Decoding Receiver Research Articles

An Iterative Detection and Decoding Receiver for LDPC-Coded MIMO Systems

This paper presents a high-throughput, area-efficient and energy-efficient iterative detection and decoding (IDD) receiver for low-density parity-check (LDPC)-coded multiple-input multiple-output (MIMO) systems. A layered non-resetting IDD technique is used to minimize the number of inner iterations for a required error performance. An area-efficient minimum mean-square error with parallel interference cancellation (MMSE-PIC) detector is devised to simplify matrix inversion. A detector-decoder interface that is used to exchange soft messages efficiently is proposed. Given the throughput specifications, inner and outer loops are optimally combined to maximize the error performance. The design specifications defined in the IEEE 802.11n standard are adopted as the design target. A 4 $\times$ 4 antenna configuration with BPSK, QPSK, 16-QAM modulations are realized in silicon. The designs that support 64-QAM and 256-QAM modulations are also demonstrated for comparison with prior work. Fabricated in 40 nm technology, the chip integrates 998k logic gates in 1.33 ${\rm mm}^{2}$ and achieves a maximum throughput of 794 Mb/s. The chip dissipates 135 mW at 0.9 V, achieving an energy efficiency of 170 pJ/bit.

Zero-forcing beamforming for physical layer security of energy harvesting wireless communications

Abstract In this paper, we consider the physical layer security for simultaneous wireless information and power transfer (SWIPT) in a multiple-input single-output (MISO) system that is consisted of three nodes: one transmitter with multiple antennas, one information decoding (ID) receiver with single antenna, and one energy harvesting (EH) receiver with single antenna. We propose a new zero-forcing based strategy that contains both the information beamforming and the energy beamforming, pointing to different receivers. To prevent the energy receiver from possibly eavesdropping the information, our target is to maximize the secrecy-rate of the ID receiver while at the same time maintaining a minimum required energy for the EH receiver. For the case that artificial noise is not used, the original non-convex problem can be directly converted into convex subproblems, where the closed-form optimal solutions are derived. For the case that artificial noise is used, the initial non-convex problem can be decomposed into two quasi-convex subproblems where closed-form solutions are derived, and the global optimal solutions are obtained with the aid of one-dimensional search. Simulations results demonstrate the trade-off between the maximum secret information rate and the transferred energy, which is characterized by the boundary of secret rate-energy (R-E) region.

Alternating Rate Profile Optimization in Single Stream MIMO Interference Channels

The multiple-input multiple-output interference channel is considered with perfect channel information at the transmitters and single-user decoding receivers. With all transmissions restricted to single stream beamforming, we consider the problem of finding all Pareto optimal rate-tuples in the achievable rate region. The problem is cast as a rate profile optimization problem. Due to its nonconvexity, we resort to an alternating approach: For fixed receivers, optimal transmission is known. For fixed transmitters, we show that optimal receive beamforming is a solution to an inverse field of values problem. We prove the solution's stationarity and compare it with existing approaches.

Multiple recursive generator-based method for peak-to-average power ratio reduction in selected mapping without side information

Orthogonal Frequency Division Multiplexing (OFDM) has been used for many wireless communication systems. However, the main drawback of this method is the high Peak-to-Average Power Ratio (PAPR). Selected Mapping (SLM) is a technique used for solving the high PAPR problem in OFDM systems. In SLM, the original data sequence is multiplied by a set of predetermined phase sequences and multiple signals with different PAPRs are generated. Then, the one with the lowest PAPR is selected for transmission. The SLM method requires sending of some bits as Side Information (SI) for each data block, which is of critical importance to the receiver for decoding. The SI bits cause a decrease in the bandwidth efficiency; furthermore, incorrect SI detection leads to the loss of an entire data block. In this paper, we exhibit a new SLM technique by using a Multiple Recursive Generator (MRG), a method of generating pseudo random sequences, to send data without explicit SI bits. We show that the proposed technique performs very well in terms of the Bit Error Rate (BER), Probability of detection failure (Pdf) and PAPR reduction.

Transmission of Visual Data over Wireless Fading Channel in Real-Time Systems Based on Superposition Coding Scheme

Real-time visual applications are among the most important requirements in the next generation wireless communication systems. In these applications, the transmitted data comprise different layers with different importance levels based on their influence on the reception quality. Furthermore, the real-time transmission nature of these applications makes them sensitive to data losses and transmission delay. To address these issues, an efficient superposition adaptive modulation and coding system, for the optimal system performance, is proposed in this paper. The proposed system switches its modulation and coding scheme adaptively to select the suitable modulation order and coding rate that best match with the instantaneous channel condition. The channel state information is estimated in receiver and fed back to transmitter. In such method, better performances in both data rate and bit error rate (BER) can be attained. Here, the source data are divided into different priority layers with different importance. Each layer bit stream is sent with specific error protection level against channel corruption. The highest error protection level is assigned to the highest priority layer, and vice versa. The modulated bit streams of all layers are then superimposed together and transmitted via Rayleigh fading channel. At the receiver side, a specific multi-stage decoding receiver is used to reconstruct the source data which demodulates the layers in the order of their priorities. Simulation results show that the proposed system provides up to 18 dB SNR and 46 % data rate gains, respectively, compared to the traditional BPSK scheme at BER of 10−4.

Asynchronous Multiuser Reception for OFDM in Underwater Acoustic Communications

Recently significant progress has been made on point-to-point underwater acoustic communications, and the interest has grown on the application of those techniques in multiuser communication settings, where the asynchronous nature of multiuser communication poses a grand challenge. This paper develops a time-asynchronous multiuser reception approach for orthogonal frequency-division multiplexing (OFDM) transmissions in underwater acoustic channels. The received data burst is segmented and apportioned to multiple processing units in an overlapped fashion, where the length of the processing unit depends on the maximum asynchronism among users on the OFDM block level. Interference cancellation is adopted to reduce the interblock interference between overlapped processing units. Within each processing unit, the residual inter-block interference from multiple users is aggregated as one external interference which can be parameterized. Multiuser channel estimation, data detection, and interference mitigation are then carried out in an iterative fashion. Simulation and emulated experimental results demonstrate the robustness of the proposed receiver with signal asynchronism among multiple users in both time-invariant and time-varying environments. It is observed that the receiver decoding performance degrades as the channel time variation and the maximum relative delay among users increase.

On an Achievable Rate of Large Rayleigh Block-Fading MIMO Channels With No CSI

Training-based transmission over Rayleigh block-fading multiple-input multiple-output (MIMO) channels is investigated. As a training method a combination of a pilot-assisted scheme and a biased signaling scheme is considered. The achievable rates of successive decoding (SD) receivers based on the linear minimum mean-squared error (LMMSE) channel estimation are analyzed in the large-system limit, by using the replica method under the assumption of replica symmetry. It is shown that negligible pilot information is best in terms of the achievable rates of the SD receivers in the large-system limit. The obtained analytical formulas of the achievable rates can improve the existing lower bound on the capacity of the MIMO channel with no channel state information (CSI), derived by Hassibi and Hochwald, for all signal-to-noise ratios (SNRs). The comparison between the obtained bound and a high SNR approximation of the channel capacity, derived by Zheng and Tse, implies that the high SNR approximation is unreliable unless quite high SNR is considered. Energy efficiency in the low SNR regime is also investigated in terms of the power per information bit required for reliable communication. The required minimum power is shown to be achieved at a positive rate for the SD receiver with no CSI, whereas it is achieved in the zero-rate limit for the case of perfect CSI available at the receiver. Moreover, numerical simulations imply that the presented large-system analysis can provide a good approximation for not so large systems. The results in this paper imply that SD schemes can provide a significant performance gain in the low-to-moderate SNR regimes, compared to conventional receivers based on one-shot channel estimation.

Robust beamforming in interference channels with imperfect transmitter channel information

We consider K links operating concurrently in the same spectral band. Each transmitter has multiple antennas, while each receiver uses a single antenna. This setting corresponds to the multiple-input single-output interference channel. We assume perfect channel state information at the single-user decoding receivers whereas the transmitters only have estimates of the true channels. The channel estimation errors are assumed to be bounded in elliptical regions whose geometry is known at the transmitters. Robust beamforming optimizes worst-case received power gains, and a Pareto optimal point is a worst-case achievable rate tuple from which it is impossible to increase a link's performance without degrading the performance of another. We characterize the robust beamforming vectors necessary to operate at any Pareto optimal point. Moreover, these beamforming vectors are parameterized by K(K−1) real-valued parameters. We analyze the system's spectral efficiency at high and low signal-to-noise ratio (SNR). Zero forcing transmission achieves full multiplexing gain at high SNR only if the estimation errors scale linearly with inverse SNR. If the errors are SNR independent, then single-user transmission is optimal at high SNR. At low SNR, robust maximum ratio transmission optimizes the minimum energy per bit for reliable communication. Numerical simulations illustrate the gained theoretical results.

Development of Communication Behaviour: Receiver Ontogeny in Túngara Frogs and a Prospectus for a Behavioural Evolutionary Development

Most studies addressing the development of animal communication have focused on signal production rather than receiver decoding, and similar emphasis has been given to learning over nonlearning. But receivers are an integral part of a communication network, and nonlearned mechanisms appear to be more ubiquitous than learned ones in the communication systems of most animals. Here we review the results of recent experiments and outline future directions for integrative studies on the development of a primarily nonlearned behaviour—recognition of communication signals during ontogeny in a tropical frog. The results suggest that antecedents to adult behaviours might be a common feature of developing organisms. Given the essential role that acoustic communication serves in reproduction for many organisms and that receivers can exert strong influence on the evolution of signals, understanding the evolutionary developmental basis of mate recognition will provide new insights into the evolution of communication systems.

Differential Coding for MAC Based Two-User MIMO Communication Systems

In this paper, we explain how to implement differential modulation in multiple access channel (MAC) based uplink two-user multiple-input multiple-output (MIMO) communication system. It is assumed that the users cannot exchange their information and transmit data over uplink MAC channels simultaneously in the same frequency band and without any orthogonal signatures (no CDMA). We derive two types of differential decoders for two-user MIMO MAC system namely 1) Partial differential decoder, 2) Heuristic based differential decoders. The partial differential decoder is able to avoid the knowledge of the channel gains of one user at the receiver for joint decoding of the data of both users. Whereas, the heuristic differential decoders are obtained heuristically and work without any channel knowledge of both users. For the heuristic differential decoder to work properly, the data of one user must be rotated before transmission. An upper bound of the pairwise error probability (PEP) is derived for the proposed scheme. The upper bound of the PEP is minimized for obtaining an optimized value of the rotation angle.

On Optimal Link Activation With Interference Cancelation in Wireless Networking

A fundamental aspect in performance engineering of wireless networks is optimizing the set of links that can be concurrently activated to meet given signal-to-interference-plus-noise ratio (SINR) thresholds. The solution of this combinatorial problem is the key element in scheduling and cross-layer resource management. In this paper, we assume multiuser decoding (MUD) receivers, which can cancel strongly interfering signals. As a result, in contrast to classical spatial reuse, links being close to each other are more likely to be active concurrently. Our focus is to gauge the gain of successive interference cancelation (SIC) and the simpler, yet instructive, case of parallel interference cancelation (PIC) in the context of optimal link activation (LA). We show that both problems are NP-hard, and we develop compact integer linear programming (ILP) formulations to approach global optimality. We provide an extensive numerical performance evaluation, indicating that, for low to medium SINR thresholds, the improvement is quite substantial, particularly with SIC, whereas for high SINR thresholds, the improvement diminishes, and both schemes perform equally well.

Quasi-Orthogonal Space-Time Block Codes for Two Transmit Antennas and Three Time Slots

In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed for systems with two transmit antennas and three time slots, where the Alamouti code is not applicable due to the odd time slots. The proposed Q-STBC codes achieve rate one and full diversity with low complexity maximum likelihood decoding. The Q-STBC design also shows excellent properties in other practical aspects, such as the compatibility with the single antenna transmission mode, low power fluctuation, and low receiver decoding and transmitter encoding complexity.

Information Theoretic Criterion for Stopping Turbo Iteration

Most existing stopping criteria for turbo decoding have their root in hypothesis test, requiring a subjective threshold for decision making. A consequence is that the turbo decoding receiver so-constructed can converge at high signal-to-noise ratios (SNRs) but fails at low SNRs, thereby calling for a new design philosophy for stopping criteria. In this correspondence, the problem is tackled in the framework of information theoretic criterion, which enables the turbo decoding to properly work in a changing SNR environment. Numerical results are presented for illustrating the good performance of the proposed method.

10 Gb/s-Based PON Over OCDMA Uplink Burst Transmission Using SSFBG Encoder/Multi-Port Decoder and Burst-Mode Receiver

In this paper, we propose a novel 10 Gb/s-based passive optical network (PON) over optical code division multiple access (OCDMA) system to realize the new generation full capacity optical access network which is easily upgraded from existing time division multiplexing PON (TDM-PON) without sacrificing the currently uplink bandwidth assigned to the individual user. 16-ONU (4-OCDMA x 4-packet) uplink burst transmission, an upgrade scenario by a factor of four of conventional 10 Gb/s-based PON, is experimentally demonstrated by using multi-level phase-shift-keying (PSK) super-structured fiber Bragg grating (SSFBG) encoder/multi-port decoder and burst-mode receiver. In the discussions, it will be shown that 32 users can be accommodated in 10 Gb/s-based PON over OCDMA system, and a key is newly introduced multi-level phase-shifted en/decoding, of which auto-correlation waveform can be preferably adopted in the burst-mode reception at 10 Gb/s.

Using Delayed Feedback for Antenna Selection in MIMO Systems

Antenna selection in multiple-input-multipleoutput (MIMO) systems preserves diversity gain while significantly reducing hardware complexity. However, imperfect channel state information (CSI) affects performance. In this paper, we first analyze the performance of a MIMO system employing antenna selection at the transmitter and maximal ratio combining (MRC) at the receiver in the presence of feedback delay and channel estimation errors. Then, we determine whether channel prediction can compensate for the effect of feedback delay. Outage probability is analyzed as a function of ?, the correlation coefficient between the CSI used at the receiver for decoding (CSIR) and the CSI used at the transmitter for selection (CSIT). Analytical results show that the effect of feedback delay is more significant than the effect of estimation error. In order to overcome the effect of delay, ? should increase with SNR. For a given SNR, the length of the linear minimum mean square error (LMMSE) prediction filter required is calculated and shown to increase with SNR. Finally, we determine the asymptotic diversity order as a function of the feedback quality. Results show that if 1 - ? ? SNR-1, the diversity order with imperfect CSI is same as that with perfect CSI.

Turbo decoder SNR estimation with RAKE reception

The joint performance of a turbo decoder and RAKE receiver using the MAP algorithm depends on the accuracy of the channel reliability factor. In a high data rate/low processing gain environment, inherent interference that results from non-idealities of the RAKE receiver complicate the estimation of the channel reliability factor. The combined performance of a turbo decoder and RAKE receiver is analyzed in a time dispersive and time-varying channel with distinct multipath components. Approaches are examined for estimating the channel reliability factor using the limited information that is known by the RAKE receiver. The sensitivity of performance to SNR mismatches is computed. The impact of the processing gain and the number of multipath components on BER performance is analyzed along with the effect of the channel time coherence. By accounting for the non-ideal RAKE interference effects, improvements in the channel reliability factor calculation result in BER performance improvements on the order of 0.5-2 dB.

Differential diversity-embedding space-time block coding for 2 and 4 transmit antennas

Diversity-embedding space-time block coding (DE-STBC), introduced in the work of Diggavi et al. (2003), enables unequal error protection (UEP) using multiple transmit antennas. Even though these codes do not require channel state information (CSI) at the transmitter, they do need it at the receiver for decoding. A novel differential DE-STBC scheme is proposed in this paper to eliminate the need for channel estimation at the receiver which is especially costly with multiple transmit and receive antennas. Most previously proposed differential schemes in the literature are based on orthogonal STBC and hence are not applicable to the non- orthogonal family of DE-STBC considered in this paper.

Differentially Encoded LDPC Codes—Part I: Special Case of Product Accumulate Codes

Part I of a two-part series investigates product accumulate codes, a special class of differentially-encoded low density parity check (DE-LDPC) codes with high performance and low complexity, on flat Rayleigh fading channels. In the coherent detection case, Divsalar's simple bounds and iterative thresholds using density evolution are computed to quantify the code performance at finite and infinite lengths, respectively. In the noncoherent detection case, a simple iterative differential detection and decoding (IDDD) receiver is proposed and shown to be robust for different Doppler shifts. Extrinsic information transfer (EXIT) charts reveal that, with pilot symbol assisted differential detection, the widespread practice of inserting pilot symbols to terminate the trellis actually incurs a loss in capacity, and a more efficient way is to separate pilots from the trellis. Through analysis and simulations, it is shown that PA codes performvery well with both coherent and noncoherent detections. The more general case of DE-LDPC codes, where the LDPC part may take arbitrary degree profiles, is studied in Part II Li 2008.

Multirate Layered Space-Time Coding and Successive Interference Cancellation Receivers in Quasi-Static Fading Channels

We investigate the performance of multirate layered space-time coded MIMO systems with successive decoding and interference cancellation (SDIC) receivers in quasi-static Rayleigh fading channels. The proposed framework can be viewed as a class of diagonal layered space-time coded system with each of the layers is encoded independently with different rates subject to equal per-layer outage probabilities. We derive the probability density functions of the per-layer mutual informations, which can be used to estimate the per-layer rates. Using these densities we show that the proposed transceiver increases the outage capacity. We also present simulation results illustrating the outage capacity performance for a variety of transmit and receive antenna combinations and the associated near optimal per-layer rates of input signals. In particular we show that for sufficiently large numbers of transmit and receive antennas, the system can achieve near capacity in quasi-static fading environments. Based on these results, multirate codes are designed using punctured turbo codes and simulation results show significant gains in packet error-rate (PER) performances compared to that of V-BLAST architectures with lower receiver complexities.

A low-complexity receiver for iterative parallel interference cancellation and decoding in MIMO–OFDM systems

A novel low-complexity iterative receiver for coded multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is proposed in this letter. The soft-in soft-out (SISO) detector is simply a parallel interference cancellation (PIC)–maximum ratio combining (MRC) operation. However, system performance would be degraded because of ignoring the existence of the residual interference from other transmit antennas. In our scheme, the log likelihood ratios (LLRs) of encoded bits after channel decoding are multiplied by a constant factor to achieve a performance gain. The constant factor is optimized according to the extrinsic information transfer (EXIT) chart. Simulation results show that the proposed iterative receiver can significantly improve the system performance and converge to the matched filter bound (MFB) with low computational complexity at high signal-to-noise ratios (SNRs).