Achievable Bit Error Rate Performance Research Articles

Spatial Scattering Modulation for Uplink Millimeter-Wave Systems

In this letter, a new spatial scattering modulation (SSM) is proposed for uplink millimeter-wave (mmWave) systems that support a single user terminal (UT). By utilizing the analog and hybrid beamforming with a large antenna array and phase shifters for mmWave communications systems, an architecture, where the UT has a single radio-frequency (RF) chain, whereas the base station has more than one RF chain, is adopted. In this architecture, the proposed SSM modulates some information bits on the spatial directions of scattering clusters in the angular domain, so that a higher spectral efficiency can be achieved with the use of a lower order modulation. For a particular number of scattering clusters and a number of RF chains, a closed-form expression for the upper bound on the bit-error rate (BER) is derived for the proposed SSM. Monte Carlo simulations are also conducted to verify the achievable BER performance.

Dual-Mode Index Modulation Aided OFDM With Constellation Power Allocation and Low-Complexity Detector Design

Dual-mode index modulation aided orthogonal frequency division multiplexing (DM-OFDM) is recently proposed, which modulates all subcarriers to eliminate the limits of spectrum efficiency (SE) in OFDM with index modulation (OFDM-IM). In DM-OFDM, the subcarriers within each subblock are divided into two groups, which are modulated by two distinguishable constellation alphabets drawn from the inner and the outer constellation points of a given M-ary QAM constellation. In this paper, a new DM-OFDM scheme, called DM-OFDM with constellation power allocation (DM-OFDM-CPA) is proposed, where the two groups of subcarriers within each subblock are set at different power levels and modulated by different M-ary PSK symbols, leading to the improvement of the system performance at low-order modulation. At the receiver, a low-complexity maximum likelihood (LC-ML) detector and two reduced search complexity detectors, based on energy detection and log-likelihood ratio (LLR) criterion, respectively, are employed for demodulation. Then, the bit error rate (BER) analyses based on pairwise error probability are provided for the proposed DM-OFDM-CPA, and the power ratio between the two groups is optimized to maximize achievable BER performance for a given signal to noise ratio. The simulation results confirm that at a given SE, the proposed DM-OFDM-CPA achieves a significantly better BER performance than the existing OFDM-IM. When the modulation order is lower than 16, it outperforms the classic DM-OFDM. The results also show that two reduced search complexity detectors, especially the LLR detector, provide similar performance to the LC-ML detector in the DM-OFDM-CPA.

Performance Analysis of Analog Network Coding with Imperfect Channel Estimation in a Frequency-Selective Fading Channel

Broadcast nature of the wireless channel enables wireless communications to make use of network coding at the physical layer (PNC) to improve the network capacity. Recently, narrowband and later broadband analog network coding (ANC) were introduced as a simpler implementation of PNC. The ANC schemes require two time slots while in PNC three time slots are required for bi-directional communication between two nodes and hence ANC is more spectrum efficient. The coherent detection and self-information removal in ANC require accurate channel state information (CSI). {In this paper, we theoretically analyze the bit error rate (BER) performance with imperfect knowledge of CSI for broadband ANC using orthogonal frequency division multiplexing (OFDM), where the channel estimation error is modeled as a zero-mean complex Gaussian random variable. We investigate the BER performance for three cases: (i) the effect of imperfect self-information removal due to channel estimation (CE) error with fading tracking errors, (ii) the effect of imperfect self-information removal due to CE error without fading tracking errors}, and (iii) the ideal CE case. We discuss how, and by how much, our results obtained by theoretical analysis can be used for design of broadband ANC system with the imperfect knowledge of CSI. Our results show that imperfect channel estimation due to the noise effect has less impact on self-information removal than the imperfect channel estimation due to fading tracking errors. The tracking against fading is an important problem for accurate self-information removal as well as coherent detection and thus, the effect of channel time-selectivity is also theoretically studied. The achievable BER performance gains due to the polynomial time-domain channel interpolation are investigated using the derived close-form BER expressions and it was shown that the broadband ANC schemes with practical CE in a time- and frequency-selective channel should include a more sophisticated channel interpolation techniques since the impact of Doppler shift has prevalent effect on the achievable BER performance.

On Channel Estimation for Analog Network Coding in a Frequency-Selective Fading Channel

Recently, broadband analog network coding (ANC) was introduced for high-speed transmission over the wireless (frequency-selective fading) channel. However, ANC requires the knowledge of channel state information (CSI) for self-information removal and coherent signal detection. In ANC, the users' pilot signals interfere during the first slot, which renders the relay unable to estimate CSIs of different users, and, consequently, four time-slot pilot-assisted channel estimation (CE) is required to avoid interference. Naturally, this will reduce the capacity of ANC scheme. In this paper, we theoretically analyze the bit error rate (BER) performance of bi-directional broadband ANC communication based on orthogonal frequency division multiplexing (OFDM) radio access. We also theoretically analyze the performance of the channel estimator's mean square error (MSE). The analysis is based on the assumption of perfect timing and frequency synchronization. The achievable BER performance and the estimator's MSE for broadband ANC is evaluated by numerical and computer simulation. We discuss how, and by how much, the imperfect knowledge of CSI affects the BER performance of broadband ANC. It is shown that the CE scheme achieves a slightly higher BER in comparison with ideal CE case for a low and moderate mobile terminal speed in a frequency-selective fading channel.

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.

On the Construction of Orthogonal Spreading Code Groups for MC-CDMA with FDE in a Frequency Selective Channel

The bit error rate (BER) performance of multicode multi-carrier code division multiple access (MC-CDMA) severely degrades due to the inter-code interference (ICI) in a strong frequency-selective channel. Recently a spreading code group construction method was proposed for MC-CDMA. The Walsh-Hadmard (WH) codes are divided into a number of code groups such that the code orthogonality can be maintained within each group even in a strong frequency-selective channel; any code pair taken from different groups is not orthogonal. The number of spreading codes in each group is determined by the maximum time delay difference of the channel. In this paper, we point out that the number of codes in each group is determined by the distribution of time delay differences among the propagation paths of the channel, not the maximum time delay difference. Based on that observation, we show that more orthogonal spreading codes can exist in each code group. The conditional BER is derived taking into account the interference from other code groups and the achievable downlink BER performance using the proposed spreading code group construction is numerically evaluated in a frequency-selective Rayleigh fading channel.

Frequency-Domain Block Signal Detection for Single-Carrier Transmission

One-tap frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can significantly improve the bit error rate (BER) performance of single-carrier (SC) transmission in a frequency-selective fading channel. However, a big performance gap from the theoretical lower bound still exists due to the presence of residual inter-symbol interference (ISI) after MMSE-FDE. In this paper, we point out that the frequency-domain received SC signal can be expressed using the matrix representation similar to the multiple-input multiple-output (MIMO) multiplexing and therefore, signal detection schemes developed for MIMO multiplexing, other than simple one-tap MMSE-FDE, can be applied to SC transmission. Then, for the reception of SC signals, we propose a new signal detection scheme, which combines FDE with MIMO signal detection, such as MMSE detection and Vertical-Bell Laboratories layered space-time architecture (V-BLAST) detection (we call this frequency-domain block signal detection). The achievable average BER performance using the proposed frequency-domain block signal detection is evaluated by computer simulation.

Finite-resolution digital receiver design for impulse radio ultra-wideband communication

Receiver design for impulse radio based ultrawideband (UWB) communication is a challenge. High sampling rate high resolution digital receiver is usually difficult to implement. Some tradeoffs can be made on the digital receiver, such as limiting amplitude resolution to only one bit, which results in a previously considered monobit receiver. In this paper, we consider the design of finite-resolution digital UWB receivers. We derive the optimal post-quantization processing, and analyze the achievable bit-error rate performance using an approximation of the log-likelihood ratio. Optimal thresholds for 4- and 3-level quantization are obtained. Training-based receiver template estimation is presented. Our work discloses the incremental gain that additional quantization levels offer and the results provide useful guidelines for designing impulse radio UWB digital receivers.

Joint Tomlinson-Harashima Precoding and Frequency-Domain Equalization for Broadband Single-Carrier Transmission

The performance of single-carrier (SC) transmission in a frequency-selective fading channel degrades due to a severe inter-symbol interference (ISI). Using frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can improve the bit error rate (BER) performance of SC transmission. However, the residual ISI after FDE limits the performance improvement. In this paper, we propose a joint use of Tomlinson-Harashima precoding (THP) and FDE to remove the residual ISI. An approximate conditional BER analysis is presented for the given channel condition. The achievable average BER performance is evaluated by Monte-Carlo numerical computation method using the derived conditional BER. The BER analysis is confirmed by computer simulation of the signal transmission.

Performance of multiantenna multicarrier direct-sequence code division multiple access using orthogonal variable spreading factor codes-assisted space–time spreading in time-selective fading channels

A downlink (base-to-mobile) multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) system employing multiple antennas at both the base station and each of the mobile terminals is investigated, when communicating over fast time-varying fading channels resulting in time-selective fading. In the considered multiantenna MC DS-CDMA, space–time spreading (STS) based on the family of orthogonal variable spreading factor (OVSF) codes is proposed in order to achieve the time diversity because of the time-selective fading, in addition to the transmit/receive diversity. In this contribution, the closed-form expressions for the single-user bit-error rate (BER) are derived, in order to gain insight into the achievable BER performance of the multiantenna MC DS-CDMA. The BER performance of the multiantenna MC DS-CDMA system is investigated, when communicating over correlated time-selective Rayleigh fading channels. The study and performance results show that the multiantenna MC DS-CDMA using OVSF codes-assisted STS constitutes a high-efficiency downlink space–time transmission scheme. It is capable of achieving the full diversity provided by the time-selective fading and multiple transmit/receive antennas. Furthermore, the proposed multiantenna MC DS-CDMA is capable of achieving a self-balance between the time diversity achieved and the multiuser interference suppression capability, when using low-complexity correlation detection.

Single-user performance of direct-sequence code-division multiple-access using relay diversity and power allocation

In this contribution, the authors investigate the single-user-bound performance of a direct-sequence code-division multiple-access (DS-CDMA) system, where one source mobile terminal (MT) communicates with its base-station (BS) with the assistance of multiple relays. The authors assume that the communications channels experience both propagation pathloss and fast fading, and that the channels from the source MT to the BS and relays as well as that from the relays to the BS may experience different fast fading modelled correspondingly by Nakagami-m distributions. In the study, they assume both the single-user combining using maximal ratio combining and the multiuser combining, which are derived based on the maximum signal-tointerference-plus-noise ratio criterion. The bit-error-rate (BER) performance of the DS-CDMA is investigated associated with considering the locations of the relays as well as the power-allocation among the source MT and relays. From the study and simulation results, it can be shown that the achievable BER performance of the DS-CDMA depends on the locations of the relays and also on the power-allocation among the source MT and relays. When the relays of a source MT are chosen from a different area, the power-allocation should also be adjusted correspondingly in order to achieve the minimum BER. Furthermore, when optimum power allocation is assumed, the BER performance of the DS-CDMA can be significantly improved, when increasing the number of relays assisting the source MT.

Application of Adaptive QAM Modulation and Diversity Scheme for 30 GHz Cellular Communications under the Impact of Rain Attention in Indonesia

In millimeter-wave wireless cellular systems like Local Multipoint Distribution Services (LMDS) rain attenuation is an essential factor of performance degradation. It can cause signal outages and poor quality of signal reception. To mitigate the problem, a combination of diversity and adaptive modulation is proposed. To investigate the impact of the use of these techniques, a simulation is performed for a 30 GHz cellular system to obtain SNR (signalto- noise ratio), diversity gain, modulation level and BER (bit error rate). Analysis of the implementation of the combined techniques is accomplished by taking into account such factors as length of links and the combining method Simulation results show that diversity can improve the overall system SNR. Diversity gain of up to 15 dB can be achieved on two 4-km converging links at 0.01% outage probability when maximal-ratio combining (MRC) is used. For systems with luxurious link design for which the clearsky SNR is more than 30 dB, as considered in this paper, diversity and adaptive modulation do not significantly contribute to improvement of achievable transmission rate and BER performance. However, for systems with lower values of clear-sky SNR, use of both techniques will be more worthwhil.

Frequency-Domain Multi-Stage Soft Interference Cancellation for DS-CDMA Uplink Signal Transmission

SUMMARY It is well-known that, in DS-CDMA downlink signal transmission, frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion can replace rake combining to achieve much improved bit error rate (BER) performance in severe frequencyselective fading channel. However, in uplink signal transmission, as each user’s signal goes through a different channel, a severe multi-user interference (MUI) is produced and the uplink BER performance severely degrades compared to the downlink. When a small spreading factor is used, the uplink BER performance further degrades due to inter-chip interference (ICI). In this paper, we propose a frequency-domain multi-stage soft interference cancellation scheme for the DS-CDMA uplink and the achievable BER performance is evaluated by computer simulation. The BER performance comparison of the proposed cancellation technique and the multiuser detection (MUD) is also presented.

Iterative Channel Estimation for Frequency-Domain Equalization of DSSS Signals

As the channel frequency selectivity becomes severer, the bit error rate (BER) performance of direct sequence spread spectrum (DSSS) signal transmission with rake combining degrades due to an increasing inter-path interference (IPI). Frequency-domain equalization (FDE) can replace rake combining with much improved BER performance in a severe frequency-selective fading channel. For FDE, accurate estimation of the channel transfer function is required. In this paper, we propose an iterative channel estimation that uses pilot chips which are time-multiplexed within each chip block for fast Fourier transform (FFT). The pilot acts as a cyclic-prefix of FFT block as well. The achievable BER performance is evaluated by computer simulation. It is shown that the proposed channel estimation has a very good tracking ability against fast fading.

On the performance of band-limited asynchronous DS-CDMA over nakagami-m channels

In this paper we investigated the BER performance of DS-CDMA using various chip-waveforms, which include three time-limited chip-waveforms and two band-limited chip-waveforms. Closed-form formulae were derived for evaluating the achievable bit-error rate performance with the aid of the standard Gaussian approximation, when communicating over a Nakagami-m channel. The time-limited waveforms impose a low implementational complexity, since they maybe over sampled and read from a look-up table. However, they are outperformed by the frequency-domain raised-cosine waveform as well as the optimum waveform specifically designed by Cho and Lehnert for achieving the lowest possible bit error rate

Improvement and Analysis of Iterative Decision- Feedback Differential Demodulation

In this letter, we consider iterative decision-feedback differential demodulation (iterative DFDM), which was proposed previously as a low-complexity solution for power-efficient transmission over flat fading channels without channel state information at the receiver. We devise a modified demodulator (inner decoder), which improves both the achievable bit-error rate performance and the convergence of iterative DFDM without increasing complexity. We also establish an equivalent decoder model for iterative DFDM which enables a convergence analysis by means of extrinsic information transfer charts.