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Constant Envelope OFDM
, 2008
"... This paper describes a transformation technique aimed at solving the peaktoaverage power ratio (PAPR) problem associated with OFDM (orthogonal frequencydivision multiplexing). Constant envelope OFDM (CEOFDM) transforms the OFDM signal, by way of phase modulation, to a signal designed for effici ..."
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This paper describes a transformation technique aimed at solving the peaktoaverage power ratio (PAPR) problem associated with OFDM (orthogonal frequencydivision multiplexing). Constant envelope OFDM (CEOFDM) transforms the OFDM signal, by way of phase modulation, to a signal designed for efficient power amplification. At the receiver, the inverse transformation—phase demodulation—is applied prior to the conventional OFDM demodulator. The performance of CEOFDM is analyzed in additive white Gaussian noise (AWGN) and fading channels. CEOFDM is shown to achieve good performance in dense multipath with the use of cyclic prefix transmission in conjunction with a frequencydomain equalizer (FDE). By way of computer simulation and hardware realization, CEOFDM is shown to compare favorably to conventional OFDM.
Constant Envelope OFDM with Channel Coding
"... Abstract—This paper studies the application of convolutional ..."
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Abstract—This paper studies the application of convolutional
CONSTANT ENVELOPE OFDM IN MULTIPATH RAYLEIGH FADING CHANNELS
"... In this paper we consider the problem of equalizing constant envelope orthogonal frequency division multiplexing (CEOFDM) signals that have been corrupted by frequencyselective multipath fading channels. A cyclic prefix guard interval is used to avoid interblock interference (IBI), and to make pos ..."
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In this paper we consider the problem of equalizing constant envelope orthogonal frequency division multiplexing (CEOFDM) signals that have been corrupted by frequencyselective multipath fading channels. A cyclic prefix guard interval is used to avoid interblock interference (IBI), and to make possible frequencydomain equalization (FDE) using the discrete Fourier transform. It is shown that CEOFDM exploits the multipath diversity of the channel due to frequency spreading of the data symbols. CEOFDM compares favorably with conventional OFDM when the impact of nonlinear power amplification and power backoff is taken into account. I.
CHANNEL ESTIMATION AND EQUALIZATION FOR CEOFDM IN MULTIPATH FADING CHANNELS
"... Abstract In OFDM, the orthogonal subcarriers can be assumed to undergo flat fading in a frequency selective channel permitting operation without an equalizer especially when differential data encoding is used. However, in CEOFDM, the data symbols are no longer confined to orthogonal subcarriers a ..."
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Abstract In OFDM, the orthogonal subcarriers can be assumed to undergo flat fading in a frequency selective channel permitting operation without an equalizer especially when differential data encoding is used. However, in CEOFDM, the data symbols are no longer confined to orthogonal subcarriers and, therefore, an equalizer is required for operation in frequency selective channels. A frequency domain equalizer (FDE) is known to perform well for OFDM as well as CEOFDM [3]. In this paper, we study the performance of CEOFDM in multipath fading channels while employing a FDE. The quality of the channel estimate which is obtained using a training signal directly affects the performance of the equalizer. We investigate channel estimation using both the least squares (LS) as well as the linear minimum mean square error (LMMSE) techniques and compare the equalizer performance for both these cases. It is desirable to have a training signal that has a low PAPR in time domain while also having a flat power spectrum in the frequency domain. While CEOFDM has a constant envelope, it does not have a flat spectrum in the frequency domain. Therefore, we also investigate various training signals for channel estimation and compare their performance in the presence of an amplifier. I.
THRESHOLD EXTENDING RECEIVER STRUCTURES FOR CEOFDM
"... the high peaktoaverage power ratio (PAPR) problem in OFDM. However, since CEOFDM is based on angle modulation, it is susceptible to the well known threshold effect. This paper considers several threshold extending receiver structures for CEOFDM. The simple arctangent receiver [4] is compared to ..."
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the high peaktoaverage power ratio (PAPR) problem in OFDM. However, since CEOFDM is based on angle modulation, it is susceptible to the well known threshold effect. This paper considers several threshold extending receiver structures for CEOFDM. The simple arctangent receiver [4] is compared to the conventional limiterdiscriminator type FM receiver and a secondorder phase locked loop structure. A novel cycle slip eliminator (CSE) is also developed to detect and cancel cycle slips and is shown to provide significant threshold extension. It is observed that the optimum receiver design depends on the CEOFDM modulation index. The various schemes are compared in terms of threshold extension capability and complexity for a wide range of modulation indexes. I.
Performance Evaluation of Constant Envelope OFDM working in 60 GHz Band
"... Abstract — The 60 GHz band is of much interest since this is the band in which a massive amount of spectral space (5 GHz) has been allocated unlicensed worldwide for dense wireless local communications. OFDM has gained much popularity in the field of wireless communication because of its ability to ..."
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Abstract — The 60 GHz band is of much interest since this is the band in which a massive amount of spectral space (5 GHz) has been allocated unlicensed worldwide for dense wireless local communications. OFDM has gained much popularity in the field of wireless communication because of its ability to transfer the data at higher rate, high bandwidth efficiency and its robustness with regard to multipath and delay. But the major hurdle is high PAPR leading to intermodulation distortion and outofband spectral growth. Constant envelope OFDM transforms the OFDM signal, to a signal with nearly zero dB PAPR. The PAPR performance of conventional OFDM system improves with constant envelope OFDM system. CE OFDM scheme provides PAPR to 0 dB; this paper analyzes the performance of CE OFDM on grounds of BER. A constant envelope OFDM system is considered for calculating bit error rate with additive white Gaussian noise (AWGN) channel and SalehValenzuela (SV) channel model at 60 GHz. The BER is calculated for signalling format BPSK and the performance of CE OFDM is analyzed at 60
DSA Networks
, 2007
"... With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. Existing “commandandcontrol ” spectrum allocations defined by government regulatory agencies, such as federal communications commissi ..."
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With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. Existing “commandandcontrol ” spectrum allocations defined by government regulatory agencies, such as federal communications commission (FCC), prohibit unlicensed access to licensed spectrum, constraining them instead to several heavily populated, interferenceprone frequency bands. However, it has been shown that the spectrum is not utilized efficiently across time and frequency. Therefore, FCC is currently working on the concept of unlicensed users “borrowing ” spectrum from incumbent license holders temporarily to improve the spectrum utilization. This concept is called dynamic spectrum access (DSA). Cognitive radios offer versatile, powerful, and portable wireless transceivers enabling DSA. This dissertation investigates physical layer techniques to enhance a cognitive radio performance. Multicarrier techniques, such as orthogonal frequency division multiplexing (OFDM), support huge data rates that are robust to channel impairments. However, with a growing
University sidi Mohammed ben Abdellah,
"... Orthogonal frequency division multiplexing (OFDM) OFDM has been adopted for high speed data transmission of multimedia traffic such as HomePlug A/V and Mobile WiMax. However, OFDM also has a drawback of a high PAPR (peaktoaveragepowerratio). Due to this high PAPR amplifier usually does not act i ..."
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Orthogonal frequency division multiplexing (OFDM) OFDM has been adopted for high speed data transmission of multimedia traffic such as HomePlug A/V and Mobile WiMax. However, OFDM also has a drawback of a high PAPR (peaktoaveragepowerratio). Due to this high PAPR amplifier usually does not act in dynamic range. One potential solution for reducing the peaktoaverage power ratio (PAPR) in an OFDM system is to utilize a constant envelope OFDM (CEOFDM) system. Furthermore, by utilizing continuous phase modulation (CPM) in a CEOFDM system, the PAPR can be effectively reduced to 0 dB, allowing for the signal to be amplified with a power efficient nonlinear power amplifier with Input BackOff (IBO) of 0 dB. This paper describes a CEOFDM based modem for Power Line Communications (PLC) over the low voltage distribution network. Relying on a preliminary characterization of a PLC network, a complete description of the modem is given. Also CEOFDM is compared with conventional OFDM under HomePlug 1.0 in the presence of power amplifier nonlinearities, considering different values of IBO.