3G Code Division Multiple Access Research Articles

Interference analysis and capacity for forward link 3G CDMA network with adaptive antennas

AbstractIn code division multiple access (CDMA) systems, the capacity of forward link (FL) communication to mobile receivers is limited primarily by co‐channel interference (CCI). Adaptive antenna arrays (AAAs) that use antenna arrays along with advanced signal processing at the base station (BS) have been proposed to mitigate this limitation. For a 3G CDMA cellular network, where each BS equipped with an AAA serves mixture of voice and data users within its coverage, we study FL capacity and investigate the effects of different factors (array topology, multipath angle spread, data rate, and beamforming algorithm) on this capacity under Rayleigh fading channel. By modeling the instantaneous signal‐to‐interference power ratio received at the mobile, we derive the system outage equation that considers blocking of either desired voice or data user. Simulation results show that for the same element spacing and number of antenna elements per cell, the uniform circular array (UCA) topology results in larger capacity than the sectorized uniform linear array (ULA) topology does, and that a larger angle spread or data user rate reduces FL capacity. Copyright © 2007 John Wiley & Sons, Ltd.

Modeling and Performance Evaluation of 3G CDMA Networks with Beamforming

The second generation (2G) code-division multiple access (CDMA) IS-95A cellular network has been deployed for almost ten years. Although the system design rules and operating procedures for voice services are well established and understood, these rules and procedures need to be re-examined in light of several technology innovations. These innovations include the launch of third generation (3G) cdma2000 1× high-rate data services and the new research results in interference cancellation, antenna array and multiple-input multiple-output (MIMO) technologies. We have built a 3G cdma2000 1× cellular simulator, which simulates the physical layer using MATLAB and networking layers using OPNET Modeler, to investigate various design issues of cdma2000 1× networks. This paper explores the use of a simple beamforming model and investigates the effectiveness of deploying antenna array techniques in cdma2000 1× networks. The capacity improvement for CDMA networks using antenna array techniques is evaluated under different deployment scenarios (voice versus data services and various number of antenna elements). Based on the performance evaluation results it is proposed to utilize beamforming as one of the elements in quality of service (QOS) provisioning for data services and to couple antenna arrays with dynamic soft handoff threshold adjustment for further improvement in the system capacity.

Enhancing data throughput and lower correlations quasi orthogonal functions for 3G CDMA systems

AbstractThe forward link of the 3G code‐division multiple‐access (CDMA) system may become limited under the increasing of the number of users. The conventional channelization code, Walsh code, has not enough sizes for much possible users, therefore, the quasi orthogonal function (QOF), which can process optimal cross‐correlation with Walsh code, is considered.To obtain lower correlations and better performance in 3G CDMA system, we investigate a quasi orthogonal function on Jacket matrices in this paper. Secondly, to simplify the detector and improve the bit error rate (BER) performance, we provide a novel detection scheme for QOF CDMA system. Finally, we give a brief discussion about a simple recursive generation of the bent sequences for QOF mask function. Copyright © 2005 John Wiley & Sons, Ltd.

Joint Reliability of Medium Access Control and Radio Link Protocol in 3G CDMA Systems

In this paper, we study the reliability as offered jointly by the medium access control (MAC) and the radio link protocol (RLP) for third generation (3G) code division multiple access (CDMA) standards. The retransmission mechanism supported at the RLP layer has a considerable amount of delay (80-100 ms) associated with it; hence, it may not be able to support applications with strict delay requirements. On the other hand, if retransmissions are also performed at a lower layer, such as the MAC layer, then the performance of CDMA systems can be improved because of the fast retransmissions at the MAC layer. We show how the performance of RLP improves with respect to three metrics - mean delay, throughput, and RLP recovery -when a finite number of retransmissions is allowed at the MAC layer. Synthetically generated Web traffic is used as the application, the objects of which are fragmented into equal-sized RLP frames. We consider soft packet combining support at the receiver, which effectively lowers the frame error rate. We also consider the possibility of misinterpretations of acknowledgments. Simulation experiments are conducted to verify the performance as offered jointly by the MAC and the RLP, particularly for cdma2000 standard and wideband CDMA (WCDMA) systems. The improvement in the TCP throughput is also evaluated.

Pilot Interference Cancellation Technology for CDMA Cellular Networks

This paper considers the link-level and network-level performance of code division multiple access (CDMA) pilot interference cancellation (pilot IC) technology, a low-complexity advanced receiver technology being considered for use in commercial third generation (3G) CDMA cellular systems. The concept behind this technology is to estimate and cancel at the handset receiver the interference effects associated with CDMA downlink pilot signals broadcast from the base stations of the network. The canceling of interference at the receiver improves the signal-to-interference/noise ratio (SINR), which enables increased cell capacity or throughput. In this paper, we derive SINR expressions for evaluating the probability of error performance of both the RAKE and pilot IC handset receivers, under conventional random spreading code assumptions. The approach can easily and accurately model a wide variety of transmitter, channel, and receiver conditions, including the effects of channel estimation. We also utilize radio network simulations to illustrate and quantify the capacity gains available for 3G CDMA networks through the use of pilot IC handsets. Network simulations are also used to examine the reduced level of soft-handoff found to be possible in pilot IC-based networks and the increased flexibility available in setting pilot power levels. We further consider the impact of using stronger pilot signals for improving the demodulation performance of sensitive higher-order modulation constellations that are needed to support spectrally efficient high-rate data services.

Reduced-Rank Chip-Level MMSE Equalization for the 3G CDMA Forward Link with Code-Multiplexed Pilot

This paper deals with synchronous direct-sequence code-division multiple access (CDMA) transmission using orthogonal channel codes in frequency selective multipath, motivated by the forward link in 3G CDMA systems. The chip-level minimum mean square error (MMSE) estimate of the (multiuser) synchronous sum signal transmitted by the base, followed by a correlate and sum, has been shown to perform very well in saturated systems compared to a Rake receiver. In this paper, we present the reduced-rank, chip-level MMSE estimation based on the multistage nested Wiener filter (MSNWF). We show that, for the case of a known channel, only a small number of stages of the MSNWF is needed to achieve near full-rank MSE performance over a practical single-to-noise ratio (SNR) range. This holds true even for an edge-of-cell scenario, where two base stations are contributing near equal-power signals, as well as for the single base station case. We then utilize the code-multiplexed pilot channel to train the MSNWF coefficients and show that adaptive MSNWF operating in a very low rank subspace performs slightly better than full-rank recursive least square (RLS) and significantly better than least mean square (LMS). An important advantage of the MSNWF is that it can be implemented in a lattice structure, which involves significantly less computation than RLS. We also present structured MMSE equalizers that exploit the estimate of the multipath arrival times and the underlying channel structure to project the data vector onto a much lower dimensional subspace. Specifically, due to the sparseness of high-speed CDMA multipath channels, the channel vector lies in the subspace spanned by a small number of columns of the pulse shaping filter convolution matrix. We demonstrate that the performance of these structured low-rank equalizers is much superior to unstructured equalizers in terms of convergence speed and error rates.

Smart cell sectorization for third generation CDMA systems

AbstractSmart antennas are a powerful means to provide the increased bandwidth efficiency needed to deliver advanced third generation (3G) interactive multimedia services anywhere and anytime. In this paper we focus on the development of smart antennas located at the base stations of a code division multiple access (CDMA) cellular system. First, we review the main characteristics of antenna array systems and highlight some issues related to the inclusion of smart antennas in a 3G CDMA system. A classification of the proposed beamforming techniques and a discussion on the advantages and drawbacks of smart antennas are provided. Then, we introduce an original smart antenna technique based on rotation and resizing of the available sectors much simpler than common smart antennas based on beamforming techniques addressing a specific user. We discuss on the impact of the proposed technique in the base station architecture. Finally, we provide simulation results in order to show the effectiveness of the proposed approach and to relate transmission performance to system parameters. It turns out that the smart sectorization technique provides significant capacity improvements under statistically uniform user distribution (up to about 80 per cent for data traffic). Copyright © 2002 John Wiley & Sons, Ltd.