Transmission capacity of wireless ad hoc networks with outage constraints

In this paper, upper and lower bounds on the transmission capacity of spread-spectrum (SS) wireless ad hoc networks are derived. We define transmission capacity as the product of the maximum density of successful transmissions multiplied by their data rate, given an outage constraint. Assuming that the nodes are randomly distributed in space according to a Poisson point process, we derive upper and lower bounds for frequency hopping (FH-CDMA) and direct sequence (DS-CDMA) SS networks, which incorporate traditional modulation types (no spreading) as a special case. These bounds cleanly summarize how ad hoc network capacity is affected by the outage probability, spreading factor, transmission power, target signal-to-noise ratio (SNR), and other system parameters. Using these bounds, it can be shown that FH-CDMA obtains a higher transmission capacity than DS-CDMA on the order of M/sup 1-2//spl alpha//, where M is the spreading factor and /spl alpha/>2 is the path loss exponent. A tangential contribution is an (apparently) novel technique for obtaining tight bounds on tail probabilities of additive functionals of homogeneous Poisson point processes.     

Downlink capacity evaluation of cellular networks with known-interference cancellation

Recently, the capacity region of a multiple-input multiple-output (MIMO) Gaussian broadcast channel, with Gaussian codebooks and known-interference cancellation through dirty paper coding, was shown to equal the union of the capacity regions of a collection of MIMO multiple-access channels. We use this duality result to evaluate the system capacity achievable in a cellular wireless network with multiple antennas at the base station and multiple antennas at each terminal. Some fundamental properties of the rate region are exhibited and algorithms for determining the optimal weighted rate sum and the optimal covariance matrices for achieving a given rate vector on the boundary of the rate region are presented. These algorithms are then used in a simulation study to determine potential capacity enhancements to a cellular system through known-interference cancellation. We study both the circuit data scenario in which each user requires a constant data rate in every frame and the packet data scenario in which users can be assigned a variable rate in each frame so as to maximize the long-term average throughput. In the case of circuit data, the outage probability as a function of the number of active users served at a given rate is determined through simulations. For the packet data case, long-term average throughputs that can be achieved using the proportionally fair scheduling algorithm are determined. We generalize the zero-forcing beamforming technique to the multiple receive antennas case and use this as the baseline for the packet data throughput evaluation.     

On capacity of cognitive radio networks with average interference power constraints

Cognitive radio (CR) has been considered as a promising technology to improve the spectrum utilization. In this paper we analyze the capacity of a CR network with average received interference power constraints. Under the assumptions of uniform node placements and a simple power control scheme, the maximum transmit power of a target CR transmitter is characterized by its cumulative distribution function (CDF). We study two CR scenarios for future applications. The first scenario is called the CR based central access network, which aims at providing broadband access to CR devices. In the second scenario, the so-called CR assisted virtual multiple-input multiple-output (MIMO) network, CR is used to improve the access capability of a cellular system. The uplink ergodic channel capacities of both scenarios are derived and analyzed with an emphasis on understanding the impact of numbers of primary users and CR users on the capacity. Numerical and simulation results suggest that the CR based central access network is more suitable for less-populated rural areas where a relatively low density of primary receivers is expected; while the CR assisted virtual MIMO network performs better in urban environments with a dense population of mobile CR users.     

On the capacity of mobile ad hoc networks with delay constraints

Previous work on ad hoc network capacity has focused primarily on source-destination throughput requirements for different models and transmission scenarios, with an emphasis on delay tolerant applications. In such problems, network capacity enhancement is achieved as a tradeoff with transmission delay. In this paper, the capacity of ad hoc networks supporting delay sensitive traffic is studied. First, a general framework is . proposed for characterizing the interactions between the physical and the network layer in an ad hoc network. Then, CDMA ad hoc networks, in which advanced signal processing techniques such as multiuser detection are relied upon to enhance the user capacity, are analyzed. The network capacity is characterized using a combination of geometric arguments and large scale analysis, for several network scenarios employing matched filters, decorrelators and minimum-mean-square-error receivers. Insight into the network performance for finite systems is also provided by means of simulations. Both analysis and simulations show a significant network capacity gain for ad hoc networks employing multiuser detectors, compared with those using matched filter receivers, as well as very good performance even under tight delay and transmission power requirements.     

On the teletraffic capacity of CDMA cellular networks

The aim of this paper is to contribute to the understanding of the teletraffic behavior of code-division multiple-access (CDMA) cellular networks. In particular, we examine a technique to assess the reverse link traffic capacity and its sensitivity to various propagation and system parameters. We begin by discussing methods of characterizing interference from other users in the network. These methods are extremely important in the development of the traffic models. We begin with a review of several existing approaches to the problem of handling other-cell interference before presenting a novel characterization of the interference in the form of an analytic expression for the interference distribution function in the deterministic propagation environment. We then look at extending the capacity analyses that assume a fixed and equal number of users in every cell to handle the random nature of call arrivals and departures. The simplest way to do this is by modeling each cell of the network as an independent M/G/x∞ queue. This allows us to replace the deterministic number of users in each cell by an independent Poisson random variable for each cell. The resulting compound Poisson sums have some very nice properties that allow us to calculate an outage probability by analyzing a single random sum. This leads to a very efficient technique for assessing the reverse link traffic capacity of CDMA cellular networks     

Dynamic fair scheduling with QoS constraints in multimedia wideband CDMA cellular networks

A class of dynamic fair scheduling schemes based on the generalized processor sharing (GPS) fair service discipline, under the generic name code-division GPS (CDGPS), is proposed for a wideband direct-sequence code-division multiple-access (CDMA) cellular network to support multimedia traffic. The CDGPS scheduler makes use of both the traffic characteristics in the link layer and the adaptivity of the wideband CDMA physical layer to perform fair scheduling on a time-slot by time-slot basis, by using a dynamic rate-scheduling approach rather than the conventional time-scheduling approach. Soft uplink capacity is characterized for designing an efficient CDGPS resource allocation procedure. A credit-based CDGPS (C-CDGPS) scheme is proposed to further improve the utilization of the soft capacity by trading off the short-term fairness. Theoretical analysis shows that, with the C-CDGPS scheme, tight delay bounds can be provided to delay-sensitive traffic, and short-term unfairness can be bounded so that long-term weighted fairness for all users can still be satisfied. Simulation results show that bounded delays, increased throughput, and long-term fairness can be achieved for both homogeneous and heterogeneous traffic.     

Teletraffic capacity of CDMA cellular mobile networks and adaptive antennas

The teletraffic capacity of a CDMA mobile network with adaptive antennas at the receiver base station is considered and a simplified expression for the system outage probability associated with the teletraffic capacity is obtained. Analytical as well as numerical results show that the outage probability, and consequently the teletraffic capacity of the system, is improved using adaptive antennas at the receiver base station. Copyright © 2002 John Wiley & Sons, Ltd.     

Inter-cell interference in multi-tier heterogeneous cellular networks: modeling and constraints

Telecommunication Systems - Interference is the main source of capacity limitation in wireless networks. In some medium access technologies in cellular networks, such as OFDMA, the allocation of...     

Scheduling with base station diversity and fairness analysis for the downlink of CDMA cellular networks

Efficient packet scheduling in CDMA cellular networks is a challenging problem due to the time variant and stochastic nature of the channel fading process. Selection diversity is one of the most effective techniques utilizing random and independent variations of diverse channels to improve the performance of communication over fading channels. In this paper, we propose two packet scheduling schemes exploiting base station selection diversity in the downlink of CDMA cellular networks. The proposed schemes rely on the limited instantaneous channel state information (CSI) to select the best user from the best serving base station at each time slot. This technique increases the system throughput by increasing multiuser diversity gain and reducing the effective interference among adjacent base stations. Results of Monte Carlo simulations are given to demonstrate the improvement of system throughput using the proposed scheduling schemes. In addition, we investigate fairness issue of wireless scheduling schemes. Due to different characteristics of wireless scheduling schemes, the existing fairness indexes may result in misleading comparison among different schemes. We propose a new fairness index to compare the overall satisfaction of the network users for different scheduling schemes. Copyright © 2006 John Wiley & Sons, Ltd.     

A capacity degradation model under interferences for sectorized cellular networks with fractional frequency reuse

This paper presents a capacity degradation model under interferences for sectorized cellular networks with fractional frequency reuse. In a sectorized fractional frequency reuse network, allocated bandwidth consists of a number of frequency partitions. To avoid intra‐cell interferences, each frequency partition is then assigned to two different groups, the super group (Sup‐G) and the regular group. However, because a Sup‐G in a cell employs the same frequency partition as the other Sup‐Gs in the neighboring cells, inter‐cell interferences may become serious when the radius of the Sup‐G is largely increased. In the worse case, the largely increasing inter‐cell interferences will eventually degrade the overall system capacity. Additionally, different density distributions of mobile stations may have different levels of impact on the capacity degradation. In this paper, both folded normal distribution and uniform distribution are considered in building the capacity degradation model. Numerical simulations show that by carefully adjusting the ratio between the radius of the Sup‐G and the radius of a cell, (i) an mobile station could receive the same capacity no matter where it is residing, and (ii) the maximum system capacity can be therefore achieved. Copyright © 2013 John Wiley & Sons, Ltd.     

Dimensioning telephone networks with budget constraints

We present a theoretical study of a modified version of the dimensioning problem for telephone networks where the network does not contain any existing capacity and where the available capital is severely limited, a situation which can occur in private networks as well as in the public networks of developing countries. In the latter, case, the budget constraint is generally of paramount importance. This has two effects. First, the grade of service constraint is replaced by a budget constraint. Another difference from the original problem arises because the network may be operating under overload most of the time. This paper examines some cases of overload for which the link ordering is maintained. The main result of this paper is the derivation of a set of equations similar to the classical optimality equations that lead to the ECCS method, but for the modified version of the problem. As a consequence, we expect that it will be possible to obtain a fast iterative heuristic algorithm similar to the one currently used to solve the classical problem. A number of other points of theoretical interest are also discussed, mainly with the objective of gaining insight into the structure of the modified problem.     

Distributed device networks with security constraints

In today's globalized business world, outsourcing, joint ventures, mobile and cross-border collaborations have led to work environments distributed across multiple organizational and geographical boundaries. The new requirements of portability, configurability and interoperability of distributed device networks put forward new challenges and security risks to the system's design and implementation. There are critical demands on highly secured collaborative control environments and security enhancing mechanisms for distributed device control, configuration, monitoring, and interoperation. This paper addresses the collaborative control issues of distributed device networks under open and dynamic environments. The security challenges of authenticity, integrity, confidentiality, and execution safety are considered as primary design constraints. By adopting policy-based network security technologies and XML processing technologies, two new modules of Secure Device Control Gateway and Security Agent are introduced into regular distributed device control networks to provide security and safety enhancing mechanisms. The core architectures, applied mechanisms, and implementation considerations are presented in detail in this paper.     

Planning OBS networks with QoS constraints

The design of OBS networks that guarantee QoS provisioning for different classes of traffic is a major topic under current research. In this work we formulate a unified framework for studying QoS in OBS networks with a GMPLS-based control plane. We use this framework in order to investigate two problems. First, the configuration of the parameters of an aggregation strategy so that a given Forwarding Equivalency Class observes its corresponding QoS requirements. Second, we address the problem of planning a whole OBS network given a series of QoS constraints for each one of the Forwarding Equivalency Classes in the network. The presented QoS framework constitutes a valuable tool for studying QoS-related issues in OBS networks.     

三维小基站蜂窝网络上行覆盖概率与容量分析

本文针对小基站网络立体分布特性,采用全新的三维视角分析小基站网络架构,提出了一种基于三维泊松点过程（3-D Poison Point Process,3-D PPP）的上行小基站网络模型。其核心思想是将移动台和小基站分别描述成两个独立的3-D PPP模型。首先,本文推导了小基站网络上行覆盖概率的数学表达式。接下来,基于覆盖概率的表达式,推导了上行平均信道容量的闭合表达式。通过一系列合理的假设,上行覆盖概率以及信道容量可以通过快速积分直接计算。与传统的二维模型以及用户/小基站的实际布局相比较,本文提出的模型更接近实际,能够为覆盖概率和系统容量提供更贴近的边界值。      

Channel assignment algorithms satisfying cochannel and adjacent channel reuse constraints in cellular mobile networks

Improved channel assignment algorithms for cellular networks were designed by modeling the interference constraints in terms of a hypergraph. However, these algorithms only considered cochannel reuse constraints. Receiver filter responses impose restrictions on simultaneous adjacent channel usage in the same cell or in neighboring cells. We first present some heuristics for designing fixed channel assignment algorithms with a minimum number of channels satisfying both cochannel and adjacent channel reuse constraints. An asymptotically tight upper bound for the traffic carried by the system in the presence of arbitrary cochannel and adjacent channel use constraints was developed by Deora (1995). However, this bound is computationally intractable even for small systems like a regular hexagonal cellular system of 19 cells. We have obtained approximations to this bound using the optimal solutions for cochannel reuse constraints only and a further graph theoretic approach. Our approximations are computationally much more efficient and have turned out to track very closely the exact performance bounds in most cases of interest.     

Load-balance cell association for improving network capacity in heterogeneous cellular networks

Heterogeneous cellular networks improve the spectrum efficiency and coverage of wireless communication networks by deploying low power base station （BS） overlapping the conventional macro cell. But due to the disparity between the transmit powers of the macro BS and the low power BS, cell association strategy developed for the conventional homogeneous networks may lead to a highly unbalanced traffic loading with most of the traffic concentrated on the macro BS. In this paper, we propose a load-balance cell association scheme for heterogeneous cellular network aiming to maximize the network capacity. By relaxing the association constraints, we can get the upper bound of optimal solution and convert the primal problem into a convex optimization problem. Furthermore we propose a Lagrange multipliers based distributed algorithm by using Lagrange dual theory to solve the convex optimization, which converges to an optimal solution with a theoretical performance guarantee. With the proposed algorithm, mobile terminals （MTs） need to jointly consider their traffic type, received signal-to-interference-noise-ratios （SINRs） from BSs, and the load of BSs when they choose server BS. Simulation results show that the load balance between macro and pico BS is achieved and network capacity is improved significantly by our proposed cell association algorithm.     

Asymptotic capacity of two-dimensional channels with checkerboard constraints

A checkerboard constraint is a bounded measurable set S/spl sub/R/sup 2/, containing the origin. A binary labeling of the Z/sup 2/ lattice satisfies the checkerboard constraint S if whenever t/spl isin/Z/sup 2/ is labeled 1, all of the other Z/sup 2/-lattice points in the translate t+S are labeled 0. Two-dimensional channels that only allow labelings of Z/sup 2/ satisfying checkerboard constraints are studied. Let A(S) be the area of S, and let A(S)/spl rarr//spl infin/ mean that S retains its shape but is inflated in size in the form /spl alpha/S, as /spl alpha//spl rarr//spl infin/. It is shown that for any open checkerboard constraint S, there exist positive reals K/sub 1/ and K/sub 2/ such that as A(S)/spl rarr//spl infin/, the channel capacity C/sub S/ decays to zero at least as fast as (K/sub 1/log/sub 2/A(S))/A(S) and at most as fast as (K/sub 2/log/sub 2/A(S))/A(S). It is also shown that if S is an open convex and symmetric checkerboard constraint, then as A(S)/spl rarr//spl infin/, the capacity decays exactly at the rate 4/spl delta/(S)(log/sub 2/A(S))/A(S), where /spl delta/(S) is the packing density of the set S. An implication is that the capacity of such checkerboard constrained channels is asymptotically determined only by the areas of the constraint and the smallest (possibly degenerate) hexagon that can be circumscribed about the constraint. In particular, this establishes that channels with square, diamond, or hexagonal checkerboard constraints all asymptotically have the same capacity, since /spl delta/(S)=1 for such constraints.     

Exact capacity analysis of multiuser diversity combined with transmit diversity

Expressions for the average channel capacity of a multiuser diversity system combined with transmit diversity at each link are presented under the assumption of independent Rayleigh fading. The analysis results exactly agree with the simulation results and definitely show the impact of transmit diversity on multiuser diversity.     

Adaptive orthogonal frequency division multiplexing channel capacity employing diversity in cellular fading environments with symmetric scattering distributions

Gaussian and hyperbolic angle‐of‐arrival probability density functions are used to derive channel capacity of orthogonal frequency division multiplexing transmission employing diversity techniques and adaptive policies in cellular wireless fading environments. The intercarrier interference (ICI) power is quantified and given as a function of Doppler shift f_d, symbol duration T_s, frequency correction ζ and propagation ratio τ. Two scattering distributions, which have been shown to closely fit experimental empirical data, are examined in this paper: (i) Gaussian and (ii) hyperbolic. A new signal‐to‐interference‐and‐noise ratio probability density function is derived as a function of the ICI power using diversity techniques and adaptive policies. From that, effects of f_dT_s, ζ and τ on channel capacity can be discussed. The main contribution of this work is to model ICI as a function of f_d and symbol duration T_s. Two diversity techniques are considered: (i) maximal ratio combining and (ii) selective combining. Three adaptive policies are studied: (i) optimal rate adaptation, (ii) optimal rate and power adaptation and (iii) channel inversion with fixed rate. Closed‐form expressions and bounds on various channel capacity with orthogonal frequency division multiplexing transmission under different scenarios are derived. Copyright © 2012 John Wiley & Sons, Ltd.