Showing papers on "Channel allocation schemes published in 2000"

Increase in capacity of multiuser OFDM system using dynamic subchannel allocation

Abstract: This paper investigates the problem of dynamic multiuser subchannel allocation in the downlink of OFDM systems. The assumptions are that the channel model is quasi-static and that the base station has perfect channel information. In traditional TDMA or FDMA systems, resource allocation for each user is non-adaptively fixed, and the water-filling power spectrum is known to be optimal. Since the subchannel allocations among the users are not optimized, a group of users is likely to suffer from poor channel gains resulting from large path loss and random fading. To resolve this problem, we derive a multiuser convex optimization problem to find the optimal allocation of subchannels, and propose a low-complexity adaptive subchannel allocation algorithm. Simulation results show that the proposed algorithm performs almost as well as the optimal solution. Also, a higher spectral efficiency is achieved for a larger number of users in a cell due to the multiuser diversity.

A new multi-channel MAC protocol with on-demand channel assignment for multi-hop mobile ad hoc networks

Abstract: The wireless mobile ad hoc network (MANET) architecture has received a lot of attention recently. This paper considers the access of multiple channels in a MANET with multi-hop communication behavior. We point out several interesting issues when using multiple channels. We then propose a new multi-channel MAC protocol, which is characterized by the following features: (i) it follows an "on-demand" style to assign channels to mobile hosts, (ii) the number of channels required is independent of the network topology and degree, (iii) it flexibly adapts to host mobility and only exchanges few control messages to achieve channel assignment and medium access, and (iv) no clock synchronization is required. Compared to existing protocols, some assign channels to hosts statically (thus a host will occupy a channel even when it has no intention to transmit) some require a number of channels which is a function of the maximum connectivity, and some necessitate a clock synchronization among all hosts in the MANET. Extensive simulations are conducted to evaluate the proposed protocol.

Channel assignment schemes for cellular mobile telecommunication systems: A comprehensive survey

Abstract: This article provides a detailed discussion of wireless resource and channel allocation schemes. The authors provide a survey of a large number of published papers in the area of fixed, dynamic, and hybrid allocation schemes and compare their trade-offs in terms of complexity and performance. We also investigate these channel allocation schemes based on other factors such as distributed⁄centralized control and adaptability to traffic conditions. Moreover, we provide a detailed discussion on reuse partitioning schemes, the effect of handoffs, and prioritization schemes. Finally, we discuss other important issues in resource allocation such as overlay cells, frequency planning, and power control.

A game theoretic framework for bandwidth allocation and pricing in broadband networks

Abstract: In this paper, we present a game theoretic framework for bandwidth allocation for elastic services in high-speed networks. The framework is based on the idea of the Nash bargaining solution from cooperative game theory, which not only provides the rate settings of users that are Pareto optimal from the point of view of the whole system, but are also consistent with the fairness axioms of game theory. We first consider the centralized problem and then show that this procedure can be decentralized so that greedy optimization by users yields the system optimal bandwidth allocations. We propose a distributed algorithm for implementing the optimal and fair bandwidth allocation and provide conditions for its convergence. The paper concludes with the pricing of elastic connections based on users' bandwidth requirements and users' budget. We show that the above bargaining framework can be used to characterize a rate allocation and a pricing policy which takes into account users' budget in a fair way and such that the total network revenue is maximized.

Predictive schemes for handoff prioritization in cellular networks based on mobile positioning

Abstract: We propose and evaluate new schemes for channel reservation motivated by the rapidly evolving technology of mobile positioning. The schemes, called predictive channel reservation (PCR), work by sending reservation requests to neighboring cells based on extrapolating the motion of mobile stations (MSs). A number of design enhancements are incorporated to minimize the effect of false reservations and to improve the throughput of the cellular system. These enhancements include: (1) reservation pooling; (2) queuing of reservation requests; (3) hybrid approach for integrating guard channels (GCs); and (4) using a threshold distance (TD) to control the timing of reservation requests. The design enhancements have produced a set of highly efficient schemes that achieve significant reduction in handoff blocking rates while only incurring remarkably small increases in the new call blocking rates. The PCR approach has also been used to solve the MINBLOCK optimization problem and has given significant improvement over the fractional guard channel (FGC) protocol. Detailed performance results of the different variations of the PCR scheme and comparisons with conventional channel reservation schemes are presented. An analytical Markov model for the hybrid predictive version of the scheme is developed and its applicability and numerical results are discussed.

Satellite Systems for Personal and Broadband Communications

Abstract: I. Basics.- 1. Introduction.- 1.1 Mobile and Personal Satellite Communications.- 1.1.1 Applications of Mobile Satellite Communications.- 1.1.2 Personal Satellite Communications.- 1.1.3 UMTS, IMT-2000.- 1.2 Broadband Multimedia Satellite Communications.- 1.3 Frequency Bands.- 1.4 Key Aspects of Satellite Communication Systems.- 2. Satellite Orbits, Constellations, and System Concepts.- 2.1 Satellite Orbits.- 2.1.1 Elliptical and Circular Orbits.- 2.1.2 Satellite Velocity and Orbit Period.- 2.1.3 Orientation of the Orbit Plane.- 2.1.4 Typical Circular Orbits.- 2.1.5 Orbit Perturbations.- 2.1.6 Ground Tracks.- 2.2 Satellite - Earth Geometry.- 2.2.1 Geometric Relations between Satellite and Earth Terminal.- 2.2.2 Coverage Area.- 2.3 Satellite Constellations.- 2.3.1 Inclined Walker Constellations.- 2.3.2 Polar Constellations.- 2.3.3 Asynchronous Polar Constellations.- 2.4 GEO System Concept.- 2.4.1 Inmarsat-3.- 2.4.2 EAST (Euro African Satellite Telecommunications).- 2.5 LEO System Concept.- 2.5.1 Globalstar.- 2.5.2 Intersatellite Links and On-Board Processing.- 2.5.3 Iridium.- 2.6 MEO System Concept.- 2.6.1 ICO.- 2.7 Satellite Launches.- 3. Signal Propagation and Link Budget.- 3.1 Satellite Link Budget.- 3.1.1 Antenna Characteristics.- 3.1.2 Free Space Loss and Received Power.- 3.1.3 Link Budget.- 3.1.4 Spot Beam Concept.- 3.2 Peculiarities of Satellite Links.- 3.2.1 Dependence on Elevation.- 3.2.2 Time Dependence of Satellite Links.- 3.2.3 Faraday Rotation.- 3.3 Signal Shadowing and Multipath Fading.- 3.3.1 Narrowband Model for the Land Mobile Satellite Channel.- 3.3.2 Satellite Channels at Higher Frequencies.- 3.3.3 Wideband Model for the Land Mobile Satellite Channel.- 3.4 Link Availability and Satellite Diversity.- 3.4.1 Concept of Satellite Diversity.- 3.4.2 Correlation of Channels.- 3.4.3 Link Availability and Satellite Diversity Service Area.- 3.5 System Implications.- 4. Signal Transmission.- 4.1 Speech Coding.- 4.1.1 Quality of Coded Speech.- 4.1.2 Overview of Speech Coding Schemes.- 4.2 Modulation.- 4.2.1 Modulation Schemes for Mobile Satellite Communications.- 4.2.2 Bandwidth Requirement of Modulated Signals.- 4.2.3 Bit Error Rate in the Gaussian Channel.- 4.2.4 Bit Error Rate in the Ricean and Rayleigh Fading Channel.- 4.3 Channel Coding (Forward Error Correction, FEC).- 4.3.1 Convolutional Coding.- 4.3.2 Block Coding.- 4.3.3 Error Protection with Cyclic Redundancy Check (CRC).- 4.3.4 RS Codes.- 4.3.5 Performance of Block Codes.- 4.3.6 Performance of Block Codes in Fading Channels.- 4.4 Automatic Repeat Request (ARQ).- 4.4.1 Stop-and-Wait ARQ.- 4.4.2 Go-Back-N ARQ.- 4.4.3 Selective-Repeat ARQ.- 4.5 Typical Error Control Schemes in Mobile Satellite Communications.- II. Satellite Systems for Mobile/Personal Communications.- 5. Multiple Access.- 5.1 Duplexing.- 5.1.1 Frequency-Division Duplexing (FDD).- 5.1.2 Time-Division Duplexing (TDD).- 5.2 Multiplexing.- 5.3 Multiple Access.- 5.4 Slotted Aloha Multiple Access.- 5.4.1 The Principle of Slotted Aloha.- 5.4.2 Throughput of Slotted Aloha.- 5.4.3 Mean Transmission Delay for Slotted Aloha.- 5.4.4 Pure Aloha Multiple Access.- 5.5 Frequency-Division Multiple Access, FDMA.- 5.5.1 Adjacent Channel Interference.- 5.5.2 Required Bandwidth for FDMA.- 5.5.3 Intermodulation.- 5.5.4 Pros and Cons of FDMA.- 5.6 Time-Division Multiple Access, TDMA.- 5.6.1 Bandwidth Demand and Efficiency of TDMA.- 5.6.2 Burst Synchronization in the Receiving Satellite.- 5.6.3 Slot Synchronization in the Transmitting TDMA Terminals.- 5.6.4 Pros and Cons of TDMA.- 5.7 Code-Division Multiple Access, CDMA.- 5.8 Direct-Sequence CDMA (DS-CDMA).- 5.8.1 Generation and Characteristics of Signature Sequences.- 5.8.2 Investigation of Asynchronous DS-CDMA in the Time Domain.- 5.8.3 Investigation of Asynchronous DS-CDMA in the Frequency Domain.- 5.8.4 Multi-Frequency CDMA, MF-CDMA.- 5.8.5 Qualcomm Return Link CDMA (Globalstar).- 5.8.6 Synchronous Orthogonal DS-CDMA with Coherent Detection.- 5.9 CDMA Receivers.- 5.9.1 PN Code Synchronization in the CDMA Receiver.- 5.9.2 Rake Receiver.- 5.9.3 CDMA Multiuser Detection.- 5.10 Characteristics of CDMA.- 5.11 CDMA for the Satellite UMTS Air Interface.- 5.11.1 The ESA Wideband CDMA Scheme.- 5.11.2 The ESA Wideband Hybrid CDMA/TDMA Scheme.- 6. Cellular Satellite Systems.- 6.1 Introduction.- 6.1.1 Concept of the Hexagonal Radio Cell Pattern.- 6.1.2 Cell Cluster and Frequency Reuse.- 6.2 Co-Channel Interference in the Uplink.- 6.2.1 Co-Channel Interference for FDMA and TDMA Uplinks.- 6.2.2 Co-Channel Interference for an Asynchronous DS-CDMA Uplink.- 6.3 Co-Channel Interference in the Downlink.- 6.3.1 Co-Channel Interference for FDMA and TDMA Downlinks.- 6.3.2 Co-Channel Interference for CDMA Downlinks.- 6.4 Bandwidth Demand and Traffic Capacity of Cellular Satellite Networks.- 6.4.1 Total System Bandwidth.- 6.4.2 Traffic Capacity per Radio Cell.- 6.4.3 Traffic Capacity of the System.- 6.4.4 Required User Link Capacity of a Satellite.- 6.4.5 Overall Network Capacity Considerations.- 7. Network Aspects.- 7.1 Architecture of Satellite Systems for Mobile/Personal Communications.- 7.2 Network Control.- 7.2.1 Tasks of Network Control.- 7.2.2 Signaling Channels of the Air Interface.- 7.3 Mobility Management.- 7.3.1 Service Area of a Gateway Station.- 7.3.2 Location Area.- 7.3.3 Registration and Location Update.- 7.4 Paging.- 7.5 Call Control.- 7.5.1 Setup of a Mobile Originating Call.- 7.5.2 Setup of a Mobile Terminating Call.- 7.6 Dynamic Channel Allocation.- 7.6.1 C/I-Based DCA.- 7.6.2 DCA Using a Cost Function.- 7.7 Handover.- 7.7.1 Handover Decision.- 7.7.2 Handover Procedure.- 7.7.3 Channel Allocation at Handover.- 7.8 Call Completion Probability.- 7.9 Routing.- 7.9.1 Routing in LEO/MEO Satellite Networks.- 7.9.2 Off-Line Dynamic ISL Routing Concept.- 7.9.3 On-line Adaptive ISL Routing.- 7.10 Integration of Terrestrial and Satellite Mobile Networks.- 8. Satellite Technology.- 8.1 Satellite Subsystems.- 8.2 Antenna Technology.- 8.2.1 GEO Antennas for Mobile Links with Spot Beams.- 8.2.2 LEO/MEO Antennas.- 8.3 Payload Architecture.- 9. Regulatory, Organizational, and Financial Aspects.- 9.1 Allocation of Frequency Bands.- 9.2 Licensing/Regulation.- 9.2.1 Granting a System License.- 9.2.2 Licensing in the USA.- 9.2.3 Licensing in Europe.- 9.2.4 Common Use of Frequency Bands by Several Systems.- 9.2.5 Global Licensing and Political Aspects.- 9.3 Financing and Marketing of S-PCN Systems.- 9.4 Operation of S-PCN Systems.- III. Satellite Systems for Broadband Multimedia Communicat ions.- 10. Multimedia Communications in Satellite Systems.- 10.1 Types of Broadband Communication Networks.- 10.1.1 Traditional Circuit-Switched Networks and the Packet-Switched Internet.- 10.1.2 New Multimedia Satellite Systems Using New Satellite Orbits.- 10.2 Multimedia Services and Traffic Characterization.- 10.2.1 Video Traffic and MPEG Coding.- 10.2.2 Self-Similar Traffic.- 10.3 ATM-Based Communication in Satellite Systems.- 10.3.1 Principles of ATM.- 10.3.2 Implications for ATM-Based Satellite Networks.- 10.4 Internet Services via Satellite Systems.- 10.4.1 Principles of TCP/IP.- 10.4.2 Internet Protocol (IP).- 10.4.3 Transport Control Protocol (TCP).- 10.4.4 TCP/IP in the Satellite Environment.- 10.4.5 IP over ATM in the Satellite Environment.- 11. ATM-Based Satellite Networks.- 11.1 System Architecture.- 11.2 Services.- 11.3 Protocol Architecture.- 11.4 ATM Resource Management.- 11.4.1 Connection Admission Control and Usage Parameter Control.- 11.4.2 Congestion Control, Traffic Shaping, and Flow Control.- 11.5 Multiple Access for ATM Satellite Systems.- 11.5.1 TDMA-Based Multiple Access.- 11.5.2 CDMA-Based Multiple Access.- 11.6 Radio Resource Management.- 11.7 Error Control.- 12. Network Dimensioning.- 12.1 Spot Beam Capacity Dimensioning for GEO Systems.- 12.1.1 Motivation and Approach.- 12.1.2 Market Prediction.- 12.1.3 Generic Multiservice Source Traffic Model.- 12.1.4 Calculation of the Spot Beam Capacity Requirements.- 12.1.5 System Bandwidth Demand Calculation.- 12.1.6 Applied Spot Beam Capacity Dimensioning: A Case Study.- 12.2 ISL Capacity Dimensioning for LEO Systems.- 12.2.1 Topological Design of the ISL Network.- 12.2.2 ISL Routing Concept.- 12.2.3 Network Dimensioning.- 12.2.4 Numerical Example.- 12.2.5 Extensions of the Dimensioning Approach.- A. Satellite Spot Beams and Map Transformations.- A.1 Map Projections and Satellite Views.- A.2 Generation of Satellite Spot Beams.- B. Parameters of the Land Mobile Satellite Channel.- B.1 Narrowband Two-State Model at L Band.- B.2 Narrowband Two-State Model at EHF Band.- B.3 Wideband Model at L Band.- C. Existing and Planned Satellite Systems.- C.1 Survey of Satellite Systems.- C.2 ACeS (Asia Cellular Satellite).- C.3 Astrolink.- C.4 EuroSkyWay.- C.5 Globalstar.- C.6 ICO (Intermediate Circular Orbits).- C.7 Inmarsat-3/Inmarsat mini-M.- C.8 Iridium.- C.9 Orbcomm.- CIO SkyBridge.- C.11 Sky Station.- C.12 Spaceway.- C.13 Teledesic.- References.

Cellular performance bounds via shotgun cellular systems

Abstract: This paper considers two-dimensional interference-limited cellular radio systems. It introduces the shotgun cellular system that places base stations randomly and assigns channels randomly. Such systems are shown to provide lower bounds to cellular performance that are easy to compute, independent of shadow fading, and apply to a number of design scenarios. Traditional hexagonal systems provide an upper performance bound. The difference between upper and lower bounds is small under operating conditions typical in modern TDMA and CDMA cellular systems. Furthermore, in the strong shadow fading limit, the bounds converge. To give insights into the design of practical systems, several variations are explored including mobile access methods, sectorizing, channel assignments, and placement with deviations. Together these results indicate cellular performance is very robust and little is lost in making rapid minimally planned deployments.

OVSF code channel assignment for IMT-2000

Abstract: Code channel assignment deals with the problem that how different codes are allocated to different connections. In the 3GPP technical specifications, the channelization codes used for spreading are orthogonal variable spreading factor (OVSF) codes. It can preserve the orthogonality between user's physical channels. OVSF codes are valuable resources in CDMA systems and should be properly managed. The objective of this paper is to find a code channel assignment method to support as many users as possible with less complexity. We proposed a code channel assignment method for user equipment (UE) that has the capability to support multi-rate services using multi-code transmission. A single table is used to allocate codes to a UE according to its requested data rate. Therefore, the allocation and releasing procedures, which can be accomplished in a very short period of time, are efficient.

Enhanced channel allocation among multiple carriers in a spread spectrum communications system

Abstract: A method for allocating traffic between multiple carriers in a wireless communications system measures loading on the communication system and selects an appropriate carrier from multiple carriers, based upon the loading measured. A first carrier is selected if the load on the first carrier is lower than or equal to the lowest loading of any supplemental carrier among the multiple carriers. If the load on the first carrier is not lower, then the subscriber may be assigned either to a supplemental carrier or the first carrier. The carrier assignment of the subscriber depends upon a predetermined threshold, which preferably considers actual or estimated differential interference between the first carrier and the supplemental carrier.

Power controlled multiple access (PCMA) in wireless communication networks

Abstract: We address the issue of power-controlled shared channel access in future wireless networks supporting packetized data traffic, beyond the voice-oriented continuous traffic primarily supported by current-generation networks. First, some novel formulations of the power control problem are introduced, which become progressively more general by incorporating various relevant costs. The analysis of the models under simple, yet natural, assumptions yields certain ubiquitous structural properties of 'optimal' power control algorithms. Based on such structural properties, we design a new family of distributed and asynchronous PCMA algorithms and evaluate them experimentally by simulation. They are found to perform substantially better than a standard benchmark algorithm for power control. This is a first step towards the design of full PCMA protocols for autonomous channel access in high-performance wireless networks.

Channel allocation using enhanced pathloss estimates

Abstract: A method and apparatus for channel allocation using pathloss estimates. Pathloss values between mobile stations located in one cell and base stations located in surrounding cells are calculated. Using the calculated pathloss values the system can determine the amount of interference which will be caused to transmissions in the surrounding base stations by allocating a certain channel to a base station located in the one cell. The system also can determine the source of the interference and use such a determination in the allocation of channels.

On the design and capacity planning of a wireless local area network

Abstract: The design of a wireless local area network (WLAN) has two major issues: determining the best placement of base stations (BS) and assigning the frequency channels for those stations The correct BS placement minimizes installation costs Adequate channel assignment reduces signal interference and improve network throughput This paper reports a real experience where we applied the concepts of two classical outdoor problems namely the optimal base placement problem and the fixed channel assignment problem to build a WLAN in an indoor environment

Control signalling and dynamic channel allocation in a wireless network

Abstract: A dynamic channel allocation method and system for use in a wireless network operates by monitoring at least the allocated channel allocated to a particular network node to generate one or more channel metrics relating to radio conditions on the channel. The metrics generated are Received signal power, signal to noise ratio of transmissions on the network and long-term mean square of the equaliser error used in each terminal. The generated metrics are communicated back to the cell access point or the network control server over a signalling channel, and a new frequency is allocated to the cell if it is determined from the metrics that the presently allocated channel is suffering interference. The signalling channel is preferably an ATM VPI/VCI pair, such that signalling messages are transmitted as ATM cells which can be communicated across the wireless channel using the sane signalling frame as is used for payload cells.

Fairness measures for resource allocation

Abstract: In many optimization problems, one seeks to allocate a limited set of resources to a set of individuals with demands. Thus, such allocations can naturally be viewed as vectors, with one coordinate representing each individual. Motivated by work in network routing and bandwidth assignment, we consider the problem of producing solutions that simultaneously approximate all feasible allocations in a coordinate-wise sense. This is a very strong type of "global" approximation guarantee, and we explore its consequences in a range of discrete optimization problems, including facility location, scheduling, and bandwidth assignment in networks. A fundamental issue-one not encountered in the traditional design of approximation algorithms-is that good approximations in this global sense need not exist for every problem instance; there is no a priori reason why there should be an allocation that simultaneously approximates all others. As a result, the existential questions concerning such good allocations lead to a new perspective on a number of basic problems in resource allocation, and on the structure of their feasible solutions.

Assignment methods for spatial reuse TDMA

Abstract: Spatial reuse TDMA is an access scheme for multi-hop radio networks. The idea is to increase capacity by letting several radio terminals use the same time slot when possible. A time slot can be shared when the radio units are geographically separated such that small interference is obtained. STDMA schedules can assign transmission rights to nodes or alternatively assign transmission rights to links, i.e. transmitter/receiver pairs. Here we compare these two methods and determine which one is preferable. We show that only the connectivity of the network and the input traffic load of the network is needed in order to determine whether node or link assignment is preferable.

Performance evaluation of prioritized handoff schemes in mobile cellular networks

Abstract: This paper deals with the performance analysis of two prioritized handoff schemes for mobile cellular networks in which handoff attempts finding all channels busy are queued for a maximum time. Fixed channel assignment is assumed. In the first prioritized handoff scheme considered, handoff attempts are queued according to the first-in-first-out (FIFO) policy. Conversely, the second scheme resorts to an ideal nonpreemptive priority queueing policy to enhance system performance. Differently from previous works, in this paper the performance analysis is carried out on the basis of a model which takes into account the event that a call may terminate when the mobile user is waiting for a handoff. Comparisons with simulation results and analytical predictions derived by means of alternative approaches highlight a better estimation accuracy for the proposed method. Moreover, it is also demonstrated here that the FIFO policy allows performance very close to that of the ideal prioritized handoff scheme and, hence, that it is a solution suitable for applications in mobile cellular networks where a high service quality is required.

Distributed fault-tolerant channel allocation for cellular networks

Abstract: A channel allocation algorithm includes channel acquisition and channel selection algorithms. Most of the previous work concentrates on the channel selection algorithm since early channel acquisition algorithms are centralized and rely on a mobile switching center (MSC) to accomplish channel acquisition. Distributed channel acquisition algorithms have received considerable attention due to their high reliability and scalability. However, in these algorithms, a borrower needs to consult with its interference neighbors in order to borrow a channel. Thus, the borrower fails to borrow channels when it cannot communicate with any interference neighbor. In real-life networks, under heavy traffic load, a cell has a large probability to experience an intermittent network congestion or even a communication link failure. In existing distributed algorithms, since a cell has to consult with a large number of interference neighbors to borrow a channel, the failure rate will be much higher under heavy traffic load. Therefore, previous distributed channel allocation algorithms are not suitable for real-life networks. We first propose a fault-tolerant channel acquisition algorithm which tolerates communication link failures and node (MH or MSS) failures. Then, we present a channel selection algorithm and integrate it into the distributed acquisition algorithm. Detailed simulation experiments are carried out in order to evaluate our proposed methodology. Simulation results show that our algorithm significantly reduces the failure rate under network congestion, communication link failures, and node failures compared to nonfault-tolerant channel allocation algorithms. Moreover, our algorithm has low message overhead compared to known distributed channel allocation algorithms, and outperforms them in terms of failure rate under uniform as well as nonuniform traffic distribution.

Optical communications system with dynamic channel allocation

Abstract: An optical communications system apparatus and methods of operating an optical communications system is described (fig. 1). The system advantageously may utilize existing optical fiber networks (1100, fig. 1) and provide significantly increased channel capacity. In accordance with one aspect of the invention the system apparatus provides for a plurality of communications channels (1000, fig. 1) and a processor unit (1335, 1337, 1345, 1347, 1353, fig. 1) receives requests for allocation of one or more channels from a node (1331, 1333, 1341, 1343, 1351, fig. 1) coupled to the optical communications system. The system apparatus dynamically allocates one or more channels selected from unused channels.

MACA-an efficient channel allocation scheme in cellular networks

Abstract: In a cellular network, a fixed number of channels is normally assigned to each cell. However, under this scheme, the channel usage may not be efficient because of the variability in the offered traffic. Different approaches such as channel borrowing (CB) and dynamic channel allocation (DCA) have been proposed to accommodate variable traffic. In this paper, we expand on the CB scheme and propose a new channel allocation scheme-mobile-assisted connection-admission (MACA) algorithm-to achieve load balancing in a cellular network. In this scheme, some special channels are used to connect mobile units from different cells; thus, a mobile unit, which is unable to connect to its own base station because it is in a heavily-loaded "hot" cell, may be able to get connected to its neighboring cold cell's base station through a two-hop link. We find that MACA can greatly improve the performance of a cellular network.

Adaptive modulation, power allocation and control for OFDM wireless networks

Abstract: Orthogonal frequency division multiplexing (OFDM) is a promising multiplexing technique for high data rate transmission over wireless radio channels. In this paper, we consider a low mobility, wireless OFDM cellular system. Since a cellular system uses a frequency reuse concept to enhance the efficiency of spectral utilization, it introduces so called cochannel interference (CCI) which is one of the major sources of performance degradation. To mitigate the effect of CCI while satisfying required quality of service, the power level of each subchannel of the OFDM system should be allocated to and controlled at an optimal value such that the system throughput can be maximized by employing adaptive modulation. Due to the effect of the CCI in the multi-cell OFDM system, the optimal values of power levels are very difficult to find. A new distributed suboptimal power allocation algorithm for the multi-cell OFDM system is proposed to increase the system throughput. Numerical results show the advantages of the proposed algorithm over those of the equal power allocation algorithm in various channel conditions.

Channel allocation and release for packet data services

Abstract: A telecommunications system (18) comprises a control node (24) and a base station node (22). The control node (24) maintains a first list (42) of idle radio channels which is consulted in order to obtain channels for a first type of telecommunications service. A second list (56) of idle radio channels is maintained for a specialized telecommunications service, the idle radio channels of the second list being radio channels which are unallocated with respect to the specialized telecommunications service but yet activated (e.g., having an established transmission path and synchronization). The second list of idle radio channels is initially consulted in order to obtain channels for the specialized telecommunications service. If no channels are available for the specialized telecommunications service on the second list, idle channels from the first list are adapted and utilized for the specialized telecommunications service. The specialized telecommunications service preferably involves packet data transfer (e.g., GPRS). As one aspect of the invention, any potential capacity problem is addressed by providing timers for channels on the second list. There is one timer corresponding to each channel on the second list, which timer is started when there is no more traffic ongoing on that channel. The channel remains activated with respect to the specialized telecommunications service, which makes fast specialized service access possible for all such users in that cell. As long as the timer has not expired, the channel on the second list is available for specialized service traffic without any new activation. However, when the timer expires, the channel is released and put on the first list, where it is once again available for all traffic. The timer values can be dynamically adjusted or varied, e.g., depending on processor load or traffic load at a cell.

A simple loss differentiation approach to layered multicast

Abstract: Layered multicast is a promising technique for broadcasting adaptive-quality TV video to heterogeneous receivers. While several-layered multicast approaches have been proposed, prior work has identified several problems including significant and persistent instability in video quality, arbitrary unfairness with other sessions, low access link utilization due to conservative bandwidth allocation, and problems with receiver synchronization. In this paper we propose a new layered multicast scheme, where we exploit a simple, coarse-grained, two-tier loss differentiation architecture to achieve stable and fair bandwidth allocation for viewers. Despite the simplicity of our loss differentiation model, we show that it achieves most of the benefits of complex and costly priority dropping schemes. In addition, our protocol is receiver-driven and thus retains the incentives to limit bandwidth usage that are not present in existing priority dropping schemes.

Performance analysis of a dual-threshold reservation (DTR) scheme for voice/data integrated mobile wireless networks

Abstract: The emerging next generation of wireless cellular networks has to provide the quality-of-service (QoS) for a variety of applications. This paper addresses bandwidth allocation for a voice and data integrated mobile wireless network. Specifically, we propose a new bandwidth allocation scheme called dual-threshold reservation (DTR) scheme, which is a natural extension from well-known guarded channel (GC) scheme used in cellular networks supporting voice traffic. The basic idea is to use two thresholds, one for reserving channels for voice handoff, while the other is used to block data traffic into the network in order to preserve the voice performance in terms of handoff dropping and call blocking probabilities. We develop an analytical model which can obtain its performance using an iterative technique. Results obtained from the analytical model are used to illustrate the system tradeoff.

Some observations on fairness of bandwidth sharing

Abstract: This paper reviews the engineering solutions and economic models for fair allocation of network bandwidth to elastic flows. Using examples, it gives insight to proportional fairness, and how it compares to the fairness achieved by TCP. The second topic is a discussion of fair bandwidth allocation between multicast and unicast flows. By separating the discussion into economic and engineering viewpoints, this paper discusses ideal solutions and suggests practical approaches to achieving reasonable fairness.

Bandwidth feedback control of TCP and real time sources in the Internet

Abstract: This paper proposes a feedback based algorithm for congestion control and bandwidth allocation in the presence of either TCP traffic or both TCP and real time traffic. In this proposal, the network layer conveys bandwidth and propagation delay measurements to data sources, for instance using IPv6 optional fields. TCP sources use this bandwidth delay product to control their congestion window, while video sources use the available bandwidth feedback to adjust their data sending rate. The experiments show that with this approach, the network achieves stable equilibrium, and users, either transmitting TCP traffic or real-time traffic, can share network resources fairly. Furthermore, since TCP sources learn about the available bandwidth independent of packet loss, there is no need to reduce the congestion window following a packet loss. This provides a way to improve the TCP performance in wireless networks where it is difficult to distinguish between congestion loss and radio channel interference loss.

A three-stage heuristic combined neural-network algorithm for channel assignment in cellular mobile systems

Abstract: A three-stage algorithm of combining sequential heuristic methods into a parallel neural network is presented for the channel assignment problem in cellular mobile communication systems in this paper. The goal of this NP-complete problem is to find a channel assignment to requested calls with the minimum number of channels subject to interference constraints between channels. The three-stage algorithm consists of: (1) the regular interval assignment stage; (2) the greedy assignment stage; and (3) the neural-network assignment stage. In the first stage, the calls in a cell determining the lower bound on the total number of channels are assigned channels at regular intervals. In the second stage, the calls in a cell with the largest degree and its adjacent cells are assigned channels by a greedy heuristic method. In the third stage, the calls in the remaining cells are assigned channels by a binary neural network. The performance is verified through solving well-known benchmark problems. Especially for Sivarajan's benchmark problems, our three-stage algorithm first achieves the lower bound solutions in all of the 13 instances, while the computation time is comparable with existing algorithms.

Reducing call dropping in distributed dynamic channel assignment algorithms by incorporating power control in wireless ad hoc networks

Abstract: 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.

Signal scanning systems and methods for multiple-mode cellular radiotelephones

Abstract: Multiple-mode cellular radiotelephones use a wide bandwidth receiving mode while scanning for signals in a narrow bandwidth receiving mode. Thus, when it is desired to scan the received frequency band to search for the presence of narrowband signals, the wider receiver bandwidth is first selected. When significant signal energy is identified in the wider bandwidth, a further scan using the narrowband mode may then be provided in order to locate the narrow bandwidth channel containing the strongest signal. In another embodiment, the signals that are received in the wider bandwidth mode are digitized to obtain complex signal samples. The complex signal samples are then processed to determine energy in each of a plurality of narrower bandwidths corresponding to channels in the narrower bandwidth cellular radiotelephone standards. Accelerated scanning of TDMA cellular channels may be obtained by tuning the cellular radiotelephone to a succession of frequency channels within one TDMA time slot and measuring signal strength for each of the succession of frequency channels. Tuning and measuring is then repeated for remaining ones of the TDMA time slots in the TDMA frame, preferably using the same channels in the same order. For each frequency channel, the signal strength that is the greatest measured signal strength of the frequency channel in all of the TDMA slots is assigned to that frequency channel. The assigned signal strengths may then be used to select a frequency channel for TDMA signal acquisition. Historical information may also be used to accelerate scanning of cellular channels by a cellular radiotelephone.

Efficiency comparison of channel allocation schemes for digital mobile communication networks

Abstract: This paper provides network designers and operators with simple guidelines on traffic measurements and efficiency evaluation of various channel allocation schemes in digital mobile telecommunications networks. The paper evaluates the efficiency obtained by implementing the following channel allocation schemes: (1) fixed uniform channel allocation (FUCA); (2) fixed nonuniform channel allocation (FNCA); (3) dynamic channel allocation (DCA) where the number of frequency carriers is adaptive and dependent on the load; and (4) dynamic frequency/time channel allocation (DFTCA) (a new scheme which is the most efficient) where the number of channels is adaptive (based on the load), allowing two channels of the same frequency carrier to be used in two neighboring cells. The analysis is based on standard queuing models under the following assumptions: (1) Poisson call arrivals in each cell; (2) exponential call holding time; (3) exponential mobile travel time; and (4) exponential sojourn time of a mobile in a cell. Numerical results are presented to provide insight into the accuracy of the models and efficiency gain by dynamic frequency time channel allocation under different traffic conditions (including conditions related to highway traffic).

Adaptive dynamic channel allocation scheme for spotbeam handover in LEO satellite networks

Abstract: Among satellite systems, the low Earth orbit (LEO) satellite system will have an important role in new future communication services, because of its lower propagation delay, lower user terminal and satellite power consumption, and efficient spectrum utilization using a smaller coverage area than its geostationary (GEO) counterpart. However a number of mobility problems that did not exist in GEO satellite systems should be solved. One noticeable mobility problem is the spotbeam handover which occurs most frequently in LEO satellite systems. The frequent spotbeam handover requires a technique to decrease the handover blocking probability. An adaptive dynamic channel allocation (ADCA) scheme is introduced for LEO satellite networks. The ADCA scheme estimates the future number of handover events based on the user location database, and reserves the corresponding number of channels in order to decrease the overall handover blocking probabilities. The performance evaluation shows that the handover blocking probabilities of the ADCA technique substantially decrease in comparison with the other channel allocation schemes.