Enhancing Data Efficiency in IEEE- 802.11a Using Frequency and Time domain Equalization
01 Nov 2005-pp 1-5
TL;DR: Increase in data rate is achieved by removing the cyclic prefix between the OFDM symbols by proposing two methods of equalization, which minimizes the noise amplification caused by ZF-FEQ.
Abstract: In this paper, increase in data rate is achieved by removing the cyclic prefix between the OFDM symbols. The intersymbol interference and intercarrier interference caused by the removal of cyclic prefix are removed by equalization. We propose two methods of equalization. In the first method, the zero frequency domain equalization (ZF-FEQ) is done by making use of spill over in the unused carriers. The pre-FFT time domain Equalizer minimizes the noise amplification caused by ZF-FEQ. In the second method, the Inter Symbol Interference and Inter Carrier Interference are removed at the transmitter itself by transmitting data in the unused carriers, which is the combination of data in the used carriers. The requirement of power in the unused carriers increases as the length of the channel increases. Using the TEQ, the effective length of the channel is reduced to minimum. The simulation results are presented in support of these two methods.
References
More filters
TL;DR: Various methods of determining the coefficients for this time-domain finite impulse response (FIR) filter are explored and an optimal shortening and a least-squares approach are developed for shortening the channel's impulse response.
Abstract: In discrete multitone (DMT) transceivers an intelligent guard time sequence, called a cyclic prefix (CP), is inserted between symbols to ensure that samples from one symbol do not interfere with the samples of another symbol. The length of the CP is determined by the length of the impulse response of the effective physical channel. Using a long CP reduces the throughput of the transceiver, To avoid using a long CP, a short time-domain finite impulse response (FIR) filter is used to shorten the effective channels impulse response. This paper explores various methods of determining the coefficients for this time-domain filter. An optimal shortening and a least-squares (LS) approach are developed for shortening the channel's impulse response. To provide a computationally efficient algorithm a variation of the LS approach is explored. In full-duplex transceivers the length of the effective echo path impacts the computational requirements of the transceiver. A new paradigm of joint shortening is introduced and three methods are developed to jointly shorten the channel and the echo impulse responses in order to reduce the length of the CP and reduce computational requirements for the echo canceller.
556 citations
"Enhancing Data Efficiency in IEEE- ..." refers background or methods in this paper
...But for high rate OFDM systems, the TEQ algorithms with high complexity [1]-[2] can not be used....
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...Since the use of CP reduces the data efficiency of the OFDM system, several approaches have been proposed to solve this problem, such as time domain equalizer, per tone equalizer and FEQ [1]-[4]....
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28 Nov 1994
TL;DR: The equalized DMT is shown to recover a significant portion of the performance loss incurred because of the use of a moderate-size FFT in the DMT to reduce latency and implementation cost.
Abstract: A new criterion for partially-equalizing severe ISI channels to reduce the cyclic prefix overhead of the discrete multitone (DMT) transceiver, assuming a fixed transmission bandwidth, is introduced. The equalized DMT is shown to recover a significant portion of the performance loss incurred because of the use of a moderate-size FFT in the DMT to reduce latency and implementation cost. In particular, equalizers designed using our new criterion result in a higher DMT performance margin than traditional mean-square-error DMT equalizers. Finally, additional promising methods that further enhance the performance of the equalized DMT are investigated.
429 citations
TL;DR: An alternative receiver structure is presented for discrete multitone-based systems that is modified into a structure with a (complex) multitap FEQ per tone by solving a minimum mean-square-error problem, resulting in a larger bit rate while complexity during data transmission is kept at the same level.
Abstract: An alternative receiver structure is presented for discrete multitone-based systems. The usual structure consisting of a (real) time-domain equalizer in combination with a (complex) 1-tap frequency-domain equalizer (FEQ) per tone, is modified into a structure with a (complex) multitap FEQ per tone. By solving a minimum mean-square-error problem, the signal-to-noise ratio is maximized for each individual tone. The result is a larger bit rate while complexity during data transmission is kept at the same level. Moreover, the per tone equalization is shown to have a reduced sensitivity to the synchronization delay.
272 citations
TL;DR: A new, low-complexity frequency-domain equalizer for discrete multitone (DMT) systems, which, in the absence of a guard interval, utilizes existing redundancy in the frequency- domain to completely eliminate intersymbol and interchannel interference.
Abstract: We propose a new, low-complexity frequency-domain equalizer for discrete multitone (DMT) systems, which, in the absence of a guard interval, utilizes existing redundancy in the frequency-domain to completely eliminate intersymbol and interchannel interference. A perfect reconstruction condition is derived for the noise-free case leading to a sparse equalizer matrix structure. It is furthermore shown that under realistic scenarios minimum mean square error adaptation of the equalizer coefficients allows for nearly perfect reconstruction already for a much smaller amount of redundancy than indicated by the perfect reconstruction condition. The new equalization scheme has at least the same potential compared with traditional DMT while offering new degrees of freedom for designing short-latency DMT systems.
77 citations
"Enhancing Data Efficiency in IEEE- ..." refers background or methods in this paper
...In FEQ, with only a few linear combinations of unused carrier output samples, ISI and ICI can be totally eliminated even in receiver structures without CP [4]....
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...Since the use of CP reduces the data efficiency of the OFDM system, several approaches have been proposed to solve this problem, such as time domain equalizer, per tone equalizer and FEQ [1]-[4]....
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...15) that the noise is not amplified as is done in [4]....
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TL;DR: Analytical and simulation results show that the proposed method can reduce computational complexity, while providing the same spectral efficiency as the frequency-domain equalizer (Trautmann and Fleige, 2002), in the presence of additive white Gaussian noise.
Abstract: In this letter, we describe a new method to eliminate intersymbol interference (ISI) and interchannel interference (ICI) for discrete multitone/orthogonal frequency division multiplexing (DMT/OFDM) systems with insufficient cyclic prefix (CP). The proposed structure prevents ICI with a preprocessing method that utilizes redundancy in the frequency domain at the transmitter and removes ISI with a simple cancellation method at the receiver. Analytical and simulation results show that the proposed method can reduce computational complexity, while providing the same spectral efficiency as the frequency-domain equalizer (Trautmann and Fleige, 2002), which utilizes redundancy in the frequency domain at the receiver, in the presence of additive white Gaussian noise.
47 citations
"Enhancing Data Efficiency in IEEE- ..." refers methods in this paper
...In [6] a method is proposed to remove the ISI and ICI at the transmitter itself by transmitting the data in the unused carriers, which is the combination of data in the used carriers....
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