M Tech (EC) Dissertations

Permanent URI for this collectionhttp://ir.daiict.ac.in/handle/123456789/6

Browse

Filters

20212

Settings

Subject: search.filters.subject.OTFS

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Gradient based Adaptive Channel Estimation for Orthogonal Time Frequency Space (OTFS)
    (2021) Upalekar, Divya Subhash; Das, Rajib Lochan; Vasavada, Yash
    The next generation wireless system with high mobility requirements brings the challenge to mitigate the effect of a time-varying channel. Conventional multicarrier systems like Orthogonal frequency division multiplexing (OFDM) are designed to mitigate the multipath effects that cause Inter Symbol Interference (ISI), Since OFDM is highly sensitive to inter carrier interference (ICI), it is not wellsuited for the high mobility scenarios with significant Doppler shifts and frequency dispersion. As the Doppler spread and phase noise leads to the inter carrier interference (ICI). Unlike the traditional time-frequency domain schemes,the OTFS system transmits the information symbols in the delay-Doppler domain. OTFS converts a doubly-dispersive time-frequency channel into a nearly static channel in the delay-Doppler domain by means of the Symplectic Fourier transform . In the delay-Doppler domain, the information symbols experiences constant fading, thus the OTFS system performs better than the OFDM system even in the presence of high Doppler. One of the channel estimation schemes for the OTFS system is pilot based estimation in which pilots are transmitted in the delay-Doppler domain. In this method, the delay-Doppler coordinates are estimated using the spreading of the pilot output in the time-frequency domain due to transformations. The channel coefficients estimated by these method are accurate in the absence of noise, but in the presence of noise the channel path gain value estimates were affected. Additional pilot power is required for this method to get the accurate estimate. In the proposed channel estimation algorithm, these slowly varying channel path gain values are estimated using the Gradient based adaptive algorithms. In this method the pilot based approach is combined with the adaptive methods to gain the advantages of both the methods. This method uses a single pilot symbol surrounded by some guard symbols, for the estimation of the delay-Doppler domain channel. In this method the additional pilots were inserted to support the adaptive algorithms, but it can give accurate results even in presence of noise.
  • Thumbnail Image
    ItemOpen Access
    Channel Estimation for Orthogonal Time Frequency Space Modulation using Recursive Least Squares
    (2021) Singh, Bhavesh Amar; Das, Rajib Lochan; Vasavada, Yash
    For its capacity to provide high data rates to a wide number of users, 4G wireless communications had a huge success in the previous decade. With the Internet of Things (IoT) and high mobility scenarios such as vehicle-to-vehicle (V2X) connections on the horizon, the Orthogonal Time Frequency Space (OTFS) modulation scheme has ignited lot of attention in recent years as a viable alternative to OFDM, especially in scenarios involving high user mobility. OTFS has its specialty that it is designed in the delay-Doppler domain. OTFS modulation, when combined with an appropriate equaliser, easily leverages the whole channel variety in both time and frequency. It transforms a fading, time-varying wireless channel used by modulated communications like OFDM into a time-independent channel with a nearly complex channel gain for all symbols. This thesis makes a note on existing drawbacks of OFDM and highlights the usage of a new 2-D modulation scheme called OTFS modulation. It goes on to detail the various methods of channel estimate currently in use while installing OTFS and suggests the use of an adaptive algorithm for channel estimation in the delay-Doppler domain. The proposed algorithm, unlike widely used channel estimation methods, estimates channel gain in the time domain and Doppler taps in the delay-Doppler domain.