In this letter, we present the performance of broadband bi-directional transmission with analog network coding (ANC) in a frequency-selective fading channel. To cope with the channel frequency-selectivity we introduce the use of frequency domain equalization (FDE) with broadband ANC based on orthogonal frequency division multiplexing (OFDM) and single carrier (SC) radio access. We evaluate, by theory and computer simulation, the achievable bit error rate (BER) and ergodic capacity of bi-directional ANC scheme based on OFDM and SCFDE radio access in a frequency-selective fading channel. Our results show that SC-FDE achieves a better BER performance, but on the other hand, a lower ergodic capacity in comparison with OFDM in a frequency-selective fading channel. Through both analysis and computer simulation, our findings show that a drawback of ANC scheme is its lack of diversity combining at the destination, which causes a slightly lower ergodic capacity in comparison with cooperative relaying irrespective of radio access scheme.

Network capacity for bidirectional communication between pairs of wireless end users assisted by a relay terminal can be improved by network coding at the physical layer (PNC). Narrowband analog network coding (ANC) was introduced as a simpler implementation of PNC in a flat (i.e., frequency-nonselective fading) channel. Recently, broadband ANC has been studied for communication over a frequency-selective fading channel. In ANC, the end user removes its own information from the received signal before detecting the data of the other user. Clearly, the network performance of ANC scheme depends on the self-information removal at the destination terminal. In this paper, we discuss the impact of imperfect self-information removal on the performance of broadband ANC in terms of the bit error rate (BER) and achievable throughput in a frequency-selective fading channel. The theoretical minimum mean square error (MMSE) equalization weight for ANC based on single carrier with frequency domain equalization (SC-FDE) radio access is derived by taking into account the self-interference. We have used analysis and computer simulation to evaluate how the imperfect removal of self-information influences the achievable BER and throughput.

Orthogonal frequency division multiplexing (OFDM) has been adopted for several wireless network standards due to its robustness against multipath fading. Main drawback of OFDM is its high peak-to-average power ratio (PAPR) that causes a signal degradation in a peak-limiting (e.g., clipping) channel leading to a higher bit error rate (BER). At the receiver, the effect of peak-limitation can be removed to some extent to improve the system performance. In this paper, a combined decision-feedback equalization with clipping noise reduction technique is presented. An iterative equalization weight that minimizes the mean square error (MSE) with respect to residual clipping noise is derived. It is shown that the bit error rate (BER) performance of OFDM with proposed technique can be significantly improved in a peak-limited and frequency-selective fading channel.

Radio channel is characterized by a multipath propagation that is suitable for application of network coding (NC) to improve the network capacity. In particular, physical layer network coding (PNC) scheme is known to double the network capacity of bi-directional communication between pairs of end users assisted by a relay terminal in a Gaussian channel. Recently, analog network coding (ANC) has been proposed with a simpler implementation complexity in comparison with PNC scheme, but the same achievable network capacity. On the other hand, an important question is how much the channel capacity is improved over a conventional point-to-point communication in a frequency-selective fading channel. In this paper, we present the ergodic channel capacity analysis of bi-directional transmission with analog network coding in a frequency-selective fading channel. The channel capacity expression for transmission with frequency domain equalization (FDE) is derived based on the Gaussian approximation of the inter-symbol interference (ISI) after FDE.

Wireless communications are characterized by a multipath propagation that is suitable for application of network coding (NC) to improve the network performance. In particular, a physical layer network coding (PNC) is a promising technique to further improve network capacity for bi-directional information exchange between pairs of end users assisted by a relay terminal. In this paper, we present the performance of bi-directional transmission with PNC in a multipath channel. We introduce the use of frequency domain equalization (FDE) with orthogonal frequency division multiplexing (OFDM) and single carrier (SC) transmission to cope with the channel distortion. The equalization weights based on minimum mean square error (MMSE) criteria required for SC-FDE signaling are derived.

Cooperative networking schemes provide spatial diversity gain (named cooperative diversity gain) using the antennas of spatially distributed users to form a multi an- tenna transmit situation. A variety of algorithms for orthogonal frequency division multiplexing (OFDM) networks have been developed to achieve cooperative diversity gain. OFDM signals, however, have a problem with a high peak-to-average power ratio (PAPR) leading to lower power efficiency, which may significantly increase the user power consumption. In this paper, instead of conventional OFDM, we present the performance of coop- erative network based on OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) in a frequency- selective fading channel. To fully exploit the channel frequency- selectivity and achieve a larger frequency diversity gain the equalization weights required for OFDM/TDM signaling based on MMSE criteria are derived. multiplexing (12) (in this paper called OFDM/TDM) can be used to solve the PAPR problem to some extent (13). In OFDM/TDM design, the inverse fast Fourier transform (IFFT) time window (i.e., OFDM/TDM frame) of conventional OFDM is divided into K slots. Within each slot an OFDM signal with reduced number of subcarriers is transmitted with- out the guard interval (GI) insertion. Unlike the conventional OFDM, only one GI is inserted in each frame and frequency domain equalization is used to exploit the channel frequency- selectivity. In this paper, we present the performance of cooperative relay network based on OFDM/TDM using minimum mean square error frequency domain equalization (MMSE-FDE) (13) in a frequency-selective fading channel. To fully ex- ploit the channel frequency-selectivity and achieve a larger frequency diversity gain the equalization weights required for OFDM/TDM signaling based on MMSE criteria are de- rived. Unlike cooperative relay network based on conventional OFDM, the use of OFDM/TDM achieves a better quality of service (i.e., a lower bit error rate (BER)) with a higher transmit power efficiency. The remainder of this paper is organized as follows. Sec- tion II presents the system model. We derive the required equalization weights for OFDM/TDM to achieve improved performance in Sect. III. In Sect. IV, computer simulation results and discussions are presented. Section V concludes the paper.

The use of frequency-domain interleaving on a frame-by-frame basis for orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (OFDM/TDM) is presented. In conventional OFDM, FDE is not designed to exploit the channel frequency-selectivity and consequently, the frequency diversity gain cannot be obtained. To further improve the bit error rate (BER) performance of conventional OFDM an interleaving technique may be applied, but FDE cannot be fully exploited. In this letter, the OFDM/TDM signal (i.e., several concatenated OFDM signals) frequency components are interleaved at the transmitter and then, minimum mean square error frequency-domain equalization (MMSE-FDE) is applied at the receiver to obtain a larger frequency diversity gain. It is shown that frequency-domain interleaving on a frame-by-frame basis for OFDM/TDM using MMSE-FDE achieves improved BER performance in comparison with conventional OFDM due to enhanced frequency diversity gain.

MMSE-FDE can improve the transmission performance of OFDM combined with time division multiplexing (OFDM/TDM), but knowledge of the channel state information and the noise variance is required to compute the MMSE weight. In this paper, a performance evaluation of OFDM/TDM using MMSE-FDE with pilot-assisted channel estimation over a fast fading channel is presented. To improve the tracking ability against fast fading a robust pilot-assisted channel estimation is presented that uses time-domain filtering on a slot-by-slot basis and frequency-domain interpolation. We derive the mean square error (MSE) of the channel estimator and then discuss a tradeoff between improving the tracking ability against fading and the noise reduction. The achievable bit error rate (BER) performance is evaluated by computer simulation and compared with conventional OFDM. It is shown that the OFDM/TDM using MMSE-FDE achieves a lower BER and a better tracking ability against fast fading in comparison with conventional OFDM.

Orthogonal frequency division multiplexing (OFDM) system with frequency domain equalization (FDE) requires reliable channel estimation (CE). In practice, pilot assisted CE can be either based on timeor frequency-domain multiplexed pilot symbols (i.e. TDM-pilot and FDM-pilot). It this paper, the impact of quantization noise introduced by digital-to-analog (DA) and analog-to-digital (AD) converters is examined. Furthermore, the trade-off between the resolution of DA/AD converters and back-off levels of the DA converter is evaluated. The simulation results are provided in terms of bit error rate (BER) for different configurations of the OFDM system. We show, that TDM-pilot CE scheme requires lower DA and AD converter resolutions than FDM-pilot CE scheme to achieve comparable performance. This is a consequence of pilot symbols’ amplitude clipping at the DA converter and/or large amplitudes that need to be covered by AD converter in the case of FDM-pilot CE scheme. This is not the case in TDM-pilot CE scheme, where Chu pilot sequence with constant amplitude of pilot symbols is applied.

In type II hybrid ARQ (HARQ) schemes, the uncoded information bits are transmitted first, while the error correction parity bits are sent upon request. Consequently, frequency diversity cannot be exploited during the first transmission. In this paper, we present the use of OFDM/TDM with MMSE-FDE and type II HARQ to increase throughput of OFDM due to frequency diversity gain.

Orthogonal frequency division multiplexing (OFDM) signals have a problem with high peak-to-average power ratio (PAPR). A distortionless selective mapping (SLM) has been proposed to reduce the PAPR, but a high computational complexity prohibits its application to OFDM with a large number of subcarriers. Recently, OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) was proposed to improve the transmission performance of conventional OFDM in terms of the bit error rate (BER) and the PAPR. The PAPR problem, however, cannot be completely eliminated. In this paper, we propose a new SLM to further reduce the PAPR of OFDM/TDM. Unlike the conventional OFDM, where SLM is applied over subcarriers in the frequency domain, we propose the new SLM for OFDM/TDM by exploiting both time and frequency dimensions of OFDM/TDM signal. It is shown, by computer simulation that proposed SLM for OFDM/TDM increases the number of candidate sequences in comparison with the conventional SLM, while reducing the PAPR. Furthermore, OFDM/TDM with proposed SLM achieves a lower PAPR than the conventional OFDM with same or reduced computational complexity.

Orthogonal frequency division multiplexing (OFDM) is adopted for several wireless network standards due to its high capacity and robustness against multipath fading. OFDM, however, has a problem with high peak-to-average power ratio (PAPR) that strictly limits its application. Recently, OFDM combined with time division multiplexing (TDM) using minimum mean square error frequency domain equalization (MMSE-FDE) was proposed to improve the transmission performance of conventional OFDM in terms of the bit error rate (BER) while reducing the PAPR. In this paper, we theoretically analyze and discuss the trade-off for OFDM/TDM using MMSE-FDE between the channel capacity and the PAPR in a nonlinear and frequency-selective fading channel. Our results show that OFDM/TDM using MMSE-FDE achieves a larger capacity with a lower PAPR in comparison with the conventional OFDM. It is also shown that the channel capacity of OFDM/TDM using MMSE-FDE is bounded between the conventional OFDM and single-carrier (SC) transmission.

In this paper, frequency-domain interleaving on a frame-by-frame basis for orthogonal frequency division multiplexing combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) is presented. The OFDM/TDM frame signal (i.e., several concatenated OFDM signals) frequency components are interleaved to enhance channel frequency-selectivity and then, MMSE-FDE is applied at the receiver to obtain frequency diversity gain. The bit error rate (BER) performance of OFDM/TDM with and without channel coding is evaluated by computer simulation. It was shown, that frequency-domain interleaving on the frame-by-frame basis for OFDM/TDM using MMSE- FDE achieves a better BER performance in comparison with conventional OFDM due to enhanced frequency diversity gain.

Orthogonal frequency division multiplexing (OFDM) is currently under intense research for broadband wireless transmission due to its robustness against multipath fading. However, OFDM signals have a problem with high peak-to-average power ratio (PAPR) and thus, a power amplifier must be carefully manufactured to have a linear input-output characteristic or to have a large input power backoff. Recently, OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency domain equalization (MMSE-FDE) was proposed to improve the bit error rate (BER) performance of conventional OFDM while reducing the PAPR. In this paper, by extensive computer simulation, we present a comprehensive performance comparison between OFDM/TDM using MMSE-FDE and conventional OFDM over a frequency-selective fading channel. We discuss about the trade-off among the transmit peak-power efficiency, the spectrum splatter and the BER performance. Our results show that OFDM/TDM using MMSE-FDE achieves almost the same coded BER performance with a several decibels better peak-power efficiency than conventional OFDM, which is significant reduction of amplifier transmit-power backoff, but with a slight decrease in spectrum efficiency.

OFDM combined with TDM (OFDM/TDM) can be used to reduce a high peak-to-average power ratio (PAPR) of OFDM, but the PAPR reduction is not sufficient. To further reduce the PAPR, an amplitude clipping can be applied. In this letter, we investigate the effect of clipping on OFDM/TDM with and without channel coding. It is shown that amplitude clipped OFDM/TDM has an advantage over clipped OFDM with respect to the PAPR.