CDMA Mobile Communication Systems Research Articles

Analysis of Interference and Signal Quality in Cellular Wireless Networks

An analytical model to compute the effect of co-channel interference from the base stations at the Multi-cell CDMA systems is proposed. The objective is to study the effect of multiple-access interference generated by the neighbor cells on multi-cell CDMA and W-CDMA systems capacity. The potential of adaptive antennas in interference reduction and signal quality improvement in CDMA mobile communications systems is analyzed. The study shows that improvement in base-station sensitivity can boost system performance.

Object identification methodology in multi-user digital beamforming system

In the content of traditional Digital BeamForming(DBF),it cannot implement the identification between the user signals and interferences,although the Direction Of Arrival(DOA) estimation strategy digs out the spacial information of these signals.Similar as the multi-user detection in CDMA mobile communication system,different users were allocated with one pseudo-random(PN) codes in the transmitters respectively.Furthermore,the receiver generated the replicas of transmitted PN codes and did correlation calculation with the received signals to harnesses the identification.The simulation results illustrate that the proposed approach picks up the desired signals and ensures the low false alarm rate and missing detection rate.

Comparison and Analysis of Trisector Cell using Antenna Beam-width for CDMA Cellular Mobile Communication Systems

The cell sectorization techniques are widely used in cellular systems to reduce co-channel interference by means of directional antennas. Cell sectorization and improvement of the chip energy/others interference ratio (Ec /Io ) are technologies to offer good quality of services (QoSs) and coverage for new and sophisticated power control to achieve high capacity. In this study, we analyze and compare performances of two trisector cell architectures with different antenna beam-widths-a wide-beam trisector cell (WBTC) and a narrow-beam trisector cell (NBTC)-in order to achieve effective cell sectoring in CDMA and cellular mobile communication systems. These architectures are outcomes of cell sectorization, which is widely employed in cellular systems for reducing co-channel interference. We verify the effectiveness and validity of the NBTC architecture by theoretically comparing it with the WBTC architecture (using parameters such as softer handoff and interference ratio). Further, we analyze results of a simulation of the WBTC and NBTC and of a field measurement performed in Namwon city in Korea. From the analysis, we find that the NBTC architecture is more efficient than the WBTC architecture in minimizing interference from adjacent BSs and increasing cell coverage while maintaining a good QoS.

이동 통신 기지국 안테나의 수동 상호 변조 왜곡에 진동이 미치는 영향 분석 및 개선 방안

본 논문은 800 MHz 대역의 CDMA 이동 통신 기지국의 안테나에서 보편적으로 발생되고 있는 수동 상호 변조 왜곡 특성에 대하여 조명해 보고 진동이 수동 상호 변조 왜곡에 미치는 영향을 분석하여 그에 대한 개선 방안을 연구하였다. 이동 통신 기지국은 대부분 건물 옥상이나 철탑 등 고지대에 위치하게 된다. 그렇기 때문에 비, 바람 등 자연 환경적인 요인이나 차량 등 생활 환경적인 요인에 의해 미세한 흔들림 곧, 진동이라는 영향을 수없이 받고 있다. 이에 착안하여 이동 통신 안테나가 진동에 의해 영향을 받고 있다는 것을 실험을 통해 입증해 냄으로써 실제 이동 통신 운용 필드에서 진동이라는 요인에 의해 안테나의 수동 상호 변조 왜곡 특성이 쉽게 열화된다는 것을 증명해 보였다. 또한, 진동에 잘 견딜 수 있는 안테나 구조에 대한 개선 방안을 제시하였고, 구조 개선 전후 안테나의 수동 상호 변조 왜곡 특성을 실험적으로 비교함으로써 그 열화 정도를 35 dB 이상 향상시킬 수 있었다. This work investigates the effects of vibration on the passive intermodulation distortion characteristics of base station antennas for 800 MHz CDMA mobile communication systems. In general, base station antennas are located at high positions such as on building rooftops or iron towers. Thus the antennas are always affected by random vibrations, coming from various natural environmental factors such as rain and wind, or from living environmental factors such as vehicles and trains passing by. The measured intermodulation distortion characteristics before and after vibration accelerated degradation test show that vibrations are indeed the main cause for the intermodulation distortion performances of such antennas. To minimize the effects of vibrations, a new antenna design isptoposed that has an improved tolerance for vibrations. Experimental results show that the proposed antenna design dramatically reduces the degradation of the intermodulation distortion more than 35 dB.

Coverage Shrinking and Available Data Rate Variations for 3G CDMA Mobile Cellular Systems

In 3G CDMA mobile communication systems, high data rate services are essential for many key applications. When an MS approaches the cell border, link performance is degraded and more power should be allocated to maintain the link performance. Since the maximum available signal power is limited, the link adaptation mechanism may diminish the data rate to maintain link performance. This implies that the valid coverage shrinks when the data rate increases. The shrinking of valid coverage under a predetermined data rate will strongly impact on the reliability of high data rate services. In this work, the encoded bit error probabilities of 3G CDMA mobile communication systems, over large-scale and large-small-scale fading channels, were analyzed based on SGA and SIGA methods. Analytic methods were also proposed to investigate the issues of coverage shrinking and service data rate variations. Furthermore, the outage probability, cell coverage percentage and the staying probabilities of available data rates were well examined. The proposed analytic methods can be applied, as a preliminary research, to the design of cellular-system-related techniques, such as QoS control, available data rate prediction, power reservation, and service adaptation.

Feasibility condition for the uplink of a CDMA multiservice mobile communication system with repeaters

This paper derives a general analytical expression of the feasibility condition for the uplink of a CDMA mobile communications system in a general scenario where the users in the system belong to an arbitrary number of service classes and the coverage deployment includes the presence of repeaters. An explicit expression of the admission region is derived and the dependencies on the parameter values are shown. An example is presented in order to illustrate the application of the proposed methodology in a real case.

Call admission control for CDMA mobile communications systems supporting multimedia services

The call admission control (CAC) belongs to the category of resource management. Since the radio spectrum is very scarce resource, CAC is one of the most important engineering issues for mobile communications. In this paper, we propose a CAC scheme for direct sequence code-division multiple-access cellular systems supporting mobile multimedia communications services. There are multiple call classes in multimedia services and the required signal-to-interference ratio (SIR) varies with call classes. Call admission decision in the proposed scheme is based on SIR measurement. We take account of the traffic asymmetry between uplink and downlink, which is the most important characteristic of multimedia traffic. In addition, the proposed scheme guarantees the priority of handoff call requests over new call requests. We evaluate the performance of the proposed scheme using Markov analysis. The performance measures which we focus on are the system throughput and the blocking probabilities of handoff calls and new calls. The outage probability of a call in progress is also calculated, which is the probability that the measured bit energy-to-noise density ratio of the call is smaller than the required value for maintaining adequate transmission quality. We present some numerical examples with practically meaningful parameter values and, as a result, show that the proposed CAC scheme can operate well in the mobile multimedia systems such as the International Mobile Telecommunications-2000 (IMT-2000) systems.

Macroscopic diversity for CDMA mobile system

A novel system of macroscopic diversity with voting rule in CDMA cellular system is suggested in order to raise the coverage and quality of service of CDMA mobile communication system. The estimation of the impact of macroscopic diversity on performance of CDMA cellular system is analyzed and investigated.

2-D rake receiver based on space-time channel parameter estimation

2-D RAKE receiver is an efficient way to realize the space-time processing for CDMA systems with aperiodic spreading codes. The Direction Of Arrival (DOA) and the relative time delay of every user’s multipath must be known to realize the 2-D RAKE receiver. In the third generation CDMA mobile communication system, auxiliary pilot channel is used in the uplink channels. The different user’s Vector Channel Impulse Response (VCIR) can be estimated from the pilot channel easily. The VCIR contains spatial and temporal information. In this paper, by utilizing the known pulse shape function, a parameter matrix method used to estimate the Spatial Signature Vector (SSV) and the relative time delay is proposed in frequency domain. The DOA can be estimated from the SSV. By reconstructing the SSV and utilizing approximate Capon space filter, the performance of the 2-D RAKE receiver with uniform circular array can be improved with a little additional computation work.

A near-optimum MAC protocol based on the distributed queueing random access protocol (DQRAP) for a CDMA mobile communication system

This paper presents and analyzes a new near-optimum medium access control (MAC) protocol. The proposed access scheme is suitable for a CDMA mobile communication environment, and keeps under control and upper bounded the number of simultaneous transmissions. It has a delay performance approaching that of an ideal optimum M/M/K system, where K is the number of spreading codes being used (maximum number of simultaneous transmissions). The protocol is a free random access protocol when the traffic load is light, and switches smoothly and automatically to a reservation protocol when traffic load becomes heavier. It is based on distributed queues and a collision resolution algorithm. Moreover, a physical receiver structure is proposed and analyzed in order to preserve the robustness of the protocol in a wireless link. The results obtained show that the protocol outperforms other well known medium access protocols in terms of stability and delay, even when taking into account the loss caused by channel propagation conditions.

Mobility model and performance analysis for zone-based registration in CDMA mobile communication system

In this paper, we describe a mobility model and analysis for zone-based registration in the CDMA mobile communication system. We first propose a simple and proper mobility function for single zone-based registration. We establish the circumstances of multiple zone-based registration, which is based on the mobility function of single zone-based registration, and perform computer simulations for the circumstances. Using the simulation results, we obtain the optimal number of zones, N, that minimizes signaling traffic on radio channels. Results show that, in most cases, N is 2. We also show that multiple zone-based registration has lower signaling traffic on radio channels than single zone-based registration, and zone?based registration must be implemented as multiple zone?based registration.

Multiuser detection and diversity reception for asynchronous CDMA mobile communication

In CDMA mobile communication systems, multiple access interference can be canceled by multiuser detection technique. The Degradation by channel fading can be reduced by diversity reception. This paper investigates a family of multiuser receivers that combined decorrelating detection, antenna diversity and RAKE multipath diversity. The performance of the multiuser receivers is analyzed. The results demonstrate a significant increase in the performance of the receivers by using multiuser detection and diversity reception.

Power control mixing C/I balancing and constant-received signal strength in CDMA mobile communications system

A power control algorithm mixing C/I balancing with constant-received power control has been proposed. It is shown that the outage probability can be reduced by using the new algorithm. The new algorithm also provides better performance than the approximated optimum centralised power control algorithm if the number of removed mobiles is small.

Development of the Home Location Register/Authentication Center in the CDMA Mobile System

In this paper, a home location register (HLR) for CDMA mobile communication system (CMS) is introduced. It stores the mobile station (MS) subscribers locations and supplementary service information. Call processing procedures for HLR are developed to receive and store subscriber's location coming from mobile exchange (MX) during the location registration, and to transfer subscriber's location and supplementary service information to the MX during the mobile-terminated call setup. For fast call processing by increasing database access speed, a memory-resident database management system is devised. For Easy and secure HLR operation, administration and maintenance functions and overload control mechanisms are implemented. Designed HLR hardware platform is expandable and flexible enough to reallocated software blocks to any subsystems within the platform. It is configurable according to the size of subscribers. An authentication center (AC) is developed on the same platform. It screens the qualified MS from the unqualified. The calls to and from the unqualified MS are rejected in CMS. To authenticate the MS, the AC generates a new authentication parameter called using shared secret data (SSD) and compared it with the other AUTHR received from the MS. The MC also generates and stores seed keys called A-keys which are used to generate SSDs. The HLR requirements, the AC requirements, software architecture, hardware platform, and test results are discussed.

The capacity calculation for CDMA mobile satellite communication system

On the basis of considering downlink power flux density limit, shadowing effect frequency reuse in different systems and adjoining beams of same system, adopting voice activity and polarization isolation techniques, the capacity of CDMA mobile satellite communication system at different downlink power flux density limit modes, channel spread bandwidth and mobile user’s quality factor of receiving system(G/T) are analysed and calculated, and compared with the ones of TDMA and FDMA. The conclusions are given at the end of this paper.

Recurrent neural network array for CDMA mobile communication systems

The application of a recurrent neural network structure to adaptive antenna arrays in a CDMA system is presented. This novel approach enables space and time diversity combining of the signals, and is evaluated over multipath fading channels. Computer simulation results show that the recurrent structure performs better and has a lower computational complexity than the RLS-based adaptive array.