Wideband Code-division Multiple-access Downlink Research Articles

WCDMA downlink capacity of cigar-shaped microcells for long tunnels

In this paper, the Wideband Code Division Multiple Access (WCDMA) downlink capacity and the interference statistics of long tunnel cigar-shaped microcells are analyzed. The hybrid model of propagation is used in the analysis where a model of 10 cigar-shaped microcells is used. The downlink capacity is given for different sector radio R, break point distance R b and propagation parameters (s and ?). It is found that the effect of changing the value of the propagation parameter s is very small. Also, it is noticed that, increasing the propagation parameter ? will increase the sector downlink. It is found that, the effect of changing the break point distance R b is quasi null. Finally it is noticed that the imperfect power control reduces the downlink capacity by 4 %.

Experimental verification for time advancement of negative group delay in RF electronic circuits

An experiment was performed on the signal cancellation loop that utilises a carrier wave (CW) and wideband code division multiple access (WCDMA) signals to show that negative group delays can be used to cancel out positive group delays. According to the closed loop measurements, a 30 dB signal cancellation for a CW signal and a WCDMA 4FA signal were obtained over a 30 MHz bandwidth at the WCDMA downlink band, with a fabricated two-stage planar negative group delay circuit.

WCDMA downlink capacity of cigar‐shaped microcells for underground metro service

AbstractIn this paper, the wideband code division multiple access (WCDMA) downlink capacity and the interference statistics of underground cigar‐shaped microcells utilised to serve users within metros are analysed. The hybrid model of propagation is used in the analysis where a model of eight cigar‐shaped microcells is used. The downlink capacity is given for different sector radio R, train length Ltrain, break point distance Rb and propagation parameters (s and γ). It is found that increasing the sector range up to 1250 m will increase the sector downlink capacity. Also, it is found that the effect of changing the value of the propagation parameter s is very small. It is noticed that increasing the train length Ltrain will increase the downlink capacity. Also, it is noticed that, increasing the propagation parameter γ will reduce the sector downlink. Finally, it is found that, the effect of changing the break point distance Rb is quasi‐null. Copyright © 2008 John Wiley & Sons, Ltd.

A hybrid equalizer/Rake receiver for the Wideband CDMA Downlink in large delay spread channels

Abstract. Signals transmitted over a multi-path propagation channel exhibit Inter-Path Interference (IPI) and fading. The receiver has to employ measures to mitigate these effects or it will incur severe performance degradation. A classic approach in Code Division Multiple Access (CDMA) communications is the Rake receiver. Alternatively, a Linear Minimum Mean Square Error (LMMSE) equalizer can further improve performance. This paper compares performance and computational complexity of these two algorithms. A hybrid solution will be introduced in order to decrease computational complexity while retaining most of the interference suppression capabilities of the LMMSE equalizer.

Differential quality-of-service provision in mobile networks

In the Third-Generation Partnership Proposal technical specification, the 3GPP Wideband Code Division Multiple Access standard will support data rates up to 2 Mbps with Orthogonal Variable Spreading Factor (OVSF) codes. The use of OVSF codes can provide variable data rates to flexibly support the applications with various Quality of Service (QoS) classes introduced by Universal Mobile Telecommunications System (UMTS). In tradition, bandwidth congestion rate can only represent the bandwidth occupied ratio, which may not be suitable for OVSF code tree Wide-band Code-Division Multiple Access (W-CDMA) system. In this paper, we propose a new bandwidth adaptation scheme and a novel parameter, Dense Ratio (DR), which efficiently represents a W-CDMA downlink status between data traffic sources. After simulations, our proposed bandwidth adaptation scheme can reduce the new call blocking probability and thus improve the system utilisation for W-CDMA systems.

WCDMA downlink capacity of cigar-shaped microcells using soft hand-over with SIR-based power control for over-ground train service

In this paper, the downlink sector capacity of a cigar-shaped microcells using wideband code-division multiple-access (WCDMA) with soft hand-over (SHO) mode is analyzed. The two-slope propagation loss with log-normal shadowing is used in the analysis where a model of eight cigar-shaped microcells is utilized to calculate the downlink sector capacity. The performance of the downlink is studied for different sector radii, standard deviations of the shadowing and propagation exponents. It is found that, for a sector range higher than 940 m, increasing the sector range will reduce the downlink sector capacity. Also it is found that increasing the value of the propagation parameters will reduce the downlink sector capacity. In many cases, the downlink sector capacity will be code limited since the theoretical downlink sector capacity is higher than the number of codes assigned to each sector. The high theoretical downlink sector capacity is due to the low value (0.06–0.1) of the WCDMA orthogonality factor of rural zone microcells.

A multipath interference cancellation technique for WCDMA downlink receivers

AbstractIn this paper, we present a simple interference cancellation technique for the downlink of wideband code‐division multiple‐access (WCDMA) systems in multipath environment. With the same knowledge required by a RAKE receiver, the present method acts as an equalizer and cancels the interfering multipath signals from the received signal to retrieve the orthogonality property of the received signal. The present receiver has a simple structure and it has significant performance gain against the RAKE receiver. In addition, the noise enhancement is negligible when there is a line of sight path or the channel power delay profile has an exponential decaying form. Copyright © 2006 John Wiley & Sons, Ltd.

A new multipath interference mitigation technique for high-speed packet transmission in WCDMA downlink

In order to increase throughput using high order data modulations in wide-band code-division multiple-access (WCDMA) downlink, it is necessary to eliminate multipath interferences. In a multipath interference canceller (MPIC) was proposed, which enables the use of high order modulations in multipath fading channels. However, only packet channels and pilot channels were considered as transmitted code channels. Code channels dedicated to other users and remaining common code channels coexist in practice, and such unknown code channels degrade the performance of MPIC significantly. In this letter, we propose a multipath interference mitigation scheme that removes all the intracell interferences by orthogonal variable spreading factor (OVSF) code characteristics. Simulation results show that the proposed scheme makes it possible to improve total throughput using high order modulations in WCDMA downlink.

Characterizing the orthogonality factor in WCDMA downlinks

The loss of orthogonality between the spreading codes in a wideband code-division multiple-access downlink is modeled in analysis and simulations by means of the orthogonality factor (OF). The OF, which is an important parameter limiting downlink capacity, increases with the multipath dispersion in the channel. We utilize this relationship between the OF and the channel dispersion to show a novel, simple, and accurate way to determine the time-averaged OF directly from the channel delay profile. To this end, we define the diversity factor (DF) of a channel profile, derive the expression for it, and show that the DF and the OF are related by a simple mathematical relationship. We then verify our approach over an entire ensemble of channel profiles generated by the general COST259 macrocellular channel model.

Capacity reduction of WCDMA downlink in the presence of interference from adjacent narrow-band system

One of the main challenges when implementing the future mobile multimedia networks is the cost-effective network evolution from second- to third-generation systems. This evolution path may include the use of different technologies at the same frequency band. The performance of the wide-band code-division multiple-access (WCDMA) downlink is studied in the case when there are narrow-band (NB) interference sources at the adjacent frequencies. A simple, analytical method to calculate the downlink capacity reduction of the WCDMA macrocell in this case is presented. The analysis takes into account different downlink interference mechanisms: wide-band noise from the transmitter as well as adjacent channel interference, intermodulation, and cross-modulation originating in the mobile receiver. The effect of each interference component to the capacity of the WCDMA macrocellular network has been evaluated with numerical examples. The analysis shows that capacity per cell is sensitive to the cell size, and therefore very careful network planning is needed in order to operate the WCDMA networks efficiently. The results of this paper can be utilized when implementing the WCDMA system to the same band with existing narrow-band systems, for instance, with the PCS 1900 band in United States and GSM 1800 band in Europe.

Bit error probability analysis for FRAMES WCDMA downlink receivers

The wide-band code-division multiple-access (WCDMA) concept FMA2 developed in the European Future Radio Wide-Band Multiple-Access Systems (FRAMES) project supports variable-data-rate transmission. The data rate can be altered by changing either the spreading factor or by using multiple spreading codes in parallel. In order to facilitate flexible changing of the data rate, variable-length orthogonal Walsh codes are used for channel separation, followed by the scrambling code. Optional short scrambling codes can be used if interference suppression is used. The downlink performance of the FMA2 system using both the conventional RAKE and LMMSE-RAKE receivers is studied. According to the numerical results, the performance of the conventional RAKE receivers is significantly degraded at the highest data rates, whereas the LMMSE-RAKE performs well in those cases also.