Manifold Optimization Approach for Data Detection in Massive Multiuser MIMO Systems

The high throughput with low latency, massively connected devices, and effective utilization of spectrum for current wireless communication systems can be realized by adopting the fifth-generation (5G) new radio (NR) air interface. The key remarkable features that 5G NR presents are Ultra-Reliable Low-Latency Communications (URLLC), enhanced Mobile Broadband (eMBB), and massive Machine Type Communications (mMTC). To meet thereof features, 5G NR exerts different multiple access and modulation techniques. This paper addresses the physical layer of 5G NR and more explicitly explores the transmission of 5G NR over the physical uplink shared channel (PUSCH) considering several parameters. For example, different sub-carrier spacings (SCSs) are taken into account for analyzing the performance of PUSCH in terms of throughput versus Signal-to-Noise Ratio (SNR). Moreover, the effect of the well-known modulation techniques such as Quadrature Phase Shift Keying (QPSK), different order of Quadrature Amplitude Modulation (QAM) (i.e., 16, 64, and 256) on throughput is studied. Later on, the number of base station (BS) and user equipment (UE) antennas are varied. Lastly, the performance of PUSCH over different propagation channel models (clustered delay line (CDL) and tap delay line (TDL)) is also investigated in this paper. The extensive simulation studies have proved that QPSK exhibits finer outcomes in low SNR regions while 256-QAM shows remarkable results in high SNR regions. The maximum throughput can be realized even in low SNR regime if the number of BS antennas is increased. In addition, high throughput value can be attained by increasing SCS.

An underwater acoustic multimedia communication (UWAMC) system is proposed with 2400 transmission modes according to time-varying multipath underwater acoustic (UWA) channel conditions. The orthogonal variable spreading factor (OVSF) scheme and Gold sequence (GS) scramble code are integrated into multi-input multi-output UWAMC system based on orthogonal frequency-division multiplexing to achieve the quality of service of multimedia transmission in the UWA channel. Binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) adaptive modulation, direct mapping (DM) or space–time block code (STBC) transmission strategies, convolution channel code with rate 1/2 and 1/3, and a power assignment mechanism were adopted in the proposed system. Simulation results show that the bit error rate (BER) and power saving ratio (PSR) performance of the STBC strategy with transmission diversity is superior to that of the DM strategy without transmission diversity, and the performance of the BERs and PSRs of the transmission scheme with the GS scramble code surpasses that of the scheme without the code. The performance of the BERs and PSRs of BPSK modulation with a channel code rate of 1/3 is better than that of BPSK modulation with a channel code rate of 1/2, and the performances of BERs and PSRs of BPSK modulation with a channel code rate of 1/3 are better than that of QPSK modulation with a channel code rate of 1/3. As the length of the OVSF codes increases, the UWAMC system’s BERs decrease, and its PSRs increase. The UWAMC system can achieve either maximum transmission speed or maximum transmission power efficiency.

SUMMARYThis paper introduces limited feedback technique into physical‐layer network coding (PLNC) scheme, which is the most spectrally efficient protocol in two‐way relay channels, consisted of one relay and two end nodes (sources). Decode‐and‐forward (DF) and partial‐decode‐and‐forward (PDF) strategies are considered for PLNC, and all nodes are assumed to have two antennas to allow transmission by Alamouti's orthogonal space–time block code to provide diversity. In DF, by limited feedback, one of the sources is informed about instantaneous channel state information (CSI) to increase the bit error rate (BER) performance at relay. The closed‐form upper and lower bounds on the bit error probability are derived for binary phase‐shift keying (BPSK) and quadrature PSK (QPSK) modulations and approved via computer simulations. In PDF strategy, each source has to know CSI between relay and the other source for decoding, which causes extra protocol complexity. Moreover, for the system in which all nodes have two antennas, classical PDF strategy does not satisfy orthogonality at the end nodes. Therefore, in this paper, a modified‐PDF (MPDF) strategy with limited feedback is proposed. In MPDF, for decoding at the end nodes, differential phase information between channel fading coefficients having maximum amplitudes is fed back to the sources by relay. This approach enables single‐symbol decoding, besides full diversity, and sources do not need to know CSI between relay and the other source. It is shown via computer simulations that MPDF strategy provides significantly better BER performance than the classical PDF for BPSK and QPSK modulations.Copyright © 2012 John Wiley & Sons, Ltd.

Filter bank multicarrier with pulse amplitude modulation (FBMC-PAM) is a candidate waveform for the fifth generation of wireless networks (5G). It can transmit at the same rate as orthogonal frequency division multiplexing (OFDM) opposed to the conventional FBMC-based systems. It also has a minimum overlapping factor leading to a transmit signal with a shorter ramp-up and ramp-down than the existing FBMC- based systems. However, this brings some shortcomings to the FBMCPAM system in terms of equalization. In this paper, performance of FBMC-PAM is studied in massive multiple-input multipleoutput (MIMO) channels. It is discussed that although in massive MIMO channels, multiuser interference as well as channel noise average out, there remains some residual interference due to the channel distortions even for an infinite number of base station (BS) antennas. Consequently, the signal to interference ratio (SIR) saturates after the number of BS antennas reaches a certain value. To quantify this saturation level, we find an upper bound for the SIR performance of FBMC-PAM in such channels. Then, our theoretical analysis is confirmed through simulations. Moreover, it is shown that by choosing an appropriate number of subcarriers, although the SIR saturates, FBMC-PAM can equalize the channel efficiently and the error floor in the bit error rate (BER) can be completely removed.We have chosen OFDM as a benchmark, because of its infinite SIR in multipath channels. We also show that FBMC-PAM provides even a better BER performance than OFDM due to its higher bandwidth efficiency.

The author proposed soft decision feedback equalisation for orthogonal frequency division multiplexing (OFDM) transmission over doubly selective channels which is used for turbo equalisation. The doubly selective channel is approximated using the basis expansion model (BEM). The decision feedback equaliser (DFE) is obtained and updated for every sub-carrier which results in a per-tone DFE. On the basis of the Gaussian approximation, expressions for the a priori, the a posteriori and the extrinsic information have been derived for quadrature phase shift keying (QPSK) modulation. For turbo equalisation, where iterative joint channel equalisation and channel decoding is executed, in the first iteration, estimates are based on the feed-forward filter which are fed to the channel decoder. These estimates are not reliable and may incur error propagation and poor turbo equalisation performance. For more reliable estimates in the first iteration, the DFE is initialised as a linear minimum mean square error (LMMSE) equaliser. The per-tone LMMSE soft-output equaliser is also derived, and expressions for the a priori, a posteriori and extrinsic information are obtained viewing the LMMSE equaliser as a special case of the DFE. The extrinsic information in both cases was derived based on the Gaussian approximation. Numerical results for bit-error rate performance assuming the BEM channel model and Jakes' channel model are shown to confirm our findings.

Chirp signal can be modulated to transmit digital data. We investigated quadrature phase shift keying (QPSK) modulation for chirp signals and analyzed the bit error rate (BER) performance in multipath fading channel. In receiver, synchronous demodulation is used to demodulate received chirp signal, and the output of multipath signal in matched filter has two factors to interfere with the decision vector of direct signal. When the initial frequency equals to the frequency deviation during a half symbol duration, and the chirp rate is negative slope, the output of multipath signal in matched filter has the same phase or the reverse phase as that of direct signal, the impact of multipath signal on BER performance of demodulation is alleviated. Finally, numerical simulation results show the effectiveness of the scheme for mitigating multipath interference.

This letter considers an efficient pilot scheme for two-way relay system with massive antennas in the relay base station (BS). For such a system, we prove that user terminals (UTs) in the same communication pair can reuse the pilot sequence without performance loss. Hence, only K pilot symbols are required to support 2K UTs while 2K pilot symbols are needed in conventional cases. We analyze the asymptotic performance when the BS's antenna number grows infinite. In such a case, the inter-pair interference and noise vanish, and the self-interference determined by the second-order statistics of channel vectors can be feasibly tackled. In this way, the desired signal can be obtained by subtracting the self-interference from the received signal, and the capacity increases with the BS's antenna number.

This work proposes a new adaptive pilot pattern used for pilot arrangement at the mobile station and a new channel estimation at the base station. It addresses the bit error rate (BER) performance optimization of wireless channel estimation in massive multiple-input multiple-output systems. First, we propose a new adaptive pilot pattern (APP) that offers a lower BER than the conventional pilot patterns. Then, we suggest a new channel estimation algorithm based on the APP. It is called the shifted APP-channel estimation (SACE). As a result, APP guarantees an optimal BER performance for the different system configurations, channel models, and carrier frequencies. It offers better BER performance than conventional pilot patterns, such as the long-term evolution (LTE) pilot pattern. Moreover, the shifted APP-based channel estimation algorithm solves the error floor caused by the usage of multiple subcarriers. It also offers a signal-to-noise ratio (SNR) improvement that reaches 17 dB at BER $= 10^{-2}$ compared to the conventional minimum mean square error (MMSE) channel estimation.

In this paper, we investigate the robustness of the Unique Word Orthogonal Frequency Division Multiplexing (UW-OFDM) technique for channel estimation issue. We consider the UW-OFDM technique instead of Zero-Padding (ZP) OFDM one to construct the OFDM symbols for MultiBand Orthogonal Frequency Division Multiplexing Ultra WideBand (MB-OFDM UWB) systems. Then, we propose a two-step LMMSE channel estimator. In the first step, by using the knowledge of UW sequence in the receiver side, the Channel Frequency Response (CFR) is estimated. In the second step, the Linear Minimum Mean-Squared Error (LMMSE) channel estimation is performed using the estimated CFR of the first step and the Channel Estimation Sequence (CES) included in the frame preamble. We evaluate the performance of the proposals in terms of Bit Error Rate (BER) by computer simulations. We show that the consideration of UW-OFDM technique provides, not only reduction of complexity, but also improvement in BER performance. Moreover, we show that the two-step LMMSE channel estimation does not affect the system performance mainly for low Signal-to-Noise Ratio (SNR).

Time division duplex (TDD) pre-equalized orthogonal frequency division multiplexing (OFDM) systems can save system resources by omitting pilot symbols. Meanwhile, a new problem arises that the timing error would degrade system performance, because this error cannot be revised in the absence of pilot symbols. The paper investigates the impact of timing error on the receiver's bit error rate (BER) performance for TDD pre-equalized OFDM systems using phase-shift keying (PSK) modulation. The analytic binary PSK (BPSK) and quadrature PSK (QPSK) BER expressions of ideally and nonideally pre-equalized OFDM systems are obtained, in multipath Rayleigh fading environment. The corresponding simulations verify the analytic expressions. Compared with the theoretical system performance bound, the performance of ideal and nonideal pre-equalized BPSK systems entail loss of 1 dB and 3 dB respectively when the normalized timing error is 1/8. When it is 1/4, the performances of both systems degrade severely. At the same time, the gap between them diminishes. In that case, timing error becomes dominant among those elements which would affect systems performance. The higher the modulation order adopted, the more sensitive to timing error the system performance becomes.

Joint transmit-receive diversity (JTRD) is expected to significantly improve the transmission performance in a multi-input multi-output (MIMO) fading channel. In practical situations, the number of base station (BS) antennas is much larger than that of user equipment (UE) antennas, resulting in an asymmetric MIMO fading channel. In this paper, a practical user-driven suboptimal JTRD scheme assuming time division duplex (TDD) in such an asymmetric MIMO fading channel is investigated. In a user-driven suboptimal JTRD scheme, firstly the user equipment (UE) determines its diversity weight vector, and then, BS determines its diversity weight vector so as to maximize the resulting composite channel gain for the given UE diversity weight vector. While the optimal JTRD jointly optimizes the diversity weight vectors at BS and UE by solving the eigen-equations composed of MIMO channel matrix. In principle, the user-driven suboptimal JTRD provides lower diversity gain than the optimal JTRD. In this paper, it is shown by numerical link capacity evaluation that in an asymmetric MIMO fading channel, where the number of BS antennas is much larger than that of UE antennas, the use of selection diversity in user-driven suboptimal diversity provides a slightly higher diversity gain than the use of maximal-ratio diversity and that the link capacity gap between the user-driven suboptimal JTRD and the optimal JTRD becomes quite small.

Investigation of Costas loop phase deviation effect on BER performance of space downlink coherent communication system with DPSK scheme

The use of wide-band and low-loss fiber-optic feeders to transfer the complex signal processing and control functions from the base station (BS) to a central control station (CCS) in a microcellular system, has attracted a great deal of attention. The optical feeder allows compact and cost-effective base stations, easier channel assignment control, and. flexible communication systems. This paper investigates the simultaneous influence of the effects of the wireless channel such as fading and cochannel interference (CCI) and the effects of the optical channel, like shot noise and intermodulation distortion, introduced by the laser diode on the bit error rate (BER) performance of a fiber-fed microcellular system using the /spl pi/ /4-differential quadrature phase-shift keying (DQPSK) modem scheme. The wireless channel is assumed to be a frequency-selective, slow, and CCI-limited Nakagami fading channel. The BER performance of the system is studied under various channel conditions using an exact model and a simplified model and a comparative study with a nonfiber-fed system is carried out. The tradeoff between the system capacity and the BER performance in fiber-optic microcellular (FOM) systems is also discussed. The results obtained justify the application of fiber-optic feeders as the remoting infrastructure for future microcellular systems.

In Multi User (MU) Massive MIMO Base Station is provided with large number of antennas to serve number of single antenna user terminals. It offers several benefits over conventional MIMO and takes the advantage of multipath propagation by sending and receiving multiple data signals in same time-frequency resource which increases the throughput, coverage, and reliability. Massive MIMO, averages out the small scale fading and thermal noise. This averaging is done as the number of BS antennas increases without limit (M ≫ K). One of the limiting factor for the performance of Massive MIMO system is pilot contamination. Reuse of the orthogonal pilot sequences in adjacent cells cause pilot contamination. Pilot contamination causes poor channel estimation at the BS and degrades the performance of the system. The proposed scheme improves the performance of downlink by optimized allocation of pilot sequences and using fractional frequency reuse factor (1/N). All the available pilot signals are equally divided among the cells as per the cluster size (N = 1, 3, 7). In the proposed scheme orthogonal pilot signal is transmitted by each user terminal to get the Channel State Information (CSI) to estimate the channel. SIR and terminal capacity for the downlink are calculated for the given number of user terminals using linear precoding (Matched Filter and Zero Forcing) schemes which are the function of the estimated channel and the pilot transmission power (ρ p ). It is observed that there is significant improvement in Pilot Signal to Interference Plus Noise (PSINR), SIR and terminal capacity by reducing fractional frequency reuse factor i.e. (N = 1, 3, 7).

ABSTRACTIn massive MIMO systems, inter-user interference has effect on the transmitted signals, so linear precoding techniques are employed for multiuser transmission channels to remove this inter-user interference. It is very complicated to design a suitable linear precoding technique having low computational complexity, which will give an excellent Bit Error Rate (BER) performance. In this paper, we analyse BER under imperfect Channel-State-Information (CSI) using Zero-Forcing (ZF) linear precoding scheme in the downlink, massive MIMO in Time-Division-Duplex (TDD) mode. We derive the closed-form expressions for BER that are obtained from the new expressions derived for Signal-Interference-Noise Ratio (SINR), and then analysis with different parameters using numerical and Monte Carlo simulated results is carried out in MATLAB under imperfect CSI. It was found that our theoretical analysis agrees well with the simulated results. In our analysis, BER was observed in most cases to be good when the number of Base Station (BS) antennas is large enough to accommodate the served users, but when the number of users grows up, the BER performance degrades depending on how many BS antennas are capable of handling the additional users. Also, increasing the downlink transmit power was found to improve the performance, but it is not an energy-efficient way for massive MIMO.