Mohammad Mamunur Rashid

On the performance of directional communications in ultra-dense networks

Extreme densification of base stations is imminent in the next generation of cellular networks to meet the exponentially increasing demand for mobile data traffic. In such ultra-dense networks (UDNs), the remarkably high inter-cell interference can reduce or even negate the densification gain. On the other hand, directional communications can significantly bring down the interference levels in UDNs. Hence, it is of importance to evaluate the network performance of UDNs with directional communications. Through Monte Carlo simulations, this paper analyzes the characteristics of coverage probability, area spectral efficiency (ASE), and per-user throughput with respect to extreme network densification. Our simulation results show that directional communications can deliver significantly higher network performance with tens of times higher ASE when compared to non-directional communications in UDNs.

Rate Allocation for Simultaneous Multi-Class Service Transmission Over Dynamic Spectrum Access-Based Networks

In this paper, we study rate allocation mechanisms that allocate available transmission rate of a particular secondary user (SU) among its different classes of services assuming that a specific channel assignment algorithm across active SUs is in place. In particular, we formulate the rate allocation mechanism of a SU between its two different classes of services namely, delay sensitive (DS) and best effort (BE) services as a Markov decision process. Then the optimal rate allocation mechanism that minimizes the average queuing delay of DS packets while guaranteeing the packet loss probabilities of both classes of packets is obtained using a linear programming technique. Since the optimal rate allocation mechanism can be complex for implementation in a SU device due to its probabilistic nature, we also study a low-complexity suboptimal rate allocation mechanism. For this suboptimal scheme, we develop a queuing analytic model to measure and compare different data-link layer performance parameters e.g., packet loss probability and queuing delay distribution. The developed analytic model for the suboptimal scheme is further useful for a call admission decision. We compare the performances of the suboptimal rate allocation mechanism with its optimal counterpart. Presented simulation results show that the suboptimal mechanism has a quite similar performance as the optimal mechanism.

Group Resource Allocation for Increasing VoIP Capacity over WiMAX

High demand for mobile voice puts forth the requirement of high VoIP capacity over WiMAX networks. Although WiMAX networks are well-known for high-speed internet access on the go, VoIP capacity over WiMAX is low due to large control overhead. In this paper, we propose Group Resource Allocation (GRA) mechanism that reduces the control overhead and hence increases VoIP Capacity over WiMAX. In GRA multiple users are provided allocation as a group. Grouping is based on common traffic and channel characteristics and uses bitmaps to signal resource allocation information to users. Grouping of users and use of bitmaps reduces control overhead. Simulation results show that a 40% gain in VoIP capacity over WiMAX can be achieved with Group Resource Allocation.