Raksha Upadhyay

Performance Improvement of Wi-Max IEEE 802.16e in Presence of Different FEC Codes

IEEE 802.16e, mobile Wi-Max, is a wireless technology used to provide very high data rate over large areas to a large number of users where broadband is unavailable. In mobile wireless environment the channel is hostile and behaves adversely. To combat the fading caused by wireless channel IEEE 802.16e uses OFDMA (Orthogonal Frequency Division Multiple Access) as a transmission scheme based on multicarrier modulation.. To investigate the performance of mobile Wi-Max, its physical layer is simulated using Matlab and bit error rate (BER) performance is observed. Further performance improvement is achieved using forward error correction codes (FEC). Two codes, convolution code (CC) and low density parity check code (LDPC) are considered for this purpose. BER performance is evaluated for these codes under different conditions. Finally, BER performance is compared using different FEC for mobile Wi-max.

Survivability of a integrated fiber-wireless (FiWi) access networks

In past few years there is a huge development in the field of FiWi technology due to continuously increase in the number of users of the internet. FiWi technology now a days proving itself a main tool in the field of telecommunication by its own merits over the other existing technologies. The FiWi technology provides huge amount of bandwidth and stability to the network user in a flexible manner i.e. network provide “Anywhere Anytime” connection service to the user at very high speed. The existing technology viz PON offers higher bandwidth and stability but at relatively higher cost due to the use of expensive optical devices. On the other hand WMN technology offers us communication among the users with a better flexibility at relatively lower cost but its bandwidth is limited due to channel interference. So, the efforts are put to combine the merits of both the technologies resulting in a new technology named as “FiWi”. Various algorithms are proposed to enhance the performance of a FiWi access network. In this paper, a detailed discussion is made on survivability issues in FiWi networks against the different level of failures in the network. This paper is basically a review paper in which the main aim is to emphasize on the recent trends of survivability in the FiWi networks.

ONU placement in Fiber-Wireless (FiWi) access networks using teacher phase of Teaching Learning Based Optimization (TLBO) algorithm

Nowadays, there is a huge requirement of bandwidth and mobility to end users. For fulfilling this, Fiber-Wireless (FiWi) networks are designed consolidating the advantages of both optical and wireless networks. Optical networks provide high bandwidth and stability while wireless networks provide cost efficiency and mobility. In FiWi networks Optical Network Units (ONU) placement is a very important issue since ONU links both optical and wireless end of the network. Reducing ONUs in the network directly leads to cost efficiency of that network. For the same purpose, we implement an algorithm based on teacher phase of Teaching Learning Based Optimization (TLBO). The implemented algorithm reduces required ONUs in the network.

Fiber-wireless (Fi-Wi) architectural technologies: A survey

The paper aims to present various architectural technologies of Fiber-Wireless (Fi-Wi) networks, based on previous and current interest of researchers. Fi-Wi networks recently become more powerful & impactful in the access technology solution & prototypes. The survey overviews the architectural knowledge & enabling technologies involved and comparing it with future development of wireless & optical network respectively. Radio-over-Fiber (RoF) transmission is used to achieve high level of integration with simplified wireless base station. On the other hand Radio-and-Fiber (R&F) networks are the most beneficial architecture implementation which is used to build Wireless Local Area Network (WLAN) based Fi-Wi networks.

MIKBIT- Modified DSR for MANET

Various reactive and proactive routing protocols are being used in Mobile ad hoc networks (MANETs). Dynamic Source Routing (DSR) is one of the reactive routing protocols but high overhead involved in flooding while route creation is a limiting factor of DSR protocol. The paper aims to minimize the number of route requests (RREQs), which is a significant source of overhead for the DSR. In this paper, the modification of DSR algorithm is done to enhance its performance. In the proposed modified DSR i.e. Mobile internetwork broadcast infrastructure technique (MIKBIT) multicasting approach is used to reduce packet overheads. The considered network is IEEE 802.15.4, which is the emerging next generation wireless standard designed for low-rate wireless personal area networks (LR-WPAN). The performance parameters such as throughput, average end-to-end delay, average jitter and packet delivery ratio are evaluated for the proposed algorithm and compared with that of existing DSR routing protocol. Substantial improvement is achieved using the proposed algorithm.

Collision Resolution Schemes with Nonoverlapped Contention Slots for Heterogeneous and Homogeneous WLANs

CSMA/CA-based DCF of 802.11 MAC layer employs a best-effort delivery model, in which stations compete for channel access with the same priority. In a heterogeneous network, providing different priorities to different applications for required quality of service is a challenging task, since heterogeneous conditions result in unfairness among stations and degradation in the throughput. This paper proposes a class of collision resolution schemes for 802.11 having contention window control with nonoverlapped contention slots. In the first scheme, window ranges of two consecutive stages are nonoverlapped, and it is called nonoverlapped contention slots (NOCS) scheme. In the other scheme, termed as NOCS-offset, an offset is introduced between window ranges of two stages. Selection of a random value by a station for its contention with discontinuous distribution results in reduced probability of collision. Analytical and simulation results show that the proposed scheme exhibits higher throughput and fairness with reduced delay and collision probability in homogeneous and heterogeneous networks. Performance of the proposed scheme is evaluated for mix traffic and high data rate environment with advanced back-off management techniques to meet the requirements of the present applications.

Time and frequency synchronization techniques for OFDM systems

Orthogonal frequency division multiplexing (OFDM is a multi-carrier modulation technique which uses several orthogonal subcarriers to transmit/receive a high data rate signal. Proper synchronization must be done for the adequate working of the system. Initially Schmidl and Cox proposed a method, in which with the help of a training symbol, with two identical halves synchronization is achieved. Thereafter many methods have been developed. The aim of this paper is to study and compare various methods for time and frequency synchronization. In addition we provide the effects of adding identical parts to the preambles on the Schmidl and Cox proposed training symbol. The synchronization techniques are examined in Gaussian and Multipath fading environments for comparison. The results of the performance comparison are presented in terms of the timing metric defined differently by various methods.

Class of collision resolution schemes with multistep distribution for IEEE 802.11

Traditional Medium Access Control (MAC) algorithms for Distributed Co-ordination Function (DCF) in IEEE 802.11 extend window ranges after each packet collision in the next stage. As these window ranges intersect with window ranges of other stages, the system is collision prone. This paper proposes a class of collision resolution schemes for 802.11 contention window control with multistep distribution and called as Overlapped Contention Slots with Multistep Distribution (OCS-MD). It is shown that proper selection of different steps in the distribution of OCS-MD increases the mean value of back-off counter as compared to standard Binary Exponential Back-off (BEB). This reduces probability of window intersection of different stages, resulting in lesser probability of collision. The system model is formulated for the proposed schemes. Analytical results are validated against those obtained from simulation. The performance results show that the proposed algorithm enhances the system performance in terms of throughput and collision probability with comparable mean delay and fairness than existing scheme. Moreover these schemes can be easily incorporated with little modifications in existing 802.11 standard.

Saturation Throughput Analysis of 802.11 DCF in Presence of Different Receiver Combining Techniques

The Performance of IEEE 802.11 distributed co- ordination function (DCF), under ideal channel conditions degrades mainly due to packet collisions at MAC layer. However, studies reveal that MAC layer performance significantly reduces when wireless networks encounter channel fading at physical layer. Since fading results in burst errors, in addition to errors caused by collisions at MAC layer. In this paper, cross layer analysis is performed between MAC layer and physical layer. An analytical expression for throughput computation is used to investigate the effect of fading on the MAC layer performance which is verified through simulation. Further to enhance the network throughput in fading, receiver diversities are used. Selection Combining (SC), Equal Gain Combining (EGC) and Maximal Ratio Combining (MRC) diversity techniques are used at physical layer to calculate the enhancement of the system throughput of MAC layer. Outcomes for different diversities are compared and proposed that the same analysis can be useful for upcoming standards of WLAN using MIMO techniques.

Investigation effect of phase noise of OFDM system and realization LO (local oscillator) with and without phase locked loop (PLL)

A phase locked loop (PLL) operates on the serialized received modulation symbols and provides an independent phase correction value for each received modulation symbol. Each received modulation symbol is corrected with its own phase correction value to obtain a phase-corrected symbol. The phase error in each phase-corrected symbol is detected to obtain a phase error estimate for that phase-corrected symbol. Orthogonal Frequency Division Multiplexing (OFDM) technique has received a great attention and has been widely used in the wireless communication systems for its high spectrum efficiency and robustness to the narrowband interference and multipath fading. OFDM can provide enormous data rates with sufficient robustness to radio channel impairments. Orthogonal frequency division multiplexing is one of the multi-carrier modulation (MCM) techniques that transmit signals through multiple carriers. These carriers (subcarriers) have different frequencies and they are orthogonal to each other. But it yields however some disadvantages too, one being an increased sensitivity to phase noise, which is generated in the local oscillators. The phase-corrected symbols are not correlated because independent phase correction values are used for the received. In this Paper, We are investigating the effect of phase noise upon OFDM system and realized local oscillator (LO)by using phase locked loop (PLL)[1][2]. Then system performance is evaluated as a degradation of the effective signal-to-noise ratio due to phase noise, in terms of BER simulations with and without PLL for different channel conditions.