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Bluetooth Technology

Bluetooth is a WPAN (Wireless Personal Area Network) commmunications protocol designed by the Bluetooth SIG(Special Interest Group). It replaces clables connecting many different types of devices like mobile phones and headsets, heart monitors & medical equipment. A2DP(Advanced Audio Distribution Profile) – it enables wireless transmission of stereo audio from an A2DP smartphone (or computer) to […] Read more»

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Long Term Evolution (LTE)

Long term Evolution commonly known as LTE, is a standard for wireless communication of high speed data. Usually a mobile phone or USB data terminal is used as an access device. This technology is commonly marketed as 4G LTE. This technology is an evolution of the GSM/UMTS standards developed by 3 rd Generation Partnership Project (3GPP). LTE is an update to […] Read more»

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Modulation Techniques

Pulse shaping is the process of changing the waveform of the transmitted signals, to make them better suited for the communication channel ISI can be controlled using pulse shaping. Zero ISI Nyquist Criterian Raised Cosine     Read more»

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Speech Coding

Speech coders Types: 1. waveform coders: speech modeling is not required -DPCM: transmit difference between successive sample values, d[k] = m[k] – m[k-1], and reconstructed by adding d[k] to previous sample m[k-1] -ADPCM -SBC -ATC 2. Source coders modeling vocal tract, vocal tract filter parameters are created at encoder, model parameters are sent to receiver, […] Read more»

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Wireless Communication System and standard

GSM services: – tele services, voice calls – bearer or data services – supplementary services, call holding, call waiting, call forwarding, multi party call conferencing GSM architecture: – MS Mobile station, consists of mobile equipment and subscriber identity module – BSS, base station subsystem, consists of base station transreceiver and base station controller -NSS, network […] Read more»

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Multiple access techniques

FDM: – frequency division multiplexing – it is an analog multiplexing technique that combines low bandwidth analog channels into one large bandwidth analog channel TDM: – time division multiplexing – digital multiplexing technique for combining several low-rate digital channels into one high-rate digital channel Duplexing means sending and receiving simultaneously. FDD: – two bands of […] Read more»

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Equalization, Diversity and RAKE receivers

Equalization Equalization is a technique that compensates for ISI created by multipath in frequency selective, time dispersive channels. If signal bandwidth exceeds coherence bandwidth of channel, ISI occurs and pulses are spread in time causing bit errors. An equalizer compensates for amplitude and delay distortions introduced by the channel. Equalizer is a digital filter used […] Read more»

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Interleaving

An effective method of combating burst errors occurring on a fading channel. – Spread the codeword – Position bits away from one another so that they experience independent fading effects Read more»

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Viterbi Algorithm for Convolutional code decoding

Steps: 1. Traverse through trellis 2. Compute hamming distance between the branches of received word and those in the trellis – at each level, consider two paths entering the same node – from those two paths, the one that is closer to received word is retained, and the other path is discarded – proceeding this […] Read more»