Manju V. Hegde

Conditional connectivity measures for large multiprocessor systems

Introduces a new measure of conditional connectivity for large regular graphs by requiring each vertex to have at least g good neighbors in the graph. Based on this requirement, the vertex connectivity for the n-dimensional cube is obtained, and the minimal sets of faulty nodes that disconnect the cube are characterized. >

Multicell CDMA network design

Traditional design rules for cellular networks are not directly applicable to code division multiple access (CDMA) networks where intercell interference is not mitigated by cell placement and careful frequency planning. For transmission quality requirements, a minimum signal-to-interference ratio (SIR) must be achieved. The base-station location, its pilot-signal power (which determines the size of the cell), and the transmission power of the mobiles all affect the received SIR. In addition, because of the need for power control in CDMA networks, large cells can cause a lot of interference to adjacent small cells, posing another constraint to design. In order to maximize the network capacity associated with a design, we develop a methodology to calculate the sensitivity of capacity to base-station location, pilot-signal power, and transmission power of each mobile. To alleviate the problem caused by different cell sizes, we introduce the power compensation factor, by which the nominal power of the mobiles in every cell is adjusted. We then use the calculated sensitivities in an iterative algorithm to determine the optimal locations of the base stations, pilot-signal powers, and power compensation factors in order to maximize the capacity. We show examples of how networks using these design techniques provide higher capacity than those designed using traditional techniques.

A nonblocking architecture for broadband multichannel switching

The paper investigates multichannel switching as a promising alternative to traditional single-channel switching where virtual paths established in a switch are between a single input channel and a single output channel. A particular non-blocking condition is derived for flip networks, which is exploited to realize a multichannel switching architecture that supports an arbitrary number of channel groups. The architecture is internally nonblocking and bufferless. Using one flip network recursively a number of times based on the number of channel groups, the resulting architecture becomes efficient in the sense that the cross point complexity is O(N log/sub 2/ N) for N inputs. Other distinguishing features are the abilities to provide multicasting, superrate switching (i.e., rates that exceed the capacity of a single channel are accommodated), multirate switching (i.e., bit pipes of different rates are supported simultaneously), multiple performance requirements (i.e., services with different performance requirements are treated accordingly), and fair access to all inputs (i.e., no input is systematically discriminated against). In multichannel switching, cells belonging to a single session can traverse multiple channels. Providing the cell sequencing integrity becomes a challenging issue. The architecture proposed in the paper accomplishes the task without employing any cell resequencing mechanism. >

Cell placement in a CDMA network

Traditional design rules, wherein cells are dimensioned in order to get an equal amount of demand in each cell are not directly applicable to CDMA networks where large cells can cause a lot of interference to adjacent small cells. In order to enable iterative cell placement we use a computationally efficient iterative process to calculate the inter-cell and intra-cell interferences as a function of pilot-signal power and base station location. These techniques enable us to improve the placement of cells in a CDMA network so as to enhance network capacity. We show examples of how networks using this design technique will provide higher capacity than ones designed using conventional techniques.

Neural network design using linear programming and relaxation

Two new approaches to designing Hopfield neural networks using linear programming and relaxation are presented. These approaches are shown to be the natural ones given the form of the network dynamics. Computer simulations show that linear programming and relaxation are more effective than the sum of outer products rule in that they provide a larger capacity for the network. The new approaches are also shown to make the design process very flexible: they can guarantee that the given memories are all fixed points, they can incorporate a minimum radius of attraction, and they can accommodate restricted connectivities or regular network topologies. Statistical experiments are presented to illustrate these claims.<<ETX>>

Call admission control scheme for arbitrary traffic distribution in CDMA cellular systems

Designing a call admission control (CAC) algorithm that guarantees call blocking probabilities for arbitrary traffic distribution in CDMA networks is difficult. Previous approaches have assumed a uniform traffic distribution or excluded mobility to simplify the design complexity. We define a set of feasible call configurations that results in a CAC algorithm that captures the effect of having an arbitrary traffic distribution and whose complexity scales linearly with the number of cells. To study the effect of mobility and to differentiate between the effects of blocking new calls and blocking handoff calls, we define a net revenue function. The net revenue is the sum of the revenue generated by accepting a new call and the cost of a forced termination due to a handoff failure. The net revenue depends implicitly on the CAC algorithm. We calculate the implied costs which are the derivatives of the implicitly defined net revenue function and capture the effect of increases in the number of calls admitted in one cell on the revenue of the entire network. Given a network topology with established traffic levels, the implied costs are used in the calculation of a CAC algorithm that enhances revenue and equalizes call blocking probabilities. Moreover, our algorithm provides guaranteed grade-of-service for all the cells in the network for an arbitrary traffic distribution.

Peer-to-peer communication in wireless local area networks

A new MAC protocol which supports peer-to-peer direct communication is introduced for a packet switched wireless network. Terminals that are located within range of each other and are sufficiently isolated from the base station can communicate with their peers directly without the use of the base station as a relay. Slotted Aloha is used as the access protocol. Throughput and delay of the protocol are evaluated. Numerical results are presented which show that significant improvements in throughput/delay performance can be obtained over a system using slotted Aloha without peer-to-peer communication.

The deflecting multicast switch

We introduce a novel multicast switching paradigm, the deflecting multicast switch (DMS), which accomplishes the replication and routing functions of a multicast switch simultaneously. The architecture is shown to have low connection complexity and can be implemented in a modular fashion. A self-routing and self-replication algorithm with minimal control overhead is described which allows for distributed control of these functions. A key requirement of ATM, namely the maintenance of cell sequence in a session, is easily ensured. Analytical results are presented for the calculation of the cell loss probability, the number of stages to guarantee an upper bound on the cell loss probability and the buffer delays. For the case of uniform traffic patterns, numerical results are presented which exhibit the number of stages required for a fixed cell loss probability as well as the buffer delays.

Guaranteed cell sequence in nonblocking multi-channel switching

The paper investigates multi-channel switching as a promising alternative to traditional single-channel switching where virtual paths established in a switch are between a single input channel and a single output channel. Building on a particular nonblocking condition for the flip networks, a multi-channel switching architecture that supports an arbitrary number of channel groups is formulated. In multi-channel switching, cells belonging to a single session can traverse multiple channels. The architecture proposed in the paper provides the time ordering integrity among those cells without employing any resequencing mechanism.<<ETX>>

Nonblocking multi-channel switching in ATM networks

Multi-channel switches have been proposed and studied in the literature as a means of alleviating the processing speed constraint of electronic switches. Multi-channel switches can provide higher performance (e.g., throughput, cell loss probability, delay) by exploiting the concept of channel grouping. Instead of being routed to a specific output channel, a cell is routed to any channel belonging to an appropriate channel group which may be defined as a collection of channels transmitted over a single optical fiber. The main goal of the paper is to develop a switching paradigm that accomplishes multichannel switching as a generalization of single-channel switching paradigms that are currently prevalent. The resulting architecture must maintain the required features of single-channel switching (such as multicasting, and simplicity in hardware) while providing the advantages of multichannel switching (such as multi-rate and super-rate switching, and higher performance).<<ETX>>