Where an is the data symbol on the n-th subcarrier. Equation (1) is equivalent to the N-point inverse discrete Fourier transform (IDFT). Spacing of subcarriers and frequencies are carefully selected to achieve subcarrier orthogonality.
1/T ∫_0^T▒〖x(t) y(t) dt =0〗 (2)
Equation (2) means that the signals are uncorrelated i.e. they are two different and independent signals. In OFDM, sinc -shaped pulses are used as subcarrier spectra. According to the properties of sinc-pulses, zero crossings are located at the multiples of 1/T. The use of sinc-pulses and subcarrier center frequency fi selection with equation (3) ensures that the subcarrier orthogonality is maintained.
f_i= f_c + i/T i= (-N)/2……N/2 (3)
Where fc is the channel center frequency and N is the number of sub-channels. This way each subcarrier has the maximum at its own center frequency and zero at the center frequency of the other subcarrier.
Fig.2. OFDM Transmitter Model
After serial-to-parallel conversion, inverse discrete Fourier Transform (IDFT) is applied to each stream. In practice, this transform can be implemented very efficiently by the inverse fast Fourier Transform (IFFT). This equals transition from frequency-domain to time-domain. After IFFT, all parallel data is summed and transmitted.
CHALLENGES IN USE OF OFDM
One of the major problems with OFDM system is the high peak to average power ratio (PAPR) which occurs in the modulated signal. High PAPR occurs when the signal in the subchannels add constructively in phase. Because of modulation, high peaks are produced. Once multiple sinusoids, which are in phase, added together to form multi carrier signal high peaks are generated. On the other hand, the ...
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... region. However, this solution decreases the PA power efficiency. On the other hand, PAPR reduction technique gives a more power efficient solution.
BACK-OFF OPERATION OF POWER AMPLIFIER
In order to ensure that the PA operates in its linear region, the input signal are attenuated and said to be in power back-off mode. This application of power back-off results in increase in the PA power specifications. As a result, the PA design is oversized, resulting in a reduced power efficiency. This is the main reason that power back-off is restricted to applications where low requirements of PA efficiency is required. Quantities to measure the level of power back-off are: input power back-off (IPBO), and output power back-off (OPBO). They are defined by equations (4) and (5).
IPBO=10 〖log〗_(10 ) P_(i,sat)/P_i (4)
The allocation of 16 clock cycles for FMULT is shown in Table 1. At 0th clock cycles, the channel will be selected and everything will be reset. In the first clock cycle, the signal An and SR will be loaded. Later, mantissa multiplication takes place from 2nd to 9th clock cycles; exponent addition takes place from 2nd to 7th clock cycles...
Owsinski, Bobby. The Mastering Engineer's Handbook: The Audio Mastering Handbook. Boston, MAT: Thomson Course Technology PTR, 2008. Print.
...ics, a manual computation of successive RR intervals is resorted to. This series of RR intervals is subjected to both time domain and frequency domain analyses.
My research interest of working with coding theory, information theory, multiple access methods, and adaptive equalization, all match considerably with the research focuses of EECS Berkeley’s faculty. EECS Berkeley has the finest faculty and the most developed research facilities in the World of Electrical Engineering, and more specifically, in the field of wireless & mobile communications.
.... A. (2012). LTE, LTE-advanced, and WiMAX: Towards IMT-advanced networks. Chichester, West Sussex, U.K: Wiley.
Since, all of the satellite signals are modulated onto the same carrier frequency, the signals must be separated after demodulation. This is done by assigning each satellite a unique binary sequence known as a Gold code. The signals are decoded after demodulation using addition of the Gold codes corresponding to the satellites monitored by the receiver.
Introduction: With the advancement in technologies, concentrating on transceivers is increasing. Transceivers operate at various frequencies. The author uses Wilkinson power divider (using three section transmission line transformer) which operates at three different arbitrary frequencies simultaneously to generate the required specifications. This condition of using three different frequencies on contrary to using dual frequencies makes this /or made this paper publishable. This circuit operates in the frequency range 900 MHz - 2.3 GHz.
2. John M. Eargle, 2002. JBL Audio Engineering for Sound Reinforcement. Edition. JBL Pro Audio Publications.,
The uses of Digital Signal Processing in communications has become so large scale that nearly any form of analog communication is considered obsolete. Today, nearly any form of communication used, aside from verbal communication, relates to Digital Signal Processing. Some of the more prominent uses for DSP in communications are; local area networks, cell pho...
throughput by transmitting independent data streams on the different transmit branches simultaneously and at the same carrier frequency.
Spread spectrum techniques spread information over a very large bandwidth specifically, a bandwidth that is much larger than the inverse of the data rate. In this paper we are discussing various ways of providing multiple access by spreading the spectrum. We start out with the conceptually simplest approach, Frequency Hopping (FH). We then proceed to the most popular form of spread spectrum, Direct Sequence-Code D...
[2] A. Shatnawi, A. Abu-El-Haija, A. Elabdalla, “A Digital Receiver for Dual-Tone Multi-frequency (DTMF) Signals”, Technology Conference, Ottawa, CA, May 1997.
Spectrum Decision Making calls for reconfiguration for the channel and protocol required for constantly adapting to mobile changing environments and adjustment of output power or even alteration of transmission parameters (such as modulation formats (e.g. low to high order QAM), variable symbol rates, different channel coding schemes) and characteristics by the Cognitive radio devices. CR should be able to use multiple antennas for interference knolling, capacity increase or range extension.
[8] J Bradbury (2000) . Linear Predictive Coding, Mc G. Hill Retrieved from my.fit.edu,pp 4