New M.E.Thesis Submitted from ECE student

OPTIMIZED DESIGN OF PULSE SHAPING FILTERS FOR WIRELESS COMMUNICATION SYSTEMS By Mandeep S. Saini,Electronics


Abstract
An area efficient pulse shaping filtering technique is presented to reduce the implementation cost in wireless communication. Pulse shaping filter has been designed using raised cosine filter, nyquist filter and half band filter techniques. All designs have been compared in terms of performance and hardware requirement. The Park McClellan algorithm based equiripple technique has been used to optimize proposed design. The results show that the performance of the half band designs is almost identical to the raised cosine filter with significant reduction in hardware requirements. The proposed IIR half band design results in lowest filter order to provide cost effective solution for wireless communication systems. The wide diffusion of wireless terminals like cellular phones is opening new challenges in the field of mobile telecommunications. Besides, the possibility to transmit not only voice but even data between terminals and end users of many kinds has fostered the development of new technologies and new standards for cellular communications. Recently, there is increasingly strong interest on implementing multimode terminals, which are able to process different types of signals, i.e. WCDMA, GPRS, WLAN and Bluetooth. These versatile mobile terminals favor simple receiver architectures because otherwise they’d be too costly and bulky for practical applications. As digital technology ramps up for this century, an ever-increasing number of RF applications will involve the transmission of digital data from one point to another. The general scheme is to convert the data into a suitable baseband signal that is then modulated onto an RF carrier. Pulse shaping filters are used at the heart of many modern data transmission systems like mobile phones, HDTV, SDR to keep a signal in an allotted bandwidth, maximize its data transmission rate and Minimize transmission errors. The ideal pulse shaping filter has two properties:

i. A high stop band attenuation to reduce the inter channel interference as much as possible.

ii. Minimized inter symbol interferences (ISI) to achieve a bit error rate as low as possible. The RRC filters are required to avoid inter-symbol interference and constrain the amount of bandwidth required for transmission. Root raised cosine (RRC) is a favorable filter to do pulse shaping as it transition band is shaped like a cosine curve and the response meets the nyquistcriteria. The first nyquist criterion states that in order to achieve an ISI-free transmission, the impulse response of the shaping filter should have zero crossings at multiples of the symbol period. A time-domain sinc pulse meets these requirements since its frequency response is a brick wall but this filter is not realizable. We can however approximate it by sampling the impulse response of the ideal continuous filter. The sampling rate must be at least twice the symbol rate of the message to transmit. That is, the filter must interpolate the data by at least a factor of two and often more to simplify the analog circuitry. In its simplest system configuration, a pulse shaping interpolator at the transmitter is associated with a simple down sampler at the receiver. The FIR structure with linear phase technique is efficient as it takes advantage of symmetrical coefficients and uses half the required multiplications and additions.

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