Abstract Ad-hoc networking is a concept in computer communications, which means that users wanting to communicate with each other form a temporary network, without any form of centralized administration. Each node participating in the network acts both as host and a router and must therefore be willing to forward packets for other nodes.In a multi-hop wireless packet network, a packet traverses more than one wireless link in traveling from its source to its destination. Such wireless networks have received considerable attention recently in the context of ad hoc networks. Ad-Hoc networks are self-organizing multi-hop wireless networks where not all links along the path of a packet can be activated simultaneously. Hence the performance of a higher level mechanism, such as congestion window or Transport Layer protocol (TCP) will depend crucially on how the links are scheduled for transmission. In multiple access networks, such as the IEEE802.11 wireless LAN, the scheduling of transmissions is done by the medium access control (MAC) protocol. This transmission scheduling is completely unaware of the needs of the TCP congestion window protocol. This thesis is concerned with the poor interaction between the TCP adaptive window protocol, the IEEE 802.11 MAC protocol, and the IEEE 802.11 Ad-Hoc routing protocol. Our thesis follow on the work done by the researchers K. Nahm and C. Kuo in the paper entitled “TCP over 802.11 Multihop networks issues and Performance Enhancement” [1]. Our contributions are two-fold. First we have repeated and confirmed the simulation results reported by K.Nahm and C.Kuo using NS-2 network simulator. Second we have introduced a simple modification in the 802.11 DSR routing protocol which reduces the unnecessary VI reroutings triggered by MAC packet collisions and enforces the TCP to enter the fast retransmit / fast recovery phase to quickly recover the packet loses. This modification has been simulated using NS-2 network simulator and from the results we have found that it provides a substantial improvement in TCP performance in the situations that we have considered in the simulation models
يحي الشارف المبروك (2009)

Transmit Antenna Selection using Orthogonal Space-Time Block Codes (TAS-OSTBC) aided Millimeter-wave (mmWave) communications is proposed in this paper. The TAS transmitter is characterized by a lower number of Radio Frequency (RF) chains than the number of transmit antennas, hence it is capable of reducing both the energy consumption as well as the transmitter cost. The proposed scheme combines TAS-OSTBC system with Hybrid Analog-Digital Beamforming for 60 GHz mmWave communications and using Hadamard transform. The computer simulation results demonstrate that the TAS-OSTBC scheme with fully digital SVD-based precoding has better Bit Error Rate (BER) performance than that of the conventional TAS system with OSTBC scheme. Furthermore, the error performance is significantly improved by applying Uniform Linear Array (ULA) antennas which improve the system performance as the number of array elements increases due to providing a beamforming gain. It is also found that the BER performance is further improved by applying Hadamard transform with an SNR improvement of about 3dB over the conventional systems without using Hadamard transform.
Taissir Y. Elganimi, Mohammed S. Alshawish, Moustafa M. Abdalla(4-2019)

Abstract In wireless communication systems the data rate, capacity, coverage, and spectral efficiency; can be enhanced with multi-carrier transmission and multi-antenna, then the overall wireless communication system performance is greatly enhanced by combining OFDM and MIMO schemes, MIMO helps in increasing the throughput where as OFDM spreading out the frequency selective fading channel over many symbols. In this thesis evaluating performance of the system depends on both link and system levels, where the measure of performance is represented in the throughput, cell radius and the effective signal to interference plus noise ratio (SINR). It also depends on the employed capacity criterion and it takes into account the impact of adaptive modulation and coding. the worked scenarios start from a link level extending to a system level in 3GPP LTE. To achieve the above a number of tasks followed by observations are carried out. They start by analysis of the equations and a Matlab program is written to calculate the cell edge throughput, cell coverage and DL capacity. After the programs implementation, the multi antenna transmission effect is noted on the arrival throughput when taking into account the modulation technique. When increasing the order of the antenna and the throughput is also increased, but it must be traded off with the probability of error; Coverage has also improved by decreasing the order of the modulation technique. For the system level with different traffic, the overall throughput of the system and the capacity of the network are determined by the number of resource blocks (RBs). These RBs depend on the bit rate of the service and bit rate for each RB. The adopted scenarios in this thesis start from link to system, where the features are represented in a flexible base station and user configurations, channel modeling with path loss, user mobility, also at different transmitter and receiver (MIMO). The approaches are useful in single user and multi-user MIMO, then all of the above can be standardized by metrics: capacity, throughput, spectral efficiency, user QoS etc. Finally thesis conclusion and some future work as an extension of this work are presented.
احمد محمد التانزفتى (2013)