Theses and Dissertations

Permanent URI for this collectionhttp://ir.daiict.ac.in/handle/123456789/1

Browse

Filters

20052

Settings

Has files: YesSubject: search.filters.subject.Communication network

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Performance evaluation of OFDM technique for high speed communication applications
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2005) Kabra, Mukul; Maskara, S. L.
    The Internet revolution has created the need for wireless technologies that can deliver data at high speeds in a spectrally efficient manner. However, supporting such high data rates with sufficient robustness to radio channel impairments requires careful selection of modulation techniques. The demand for high-speed mobile wireless communications is rapidly growing. OFDM technology promises to be a key technique for achieving the high data capacity and spectral efficiency requirements for wireless communication systems of the near future. Orthogonal frequency division multiplexing (OFDM) is a special case of multi-carrier transmission, where a single data stream is transmitted over a number of lower rate sub-carriers. OFDM is currently being used in Europe for digital audio and video broadcasting. The IEEE standardization group decided to select OFDM as the basis for their new 5-GHz standard, targeting a range of data stream from 6 up to 54 Mbps. This standard was the first one to use OFDM in packet-based communications, while the use of OFDM until now was limited to continuous transmission systems. OFDM is also being considered as a serious candidate for fourth generation cellular systems. In this project, transmitter, channel and receiver were simulated with various parameters, to evaluate the performance and different possibilities in the implementation. Also, some considerations about forward error correction coding, interleaving, synchronization and channel estimation are given to improve the system performance.
  • Thumbnail Image
    ItemOpen Access
    Enhancing data efficiency in OFDM (IEEE 802.11a) using equalization (11A)
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2005) Reddy, S. Gangadhar; Chakka, Vijaykumar
    IEEE 802.11a OFDM signal passed through a dispersive channel introduces ISI & ICI. To avoid ISI & ICI, cyclic prefix (guard interval) is introduced between the OFDM symbols. But the cyclic prefix contributes about 20% (0.8us/4us) of the total symbol duration. Transmission of OFDM symbols without cyclic prefix increases the data efficiency, but introduces ICI & ISI. The ISI & ICI can be removed by equalization at the receiver. Spill over in the frequency domain is same as ICI & ISI. This spill over can be observed at the unused carriers also (carriers numbered from 0-6, 33, 59-64 are unused in IEEE 802.11a). Equalization is done in the frequency domain by making use of spill over in unused carriers. A relationship is brought between the length of the channel impulse response and the number of unused carriers for perfect equalization in the absence or very little AWGN-channel noise. To avoid the noise amplification caused by Zero Forcing equalization and to satisfy the relationship derived, a methodology using Time domain equalizer (TEQ) is proposed and simulation results are presented supporting it. Alternatively, computational efficient algorithm for indoor environment is suggested by transmitting data in unused carriers with the combination of used carriers. By this method, ICI & ISI is removed at the transmitter itself and it even doesn’t amplify the noise.