Morteza Naraghi-Pour

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. >

Trellis codes for 4-ary continuous phase frequency shift keying

The approach of Morales-Moreno and Pasupathy (1988) is extended for the design of trellis codes for 4-ary continuous phase frequency shift keying (CPFSK) with modulation index h=1/2. The criterion for comparison of codes is the maximum free Euclidean distance for a given rate and the number of states of the signal space code. For the same number of states of the signal space code, these codes improve the free Euclidean distance by up to 1.25 dB over previously published results. Finally, the implementation of the combined coding and modulation system is discussed. >

Blocking effects of mobility and reservations in wireless networks

We evaluate the effects of mobility and reservations on new call blocking and handoff blocking in multirate wireless networks. The model evaluated uses fixed channel assignment (FCA) with priority for handoffs over new call arrivals by reserving a number of channels for handoff calls in all the cells. The performance measures used are new call blocking and handoff drop probabilities. The methodology used is that of implied costs which we calculate from the the network net revenue which considers the revenue generated by accepting a new call into the network as well as the cost of a handoff drop in any cell. Simulation and numerical results are presented showing the accuracy of the model. We present numerical results showing the effect of reservations on the call blocking probability. The implied cost analysis shows that mobility has a significant knock-on effect on the traffic elsewhere in the network and we capture this effect through the net revenue which is sensitive to the level of mobility. We calculate the sum revenue for a given network by maximizing the net revenue using implied costs in a gradient descent algorithm. This analysis indicates that in the case of multiple classes of traffic the call carrying capacity of the network is sensitive to the choice of reservation parameters.

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.

Shadow prices for LLR and ALBA

Shadow prices are calculated for least loaded routing (LLR) and aggregated least busy alternative (ALBA) routing in circuit-switched networks for the blocking probability obtained from fixed point algorithms. Numerical results are presented for the calculation of these shadow prices in small networks. As an application of these shadow prices, we also formulate a constrained optimization problem to calculate the sum capacity of LLR and ALBA for a given network. Comparison of the sum capacities indicate that the optimization using shadow prices results in a significant improvement. This provides evidence that matching capacity distribution to traffic is important even when adaptive routing schemes such as LLR and ALBA are used in the network. We also calculate upper bounds on the sum capacity which serve to indicate how well the optimized LLR and ALBA perform. The numerical results also confirm that with a small number of states the capacity of ALBA approaches that of LLR.

Integrated voice-data transmission in CDMA packet PCNs

We present a new multiple access protocol based on DS-CDMA and slotted Aloha random access protocol with reservation for integrated voice-data transmission for packet personal communication networks (PCN). Voice terminals are assigned a code which they relinquish during their silence periods to be used by the data terminals. The data terminals contend for the codes using a reservation slotted Aloha protocol. We analyze the performance of the protocol incorporating the multiple access effects as well as the self interference associated with DS-CDMA systems.

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.

A Unitary MUSIC-Like Algorithm for Coherent Sources

This paper proposes a method for direction of arrival (DOA) estimation which can be applied in case of both non-coherent and coherent sources. In comparison to the well-known subspace algorithms such as MUSIC, the proposed method has several advantages. First, in contrast to MUSIC, no forward/backward spatial smoothing for the covariance matrix is needed in the case of coherent sources. Second, the proposed method is more suitable for realtime implementation since it only requires one or a few snapshots in order to provide an accurate DOA estimation, whereas MUSIC requires a large number of snapshots. Third, the proposed method exploits the eigenvalue decomposition (EVD) of a real-valued covariance matrix thereby reducing the computational cost by at least a factor of four. Simulation results show that the proposed method can estimate the DO As of the incident sources with high accuracy even when the sources are coherent.

Convolutional coding for finite-state channels

We propose new decoders for decoding convolutional codes over finite-state channels. These decoders are sequential and utilize the information about the channel state sequence contained in the channel output sequence. The performance of these decoders is evaluated by simulation and compared to the performance of memoryless decoders with and without interleaving. Our results show that the performance of these decoders is good whenever the channel statistics are such that the joint estimate of the channel state sequence and the channel input sequence is good, as, for example, when the channel is bursty. In these cases using even a partial search decoder such as the Fano decoder over the appropriate trellis is nearly optimal. However, when the information between the output sequence and the sequence of channel states and inputs diminishes, the memoryless decoder with interleaving outperforms even the optimal decoder which knows the channel state.

DPCM encoding of regenerative composite processes

Fixed (nonadaptive) and forward adaptive differential pulse code modulation of regenerative composite sources is investigated. In the fixed code, an approximate formula is given for the optimal value of the prediction coefficient. This is then used as an initial guess to optimize the code (predictor and quantizer) through a numerical method. In the forward adaptive scheme, the state of the switch in the composite source is estimated using a MAP sequence estimation algorithm, and the code is then matched to the mode process corresponding to the estimated switch state. The performance of the two systems is evaluated with quantizers of 4, 8, and 16 levels. The results show that the forward adaptive scheme significantly outperforms optimized fixed DPCM in the sense of mean-squared error. Stochastic stability of the code is also established for the fixed DPCM scheme as well as for an adaptive scheme which receives the switch state as side information. >