Improved BER performance on MB-OFDM UWB system using adaptive bit loading

We propose a sub-band spreading technique for adaptive modulation (AM) in orthogonal frequency division multiplexing (OFDM) systems in order to reduce signaling overheads and to average frequency selective fading channels causing different signal-to-noise ratio (SNR) values for subcarriers in each sub-band. The conventional sub-band based AM schemes can also reduce signaling overheads and complexity for allocating a resource per sub-band at a time. However, they may suffer from the channel variation in a sub-band when the sub-band size is larger than the channel coherence bandwidth (BW). The sub-band spreading at the transmitter enables the received symbols in each sub-band to have an identical reliability even in a frequency selective fading channel. We rigorously analyze the averaged SNR value at the receiver of the sub-band spreading system and the analyzed average SNR in a sub-band is used for an adaptation criterion. The proposed AM scheme outperforms the conventional sub-band based OFDM scheme without spreading, and it can yield better throughput performance than the conventional subcarrier based AM schemes when we consider the signaling overheads.

This paper deals with low-complexity joint channel estimation and decoding for faster-than-Nyquist (FTN) signaling over frequency selective fading channels. The inter-symbol interference (ISI) imposed by FTN signaling and the frequency selective channel are intentionally separated to fully exploit the known structure of the FTN-induced ISI. Colored noise due to the faster sampling rate than that of the Nyquist signaling system is approximated by autoregressive process. A Forney style factor graph representation of the FTN system is developed and Gaussian message passing is performed on the graph. Expectation propagation (EP) is employed to approximate the message from channel decoder to Gaussian distribution. Since the inner product between FTN symbols and channel coefficients is infeasible by belief propagation (BP), we propose to perform variational message passing (VMP) on an equivalent soft node in factor graph to tackle this problem. Simulation results demonstrate that the proposed low-complexity hybrid BP-EP-VMP algorithm outperforms the existing methods in FTN system. Compared with the Nyquist counterpart, FTN signaling with the proposed algorithm is able to increase the transmission rate by over 40%, with only negligible BER performance loss.

We consider a three-node wireless relay system with frequency selective quasi-static fading channels between the nodes. We assume practical constraints require the relay to operate in half-duplex mode and employ a low-complexity non-orthogonal amplify-forward protocol. Assuming full channel state information and optimal energy allocation between source and relay, we study upper bounds of the outage probability for such channels. Compared to relay systems in flat fading channels, our results reveal that the additional diversity offered by frequency selective fading channels significantly improves outage performance. The results also suggest, however, that relays may offer a limited improvement in diversity when multipath fading in the source-destination link is sufficiently rich.

In this paper, a closed form expression for the bit error rate performance of the multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) communication system in the presence of interference is analytically analysed. The considered channel is the Saleh-Valenzuela multipath fading channel model. The interference is modelled as the OFDM-based IEEE802.11n wireless local area networks (WLANs). The dependence of the bit error rate performance of the MB-OFDM UWB communication system on the transmission range along with the impact of interference is also analytically investigated. Numerical results are validated with the aid of simulations. It is shown that the range performance of the MB-OFDM UWB communication system is severely deteriorated due to the presence of such interference.

In multi-user millimeter wave (mmWave) multiple input multiple output (MIMO) systems, obtaining accurate information/knowledge regarding the channel state is crucial to achieving multi-user interference cancellation and reliable beamforming (BF)–to compensate for severe path loss. This knowledge is nonetheless very challenging to acquire in practice since large antenna arrays experience a low signal-to-noise ratio (SNR) before BF. In this paper, a multi-user channel estimation (CE) scheme namely generalized-block compressed sampling matching pursuit (G-BCoSaMP), is proposed for multi-user mmWave MIMO systems over frequency selective fading channels. This scheme exploits the cluster-structured sparsity in the angular and delay domain of mmWave channels determined by the actual spatial frequencies of each path. As the corresponding spatial frequencies of multi-user mmWave MIMO systems with Hybrid BF often fall between the discrete Fourier transform (DFT) bins due to the continuous Angle of Arrival (AoA)/Angle of Departure (AoD), the proposed G-BCoSaMP algorithm can address the resulting power leakage problem. Simulation results show that the proposed algorithm is effective and offer a better CE performance in terms of MSE when compared to the generalized block orthogonal matching pursuit (G-BOMP) algorithm that does not possess a pruning step.

In this paper, we analyze the Bit Error Rate (BER) performance of Golden coded Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over Rician multipath fading channel. We also compare the performance of the MIMO-OFDM system using Golden code in Rayleigh and Rician multipath fading channels. We discuss the effects of the presence of line-of-sight (LoS) component in the multipath fading environment which renders the improvement in the overall performance of the Golden coded MIMO-OFDM. This paper discusses the performance of Golden codes in a frequency selective Rician fading channel. To deal with the frequency selective fading channel, we use the OFDM (Orthogonal Frequency Division Multiplexing) modulation. The BER performance of the Golden coded MIMO-OFDM system under several propagation conditions has been evaluated. Keywords—MIMO, OFDM, Golden STBC, Rayleigh fading, Rician fading.

For the reception of multicode direct sequence (DS)-CDMA signals, the MMSE frequency domain equalisation is applied instead of RAKE combining. The achievable BER performance in a frequency selective Rayleigh fading channel is evaluated by computer simulation. It is shown by computer simulation that the DS-CDMA with MMSE frequency domain equalisation outperforms the DS-CDMA with RAKE combining and shows only slight performance degradation compared to the MC-CDMA with minimum mean square error combining (MMSEC).

We propose a new block time-reversal conjugate based quasi-orthogonal space-time block encoding and decoding (QO-STBC) scheme for a wireless system with four transmit antennas in frequency selective fading channels. The proposed scheme effectively combats channel dispersion and frequency selectivity due to multipath, yet still provides full diversity gain. We also propose a maximum likelihood (ML) solution, with a simple decoupled structure, to decode the block time-reversal conjugate QO-STBC symbols at low complexity for channels with short delay.

This paper presents the performance of turbo codes with multilevel modulation over frequency selective Rayleigh fading channel. The method of turbo equalization with 8-PSK modulation proposed by V. Franz and G. Bauch (1999) is modified here for 8-PSK and 16-QAM modulation in order to be applied to turbo codes. The joint turbo equalization and turbo decoding receiver is presented. From simulation results, good BER performance can be achieved with only 3 iterations.

Cognitive Radio (CR) has attracted strong interest recently to solve the spectrum congestion problem. In conventional cognitive radio, either overlay waveform is used to exploit unused (white) spectrum holes to avoid interference to primary users, or underlay waveform is employed to spread over a ultrawide bandwidth with extremely low power spectrum density to minimize interference to primary users. In our previous work, we proposed a novel hybrid overlay/underlay waveform to combine the benefits of both overlay and underlay waveform, creating a soft decision cognitive radio to exploit both the unused (white) spectral regions and the underused (gray) spectral areas. Extending the spectrally modulated spectrally encoded (SMSE) framework, we provide the framework for the proposed soft decision cognitive radio. We also evaluate the performance of the hybrid overlay/underlay waveform in frequency selective fading channels. A simulated performance analysis of overlay, underlay and hybrid overlay/underlay waveforms in frequency selective fading channels is presented and benefits discussed.

Orthogonal frequency division multiplexing (OFDM) is one key technology in wireless multimedia communication. In this paper, the performance of channel estimation methods for OFDM systems based on block-type under frequency selective fading channels is discussed. Analysis of a 3G carrier model with 1 MHz bandwidth under frequency selective fading channels is made. The pilot signal estimation based on LS, MMSE, LMMSE (a simplified MMSE algorithm with low-rank approximation using singular value decomposition) criteria, and channel interpolation based on the simple linear interpolation method. Simulation indicates its good anti-multi-path performance and anti-doppler frequency shift ability.

Performance Analysis of Wireless Adhoc Networks in Flat Fading and Frequency Selective Fading channels

Multiple Input Multiple Output (MIMO) technology is a technique that can be used to overcome multipath fading. The multipath fading is caused by signals coming from several paths that experience different attenuations, delays and phases. In a multipath condition, an impulse that sent by the transmitter, will be received by the recipient not as an impulse but as a pulse with a spread width that called delay spread. Delay spread can cause intersymbol interference (ISI) and bit translation errors from the information received. To determine the effect of delay spread on the MIMO system, then MIMO system performance research was performed on flat fading and frequency selective fading channels using the Space Time Block Code (STBC) coding technique. This research was conducted using MatLab 2018a software. The simulation results show that the MIMO STBC system performance on flat fading channels is better than the MIMO STBC system performance on the frequency selective fading channel. This result is analyzed based on the value of BER vs. Eb/No and eye diagram.

In this paper, a coded convolutional spreading codedivision multiaccess with cyclic prefix (CS-CDMA/CP) system in conjunction with iterative receivers is proposed for synchronous downlink transmission over frequency selective fading channels and its performance is compared with the uncoded CS-CDMA/CP employing maximum-likelihood sequence estimation (MLSE) receiver as well as with the conventional coded direct sequence CDMA (DS-CDMA) employing (maximal ratio combining-) MRC-RAKE. Contrary to the uncoded CSCDMA/ CP system which suffers from performance degradation at low signal-to-noise power ratios (SNRs), it is demonstrated that the proposed scheme can attain almost the full path diversity gain over all SNRs with single-user complexity. Compared with the coded DS-CDMA system with single-user receivers, the proposed system is free from multiuser interference (MUI) whenever the multipath delay of the channel does not exceed the designed maximum delay. It is also demonstrated, moreover, that the proposed system shows a robust performance even if the channel length exceed the designed maximum delay slightly. Because of the subblock structure of CS-CDMA/CP, the proposed system can utilize time-diversity effects, when the channel subjects fast fading, and this greatly improves the resultant performance. Finally, it is shown that the receiver complexity of the proposed system is compared quite favorably with the iterative multiuser receivers for coded DS-CDMA systems of comparable performance.

V-BLAST (Vertically-layered Bell Laboratories Layered Space-Time) is a multiple transmit and receive antenna system that provides very high capacity compared to single antenna systems. However, most research in this area had assumed a flat-fading channel environment. This paper considers a frequency selective Rayleigh fading channel environment for multi-input and multi-output (MIMO) systems. Three different detection techniques with ordered successive interference cancellation are proposed: (1) zero-forcing maximal ratio combining (ZF-MRC); (2) layered maximum likelihood detection (L-MLD); and (3) group maximum likelihood detection (G-MLD). All these schemes consider the delayed elements in each transmit-receive antenna pair as imaginary antennas transmitting delayed versions of the substreams. Constraints on the number of receive antennas are also discussed, with G-MLD requiring the least elements. Simulation results show that G-MLD provides the best performance with ZF-MRC performing the worst.