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Macroscopic Diversity Performance Measured in the 800-MHz Portable Radio Communications Environment
Abstract
Analysis of 816 MHz residential propagation data is presented,
demonstrating the usefulness of macroscopic selection diversity in
combatting shadow fading produced by buildings and other large
geographic features in the portable radio communication environment.
Macroscopic diversity can reduce the link margin needed for 99%
reliability by 10 dB. The analysis of these data indicates that
log-normal shadow fading is partially correlated on the paths between a
portable user and several surrounding ports. A two-component
shadow-fading model duplicates this behavior. One log-normal term is
identical for all paths from a given location and characterizes the
propagation losses associated with the location. A second log-normal
component is independent for each path and characterizes the remainder
of the path to the port. The model fits the propagation data as well. A
standard deviation of 8 dB for the path-specific term fits subsets of
the available data well and is consistent with the standard deviation of
shadow fading in the mobile (vehicular) communication environment
... The shadowing cross-correlation represents the correlation among the shadow effect of different links merging at the same receiver but emerging from different transmitters. Since cross-correlation has been early evidenced in the work by Graziano in 1978 [20], several measurement campaigns have been carried out in order to catch the physical behavior as well as to derive mathematical modeling [6,46,61,69]. Field measurements were performed under a different environment supporting the intuitive conjecture that links with a common terminal are in general correlated. Arnold et al. [6] studied this issue in the context of macrodiversity gain, analyzing 800 MHz data collected in a residential environment with indoor and outdoor transmitters for a single mobile receiver. ...
... Field measurements were performed under a different environment supporting the intuitive conjecture that links with a common terminal are in general correlated. Arnold et al. [6] studied this issue in the context of macrodiversity gain, analyzing 800 MHz data collected in a residential environment with indoor and outdoor transmitters for a single mobile receiver. Interestingly, some field measurements failed to bare significant correlation. ...
... An extension of this model in order to introduce dependency between link attenuations is to break the shadowing effect into two independent components [6,63] [6], was shown to well match the measured data for outdoor to indoor links having similar length. In other words the random component of the dB loss for the ith base station is expressed as: ...
... For indoor users served by outdoor BSs we use a model based on [15] but changed slightly in order to be easier to implement together with the outdoor model. For the correlated shadow fading, we did not find a suitable model in the literature and therefore proposed and used a new model based on ideas in [9], [16], [63]. Our model is summarized in [20] and described in more detail in Chapter 3. ...
... In cases where correlation of the shadow fading is not important, we will use the simple uncorrelated model. According to Arnold [9], shadow fading consists of two parts: one contribution from the signal path and one from the location around the mobile. In the following, we propose a model for correlated shadow fading based on ideas by Arnold et al [9], [16], [63]. ...
... According to Arnold [9], shadow fading consists of two parts: one contribution from the signal path and one from the location around the mobile. In the following, we propose a model for correlated shadow fading based on ideas by Arnold et al [9], [16], [63]. We cover the simulation area with a regular grid with resolution ∆g. ...
... , notably with f (x) = e −x/d 0 [39]. We argue that these models are difficult to reconcile with the propagation arguments for correlation in shadowing given in [32], [38], [40]. ...
... As the paths add, the power of the common term grows as N 2 , while the power of the sum of the iid terms only grows as N and becomes more and more negligible, relatively speaking. This is analogous to what happens in our proof in Appendix A. This interpretation is also consistent with the physical basis for correlation in shadowing given in [24], [32], [38], [40]. From the analytical expressions (8) and (10), one can directly observe the effect of the problem parameters on the distribution of I. Of particular interest is that only one scalar quantity depends on the shadowing correlation function ...
... @BULLET It may be useful to study the total interference as a random process in time, particularly in mobility scenarios. Several models are available for describing the auto-correlation function of the shadowing on a mobile link [24], [39], [40], [45]. ...
... Recent work on various aspects of wireless communications has indicated a wide gap between results obtained assuming independent shadowing paths and between those that introduce correlation in shadowing propagation models [1]–[5]. Older works show that shadowing correlation significantly affects handover behavior [6]–[9], interference power [10]–[14] (and consequently system performance) [15]–[17] , and the performance of macrodiversity schemes [10], [18]–[23]. Furthermore, shadowing in decibels has been measured [18], [24]–[39] to have significant correlation in various scenarios. ...
... Older works show that shadowing correlation significantly affects handover behavior [6]–[9], interference power [10]–[14] (and consequently system performance) [15]–[17] , and the performance of macrodiversity schemes [10], [18]–[23]. Furthermore, shadowing in decibels has been measured [18], [24]–[39] to have significant correlation in various scenarios. Because of these two facts, we believe that the general wireless community is becoming convinced of the importance of modeling correlation in shadowing [2]–[5], [12], [23], [40]–[49]. ...
... Shadowing represents the variability of the logarithm of the received power around its expected value: we denote this quantity S, with VAR{S} < ∞. The small-scale effect of fading has been removed in the spatial dimension by averaging over a local region [45] of about 50 wavelengths [56], [62], that is, approximately 8–34 m for classic cellular channels [18], [24], [25], [27], [29], [37], [38] ...
There is emerging interest in more detailed models for wireless shadowing, which may include nonconstant shadowing variance, non-lognormal shadowing, and, most importantly, correlation between paths; we focus on this last aspect. This paper offers a structured synthesis of the existing literature on autocorrelation and cross-correlation in wireless shadowing and attempts to fill existing gaps in the analysis of correlation models. We make a survey of these models and argue, as has previously been observed, that certain models are not mathematically feasible, which may lead to problems in simulations or analysis. We then state some theorems that test whether the models are positive semidefinite, which is the central necessary condition for feasibility, and evaluate the existing models accordingly. Additionally, we evaluate the models according to their physical plausibility, which leads us to choose one model among many as arguably the best one in existence so far. This paper should be useful as a guide on how to implement shadowing correlation in one's work, how to choose an appropriate correlation model, and how to modify existing models or create new models so that they fulfill mathematical feasibility.
... Based on the above descriptions, we can find that there will be more than one base stations simultaneously serving a MR in the 5G C/U-plane decoupled heterogenous railway wireless system. According to [19], the cross-correlated shadow fading model can be employed for theoretical analyses in such networks. In this paper, we use three performance metrics to evaluate the performance of the proposed C/U-plane staggered handover schemes, which are described below: ...
... In the 5G C/U-plane decoupled heterogeneous railway wireless sys- tem, the macro cell (providing the C-plane) and small cell (providing the U-plane) deployed at different locations simul- taneously serve the same train. According to [19], there are some common components between the propagation paths of macro and small cell signals, especially for the area near the train. As a consequence, the shadow fading of macro and small cells are cross-correlated. ...
Previously, we proposed a broadband fifth-generation (5G) control/user (C/U)-plane decoupled heterogeneous railway wireless system to meet the exponentially increasing capacity demands in railway. Nevertheless, service interruptions due to the handovers in overlapping registration areas are still challenging in railway wireless systems. How to achieve soft and fast handovers to overcome these challenges attracts intensive attention finally. In this paper, we propose a novel network architecture for 5G C/U-plane decoupled heterogeneous railway wireless systems to physically separate and stagger the C-plane and U-plane handovers. During the C-plane handover process that occurs between the macro-cells, the U-plane is always kept connected without any handover, which achieves non-interruptible soft handover. Moreover, since there are no handovers in the U-plane, the handover procedure is significantly simplified, thereby accelerating the handover process. Similarly, during the U-plane handover process, which happens between the small cells, the C-plane is kept connected all the time, saving the otherwise intensive C-plane handover signaling. Besides, the coordinated multi-point transmission and reception (CoMP) and bi-casting technologies are applied to establish the target U-plane connection ahead of cutting off the old one, so that no interruption occurs during the U-plane handover process. This paper demonstrates that the proposed handover schemes can greatly improve the handover performance.
... In evaluating the avera-ge probability of error of wireless communication system with micro-and macrodiversity reception, it is usually assumed, for analytical convenience, that the macrodiversity branches are uncorrelated. However, measurements in several environments have shown that, for example, in mobile communication a lognormal shadow fading on the paths between a mobile user and the surrounding base stations are usually correlated [19], [20]. We may apply this example for wireless sensor network system assuming that a lognormal shadow fading on the paths between a sensor sink and sensors are correlated. ...
... We assume that there exists a constant correlation between the mean signal po-wers at any two sensor nodes, i.e., ρ ρ = ij for j i ≠ . It can be shown that with this model, the correlation between local-mean powers of the received signals at the sensor sink may be the same even when the sensor nodes are at unequal distances from the sensor sink since the correlation depends on the standard deviation of the shadowing process rather than the area mean, which is distance dependent [19]. For the constant correlation model, it is straightforward to show that using results in [21] the cdf of Q is given by ...
The effect of correlated lognormal shadowing on the average probability of error performance of narrow-band wireless sensor network systems with micro-and macrodiversity reception in a Rician fading channel is investigated by considering a constant correlation model for the shadowed signals at the fusion center or sensor sink of wireless sensor network with radio channel. The performance degradation due to correlated shadowing is illustrated by considering both coherent and differentially coherent binary phase-shift keying schemes. Numerical results presented show that when the sensors in a wireless sensor network system are very closely spaced, the effect of correlated shadowing on system performance cannot be ignored. The obtained results allow us to define the lower and upper bounds on wireless sensor network system performance.
... In [SESV07] an additive model is proposed as a physical basis and explanation for the log-normality of the shadow fading. The shadow fading is in most literature assumed to be the effect of physical shadowing caused by objects in the signal propagation path, [ACM88], [WL02]. However, some studies conjecture it to be the result of the random interference pattern created of a few strong multipath components, as for example in [AS97]. ...
... This may be explained by the common indoor part of the channel, contributing more to the overall correlation. A similar argument was made in [ACM88], where the effect of shadow fading correlation on the macro-diversity was studied. Therein, the shadow fading was argued to be the sum of two components; an outdoor part S i for i = 1..3 and an indoor part S x for each of the base stations i, as shown in Figure6.8. ...
Future wireless communication systems will utilize the spatialproperties of the wireless channel to improve the spectralefficiency and thus increase capacity. This is realized bydeploying multiple antennas at both the transmitter and receiver.Development and analysis of communication systems utilizing thespatial properties of the channel requires channel models thatproperly reflect these characteristics.
Due to the unpredictable nature of the wireless channel, a commonapproach is to model its effects statistically. A few largeworld-wide cooperations, like the third generation partnershipproject (3GPP) or wireless world initiative new radio (WINNER)project, have developed channel models intended for reference andstandardization use. These models are partly based on some bulkparameters that describe the characteristics of the channel overlarger areas of several wavelengths. Such parameters includeshadow fading, angle spread, and delay spread, among others, andare within the WINNER project called large-scale (LS) parameters.In the spatial channel model (SCM) and the WINNER model, theselarge-scale parameters are, however, assumed independent betweenseparate links, i.e., between channels modelling the propagationbetween one mobile and several base stations, or between one basestation and several mobiles. Such assumptions may be valid forsingle-link, singe-cell systems, where each communication link issufficiently separated in either time or frequency. In practice,dependencies between parameters describing separate wirelesschannels is expected. Future systems will allow a dense frequencyreuse, and results from system evaluations based on models withindependent links may be inaccurate. Examples of this may be insystems that exploit the spatial nature of the channel, likemulti-user scheduling using a single carrier, or macro-diversitysystems deploying several base stations. Therefore, it isimportant to analyze multi-node measurements in order to extractand characterize this channel dependence.
This thesis focuses on representing the wireless channelstatistically. Through unique multi-site channel measurements andanalysis, key parameters describing the channel namely shadowfading, delay spread and angle spread at both the base station andthe mobile station are extracted. For these parameters, the firstand the second order statistics are derived, and plausibledistributions and models are proposed. Further, the spatial andcorrelation properties of these parameters are analyzed. Moreover,a study highlighting the effect of the independent channelassumption is given, showing the importance of modelling thespatial dependence between the LS parameters when analyzingsystems that utilize the channel's spatial properties.Incorporating the models and correlation properties found hereinfor the LS parameters results in channel models appropriate formulti-node communication analysis and evaluation.
ACCESS
... All nodes have a transmit power of 40dBm and the thermal noise floor is ½¿¼dBm, corresponding to a receiver noise temperature of 300K and channel bandwidth of 25kHz. An Ö path loss relationship [8] and correlated lognormal shadow fading with a standard deviation of 8dB [9] are 1 In practice it would be difficult to detect a dropped call, or a blocked call caused by the MINSNR threshold. These performance measures are used solely as a means of determining the capacity of a system. ...
... All nodes have a transmit power of 40dBm and the thermal noise floor is ½¿¼dBm, corresponding to a receiver noise temperature of 300K and channel bandwidth of 25kHz. An Ö path loss relationship [8] and correlated lognormal shadow fading with a standard deviation of 8dB [9] are used. Two coupled features affecting the performance of the allinformed net were identified; the number of users in the net, and the effects of lognormal shadowing. ...
The performance of an all-informed net communications architecture
which employs a distributed channel assignment scheme is considered
using both analysis and simulation for a terrestrial radio environment.
Simulation is carried out using a commercial protocol modelling tool and
a novel technique is developed which reduces simulation times
significantly. It is found that the call blocking performance of the
architecture is determined largely by lognormal shadowing, if the number
of nodes per net is large and it is required that all nodes can
simultaneously receive voice calls. However, the call dropping
performance is largely invariant to the number of nodes per net,
providing there are at least 20 users per net
... In all the cases, the simulation results match with our theoretical results. 2 If cov(Xi, Xj ) ≥ 0 then Xi and Xj are positively correlated RVs, where cov(Xi, Xj ) denotes the covariance between Xi and Xj [28]. 4 ...
When the user channel experiences Nakagami-m fading, the coverage probability expressions are theoretically compared for the following cases: (i). The N interferers are independent $\eta$-$\mu$ random variables (RVs). (ii). The N interferers are correlated $\eta$-$\mu$ RVs. It is analytically shown that the coverage probability in the presence of correlated interferers is greater than or equal to the coverage probability in the presence of independent interferers when the shape parameter of the channel between the user and its base station (BS) is not greater than one. Further, rate is compared for the following cases: (i). The user channel experiences $\eta$-$\mu$ RV and the $N$ interferers are independent $\eta$-$\mu$ RVs. (ii). The N interferers are correlated $\eta$-$\mu$ RVs. It is analytically shown that the rate in the presence of correlated interferers is greater than or equal to the rate in the presence of independent interferers. Simulation results are provided and these match with the obtained theoretical results. The utility of our results are also discussed.
... The random variable S models the shadowing effect of large objects in the environment between the transmitter and the receiver. As a result, it is modelled as the product of transmitter and receiver location dependent factors [54]. Both of these factors are log-normally distributed with zero means and standard deviations of σ t and σ r , respectively. ...
... Macroscopic diversity can be used to enhance the overall performance of a communications link with respect to signal strength (for DS-CDMA this reduces the required Eb/No to support a given error rate) and signal-to-interference ratio for an interference limited system. It has been shown that macroscopic diversity can reduce the link margin required for a 99-percent reliability system by as much as lOdB [5]. ...
A study into the application of soft handoff in wideband direct
sequence code division multiple access (DS-CDMA) communications systems
is described. Soft handoff is explained in terms of macroscopic
diversity, a form of diversity combining in which signals transmitted
via independently fading paths can be combined in order to enhance the
overall performance. Results from a series of outdoor propagation
studies, specifically designed to investigate the propagation aspects of
soft handoff, are presented, and the future work activities of the
project are outlined
... Normal values for σ, reported in literature, is between 5 to 12 dB, [Gra78], but standard deviations of 16 dB and above have been reported for indoor scenarios in for example [SR92]. The shadow fading is in most literature assumed to be the effect of physical shadowing caused by objects in the signal propagation path, [ACM88], [WL02]. However, some studies conjecture it to be the result of the random interference pattern created of a few strong multipath components as for example in [AS97]. ...
Future wireless communication systems will utilize the spatial properties of the wireless channel to improve the spectral efficiency and thus increase capacity. This is realized by deploying multiple antennas at both the transmitter and receiver. Utilizing the spatial properties of the channel demands channel models that properly reflect these characteristics. Due to the unpredictable nature of the wireless channel, a common approach is to model its effects in a statistical fashion. A few large world wide cooperations, like the 3GPP or WINNER projects, have developed channel models intended for reference and standardization use. These models are partly based on bulk parameters which describe the characteristics of the channel over larger areas of several wavelengths. These parameters include shadow fading, angle spread, and delay spread among others, and are within the WINNER project called large scale (LS) parameters. Considering the variations of these parameters, it is likely that they are correlated between closely located areas. Therefore it is of key interest to model their correlation properties instead of randomizing them independently for each new simulation. In multi-cell scenarios, when considering macro diversity or evaluation other properties such as interference and/or handover schemes, the intra site correlation of the shadow fading parameters should be taken into account for proper simulations. Neglecting this correlation the interference could be over/under estimated, hence the system capacity can be over/under estimated. Further, reliable estimations of the interference levels will increase the frequency reuse, and may even permit reuse within the same cell, on spatially separated links. The thesis focuses on modelling the statistics and variations of these parameters to increase accuracy of channel models. Previous studies have looked at the autocorrelation properties of the shadow fading in outdoor environments and found it to follow an exponential decay. This means that an first order autoregressive function would be sufficient to model this effect. Research of the angular spread parameter is more scarce, and therefor this issue is studied herein. In addition to the autocorrelation properties the intra-site correlation between the different large scale parameters is of interest. It is herein found that the shadow fading is negatively correlated with angle spreads, while the angle spread at the base station and the angle spread at the mobile show positive correlation. Finally, the inter site correlation between one mobile and multiple base stations is studied as a function of the angular separation between the links. For closely located base station, ie with small angular separation as seen from the mobile, substantial inter-site correlation is found. It is further seen that the correlation of the shadow fading is more prominent than the correlation of angle spread. QC 20101109
... 1. Further studies on the correlation of shadow fading between several sites can be found in for example [15], [17], [18], and [19]. The angular spread parameter has been less studied. ...
The inter- and intrasite correlation properties of shadow fading and power-weighted angle spread at both the mobile station and the base station are studied utilizing narrowband multisite MIMO measurements in the 1800 MHz band. The influence of the distance between two base stations on the correlation is studied in an urban environment. Measurements have been conducted for two different situations: widely separated as well as closely located base stations. Novel results regarding the correlation of the power-weighted angle spread between base station sites with different separations are presented. Furthermore, the measurements and analysis presented herein confirm the autocorrelation and cross-correlation properties of the shadow fading and the angle spread that have been observed in previous studies.
... The shadowing factor a i,l between a mobile i and base station j can be written as: a i,l = a c,j .a s,i,j , where a c,i is the common factor of the mobile and a s,i,j is the specific factor to base station j [11] [12]. The first factor models the effect of obstacles close to the mobile and it is common for all base stations. ...
TD-CDMA TDD technique allows UMTS to utilize the bandwidth and the rare radio resource more efficiently if dynamic channel allocation is used. This technique is suited especially for systems that offer highly asymmetric services. However, the rate of symmetry is not the same in all cells. Hence, it is possible that in some slots, called crossed slots, a set of cells is active in downlink and another set is active in uplink. Inter-BS and inter-MS interferences arise in these slots and can degrade dramatically the QoS. In this paper, we introduce a scheme to prevent mobiles that can introduce very high inter-mobile interference from being active during crossed slots. In this scheme, a mobile can be active during a crossed slot with mobiles of a neighboring cell, if the path gain between the mobile and the neighboring base station is less than a given threshold. For high loads, this scheme has shown better results than common switching point technique where crossed slots are forbidden and other interference avoidance methods.
... Macroscopic diversity can be used to enhance the overall performance of a communications link with respect to signal strength (for DS-CDMA this reduces the required Eb/No to support a given error rate) and signal-to-interference ratio for an interference limited system. It has been shown that macroscopic diversity can reduce the link margin required for a 99-percent reliability system by as much as lOdB [5]. ...
Results are presented from an initial study into the application
of soft handoff to wideband DS-CDMA systems. As a precursor, soft
handoff is explained in terms of macroscopic diversity combining,
leading to an examination of soft handoff on the system design with
particular reference to the control signalling involved with its
implementation. An outdoor propagation experiment was designed to
specifically investigate the propagation aspects of soft handoff. The
propagation equipment, environment selected and the results obtained
from this study are then presented. The paper concludes with a
discussion of the work presented and an outline of future work
activities
... This is all assuming that the receiver and antenna technology used at the subscriber site allows these links to be monitored simultaneously and continually, and the antenna main beam to be rotated, either electrically or physically, to execute the handover. In principle, it is akin to a macrodiversity scheme employed in mobile cellular systems to combat shadowing effects, taking the advantage of the fact that the effects of obstruction losses around links that connect a mobile terminal to different base stations are only partially correlated [2], [3]. ...
An examination of potential advantages of cell-site diversity with
selection combining in the context of MM-wave fixed cellular systems is
reported. The study involves simulation of converging radio links over
weather radar images of the radar reflectivity factor, from which the
specific attenuation of rain at 30 GHz is derived. The average
correlation of attenuation on two converging links as a function of
their angular separation is shown to indicate the potential benefits in
the use of cell-site diversity, especially in heavy rain. Results show
that diversity gain exhibits a dependence on angular separation θ
in the general form of sin<sup>k</sup> (θ/2). For links of
identical lengths the model reduces to a root-sinusoidal shape (k=0.5),
whereas links of unequal lengths lead to the ITU-R recommended model
(k=1). Based on the sin<sup>k</sup> (θ/2) model and observation
of the length ratio of the links, a set of criteria for determining the
benefit of cell-site diversity for a given subscriber location is
proposed
... In a more general model [9], the shadowing can be described as the product of two log-normal components, one associated with the receiving cell site (independent on distinct paths) and one associated with the transmitting mobile (equal for all paths). In the case with power control, this has no effect (except for the reduction of ), since only ratios of the shadowing variables occur, and therefore the common component cancels out. ...
In this paper, we provide a general analytical framework for the computation of the interference statistics in mobile radio cellular systems. This approach, which takes into account log-normal shadowing, distance path loss, best cell site selection and power control based on signal strength, applies to various cellular environments, including narrowband systems (e.g., IS-54 and group special mobiles GSM) and code-division multiple-access (CDMA) systems. Some examples of application are provided.
This chapter introduces a hybrid optical wireless access network. To address different challenges simultaneously, a hybrid network should be broadband, ubiquitous, scalable, and cost-effective. Both optical and wireless segments complement its counterpart to fulfill these requirements. It review WiMAX technology to date and a wireless mesh network that enables the wireless segment of the hybrid architecture. The chapter reviews a hybrid optical-wireless network architecture that consists of reconfigurable optical backhaul and wireless mesh network. The reconfigurable TDM/WDM optical backhaul aims to address the scalability issue in WMN and upgrade for hierarchical wireless access networks. TDM-PON technology is leveraged due to its scalable medium access control (MAC), flexible architecture, cost-effectiveness, and technological maturity. Reconfigurability is implemented in the optical backhaul for bandwidth reallocation to improve resource utilization. The experimental testbed demonstrates its feasibility. An integrated routing algorithm is developed for this hybrid architecture. media access protocol; optical modulation; time division multiplexing; wavelength division multiplexing
Broadband optical access network is an ideal solution to alleviate the first/last mile bottleneck of current Internet infrastructures. Richly illustrated throughout to help clarify important topics, Broadband Optical Access Networks covers the architectures, protocols enabling technologies of broadband optical access networks, and all current and future competing technologies for access networks. This comprehensive work presents the evolution of optical access networks, including reach extension, bandwidth enhancement, and discusses the convergence of optical and wireless technologies for broadband access, making it an invaluable reference for researchers, electrical engineers, and graduate students.
With the fast development of high-speed railways, the need for wireless communication to satisfy secure demand of train and application demand of passengers has become evident.As a part of large- scale propagation effects, shadow fading is of great importance to design hand-over algorithm, and to evaluate macro diversity gain in wireless communications. This paper offers an investigation on the cross-correlation property of shadow fading in high-speed railway (HSR) network, based on the empirical data measured along Xingyang to Luoyang HSR line of China. The measurements indicate that the crosscorrelation coefficient of shadow fading is correlated to the separation distance between two base stations. Several models, to describe the relation between the cross-correlation coefficient and the separation distance, are proposed and compared with each other in this paper, and a decaying exponential model is finally suggested to characterize the cross-correlation property in the HSR environments.
We report results from extensive measurements based study to understand the shadow fading correlations. We have particularly studied and analyzed common assumptions done in literature for shadow fading, which is typically modeled as a spatially correlated Gaussian random process in the logarithmic scale. We show that these assumptions, starting from the Gaussianity of the radio propagation environment, do not always hold. We then discuss the assumptions regarding spatial correlations, usually taken to depend only on the distance between the points and assuming that these correlations remain the same throughout the area under consideration. This is done by comparing received power measurements for two different propagation environments, an urban and a sub-urban one, against simulated values based on typical theoretical assumptions. We conclude by explaining how these assumptions should be carefully taken into account and how they can affect simulation results and the performance of applications.
The propagation characteristics of a slotline structure under the influence of a static magnetic field have been studied using the model developed by Mark W. Coffey and John R. Clem. The complex valued resistive boundary condition formulated using the Coffey and Clem (CC) model is used to modify the dyadic Green’s function in the spectral domain for the slot transmission line. The propagation characteristics are then calculated using the Galerkin’s procedure. The numerical results are presented for propagation parameters and quality factor for a wide range of applied field, reduced temperature and superconducting layer thickness. The increase of the magnetic field and temperature causes an increase in vortex motion which results in a corresponding change in the propagation parameters and quality factor. The variation in the quality factor with respect to the superconducting strip thickness is explained using vortex effects.
The outage probability of a composite microscopic and macroscopic diversity system is evaluated over correlated shadowed fading channels. The correlations on both a microlevel and macrolevel are taken into account for the evaluations. The expression of the desired outage probability is explicitly presented, and two evaluation approaches, i.e. a compact Gaussian-Hermite quadrature method and an effective iterative algorithm, are proposed. The accuracy and efficiency of the proposed approaches are analysed, and a guideline is provided for their application. By employing the proposed evaluation approaches, results and demonstrations are presented, which display the implied effects of the corresponding parameters on the system outage performance, and reveal the potential to facilitate the design and analysis of such composite diversity systems.
Broadband analog transport facilities using fiber or fiber/coax cable can play a significant role in the evolution of the network infrastructure for personal communications services (PCSs). Low-power PCS systems require a dense grid of radio ports to provide connectivity to the telephone network. Analog transport has a number of important advantages over digital transmission facilities, including the flexibility to support a variety of air interface formats, shared infrastructure cost with other services such as video distribution, and centralized call processing allowing the use of low cost and simple radio ports. A simulcast technique can be used in such systems to permit low rates of handoff (no handoff within each simulcast area) and sharing of hardware resources among multiple radio ports. This paper provides a detailed model and a simulation analysis of the cochannel interference and noise performance as well as the resource sharing benefit of a simulcast PCS system. Several potential PCS air interfaces are considered, including time division multiple access (TDMA) and code division multiple access (CDMA) techniques. Our investigation shows that the impact of multiple antenna noise in a simulcast system is offset by the improved signal-to-interference (SIR) ratio brought about by distributed antennas. Even with distributed antennas, multiple antenna noise places a limit on the maximum number of radio ports that can be assigned to each simulcast group. This limit, however, is shown to have little impact on the achievable resource sharing benefit of simulcasting (i.e., grouping beyond this limit has diminishing returns). A saving of 40% to 60%, in terms of the required central hardware resources, is typical for both TDMA and CDMA systems in suburban environments
The author gives results of a simulation study of the uplink and
downlink transmission quality of portable-radio-based multiple access in
a frequency-reuse radio system. In addition to shadow and Rayleigh
fading, the positional variability of portable users, differences in
uplink and downlink interference, and independence of multipath fading
for the uplink and downlink are modeled. The study has shown that
portable-radio-based multiple access can provide acceptable two-way
transmission quality in an interference-limited environment. This
assumes a simple and economical fixed-port configuration based on one
TDM/TDMA (time-division multiplexing/time-division multiple-access)
channel assigned to each port in a regular reuse pattern operating
independently in terms of control and signal processing. It is shown
that this approach provides a cost-effective design for the fixed radio
port grid
The ability to provide a CT2 radio-over-fiber system employing
macro-diversity to support cordless communications via radio
distribution points in the local loop is addressed. The functionality of
the radio-over-fiber system is described, and with the centralization of
the base equipment within a local exchange the implementation of
macro-diversity has been simplified. In order to provide quality
communication comparable to the PSTN, it is necessary to support
macro-diversity clusters to overcome the slow fading or large-scale
variation in the radio signal caused by the shadowing from buildings and
terrain. The improvement achieved through the use of macro-diversity is
demonstrated
We consider a single mobile station in a wireless cellular network, and focus on the uplink. The mobile's transmis- sions can be received by more than one base station (BS). Each BS has multiple antennas and is assumed to perform maximal ratio combining (MRC) on them. Based on the signal to noise ratio (SNR) at the output of the combiner at each BS, a system controller (e.g., the RNC in UMTS) de- cides to accept the received frame at exactly one BS and reject all other BSs. This is called "switching" and the chosen BS is the one with largest averaged received sig- nal power over some time duration. Since switching can be quite costly in terms of signaling overhead, we impose a hysteresis threshold for switching, and we study the case where switching can only occur at certain periodic inter- vals, called "switch-and-stay macrodiversity." We provide an analytical expression for the probability of outage at any given location for the mobile, i.e., the probability that the SNR at the MRC output of whichever BS is selected by the system controller is less than some chosen threshold. We can then obtain numerically the dependence of this outage probability on parameters like the hysteresis threshold and the degree of microdiversity at each BS.
This paper proposes and analyzes a criterion for database update frequency in universal portable digital communication (UPDC), based on the rate of diffusion of mobile subscribers. More frequent updates reduce the search area, which reduces expected paging time and paging traffic at the expense of database size.
As the complexity and applications of Fixed Wireless Loop (FWL) systems keeps growing, it is becoming less and less practical to fully compare their performance without resorting to simulations at some point. This paper introduces several common types of statistical relationships between links, analyzes some of their causes and effects, and shows ways to take them into account when running capacity simulations.
Macroscopic diversity improves radio link performance by combating
shadow fading. Signals from paths between a mobile and different base
stations are combined to mitigate log normal shadow fading. Link
improvement is a function of cross correlation of shadow fading on paths
between mobile and base stations. The lower the positive cross
correlation, the higher the gain from macroscopic diversity. Negative
cross correlation provides even higher gain. Signal level data were
collected from a 1900 MHz GSM system in rural and suburban areas. The
shadow fading cross correlation for several different base stations and
a mobile traveling in an area ranged from -0.34 to +0. 43. Standard
deviations for different paths ranged from 2 dB to 10 dB, and
decorrelation lengths ranged from 50 m to 500 m. The angle between paths
from the mobile to the base stations was calculated
We focus on maximum ratio combining at each base station and
switching between base stations as a simple macrodiversity technique. We
obtain analytical results for outage (uncovered fraction of a cell) and
bit error rate for systems using one or a combination of both techniques
to cover a desired area, assuming a certain correlation model for the
set of path losses of the links connecting a terminal to the receiving
base stations. Outage probabilities and bit error rates are averaged
over the entire region of interest to get an estimate of the outage
fraction in the desired region
We focus on maximum ratio combining at each base station and
switching between base stations as a simple macrodiversity technique, We
obtain analytical results for outage (uncovered fraction of a cell) and
bit error rate for systems using one or a combination of both techniques
to cover a desired area, assuming a certain correlation model for the
set of path losses of the links connecting a terminal to the receiving
base stations. Outage probabilities are averaged over the entire region
of interest to get an estimate of the outage fraction in the desired
region
This paper describes a fixed wireless local loop (FWLL) system
designed to provide data and voice services to fixed users. The FWLL
system uses electronically steerable base-station (BS) antennas that
generate multiple narrow beams which hop around when communicating with
terminals. The multiple access is provided by TDMA and the up/downlinks
operate in a frequency division duplex (FDD) mode. The same frequency
band is reused in all the cells. With the help of simulations we
evaluate the system's capacity which, in this context, is the number of
serviceable terminals per cell for a given percentage of terminals that
exceed a preset signal to interference ratio (SIR). We also study the
effect of various antenna parameters on the system's capacity. We show
an improvement in capacity if a terminal has the ability to communicate
with the BS to which it has the least path-loss instead of being
required to always communicate with the BS located geographically
closest
By adding site diversity techniques to space diversity systems,
the BER (bit error rate) floor at cell edges in cellular system, which
mainly depends on the effect of time delay spread, can be significantly
improved. Site diversity techniques can reduce the cost of installing a
system by expanding the distance between CSs (cell stations) without
increasing the transmission power. This paper presents improvement of
BER with site diversity in the presence of Rayleigh fading, log-normal
shadowing, path loss, and time delay spread. Time delay spread, which
varies with distance, is treated as noise
We discuss the procedure for performance evaluation of the
previously introduced by us multiply-detected macrodiversity (MDM)
scheme. The MDM scheme, in contrast with the traditional macrodiversity
scheme, is not based on selection, but rather on postdetection
combining. In particular, we compare the performance of the MDM scheme
with the performance of the S-macrodiversity in the presence of shadow
fading. Our performance evaluation results lead us to some insights into
the factors that contributes to the improvement of the MDM scheme
More than a factor of 3 increase in overall PCS capacity can be achieved in small, hand-held communication devices with limited battery power or in small, low-complexity base stations when incorporating simple interference cancellation techniques without training sequences in the channel access algorithm that realizes macroscopic selection diversity based on signal quality measurement. The comparison is done with respect to microscopic selection diversity and macroscopic selection diversity based on channel power measurement. Results were obtained by computer simulations
Personal communications systems (PCS) are proposed to divide the
radio spectrum into a number of frequency sets, with each port having
its own set of frequencies. The frequency sets are reused at spatially
separated radio ports to minimize cochannel interference. This paper
analyzes a radio access system that has multiple antennas spatially
distributed throughout the coverage area of a radio port, instead of a
single antenna at the radio port. The same signal is simulcast by each
antenna in the coverage area of the port. This paper presents
simulations of automatic link transfer (ALT) for ports with distributed
antennas. ALT is called “handoff” in cellular systems. A
model of shadow fading with distributed antennas is described.
Simulation results are given with different numbers of distributed
antennas and different ALT algorithms. It is shown that increasing the
number of antennas results in better overall ALT performance, with a
lower number of ALTs and higher minimum received signal power.
Minimizing the number of ALTs will reduce the impact of wireless
services on network elements
The paper analyzes a radio access system that has multiple antennas spatially distributed throughout the coverage area of a radio port, instead of a single antenna at the radio port. The same signal is simulcast by each antenna in the coverage area of the port. The signals at a given port could be multiplexed and modulated for radio transmission at a single node, then transmitted on a coaxial cable bus to and from the distributed port antennas. Frequency translation and RF amplification may need to be performed at each antenna, except for indoor applications with short coaxial cables. The paper presents calculations of signal to interference ratios (SIR) of ports with distributed antennas. It is shown that the use of distributed antennas can substantially increase the SIR above a system with a single antenna per port, and this increase is quantified
Broadband analog transport facilities using fiber or fiber/coax cable can play a significant role in the evolution of the network infrastructure for personal communications services (PCS). Low-power PCS systems require a dense grid of radio ports to provide connectivity to the telephone network. A simulcast technique can be used in such systems to permit low rates of handoff (no handoff within each simulcast area) and sharing of hardware resources among multiple radio ports. This paper presents a simulation analysis of the cochannel interference and noise performance as well as the resource sharing benefit of a simulcast PCS system. Our investigation shows that the the impact of multiple antenna noise in a simulcast system is offset by the improved signal-to-interference ratio brought about by distributed antennas. Even with distributed antennas, multiple antenna noise places a limit on the maximum number of radio ports that can be assigned to each simulcast group. This limit, however, is shown to have little impact on the achievable resource sharing benefit of simulcasting (i.e., grouping beyond this limit has diminishing returns). A saving of 40% to 60%, in terms of the required central hardware resources, is typical in suburban environments
Multi-frequency CW measurements were made in residential
environments over the frequency range of 455 MHz to 4.2 GHz, for
personal communications. The seasonal effects of vegetation were also
estimated. The base station antenna height was 8.2 m (27 ft). The
results show an additional transmission loss of about 15 dB for 300
meter (1000-foot) paths and similar antennas at 1.9 GHz, compared to 815
MHz. The standard deviation of the data and the distance exponent of the
median level also increase by approximately 10 percent. A link budget
analysis examines the implications for providing personal communications
services
Computer simulation results are given for two-way transmission
quality resulting from portable radio access. Downlink and uplink
performance were examined for a range of frequency reuse factors,
propagation models and traffic levels. The effect of traffic on the TDMA
(time-division multiple access) uplink is given as a function of
occupancy. It was found that uplink transmission quality lags behind
that of the downlink in moderate to heavy cochannel interference
environments, but not unmanageably so
An empirical propagation model and the performance of a two-branch
macroscopic diversity configuration for indoor microcells are presented.
The model is based on measurements made in three different cell types
classified according to the indoor environment. Analysis of measured
signal strength levels has shown that macroscopic diversity techniques
can be used to reduce the link margin for the required 99% area coverage
in each cell type. The reduction is dependent of the fading distribution
and the maximum achievable rate at which the best path can be selected.
The gain with selective macroscopic diversity varies from 4 dB in a cell
with high overall propagation attenuation to 10 dB in an open area cell
type with lower propagation attenuation. This reduction is obtained when
the selections between base stations are made at intervals shorter than
25 cm and the short-fading component is eliminated. The gain can be as
high as 12 dB, if all fading is taken into account and the selections
are made at intervals shorter than 4 cm
We focus on maximum ratio combining at each base station and switching between base stations (BSs) as a simple macrodiversity technique. We obtain analytical results for pointwise outage probabilities for systems using one or a combination of both techniques to cover a desired area, assuming a certain correlation model for the set of path losses of the links connecting a terminal to the receiving BSs. Pointwise outage probabilities are averaged over the entire region of interest to get an estimate of the outage in the desired region. A comparison of micro- and macrodiversity schemes in terms of the outage gives insights as to the tradeoff between the two forms of diversity in the design of a cellular system.
The performance of a multicell DS-CDMA cellular system with base
station diversity is studied taking into consideration the effects of
imperfect power control, multipath fading, shadowing and the dependence
of propagation losses to a different base station from a mobile user. It
is assumed that a mobile user is connected to the base station that
provides the least attenuation among a set of closest uniformly
correlated base stations. Analytical expressions are derived for the
average probability of error of binary phase shift keying modulated
signals for both the reverse link and the forward link. The channel is
assumed to undergo correlated lognormal shadowed Rayleigh fading.
Analytical results show that base station diversity significantly
improves system performance
There is a widespread notion within the North American cellular
industry that present cellular systems are intrinsically
interference-limited. This idea in part comes from a number of reported
simulations which were based on the assumption that mobiles always
connect to the nearest base station. We present analytical and
simulation results for the case where mobiles are connected to the best
base station (the one with the strongest signal). At the 10 percent
outage level, it is shown that the nearest server scenario tends to
underestimate the carrier-to-interference (C/I) ratio by as much as 5 dB
(with respect to the best server case). Some system imperfections which
are not traditionally assessed by such simulations are further
discussed. In particular, nonideal positioning of the base stations was
found to have negligible impact on C/I if the traditional cellular
rule-of-thumb criteria are obeyed. Nonuniform spatial distribution of
the mobiles was analyzed based on real data from the Toronto area. It
was found to have negligible impact on the average C/I performance.
Blocking problems in such a case, however, could easily reduce the
theoretical capacity with uniform loading by as much as 30 percent.
Finally, C/I deteriorations due to nonideal handoffs are examined. This
analysis is very sensitive to the handoff mechanism implementation
details. Although the results for hand-offs should be regarded with some
caution, in view of all the results presented in this article we feel
that cellular systems are in general limited by blocking rather than by
interference
Methods of substantially reducing call dropping in networks which
use distributed dynamic channel assignment (DDCA) schemes are discussed.
Interference and received power thresholds coupled with power control
are used to maintain performance, without the need for intra-cell
handoffs. It is shown that the schemes reduce call dropping and increase
capacity compared to those using fixed transmitter power. The schemes
are developed with the aid of mathematical analysis and a pictorial
model. Results are presented which show that call dropping may be
virtually eliminated in shadowing environments with the median
transmitter power being reduced by 15 dB. The various call dropping
mechanisms are discussed, and it is suggested that the residual level of
call dropping is principally a result of multiple additional call
arrivals close to an active link. Methods to make further reductions in
the call dropping probability are also proposed
A 10-cell, 10-channel line-of-sight (LOS) microcellular
environment with Poisson arrivals and exponentially distributed holding
times is stimulated. The performance of cellular systems for personal
communications networks (PCNs) is evaluated. Call blocking, bumping, and
dropping probabilities, as affected by fast fading, power control, and
traffic load, for LOS, 900-MHz microcellular environments are discussed.
It is established that DRA (dynamic resource allocation) using local
information only does not result in a performance penalty. In fact, in
the cases of interest, it performs significantly better than fixed
channel allocation, increasing capacity by about 20%, or even as much as
60% with power control. It is shown that fast fading results in a
limited increase, about 2-3 times the blocking probability, while the
use of power control translates directly, and consistently, into a
significant increase in traffic handling capacity
A computer-simulation study of user access in a universal digital
portable communications system is described. An access algorithm
consisting of relative power channel-ranking followed by data error
detection is evaluated and compared to an optimal reference in a
co-channel interference environment. For typical propagation conditions
and radio configurations, it was found that an access algorithm based on
the ranking of system channels by relative power provides a viable means
of channel selection for the portable radio. It was found that the
multiple-block data error check improved transmission quality in a
co-channel interference environment, approaching the optimum with
respect to the 99% statistical reliability criterion
The effect of correlated lognormal shadowing on the average
probability of error performance of narrow-band mobile communication
systems with micro- and macrodiversity reception in a Rician fading
channel is studied by considering a constant correlation model for the
shadowed signals at the base stations. The performance degradation due
to correlated shadowing is illustrated by considering both coherent and
differentially coherent binary phase-shift keying schemes. Numerical
results presented show that when the base stations in a cellular system
are very closely spaced, the effect of correlated shadowing on system
performance cannot be ignored
Adaptive modulation techniques have the potential to substantially
increase the spectrum efficiency and to provide different levels of
service to users, both of which are considered important for
third-generation cellular systems. In this work, we propose a general
framework to quantify the potential gains of such techniques.
Specifically, we study the throughput performance gain that may be
achieved by combining adaptive modulation and power control. Our results
show that: (1) using adaptive modulation even without any power control
provides a significant throughput advantage over using
signal-to-interference-plus-noise ratio (SINR) balancing power control
and (2) combining adaptive modulation and a suitable power control
scheme leads to a significantly higher throughput as compared to no
power control or using SINR-balancing power control. The first
observation is especially important from an implementation point of
view. Adjusting the modulation level without changing the transmission
power requires far fewer measurements and feedback as compared to the
SINR-balancing power control or the optimal power control. Hence, it is
significantly easier to implement. Although presented in the context of
adaptive modulation, the results also apply to other variable rate
transmission techniques, e.g., rate adaptive coding schemes, coded
modulation schemes, etc. This work provides valuable insight into the
performance of variable rate transmission techniques in multi-user
environments
The signal levels around and within eight suburban houses were measured at 800 MHz. These measurements are needed in refining the requirements for portable-radio communication systems that can accommodate low-power radiotelephone sets. The measurements were made from an instrumentation van having an erectable 27-foot-high antenna. Large-scale distributions of the small-scale signal medians are approximately log normal. The decrease in median signal level with distance ranges from d−3 to d−6.2 for the eight houses. Signal decreases as d−4.5 for the overall data set. At 1000 feet, regressions to signal levels range from 12.5 to 37.1 dB below free-space propagation levels for locations outside and locations inside on first and second floors. In basements, regression levels at 1000 feet range from 29 to 48.2 dB below free space. For the overall data set, regression signal levels at 1000 feet are 27.7 dB below free space. For all the basements, this value is 39.6 dB. Other signal statistics are given in this paper.
The cellular concept used in the Advanced Mobile Phone Service (amps) system to achieve spectrum efficiency requires a complex and flexible distributed system control architecture. Three major subsystems serve as the control elements: the mobile unit, the cell site, and the switching office. System control functions are partitioned among these subsystems to handle the following amps control challenges: interfacing with the nationwide switched telephone network, dialing from mobile units, supervising calls from mobile subscribers in the presence of noise and co-channel interference, performing call setup functions including paging and access, and locating and handing off mobiles between cell sites. This paper explains the techniques used to achieve the control functions of the three major subsystems and the ways they in turn participate in control of the total amps system.
Conventional space diversity reception at typical elevated base locations requites separation of 30λ for broadside incidence and even more for in-line incidence and is therefore difficult to implement. A polarization diversity system for mobile radio is proposed. This is a two-branch receiver diversity system with the advantage that the base station antennas can be spaced as closely as desired. An experimental program has been carried out to obtain the statistical properties of vertically and horizontally polarized electromagnetic waves in a suburban environment at 836 MHz. It was observed that signals of both polarizations were Rayleigh plus log normal, where one is uncorrelated and other is correlated irrespective of base or mobile antenna spacings. The local means of the two signals were highly correlated and were with ± 3 dB for almost 90 percent of the time. Variation of base transmitter heights appeared to have little effect on the ratio of the local means of the two signals. The analysis and experiment demonstrated the feasibility of providing two diversity branches at UHF by polarization diversity.
Radio transmission in the portable communications environment is plagued by deep rapid fading due to random handset orientation and multipath propagation. The letter describes a propagation experiment designed to determine the usefulness of polarisation diversity as a means of miti gating these signal impairments.
A wide range of buildings are characterised for propagation at 900 MHz. Coverage areas and distance/power laws are given for making propagation predictions according to the building construction.
The letter reports some results of a survey which studied the propagation of radio signals at 900 MHz within buildings for the operation of cordless telephones. Histograms are presented of signal strength together with computed values for bit-error ratio for digital FSK modulation. A distance/power law is derived appertaining to the propagation characteristics of the building.
In our highly mobile society, the provision of voice and data communications to people away from their wireline telephones has become a major communications frontier. Some emerging radio systems, e.g., cellular mobile radio, cordless telephone, and radio paging, have begun to penetrate this frontier. However, each of these approaches only partially satisfies portable communication needs. That is, the approaches do not provide overall portable communication service. Some of the problems involved and the technologies and system configurations needed for an advanced radio communications system are discussed. The goal for the system is to provide high quality ubiquitous service to low power portable radiotelephones and data terminals. Frequency reuse radio system configurations applicable to residential and large building environments will be described along with multipath and other 800 MHz radio propagation limitations. The system would use fixed radio ports attached to the telephone network and spaced about 2000 ft in residential areas. The residential ports would have antenna heights of less than 30 ft. The horizontal spacing of ports within large buildings would be 200 ft or more. In service areas, more than 99 percent radio link availability would be provided for 5 mW portable transmitters.
Results are presented of UHF propagation measurements conducted at 820 MHz in urban Philadelphia. The Philadelphia tests departed from previous path-loss measurements in that emphasis was placed on transmission from relatively low land-site antennas at heights of 40-70 feet above local ground level. Composite path-loss statistics have been derived for transmissions from five separate locations covering local environments considered typical of an urban area. This paper describes the measurement configuration, summarizes the data processing techniques, and presents results of the analysis.
Microwave Mobile Communications
- W C Jakes