Frequency Diversity Gain Research Articles

Performance Comparison of SER and SNR using different states of PSK in presence of various noises

To enhance the data rates of next generation wireless communication operating in frequency selective fading environments, the combination of orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) is proved to produce improved results. To analyze this combination, various changes in baseband signal processing are required which includes time and frequency synchronization, channel estimation and diversity gain. In this paper, a noise interference reduction technique for the improvement of high data rate in traditional space time coding technique (STTC) has been proposed. These codes generate the points of the constellation with the same probability. Therefore, the systematic search for good codes can be reduced to in this class. Finally, the performance of proposed techniques 2-state, 4-state and 16-state codes is evaluated by simulation and described by the Symbol Error Rate (SER) over fast Rayleigh fading channels with AWGN floor. Reduced noise based estimation schemes are widely favored as their implementation is relatively simple and most current wireless standards already provide for their use. Training sequences for multiple transmit antennas require properties of zero (or very low) cross correlation between sequences transmitted from different transmit antennas. Keywords: STTC; Symbol Error Rate; Signal to Noise Ratio; Orthogonal frequency division multiplexing.

A novel HARQ Scheme based on Frequency Diversity and Energy-MRC

In order to reduce the influence of multipath propagation on signal transmission in the OFDM wireless network, a novel HARQ scheme based on frequency diversity and Energy-MRC is proposed. This scheme takes the times of accurate transmission of previous data as reference value of present data transmission. When the data is retransmitted, the position in which information sequence lives after constellation mapping is changed before IFFT. So each time subcarrier fading relativity of the same information sequence is small, and major frequency diversity gain is obtained. In the receiving terminal, energy of the same information sequence in many times of transmission is maximal ratio combined after FFT. Under Rayleigh fading channel environment, simulation experiment shows that this scheme can reduce effectively BER(Bit Error Rate), compared with HARQ scheme without frequency diversity and MRC based on channel impulse response power. This scheme is easy to realize, and complex channel estimation is avoided.

Semi‐analytic selection of sub‐carrier allocation schemes in uplink orthogonal frequency division multiple access

The authors propose a generalised framework that analytically compares different sub-carrier allocation (SA) or sub-channelisation schemes (such as interleaved SA (ISA), localised SA (LSA) or hybrid schemes) in uplink (UL) orthogonal frequency division multiple access (OFDMA). The ultimate goal of the proposed framework is to systematically determine the best SA scheme among the considered candidates for a given condition of inter-user frequency offsets (IUFOs) and the target bit error rate (BER). As an illustration, two typical SA schemes are considered, that is, ISA and LSA for comparison. First, based on the well-known fact that multiple access interference by IUFO and frequency diversity gain are both dictated by the employed SA scheme, the authors propose a semi-analytic approach to derive coded BER curve formula as a function of frequency offset bound (FOB) for each scheme. Then, the signal-to-noise ratio gain of ISA over LSA for various target BERs and FOBs is derived. Finally, the cutoff FOB over which ISA obtains worse than LSA is obtained and its functional relationship with the target BER is investigated. By following the overall procedure in the proposed framework, the best SA scheme among the various SA candidates for the general UL OFDMA systems with arbitrary system parameters can be chosen.

협대역 통신 환경에서 Dual-band FSK 변조 방식을 이용한 주파수 옵셋 감쇄 기법

In narrowband communication systems operating in VHF and UHF bands, the performance degradation due to a frequency offset is inevitable. In this paper, we propose a frequency offset reduction scheme using the dual-band FSK modulation for narrowband communications. The proposed scheme not only offer a relatively reliable performance under a severe frequency offsets, but also can obtain a frequency diversity gain in Rayleigh fading channel.

Multi-User Interference Cancellation in Complementary Coded CDMA with Diversity Gain

This letter analyzes the performance of complementary coded code division multiple access (CC-CDMA) systems in frequency selective fading channels. Based on the evaluation of various combining algorithms for the correlation functions of M element sequences of a CC, a per-carrier parallel interference cancellation scheme based on minimum mean square error combining (MMSEC) is proposed for CC-CDMA to achieve a frequency diversity gain and multi-user interference resistance. Both analytical and simulation results verify the superiority of the proposed scheme. It is shown that combining algorithms and correlation properties of element sequences have a significant impact on the performance of CC-CDMA systems in frequency selective fading channels.

Design of low peak-to-average power ratio transceiver with enhanced link quality for coded single-carrier frequency division multiple access system

A new low peak-to-average power ratio (PAPR) transceiver is proposed for the coded single-carrier frequency division multiple access (SC-FDMA) system over frequency selective fading channels. By exploiting the constant envelope of the Chu-sequence in both frequency and time domains, the parallel spreading scheme and M-ary cyclic shift mapping technique can support the coded SC-FDMA system with a low PAPR for transmission at a high data rate. Interleaved time and frequency domain orthogonal modulation can increase the frequency diversity gain through the frequency domain equaliser and the time domain despreader. Moreover, the maximum likelihood rule is designed to detect the M-ary mapping data, which can provide M-ary gain to improve system performance. Simulation results reveal that the proposed high-rate coded SC-FDMA system can provide a lower PAPR and a better bit error rate (BER) performance than the conventional interleaved SC-FDMA system.

Joint Time-Frequency Diversity for Single-Carrier Block Transmission in Frequency Selective Channels

In time-varying frequency selective channels, to obtain high-rate joint time-frequency diversity, linear dispersion coded orthogonal frequency division multiplexing (LDC-OFDM), has recently been proposed. Compared with OFDM systems, single-carrier systems may retain the advantages of lower PAPR and lower sensitivity to carrier frequency offset (CFO) effects, which motivates this paper to investigate how to achieve joint frequency and time diversity for high-rate single-carrier block transmission systems. Two systems are proposed: linear dispersion coded cyclic-prefix single-carrier modulation (LDC-CP-SCM) and linear dispersion coded zero-padded single-carrier modulation (LDC-ZP-SCM) across either multiple CP-SCM or ZP-SCM blocks, respectively. LDC-SCM may use a layered two-stage LDC decoding with lower complexity. This paper analyzes the diversity properties of LDC-CP-SCM, and provides a sufficient condition for LDC-CP-SCM to maximize all available joint frequency and time diversity gain and coding gain. This paper shows that LDC-ZP-SCM may be effectively equipped with low-complexity minimum mean-squared error (MMSE) equalizers. A lower complexity scheme, linear transformation coded SCM (LTC-SCM), is also proposed with good diversity performance.

A Novel Nonlinear Precoding Detection Algorithm for VBLAST in MIMO-MC-CDMA Downlink System

Considering the error propagation effect and high complexity of the Vertical Bell Labs Layered Space Time (V-BLAST), a novel nonlinear ZF-THP algorithm for VBLAST in MIMO-MC-CDMA downlink system is proposed in this paper. QR decomposition is used for precoding matrix, the nonlinear Tomlinson-Harashima Precoding (THP) is used between the sub-carrier channels of MC-CDMA to eliminate interference from other signals at the transmitter, and can obtain frequency diversity gain and eliminate effectively the error propagation effect. At the receiver, zero forcing criterion is used, and the complexity of the receiver can be reduced. Simulation results show that the proposed algorithm is better than the traditional zero forcing algorithm and the linear precoding algorithm in the system BER.

OFDM Based on Low Complexity Transform to Increase Multipath Resilience and Reduce PAPR

This paper introduces a new multicarrier system using a low computational complexity transform that combines the Walsh-Hadamard transform (WHT) and the discrete Fourier transform (DFT) into a single fast orthonormal unitary transform. The proposed transform is used in a new orthogonal frequency division multiplexing ( T-OFDM) system, leading to a significant improvement in bit error rate (BER) and reasonable reduction in the peak-to-average power ratio (PAPR). Use of the proposed transform with OFDM has been found to attain high frequency diversity gain by combining all data samples resulting in the transmission over many subcarriers. Consequently, the detrimental effect arising from channel fading on the subcarrier power is minimized. Theoretical analysis of the uncoded T-OFDM performance over additive white Gaussian noise (AWGN), flat fading, quasi-static (fixed within the entire period of OFDM symbol transmission) frequency selective fading channel models with zero-forcing (ZF) and minimum mean square error (MMSE) equalizers is presented in this work. Moreover, the low superposition of the subcarriers passing through the T-transforms leads to a reduction in the high peak of the transmitted signal whilst preserving the average transmitted power and data rate. Analytical results confirmed by simulations demonstrated that the proposed T-OFDM system achieves lower PAPR and the same BER over AWGN and flat fading channels. Compared to OFDM, T-OFDM is found to have better BER when MMSE equalizer is used, but slightly worse when ZF equalizer is used.

Novel low-PAPR parallel FSOK transceiver design for MC-CDMA system over multipath fading channels

A low peak-to-average power ratio (PAPR) transceiver using a new parallel frequency-shift orthogonal keying (FSOK) technique is proposed for the multiuser uplink multi-carrier CDMA (MC-CDMA) system over multipath fading channels. By employing the frequency modulated and multiplexed FSOK techniques to combat the multiuser and parallel substream interferences, respectively, the system retains a low-PAPR transmitted signal and a low-complexity equalizer without any matrix inversion. At the basestation, a multiuser receiver is derived, which involves parallel FSOK despreading, demapping, and maximum likelihood decision rule to acquire M-ary modulation gain and frequency diversity gain. For higher link quality, a multiple input single output FSOK uplink system can flexibly be configured. Simulation results are included to demonstrate that the proposed system achieves the low-PAPR property, space-frequency diversity, and M-ary modulation gain. Compared to the existing MC-CDMA and SC-FDMA systems, the proposed system exhibits significant performance superiority.

Iterative MMSE-FDE/MUI Cancellation and Antenna Diversity for Frequency-Domain Filtered SC-FDMA Uplink

Broadband single-carrier frequency division multiple access (SC-FDMA) uplink using frequency-domain square-root Nyquist filtering is considered. The peak-to-average power ratio (PAPR) of filtered SC signals can be reduced by increasing the filter roll-off factor α. Furthermore, an additional frequency diversity gain can be obtained by making use of the excess bandwidth introduced by the transmit root Nyquist filtering. However, if the carrier-frequency separation is kept the same as in the case of α = 0, the adjacent users' signal spectra overlap with the desired users' spectrum and the multiuser interference (MUI) is produced. In this paper, we propose two frequency-domain iterative MUI cancellation schemes which can achieve the frequency diversity gain through spectrum combining. The achievable bit error rate (BER) and throughput performances are evaluated by computer simulation.

Iterative MMSE Detection with Interference Cancellation for Up-Link HARQ Using Frequency-Domain Filtered SC-FDMA MIMO Multiplexing

SUMMARY In this paper, we propose an iterative minimum mean square error detection with interference cancellation (MMSED-IC) for frequency-domain filtered single carrier (SC)-frequency-division multipleaccess (FDMA) uplink transmission. The use of a square-root Nyquist transmit filter reduces the peak-to-average power ratio (PAPR) while increases the frequency-diversity gain. However, if carrier-frequency separation among multiple-access users is kept the same as the one used for the case of roll-off factor α=0 (i.e., brick-wall filter), then the adjacent users’ spectra will overlap and multi-user interference (MUI) occurs. The proposed MMSED-IC can sufficiently suppress the MUI from adjacent users while achieving the maximum frequency-diversity gain. We apply the proposed MMSED-IC to a packet access using filtered SC-FDMA, multi-input multi-output (MIMO) multiplexing, and hybrid automatic repeat request (HARQ). It is shown by computer simulation that filtered SC-FDMA with α = 1 can achieve higher throughput than orthogonal frequency division multiple access (OFDMA).

Transmit Diversity Scheme for OFDM Systems Using the Odd DFT

A new transmission scheme for OFDM systems that uses the odd discrete Fourier transform to provide frequency diversity gain is proposed. Odd DFT allows the transmission of data subcarriers in frequencies that are centred between those employed by the traditional DFT. This fact is exploited to transmit data subcarriers on the group of frequencies that gives better performance using either traditional DFT or odd DFT. As an example, by using this approach a diversity gain up to 5.3dB at a BER of 10-4 in a typical indoor channel model can be achieved.

Joint MMSE-FDE & Spectrum Combining for a Broadband Single-Carrier Transmission in the Presence of Timing Offset

Frequency-domain equalization (FDE) based on minimum mean square error (MMSE) is considered as a promising equalization technique for a broadband single-carrier (SC) transmission. When a square-root Nyquist filter is used at a transmitter and receiver to limit the signal bandwidth, the presence of timing offset produces the inter-symbol interference (ISI) and degrades the bit error rate (BER) performance using MMSE-FDE. In this paper, we discuss the mechanism of the BER performance degradation in the presence of timing offset. Then, we propose joint MMSE-FDE & spectrum combining which can make use the excess bandwidth introduced by transmit filter to achieve larger frequency diversity gain while suppressing the negative effect of the timing offset.

On the Diversity Enhancement and Power Balancing of Per-Subcarrier Transmit Antenna Selection in OFDM Systems

In this paper, we consider multicarrier systems with multiple transmit antennas under a power-balancing constraint. Applying transmit antenna selection and discrete rate-adaptive modulation using <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary quadrature-amplitude modulation (QAM) according to the channel variation per subcarrier, we develop an optimal transmit antenna selection scheme in terms of the maximum spectral efficiency, where all the possible groupings for sending the same information-bearing signals in a group of subcarriers are searched, and the groups of subcarriers for providing the frequency diversity gain are formed. In addition, we propose a suboptimal method for reducing the computational complexity of the optimal method. The suboptimal scheme considers only the subcarriers under outage, and these subcarriers are sequentially combined until the required signal-to-noise ratio (SNR) is met. Numerical results show that the proposed suboptimal method with diversity combining outperforms the optimal antenna selection without diversity combining, as introduced in the work of Sandell and Coon, particularly for low-SNR regions, and offers the spectral efficiency close to the optimal method with diversity combining while maintaining lower complexity.

Transmission Performance of Frequency-Domain Filtered Single-Carrier Transmission Using Frequency-Domain Block Signal Detection with QRM-MLD

Recently, assuming ideal brick-wall transmit filtering, we proposed a frequency-domain block signal detection (FDBD) with maximum likelihood detection employing QR decomposition and M-algorithm (called QRM-MLD) for the reception of single-carrier (SC) signals transmitted over a frequency-selective fading channel. QR decomposition (QRD) is applied to a concatenation of the propagation channel and discrete Fourier transform (DFT). However, a large number of surviving paths is required in the M-algorithm to achieve sufficiently improved bit error rate (BER) performance. The introduction of filtering can achieve improved BER performance due to larger frequency diversity gain while keeping a lower peak-to-average power ratio (PAPR) than orthogonal frequency division multiplexing (OFDM). In this paper, we develop FDBD with QRM-MLD for filtered SC signal reception. QRD is applied to a concatenation of transmit filter, propagation channel, and DFT. We evaluate BER and throughput performances by computer simulation. From performance evaluation, we discuss how the filter roll-off factor affects the achievable BER and throughput performances and show that as the filter roll-off factor increases, the required number of surviving paths in the M-algorithm can be reduced.

Ziv–Zakai Time-Delay Estimation Bounds for Frequency-Hopping Waveforms Under Frequency-Selective Fading

Ziv-Zakai Bayesian lower bounds on time-delay estimation (TDE) are developed for frequency hopping waveforms. These wideband waveforms are readily employed for both communications and TDE. We consider random frequency-selective fading channels, described by a Gaussian tapped delay line model with inter-hop correlation. The receiver does not know the channel realization to assist in estimating the time delay but does know the channel statistics. The development incorporates a random uniform prior on the delay. The bounds provide tight mean-square error prediction for the maximum a posteriori (MAP) estimator performance over a large range of signal-to-noise ratios (SNRs). They also accurately predict the TDE frequency diversity gain from multi-frequency transmission in fading channels. The special case of independent fading is discussed, including both flat Rician and Rayleigh fading, and closed-form expressions enable easy study of the effects of SNR, frequency diversity, and channel statistics on TDE.

Joint Optimization for PAPR Reduction and Opportunistic Beamforming (OBF) in OFDM Systems

Opportunistic beamforming (OBF) is an effective way to increase the multiuser diversity (MUD) of the communication systems; with employing OBF in OFDM system, in addition to the MUD gain, frequency diversity gain is also obtainable. However, the complexity of the OBF-OFDM system is increased and the peak-to-average power-ratio (PAPR) of the OFDM signals must be reduced. The reduction of signals' PAPR and complexity of the system is modeled as the design of phase sequences in this paper. Hence, periodic phase sequences are designed and employed to reduce the OFDM signals' PAPR and the complexity of the normal OBF-OFDM system simultaneously, where the transmit data at all antennas can be generated in time domain directly via one N-point IFFT. The simulation results show that, after the proposed schemes are adopted, complexity of the OBF-OFDM system is reduced and the system throughput, both in the maximum throughput scheduling scheme and the proportional fairness scheduling scheme, is almost same as that of the normal OBF-OFDM system and greater than that of non-OBF OFDM.

Performance analysis of multicarrier code selective CDMA system with frequency repetition

In this paper, we present a new Multi-Carrier Code-selective Code Division Multiple Access System (MC CS-CDMA) with frequency repetition. The code selection process enables the proposed scheme to decrease the number of subcarriers for the same transmission data rate and total bandwidth as conventional MC DS-CDMA. The remaining bandwidth can be used for frequency repetition in order to achieve frequency diversity gain. Our results show that by maintaining a constant data rate, total bandwidth and PAPR, the proposed MC CS-CDMA system achieves a much greater performance improvement than conventional MC DS-CDMA.

Max-matching diversity in OFDMA systems

This paper considers the problem of optimal subcarrier allocation in OFDMA systems to achieve the minimum outage probability while guaranteeing fairness. The optimal subcarrier allocation algorithm and the maximum frequency diversity gain are both analyzed through the maximum matching method based on the random bipartite graph theory. Accordingly, a surprising result is found, which shows that the maximum frequency diversity gain in subcarrier-sharing OFDMA systems is the same as that in point-to-point OFDM systems that serve only one user by using N subcarriers. It is then demonstrated that this maximum frequency diversity gain can be achieved by a proposed Random Vertex Rotation based Hopcroft-Karp (RVRHK) algorithm with the time complexity of O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sup> ), where N is the number of subcarriers. Because the theoretical analysis and the RVRHK algorithm are both based on the maximum matching method, the maximum frequency diversity in OFDMA systems is referred to as the max-matching diversity in this paper.