Showing papers on "Channel allocation schemes published in 1993"

Advantages of CDMA and spread spectrum techniques over FDMA and TDMA in cellular mobile radio applications

Abstract: A unified theoretical method for the calculation of the radio capacity of multiple-access schemes such as FDMA (frequency-division multiple access), TDMA (time-division multiple access), CDMA (code-division multiple access) and SSMA (spread-spectrum multiple access) in noncellular and cellular mobile radio systems is presented for AWGN (additive white Gaussian noise) channels. The theoretical equivalence of all the considered multiple-access schemes is found. In a fading multipath environment, which is typical for mobile radio applications, there are significant differences between these multiple-access schemes. These differences are discussed in an illustrative manner revealing several advantages of CDMA and SSMA over FDMA and TDMA. Novel transmission and reception schemes called coherent multiple transmission and coherent multiple reception are briefly presented. >

Segregation method of dynamic channel allocation in a mobile radio system

Abstract: A method for adaptively allocating channels for connections between base station and mobiles is disclosed. The channels accessible to the base stations for establishing connections with mobiles are ranked in at least one priority list based on transmission loss intervals. Each channel is ranked in the priority list according to their success at previous connections. The amount of power required for a channel allocated from a list associated with a low transmission loss can be set lower thereby reducing the interference associated with the channel and increasing system capacity. A self planned system evolves where channels are allocated for connections based on their past connection history. Thus, the selection of channels which may interfere with calls in neighboring cells or which may suffer substantial interference from a neighboring base is avoided.

Channel segregation-a self-organized dynamic channel allocation method: application to TDMA/FDMA microcellular system

Abstract: Channel segregation was previously proposed as a self-organized dynamic channel assignment. Its performance was examined by applying it to frequency-division multiple access systems. Its applications to the TDMA/FDMA (time-division multiple access/frequency-division multiple access) or multicarrier TDMA system is discussed. The spectrum efficiency of the TDMA/FDMA cellular system deteriorates due to the problem of unaccessible channel: a call can be blocked in a cell even when there are idle channels because of the restriction on simultaneous use of different carrier frequencies in the cell. It is shown that channel segregation can resolve this problem with a small modification of its algorithm. The performance of the TDMA/FDMA system with channel segregation on the call blocking probability versus traffic density is analyzed with computer simulation experiments. The effect of losing the TDMA frame synchronization between cells on the performance is also discussed. >

Local packing-distributed dynamic channel allocation at cellular base station

Abstract: The local packing (LP) algorithm, a base station distributed dynamic channel allocation (DDCA) adapting to local traffic demands, is presented. The authors show that, unlike some other DCA algorithms, even when the network has a large number of channel, it maintains a favorable performance over FCA under uniform traffic in the region of interest. More importantly, the LP algorithm has a tremendous capability of alleviating congestion at traffic hot spots. For example, with 420 channels in the network, at a blocking requirement of 1%, in comparison to only 47 Erlangs per cell that FCA could support, the LP DDCA can accommodate 100 Erlangs per cell in isolated hot spot cells and 75 Erlangs per cell in contiguous expressway hot spots. This is achieved without decreasing the load anywhere else from the normal 47 Erlangs per cell. This algorithm can be implemented, distributedly at the base stations with a simple augmented channel occupancy table, or centrally at the mobile switching center. The authors outline an easy evolutional path, for AT&T Autoplex Series II cellsites, from the current wireless network architecture to one that incorporates the new DDCA. Alternatively, one can implement it centrally without the need of a distributed database. The computation complexity of this algorithm is low and independent of the network size. >

Asymptotic bounds on the performance of a class of dynamic channel assignment algorithms

Abstract: Dynamic channel assignment, adapting both to traffic variations as well as to changing mobile locations, is investigated. Several ad hoc schemes of this type have been described in the literature and found to yield interesting performance improvements. However, very little is known about the performance of the optimum assignment schemes. Both upper and lower bounds for the performance of optimum algorithms within the class of reuse-type dynamic channel assignment (DCA) for a simple propagation model are established. The authors focus on the asymptotic performance, i.e., the performance in systems with large traffic loads. As a performance measure, the probability of assignment failure (intracell handoff failure) is used. Results show that the capacity one may expect to achieve with these algorithms in the asymptotic case is just above twice the capacity of a fixed channel allocation scheme. >

Distributed dynamic channel assignment schemes

Abstract: Some distributed channel schemes for a one-dimensional cellular radio system are described. The channel assignment in the schemes proposed is based on signal strength measurements and therefore gives an improvement in capacity over schemes using reuse distance criterion for channel assignment. The proposed schemes are evaluated by simulations and their behavior with variation in traffic density, size of the channel set and number of reassignments is studied.

Method and apparatus for channel allocation integrity in a communication network

Abstract: A communication network having a master and a plurality of remotes, these remotes supporting a plurality of co-services, in which access to inbound frequencies among the remotes is shared. When a need by a remote for an extraordinary amount of bandwidth is detected, a reserved spillover frequency from a set of frequencies is reserved for that remote. This bandwidth is reallocated when the need for extraordinary bandwidth for that remote has ended.

Compact pattern based dynamic channel assignment for cellular mobile systems

Abstract: A new compact pattern based dynamic channel assignment strategy called CP-based DCA is proposed. The strategy aims at dynamically keeping the cochannel cells of any channel to a compact pattern. A compact pattern of a channel is defined as the pattern with minimum average distance between cochannel cells. CP-based DCA consists of two phases: channel allocation and channel packing. Channel allocation is used to assign an optimal idle channel to a new call. Channel packing is responsible for the restoration of the compact patterns and is performed only when a compact channel is released. Simulation results indicate that the CP-based DCA always performs better than the borrowing with directional channel locking (BDCL) strategy. The latter being the strategy that gives the lowest blocking probability among the class of known strategies that do not require system-wide information. In the designed example, CP-based DCA is shown to have 5% more traffic-carrying capacity than that of the BDCL in case of uniform traffic and 9% more traffic-carrying capacity in case of non-uniform traffic, both at a blocking rate of 0.02. Besides, the number of channels reassigned per released call in CP-based DCA is at most one and is therefore another advantage over BDCL. >

Design and performance analysis of the algorithms for channel allocation in cellular networks

Abstract: The authors consider the problem of dynamic channel allocation in cellular networks. Each cell can use any channel, subject to the interference constraints. Channel allocation algorithms are executed by the network switch in a centralized way. The authors show how to design and use objective functions aimed at proper channel allocation and improvement of network performance. As a figure of merit of network performance, they consider the blocking probability in the network as a whole, and the maximum blocking probability in any particular cell of the network ("hot-spot" in the network). They designed three specific channel allocation policies, based on three different objective functions. Compared with two other benchmark policies, the approach shows significant improvement. Performance analysis of various channel allocation policies is virtually impossible without simulations, which are prohibitively time-consuming in the case of small blocking probabilities. The authors propose an original approximate method based on a short simulation and an analytic approximation. The method exhibits good accuracy and significant improvement in efficiency. >

Instability and deadlock of distributed dynamic channel allocation

Abstract: Distributed dynamic channel allocation (DDCA) techniques are vulnerable to undesirable effects such as interruption, call deadlock, and instability. Theoretical and simulation studies of these problems are described. The interactions of power control and channel allocation, and the tradeoffs between service interruption of existing calls and blocking of new calls are shown.

Communication network with divisible auxilliary channel allocation

Abstract: A communication network having a master and a plurality of remotes, these remotes supporting a plurality of co-services, in which access to inbound frequencies among the remotes is shared. When a need by a remote for an extraordinary amount of bandwidth is detected, a reserved spillover frequency from a set of frequencies is reserved for that remote. This bandwidth is reallocated when the need for extraordinary bandwidth for that remote has ended.

Digital radio communication system and primary and secondary station for use in such a system

Abstract: A digital radio communication system (1) is known, for example based on the DECT standard, in which radio communication of digital speech or data between primary (BS1) and secondary (MS1) stations takes place via duplex FDMA/TDMA connection. Channel allocation therein is dynamic. If necessary because of the receiving conditions, the secondary station (MS1) can initiate a so-called handover by searching for a free channel offering better receiving conditions. In accordance with the invention, this handover is seamless. Digital speech bursts are exchanged via different time slots (ts) during a number of frames (fr), these being digital speech data and copy digital speech data. After verification that the copy data is valid, i.e. that communication has been established via a free channel, handover takes place. The original data and the copy data are stored in a cyclic buffer (SB5) so that the phase shift (d) between the original data and the copy data is eliminated. Subsequently, the channel via which the original data was transported is released. In one embodiment a speech pointer (SPP) for reading speech freely progresses along the cyclic buffer (SB5) and a radio pointer (RFP), progressing along the buffer (SB5) and controlling the writing of speech bursts, is adapted during handover to the phase shift (d) between time slots involved in the handover.

Call set-up in a radio communication system with dynamic channel allocation

Abstract: The call set-up technique of this invention is characterized by the use of channel information from both base station and subscriber terminal in determining the radio traffic channel upon which to set-up a new call. Communication between the base station and subscriber terminal is carried out on a signalling channel until the traffic channel is chosen. Calls are set-up so that they proceed on the radio channel which, of a set of channels under consideration by the subscriber terminal, contains the least amount of interference as measured at the subscriber terminal. The set of channels under consideration by the subscriber terminal is a subset of the entire set of channels allocated to the service. This subset is comprised of those channels having little interference, as measured by the base station. The call set-up technique thereby assures that calls proceed on channels containing little interference from the viewpoints of both base station and subscriber terminal.

Multiple access options for cellular based personal communications

Abstract: The possible evolution of time division multiple access (TDMA) by, e.g., introducing frequency hopping and/or adaptive channel allocation, is described. The possibilities of direct sequence (DS) code division multiple access (CDMA) are considered. The different multiple access methods are examined. In particular, the concept of hierarchical cell structures is emphasized. The capacity depends on both the cell capacity and the ability to support hierarchical cell structures.

Propagation models, cell planning and channel allocation for indoor applications of cellular systems

Abstract: Results of 900-MHz propagation measurements and three-dimensional path loss prediction models for a number of typical indoor cellular system environments are presented. Statistical expressions describing the observed excess path loss due to floor reflections and clutter, as well as the propagation characteristics of multistory buildings, are discussed. Radio coverage and cochannel interference predictions for indoor cell planning are presented for a modern office building. Simulations of an indoor system using adaptive channel allocation (ACA) are performed.

On the performance of packet reservation multiple access with fixed and dynamic channel allocation

Abstract: The evaluation of packet reservation multiple access (PRMA) is extended from a single cell case, investigated in several previous papers, to a cellular environment characterized by user mobility and by the interference from other cells. The analysis is based on a comparison of PRMA performances with those of classical circuit switching schemes. The comparison methodology is defined, and the comparison, performed by means of a simulation program based on a dynamic traffic model, is discussed. >

Digital cellular network/system with mobile stations communicating with base stations using frequency-hopping and having enhanced effect of interference diversity

Abstract: A digital TDMA/FDMA (Time Division Multiple Access/Frequency division Multiple Access) cellular network system, suitable for a microcellular network and to maximize the advantage to be gained from interference diversity, including base stations forming radio cells, each having a determined static frequency of a channel of the cell and including a first transceiver continuously transmitting control data of the system concerning the cell at the control channel frequency, at least in one predetermined time slot of a TDMA frame. The TDMA frame of the first transceiver includes traffic channels at least in a part of the other time slots. Each base station further includes at least one second transceiver for the traffic channels. The system further includes mobile stations connected to the base stations via a radio path. The traffic channels of the second transceiver units use frequency-hopping, at least in a part of the radio cells, in such a way that, on those traffic channels aligned with the predetermined time slots of the control data of the cell in the first transceiver, substantially all frequencies of the available frequency band, except the control data transmission frequency determined for the cell, belong to the hopping sequence. On those traffic channels which are in the other time slots, substantially all frequencies of the available frequency band belong to the hopping sequence.

An integrated dynamic resource allocation scheme for ATM networks

Abstract: Dynamic bandwidth allocation among traffic classes with different performance requirements sharing an asynchronous transfer mode (ATM) link is considered as an integrated control problem with a multilevel structure. At the lower level, call admission control rules are applied that maintain a certain grade of service, in terms of cell loss probability and cell delay, given the buffer space and bandwidth assigned to each class; unlike those used in previous works, these rules are derived on the basis of homogeneous (based on similar quantities) measures of the performance requirements. At the higher level, bandwidth shares are periodically recomputed online by an allocation controller, whose goals reflect overall cell loss and refused traffic, as well as overall average delay. These goals are expressed by an optimization problem that is solved by numerical techniques. The whole control system should provide a dynamic feedback controller, capable of reacting in real time to changes in the traffic patterns. Simulation results are presented and are discussed in regard to the efficiency of the admission controllers, the performance of the overall scheme, and the capability of reacting to sudden changes in the load of some traffic class. >

Access method for distributed dynamic channel allocation in microcells

Abstract: A method of providing local autonomous control of channel allocation of a cellular telecommunications network. In one prior art method, which can be identified as the timid method, a channel is selected for use by an incoming user if it is not being used by any of the cells which surround it. Otherwise, another channel is selected according to the same rule. The channels are tested in random order and a call is blocked if all of the channels are in use. For heavy loading, because of the vagaries of the way the demand for channels occurs, this method can result in inefficient channel deployment. In another method, which can be identified as the aggressive method, a channel is selected for use by an incoming user even if that channel is currently being used in the surrounding cells. If the channel is in use, the incoming user "bumps" the current user off the channel in the timid mode. The "bumped" user is then forced to find and use another channel. With this method, an unreasonable number of reconfigurations and an unreasonable number of dropped calls can result, especially when the system is heavily loaded. This invention integrates the aggressive and timid methods to obtain the best of both: the former's improved performance and the latter's stability. Initially, the timid mode is used to look for a channel with acceptable interference. However, if the timid mode fails to obtain a channel, the call is not necessarily blocked. Instead, the mode of operation becomes more aggressive and the first channel tested that has only modest interference is taken. The "bumped" user on that channel then attempts to locate another channel. If the "bumped" user is unsuccessful, the incoming user must then retreat and is blocked.

Method for FDMA signal multiplexing and demultiplexing

Abstract: A method for multiplexing a series of frequency division multiple access (FDMA) signals includes providing complex channels offset relative to the FDMA signals. Each FDMA signal is filtered to be centered and occupy one-half of the bandwidth of each complex channel, leaving an "off" channel between each pair of successive FDMA signals. The real part of the multiplexed output signal is processed and higher frequency signals of FDMA signals image into the "off" channels. Demultiplexing includes aligning a demultiplexing channelization pattern with the multiplexed input signal contained in input channels. The input channels are one-half a bandwidth of each of the complex channels. The input channels contain a sequence of FDMA signals separated by a reverse sequence of images of the FDMA signals. Consecutive even-numbered input channels correspond to consecutive complex channels of the complex channels and the sequence of FDMA signals can be extracted from the complex channels.

Generalized reuse partitioning in cellular mobile radio

Abstract: Reuse partitioning has been proposed as a simple dynamic channel allocation scheme in cellular radio systems. In this method, several overlaid fixed channel plans are used. Mobiles with favorable positions and high signal levels are assigned channels from plans with low reuse distance, whereas mobiles with low signal quality get channels with large cluster sizes. This concept is generalized, and an optimum method for channel assignment given some arbitrary predictor of the signal quality is proposed. Upper and lower performance bounds for the optimum assignment procedure in this class are derived, together with an explicit (suboptimum) assignment procedure. Results show that substantial capacity improvements can be achieved by using the received signal power as predictor.

Intra cell handover and channel allocation to reduce interference

Abstract: A method of reducing interference in a cellular radio communication including performing a courtesy handover of a first call to another channel to reduce interference in a second call when the presence of the first call on the same frequency as the second call causes the interference in the second call. Also, a method of setting up a call which permits a retry to a macro cell when a channel of sufficient quality is not found in a micro cell.

Dynamic resource allocation in line-of-sight microcells

Abstract: 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. >

Optimal channel allocation policies for access control of circuit-switched traffic in ISDN environments

Abstract: The problem of adaptively managing the transmission bandwidth of an integrated network by implemented optimal partitioning policies for the access control of circuit-switched traffic is studied. Precise formulations within an optimization framework of access control problems, both at an isolated multiplexer level and at the overall network level, are developed. For the simple case of a single multiplexer supporting traffic with identical bandwidth requirements, an iterative scheme with guaranteed fast convergence is presented for the determination of optimal channel allocations. For the more general scenario of a multiplexer supporting traffic with nonidentical bandwidth requirements, a methodology is developed to handle the access control problem by a mixed-integer programming formulation. This methodology is further extended to the network-wide access control scenario, and some implementational issues are discussed. A detailed quantitative evaluation of the proposed algorithm is conducted under different loading conditions, and the corresponding performance and efficiency are compared with those of other known procedures. >

All-channel concentric allocation in cellular systems

Abstract: A dynamic channel assignment algorithm for cellular systems, i.e., all-channel concentric allocation (ACCA), is proposed, and its performance is evaluated by computer simulation. Computer simulations show that system capacity (offered traffic at a blocking rate of 3%) is improved by a factor of 2.5 compared to conventional fixed channel assignment (FCA). A transmitter power control (TPC) is designated to cooperate with ACCA and enhance system capacity. Simulations confirm that ACCA with TPC accomplishes a system capacity 3.4 times greater than FCA. >

A method for communication in a tdma cellular mobile radio system using frequency hopping

Abstract: A method and means for communication in a cellular TDMA mobile radio communication system with channel hopping, where base and mobile stations transmit radio signal bursts in time slots of a plurality of radio channels in accordance with channel hopping schemes, all of the schemes used by a base and mobile stations in a cell being free from coincidence on any radio channel with any other of the schemes used for transmission within the same cell, a scheme used by a mobile station in one cell occasionally coinciding on a radio channel with a scheme used by a mobile station in an other cell, the major part of every channel shifting scheme used by a mobile station in a cell being free from coincidence on any radio channel with the major part of any channel hopping scheme used by a mobile station in another cell, signal to interference ratio or other signal characteristics such as signal strength or bit error rate for signals received by mobile stations are estimated and compared, the output power of stations being controlled, the existence of further possible channel hopping schemes in a cell, free from coincidence on every radio channel with every other of the channel hopping schemes already in use in that cell, is checked, and when another connection to a particular mobile is desired and there is a possible mobile scheme free from coincidence, the desired connection is established using the possible channel hopping scheme in the cell, only if the estimated C/I for certain mobile stations involved in connections exceed a minimum level.

Distributed channel allocation in ATM networks

Abstract: This paper proposes a distributed channel allocation mechanism for ATM networks. In this mechanism, agents are assigned to traffic sources and allocate channels to incoming calls in a distributed manner. Channel allocation is based only on the sampled channel utilization values locally available to agents. There is no direct exchange of information assumed between agents. Due to the distributed nature of the proposed mechanism, this mechanism causes oscillations during channel utilization when there is a delay associated with the sampling of channel utilizations and the processing of sampled values at agents. This oscillation increases the cell loss in a channel. According we propose methods for estimating channel utilization in order to reduce the oscillations and show their effectiveness through simulations. The proposed mechanism requires little computational processing, is simple to implement, and achieves efficient channel allocation even if highly bursty calls. It is therefore suitable for ATM networks. >

Distributed Dynamic Channel Allocation Algorithms for Microcellular Systems

Abstract: Microcellular systems offer the potential for substantial increases in capacity. However, existing frequency planning and network control are impractical. A solution to the network management problems created by the use of microcells is dynamic channel allocation (every channel available for use in every cell) with decentralized control (decisions made by the mobiles or portables rather than by a central switch). By addressing elemental situations, we show that microcellular systems can self-organize, with little loss in capacity in comparison to the best globally coordinated channel selection. Moreover, this can be done by using simple channel-allocation algorithms, with the mobile or portable unit making autonomous decisions based only on local measurements.

Real-time bandwidth allocation and path restorations in SONET-based self-healing mesh networks

Abstract: The authors present a scheme for optimal real-time bandwidth allocation and path restorations in a mesh network via SONET WDCS (wideband digital cross-connect system) in response to demand dynamics and to link and/or node failure(s). The scheme dynamically maximizes network throughput while ensuring full service restorability. In this process, the scheme integrates the dynamics of demand admission, bandwidth allocation, and spare capacity assignment. Since the physical network capacity is limited, not all the demand can be accommodated under the full restorability requirement. The demand which cannot be allocated under this requirement should be rejected at the network boundary. In the scheme, the optimal spare capacity assignment is just a consequence of the optimal network admission and optimal fully restorable bandwidth allocation. The authors also present an efficient parallel algorithm for optimal solution of the joint demand admission and restorable bandwidth allocation problem. The algorithm is suitable for real-time optimization in large networks. >

Capacity enhancements in a TDMA system

Abstract: Results from simulations of adaptive channel allocation (ACA) combined with power control (PC) are presented The simulated system conforms with the TIA standard IS-54 The results show that the tested algorithms would double the capacity compared to a system using fixed channel allocation (FCA) without power control