WCDMA Downlink Research Articles

ANALYSIS OF DATA TRANSMISSION SCHEME FOR WIDE BAND CODE DIVISION MULTIPLE ACCESS WITH RAKE RECEIVER

Fifth generation systems are required to fulfill the objectives like compatibility, flexibility, high speed data rate and low cost. Universal Mobile Telecommunication System (UMTS) use WCDMA as the air interface for 4th generation mobile system. The performance of wireless communication system is often limited by the radio channel models. In urban areas, channel is modeled as Rayleigh fading channel. This channel causes multipath channels and other problems resulting degraded performance. Hence, channel estimation before receiver helps to receive the transmitted signal using rake receiver. Rake receiver is a conventional receiver for DS-CDMA system. In this, channel is estimated adaptively using LMS algorithm and performance of this algorithm is studied for various multipath channels and step sizes. Moreover, the channel introduces Inter Symbol Interference (ISI) and channel equalizers are used to compensate for the ISI. In this work, BER vs. SNR performance of Zero Forcing Equalizer (ZFE), Minimum Mean Square Error (MMSE) and MMSE- Decision Feedback Equalizer (MMSE-DFE) in WCDMA downlink system are compared with conventional rake receiver for various spread factors in Rayleigh multipath fading channel with Additive White Gaussian Noise.

VSS와 USRP를 이용한 WCDMA Downlink 음성채널 구현

VSS와 USRP를 이용한 WCDMA Downlink 음성채널 구현

A Simplified Transistor-Based Analog Predistorter for a GaN Power Amplifier

A simplified transistor-based analog predistorter (APD) is proposed and used to linearize a GaN power amplifier (PA). The proposed APD features simple circuit topology because no additional vector modulator is needed. To demonstrate the new methodology, a GaN power amplifier centered at 2.4 GHz using the proposed APD is implemented and tested. From the measurement results, the output 1-dB gain compression point of the GaN PA with the proposed APD is increased from 35.2 dBm to 38.9 dBm under CW signal, while the efficiency is increased by 8.5%. Two-tone test is also implemented, indicating more than 10 dB third order intermodulation distortions improvement over a wide range of output power levels. For a single-carrier downlink WCDMA signal at 2.4 GHz, the experimental results demonstrate an adjacent channel leakage power ratio reduction of 13 dB.

Energy-Efficient Planning Tool for WCDMA Heterogeneous Network Deployment

The population of powerful mobile network technologies has increased in recent years also focus has been shifting from second generation mobile to third generation technology. This higher access rates have led to increased energy consumption in base stations (BTS) and network densities have been constantly growing. This paper developed an energy efficient planning tool for analytical modeling of heterogeneous networks and observed the potential energy savings statistics when deploying heterogeneous networks. A model developed from wcdma downlink equation was used in determining the energy consumption per unit area of the network. The model was also used to observe how heterogeneous network deployment contributes to the total energy consumption of the network. The result was presented in three scenarios. The first scenario presented the daily energy consumption per square kilometer and it was observed that the energy consumption by the macrocell decreases when increasing the ratio of femtocells in the network. However, the introduction of femtocells to the network ordinarily does not gauranty decrease in energy consumption the scenario depends on the power budget of the femtocells as presented in second and third scenarios where power budget of 2 W and 5 W were used respectively. By introducing femtocell of low power budget into the network, the density of the network reduces therefore, bringing about reasonable reduction in the total power consumption of the network. To that end, this research developed software that helps to observe the total energy that could be saved when deploying heterogeneous networks.

Performance Analysis of Downlink W-CDMA Systems in Weibull and Lognormal Fading Channels Using Chaotic Codes

In this paper, a subspace based blind channel estimation scheme for downlink W-CDMA systems using chaotic codes under Weibull and Lognormal fading channel conditions is proposed and compared with W-CDMA system using PN codes. The algorithm provides estimates of multiuser channels by exploiting the structural information of the data output. The subspace of the (data + noise) matrix contains sufficient information for unique determination of channels and, hence, the signature waveforms and signal constellations. The proposed channel estimation algorithm is also implemented for multiuser--orthogonal frequency division multiplexing (OFDM) system. Performance measures like bit error rate (BER) and root mean square error (RMSE) are plotted for Weibull and Lognormal fading channels. Signal constellations under Weibull and Lognormal channels are also plotted. Analytical and Simulation results for BER and RMSE are compared for W-CDMA system using PN codes and chaotic codes. Simulation results show that, chaos-based W-CDMA outperforms the PN-based W-CDMA in terms BER and RMSE. Simulation results of multiuser-OFDM system shows that performance is further improved when compared to the W-CDMA system.

The Probability of Bit Error Due to the Co-existence Interference of PCS1900 and UMTS

An efficient network is critical to support the rapid growth in traffic on mobile networks, since current network PCS1900 (2G) cannot support such a huge demand. The objective of the third-generation (3G) UMTS (Universal Mobile Telecommunication System) of wireless communication is to provide high speed wireless communication to support multimedia, large data, and video. However, the co-existence of the two mobile radio systems (PCS1900 and UMTS) which share the same frequency band leads to a major issue. A serious issue of co-existence occurs when the downlink of the system is closer to the frequency bands of the concerned system. The PCS-1900 downlink band (1,930-1,990) and WCDMA (UMTS) uplink band (1,920-1,980) widely overlap, which causes interference between UMTS mobile unit and PCS-1900 base station. Therefore the objectives of this paper is to study the effect from PCS 1900 base station interference on UMTS mobile unit performance in terms of the probability of bit error by developing the Probability of bit error equation of DSS-QPSK from the existing Probability of bit error equation. This paper also evaluates the degradation of UMTS mobile unit performance in terms of probability of bit error when the system is interfered by PCS1900 base station.

Channel Equalization of WCDMA Downlink System Using Finite Length MMSE-DFE

The performance of WCDMA system deteriorates in the presence of multipath fading environment. Fading destroys the orthogonality and is responsible for multiple access interference (MAI). Though conventional rake receiver provides reasonable performance in the WCDMA downlink system due to path diversity, but it does not restores the orthogonality. Linear equalizer restores orthogonality and suppresses MAI, but it is not efficient, since its performance depends on the spectral characteristics of the channel. To overcome this, Minimum Mean Square Error- Decision Feedback Equalizer (MMSE-DFE) with a linear, anticausal feedforward filter, causal feedback filter and simple detector is proposed in this paper. The filter taps of finite length DFE is derived using the cholesky factorization theory, capable of suppressing noise, Intersymbol Interference (ISI) and MAI. This paper describes the WCDMA downlink system using finite length MMSE-DFE and takes into consideration the effects of interference which includes additive white gaussian noise, multipath fading, ISI and MAI. Furthermore, the performance is compared with conventional rake receiver and MMSE and the simulation results are shown. Keywords - MMSE, MMSE-DFE, rake receiver, WCDMA

Performance Analysis of Subspace Based Downlink Channel Estimation for W-CDMA Systems Using Chaotic Codes

This paper presents blind channel estimation for downlink W-CDMA system that employs chaotic codes and Walsh codes for spreading information bits of the multiple users. In a W-CDMA system, while transmitting over multipath channels, both intersymbol interference (ISI) as a result of Inter Chip Interference 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 users' signature waveform. Earlier work focused on a subspace based channel estimation algorithm for asynchronous CDMA systems to estimate the multiple users' symbols, where only AWGN channel was considered. In our work, we study a similar subspace-based signature waveform estimation algorithm for downlink W-CDMA systems, which use chaotic codes instead of pseudo random codes, that provide estimates of the multiuser channel by exploiting structural information of the data output at the base station. 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. We consider Rayleigh and Rician fading channel model to quantify the multipath channel effects. Performance measures like bit error rate and root mean square error are plotted for both chaotic codes and Walsh codes under Rayleigh and Rician fading channels.

Modeling and Digital Predistortion of Class-D Outphasing RF Power Amplifiers

This paper presents a direct model structure for describing class-D outphasing power amplifiers (PAs) and a method for digitally predistorting these amplifiers. The direct model structure is based on modeling differences in gain and delay, nonlinear interactions between the two paths, and differences in the amplifier behavior. The digital predistortion method is designed to operate only on the input signals' phases, to correct for both amplitude and phase mismatches. This eliminates the need for additional voltage supplies to compensate for gain mismatch. Model and predistortion performance are evaluated on a 32-dBm peak-output-power class-D outphasing PA in CMOS with on-chip transformers. The excitation signal is a 5-MHz downlink WCDMA signal with peak-to-average power ratio of 9.5 dB. Using the proposed digital predistorter, the 5-MHz adjacent channel leakage power ratio (ACLR) was improved by 13.5 dB, from -32.1 to -45.6 dBc. The 10-MHz ACLR was improved by 6.4 dB, from -44.3 to -50.7 dBc, making the amplifier pass the 3GPP ACLR requirements.

Class-Based Fair Code Allocation with Delay Guarantees for OVSF-CDMA and VSF-OFCDM in Next-Generation Cellular Networks

This paper presents a novel class-based fair code allocation (CFCA) protocol to support delay and rate guarantees for real-time flows and to provide fairness for non-real-time flows on the downlink of WCDMA- and VSF-OFCDM-based cellular networks. CFCA not only assigns bandwidth dynamically to different flows but also determines those appropriate OVSF codes whose assignment results in the minimum overhead for code reassignments during dynamic bandwidth allocation. To reduce the overhead of code reassignments, this paper introduces the concept of affinity-mate and enables bandwidth allocation and code placement to interact with each other. A new performance metric, called class-based rate degradation ratio (CRD), is introduced to ensure fairness in providing rate and delay guarantees by measuring the rate degradations of flows based on their traffic types. The simulation results show that code reassignment overhead can be reduced by up to 60% for high network loads. For low network loads, fairness is achieved fully, but for high network loads the average rate requirement is met fairly for 95% of the flows.

Study of Rate Assignment on the Downlink of WCDMA

In the paper, firstly we can know the power control is one of the most important technologies of radio resource management in WCDMA system, secondly the base principle of the outer loop power control is analyzed theoretically, and at the same time, both the utility function-based power control algorithm and the power control algorithm with the base station assignment are briefly discussed. The two algorithms are connected according to their advantages and disadvantages, a rate assignment algorithm on the downlink for the data transmission is proposed. The optimization goal of the resource allocation strategy is choosing appropriate utility function. The utility function reflects a flexible tradeoff between total system throughput and fairness. The power is distributed through the control module and the scheduling module. The simulations show the performance of the algorithm.

GaN HEMT PA with over 84% power added efficiency

Described are the design procedure and measured performance of a PA targeted for the W-CDMA downlink band exhibiting over 84% PAE at 2.14 GHz. The PA is designed with an uncharacterised GaN HEMT. A measurement-based design approach is used to optimise the source and load impedance at the fundamental frequency with class- F−1 harmonic terminations enforced. S-parameters extracted from a full-wave EM model characterising the impedance transformation from the virtual drain of the GaN HEMT to an output matching circuit are used to design class-F−1 second- and third-harmonic terminations. The highest efficiency for the final PA occurred 10 MHz off the design frequency, exhibiting 84.9% PAE, 8.2 W output power and 18.4 dB of gain at 2.15 GHz.

Scheduling performance in downlink WCDMA networks with AMC and fast cell selection

This paper is concerned with the analysis of scheduling performance in downlink WCDMA networks that employ adaptive modulation and coding (AMC) and fast cell selection (FCS). The scheduling schemes investigated include (i) the round robin (RR) scheme, (ii) the maximum carrier-to-interference ratio (C/I) scheme, (iii) the simplified proportional fair (PF) scheme, and (iv) the conventional PF scheme. The channel model includes large-scale signal attenuation and small-scale fading. By using a form analogous to Shannon's channel capacity formula, a logarithmic relationship between the instantaneous data rate and the C/I with AMC is first established. Using the so-called Poisson scheme in which the probabilities of the occurrence of the events in Bernoulli trials depend on the trial index, FCS implementation is then examined in detail. Finally, a complete set of analytical expressions on the average system throughput, the peak data rate and the fairness for the abovementioned scheduling schemes are derived.

Minimizing the Call Setup Delay Caused by Reconfigurations of Dedicated Channels at the Downlink of WCDMA

Reconfigurations of downlink dedicated channels are often necessary during call setup to eliminate code blocking encountered in 3G WCDMA systems. These reconfigurations increase not only the signaling overhead, but also the setup delay of the incoming call and may yield prohibitive delays if performed inefficiently. In this paper, we introduce a reconfiguration scheme which manages to minimize this additional setup delay with a tolerable increase in signaling overhead.

Combined CAC Scheme Supporting Multiple Services with 3G W-CDMA DownLink Power Allocation

The downlink call admission control (CAC) scheme we call the combined CAC scheme is proposed to improve the call blocking for the 3rd (3G) generation W-CDMA system. The blocking probability of attempted calls would increase if a large number of users tries to place calls in a hot spot area. In this situation, the proposed scheme can mitigate the degradation of the GoS (grade of service) of multiple services by using the available radio channels of the neighboring cells and enhance the channel capacity by about 20% for the blocking probability of 1% under the given example condition of voice service.

Analysis of throughput and fairness with downlink scheduling in WCDMA networks

This paper is concerned with the throughput and fairness analysis in a downlink WCDMA network. The channel model is assumed to include path loss, lognormal shadowing and fast Rayleigh fading. The scheduling schemes investigated are (i) the round robin scheme, (ii) the maximum carrier-to-interference ratio (C/I) scheme, (iii) the proportional fair scheme, (iv) the maximum instantaneous signal scheme, and (v) the fading-based signal power scheme. By using an approximation of the probability density function of C/I, throughput and fairness expressions are derived, and a performance comparison among the five scheduling schemes is given. The results indicate that throughput and fairness performance of each scheduling scheme depends on mobile users' location. Tn general, the round robin scheme has the worst throughput performance as compared to the other four schemes. The proportional fair scheme and the fading-based signal power scheme can provide relatively better tradeoffs between the throughput and the fairness. The findings presented here are not only of fundamental theoretical value, but are also of practical interest to the designers of third-generation mobile communication systems based on WCDMA technology.

Capacity Analysis in Downlink WCDMA Systems Using Soft Handover Techniques With SIR-Based Power Control and Site Selection Diversity Transmission

This paper analyzes the downlink performance of a wideband code-division multiple-access system with site selection diversity transmission power control during soft handover (SHO) mode. Signal-to-interference ratio power control techniques are modeled and used in the simulations of this analysis. The study is focused on finding the optimum SHO margin in terms of maximum system capacity under energy-per-bit to noise spectral density ratio (Eb/N0 ) quality requirements. The results of this analysis show an increase in user capacity of about 15%-20% for optimum SHO margins of 5-5.5 dB. Nevertheless, the resources required (number of scrambling codes) by the base station increase faster than the number of active users in terms of SHO margin up to values of approximately 9.5 dB

Effect of the Power Ramping under Retransmission in an ARQ for the WCDMA Downlink in One Path Rayleigh Fading Channel

In this paper, we propose and analyze a scheme for wireless channels, which is the combination of an automatic repeat request (ARQ) scheme and power ramping. The power ramping is used for more reliable downlink data transmission. This technique gradually increases the transmission power at each retransmission attempt. Simulation results demonstrate that when the power step size is 0.5 dB, the average throughput gain may be as high as 2.3% to 5.4% with properly selected parameters.

Other-Cell-Interference Factor Distribution Model in Downlink WCDMA Systems

Interference performance is among the most important issues especially in WCDMA cellular networks planning coverage and capacity. F-factor has been introduced in previous works to model the interference in WCDMA downlink dimensioning process. In this paper, we establish its PDF expression assuming one interferer in the serving cell both with and without correlated shadowing effect. Uniform and non-uniform traffic situations are distinguished through the study of both uniform and non-uniform traffic load cases. Then, we generalize the expression for multiple interfering cell tiers. We show the impact of this evaluation on the design process in order to increase the capacity of a network.

Experimental optimization of the 2nd loop configuration for feedforward amplifiers in terms of their efficiency and linearity

In this paper, we report the results of the experimental optimization of the 2nd-loop configuration for feedforward amplifiers in terms of their efficiency and linearity. We consider two parameters in the 2nd-loop of a feedforward amplifier: (i) the size ratio between the main and error amplifiers and (ii) the coupling factor of the error signal coupler. Experiments are performed using a multicarrier down-link WCDMA signal under various configurations. The measured data, which are normalized with respect to the overall power capacity of the main and error amplifiers, show that, among the different 2nd-loop configurations, the best compromised efficiency (13.4%) at a given adjacent channel leakage ratio (ACLR) level (−50 dBc) is observed for a size ratio of around 3.0 and a coupling factor of around 7.2 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 617–621, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21425