09-05-2012, 03:03 PM
ADAPTIVE FREQUENCY HOPPING
final ppt.pptx (Size: 99.13 KB / Downloads: 31)
INTRODUCTION :
An Adaptive Frequency Hopping Scheme can increase the interference rejection capability of the frequency hopping system, which adopt digital signal processing technology So it is proposed in military communication gradually. An adaptive frequency hopping scheme is based on real time channel evaluation s, which makes use of them to analyze and to evaluate the frequency status.
The key idea behind adaptive frequency hopping is use only “good” frequencies , by avoidind the “bad” frequency channels perhaps those “bad” Frequency channels are experiencing frequency selective Fading, or perhaps some third party is trying to communicate on those bands , or perhaps those bands are being actively jammed.
Therefore , Adaptive frequency Hopping should be complemented by a mechanism for detecting Good/Bad channels .
LITERATURE SURVEY :
Adaptive Frequency Hopping technique is proposed to mitigate the interference between Bluetooth and Wireless local area networks. The new Adaptive Frequency Hopping technique optimizes the carrier spacing according to the network load and noise level . For a given overall bandwidth and data rate , reducing the separation between adjacent channels has a positive effect of increasing the number of available hopping channels. This can definitely decrease the collision rate. On the otherhand decreasing the channel spacing that minimize the network throughout. Rayleigh Fading was considered and results show that the new Adaptive frequency Hopping technique outperforms existing Adaptive frequency Hopping techniques for a wide range of network loads.
MULTIUSER OFDM
Introduction :
In most communication systems two-way communications is required and multiple users must be supported. OFDM can be applied in a multiuser application producing a highly flexible, efficient communications system. The system design of a multiuser OFDM system is dependent on the intended application and hardware complexity. OFDM has been widely used in broadcast systems. It is being used for Digital Audio Broadcasting and for Digital Video Broadcasting in Europe and Australia. It was selected for these systems primarily because of its high spectral efficiency and multipath tolerance. OFDM transmits data as a set of parallel low bandwidth (100 Hz - 50 kHz) carriers
CONCLUSION :
Multiuser OFDM and some of the new techniques that can enhance system performance. Multiuser OFDM allows for highly flexible communications, thus can be made to adapt to radio channel conditions. This adaptability results in a high spectral efficiency and reliability.