Cyclic Prefix Removal Research Articles

INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Removal of Cyclic Prefix in Adaptive OFDM for Dynamic Spectrum Access using DWT and WT

INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Removal of Cyclic Prefix in Adaptive OFDM for Dynamic Spectrum Access using DWT and WT

OFDM-IM Based Dual-Hop System Using Fixed-Gain Amplify-and-Forward Relay With Pre-Processing Capability

Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) has recently attracted many researchers’ attention due to its superior spectrum efficiency and reliability compared to the traditional OFDM. Cooperative decode-and-forward relaying has been incorporated with OFDM-IM, which provides a higher energy efficiency and better network coverage. However, it might not be feasible in realistic applications, owing to the high system complexity and transmission delay rendered by complex decoding and channel estimation procedures. Therefore, in this paper, we propose a fixed-gain (FG) amplify-and-forward (AF) relay-assisted OFDM-IM system, which does not need to perform complex decoding and channel estimation at the relay, but only requires a pre-processing capability at the relay, e.g., cyclic prefix removal and re-insertion. Therefore, the system complexity can be reduced and the forwarding delay as well as power consumption caused by processing at the relay also decline. We analyze the average outage probability, block error rate, and achievable rate of the proposed system and verify all analysis by numerical results. The proposed FG AF relay-assisted OFDM-IM provides a simple solution to the implementation of OFDM-IM in new network paradigms, where nodes are simple, power limited, and/or complexity limited.

An 8X-Parallelism Memory Access Reordering Polyphase Network for 60 GHz FBMC-OQAM Baseband Receiver

Filter bank multi-carrier (FBMC) is a kind of new waveform that is an important topic in 5th generation wireless systems (5G). In this paper, we propose a novel memory access reordering polyphase network (PPN) for FBMC offset QAM (OQAM) system at 60 GHz band. The novel PPN architecture has lower complexity than the state-of-the-art designs, and it can be used in any FBMC-OQAM baseband design. To evaluate the system performance and hardware complexity of baseband receiver in millimeter wave (mmW) band, the proposed PPN is integrated into our 8X-parallelism 60 GHz band baseband receiver. The out-of-band (OOB) radiation in fixed-point simulation has 25 dB improvement as compared with OFDM. Furthermore, the transmission efficiency of FBMC-OQAM baseband receiver can improve 52% due to using more data subcarriers and removal of cyclic prefix (CP). The proposed PPN is synthesized with 40 nm 1P9M general purposes (GP) process, and can operate at 330/500 MHz clock rate with power consumption of 17/26 mW, providing the maximum PHY data rate up to 21.4 Gb/s.

Practical designs for out-of-band emission suppression and adjacent channel interference rejection for orthogonal frequency division multiplexing-based cognitive radios

Opposite to the conventional wisdom, practical considerations for out-of-band emission (OOBE) suppression and adjacent channel interference (ACI) rejection in orthogonal frequency division multiplexing (OFDM) -based cognitive radio systems are not completely alike. For example, ACI will increase after discarding the cyclic prefix (CP) because the interference signal is also truncated during the CP removal process. Furthermore, effective OOBE is much larger than the estimated OOBE if there is a timing offset (TO) between the primary and secondary users. To the best of our knowledge, these and some other practical issues have not been well addressed. Various important practical issues (including multipath delay spread, high peak-to-average power ratio (PAPR), spectral efficiency loss, high complexity, sensitivities to frequency and timing offsets, non-contiguous and dynamically changing spectrum, CP removal, spectral containment, etc.) concerning OOBE suppression and ACI rejection are studied in this paper. Numerical results show that none of the existing approaches can deal with all practical issues satisfactorily. Hybrid combinations of frequency-domain approaches (spectral precoding and PAPR precoding) and time-domain approaches (windowing and filtering) are developed to maintain the merits and mitigate the drawbacks of each constituent approach in order to deal with these practical challenges. It is shown that a combination of filtering and precoding provides the best OOBE suppression and a combination of windowing and precoding provides the best ACI rejection characteristics in our numerical examples.

Joint blind channel shortening and compensation of transmitter I/Q imbalances and CFOs for uplink SC-IFDMA systems

This paper deals with receiver design for the uplink of a single-carrier interleaved frequency-division multiple-access (SC-IFDMA) system, which is a promising candidate for non-adaptive transmission in next-generation wireless systems. In particular, channel shortening is required in asynchronous SC-IFDMA systems operating over highly-dispersive channels, since the length of the cyclic prefix (CP) is insufficient to compensate for the combined effects of timing offsets and channel dispersion; other major sources of performance degradation are the in-phase/quadrature-phase (I/Q) imbalance introduced at each transmitter, and the carrier frequency offsets (CFOs) between the transmitters and the receiver. The proposed multistage receiver is designed to jointly counteract all these impairments: specifically, the minimum mean-output energy (MMOE) criterion is adopted to synthesize a time-domain equalizer, which performs blind multiuser channel shortening of all the user channels (including the corresponding time offsets), without requiring a priori knowledge of the channel impulse responses to be shortened, or compensation of the CFOs and transmitter I/Q imbalances. Moreover, after channel shortening and (total or partial) CP removal, the MMOE criterion is also employed to compensate for the CFOs and mitigate I/Q impairments. Monte Carlo computer simulations are carried out to assess the effectiveness of the proposed receiver.

Per-symbol-based digital back-propagation approach for PDM-CO-OFDM transmission systems

For polarization-division-multiplexing coherent optical orthogonal frequency division multiplexing (PDM-CO-OFDM) systems, we propose a per-symbol-based digital back-propagation (DBP) approach which, after cyclic prefix removal, conducts DBP for each OFDM symbol. Compared with previous DBP, this new proposal avoids the use of inefficient overlap-and-add operation and saves one fast Fourier transform (FFT) module, therefore simplifying the hardware implementation. Transmitting a 16-QAM, 42.8-Gb/s PDM-CO-OFDM signal over 960-km standard single mode fiber (SSMF), we compare the previous and the proposed DBP approaches with different receiver's sampling rates and different step lengths in each DBP iteration, and found that the proposed DBP can achieve a similar performance as that of the previous DBP while enjoying a simpler implementation. We have also specifically introduced a small self-phase modulation (SPM) model for DBP and demonstrated its feasibility with the same experimental setup.

A Cyclic Shift Relaying Scheme for Asynchronous Two-way Relay Networks

Perfect time synchronization among multiple relay nodes is quite difficult to realize in distributed relay networks. In this paper, we proposed a cyclic prefix (CP) assisted cyclic shift relaying (CFR) scheme for asynchronous two-way amplify-and-forward (AF) relay networks over flat fading channels. In the proposed scheme, a CP is inserted at the two source nodes to combat the asynchronous delays. Each relay amplifies the received mixed asynchronous signals after CP removal, and a cyclic delay is introduced to further improve the system performance. With the CP and the cyclic delay, the multiple flat fading relay channels are transformed into a multipath fading channel. As a result, low complexity frequency domain equalizers, such as zero-forcing and minimum mean square error (MMSE) equalizer, can be used to recover the transmit signal. Furthermore, the performance of the proposed CFR scheme with MMSE equalizer is analyzed and closed-form expression for the lower bound of uncoded bit error rate (BER) performance is derived. Based upon this lower bound, we also investigate the power allocation among the sources and the relays to improve the system performance. Finally, extensive numerical results are provided to show the BER and frame error rate performance of the proposed CFR scheme.

Blind Channel Shortening for Space-Time-Frequency Block Coded MIMO-OFDM Systems

This paper deals with multiple-input multiple-output (MIMO) broadband wireless communication systems, employing orthogonal frequency-division multiplexing (OFDM) with cyclic prefix (CP) in combination with space-time-frequency block coding (STFBC). In order to exploit the benefits of OFDM and STFBC in highly frequency-selective channels, without incurring in a significant increase of receiver complexity, a channel shortening prefilter is inserted at the receiver, aimed at reducing the length of the MIMO channel impulse response before CP removal. Two MIMO channel shorteners are proposed, both relying on linearly-constrained minimization of the mean-output-energy of the signal at the output of the channel shortener, where the linear constraints are optimally chosen so as to maximize the signal-to-noise ratio either at the output of the channel shortener or at the input of the STFBC maximum-likelihood decoder. Unlike other solutions proposed in the literature, these shortening designs are blind ones, i.e., a priori knowledge of the MIMO channel impulse response to be shortened is not required, and can be carried out in closed-form, i.e., iterative computation of the prefilter weights is not necessary. Numerical simulations show that, without a substantial increase in computational complexity, receivers equipped with the proposed blind channel shorteners pay only a negligible performance penalty with respect to non-blind channel shorteners, while being significantly more robust to finite sample-size effects.

A low‐complexity MSK‐based M‐ary cyclic‐shift keying transceiver for direct sequence spread spectrum system over multipath fading channels

AbstractIn this paper, a low‐complexity spread spectrum system with M‐ary cyclic‐shift keying (MCSK) symbol spreading is proposed. In addition, by using the minimum‐shift‐keying (MSK) as the chip‐level modulation, we obtain a high‐rate QPSK‐MCSK transceiver scheme which not only provides a constant‐envelop and continuous‐phase transmitted signal, but can also achieve a better performance than the conventional direct sequence spread spectrum (DSSS) system. At the transmitter, the data stream is first mapped into QPSK‐MCSK symbols in terms of orthogonal Gold code sequences, then followed by the cyclic prefix (CP) insertion for combating the interblock interference, and finally applying the MSK scheme to maintain the constant‐envelope property. The receiver first performs MSK demodulation, then CP removal, and finally the channel‐included MCSK despreading and symbol demapping. Furthermore, the single input single output (SISO) QPSK‐MCSK transceiver can be easily extended to the multiple input single output (MISO) case by incorporating the space–time block coding for high‐link quality. Simulation results show that the proposed SISO and MISO QPSK‐MCSK systems significantly outperform the conventional DSSS counterparts under the AWGN channel, and attain a more robust performance under the multipath fading channel. Copyright © 2011 John Wiley & Sons, Ltd.

Semiblind Channel Estimation for MIMO Single Carrier With Frequency-Domain Equalization Systems

We propose a semiblind channel-estimation method for multiple-input multiple-output (MIMO) single carrier with frequency-domain equalization systems. By taking advantage of periodic precoding and the block circulant channel model after cyclic prefix removal, we obtain the channel-product matrices by solving a series of decoupled linear systems, which is gained from the covariance matrix of the received data. Then, the channel-impulse-response matrix is obtained by computing the positive eigenvalues and eigenvectors of a Hermitian matrix formed from the channel-product matrices. We also propose an optimal design of the precoding sequence, which minimizes the noise effect and numerical error in covariance matrix estimation, and discuss the impact of the optimal sequence on channel equalization. With the proposed framework, the method is shown to be robust with respect to channel-order overestimation, and the identifiability condition is simply that the channel-impulse-response matrix has full column rank. Due to the identifiability condition, the method is applicable to MIMO channels with more transmitters or more receivers. Simulations are used to demonstrate the performance of the proposed method.

Spatial Diversity Scheme to Efficiently Cancel ISI and ICI in OFDM-OQAM Systems

This paper is based on an Offset Quadrature Amplitude Modulation (OQAM) Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme that is operated without a Cyclic Prefix (CP), where the multiple transmitting antennas are employed to substantially reduce the inherent intersymbol and intercarrier interference. The proposed scheme avoids the use of the CDMA technology to get rid of the interference. The nonemployment of the CP increases the spectral efficiency in comparison with classical CP-OFDM systems, as it does not employ the CP for its correct performance. On the other hand, the non-employment of the CP comes at cost of Intersymbol Interference (ISI). This paper presents a method which cancels the interference terms by employing a multiantenna precoding strategy based on spatial diversity OQAM-OFDM scheme, so that the overall system can get the advantage of the CP removal while no ISI is generated. Moreover, the proposed system benefits from the multiuser gain through an opportunistic scheduler at the transmitter side to select the user with the best channel characteristics at each instant. The resultant scheme OQAM-OFDM-MIMO data rate is obtained in a closed form expression and proved to be higher than the classical CP-OFDM systems.