread spectrum sequence with the Quadrature Phase Shift Keying (QPSK) modulation technique when the system is subjected to multipath Rayleigh fading and Additive White Gaussian Noise (AWGN). The research has been done using MATLAB for simulation and evaluation of the bit error rate for the WCDMA system models.

Research on the Suppression of GMR Interference in WCDMA Satellite System

As the satellite and space spectrum resource are constrained, most time, the WCDMA (Wideband Code Division Multiple Access) satellite system and the GMR (GEO-mobile radio interface) system have to transport information in the same frequency band. In this case the main interference is the narrowband interference which comes from the GMR system. The paper researched the method of the narrowband interference suppression in the WCDMA satellite system. Furthermore, because the WCDMA system also contains a multi-access interference, the paper proposed a code-aided interference suppression technology, which can suppress both the MAI (Multiple Address Interference) and NBI (Narrow Band Interference), into the WCDMA satellite system to eliminate the GMR interference. Theoretic analysis and system simulation show that, the GMR signal interference can effectively be inhibited with a more mature and better MMSE (Minimum Mean Square Error) and ZF (Zero-force) code-aided technology, the co-channel transmission performance of the WCDMA systems can be protected well.

Interference Management in Lte Downlink Networks

Two major challenges for evolving LTE (Long Term Evolution) networks are to achieve enhanced system capacity and cell coverage compared with WCDMA (Wideband Code Division Multiple Access) system. Effective utilization of radio resources as well as dense spectrum reuse are at the core to attain these targets. However, dense frequency reuse may increase inter-cell interference, which in turn severely limits the capacity of users in the system. Inter-cell interference can restrict overall system performance in terms of throughput and spectral efficiency, especially for the users located at the cell edge area. Hence, careful management of inter-cell interferences becomes crucial to improve LTE system performance. In this paper, interference mitigation schemes for LTE downlink networks are investigated.

PN codes versus chaotic codes: Performance comparison in a Gaussian approximated wideband CDMA system over Weibull fading channels

The performance of a Wideband Code Division Multiple Access (W-CDMA) system using Pseudo Noise (PN) codes and chaotic codes in the presence of a Weibull fading channel is studied in this paper. The W-CDMA system modeled using Gaussian Approximation is analyzed on a Weibull fading channel which fades the amplitude of the transmitted signal randomly according to the Weibull distribution. Closed-form expressions for Bit Error Rate (BER) are derived and expressed in terms of Meijer׳s-G function. Performance measures in terms of BER are plotted versus Signal-to-Noise Ratio (SNR) for various values of fading severity, average fading power, and channel memory using PN and chaotic codes. Performance comparison between PN codes and chaotic codes are also analyzed.

A New Technique for Capacity Enhancement in WCDMA Uplink with Synchronization

Cellular phones have experienced an exponential growth worldwide over the last decade with more than one billion cell phone users projected in the near future. On the other hand, service providers must support new technology and infrastructure in order to fulfill their customers' requirements. These requirements include the capacity of network. The large expectances created for Wide Band Code Division Multiple Access (WCDMA) are based on its flexibility for multimedia capabilities and the high capacity it will provide. However, the demanded traffic grows rapidly, and new capacity enhancements are required in order to satisfy the future needs. Uplink synchronization can be a method to reduce the multiple access interference (MAI) by exploiting the uplink orthogonality and thereby increase the capacity of WCDMA systems. In this paper, the performance of uplink synchronous WCDMA has been assessed in terms of the capacity gain relative to an equivalent asynchronous system. The capacity gain has been evaluated theoretically and by means of MATLAB simulations for scenarios with different orthogonality factors. Orthogonality of codes is directly dependent on synchronization which in turn increases the capacity gain. In this study, it is proposed that synchronization plays an important role in enhancing the capacity gain of uplink WCDMA system. Also, an alternative solution is proposed to increase the capacity in the uplink of a synchronized WCDMA system by introducing variable modulation.

Theoretical analysis and simulation of a code division multiple access system (CDMA) for secure signal transmission in wideband channels

Theoretical analysis and simulation of a code division multiple access system (CDMA) for secure signal transmission in wideband channels

Using hierarchical data mining to characterize performance of wireless system configurations

This paper presents a statistical framework for assessing wireless systems performance using hierarchical data mining techniques. We consider WCDMA (wideband code division multiple access) systems with two-branch STTD (space time transmit diversity) and 1/2 rate convolutional coding (forward error correction codes). Monte Carlo simulation estimates the bit error probability (BEP) of the system across a wide range of signal-to-noise ratios (SNRs). A performance database of simulation runs is collected over a targeted space of system configurations. This database is then mined to obtain regions of the configuration space that exhibit acceptable average performance. The shape of the mined regions illustrates the joint influence of configuration parameters on system performance. The role of data mining in this application is to provide explainable and statistically valid design conclusions. The research issue is to define statistically meaningful aggregation of data in a manner that permits efficient and effective data mining algorithms. We achieve a good compromise between these goals and help establish the applicability of data mining for characterizing wireless systems performance.

Design of effective Receiver in Wireless Network using turbo code

In this paper, we considered the received signal of the wideband CDMA systems using turbo code in the multipath channel environments, and analyze the performance of the system. This study is to analyze the performance for the variable system bandwidth according to the number of branches of rake receiver by passing the received signal through a rake receiver with a turbo code in Rayleigh fading channel environments. For the design of receiver in wideband CDMA systems, we presented the efficient parameters for the number of iterative decoding and the number of branches of rake receiver.

Low cost method for location service in the WCDMA system

A new and low cost method for a location service (LCS) in the Wideband Code Division Multiple Access (WCDMA) system is outlined. This method, which is called TDOA+RTT, enables calculation of the geographical position of a mobile station (MS) without knowledge of relative time differences (RTDs) between base stations (BSs). The TDOA+RTT method is based on the measurement of round trip times (RTTs) between the MS and the serving BS, and the solution of a nonlinear system of equations with six variables. The elimination of the RTD parameters significantly simplifies the localisation process in 3G (3rd Generation) real-life cellular networks. The paper concentrates on solving the nonlinear system of equations with six variables. In this context, a new algorithm for solving nonlinear equations is proposed.

Effect of Group Delay in WCDMA based Pulse Shaping Filter using Discrete-Time Eye Scope

The application of signal processing techniques to wireless communications is an emerging area that has recently achieved dramatic improvement in results and holds the potential for even greater results in the future as an increasing number of researchers from the signal processing and communication areas participate in this expanding field. Today, wireless multimedia is moving from vision to reality. Service providers are deploying third generation (3G) wireless base stations that enable the user to surf the web, check email, conduct videoconferences, and access a wide range of new services from their wireless devices. Underlying 3G innovations, Wideband Code Division Multiple Access (WCDMA) technology is pushing the expectations of wireless networks far beyond the previous limitations of 1G and 2G. To deliver on the promise of 3G, WCDMA system must handle the greater capacity, higher data rates, and support multimedia standards, while at the same time reduces the size, cost and the power consumption. The large expectations through WCDMA are based on its flexibility for multimedia capabilities and the high capacity. However, the demanded traffic grows rapidly and new capacity enhancements are required in order to satisfy the future needs. The present paper deals with Effect of group delay in WCDMA based pulse shaping filter using discrete-time eye scope.

Performance Analysis of WCDMA using Different Spreading Codes

Recently, Wideband Code Division Multiple Access (WCDMA) technology has emerged as the most widely adopted third generation (3G) air interface. Conventionally, the Pseudo random Noise (PN) sequence and gold code sequence are used as spreading codes in WCDMA. However enhanced performance using these sequences is achieved by increasing the length of the sequence. In this paper, Bit Error Rate (BER) performance of WCDMA is determined and analyzed by considering various spreading codes of affordable spreading factor in the presence of Rayleigh channel with AWGN. The performance of WCDMA system using Walsh Code is also compared with other spreading sequences such as PN and gold sequence for various Spreading Factors (SFs). However, simulation results show that the BER of WCDMA can be improved drastically by using Walsh code.

Real Time Implementation and Performance Evaluation of WCDMA System over AWGN Channel on TMS320C6713DSK

Wideband Code Division Multiple Access (WCDMA) technology has emerged as the most widely adopted air interface technology for third generation Universal Mobile Telecommunication System (UMTS) network architecture. This paper presents a real time implementation of WCDMA system on TMS320C6713DSK. A comparison between the bit error rate (BER) performance of the proposed WCDMA system on TMS320C6713DSK and the simulated WCDMA system on Simulink is presented to validate proposed implementation. Synthesis reports show that the system fits real time applications.

Subspace based downlink channel estimation for W-CDMA systems

Wideband code division multiple access (W-CDMA) is a third generation (3G) mobile wireless technology that promises much higher data speeds for mobile and portable wireless devices than those which are commonly offered in todayʼs market. In W-CDMA systems transmitting over multipath channels, both Inter Symbol Interference (ISI) as a result of Inter Chip Interference (ICI) and Multiple Access Interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired usersʼ signature waveform. Torlak and Xu (1997) [1] proposed a subspace based channel estimation algorithm for Asynchronous CDMA (A-CDMA) systems to estimate the multiple usersʼ symbols. In our work, we study a similar subspace based channel estimation scheme for downlink W-CDMA systems that provide estimates of the subchannels of multiple users by exploiting the structural information of the data output. In particular, we show that the subspace of the (data + noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellation. Performance measures like Bit Error Rate (BER) and Root Mean Square Error (RMSE) are plotted for Rayleigh and Rician fading channels.

Performance analysis of downlink W-CDMA systems in Weibull, Lognormal and Nakagami fading channels

Wideband Code Division Multiple Access (W-CDMA) is a third generation (3G) mobile wireless technology that promises much higher data speeds to mobile and portable wireless devices than those which are commonly offered in todayʼs market. In W-CDMA systems transmitting over multipath channels, both Inter Symbol Interference (ISI) as a result of Inter Chip interference (ICI) and Multiple Access Interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired usersʼ signature waveform. Torlak and Xu proposed a blind estimation algorithm for Asynchronous CDMA (A-CDMA) systems to estimate the multiuser channels (Torlak and Xu, 1997 [1]). In our work, we study a similar blind channel estimation scheme for downlink W-CDMA systems that provides estimates of the multiuser channels by exploiting the structural information of the data output. In particular, we show that the subspace of the (data + noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellations. Performance measures like Bit Error Rate (BER) and Root Mean Square Error (RMSE) are plotted for the Weibull and Lognormal fading channels. Estimated signal constellations under the Weibull, Lognormal and Nakagami fading channels are also plotted.