Performance of switched-beam smart antennas for cellular radiosystems

The performance and feasibility of switched-beam smart antennas for cellular radio systems is investigated. Switched-beam smart antenna systems are shown to either increase the capacity or extend the radio coverage by increasing the carrier-to-interference ratio (CIR). The trunking efficiency degradation caused by narrow-beam sectoring can be recovered or even improved by using a variety of trunkpool techniques. One drawback of switched-beam smart antennas is that the improvement in reverse-channel performance is not uniform over the entire cell area, and this presents a limiting factor on the achievable gains, practical considerations such as power control and the limited deployment of smart antenna cells are also addressed     

Downlink outage predictions for cellular radio systems

A general model for predicting downlink outage due to co-channel interference in cellular radio systems is presented. The model accounts for path loss, log-normal shadowing, Rayleigh fading, and vehicle velocity. The outage predictions are obtained by computer simulation. Various outage control techniques are evaluated, including cell sectoring, transmitter control, and hands-off. It is shown that down link power control is quite useful when hand-offs are used, and that shadowing can have a large effect on the outage predictions. The outage predictions are applied to a digital cellular system that uses quadrature differential phase shift keying (QDPSK) modulation and Reed-Solomon (RS) coding. It is shown that the performance of a coded digital cellular system is largely limited by rapidly moving vehicles     

Performance limits for channelized cellular telephone systems

Studies the performance of channel assignment algorithms for “channelized” (e.g., FDMA or TDMA) cellular telephone systems, via mathematical models, each of which is characterized by a pair (H,p), where H is a hypergraph describing the channel reuse restrictions, and p is a probability vector describing the variation of traffic intensity from cell to cell. For a given channel assignment algorithm, the authors define T(r) to be the amount of carried traffic, as a function of the offered traffic, where both r and T(r) are measured in Erlangs per channel. They show that for a given H and p, there exists a function T_H,p(r), which can be computed by linear programming, such that for every channel assignment algorithm, T(r)⩽T_H,p(r). Moreover, they show that there exist channel assignment algorithms whose performance approaches T_H,p (r) arbitrarily closely as the number of channels increases. As a corollary, they show that for a given (H,p) there is a number r₀ , which also can be computed by linear programming, such that if the offered traffic exceeds r₀, then for any channel assignment algorithm, a positive fraction of all call requests must be blocked, whereas if the offered traffic is less than r₀, all call requests can be honored, if the number of channels is sufficiently large. The authors call r₀, whose units are Erlangs per channel, the capacity of the cellular system     

Four-sector cross-shaped urban microcellular systems withintelligent switched-beam antennas

A four-sector cross-shaped urban microcellular system with intelligent switched-beam antennas is proposed. Each sector covers a street block with a base station located at an intersection, and an intelligent beam-switching scheme is used to locate mobile users in the most suitable beam coverage. Due to directional narrow-beam patterns and waveguide effects of tall buildings, radio signals along vertical and horizontal streets do not interfere with each other. Therefore, a channel can be reused simultaneously in multiple neighboring cells as long as cochannels do not encounter each other along the line of sight. The proposed scheme has a channel reuse efficiency of 0.95 for a traffic load of 0.02 [new-call arrivals/s/cell]. The system also increases system capacity more than three times with a blocking probability of 1% and considerably reduces handoff traffic when compared with a conventional cross-shaped microcellular system with an omnidirectional beam pattern     

Performance predictions for vertical-cavity semiconductor laseramplifiers

Vertical-cavity surface-emitting laser structures are studied theoretically to examine their potential for optical amplification. The major advantages of such a device are the minimal insertion loss and the polarization insensitivity of the gain which the transverse geometry provides. Although single-pass gain is necessarily low owing to a short optical cavity, operation as a Fabry-Perot amplifier in either the reflection or transmission mode ran provide high-performance characteristics. A comparison between edge- and surface-emitting amplifiers shows where advantageous operation can be obtained, and suggests how the best use of the surface-emitting amplifier performance can be made. By considering contrasting device dimensions, we show that gain, saturation output power, and noise characteristics suitable for both fiber optic and array processing configurations are readily attainable     

Performance of PRMA: a packet voice protocol for cellular systems

Equilibrium point analysis is used to evaluate system behavior in a packet reservation multiple access (PRMA) protocol based network. The authors derive the probability of packet dropping given the number of simultaneous conversations. The authors establish conditions for system stability and efficiency. Numerical calculations based on the theory show close agreement with computer simulations. They also provide valuable guides to system design. Because PRMA is a statistical multiplexer, the channel becomes congested when too many terminals are active. For a particular example it is shown that speech activity detection permits 37 speech terminals to share a PRMA channel with 20 slots per frame, with a packet dropping probability of less than 1%     

Performance enhancement of CDMA cellular systems with augmentedantenna arrays

The use of base station adaptive antenna arrays is an attractive way to increase the capacity of code division multiple access cellular systems. In this paper, a system with an adaptive minimum redundancy array (MRA) at the base stations is proposed. This system uses the high-resolution signal angle of the arrival estimation algorithm, ESPRIT, in conjunction with array augmentation techniques, and linear least squares adaptation. For the MRA, we propose to use virtual array elements at the locations where there is no sensor element. All real and virtual sensor outputs are weighted and combined to extract the desired signal components and suppress interference. To simplify the evaluation of the interference from adjacent cells, the concentric circle cell geometry is employed in place of the common hexagonal cell geometry. The performance of the proposed system is quantified by comparison with the omnidirectional antenna, and the adaptive uniform linear array (ULA) with the same number of elements and same array aperture, using realistic simulations. It is shown that, for a four-element array, there is about a 4- and a 1-dB improvement in the despread output signal-to-interference-plus-noise ratio of the proposed system over the omnidirectional antenna and the conventional ULA, respectively     

Performance analysis of cellular mobile communication systems fordata transmission

Buffers are used to overcome the data losses due to the interruption of data transmission when a mobile station is handed over in a cellular network. Data traffic from a wireline network to its mobile data terminal, such as access to large commercial databases or data transmission from a main computer to its remote mobile terminal, is studied. Compound Poisson (CP) is used to approximate the arrival process of the data traffic, and a modulated D (MD) distribution is used to approximate the service and handover process. The performance of the queueing model CP/MD/1/N is analyzed. Probability generating functions and characteristic functions are used to evaluate the mean queue length and the mean burst delay for an infinite buffer system and the overflow probabilities versus the buffer size for a finite buffer system. A method is presented to find the probability transition matrix entries by recursively taking derivatives of the probability generating function of the number of the characters arriving during the service-time. The queue length distributions for a finite buffer, both at departure instants and at arbitrary time instants are derived. Comparison with simulation indicates that the model is accurate. The numerical results of the model confirm the effectiveness of the scheme     

Performance analysis of session oriented data communications for mobile computing in cellular systems

Future cellular communication systems must seamlessly support services for a wide range of user needs, including voice, data, video and multi‐media. It is envisioned that mobile users may do much computer processing in an off‐line mode but must occasionally connect to a network in order to exchange data and/or files. For this purpose a communication session is initiated. During the session the user has access to network resources, although this access may be shared with others. Owing to the mobile environment, the user's connection to the network during a session may be severed. Since the mobile user can act semi‐autonomously, such disconnections can be transparent. That is, the mobile user can continue to function in an off‐line mode while the system will begin transparent automatic reconnection attempts to reestablish a link to the network. Only after a fixed (given) number of such attempts to reconnect have failed, is the session deemed to have failed. The issue is complicated by the hostile mobile radio environment and by user mobility. We consider session‐oriented communications and develop a tractable analytical model for traffic performance based on multi‐dimensional birth–death processes. The approach allows consideration of various platform types, such as pedestrians, automobiles, and buses, which may have very different mobility characteristics. Performance characteristics, such as: blocking, forced session termination, carried traffic, the average time per suspension, and the average number of suspensions per session, are calculated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physical optics and field-strength predictions for wireless systems

Physical optics, or Fresnel-Kirchhoff theory, is often used for studies of particular problems in terrestrial radio-wave propagation. With efficient techniques of numerical integration, it can also be used effectively for routine predictions and for designing terrestrial wireless systems. A computer program of this type has been in use for several years. It is most useful in situations in which the base station (BS) antenna is above local clutter, and over areas large enough that ground cover can be characterized with categories such as "open," "forest," "dense residential," etc., rather than individual buildings. The main calculation is a marching algorithm that simulates diffraction over all the variations in terrain height along radials from the BS. A secondary calculation estimates the additional attenuation due to buildings and trees close to the mobile antenna. This part of the calculation is based on several parameters characterizing the local environment of the mobile antenna. Calculations are slow compared to many traditional methods, but are fast enough for routine use on a PC     

Performance analysis of channelized cellular systems with dynamic channel allocation

We present an analytical model to compute the blocking probability in channelized cellular systems with dynamic channel allocation. We model the channel occupancy in a cell by a two-dimensional (2D) Markov chain, which can be solved to obtain the blocking probability in each cell. We apply our analytical model to linear highway systems with and without lognormal shadowing and then extend it to 2D cellular systems with lognormal shadowing. We show that, for linear highway systems, distributed dynamic channel-allocation schemes perform similarly to the centralized dynamic channel-allocation schemes in terms of blocking probability. However, for 2D cellular systems, the improvement in the performance is significant and the reduction in the blocking probability in systems with distributed dynamic channel allocation is by almost one order of magnitude, when compared to that in systems with centralized dynamic channel allocation. In practice, our analysis of linear highway systems is applicable to Digital European Cordless Telephony (DECT) and that of 2D cellular systems is applicable to global systems for mobile communications (GSM).     

Performance characteristics of cellular systems with different link adaptation strategies

In this paper, the theoretical performance of cellular systems with different types of link adaptation is analyzed. A general link and system performance analysis framework is developed to enable the system-level performance characteristics of the various link adaptation strategies to be studied and compared. More specifically, this framework is used to compare the downlink performance of fully loaded cellular systems with fixed power and modulation/coding, adaptive modulation/coding (AMC), adaptive power allocation (APA) with system-level AMC, and water-filling (WF). Performance is studied first for idealized methods, and then for cases where some practical constraints are imposed. Finally, a hybrid link adaptation scheme is introduced and studied. The hybrid scheme is shown to overcome most of the performance loss caused by the practical constraints. Moreover, the hybrid scheme, as opposed to WF, enables the system to be tuned to meet the most important performance objective for the system under consideration, such as coverage reliability, capacity, or data rate distribution. The algorithms and the framework presented in this paper can be used to improve the link adaptation performance of modern cellular systems such as HSDPA.     

Performance and implementation of dynamic frequency hopping inlimited-bandwidth cellular systems

We evaluate the performance of a previously proposed dynamic frequency hopping (DFH) when applied to cellular systems with a limited total bandwidth. We also illustrate a practical implementation for DFH deployment using network-assisted resource allocation (NARA). The performance evaluation is accomplished by system-level simulations of a system with 12 carriers and 1/1 frequency reuse, based on the EDGE-Compact specification. Voice-only circuit-switched operation is assumed. The fading channel, multicell interference, voice activity, and antenna sectorization are modeled. We present the performance of dynamic frequency hopping compared to random frequency hopping and fixed channel assignment by showing the distributions of the word error rates. The sensitivity to occupancy, Rayleigh fading assumptions, number of carriers, voice activity, and measurement errors are studied. We also compare the uplink and downlink performance. The results indicate that DFH can significantly improve the performance compared to random frequency hopping. For example, at a 2 % frame error rate with 90% coverage, the capacity improvement of DFH is almost 100% when compared with fixed channel assignment, and about 50% when compared to random frequency hopping. The amount of improvement for the uplink direction is smaller than the improvement for the downlink direction, especially for higher occupancies     

Performance analysis of cellular mobile communication systems withdynamic channel assignment

The traffic analysis of small-cell mobile networks with dynamic channel assignment is investigated to determine their blocking performance, using a hybrid method of analysis and simulation. The authors particularly focus on the performance problems presented by networks with heterogeneous cell traffic loads, the impact of traffic volatility among the cells, and the impact of multichannel traffic on the channel blocking probabilities. Significant improvement in network performance with dynamic channel assignment is established by numerical results     

Performance evaluation for cellular CDMA

The authors consider the performance of a cellular radio, direct-sequence code-division multiple access, (CDMA) system. The base-to-mobile link is modeled as a flat Rayleigh fading channel, with all signals transmitted from a given base station fading in unison. For the mobile-to-base link, the authors use a similar model, except that the waveforms from all users are assumed to experience independent fading. The effects of imperfect power control are shown     

A beam-forming network for a circular switched-beam phased arrayantenna

This paper reports on the design and development of a dividing/phasing network for a compact switched-beam array antenna for land-vehicle mobile satellite communications. The device is formed by a switched radial divider/combiner and 1-bit phase shifters and generates a sufficient number of beams for the proper satellite tracking     

Performance analysis of a truncated closed-loop power-control scheme for DS/CDMA cellular systems

This paper analyzes the system performance of a truncated closed-loop power-control (TCPC) scheme for uplinks in direct-sequence/code-division multiple-access cellular systems over frequency-selective fading channels. In this TCPC scheme, a mobile station (MS) suspends its transmission when the short-term fading is less than a preset cutoff threshold; otherwise, the MS transmits with power adapted to compensate for the short-term fading so that the received signal power level remains constant. Closed-form formulas are successfully derived for performance measures, such as system capacity, average system transmission rate, MS average transmission rate, MS power consumption, and MS suspension delay. Numerical results show that the analysis provides reasonable accuracy and that the TCPC scheme can substantially improve the system capacity, the average system transmission rate, and power saving over conventional closed-loop power-control schemes. Moreover, the TCPC scheme under realistic consideration of power-control error due to power-control step size, power-control period, power-control command loop delay, and MS velocity is further investigated. A closed-form formula is obtained to accurately approximate the system capacity of the realistic TCPC scheme.     

Performance predictions of interconnect networks for advanced technology nodes

New materials are required for upcoming technologies to maintain good performance levels and increase circuit lifetime. Predictive simulations are thus performed looking at several fundamental barriers and restoration treatments in order to achieve good signal propagation and strong reliability for integrated circuits. Precise recommendations are finally proposed for both 32 nm and 22 nm technology nodes.     

On the analysis of switched-beam antennas for the W-CDMA downlink

Smart antennas are widely recognized as an enabling technology for addressing the demand of future wireless network capacity when employed in place of traditional fixed-coverage sector antennas. Furthermore, switched-beam antenna systems offer a robust implementation against multipath propagation effects and reduced complexity that is inherent with fully adaptive implementations. This paper introduces a simple closed-form expression for evaluating the capacity increase of W-CDMA cellular networks employing switched-beam antennas. The expression incorporates the effect of practical antenna patterns and the impact of multipath scattering on code orthogonality, as well as that of pilot signal power. The results show that a reduction in downlink interference of approximately 6 dB can be achieved by installing an eight-beam antenna system in a 120/spl deg/ sector configuration when representative values of these parameters are taken into account.     

Performance analysis of flexible hierarchical cellular systems witha bandwidth-efficient handoff scheme

In this paper, a bandwidth-efficient handoff strategy is proposed and analyzed for hierarchical cellular systems. Mobile subscribers are divided into two classes, i.e., low- and high-mobility subscribers. In our bandwidth-efficient handoff strategy, each of the originating and handoff calls of both slow and fast mobile subscribers first tries to get a channel in a microcell. Macrocells are overlaid over the microcells to handle overflowed calls. A call overflowed into a macrocell requests a take-back to the new microcell at each border crossing of the microcells. The request will be accommodated by the target microcell if there is any idle traffic channel in the cell. An analytical model is developed, and the most important performance measures such as the blocking probability of originating calls and the forced termination probability of calls are evaluated. It is shown through extensive comparisons with other candidate handoff strategies that if the total traffic load of the system is not very heavy, our scheme has the best bandwidth efficiency and can provide better quality of service for mobile subscribers without bringing too much processing expense to the system