There is a fundamental
tradeoff between "call blocking probability" and "call dropping
probability" in cellular systems. While both blocked calls and dropped
calls are undesirable, dropped calls are annoying and must be eliminated if possible.
Call dropping probability can be decreased at the cost of increased call
blocking probability. For this, some resources are reserved in each cell for
calls that are transferred from neighboring cells. In this project, OPNET
simulations were used to determine optimal resource that need to be reserved.
Two different scenarios were modeled - Metropolitan model and Highway model. In
metropolitan model, people were assumed to be moving in random directions at
various speeds - walking, vehicular. The highway model represents cars moving
on a typical highway. It was determined that fixed resource allocation does not
perform very well. Resource reservation schemes that take into account the
speed and general direction of movement of callers perform better.
The objective of this project was to study and
compare the performance of two MANET routing protocols: Temporarily Ordered
Routing Algorithm (TORA) and Dynamic Source Routing (DSR). The simulation model
consists of a set of nodes moving in random directions at variable speeds.
Number of nodes and average speed are the variables that affect the protocol
performance. Results show that DSR outperforms TORA in terms of the number of
MANET control packets used to maintain/erase routes. Also, it is concluded that
TORA is a better choice than DSR for fast moving highly connected set of nodes.
It is observed that DSR provides better data throughput than TORA and that
routes can be created faster in DSR than in TORA.
This project involves modification of standard 802.11b protocol for improved performance in lightly loaded conditions. An event based simulation program written in C is used to model a standard 802.11b network in adhoc configuration. Varying the Number of Stations, Packet Size and Arrival Rate changes network load. The effect of these variations on parameters like data throughput and packet delay is studied and the protocol is modified for lightly loaded networks. For lightly loaded networks with small sized packets, a reduction in minimum contention window produces favorable results. But on the other hand, small contention windows are not very helpful in lightly loaded networks with long packets.
Literature survey of QoS issues in 3G wireless Networks.
Literature search on TCP over wireless networks: TCP Snoop, M-TCP etc. and UMTS RLC/MAC operation.
The inadequacy of conventional receivers in Multiple Access Interference (MAI) environment spurs the research in multiuser receiver architectures. Multiuser receivers mitigate MAI, improve accuracy of the signal estimate, and therefore result in reduced bit error rates. In this project we investigate the various multiuser receivers namely: Optimal, Decorrelator, Minimum mean square error, Parallel interference cancellation and Successive interference cancellation receivers. MATLAB simulations are used to compare the performance of these receivers with conventional receiver.
The simulation program uses transmitter power, radio frequency, path loss exponent and standard deviation of log normal distribution as inputs to generate samples of propagation path loss. It also uses receiver antenna gain, receiver bandwidth and noise figure to determine noise power at receiver. This information is used to determine the percentage of time the SNR at the receiver is greater than minimum. This is used to determine cell size and minimum separation between cells.
WINSOCK programming was used to implement the server. The server supports GET/POST methods and persistent connections.
DASA, EDF and RMA were implemented using uClinux/RTlinux on a Lieno uCsimm kit (that uses motorola’s Dragonball processor). It was shown that even though DASA should theoretically perform best in overload conditions, it performs worse than RMA because of the processing overhead involved.