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Title: Variable Rate Schemes for Wireless Applications
Authors: Mukati, V.
Keywords: Electrical Engineering
Issue Date: 2015
Abstract: With the increasing demand for increased coverage area, higher QoS, ubiquitous availability, flexibility and expandability, variable rate communication is gaining popularity over single rate systems for multipath channel. To fulfill the requirement to support variable rate data transmission over Pedestrian and Land Mobile Satellite (LMS) channel, first part of this thesis presents the variable rate multicarrier based transmission scheme. In particular, complementary code keying (CCK) and orthogonal frequency division multiplexing (OFDM) are combined to get the advantage of individual scheme and is tested over slowly varying frequency selective channel. The main advantage obtained over the classical single carrier based CCK scheme is the higher resistance towards the longer delay spread. Simulation results in terms of BER show the noticeable improvement in the performance as compared to the single carrier based variable rate scheme. Also the Peak-to-Average Power Ratio (PAPR) performance for the different rates of the proposed scheme has been shown. The PAPR performance of the proposed scheme degrades with the increase in the data transmission rate. Later, the proposed scheme has been compared with the variable rate single user Spread-OFDM and Variable spreading length (VSL)-OFDM. Spread-OFDM shows the best performance amongst the three. Detailed BER analysis for Spread-OFDM over AWGN and frequency selective channel has been done and verifies the simulation results. Study of Adaptive modulation, which is a promising technique, has also been done. This technique is being extensively used in many next generation wireless technology especially IEEE 802.11a WLAN, for providing variable rate tramsmission to ensure robust and spectral efficient communication over fading channel. Later, Carrier Interferometry (CI) spread OFDMA system with orthogonal subcarrier grouping (CI/GO-OFDMA) to support variable rate user classes has been proposed. Proposed scheme is compared with the conventional GO-OFDMA and VSL MC-CDMA transmission scheme over pedestrian channel. This work highlights the application of CI codes which can be generated for any integer to ensure efficient multicarrier variable rate transmission scheme. Simulation results clearly shows that the BER performance of CI based GO-OFDMA scheme significantly outperforms variable rate VSL MC-CDMA scheme for four different data rate users. CI codes with GO-OFDMA also ensures low PAPR, and comparable complexity compared to VSL MC-CDMA.
Appears in Collections:03. EE

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